Patent Publication Number: US-2013240056-A1

Title: Apparatus and methods for deposition reactors

Description:
FIELD OF THE INVENTION 
     The present invention generally relates to apparatus and methods for deposition reactors. More particularly, but not exclusively, the invention relates to precursor sources, apparatus and methods for such deposition reactors in which material is deposited on surfaces by sequential self-saturating surface reactions. 
     BACKGROUND OF THE INVENTION 
     Atomic Layer Epitaxy (ALE) method was invented by Dr. Tuomo Suntola in the early 1970&#39;s. Another generic name for the method is Atomic Layer Deposition (ALD) and it is nowadays used instead of ALE. ALD is a special chemical deposition method based on the sequential introduction of at least two reactive precursor species to a substrate that is located within a heated reaction space. The growth mechanism of ALD relies on the bond strength differences between chemical adsorption (chemisorption) and physical adsorption (physisorption). ALD utilizes chemisorption and eliminates physisorption during the deposition process. During chemisorption a strong chemical bond is formed between atom(s) of a solid phase surface and a molecule that is arriving from the gas phase. Bonding by physisorption is much weaker because only van der Waals forces are involved. Physisorption bonds are easily broken by thermal energy when the local temperature is above the condensation temperature of the molecules. 
     By definition the reaction space of an ALD reactor comprises all the heated surfaces that can be exposed alternately and sequentially to each of the ALD precursor used for the deposition of thin films. A basic ALD deposition cycle consists of four sequential steps: pulse A, purge A, pulse B and purge B. Pulse A typically consists of metal precursor vapor and pulse B of non-metal precursor vapor, especially nitrogen or oxygen precursor vapor. Inactive gas, such as nitrogen or argon, and a vacuum pump are used for purging gaseous reaction by-products and the residual reactant molecules from the reaction space. A deposition sequence comprises at least one deposition cycle. Deposition cycles are repeated until the deposition sequence has produced a thin film of desired thickness. 
     Precursor species form through chemisorption a chemical bond to reactive sites of the heated surfaces. Conditions are typically arranged in such a way that no more than a molecular monolayer of a solid material forms on the surfaces during one precursor pulse. The growth process is thus self-terminating or saturative. For example, the first precursor can include ligands that remain attached to the adsorbed species and saturate the surface, which prevents further chemisorption. Reaction space temperature is maintained above condensation temperatures and below thermal decomposition temperatures of the utilized precursors such that the precursor molecule species chemisorb on the substrate(s) essentially intact. Essentially intact means that volatile ligands may come off the precursor molecule when the precursor molecules species chemisorb on the surface. The surface becomes essentially saturated with the first type of reactive sites, i.e. adsorbed species of the first precursor molecules. This chemisorption step is typically followed by a first purge step (purge A) wherein the excess first precursor and possible reaction by-products are removed from the reaction space. Second precursor vapor is then introduced into the reaction space. Second precursor molecules typically react with the adsorbed species of the first precursor molecules, thereby forming the desired thin film material. This growth terminates once the entire amount of the adsorbed first precursor has been consumed and the surface has essentially been saturated with the second type of reactive sites. The excess of second precursor vapor and possible reaction by-product vapors are then removed by a second purge step (purge B). The cycle is then repeated until the film has grown to a desired thickness. Deposition cycles can also be more complex. For example, the cycles can include three or more reactant vapor pulses separated by purging steps. All these deposition cycles form a timed deposition sequence that is controlled by a logic unit or a microprocessor. 
     Thin films grown by ALD are dense, pinhole free and have uniform thickness. For example, aluminum oxide grown from trimethylaluminum (CH 3 ) 3 Al, also referred to as TMA, and water at 250-300° C. has usually about 1% non-uniformity over the 100-200 mm wafer. Metal oxide thin films grown by ALD are suitable for gate dielectrics, electroluminescent display insulators, capacitor dielectrics and passivation layers. Metal nitride thin films grown by ALD are suitable for diffusion barriers, e.g., in dual damascene structures. Precursors for the ALD growth of thin films and thin film materials deposited by the ALD method are disclosed, for example, in a review article M Ritala et al., “ Atomic Layer Deposition”, Handbook of Thin Film Materials, Volume  1 : Deposition and Processing of Thin Films, Chapter  2, Academic Press, 2002, p. 103, and R Puurunen, “ Surface chemistry of atomic layer deposition: A case study for the trimethylaluminium/water process”, Journal of Applied Physics, vol.  97 (2005) pp. 121301-121352 which are incorporated herein by reference. 
     Apparatuses suited for the implementation of ALE and ALD methods are disclosed, for example, in review articles T. Suntola, “ Atomic Layer Epitaxy”, Materials Science Reports,  4(7) 1989, Elsevier Science Publishers B. V., p. 261, and T. Suntola, “ Atomic Layer Epitaxy”, Handbook of Crystal Growth  3 , Thin Films and Epitaxy, Part B: Growth Mechanisms and Dynamics, Chapter  14, Elsevier Science Publishers B. V, 1994, p. 601 which are incorporated herein by reference. 
     A precursor source is disclosed in U.S. patent application publication no. US 2007/0117383 A1, which is incorporated herein by reference. 
     Another precursor source is disclosed in WO patent application publication no. WO 2006/111618 A1, also incorporated herein by reference. 
     Various existing precursor sources have a number of problems. One general problem is that preventing the condensation of precursor vapor in source chemical lines has required complicated and expensive heating systems. Another general problem is that preventing crust formation on the solid precursor surface has required complicated source structures. Still another general problem is that existing precursor sources are very bulky and service of the precursor source has been time-consuming. 
     SUMMARY 
     According to a first aspect of the invention there is provided an apparatus comprising: 
     a precursor source configured for depositing material on a heated substrate in a deposition reactor by sequential self-saturating surface reactions;
 
an in-feed line for feeding precursor vapor from the precursor source to a reaction chamber comprised by the reactor containing the substrate; and
 
a structure configured for utilizing heat from a reaction chamber heater for preventing condensation of precursor vapor into liquid or solid phase between the precursor source and the reaction chamber.
 
     There may be one or more substrates. 
     In an embodiment, the precursor source comprises a protrusion configured for receiving heat from the reactor. In an embodiment, the apparatus comprises an inner neck in the protrusion and an outer neck around the protrusion, the inner neck and an outer neck forming a gap there between. In an embodiment, the apparatus comprises a heat conductor part around the in-feed line configured for decreasing thermal energy loss from the protrusion to the surroundings. 
     In an embodiment, the apparatus comprises a source framework configured for receiving a detachably attachable (or removable) source cartridge. 
     In an embodiment, the apparatus comprises a heater for heating the source cartridge or source block. 
     According to a second aspect of the invention there is provided an apparatus comprising: 
     a precursor source configured for depositing material on a heated substrate in a deposition reactor by sequential self-saturating surface reactions;
 
two pulsing valves embedded into the precursor source configured to control feeding of precursor vapor from the precursor source to a reaction chamber comprised by the reactor containing the substrate; and
 
a bypass line between the pulsing valves for feeding inactive gas from a pulsing valve to another pulsing valve.
 
     In an embodiment, the apparatus comprises a flow restrictor in the bypass line. 
     According to a third aspect of the invention there is provided an apparatus comprising: 
     a precursor source configured for depositing material on a heated substrate in a deposition reactor by sequential self-saturating surface reactions;
 
a pulsing valve embedded into the precursor source configured to control feeding of precursor vapor from the precursor source to a reaction chamber comprised by the reactor containing the substrate, the apparatus being configured to:
 
convey inactive gas via the pulsing valve to a precursor source cartridge to raise pressure and to ease subsequent flow of a mixture of precursor vapor and inactive gas towards the reaction chamber.
 
     In an embodiment, the apparatus is configured to: 
     close the precursor cartridge after the pressure raise until the commencement of a next precursor pulse period, and further configured to:
 
open a route towards the reaction chamber via the pulsing valve upon commencement of the next precursor pulse period.
 
     According to a fourth aspect of the invention there is provided a precursor source comprising: 
     a detachably attachable precursor cartridge;
 
a first fitting configured for attaching and detaching the precursor cartridge to and from the precursor source; and
 
a second fitting for attaching and detaching the precursor source to and from the deposition reactor device.
 
     In an embodiment, the precursor source comprises a particle filter in connection with the first fitting. In an embodiment, the precursor source comprises a sealing part or valve configured for sealing the precursor cartridge to prevent precursor material flow from inside the precursor cartridge to the first fitting. 
     In an embodiment, the precursor source comprises: 
     a third fitting on a first side of the sealing part or valve; and
 
a fourth fitting on another side of the sealing part or valve, wherein
 
said third and fourth fittings are configured to open for detaching said sealing part or valve and for cleaning the cartridge.
 
     According to a fifth aspect of the invention there is provided a precursor cartridge comprising: 
     a precursor boat comprising precursor material; and
 
a sinter cartridge for receiving said the precursor boat loaded therein.
 
     In an embodiment, the precursor boat loaded with source chemical is horizontally arranged to enter the sinter cartridge via a loading port. 
     According to a sixth aspect of the invention there is provided a method comprising: 
     feeding precursor vapor along an in-feed line from a precursor source of a deposition reactor to a reaction chamber containing a heated substrate;
 
depositing material on the heated substrate in the deposition reactor by sequential self-saturating surface reactions; and
 
using heat from a reaction chamber heater for preventing condensation of precursor vapor into liquid or solid phase between the precursor source and the reaction chamber.
 
     In an embodiment, the method comprises receiving heat from the reactor into a protrusion in the source, the protrusion having the in-feed line, wherein said received heat heats the in-feed line. 
     In an embodiment, the method comprises arranging a heat conductor part around the in-feed line for decreasing thermal energy loss from the protrusion to the surroundings. 
     According to a seventh aspect of the invention there is provided a method comprising: 
     depositing material on a heated substrate in a deposition reactor by sequential self-saturating surface reactions;
 
controlling feeding of precursor vapor from a precursor source to a reaction chamber comprised by the reactor containing the substrate with two pulsing valves embedded into the precursor source; and
 
feeding inactive gas from a pulsing valve to another pulsing valve via a bypass line.
 
     According to an eighth aspect of the invention there is provided a method comprising: 
     depositing material on a heated substrate in a deposition reactor by sequential self-saturating surface reactions;
 
controlling feeding of precursor vapor from a precursor source to a reaction chamber comprised by the reactor containing the substrate with a pulsing valve embedded into the precursor source; and
 
conveying inactive gas via the pulsing valve to a precursor source cartridge to raise pressure and to ease subsequent flow of a mixture of precursor vapor and inactive gas towards the reaction chamber.
 
     According to an ninth aspect of the invention there is provided a method comprising: 
     operating a precursor source; and
 
receiving a horizontal precursor boat loaded with source chemical into a sinter cartridge of the precursor source.
 
     According to yet another aspect of the invention there is provided a detachably attachable precursor cartridge for use in the precursor source of any other aspect. 
     In an embodiment, a precursor source for the deposition of material on a substrate is provided, the precursor source comprising: a framework for attaching dosage valves, a framework for attaching precursor cartridge, a feed-through conduit, at least one dosage valve, integral by-pass flow conduit; and a removable precursor cartridge. 
     In another embodiment, a precursor source for the deposition of material on a substrate is provided, the precursor source comprising: a framework for attaching dosage valves and housing a precursor volume, a feed-through conduit, at least one dosage valve; and integral by-pass flow conduit. 
     The apparatus, sources, precursor cartridges and methods may be intended for growing material or thin films on heated surfaces by sequential self-saturating surface reactions below the atmospheric pressure, the apparatus thereby being an ALD (Atomic Layer Deposition) or ALE (Atomic Layer Epitaxy) apparatus or similar. The desired thickness of the thin films would typically be in the area extending from one monolayer or molecular layer up to 1000 nm or further. 
     The apparatus, sources, source cartridges and methods may be intended for generating source chemical vapor, for growing material or thin films on heated surfaces by sequential self-saturating surface reactions below the atmospheric pressure. Source chemical vapor may be generated, for example, by heating solid or liquid chemicals. They may, for example, have a vapor pressure of less than about 10 hPa at room temperature. 
     Certain embodiments provide a modular precursor source for deposition reactors that has a simplified heating system. Certain embodiments provide a modular precursor source that has controlled temperature gradient over the source for preventing crust formation. Certain embodiments provide a modular precursor source that has compact footprint. 
     In certain embodiments precursor sources are used that generate vapor from solid or liquid chemicals at elevated temperatures. Certain embodiments relate to apparatus and methods for generating source chemical vapor from low vapor pressure precursors. 
     According to an embodiment a heated precursor source comprises a removable precursor cartridge, and means of heating the precursor source with an embedded heating system. The heated precursor source may comprise means of cooling the precursor source with controlled removal of heat from a selected area of the precursor source for creating a temperature gradient over the precursor source. The heated precursor source may comprise a structure for utilizing reaction chamber heat for preventing the condensation of precursor vapor into liquid or solid phase between the precursor source and the reaction chamber. 
     It should be clear for a skilled person that the various aspects, although presented as separate aspects, can be combined in any suitable way. Also, the embodiments disclosed in the specification and the subject-matter of dependent claims relating to one aspect can be applied to other aspects of the invention. Furthermore, an embodiment of a certain aspect can be combined with other embodiment(s) of the same aspect in any suitable way. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In the following, the invention will be described in more detail with the help of exemplifying embodiments illustrated in the appended drawings, in which like reference numbers are employed for similar features in different embodiments and, in which: 
         FIG. 1  is a schematic drawing of a prior art construction where a non-heated liquid source system has been attached to a deposition reactor; 
         FIG. 2  is another schematic drawing of a prior art construction where a non-heated liquid source system has been attached to a deposition reactor; 
         FIG. 3  is a schematic drawing of a heated precursor source that has two dosage valves; 
         FIG. 4  is a schematic drawing of a heated precursor source that has one dosage valve; 
         FIG. 5  is a schematic drawing depicting a precursor source that has an internal cartridge sealing; 
         FIG. 6  is another schematic drawing depicting a precursor source that has an internal cartridge sealing; 
         FIG. 7  is a schematic drawing depicting a state of precursor source process instrumentation during a precursor pulse period; 
         FIG. 8  is a schematic drawing depicting a state of precursor source process instrumentation during a gas charge period, 
         FIG. 9  is a schematic drawing depicting a state of precursor source process instrumentation during a purge period; 
         FIG. 10  is a schematic drawing depicting pressures and timing of a precursor source according to one embodiment; 
         FIG. 11  is a schematic drawing depicting the pressures and timing of a precursor source according to another embodiment; 
         FIG. 12  is a schematic drawing depicting a heated precursor source comprising inactive gas in-feed system; 
         FIG. 13  is a schematic drawing of a heated precursor source comprising valve less inactive gas in-feed system; 
         FIG. 14  is a schematic drawing depicting a heated precursor source comprising a removable precursor container according to one embodiment; 
         FIG. 15  is a schematic drawing depicting a removable precursor container for a heated precursor source according to another embodiment; 
         FIG. 16  is a schematic drawing depicting a heated precursor source according to another embodiment; 
         FIG. 17  is a schematic drawing depicting a heated precursor source according to another embodiment; 
         FIG. 18  is a schematic drawing depicting a sealable precursor cartridge according to one embodiment; 
         FIG. 19  is a schematic drawing depicting the use of a sealable precursor cartridge according to one embodiment; 
         FIG. 20  is a schematic drawing depicting a heated source suitable for a sealable precursor cartridge; 
         FIG. 21  is a schematic drawing depicting a sealable precursor cartridge in a closed position; and 
         FIG. 22  is a schematic drawing depicting a sealable precursor cartridge in an open position. 
     
    
    
     DETAILED DESCRIPTION 
     Without wishing to be restricted by the following explanations and theoretical considerations, embodiments of the invention will now be described in detail with the help of figures and examples. The scope of the invention is not meant to be limited to these figures and examples. A person skilled in the art will understand that variations of the apparatuses and the methods can be constructed without departing from the scope of the invention. 
       FIG. 1  depicts a schematic view of a non-heated liquid precursor source  100  during a pulse time. The source  100  is controlled with a pulsing valve  104 . During a pulse time the pulsing valve  104  is opened. Liquid precursor evaporates inside the source  100  generating precursor vapor. Precursor vapor has high enough pressure for entering the in-feed line (or in-feed conduit)  108  through the opened pulsing valve  104 . Precursor vapor flows along the conduit  102  as indicated with the arrow  146 , through the pulsing valve  104  and along the in-feed conduit  108  as indicated with the arrow  138 . The precursor vapor arrives to a heated reaction chamber  106  that houses a substrate holder  118 . The reaction chamber  106  is sealed with a reaction chamber lid  116  from an intermediate space  126 . The reactor  122  is sealed against room air with a vacuum chamber lid  124 . Precursor vapor chemisorbs on all heated surfaces inside the reaction chamber  106 . The surfaces become saturated with up to one molecular layer of the precursor vapor. Surplus precursor vapor and surface reaction byproducts flow from the reaction chamber  106  through an exhaust line  112  to a vacuum pump  110  as indicated with an arrow  148 . The vacuum pump  110  compresses the gases and compressed gases exit the vacuum pump  110  to an outlet conduit  114 . Inactive gas, e.g., nitrogen gas is used as carrier and purge gas. Inactive gas flow coming from an inactive gas source  128  is divided into two parts. One part of the flow is directed through an intermediate space conduit  132  and the other part of the flow is directed to a source line conduit  130 . The flow rate of inactive gas going to the intermediate space  126  is controlled with a first mass flow controller  140 . Inactive gas escapes from the intermediate space  126  to the exhaust line  112  through a flow restrictor  144 . The flow rate of inactive gas going to the reaction chamber  106  is controlled with a second mass flow controller  134 . Inactive gas pushes precursor vapor from the pulsing valve  104  towards the reaction chamber  106 . The substrate holder  118 , the reaction chamber lid  116  and the vacuum chamber lid  124  are controlled with a lifting mechanism  120 . 
       FIG. 2  depicts a schematic view of a non-heated liquid precursor source  100  during a purge time. The pulsing valve  104  has been closed. The liquid precursor source  100  has been isolated from the in-feed conduit  108 . Inactive gas purges residual precursor vapor towards the reaction chamber  106 . Purging cleans the gas phase of the in-feed conduit  108 . After that only pure inactive gas flows along the in-feed line/conduit  108  as indicated with an arrow  200 . Inactive gas also purges the reaction chamber  106  and cleans the gas phase of the reaction chamber from residual precursor vapor and gaseous byproducts originating from surface reactions. All gases inside the reaction chamber and the intermediate space will finally enter the exhaust line  112  and flow towards the vacuum pump  110  as indicated with the arrow  202 . 
       FIG. 3  depicts a schematic view of a heated dual valve source  300  (or source system) that can be used for vaporizing low vapor pressure precursors. The source  300  comprises a thermally conductive source framework  302 , a thermally insulating cover  304 , a first pulsing valve  306  with control system  308 , a second pulsing valve  310  with a control system  312  and a precursor cartridge  344 . The precursor cartridge  344  when heated typically contains precursor in solid or liquid phase  354  and in gas phase  356 . The control systems  308 ,  312  are typically based on pneumatic or electrical controlling methods. The source framework  302  is tightened with a conduit connector  314  to a reaction chamber in-feed line  316 . A protrusion exploits thermal energy of the reactor. The term reactor comprises here both a vacuum chamber and a reaction chamber. The protrusion comprises an internal neck  320 , an external neck  328  and a neck connector comprising a pair of flanges  322 ,  324  with a seal  326  between the said flanges for attaching the protrusion to a vacuum chamber wall  330 . A vacuum gap  332  between the external neck  328  and the internal neck  320  increases the path length for the thermal energy flow and decreases thermal energy loss from the protrusion to the surrounding room atmosphere and to the cool vacuum chamber wall  330 . An air gap  321  between the internal neck  320  and a coaxial heat conductor tube  318  increases the length of the path for the thermal energy flow and decreases thermal energy loss from the protrusion to the surrounding atmosphere and to the cool vacuum chamber wall  330 . A heater (not shown) placed in the vacuum chamber heats the internal neck  320  and the in-feed conduit  316  of the protrusion. Heat energy flow is divided into two parts. The first part of the heat energy flow moves by conduction along the first route from the internal neck  320  and the in-feed conduit  316  towards the connector  314  along the in-feed conduit  316  and the heat conductor tube  318 . The second part of the heat energy flow moves mostly by conduction along the second route from the internal neck  320 , through the flanges  322 ,  324  and along the external neck  328  to the vacuum chamber wall  330 . A coaxial heat insulator pad  325  limits the entry of the second part of the heat energy flow into the thermally insulating cover  304 . The first route keeps the in-feed conduit heated between the ALD reactor and the precursor source. The second route is as long as possible and has as small thermal conductivity as possible to minimize thermal losses from the in-feed conduit  316  to the vacuum chamber wall  330 . 
     The heated precursor source  300  is detached from the ALD reactor or attached to the ALD reactor with the conduit connector  314 , the attachment/detachment level being indicated with a dotted line  338  or with the neck connector. As an example, the conduit connector  314  is a VCR connector with a metal seal between the VCR flanges. As a further example, the conduit connector  314  is a Swagelok connector or a VCO o-ring connector. As an example, the neck connector is a clamped flange connector with an o-ring seal. 
     Titanium isopropoxide Ti(O i Pr) 4  serves as an example of source chemicals that typically should be heated to obtain sufficient precursor vapor pressure. Ti(O i Pr) 4  is loaded to a precursor cartridge  344  and an optional particle filter  352  is placed on top of the cartridge  344 . According to one embodiment the cartridge  344  is sealed with an o-ring seal  318  against the source framework  302 . The cartridge  344  may further be tightened by a tightening nut  348  at the bottom to make a leak-tight connection. The temperature of the cartridge  344  is measured with a first thermocouple  358  attached through a neck  346  of the cartridge  344 . The source framework/body  302  is heated with at least one heat source. According to one embodiment the heat source comprises an electrically heated resistor  355 . The heat resistor  355  is wired  364  to a computer-controlled power source. The temperature of the heat resistor  355  is measured with a second thermocouple  362 . A heat insulating pad  350  limits the heat energy losses from the source cartridge  344  to the room atmosphere. Two pulsing valves  306 ,  310  are sealed, for example, with metal c-rings or o-rings against the source framework  302 . The first pulsing valve  306  serves as source inlet controller for dosing inactive carrier gas (e.g., nitrogen) into the gas phase  356  of the source cartridge  344 . The second pulsing valve  310  serves as source outlet controller for dosing precursor vapor mixed with inactive carrier gas to a source outlet conduit  342  and further to the in-feed conduit  316  of the reaction chamber. Pulsing valves  306 ,  310  are, for example, three-way valves having an open purge conduit through the valve. 
     During the purge period the valves are closed meaning that the third ports of the valves, i.e. source sides of the valves  306 ,  310  are kept isolated from the purge conduit of the valves. During the purge period all of the inactive gas flows through the first valve inlet conduit  371 , through the purge conduit inside the first valve to the bypass conduit  336  leading to the second valve, through the purge conduit inside the second valve, through the source outlet conduit  342  and through the in-feed conduit  316  to the reaction chamber of the reactor. The bypass conduit may comprise a narrow passage  337  serving as an appropriate flow restrictor. During the pulse time the valves  306 ,  310  are open meaning that the third ports of the valves, i.e. source sides of the valves  306 ,  310  are kept in fluid communication with the purge conduits of the valves. During the pulse time the inactive gas flow is divided into two parts. The ratio of inactive gas flows is defined by the ratio of gas flow conductivities. The first part of the inactive gas flow goes from the purge conduit inside the first valve through the cartridge inlet conduit  334  to the gas phase  356  of the cartridge  344 . Inactive gas mixes with precursor vapor in the gas phase  356 . The resulting gas mixture flows through the cartridge outlet conduit  338  to the purge conduit inside the second valve  310 , through the source outlet conduit  342  and through the in-feed conduit  316  to the reaction chamber of the reactor. The second part of the inactive gas flow goes through the purge conduit inside the first valve to the bypass conduit  336  leading to the second valve via the optional narrow passage  337 , through the purge conduit inside the second valve where the second part of the inactive gas flow mixes with the gas mixture coming from the cartridge outlet conduit  338 , through the source outlet conduit  342  and through the in-feed conduit  316  to the reaction chamber of the reactor. 
     According to another embodiment the source inlet valve  306  is first opened, inactive gas increases the pressure of the source cartridge  344  and then the source inlet valve  306  is closed. The source outlet valve  310  is subsequently opened and the mixture of inactive gas and precursor vapor flows out of the precursor cartridge and the pressure of the precursor cartridge decreases. 
       FIG. 4  depicts a schematic view of a heated single valve precursor source  400 . The structure of the source  400  comprises a source outlet valve  410  with a control system  412 . In an embodiment, the valve  410  is fastened to the source framework  402  by bolts. Reference numeral  445  in the figure indicates holes drilled through the source framework  402  for that purpose. The source framework  402  is covered by the thermally insulating cover  404  and is attached with a connector  314  to the in-feed conduit  316  of the reactor. According to one embodiment the connector  314  is a VCR metal seal connector. The source cartridge comprises a cartridge body  456  and a cartridge neck  430 . The source cartridge is sealed against the source framework  402  with an o-ring  424  placed to the cartridge bottom area, a radial shaft seal  432  placed to the cartridge neck area or an o-ring  434  placed to the top area of the cartridge neck  430 . A locking/tightening nut  426  is tightened against a seal housing  422  and either the seal housing  422  or the cartridge is pressed against a seal making a leak-tight connection. A heat insulating pad  428  limits the heat energy losses from the source cartridge to the room atmosphere. Heated source cartridge loaded with precursor contains precursor in solid or liquid phase  416  and in gas phase  418 . If the source  400  comprises the heat source  355 , the temperature of the cartridge can be measured with the thermocouple  358  attached through a neck  420  of the cartridge. 
     During the purge time the pulsing valve  410  is kept closed. Because the purge conduit through the pulsing valve is open all the time, inactive gas flows through the valve inlet conduit  438 , through the purge conduit, through the source outlet conduit  442  and through the in-feed conduit  316  towards the reaction chamber. 
     During the pulse time the source cartridge side of the pulsing valve  410  is opened. Precursor vapor flows along the cartridge outlet conduit  436  through the valve seat of the pulsing valve  410  to the purge conduit of the pulsing valve where the vapor mixes with the inactive gas coming through the valve inlet conduit  438 . Thus, precursor vapor is injected into a stream of inactive gas. The resulting precursor vapor and inactive gas mixture flows through the source outlet conduit  442  and through the in-feed conduit  316  towards the reaction chamber. 
     According to an embodiment the pressure of the inactive gas is about 8 mbar near the valve inlet conduit  438 . Precursor is heated to a source temperature where the vapor pressure of the precursor is higher than the pressure of the inactive gas at the injection point inside the pulsing valve. Typically, the source temperature is selected from a range between +40 and +200° C. to obtain at least 10 mbar vapor pressure of the precursor. 
     Heat energy is lost in a controlled way from the bottom side of the source cartridge. Coldest spot on the surface of the gas volume determines the maximum obtained vapor pressure of the said gas volume. The coldest spot of the precursor source is at the bottom surface of the source cartridge and all other surfaces between the source cartridge and the reaction chamber are at a higher temperature than the bottom surface of the precursor cartridge. These said surfaces are in fluid communication with the source cartridge when the pulsing valve is opened. Condensation of the precursor vapor is avoided on these said surfaces because all the surfaces between the precursor cartridge bottom and the reaction chamber are at a higher temperature that the bottom of the precursor cartridge. 
       FIG. 5  depicts a schematic view of a heated source system  500  with a movable source cartridge at an open position. When the pulsing valve  410  is opened, precursor vapor flows from the source cartridge  512  to a source protrusion via a hallway part  516 , which has an aperture and forms a hallway towards the pulsing valve  410 , and further through the pulsing valve  410  towards the in-feed conduit  316 . The cartridge  512  comprises a cartridge neck  514  and the hallway part  516  comprises o-ring seals  518  and  520 . 
     According to one embodiment the source framework  402  is attached with an o-ring seal  508  to the in-feed conduit  316  of the reactor. A flat flange  504  is pressed with a coaxial bolt  502  against the o-ring  508 . Reference numeral  506  in the figure indicates threads for the coaxial bolt  502 . After removing the coaxial heat insulator pad  318  the coaxial bolt  502  can be loosened by applying a tool (for example a set wrench) to the top part of the coaxial bolt  502 . 
       FIG. 6  depicts a schematic view of the heated source system  500  with a movable source cartridge at closed position. The locking nut  426  has been opened and the source cartridge  512  has been pulled downwards. The cartridge neck  514  is sealed with o-rings  518 ,  520  and the only outlet opening is in the area sealed with the said o-rings. The precursor vapor volume  418  is effectively isolated from the rest of the source conduits. Because of the isolation of the vapor volume, source chemical vapor can condense only inside the source cartridge when the precursor source system is cooled from source temperature down to room temperature. 
       FIG. 7  depicts a schematic view of a single valve heated source  700  during a precursor pulse period. The source  700  comprises a source framework  702 , a heater  720 , a feed-through projection  728 , a pulsing valve  716  and a precursor cartridge  706 . The source framework  702  is covered with a heat insulator layer  704  for reducing heat loss from the heated source  700  to surrounding air. The precursor cartridge  706  is loaded with liquid or solid precursor so that part of the cartridge volume  752  is occupied with the solid or liquid precursor and the rest of the cartridge volume, so-called precursor vapor space,  754  is available for gas phase species. 
     The precursor cartridge  706  has a reservoir, a neck  708  for sealing the cartridge with an o-ring or a radial axis seal  762  to the source framework  702  and a tail projection  758  for handling the cartridge. A detachable heat insulator layer  760  is placed around the tail projection  758  for controlling the amount of heat energy lost from the tail projection  758  to the surrounding air. The temperature of the heater  720  is measured with a heater thermocouple  724  and the temperature of the precursor cartridge  706  is measured with a cartridge thermocouple  764 . The heater thermocouple  724  is used for controlling the power  722  fed to the heater. When the temperature of the heater exceeds the programmed maximum temperature limit, power is not fed to the heater  720 . The thermoelectric voltage obtained from the thermocouple  764  is converted with an analog/digital (AD) converted into digital value that is used with a PID controller for controlling the amount of power fed to the heater  720  for reaching correct source temperature. The source framework  702  substantially surrounds the precursor cartridge  706 . The precursor cartridge is in thermal contact with the source framework. When the source framework is heated to a constant source temperature, the precursor cartridge receives heat energy from the source framework and the temperature of the precursor cartridge reaches the temperature of the source framework. The tail projection area has slightly higher heat conductivity than the heat insulator layer  704 . Thus, a small amount of heat energy flows to the tail projection  758  keeping the surface inside the precursor cartridge near the tail projection, for example, 0.1-10° C. cooler, or in some embodiments 1-3° C. cooler, than the rest of the cartridge. The coldest spot within the continuous gas space determines the maximum vapor pressure of present chemical species. Thus, precursor vapor cannot condense on surfaces near the pulsing valve because the said surfaces are warmer than the tail projection wall and the said surfaces stay clean. The operating principle of the heated source  700  is treated with the help of a virtual pressure indicator  756  reflecting the actual gas pressure within the precursor vapor space  754 . 
     The pulsing valve  716  comprises a diaphragm flow seal (not shown), an open valve inlet  717 , controlled source inlet  718 , an open valve outlet  714  reaching towards a source outlet conduit  730  and an actuator  710 . All the pulsing valve parts except the actuator  710  are heated to the same source temperature as the source framework. The actuator  710  can be for example a pneumatic actuator, a hydraulic actuator or a solenoid actuator. The actuator  710  can be located outside of the source framework and a stem conveys mechanical power from the actuator to a valve shutter (not shown). The actuator  710  can be controlled from control system  712 . The actuator is kept in a temperature that is as low as possible, for example, 20-100° C., in some embodiments 20-50° C. to increase the lifetime of the actuator  710 . The valve shutter is preferably a normally closed metal diaphragm that controls the flow of gases from the source inlet  718  to the valve outlet  714 . Pneumatically activated high-temperature Swagelok® ALD diaphragm valve serves as an example of a pulsing valve  716  suitable for the present heated precursor source. 
     Nitrogen gas (or inactive gas) flow rate originating from an inactive gas source  736  is modulated with a computer-controlled system. According to one embodiment a mass flow controller  738  is fast enough for setting  740  new mass flow rate for inactive gas, for example, within 0.05-1 s, in some embodiments within 0.05-0.1 s. According to another embodiment a standard thermal mass flow controller  738  is used for setting basic constant mass flow rate for inactive gas and a pulsing valve  744  is used to control  746  adding more inactive gas to a source entrance conduit  780  so that the total mass flow rate of inactive gas arriving at the open valve inlet  717  is modulated between a low value and a high value. The said low value is selected, for example, from a range of 10-500 sccm, in some embodiments 50-100 sccm. The said high value is adjusted, e.g., with a needle valve  742  or a capillary and the said high value is selected, for example, from a range of 100-2000 sccm, in some embodiments 300-500 sccm, so that the high value is higher than the low value. The pressure of the source entrance conduit is measured with a pressure transducer  748  that transmits an analog or digital signal  750  to a data processing system. The said signal is used for helping the adjustment of the inactive gas flow rates to suitable ranges. One of the benefits of the present arrangement is that the relatively expensive components namely the inactive gas mass flow controller  738 , the inactive gas pulsing valve  744  and the pressure transducer  748  are in cool area and only in contact with inactive nitrogen gas. 
     Precursor vapor or mixture of precursor vapor and inactive gas is injected with the help of the flow control valve (or pulsing valve)  716  into the stream of inactive carrier gas that pushes precursor vapor towards the source outlet conduit  730  and the reaction space. 
       FIG. 8  depicts a schematic side view of the single valve heated source  700  during a gas charge period. In certain cases, the vapor pressure of the precursor can be too low for efficiently entering the reactor during a pulse period. In the embodiment shown in  FIG. 8 , the vapor pressure inside the source is raised during the gas charge period. In this embodiment, inactive gas is conveyed via the valve  716  into the precursor source container/cartridge  706  to raise the pressure. The source inlet  718  of the valve  716  is subsequently closed as shown in  FIG. 9  until the commencement of the next precursor pulse. In this closed state the mixture of precursor vapor and inactive gas is not able to flow through the source inlet  718  into the source entrance conduit  780 , nor into the source outlet conduit  730 . Upon commencement of the next precursor pulse, the valve  716  is opened so that the mixture with raised pressure flows more easily through the source inlet  718  and via the source outlet conduit  730  towards the reactor as depicted in  FIG. 7 . 
     Certain rules for the design of the heated precursor source in certain embodiments can be presented as follows: Take benefit of pressure differences because mass transport is faster by forced flow than by diffusion and gases always flow from higher pressure to the direction of lower pressure. Take benefit of temperature differences because thermal energy always moves from higher temperature to lower temperature and coldest spot inside a gas space determines the vapor pressure of chemical species within the gas space. Keep all the possible mechanical moving parts in cool area because mechanical moving parts last longer at low temperatures. 
     The operation of the heated source presented in  FIGS. 7-9  is further illustrated with the description of a deposition process. Aluminum oxide Al 2 O 3  is grown from heated aluminum chloride AlCl 3  (sometimes written as a dimer Al 2 Cl 6 ) and vaporized water H 2 O. AlCl 3  pieces are loaded into the cartridge  706  that is placed inside the heated precursor source  700 . The heated precursor source is heated to a programmed source temperature to create about 0.05-10 hPa AlCl 3  vapor pressure above the solid AlCl 3  pieces. For example, when the source temperature is 100° C., the resulting AlCl 3  vapor pressure is 1 hPa within the precursor vapor space  754 . In some embodiments it is advantageous to evaporate the source chemical at source temperatures as low as possible, while still generating sufficiently big precursor vapor dosage for covering the whole substrate surface, to avoid the decomposition of heat-sensitive precursors within the heated source. 
     A benefit of evaporating AlCl 3  at low source pressure is that low pressure increases the diffusion speed of gas molecules and helps to recover the equilibrium vapor pressure of AlCl 3  as fast as possible. In an embodiment AlCl 3  evaporates for about 0.5-4.0 s until about 0.05-10 hPa AlCl 3  vapor pressure above the solid AlCl 3  pieces is obtained. The inactive gas flow going through the source inlet conduit  780  is increased e.g. to 1000 sccm, which increases the pressure of the inactive gas in the source inlet conduit to a pressure value that is above the gas pressure within the precursor gas space  754 . Then the source side of the pulsing valve  718  is opened. Inactive gas flows from the source inlet conduit  780  to the precursor gas space, e.g., 0.2-1.0 s until the pressure of the source container  706  is increased with inactive gas to about 5-20 hPa. Inactive gas mixes with source chemical vapor. Then the flow rate of inactive gas is decreased for example from 1000 sccm to 100 sccm to decrease the gas pressure of the inactive gas in the source inlet line  780 . Now the flow direction of gases is reversed and the gas mixture flows out of the precursor vapor space  754  of the source container through the pulsing valve  716  into the reactor in-feed line  730 . Carrier gas flow, e.g. 100 sccm of nitrogen gas, pushes the inactive gas/precursor vapor mixture into the reaction space (not shown). One of the benefits of the embodiment is that only a single pulsing valve is needed in the heated area of the precursor source. 
     Within the reaction space, where a substrate is located, AlCl 3  molecules chemisorb on the substrate surface until available reactive surface sites, namely OH groups, have been consumed and the surface becomes saturated with a molecular layer of the AlCl 3  molecules, or more precisely, with the ClAl&lt; and Cl 2 Al— fractions of the AlCl 3  molecules. Here, “—” denotes a chemical bond between an Al atom and a surface oxygen atom and “&lt;” denotes two chemical bonds between the Al atom and surface oxygen atoms. The original AlCl 3  molecule has three chlorine Cl atoms attached to the center Al atom. When the AlCl 3  molecule reacts with the surface hydroxyl OH groups, one or two chlorine atoms receive a hydrogen atom and form gaseous hydrogen chloride HCl molecules as a reaction by-product. 
     The surface is now covered with chlorine atoms. The only way the AlCl 3  molecules could adhere to the Cl-covered surface is by physical adsorption (physisorption). However, the substrate temperature is kept above the condensation point of the AlCl 3  vapor, so physisorption is not possible and the surplus AlCl 3  molecules stay in the gas phase. As a result, only up to a single molecular layer of AlCl 3  molecule fractions are able to stay on the substrate surface. When the AlCl 3  exposure period ends, the source side of the pulsing valve  718  is closed and mixture of AlCl 3  vapor and inactive gas is not any longer injected from the precursor vapor space  754  into the stream of inactive gas flowing through the pulsing valve  716  and the deposition cycle proceeds to a first removal period. When the precursor vapor space  754  has been isolated with the closed pulsing valve from the surrounding gas conduits, the precursor vapor space  754  depleted from AlCl 3  vapor during the source chemical pulse starts to recover by AlCl 3  evaporating from solid AlCl 3  pieces  752 . The composition of the gas coming through the reactor in-feed conduit  730  changes rapidly from a mixture of AlCl 3  vapor and inactive gas into pure inactive gas. Residual AlCl 3  molecules and reaction by-product molecules (HCl) are guided from the reaction space towards the exhaust line by flowing inactive gas. 
     As to an oxygen source (or more generally, non-metal source) for the deposition process, a reference is made to  FIGS. 1-2 . During non-metal exposure period, H 2 O vapor is injected from the temperature-controlled liquid source  100  (through a three-way valve  104  into the stream of inactive gas and the resulting gas mixture flows through the reactor in-feed conduit  108  as indicated with an arrow  138 . The gas flow is guided from the reactor in-feed conduit to the reaction chamber  106  where the substrate  118  is located. The other precursor conduit, i.e. reactor in-feed line for the AlCl 3  source, has inactive gas flow towards the reaction chamber  106 . Thus, while one precursor conduit is used for pulsing source chemical vapor into the reaction chamber, the other precursor conduit is protected by flowing inactive gas atmosphere. 
     In the reaction space H 2 O molecules chemisorb on the substrate  118  surface, which was saturated with AlCl 3  molecule fractions during the preceding precursor exposure, until available reactive surface sites, namely surface Cl atoms, have been consumed and the surface becomes saturated with a molecular layer of the hydroxyl OH groups originating from the H 2 O molecules. After that the only way the H 2 O molecules could adhere to the surface is by physisorption. However, the substrate temperature is kept above the condensation point of the H 2 O vapor, so physisorption is not possible and the surplus H 2 O molecules stay in the gas phase. As a result, only up to a single molecular layer of H 2 O molecule fractions are able to bind to the substrate surface and form thin film material. When the H 2 O exposure time ends, H 2 O vapor is not any longer injected into the stream of inactive gas and the deposition cycle proceeds to a second removal period. 
     During the second removal period, the composition of the gas coming from the reactor in-feed conduit  108  changes rapidly from a mixture of H 2 O vapor and inactive gas into pure inactive gas. Residual H 2 O molecules and reaction by-product molecules, namely methane CH 4  molecules, are guided from the reaction space towards the exhaust line by flowing inactive gas. The substrate surface is now uniformly covered with up to a molecular layer of thin film material, in this case aluminum oxide Al 2 O 3  with surface OH groups. The substrate is now ready for the next AlCl 3  vapor exposure from the heated precursor source  700  that has recovered during the first removal period, the H 2 O exposure period and the second removal period. The deposition cycle consisting of the AlCl 3  exposure period, the first removal period, the H 2 O exposure period and the second removal period is repeated until an Al 2 O 3  film of desired thickness is obtained. Typical growth rate of Al 2 O 3  thin film obtained with the present process has been about 0.9 Å/deposition cycle. 
       FIG. 10  depicts the pressure  1006  of a first precursor source line and the pressure  1008  of a first precursor source container as a function of time in arbitrary units. In this embodiment relatively high gas pressure is kept within the source container while the vapor pressure of the precursor is recovering to an equilibrium level. A heated precursor source presented in the foregoing is used as the first precursor source. At time t 1  pulsing valve  716  ( FIG. 7 ) of the heated source  700  ( FIG. 7 ) is opened and the pressure  1008  of the precursor container gas volume  754  ( FIG. 7 ) decreases. At t 2  inactive gas flow rate is increased in the source entrance conduit  780  ( FIG. 7 ) by the mass flow controller  738  ( FIG. 7 ) or the inactive gas pulsing valve  744  ( FIG. 7 ) and gas pressure  1006  quickly increases inside the source entrance conduit  780  as measured with a line pressure transducer  748  ( FIG. 7 ). Part of inactive gas flows into the source container and pressure of the precursor container gas volume increases during the t 2 -t 3  time period  1028  until an equilibrium pressure is reached. At t 3  the pulsing valve  716  ( FIG. 7 ) is closed and the source container is isolated from the source line. Purging of the source line continues at high speed. At t 4  inactive gas flow rate is decreased to a low level in the source entrance conduit. During the t 4 -t 5  time period  1038  all the pulsing valves of the reactor stay closed and purging of the source conduits and the reaction chamber with inactive gas continues. In this case the precursor cartridge has a lot of evaporation surface and thus at time t 5  the vapor pressure of precursor has already reached equilibrium pressure, i.e. maximum attainable vapor pressure at the source temperature, and the heated precursor source is ready for the next precursor pulse. In order to maximize the available precursor vapor dosage, precursor equilibrium pressure is preferably reached before the next pulsing cycle begins at time t 8 . At time t 6  the pulsing valve of the second precursor source is opened and second precursor vapor is injected into the stream of inactive gas within the second precursor source line. At time t 7  the pulsing valve of the second precursor source is closed and the flow rate of inactive gas within the second source line is decreased. During the t 7 -t 8  time period  1036  all the pulsing valves of the reactor stay closed and purging of the source conduits and the reaction chamber with inactive gas continues. One pulsing cycle covers the t 1 -t 8  time period  1040 . At t 8  execution of the following pulsing cycle starts by opening the pulsing valve of the first precursor source in the same way as at time t 1 . 
       FIG. 11  depicts pressure  1106  of the first precursor source line and the pressure  1108  of the first precursor source container as a function of time in arbitrary units. In this embodiment relatively low gas pressure is kept within the source container while the vapor pressure of the precursor is recovering to the equilibrium level. The heated precursor source presented in the foregoing is used as the first precursor source. At time t 9  inactive gas flow rate is increased in the source entrance conduit  780  ( FIG. 7 ) by the mass flow controller  738  ( FIG. 7 ) or the inactive gas pulsing valve  744  ( FIG. 7 ) and gas pressure  1106  quickly increases inside the source entrance conduit  780  as measured with the line pressure transducer  748  ( FIG. 7 ). At time t 10  pulsing valve  716  ( FIG. 7 ) of the heated source  700  ( FIG. 7 ) is opened. Part of inactive gas flows into the source container and pressure  1108  of the precursor container gas volume increases during the t 10 -t 11  time period  1128  until an equilibrium pressure is reached. Pressure variation within the source containers mixes efficiently inactive gas with precursor vapor and as a result usable mixture of inactive gas and precursor vapor at relatively high pressure is obtained. At time t 11  inactive gas flow rate is decreased to a low level in the source entrance conduit  780  and the pressure of the source entrance conduit decreases rapidly (curve  1106 ). Simultaneously the pressure of the source container starts to decrease because the pressure of the source line becomes lower than the pressure of the source container, the pulsing valve is still open and the source container is in fluid communication with the source line. At t 12  the pulsing valve  716  ( FIG. 7 ) is closed and the source container is isolated from the source line. The precursor vapor pressure starts to increase and equilibrium precursor vapor pressure level is reached at time t 13 . Purging of the source line continues. During the t 12 -t 14  time period  1138  all the pulsing valves of the reactor stay closed and purging of the source conduits and the reaction chamber with inactive gas continues. All the residual precursor molecules and volatile reaction byproducts are pushed to the exhaust line of the reactor. In this case the precursor cartridge has a lot of evaporation surface and thus at time t 13  the vapor pressure of precursor has already reached equilibrium pressure, i.e. maximum attainable vapor pressure at the source temperature, and the heated precursor source is ready for the next precursor pulse. In order to maximize the available precursor vapor dosage, equilibrium precursor vapor pressure is preferably reached before the next pulsing cycle begins at time t 16 . At time t 14  the pulsing valve of the second precursor source is opened and second precursor vapor is injected into the stream of inactive gas within the second precursor source line. At time t 15  the pulsing valve of the second precursor source is closed and the flow rate of inactive gas within the second source line is decreased. During the t 15 -t 16  time period  1136  all the pulsing valves of the reactor stay closed and purging of the source conduits and the reaction chamber with inactive gas continues. All the residual precursor molecules and volatile reaction byproducts are pushed to the exhaust line of the reactor. One pulsing cycle covers the t 9 -t 16  time period  1140 . At t 16  execution of the following pulsing cycle starts by opening the pulsing valve of the first precursor source in the same way as at time t 9 . 
     The description of  FIG. 10  suits well for an embodiment in which the vapor pressure of a liquid or solid precursor in itself is too low for efficiently entering the reactor during a pulse period and the evaporation rate of the precursor is slow, whereas the description of  FIG. 11  suits well for an embodiment in which the vapor pressure of the precursor in itself is too low for efficiently entering the reactor during a pulse period and the evaporation rate of the precursor is sufficiently rapid for fast recovery of the precursor vapor pressure. Description of  FIG. 10  and  FIG. 11  utilizes an additional pressure raise with the aid of conveying inactive gas into the precursor container and conveying gas mixture comprising inactive gas and precursor vapor out of the precursor container in a timed way. 
       FIG. 12  depicts a schematic view of a heated precursor source  1200  having a forced primary carrier gas flow coming from the precursor loading side of the source. Primary carrier gas flow is arranged with a primary inactive gas source  1202 , inactive gas mass flow controller  1204  having I/O interface  1206  for receiving setting values for the mass flow controller and sending mass flow readings, needle valve  1210  serving as a manually adjustable flow restrictor, primary entrance conduit  1212 , sublimate collector conduit  1214  and cartridge entrance conduit  1216 . Secondary carrier and purge gas flow is arranged with a secondary inactive gas source  736  that can be a separate gas source or the same as the primary inactive gas source  1202 , and an inactive gas mass flow controller  738 . Primary carrier gas flow mixes with precursor vapor in the gas space  754  within the precursor cartridge  706  and the mixture is portioned out with the source pulsing valve  710 . Cartridge entrance conduit  1216  lengthens the path for molecular diffusion and decreases the amount of precursor vapor diffusing upwards the primary carrier gas line to the area of the sublimate collector conduit  1214 . The inner diameter of the cartridge entrance conduit  1216  can be, for example, about 1-20 mm, in some embodiments 4-8 mm and the length of the cartridge entrance conduit can be, for example, 10-100 mm, in some embodiments 30-50 mm. Tip of the cartridge entrance conduit may have a cup (not shown) for guiding the inactive gas flow towards the solid or liquid precursor  752 . 
     According to one embodiment the mass flow controller  1204  is a thermal type controller that has relative long setting time. Because ALD processes utilize short pulses typically in the order of 0.1-1 s, it is advantageous to arrange a by-pass line  1208  for the primary carrier gas flow. The by-pass line  1208  lets the inactive gas flow through the mass flow controller  1204  all the time including the purge time of the deposition when the pulsing valve  716  is closed. The by-pass line  1208  decreases flow rate fluctuations. According to another embodiment the mass flow controller is a pressure-based controller that is fast enough to respond to the pressure fluctuations generated by the pulsing valve  716 . 
     The temperature of the precursor cartridge  706  is measured with a second source thermocouple  1218 . The temperature reading is used for adjusting the amount of heating power fed  722  to the heater  720  of the precursor source. The second source thermocouple  1218  is in thermal contact with the heated volume of the precursor source. 
     The precursor source  1200  is preferably removable. Opening an outlet connection  732 , primary carrier gas line connection  1220  and secondary carrier and purge gas line connection  734  makes it possible to detach the precursor source from the deposition reactor (not shown). The precursor cartridge  706  is heated to source temperature, in some embodiments selected from the range between +40 and +200° C. The pulsing valve  716  is kept closed. Inactive gas flows from the inactive gas source  1202  through the mass flow controller  1204  to the by-pass conduit  1208 . The inactive gas flow keeps the gas space  754  of the source cartridge  706  pressurized to a selected pressure value, in some embodiments to 5-30 mbar, because the gas space  754  is in static fluid communication with inactive gas source through the primary entrance conduit  1212  and needle valve  1210 . Precursor chemical  752  vaporizes to the gas phase  754  of the precursor cartridge until a characteristic vapor pressure of the precursor chemical is reached. Some of the precursor molecules in the gas space  754  diffuse through the cartridge entrance conduit  1216  to the sublimate collector conduit  1214  where the precursor molecules condense to the inner surfaces of the sublimate collector conduit  1214 . The temperature of the sublimate collector conduit  1214  is lower than the temperature of the gas space  754  of the precursor cartridge  706 . The characteristic vapor pressure of a chemical depends on the temperature of the chemical vapor. When the temperature of the surface of the sublimate collector conduit  1214  is low enough, the characteristic vapor pressure of a chemical becomes negligible near the surface and the precursor molecules cannot diffuse upstream to the primary entrance conduit  1212 . During the heating, use and cooling of the precursor source  1200  the temperature of the surface of the sublimate collector conduit  1214  is preferably above room temperature and preferably below the source temperature measured with the second source thermocouple  1218 . When the pulse time starts the pulsing valve  716  is opened and when the pulse time ends the pulsing valve  716  is closed. During the pulse time the gas space  754  of the precursor cartridge is in fluid communication with the source outlet conduit  730  through the opened pulsing valve and precursor vapor is pushed with the help of the primary inactive gas flow from the precursor cartridge towards the reaction space housing the substrate (not shown). 
       FIG. 13  depicts a schematic view of a heated precursor source  1300  that has a single pulsing valve  410  and a sublimate collector conduit  1302  separated from the precursor cartridge  344 . The sublimate collector conduit  1302  is fitted with a seal  1306  to the source body  402 . First the pulsing valve  310  is kept closed. Liquid or solid precursor  1328  is heated to source temperature, for example, to a temperature selected from the range between +40 and +200° C. Precursor  1328  vaporizes and increases the pressure of the gas space  1330  of the precursor cartridge  344  until characteristic vapor pressure of the precursor is reached. During the pulse time the pulsing valve  410  is open. Inactive carrier gas flows from external inactive gas source  1304  through the sublimate collector space into the gas space  1330  of the precursor cartridge where the inactive carrier gas mixes with precursor vapor. The resulting mixture flows through the pulsing valve  410  to the source outlet conduit  442  and further to the reaction space that houses the substrate (not shown). During the purge time the pulsing valve  410  is closed and precursor vapor stops flowing through the precursor source. Some precursor molecules diffuse through the gas space  1330  to the sublimate collector conduit  1302  kept at lower temperature than the precursor cartridge  344  and form a condensate  1310  on the inner surfaces of the sublimate collector conduit. 
       FIG. 14  depicts a heated precursor source  1400  comprising a precursor cartridge  1402  that can be sealed with a manual cartridge valve  1408  and detached from the heated precursor source by opening a fitting  1412 . The precursor source  1400  comprises a second fitting  1422  for attaching and detaching the precursor source  1400  to and from the deposition reactor device. A three-way pulsing valve  1405  comprising a valve body  1418  is controlled pneumatically. For that purpose the pulsing valve may contain a connection  1420  for receiving compressed air. The precursor source comprises a thermally conductive source body  1424 , a heater cartridge  1426  with a power supply  1428  and temperature measurement  1430  with the aid of a thermocouple, a heat insulator layer  1432  and a cover  1434 . Near the bottom of the precursor cartridge  1402 , the precursor source further comprises a thermally conductive protrusion  1406  having a machined channel for housing a bent thermocouple  1438  with a connection  1436  to a computer-controlled system (not shown). 
     The precursor source  1400  may have in between flanges of the fitting  1412  a seal  1414  having a particle filter (or gasket filter)  1416  made of metal or ceramic material and pointing down towards the cartridge valve  1408 . The particle filter  1416  prevents solid precursor particles to enter the pulsing valve  1418  and reactor in-feed lines any further. Precursor particles that travel upwards are stopped on an outer surface of the particle filter  1416  and are dropped back to the precursor cartridge  1402 . 
     A method of purging the source line before replacing the precursor cartridge  1402  is described hereinafter. Manual cartridge valve  1408  is closed. The heated precursor source is heated to a sufficiently high temperature to generate precursor vapor pressure from any solid or liquid precursor residue on the walls of the conduits. The pulsing valve  1405  is opened. The flow rate of inactive gas through the three-way pulsing valve  1405  to the source outlet conduit  1442  is modulated between high value, e.g., 1000 sccm and low value, e.g., 100 sccm. High flow rate increases the pressure of the inactive gas at the three-way pulsing valve  1405  and low flow rate decreasing the pressure of the inactive gas at the three-way pulsing valve  1405  creating a gas pumping effect. Variable gas pressure empties dead ends and gas pockets efficiently from any gaseous residual precursor. The temperature should be high enough to vaporize solid or liquid precursor residues. Source temperatures capable of generating at least about 0.1 hPa precursor vapor pressure can be generally used for enhancing the purging speed. In an embodiment, the reaction space is heated to a temperature at least as high as the precursor source to prevent the condensation of the precursor vapor on the surfaces of the reaction space. 
     The intermediate conduit  1444  and source outlet conduit  1442  are pressurized with inactive gas for example from 5 hPa to 20 hPa for 1 minute and then evacuated from 20 hPa back to 5 hPa for 1 minute. The pressurization and evacuation cycle is repeated a number of times, for example, at least 5 times, in some embodiments at least 10 times, to remove residual precursor from the conduits. 
     The precursor source  1400  may also comprise a third fitting  1410  which can be closed by a chemical manufacturer after filling the cartridge with precursor material. The precursor source  1400  may also comprise a fourth fitting  1404  which can be opened for cleaning the cartridge. 
       FIG. 15  depicts a removable precursor container  1500  for a heated precursor source according to another embodiment. The container  1500  comprises a precursor chamber  1502 , a precursor reservoir  1514  for holding the precursor, a fitting  1504  for loading and unloading the precursor reservoir  1514  and a valve  1508  for isolating the gas space of the precursor chamber from source outlet conduit  1515 . The precursor chamber  1502  has an optional neck fitting  1506  for disassembling the precursor container  1500  for cleaning. The precursor reservoir  1514  wall is preferably sealed with a seal  1520  against the precursor chamber  1502  wall for keeping the precursor vapor away from the fitting  1504  area. The precursor reservoir  1514  optionally comprises a handle  1516  for pulling the reservoir out of the precursor chamber  1502  after opening the fitting  1504  and a filter  1518  for keeping solid precursor or powder particles from exiting the precursor reservoir. The precursor container  1500  can be attached to or detached from other parts of the precursor source by the fitting  1512 . 
       FIG. 16  depicts a heated precursor source according to another embodiment. The heated precursor source shown from the side  1600  and from the front  1602  comprises a source body  1604 , a sealable front flange  1606 , a loading port  1608 , a inactive gas inlet valve  1610 , a precursor vapor outlet valve  1612 , a mounting flange  1614 , heat insulation of the source body  1616 , heat insulation of the pulsing valves  1618  and heat insulation of the loading port  1620 . Inactive carrier and purge gas (e.g. nitrogen or argon) arrives to the heated source through a gas inlet connection  1622 . When the inactive gas inlet valve  1610  and the precursor vapor outlet valve  1612  are closed, inactive gas flows through the inlet conduit  1624 , through the source by-pass conduit  1628  and further through the source outlet conduit  1632  and through the reactor in-feed conduit  1636  to the reaction space (not shown). When the inactive gas inlet valve  1610  and the precursor vapor outlet valve  1612  are open, inactive/carrier gas flow is divided into two parts. The first part of the gas flow goes through the by-pass line  1628 . The second part of the gas flow enters a vapor space  1650  of the heated source through the vapor space inlet conduit  1626 . The second part of the gas flow is mixed with precursor vapor within the vapor space  1650  of the heated source. The resulting first gas/vapor mixture exits the vapor space through the vapor space outlet conduit  1630 . The first gas/vapor mixture is added to the first part of the gas flow coming from the source by-pass conduit  1628  forming a second gas/vapor mixture. The second gas/vapor mixture flows through the source outlet conduit  1632  and through the reactor in-feed conduit  1636  to the reaction space (not shown). A horizontal precursor boat  1642  is loaded into a sinter cartridge  1638 . The precursor boat  1642  is in some embodiments made of inert material comprising stainless steel, nickel, titanium, quartz glass, SiC or Al 2 O 3 . The sinter cartridge  1638  is attached with a fitting  1640  to the sealable front flange  1606 . 
       FIG. 17  depicts a heated precursor source according to another embodiment. The heated precursor source shown from the side  1700  and from the front  1702  comprises a source body  1704 , a sealable front flange  1706 , a loading port  1708 , an inactive gas inlet valve  1714 , a precursor vapor outlet valve  1716 , a mounting flange  1614 , heat insulation of the source body and pulsing valves  1740 , heat insulation of the loading port  1738  and heat insulation of the in-feed line  1742 . The heat insulation of the source body and pulsing valves  1740  can alternatively be implemented as separate insulations: one for the source body and one for the pulsing valves. 
     The heated precursor source  1700 ,  1702  brings certain benefits. The pulsing valves  1714 ,  1716  are attached to the back side of the source body  1704  in horizontal direction. The loading port  1708  of the source is towards the front side of the reactor and towards the operator of the heated source. The loading and unloading of the precursor cartridge  1758  is straightforward. 
     The temperature of the heated source is measured with a thermocouple  1732  connected with wires  1734  to a control unit (not shown). A heating cartridge  1736  comprises a heating element and a thermocouple for measuring the local temperature of the heating cartridge. When the inactive gas inlet valve  1714  and the precursor vapor outlet valve  1716  are closed inactive purge/carrier gas (e.g. nitrogen or argon) flows through the following conduits: source inlet connection  1718 , the inactive gas inlet valve  1714 , the source by-pass line having a flow restrictor  1722 , the precursor vapor outlet valve  1716 , source outlet conduit  1726 , and reactor in-feed conduit  1728 . 
     When the inactive gas inlet valve  1714  and the precursor vapor outlet valve  1716  are open, inactive/carrier gas flow is divided into two parts. The first part of the gas flow goes through the by-pass line having the flow restrictor  1722 . The second part of the gas flow enters a vapor space  1730  of the heated source through the vapor space inlet conduit  1720 . The second part of the gas flow is mixed with precursor vapor within the vapor space  1730  of the heated source. The resulting first gas/vapor mixture exits the vapor space through the vapor space outlet conduit  1724 . The first gas/vapor mixture is added to the first part of the gas flow coming from the by-pass line forming a second gas/vapor mixture. The second gas/vapor mixture flows through the source outlet conduit  1726  and through the reactor in-feed conduit  1728  to the reaction space (not shown). 
     The heated precursor system utilizes thermal energy leaking from the direction of the reaction chamber heater along the in-feed conduit  1728  towards the heated source body  1704 . Heat losses from the heated source neck  320  to the surroundings are minimized with the thermal insulation of the neck  1742 . 
     The heated precursor source  1700  is removed from the reactor for service by opening the source inlet connection  1718  and the feed-through fitting  1710 . 
       FIG. 18  depicts a sealable precursor cartridge according to one embodiment. The precursor cartridge  1800  (whose neck area magnification is shown in the top part of  FIG. 18 ) comprises a cartridge body  1804 , the cartridge neck  1805  having an cartridge opening  1834 , a slide sleeve  1806  sealed with dynamic seals  1836 ,  1838  (e.g., radial shaft seals) against the cartridge neck  1805 , a return spring  1830 , a stopper bulge  1832  and an optional handle  1808 . The precursor cartridge is filled with solid or liquid precursor chemical  1824 . Precursor vaporizes to a gas space of the cartridge  1826  until equilibrium vapor pressure characteristic of the precursor and the source temperature is reached. A cartridge furnace  1810  comprises a furnace cylinder  1822  sealable with a static seal  1820  (e.g., o-ring or a radial shaft seal) against the cartridge body  1804  and a sleeve pusher  1818 . A three-way pulsing valve  1815  is attached to a conduit  1835  leading to the cartridge furnace  1810 . The pulsing valve  1815  has a precursor source inlet  1812 , an inlet  1814  for inactive gas, and an outlet  1816  towards the reaction space (not shown). 
       FIG. 19  depicts the use of a sealable precursor cartridge. First the source system is purged with inactive gas as illustrated in the top part of  FIG. 19 . The precursor cartridge  1804  is pushed into the furnace cylinder  1810  until the furnace static seal  1820  forms a seal against the cartridge body  1804  isolating a gas space of the cartridge furnace from the surrounding gas atmosphere (e.g., room air). Inactive gas flows through the source line from the purge inlet  1814  of the pulsing valve  1815  to the outlet  1816  of the pulsing valve. When the pulsing valve precursor source inlet  1812  is opened the gas space inside the furnace cylinder  1822  becomes in fluid communication with the source line  1814 ,  1816 . Inactive gas pressure of the source line is varied with a mass flow controller (not shown). Low inactive gas flow rate (e.g., 100 sccm) drops the pressure of the source line to a low value (e.g., 4 hPa). Low flow rate is kept for a length of time, for example, about 1 minute. High inactive gas flow rate (e.g., 1000 sccm) increases the pressure of the source line to a high value (e.g., 15 hPa). High flow rate is kept for a length of time, for example, about 1 minute. The pressure fluctuation is repeated a number of times, for example, at least 10 times. The pressure fluctuation pumps residual air away from the gas space of the cartridge furnace  1810  and leaves only pure inactive gas to the gas space inside the furnace cylinder  1822 . After purging the pulsing valve inlet  1812  is closed. 
     Next the precursor cartridge is pushed inwards until the cartridge opening  1834  at the cartridge neck is exposed and the vapor space  1826  of the precursor cartridge becomes in fluid communication with the gas space of the cartridge cylinder  1822 . When the precursor cartridge  1804  is heated to the source temperature, some of the liquid or solid precursor  1824  vaporizes to the gas space  1826  of the cartridge furnace until the gas space is saturated with the precursor vapor. When the pulsing valve precursor source inlet  1812  is opened, precursor vapor flows through the pulsing valve  1815  to the outlet of the pulsing valve  1816 . Carrier gas flowing through the three-way valve from the purge inlet  1814  of the pulsing valve to the outlet  1816  of the pulsing valve pushes the precursor vapor towards the reaction chamber (not shown). When the pulsing valve inlet  1812  is closed, the gas space  1826  of the precursor cartridge depleted from the precursor vapor receives new precursor vapor from the vaporizing liquid or solid precursor  1824  until the gas space again becomes saturated with the precursor vapor and the precursor source is ready for delivering the next precursor pulse. 
     When it is time to remove the used precursor cartridge  1800  from the heated source or replace it with a new precursor cartridge, the precursor cartridge is kept at source temperature and the cartridge is pulled out of the cartridge furnace  1810  until the return spring  1830  is capable of pushing the slide sleeve  1806  over the cartridge opening  1834  isolating the vapor space of the precursor cartridge  1826  from the gas space of the cartridge furnace  1810 . The furnace static seal  1820  still touching the surface of the precursor cartridge  1800  keeps the gas space of the cartridge furnace  1810  isolated from room air. The inlet side of the pulsing valve  1815  is opened and the gas space of the cartridge furnace  1810  is purged with inactive gas that has fluctuating pressure. After all of the residual precursor has been removed from the gas space inside the cartridge cylinder  1822  by purging, the inlet side  1812  of the pulsing valve is closed. The precursor cartridge  1800  is then removed from the cartridge furnace  1810  and a new precursor cartridge is placed to cartridge furnace. 
       FIG. 20  depicts a heated precursor source (or source system) suitable for a sealable precursor cartridge. The heated precursor source  2000  comprises a source body (or framework)  302 , thermal insulator  304  for the source body, a heater cartridge  355  with an electrical power connection  362  and thermocouple connection  364  for measuring the heater cartridge temperature, a thermocouple connection  1734  for measuring the temperature of the source body  304 , space for a sealable precursor cartridge  2002 , a purge inlet conduit  371 , a source by-pass conduit  336 , a source outlet conduit  342 , a by-pass flow restrictor  337 , a cartridge inlet conduit  334  and a cartridge outlet conduit  338 . Pulsing valves  2006 ;  2008  are within the heated area  2012  of the precursor source. Source outlet conduit  342  is surrounded by thermal insulation  320  and the conduit is passively heated utilizing heat energy arriving from the direction of a reaction chamber heater (not shown). The heated precursor source  2000  may also comprise threads  2004  for a lock nut ( FIG. 21 ). Because the source inlet valve  2006  and the source outlet valve  2008  are closed, inactive carrier/purge gas can only flow through the purge inlet conduit  371  to the source by-pass conduit  336  and further to the source outlet conduit  342 . The direction of flow is shown by the arrows  2014 ,  2016  and  2022 . The by-pass flow restrictor  337  (e.g., a 20 mm long glass capillary having a 0.6 mm hole) has limited flow conductance compared to the nearby conduits. Thus, the pressure of the conduit to the upstream of the by-pass flow restrictor is higher (e.g., 3-10 hPa higher) than the pressure of the conduit to the downstream of the by-pass flow restrictor. 
       FIG. 21  depicts a sealable precursor cartridge in a closed position. According to one embodiment the sealable precursor cartridge assembly comprises a cartridge casing  2102 , a casing seal  2104  (e.g., an o-ring), a lock nut  2106  for the casing, a cartridge adapter  2108  with holes  2114  and with a tight tolerance fitting against the cartridge casing  2102 , a cartridge cap  2110 , a cartridge seal  2112  (e.g., an o-ring), a cartridge body  2116 , an adjustment bellows  2118 , an adjustment stem or screw  2120  for lifting and lowering the cartridge body together with the cartridge cap  2110 , and a cartridge thermocouple  2122  for measuring the temperature of the cartridge body  2116 . Due to the cartridge seal  2112  precursor vapor can not enter a lifter space  2125  from the gas space  2126  via holes  2114 . 
     The precursor source body  2102  is first heated with the heater cartridge  355  to a sufficiently high temperature (e.g., 80-150° C. depending on the desired precursor temperature). The maximum allowed temperature of the heater cartridge  355  is programmed by the operator of the precursor source. Typically, the maximum allowed temperature is about +50° C. higher than the desired source body temperature. When power to the heater cartridge  355  is switched on, the temperature of the heater cartridge increases and heat energy starts to stream from the heater cartridge  355  at higher temperature to the source body  2102  at lower temperature. If the temperature of the heater cartridge  355  reaches the programmed maximum allowed temperature, power to the heater cartridge is switched off. The source body  302  has high thermal conductivity and temperatures between the parts of the source body tend to become even. Because the source body  302  is covered with thermal insulation  304 , the temperature of the source body  302  is maintained with little heating power. It is advantageous to keep the bottom of the precursor cartridge at a lower temperature (e.g., 1-5° C. lower) than the source body  302 . The bottom side of the precursor cartridge has less thermal insulation than the source body  302 . The coldest spot of the precursor source is thus formed to the bottom of the precursor cartridge. The vapor pressure of a source chemical has the lowest value near the coldest spot within a closed gas volume. Because the coldest spot of the source system is away from the cartridge inlet  334  and cartridge outlet  338  conduits, condensation of the source chemical to the said conduits is avoided. 
     According to one embodiment, the source body  302  is first heated to a source temperature, and then the cartridge casing  2102  holding the precursor cartridge  2116  filled with liquid or solid precursor  2124  is sealed with the casing o-ring  2104  against the source body  302  by tightening the threaded lock nut  2106  of the casing. Residual air is removed from the lifter space  2125  by purging the space  2125  with inactive gas. Source inlet valve  2006  and source outlet valve  2008  are opened and the flow rate of the inactive gas coming through the purge inlet conduit  371  is altered between the low value (e.g., 100 sccm) and the high value (e.g., 1000 sccm) to generate fluctuating pressure at the conduits  334  and  338  and within the lifter space  2125 . Pressure variations carry residual air away from the heated source. 
       FIG. 22  depicts the sealable precursor cartridge in an open position. After purging the cartridge assembly (the cartridge adapter  2108 , the cartridge cap  2110  and the cartridge body  2116 ) is lifted with the adjustment stem or screw  2120  until there is a sufficiently large gap (e.g., 2-5 mm) between the cartridge cap  2110  and the cartridge seal  2112 . Precursor vapor flows and/or diffuses from the vapor space  2126  of the precursor cartridge via the holes  2114  through the said gap to the lifter space  2125  and further through the optional particle filter  2204  to the cartridge inlet conduit  334  and cartridge outlet conduit  338 . During the pulse time the source inlet valve  2006  and the source outlet valve  2008  are kept open. With the help of the by-pass flow restrictor  2020 , the pressure of the inactive gas at the purge inlet conduit  371  is kept at a higher value than the pressure of the precursor vapor at the cartridge inlet conduit  334 . As a result, inactive gas flowing along the inlet conduit  334  as indicated with the arrow  2202  pushes precursor vapor towards the cartridge outlet conduit  338  as indicated with the arrow  2206 . The mixture of precursor vapor and inactive gas flows through the opened source outlet valve  2008  and is then pushed with the small inactive gas flow coining along the by-pass line  336  as indicated with the arrow  2016  towards the source outlet conduit as indicated with the arrow  2022  and further towards the reaction chamber (not shown). The length of the arrows  2014 ,  2016 ,  2022 ,  2202  and  2008  are in proportion to the actual flows. 
     The presented heated precursor source systems are suitable, for example, for generating precursor vapor from solid or liquid chemicals that have a vapor pressure of at least about 0.5 hPa at temperatures below about 200° C. Chemicals that can be utilized with the presented heated precursor source systems comprise metal halides (e.g. AlCl 3 , TaCl 5 ), cyclopentadienylmetals and derivatives of cyclopentadienylmetals (e.g., bis(cyclopentadienyl)ruthenium Cp 2 Ru, tris(methylcyclopentadienyl)scandium (CH 3 Cp) 3 Sc, bis(methyl-η 5 -cyclopentadienyl)magnesium), metal alkoxides (e.g., titanium isopropoxide Ti(O i Pr) 4 , tantalum pentaethoxide Ta(OEt) 5 ), metalbetadiketonates (e.g. tris(2,2,6,6-tetramethyl-3,5-heptanedionato) lanthanum La(thd) 3 , bis(acetylacetonato) nickel Ni(acac) 2 , alkylamido metals (e.g., tetrakis(ethylmethyl)amido hafnium [(EtMe)N] 4 Hf, also known as TEMAH). 
     Thin films that can be deposited with precursor vapor obtained from heated precursor source(s) comprise binary metal oxides, such as group IIA oxides comprising magnesium oxide MgO, group IIIB oxides comprising scandium oxide Sc 2 O 3 , yttrium oxide Y 2 O 3 , lanthanum oxide La 2 O 3  and lanthanide oxides, e.g. gadolinium oxide Gd 2 O 3 , group IVB oxides comprising titanium dioxide TiO 2 , zirconium dioxide ZrO 2  and hafnium dioxide HfO 2 , group VB oxides comprising tantalum pentoxide Ta 2 O 5 , group VIB oxides comprising tungsten trioxide WO 3 , group VIIB oxides comprising manganese (III) oxide Mn 2 O 3 , group 8 oxides comprising ruthenium dioxide RuO 2 , group IB oxides comprising nickel (II) oxide NiO, copper (II) oxide CuO, group IIB oxides comprising zinc oxide ZnO, group IIIA oxides comprising aluminum oxide Al 2 O 3 , group IVA oxides comprising silicon dioxide SiO 2  and tin dioxide SnO 2 , and group VA oxides comprising bismuth oxide Bi 2 O 3 , ternary and quaternary metal oxides of said groups, such as metal aluminates and metal silicates, solid solutions of metal oxides and metal oxide nanolaminates of said groups, such as Al 2 O 3 /HfO 2 , metal nitrides, such as group IIIB nitrides comprising lanthanum nitride LaN, group IVB nitrides comprising titanium nitride TiN, group VB nitrides comprising niobium nitride NbN and tantalum nitride Ta 3 N 5 , group VI nitrides comprising molybdenum nitride MoN, group IIIA nitrides comprising aluminum nitride AlN, group IVA nitrides comprising silicon nitride Si 3 N 4 , and other metal compounds comprising tungsten nitride carbide WN x C y . 
     The source temperature of the heated precursor source can be selected in some embodiments from a range of approximately 40-200° C. It is to be noted that this range is only a typical range at the moment, also higher temperatures may be appropriate in other embodiments. The operating pressure of the heated precursor source is usually in the range of approximately 0.5-50 hPa during a deposition process, although lower or higher source pressures are possible in other embodiments. The heated precursor source(s) can be used for depositing thin films on single substrates such as 3″-12″ silicon wafers, multiple substrates on a batch process reactor such as 2-50 pieces of 3″-12″ silicon wafers, powders in a powder cartridge reactor such as 1-1000 g of 10 μm-1 mm SiO 2 . The heated precursor source(s) can be used for continuous feeding of precursor vapor in CVD reactors or preferably for pulsed feeding of precursor vapor in ALD reactors. Typically 1-3 heated precursor sources are attached to the ALD reactor. In some embodiments more than 3 heated precursor sources are attached to a reactor. The capacity of the heated precursor source is typically 1-100 g of source chemical although in some embodiments more than 100 g of source chemical are loaded into the source container for production purposes. 
     Choice of construction material depends on the source chemicals. Aluminum, stainless steel AISI 316L, titanium, nickel and hastelloy serve as examples of the construction materials. 
     In certain embodiments of the invention the whole heated precursor source together with a heater and heat insulators can easily be attached to the reactor and removed from the reactor for refilling of the source. Another benefit is that the temperature of the source system can be controlled with a simple single heater. 
     EXAMPLES 
     The following examples give further illustration of certain embodiments. 
     Example 1 
     Vapor-Generating Capacity of the Heated Precursor Source 
     Conversion Factors: 
     100 cm 3 =0.1 dm 3 =1*10 −4  m 3  
 
1 mbar=100 Pa=1 hPa
 
     Tetrakis(ethylmethylamido)hafnium, also known as TEMAH, is used as a source chemical. When the equilibrium vapor pressure of the precursor is 3 hPa at about +104° C. and the line pressure is 15 hPa, the resulting gas-vapor mixture contains 3 hPa/15 hPa * 100 vol.-%=20 vol.-% of precursor vapor. The vapor phase volume of the precursor cartridge is 100 cm 3 . If the source pressure is lowered to 5 hPa during the pulse, (15 hPa-5 hPa)/15 hPa * 100%=67% of the precursor vapor is guided out of the precursor cartridge. 67% * 3 hPa * 100 cm 3 =200 mbar*cm 3 . 
     When the source temperature is +104° C. (377 K), according to ideal gas law pV=nRT-&gt;n=pV/RT=200 Pa * 1*10 −4  m 3 /(8.31441 Jmol −1 K −1  * 377 K)=200 N/m2 * 1*10 −4  m 3 /(8.31441 Nmmol −1 K −1  * 377 K)=0.02 Nm/3135 Nmmol −1 =0.00000638 mol and m(TEMAH)=411.89 g/mol * 0.00000638 mol=0.00263 g=2.63 mg 
     In this example it is assumed that 25% of the precursor vapor chemisorbs on the substrate surface and 75% of the precursor vapor is lost to the growth of thin film on the reaction chamber walls or directly to the exhaust line of the ALD reactor. The maximum density of HfO2 is 9.68 g/cm 3  (equal to 9.68 mg/mm 3 =9.68 * 10 −9  mg/μm 3 ). According to literature the growth rate of HfO2 from TEMAH and H 2 O is 0.06 nm/cycle at +300° C. Thus, the amount of added HfO 2  on a smooth 1 cm 2  surface is 0.06 nm * 0.01*10 9  nm * 0.01*10 9  nm=6*10 12  nm 3 =6000 μm 3  and the mass is 9.68*10 −9  mg/μm 3  * 6000 μm 3 =0.0000581 mg. The molar mass of hafnium dioxide M(HfO 2 ) is 210.49 g/mol and the molar mass of TEMAH is 411.89 g/mol. Thus, 411.89 g/mol/210.49 g/mol * 0.0000581 mg=0.00011 mg of TEMAH is needed for covering 1 cm 2  of smooth surface and with 25% chemisorption efficiency 0.00045 mg of TEMAH vapor must be fed to the reaction chamber for covering 1 cm 2  of smooth substrate surface. The precursor source delivers 2.66 mg of TEMAH during the precursor pulse and thus it is capable of covering 2.66 mg/0.00045 mg/cm 2 =5900 cm 2  of smooth substrate surface which is sufficient for processing a batch of 75 pieces of 4-inch wafers. It can be estimated that a heated precursor source with a vapor space reduced by 90% from 100 cm 3  to 10 cm 3  loaded with a source chemical with a vapor pressure reduced by 80% from 3 hPa to 0.5 hPa provide already enough precursor vapor for depositing a thin film on 5900 cm 2  * 0.1 * 0.2=118 cm 2  which is enough for coating a single 100 mm (4-inch) wafer. The temperature of the source system is measured with a thermocouple that is placed near the bottom of the source cartridge. The source system is heated with a resistive heater that is placed within the source framework. The heater comprises an internal thermocouple for measuring the heater temperature. Power consumption of the heater is typically in the range of 50-500 W, preferably 100-200 W. Such a low power consumption means that 24 VDC power source with PID temperature controller can be used for driving the heater although in other embodiments pulsed line AC voltage is used with a temperature controller for driving the heater. Source outlet conduit is heated passively from two directions. Heat is moving by conduction from the source framework towards the bottom part of the source outlet conduit and by radiation and convection from the reaction chamber heater to the upper part of the source outlet conduit. Heat losses are minimized with heat insulating layers and with contoured design of the feed-through projection. The feed-through projection extends from the intermediate space of the reactor to the feed-through flange. Outer empty gap between the outer feed-through projection and the inner feed-through projection lengthens the path of heat conduction and thus decreases the amount of heat lost by conduction to the bottom flange of the reactor. Collar-shaped neck insulator circles the seal tightening nut. Inner empty gap between the heat equalizer block and inner feed-through projection makes it difficult for the heat to move from the heat equalizer block to the bottom flange of the reactor. In other embodiments the feed-through area can be equipped with another heater for maintaining the source line temperature above the condensation temperature of the precursor vapor. 
     The source system is detached without the feed-through projection from the bottom flange of the reactor by removing the neck insulator and loosening the seal tightening nut. The source system is detached with the feed-through projection from the bottom flange of the reactor by loosening the clamping seal. 
     Silicone rubber foam that stands temperatures up to 200-250° C. serves as an example of a suitable material for the heat insulator. To make a very compact source system, surfaces to be heat insulated can also be coated with a heat insulating ceramic paint such as Supertherm® paint. Supertherm® paint stands about +260° C. continuously and it blocks both heat conduction and infrared radiation. Heat loss by convection is also very small due to solid structure of the dried paint. As a comparison, about 0.25-0.5 mm thick layer of dried ceramic paint is enough for insulating the framework as efficiently as 100 mm thick piece of rubber foam. 
     The source cartridge comprises cartridge body, a cartridge seal and an optional particle filter. A threaded cartridge flange with a tip pushes the cartridge body against the source framework and the cartridge seal pressed between the cartridge body and the source framework makes the cartridge leak tight against room air. The cartridge seal can be an o-ring made of e.g. Viton rubber or perfluorinated rubber (such as Kalrez®, Simriz® or Chemraz®) that stand temperatures up to 200-230° C. Other materials suitable for the seals in the source can be selected, e.g., from Eriks o-ring technical manual. 
     The tip of the source conduit can be attached to the reaction chamber for example by tolerance fitting, VCR fitting or metal ferrule fitting. 
     Example 2 
     Deposition of a Tantalum Pentoxide Ta 2 O 5  with a Heated Precursor Source 
     Tantalum pentaethoxide Ta(OEt) 5  and water were used as precursors for the deposition of Ta 2 O 5  thin film on 4″ silicon substrate within the reaction space of the SUNALE™ R-150 ALD reactor manufactured by Picosun Oy, Finland. Ta(OEt) 5  is viscous liquid near room temperature and it has a vapor pressure of 10 hPa at +120° C., wherein 1 hPa=100 Pa=1 mbar. Because Ta(OEt) 5  has negligible vapor pressure near room temperature, a heated precursor source was used for obtaining sufficient source vapor pressure at elevated source temperatures. Ta(OEt) 5  was loaded with a needle and a syringe into a glass cartridge that was pushed to the radial axis seal of the heated precursor source. Water is liquid at room temperature and it has a vapor pressure of 23 hPa at 20° C. Liquid precursor source was used for vaporizing water near room temperature 25° C. 
     A 100-mm silicon wafer was used as a substrate. The substrate was placed to the substrate holder and the holder was lowered to the reaction chamber of the ALD reactor. The reaction space and the intermediate space were pumped down to below 1 hPa absolute pressure with a mechanical vacuum pump. While the vacuum pump was running the pressure of the reaction space was adjusted with flowing nitrogen gas to a pressure range of approximately 1-3 hPa. 
     The pressure of the intermediate space was kept about 3-5 hPa higher than the pressure of the reaction space, so that precursor vapor could not leak from the reaction space to the intermediate space. In other embodiments different kind of pressure ranges are feasible, as long as gases can be removed quickly enough from the reaction space to the exhaust line and reactive gases cannot leak towards the intermediate space. The reaction space had been preheated to 300° C. in order to speed up the heating of the substrate. After the pressure had stabilized within the reaction space, the process control waited for about 5 minutes until the temperatures within the reaction space had become even. 
     The deposition cycle consisted of four basic sequential steps: Ta(OEt) 5  vapor exposure period (0.2 s), a first removal period (2.0 s), H 2 O vapor exposure period (0.1 s) and a second removal period (4.0 s). When the process control unit had completed the deposition sequence consisting of 1000 identical deposition cycles, the pumping valves were closed and the reactor was vented with pure nitrogen gas to atmospheric pressure. The substrate holder was lifted from the reaction chamber and the substrate was unloaded from the substrate holder for measurements. As a result of the deposition experiment, a Ta 2 O 5  thin film with a thickness of 40 nm was obtained on the substrate. The growth rate of Ta 2 O 5  was 0.07 nm/cycle at 300° C. 
     Example 3 
     Deposition of a doped metal oxide thin film with three precursor sources 
     The ALD reactor was equipped with one Picosolution™ precursor source loaded with diethylzinc (DEZ), one Picosolution™ precursor source loaded with purified water and one Picohot™ source system loaded with bis(methyl-η 5 -cyclopentadienyl)magnesium (CPMM). CPMM source was heated to +95° C. resulting in a vapor pressure of about 10 hPa. The water source temperature was controlled with a peltier element cooler so that the temperature of the water source was preferably slightly below the room temperature, although temperatures above the room temperature can be used in other embodiments provided that the source line is sufficiently insulated for preventing condensation of water. In this deposition example the temperature of the cooled water source was +18° C. 
     The reaction chamber of the ALD reactor was heated to +250° C. A 6-inch silicon wafer was loaded into the reaction chamber. About 5 minutes were set to the stabilization timer in order to stabilize the temperature of the wafer to the reaction chamber temperature. 
     Water vapor was first pulsed to the reaction chamber to saturate the substrate surface with hydroxyl (OH) groups. According to other embodiments it is also possible to start the pulsing directly with the metal precursor because substrate surfaces typically contain enough OH groups to initiate the thin film growth. 
     Next, the deposition program fed pulses of DEZ, CPMM and water vapor separated with nitrogen purge gas into the reaction chamber. As a result, n-type ZnO thin film doped with Mg was grown on the wafer with a growth rate of 2 Å/cycle. 
     It should be noted that certain advantages have been described above. Of course, it is to be understood that not necessarily all such advantages may be achieved in accordance with any particular embodiment of the invention. Thus, for example, those skilled in the art will recognize that the invention may be embodied or carried out in a manner that achieves or optimizes one advantage or group of advantages as taught herein without necessarily achieving other objects or advantages as may be taught or suggested herein. 
     Moreover, although this invention has been disclosed in the context of certain preferred embodiments and examples, it will be understood by those skilled in the art that the present invention extends beyond the specifically disclosed embodiments to other alternative embodiments and/or uses of the invention and obvious modifications and equivalents thereof. In addition, while a number of variations of the invention have been shown and described in detail, other modifications, which are within the scope of this invention, will be readily apparent to those of skill in the art based upon this disclosure. For example, it is contemplated that various combinations or sub combinations of the specific features and aspects of the embodiments may be made and still fall within the scope of the invention. Accordingly, it should be understood that various features and aspects of the disclosed embodiments can be combined with or substituted for one another in order to form varying modes of the disclosed invention. Thus, it is intended that the scope of the present invention herein disclosed should not be limited by the particular disclosed embodiments described above, but should be determined only by a fair reading of the claims that follow.