Patent Publication Number: US-2022235466-A1

Title: Porous inlet

Description:
FIELD 
     The disclosed embodiments generally relate to substrate processing methods and apparatus, in particular to chemical deposition and etching methods and deposition and etching reactors. More particularly, but not exclusively, the disclosed embodiments relate to atomic layer deposition (ALD) reactors. 
     BACKGROUND 
     This section illustrates useful background information without admission of any technique described herein representative of the state of the art. The described reactor structure can however be better understood, for example, by considering the granted patent U.S. Pat. No. 8,211,235 B2. 
     In chemical deposition methods chemicals are provided into a reaction chamber by at least one in-feed line. The in-feed lines typically extend through a heated volume on their way into the reaction chamber. However, this increases the risk of the chemicals sticking onto the walls of the in-feed lines or otherwise react with the walls of the in-feed lines. 
     SUMMARY 
     Accordingly, the aspects of the disclosed embodiments are directed to providing a method and apparatus with minimized sticking of chemical or plasma on the infeed-line(s). 
     More generally, of the aspects of the disclosed embodiments are directed to providing a method and apparatus with minimized sticking of chemical or plasma on the walls of vacuum parts. Examples of vacuum parts herein are the in-feed line(s), reaction chamber, substrate holder (susceptor) and a pump fore-line via which some reaction products and residual gases exit from the reaction chamber towards a pump (for exhaust). The sticking may refer to physical adsorption down to one molecular layer in thickness. 
     According to a first example aspect of the disclosed embodiments there is provided a substrate processing apparatus, comprising: 
     a reaction chamber with an inlet opening; 
     an in-feed line to provide a reactive chemical into the reaction chamber via the inlet opening; 
     incoming gas flow control means in the in-feed line, the in-feed line extending from the flow control means to the reaction chamber, the in-feed line in this portion between the flow control means and the reaction chamber having the form of an inlet pipe with a gas-permeable wall, the inlet pipe with the gas-permeable wall extending towards the inlet opening through a volume at least partly surrounding the inlet pipe, and 
     the apparatus being configured to provide fluid to surround and enter the inlet pipe in said portion. 
     In certain embodiments, the gas-permeable wall is a wall formed of gas-passing pathways. The gas-passing pathways may include pores. There may be provided a multitude of gas-passing pathways providing a protective flow extending along the whole inner surface of the inlet pipe. In certain embodiments, the gas-permeable wall is a porous wall. In certain embodiments, the wall in itself is gas-permeable. In certain embodiments, the wall comprises at least 100 gas-passing pathways. In certain embodiments, the wall comprises at least 1000 gas-passing pathways. In certain embodiments, the wall comprises a section in which the gas-passing pathways are spread over the whole circumference of the inlet pipe and over a longitudinal distance of the inlet pipe. 
     In certain embodiments, the gas-permeable wall in itself is gas-permeable in contrast to pipes having walls with individual openings or specific injection channels. In certain embodiments, the gas-permeable wall has perforations or contains openings or gas-passing pathways throughout the gas-permeable wall section or area. In certain embodiments, the said openings or gas-passing pathways are provided in a uniform manner. In certain embodiments, the gas-permeability of the gas-permeable wall is an integral feature or property of the inlet pipe. 
     In certain embodiments, the gas-permeable wall extends to the inlet opening. However, in other embodiments the gas-permeable wall does not extend to the inlet opening, but it only extends towards the inlet opening. In such embodiments, an edge of the reaction chamber close to the inlet opening or at the inlet opening may be a hot or heated edge to reduce sticking. 
     In certain embodiments, the incoming gas flow control means comprise a valve. In certain embodiments, the incoming gas flow control means comprise a pulsing valve. In certain embodiments, the incoming gas flow control means comprise a three-way valve (or an ALD valve) or a four-way valve. Examples of such valves have been presented in WO 2018/202935 A1, and WO 2018/202949 A1. In certain embodiments, the incoming gas flow control means comprise other flow control means in addition or instead of the means described hereinbefore. 
     In certain embodiments, the volume at least partly surrounding the in-feed line is a volume outside of the reaction chamber. In certain embodiments, the volume at least partly surrounding the in-feed line is a volume at least partly surrounding the reaction chamber, for example an intermediate space in between the wall of the reaction chamber and an outer chamber (or vacuum chamber) wall. 
     In certain embodiments, the fluid to surround and enter the inlet pipe is higher pressure fluid. In certain embodiments, the expression “higher pressure” refers to the pressure of the fluid surrounding the inlet pipe to be higher than the pressure of the gas or fluid that flows within the inlet pipe (before mixing with the surrounding fluid). 
     In certain embodiments, the apparatus comprises means to provide said higher pressure fluid. 
     In certain embodiments, the apparatus is configured to prevent the reactive chemical from adhering to an inner surface of the inlet pipe. 
     In certain embodiments, the apparatus comprises: 
     an outer tube around the inlet pipe configured to provide said at least partly surrounding volume. 
     In certain embodiments, the outer tube is formed of a gas-impermeable wall. 
     In certain embodiments, the apparatus comprises: 
     an outer tube (or pipe) around the inlet pipe configured to provide the fluid to surround and enter the inlet pipe. 
     In certain embodiments, the surrounding fluid is gas. In certain embodiments, the surrounding fluid is inactive gas. 
     In certain embodiments, the apparatus is configured to pass inactive gas in between the inlet pipe and the outer tube. 
     In certain embodiments, the apparatus is configured to pass reactive fluid in between the inlet pipe and the outer tube causing a reaction between the reactive chemical and said reactive fluid within the inlet pipe. In certain embodiments, powder is formed in such a reaction. 
     In certain embodiments, the apparatus is configured to pass reactive fluid in between the inlet pipe and the outer tube causing a reaction between the reactive chemical and said reactive fluid within the inlet pipe to produce another chemical, ion, radical or other such form, species. Such species thus formed will then react within the reaction chamber with another precursor causing a surface reaction on a substrate therein. Accordingly, in certain embodiments, a chemical that is initially not reactive with another chemical may be caused to become reactive with said another chemical by activating it by material flowing through the gas permeable wall. 
     In certain embodiments, the apparatus comprises: 
     an outer chamber around the reaction chamber, the outer chamber forming the volume surrounding the reaction chamber. 
     In certain embodiments, the apparatus comprises a feedthrough in the outer chamber wall to pass inactive gas into the intermediate space. 
     In certain embodiments, the apparatus comprises an intermediate space in between the reaction chamber and an outer chamber wall, the intermediate space providing a volume at least partly surrounding the in-feed line. 
     In certain embodiments, the apparatus is configured to pump both the reaction chamber and the outer chamber into vacuum. A same pump or separate pumps may be used. 
     In certain embodiments, the apparatus comprises a heater in said at least partly surrounding volume. 
     In certain embodiments, the apparatus is configured to provide heating or cooling of the reactive chemical within the inlet pipe by thermal radiation or by the surrounding fluid (or by said higher pressure fluid) which is provided with a higher or lower temperature. 
     In certain embodiments, reactive chemical (or precursor) is pulsed via a valve (for example the pulsing valve or three-way valve) into the inlet pipe. In certain embodiments, the valve is a four-way valve. 
     In certain embodiments, the apparatus is configured to provide heating or cooling of the reactive chemical within the inlet pipe by said higher pressure fluid, where fluid in the outer tube is heated or cooled by a different method than the fluid in the inner pipe. 
     In certain embodiments, the inlet pipe comprises means of heating the inlet pipe. 
     In certain embodiments, the outer tube comprises means of heating the outer tube. 
     In certain embodiments, the apparatus comprises at least one heater element in a space in between the inlet pipe and the outer tube. In some embodiments, the at least one heater element is integrated with a surface of the inlet pipe. 
     In certain embodiments, the apparatus comprises in addition or instead of the at least one heater element at least one cooler element in the space in between the inner pipe and the outer tube. In certain embodiments, the cooler element applies a liquid circulation for cooling, with an external heat exchanger. 
     In certain embodiments, the gas or fluid flowing through the gas-permeable wall into the inlet pipe is colder than the gas or fluid already existing within the inlet pipe, or becomes colder due to an expansion through the gas-permeable wall into the inlet pipe. 
     The inlet pipe with a gas-permeable wall may be implemented, for example, by porous material such as sintered polymer, sintered metal, 3D printed material with a possible sintering step of metal or ceramic, or ceramic material(s). A specific example of porous material is material that is composed of aluminum oxide and silicon oxide (also known as Pormulit). Any solution of porous material may contain a varied grade of porosity, or e.g. fluid channels within it. A benefit of such channels, easily formed by 3D printing for example, can for example balancing or outflow at different points on the material surface. 
     In certain embodiments, the inlet pipe comprises at least one of the following: a gas-permeable pipe, a porous pipe, a perforated pipe, and a pipe section or sections with at least one gas-permeable gap or a plurality gas-permeable gaps. Such gaps or holes, in certain embodiments, form gas ejectors or structures which generate a choked flow effect. The gas-permeable/porous area may have different densities of openings, or it may be formed of any combination of the aforementioned structures or means in order to lead the fluid to pass through the wall. 
     In certain embodiments, the apparatus comprises an additional opening outside of the inlet pipe providing a flow path from outside of the reaction chamber into the reaction chamber. This flow path is additional to a flow path provided by the in-feed line (or inlet pipe). If the apparatus comprises the outer tube surrounding the inlet pipe, said additional opening can be positioned outside of the inlet pipe but inside of the outer tube. In certain embodiments, the apparatus comprises an additional opening from the outer tube directly to the reaction chamber. In certain embodiments, the fluid within the outer tube has two routes to enter the reaction chamber, one through said additional opening outside of the inlet pipe and one via the inlet pipe and through the inlet opening. Said additional opening may be arranged in a reaction chamber wall. In certain embodiments, said opening is adjustable, e.g., adjustable in size. 
     In certain embodiments, the apparatus is configured to provide the outer tube with a lower pressure, and the outer tube is open to the reaction chamber via said additional opening positioned outside of the inlet pipe but inside of the outer tube. This provides in certain embodiments a temperature separation between the inlet pipe and the intermediate space surrounding the outer tube. 
     In certain embodiments, the apparatus comprises within the inlet pipe one or more separate fluid channels. Separate herein means that any material flowing within the separate fluid channels is in no fluid communication with the reactive chemical flow in the inlet pipe. As an example, the channel(s) may be made of 3D printed material. In further embodiments, the channel may be a welded pipe. In certain embodiments, the channel has a spiral form. The channel(s) may be air channel(s). The channel(s) may be located on the inner surface of the inlet pipe. The channels may provide the inlet pipe with a heating or a cooling effect by flowing fluid within the channel having a temperature different from the temperature of reactive chemical flow in the inlet pipe. 
     In certain embodiments, the incoming gas flow control means is or comprises a three-way valve or a four-way valve. 
     In certain embodiments, the apparatus comprises a second inlet pipe with a gas permeable wall surrounded by a second outer tube upstream of the incoming gas flow control means. In certain embodiments, the volume in between the inlet pipe and the outer tube is not in direct fluid communication with the volume in between the second inlet pipe and the second outer tube. 
     In certain embodiments, the outer tube comprises a heat-insulating layer, or the apparatus comprises a heat-insulating layer around the outer tube. 
     In certain embodiments, the apparatus comprises a plurality of separate and successive gas volumes surrounding the gas-permeable wall inlet pipe in the flow direction of the inlet pipe. 
     In certain embodiments, the inlet pipe has a gas-permeable wall or is porous, and the outer tube is omitted. In certain such an embodiment, gas from an intermediate space between a reaction chamber wall and an outer (chamber) wall flow (directly) through the inlet pipe. A vacuum chamber may be provided as the outer chamber. 
     In certain embodiments, said intermediate space is omitted, but the inlet pipe and the outer tube are provided outside of the reaction chamber. A heater may be integrated with a reaction chamber outer surface. Alternatively, heating may be provided only for the incoming gases. 
     In certain embodiments, the apparatus comprises a particle filter at a reaction chamber end of the inlet pipe. 
     In certain embodiments, the apparatus comprises an outlet channel from the space between the inlet pipe and the outer tube to a pump (for exhaust). In certain embodiments, the outlet channel begins at the reaction chamber end of the volume defined by an outer surface of the inlet pipe and an inner surface of the outer tube. 
     In certain embodiments, the apparatus comprises a vertical in-feed line approaching the reaction chamber from the top. 
     In certain embodiments, the outer tube is flexible in at least length wise direction, enabling an attachment to the reaction chamber and/or a flexible attachment outside of the vacuum chamber as presented in the 
     In certain embodiments, the inlet pipe comprises segments of areas, where different gases or a mixture of different gases are brought into a gas stream flowing inside of the inlet pipe. 
     In certain embodiments, the surface material of the gas-permeable wall and the fluid flowing through the wall to inside of the inlet pipe are selected with suitable temperatures and solid material surface to create catalytic reaction(s). 
     In certain embodiments, the surface material of the gas-permeable wall and the gas flowing through the wall to inside of the inlet pipe are selected with temperatures to create catalytic reaction(s). 
     In certain embodiments, electromagnetic radiation is induced into the inlet to affect the catalytic reaction. 
     In certain embodiments, the apparatus is configured to perform sequential self-saturating surface reactions on a substrate surface in the reaction chamber. Accordingly, the apparatus is configured to apply atomic layer deposition, ALD. The substrate may be a wafer. 
     In certain embodiments, the apparatus is configured to generate powder. 
     In certain embodiments, the apparatus is configured to perform etching reactions on a substrate surface in the reaction chamber. 
     In certain embodiments, the gas passing through the gas-permeable wall is mixed with gas flowing in the in-feed line upstream of the three-way valve (or incoming gas flow control means). 
     [ 0064 ]In certain embodiments, the gas-permeable wall of the inlet pipe extends upstream of the pulsing valve/incoming gas flow control means so that the gas coming through the gas-permeable wall can be mixed with gas flowing within the inlet pipe before the pulsing valve/incoming gas flow control means. 
     In certain embodiments, the valve/incoming gas flow control means is located in the intermediate space. 
     In certain embodiments, the inlet pipe has at least one curved shape causing the fluid flow to change direction or have a separating force for particles (such as a spiral). 
     In certain embodiments, the valve attached to the inlet pipe consists of multiple valves or means to select from at least two different gases. 
     In certain embodiments, a section after valve(s) comprises or consists of a mixer (or flow direction guide). In certain embodiments, the mixer receives more than one different gas line, which may pass more than one gas or gases with different pressures or different temperatures. In certain embodiments, such a structure forms further protective flow(s) around edges of the gas-permeable pipe wall. In certain embodiments, such a structure may accelerate gas with an ejector or a choked flow effect. 
     In certain embodiments, the gas-permeable pipe wall is adapted to change its width over its length. 
     In certain embodiments, the gas-permeable pipe is adapted to form mixing of at least two incoming branches. In certain embodiments, the gas-permeable pipe is adapted for expanding to at least two outgoing branches. Accordingly, in certain embodiments, at least two outlets lead from the gas-permeable pipe (inlet pipe) to the reaction chamber. These structures facilitate establishing desired chemical reactions between chemicals before the reaction chamber if required. Cleaning after the said chemical reactions may be performed, e.g., by applying the said filter at a reaction chamber end of the inlet pipe which may, e.g., remove particles from a passing flow. 
     In certain embodiments, the inlet pipe is adapted so that it points to the substrate. 
     In certain embodiments, a plasma formation is arranged at least partially within the inlet pipe. This can be done, for example, with an RF plasma generator, placed outside of the inlet pipe. The international patent publication WO 2012/136875 shows an example of the placement. In certain embodiments, the surrounding gas flow entering the inlet pipe keeps the plasma away from the inlet pipe walls. In certain embodiments, the flow(s) are arranged to push the plasma towards the substrate, and in yet further embodiments, to enable small non-uniformity. In certain embodiments, the small non-uniformity is obtained by modifying the flow, for example with a variation in the gas flow in the inlet pipe structure. 
     In certain further embodiments, instead of the surrounding gas entering the inlet pipe, the pressures are controlled to such an extent that the flow direction is from the inside of the inlet pipe through the gas-permeable wall to the outside of the inlet pipe. 
     In certain embodiments, the reaction chamber has gas-permeable walls. In certain embodiments, the reaction chamber walls are formed of gas-passing pathways. The gas-passing pathways may include pores. There may be provided a multitude of gas-passing pathways providing a protective flow extending along the whole inner surface of the reaction chamber. In certain embodiments, the reaction chamber is formed of porous material. 
     In certain embodiments, the reaction chamber with gas-permeable walls is surrounded, at least partly, by a volume. In certain embodiments, the volume is an intermediate space formed between the gas-permeable wall of the reaction chamber and an outer chamber wall. In certain other embodiments, the volume is defined by the gas-permeable wall of the reaction chamber and an outer intermediate wall, the outer intermediate wall residing in between the gas-permeable wall of the reaction chamber and the outer chamber wall. In certain embodiments, the apparatus is configured to provide fluid to surround and enter the reaction chamber from the surrounding volume through the gas-permeable wall of the reaction chamber. 
     In certain embodiments, the apparatus comprises a substrate holder formed of porous material. In certain embodiments, the apparatus comprises a substrate holder comprising at least one gas-permeable wall. 
     In certain embodiments, the apparatus comprises a substrate holder, wherein at least a surface of the substrate holder facing a substrate is formed of gas-passing pathways. The gas-passing pathways may include pores. In certain embodiments, the surface of the substrate holder facing a substrate is porous. 
     In certain embodiments, the apparatus comprises a pump fore-line downstream of the reaction chamber, the pump fore-line having the form of a pipe with a gas-permeable wall. 
     In certain embodiments, the pipe with a gas-permeable wall of the pump fore-line is surrounded by an outer tube having a gas-impermeable wall. 
     According to a second example aspect of the disclosed embodiments there is provided a method of operating the substrate processing apparatus of the first aspect and any of its embodiments. 
     Accordingly, the second example aspect comprises: 
     providing a reactive chemical into a reaction chamber of the apparatus via an in-feed line and through a reaction chamber inlet opening; 
     controlling the in-feed line by incoming gas flow control means, the in-feed line extending from the flow control means to the reaction chamber, the in-feed line in this portion between the flow control means and the reaction chamber having the form of an inlet pipe with a gas-permeable wall, the inlet pipe with the gas-permeable wall extending towards the inlet opening through a volume at least partly surrounding the inlet pipe; and 
     providing fluid to surround and enter the inlet pipe in said portion. 
     In certain embodiments, the method comprises: 
     providing an outer tube around the inlet pipe to provide said at least partly surrounding volume. 
     In certain embodiments, the method comprises: 
     passing inactive gas into the outer tube. 
     In certain embodiments, the method comprises: 
     causing a reaction between the reactive chemical and reactive fluid within the inlet pipe by passing said reactive fluid in between the inlet pipe and the outer tube. 
     In certain embodiments, the method comprises: 
     providing an intermediate space in between the reaction chamber and an outer chamber wall, the intermediate space providing a volume at least partly surrounding the in-feed line. 
     In certain embodiments, the method comprises: 
     passing inactive gas into the intermediate space via a feedthrough in the outer chamber wall. 
     In certain embodiments, the method comprises: 
     heating the at least partly surrounding volume by a heater. 
     In certain embodiments, the method comprises: 
     heating the apparatus by at least one heater element placed in a space in between the inlet pipe and the outer tube. 
     In certain embodiments, the method comprises: 
     heating or cooling of the reactive chemical within the inlet pipe by the surrounding fluid. 
     In certain embodiments, the method comprises: 
     providing a flow into the reaction chamber directly from the outer tube. 
     In certain embodiments, the method comprises: 
     establishing a gas flow into the reaction chamber directly from the outer tube through an opening arranged in the reaction chamber wall. 
     In certain embodiments, the method comprises: 
     controlling gas flow within the in-feed line by a three-way valve. 
     In certain embodiments, the method comprises: 
     providing a second inlet pipe with a gas permeable wall surrounded by a second outer tube upstream of the incoming gas flow control means, and 
     providing fluid to surround and enter the second inlet pipe. 
     In certain embodiments, the method comprises: 
     insulating the outer tube by a heat-insulating layer. 
     In certain embodiments, the method comprises: 
     providing a plurality of separate and successive gas volumes surrounding the gas-permeable wall inlet pipe in the flow direction of the inlet pipe. 
     In certain embodiments, the method comprises: 
     removing particles with a particle filter at a reaction chamber end of the inlet pipe. 
     In certain embodiments, the method comprises: 
     exhausting material from the space between the inlet pipe and the outer tube to an outlet channel by-passing the reaction chamber. 
     In certain embodiments, the method comprises: 
     approaching the reaction chamber from the top by a vertical in-feed line. 
     In certain embodiments, the method comprises: 
     performing sequential self-saturating surface reactions on a substrate surface in the reaction chamber. 
     In certain embodiments, the reaction chamber comprises gas-permeable wall(s), and the method comprises: 
     providing fluid to surround and enter the reaction chamber through the gas permeable wall(s). 
     In certain embodiments, the reaction chamber is formed of porous material. 
     In certain embodiments, a substrate holder comprises at least one gas-permeable wall. The substrate holder may support one or more substrates within the reaction chamber. 
     In certain embodiments, the method comprises: 
     providing an interior of the substrate holder with fluid, said fluid entering from the interior of the substrate holder to the reaction chamber through the at least one gas-permeable wall. 
     In certain embodiments, the method comprises: 
     pumping both the reaction chamber and the outer chamber into vacuum. 
     According to certain further aspects of the disclosed embodiments certain further methods and apparatus are provided. In these further aspects, the embodiments presented in connection with the first and second aspect will generally apply. However, the further aspects do not contain each of the limitations that the first and second aspect contain. 
     Thus, according to a further example aspect there is provided a substrate processing apparatus, comprising: 
     a reaction chamber with an inlet opening; 
     an in-feed line to provide a reactive chemical into the reaction chamber via the inlet opening; and 
     a portion in the in-feed line upstream of the inlet opening having the form of an inlet pipe with a gas-permeable wall. 
     According to a further example aspect there is provided a method, comprising: 
     providing a reactive chemical into a reaction chamber of a substrate processing apparatus via an in-feed line and through a reaction chamber inlet opening, the in-feed line upstream of the inlet opening comprising a portion in the form of an inlet pipe with a gas-permeable wall, the method further comprising: 
     providing a fluid to enter inside of the inlet pipe from the outside of the inlet pipe through the gas-permeable wall. 
     According to a yet further example aspect there is provided a substrate processing apparatus, comprising: 
     a reaction chamber; 
     an in-feed line to provide a reactive chemical into the reaction chamber; 
     a vacuum chamber at least partly surrounding the reaction chamber; 
     an intermediate space in between a wall of the reaction chamber and a wall of the vacuum chamber, the in-feed line comprising a gas-permeable wall in the area of the intermediate space. 
     According to a yet further example aspect there is provided a method, comprising: 
     providing a reactive chemical into a reaction chamber of a substrate processing apparatus via an in-feed line 
     providing a vacuum chamber to surround the reaction chamber and an intermediate in between a wall of the reaction chamber and a wall of the vacuum chamber; and 
     flowing fluid from the intermediate space to the in-feed line through a gas-permeable wall of the in-feed line. 
     According to a yet further example aspect there is provided a substrate processing apparatus, comprising: 
     a reaction chamber; 
     an in-feed line to provide a reactive chemical into the reaction chamber, the in-feed line being in the form of an inner pipe with a gas-permeable wall and an outer tube surrounding the inner pipe. 
     In certain embodiments, the outer tube comprises heat insulation against its surroundings. 
     According to a yet further example aspect there is provided a substrate processing apparatus, comprising: 
     a reaction chamber with gas-permeable wall(s). 
     According to a yet further example aspect there is provided a substrate processing apparatus, comprising: 
     a substrate holder with gas-permeable wall(s). 
     According to a yet further example aspect there is provided a substrate holder, comprising gas-permeable wall(s). 
     Accordingly, the reaction chamber and/or substrate holder each comprise a gas-permeable wall or gas permeable walls. 
     According to a yet further example aspect there is provided a pipe exiting the reaction chamber, comprising gas-permeable wall(s). 
     What is described concerning the gas-permeable wall(s) of the inlet pipe applies also to the other parts having gas-permeable wall(s) in the same or different embodiments or aspects. Said other parts herein mean e.g. the reaction chamber with gas-permeable wall(s), the substrate holder with gas-permeable wall(s), and fore-line (pump fore-line) with gas-permeable wall(s) leading from the reaction chamber to the pump. Accordingly, the gas-permeable wall(s) of these other parts may also be porous, and corresponding features and solutions described in the context of the inlet pipe are also applicable to the aspects and embodiments concerning said other parts etc., etc. 
     Different non-binding example aspects and embodiments have been presented in the foregoing. The above embodiments and embodiments described later in this description are used to explain selected aspects or steps that may be utilized in implementations of the present disclosure. It should be appreciated that corresponding embodiments apply to other example aspects as well. Any appropriate combinations of the embodiments can be formed. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The disclosed embodiments will now be described, by way of example only, with reference to the accompanying drawings, in which: 
         FIG. 1  shows an apparatus in accordance with certain embodiments; 
         FIG. 2  shows an apparatus in accordance with further embodiments; 
         FIG. 3  shows an apparatus in accordance with further embodiments in which an outer tube is omitted; 
         FIG. 4  shows an apparatus with further embodiments in which an outer chamber is omitted; 
         FIG. 5  shows an apparatus in accordance with certain embodiments comprising a three-way valve; 
         FIG. 6  shows an apparatus in accordance with further embodiments comprising separate surrounding gas volumes; 
         FIG. 7  shows an apparatus in accordance with further embodiments comprising a particle filter; 
         FIG. 8  shows an apparatus in accordance with yet further embodiments; 
         FIG. 9  shows an apparatus in accordance with yet further embodiments with a reaction chamber with a gas-permeable wall; 
         FIG. 10  shows an apparatus in accordance with another embodiment with a porous substrate holder; 
         FIG. 11  shows fluid channels within an inlet pipe in accordance with further embodiments; 
         FIG. 12  shows an apparatus in accordance with yet other embodiments; and 
         FIG. 13  shows a yet further detail in accordance with certain embodiments. 
     
    
    
     DETAILED DESCRIPTION 
     In the following description, Atomic Layer Deposition (ALD) technology is used as an example. However, the disclosed embodiments are not limited to ALD technology, but it can be exploited in a wide variety of substrate processing apparatuses, for example, in Chemical Vapor Deposition (CVD) reactors, or in etching reactors, such as in Atomic Layer Etching (ALE) reactors. 
     The basics of an ALD growth mechanism are known to a skilled person. ALD is a special chemical deposition method based on the sequential introduction of at least two reactive precursor species to at least one substrate. It is to be understood, however, that one of these reactive precursors can be substituted by energy when using, for example, photon-enhanced ALD or plasma-assisted ALD, for example PEALD, leading to single precursor ALD processes. For example, deposition of a pure element requires only one precursor. Binary compounds, such as oxides can be created with one precursor chemical when the precursor chemical contains both of the elements of the binary material to be deposited. Thin films grown by ALD are dense, pinhole free and have uniform thickness. 
     As for substrate processing steps, the at least one substrate is typically exposed to temporally separated precursor pulses in a reaction vessel to deposit material on the substrate surfaces by sequential self-saturating surface reactions. In the context of this application, the term ALD comprises all applicable ALD based techniques and any equivalent or closely related technologies, such as, for example the following ALD sub-types: MLD (Molecular Layer Deposition), plasma-assisted ALD, for example PEALD (Plasma Enhanced Atomic Layer Deposition) and photon-enhanced Atomic Layer Deposition (known also as photo-ALD or flash enhanced ALD). 
     Alternatively or in addition, such processing can be targeted for example at the reaction chamber, for example to passivate or clean the reaction chamber. 
     A basic ALD deposition cycle consists of four sequential steps: pulse A, purge A, pulse B and purge B. Pulse A consists of a first precursor vapor and pulse B of another precursor vapor. Inactive gas and a vacuum pump are typically used for purging gaseous reaction by-products and the residual reactant molecules from the reaction space during purge A and purge B. A deposition sequence comprises at least one deposition cycle. Deposition cycles are repeated until the deposition sequence has produced a thin film or coating of desired thickness. Deposition cycles can also be either simpler or more complex. For example, the cycles can include three or more reactant vapor pulses separated by purging steps, or certain purge steps can be omitted. On the other hand, photo-enhanced ALD has a variety of options, such as only one active precursor, with various options for purging. All these deposition cycles form a timed deposition sequence that is controlled by a logic unit or a microprocessor. 
     A reaction space is a defined volume within a reaction chamber. The desired chemical reactions, such as deposition, etching, cleaning, activation or exchange reactions typically occur on the substrate surface(s) in the reaction space. 
       FIG. 1  shows an apparatus in accordance with certain embodiments. The apparatus  100  is a substrate processing apparatus which may be for example an ALD, ALE or CVD reactor. The basic structure of the apparatus  100  may be implemented for example in accordance with R- 200  ALD system available from Picosun, Espoo, Finland The apparatus comprises a reaction chamber  130  and an infeed line  101  to provide a reactive chemical (or a mixture of a reactive chemical and carrier gas in certain embodiments) to the reaction chamber  130 . The apparatus further comprises a pulsing valve  105  in the in-feed line  101 . The state (open/close) of the pulsing valve is controlled by a control system  180 . 
     The apparatus further comprises a volume outside of the reaction chamber  130  and at least partly surrounding the in-feed line  101 . In the embodiment shown in  FIG. 1 , an intermediate space  190  formed between the reaction chamber  130  and an outer chamber (that may be a vacuum chamber)  140  surrounds both the reaction chamber  130  and the in-feed line  101 . An outer tube  120  (that has gas-impermeable wall(s)) is placed around the in-feed line  101 . The in-feed line  101  extends to the pulsing valve  105  and from the pulsing valve  105  into the reaction chamber  130 . In this portion from the pulsing valve  105  to the reaction chamber  130 , the in-feed line is in the form of an inlet pipe  111  with a gas-permeable wall (also referred to as a “porous inlet”). The reaction chamber  130  comprises an inlet opening  121 , and the inlet pipe  111  with the gas-permeable wall extends to the inlet opening  121 . However, in other embodiments the gas-permeable wall does not extend all the way to the inlet opening  121 , but it only extends towards the inlet opening  121 . In such embodiments, an edge of the reaction chamber  130  close to the inlet opening  121  may be a hot or heated edge to reduce sticking. Depending on the embodiment, the inlet opening  121  is arranged at a bottom part, top part, side or corner(s) of the reaction chamber  130 . 
     The inlet pipe  111  in certain embodiments is a porous pipe or a perforated pipe. The wall of the inlet pipe  111  in certain embodiments comprises a plurality of holes or gaps, in certain embodiments directional holes, and/or sections with gaps or slits. The pipe material used may be for example metal or ceramic. The outer tube  120  as well as the intermediate space  190  surround the inlet pipe  111 . 
     The volume(s) at least partly surrounding the in-feed line  101  can be heated volume(s). In certain embodiments, the reaction chamber  130  (and the intermediate space  190 ) are heated by a heater  160  placed within the intermediate space  190 . The volume within the outer tube  120  (and inlet pipe  111 ) is heated by a heater  122  placed in between the inlet pipe  111  and the outer tube  120 . The heater  122  is controlled by the control system. The outer tube  120  in an embodiment is provided with heat insulation  124 , for example a layer of heat reflecting material. In certain embodiments, cooling of the inlet pipe  111  and/or the outer tube  120  is provided respectively by arranging one or more cooler elements. 
     The reactive chemical that flows within the inlet pipe  111  is prevented from coming to contact or adhering to the (inner) wall of the inlet pipe  111  (or the coming into contact or adherence is reduced) by providing higher pressure fluid (or gas) to surround the inlet pipe  111 . Surrounding higher pressure gas is passed into the outer tube  120  via a feedthrough or valve or similar. For example, the higher pressure gas may be passed into the outer tube  120  from a gas source  170  via a valve  106 . The higher pressure gas enters the interior of the inlet pipe  111  through the gas-permeable wall. The pressure difference between the pressure of the higher pressure gas and the pressure of the reactive gas prevents the reactive gas from attaching to the wall of the inlet pipe  111 . In other embodiments, the outer tube  120  is omitted and the surrounding gas in the intermediate space  190  acts as the higher pressure gas (as described later in the connection of  FIG. 3 ). In both cases the higher pressure gas passes through the wall of the inlet pipe and mixes with the reactive gas. The mixture flows via the inlet pipe  111  into the reaction chamber  130  in which a substrate  110  is exposed to sequential self-saturating surface reactions as controlled by the control system  180 . 
     The remaining reactants and reaction by-products (if any) are pumped towards a vacuum pump  150  via a fore-line  145 . 
     In certain embodiments, the apparatus  100  is configured to pump both the reaction chamber  130  and the outer chamber into vacuum  140 . Accordingly, the apparatus operates in vacuum conditions. 
     As mentioned, the pulsing valve  105  is controlled by the control system  180 . Similarly, the control system  180  controls the whole operation of the apparatus  100 . The control system  180  comprises at least one processor and at least one memory comprising a computer program or software. The software includes instructions or a program code to be executed by the at least one processor to control the apparatus  100 . The software may typically comprise an operating system and different applications. 
     The at least one memory may form part of the apparatus or it may comprise an attachable module. The control system  180  further comprises at least one communication unit. The communication unit provides for an interface for internal communication of the apparatus  100 . In certain embodiments, the control system  180  uses the communication unit to send instructions or commands to and to receive data from different parts of the apparatus  100 , for example, measuring and control devices, valves, pumps, and heaters, etc. 
     The control system  180  may further comprise a user interface to co-operate with a user, for example, to receive input such as process parameters from the user. In certain embodiments, the control system  180  may be at least partly implemented by a portable device, or by such external systems as factory automation. 
     As to the operation of the apparatus  100 , the control system  180  controls the process timings of the apparatus in accordance with ALD, for example. In certain embodiments, the apparatus  100  is configured, by means of being programmed, for example, to pass higher pressure gas into the intermediate space or outer tube  120 . The passing of higher pressure gas into the intermediate space or outer tube  120  in certain embodiments involves controlling the valve  106  illustrated by one of the dotted lines in  FIG. 1 . 
     In certain embodiments, the apparatus  100  is configured to provide heating or cooling of the reactive chemical within the inlet pipe  111  by the higher pressure fluid (higher than the pressure in the inlet pipe  111 ). In those embodiments, the temperature of the surrounding fluid (gas) is controlled by the control system  180  to achieve the desired heating or cooling effect. In certain example embodiments, a heated surrounding fluid (which can be gas) keeps the whole inlet pipe heated. In certain embodiments, the heated fluid is used to heat up the incoming reactive chemical to the temperature of the reaction chamber  130 , or to a temperature above it, i.e., elevated temperature. In certain embodiments, such an elevated temperature enables a reaction between the incoming reactive chemical and the heated fluid. The reaction in certain embodiments is limited to the area of the gas-permeable wall of the inlet pipe  111  or within the inlet pipe  111 . In certain embodiments, the heating can be performed with inactive gas entering the inlet pipe  111  through the gas-permeable wall to cause breaking of the reactive chemicals coming through valve  105  to radicals or ions, for example. 
     Instead of or in addition to the heater  122 , the heating of the volume inside of the outer tube  120  and the volume inside of the inlet pipe  111  may be implemented by another heater. Examples of such heaters are as follows: an infrared (IR) heater placed in between the pipes (inlet pipe  111  or outer tube  120 ) whose IR radiation hits at least one of the pipes or the fluid in at least one of the pipes; a heater element, such as a resistor wire, placed against the inlet pipe  111 ; a heater element manufactured on the surface of the gas-permeable wall, for example a thick-film wire printed on said surface that may be made, e.g., of silver ink or paste, and a heater manufactured, e.g., molded, into inside of the outer tube  120  in between an outer and inner surface of the tube  120 . 
     In yet further embodiments, fluid (which can be gas) that is reactive with the chemical flowing within the inlet pipe  111  is used as the surrounding fluid. In these embodiments, the surrounding fluid passing through the inlet pipe wall mixes and reacts with the chemical flowing within the inlet pipe  111 . In certain embodiments, short life-time chemicals produced in this way can be effectively used in the reactions on the substrate. 
     In yet further embodiments, the contact of the reactive chemical to the inlet pipe wall is not prevented, but generated, e.g., for a cleaning or catalytic reaction purpose, by adjusting the flow direction through the gas-permeable wall. In certain embodiments, fine structures of pores of holes in the wall are directed to adjust the flow: For non-adhering performance the flow may be towards the reaction chamber  130 , whereas for improved mixing of the reactive chemical with the surrounding fluid the flow can be directed away from the reaction chamber  130 . In certain implementations and conditions, the gas-permeable inlet pipe&#39;s surface is in different temperature than the gas flowing through it, to prevent chemical adhesion to the inlet pipe wall. In other implementations, there is an electrical bias in the gas and the wall of the inlet pipe  111 , which decreases or prevents the adhesion of specific species. Such a bias can be used to ionize the chemical in the inlet pipe by such means that the valve  105  is at a bias voltage different than the inlet wall or electrode inside of the inlet  111 . Alternatively, the ionization can be performed by chemical decomposition, including, but not limited to photo-excitation known as such for UV-processes. Further the valve  105  can be a place where plasma is generated, and thus the plasma becomes charged gas which is guided by charged surfaces. A charged surface may refer to the presence of a magnetic field. 
     In the embodiment shown in  FIG. 1  as well as in other embodiments, a line providing the higher pressure fluid (from the source  170  or a respective source) may comprise its own gas pressure control (e.g., regulator) and/or flow control not shown in the Figures. The valve  106  (or respective valve) is optional. 
       FIG. 2  shows an apparatus in accordance with certain further embodiments. The apparatus shown in  FIG. 2  corresponds to the structural features and operation of the apparatus shown in  FIG. 1  except that the apparatus shown in  FIG. 2  comprises an optional opening  123  in the reaction chamber  130  wall directly leading from the outer tube  120  to the reaction chamber  130 . The heat insulating layer  124  has not been drawn, but it may be present in the embodiment of  FIG. 2 . 
     The opening  123  allows gas flow from the outer tube  120  into the reaction chamber  130  without passing an intermediate element. In certain embodiments, such a gas flow is restricted or adjusted by the control system  180 . The mentioned flow to the reaction chamber  130  and/or possible adjustment of the flow in certain embodiments is used to limit the pressure (for example, excessively high pressure) over the gas-permeable wall or pipe  111 . In addition or instead, the mentioned flow to the reaction chamber  130  aids in guiding the flow of the chemical(s) coming through the valve  105  and the inlet pipe  111  towards the substrate  110 . In certain embodiments, the mentioned flow via the opening  123  is used to purge chemicals incoming into the reaction chamber  130  constantly, even during the pulses (or pulse periods). In certain embodiments, this flow is guided to a pump rather than to the substrate. 
       FIG. 3  shows an apparatus in accordance with certain further embodiments. The apparatus shown in  FIG. 3  corresponds to the structural features and operation of the apparatus shown in  FIG. 1  except that in the apparatus shown in  FIG. 3  the outer tube  120  is omitted. Accordingly, the inlet pipe  111  is directly surrounded by the intermediate space  190 . The higher pressure gas is passed into the intermediate space  190  from the gas source  170  via the valve  106  and via an outer chamber  140  feedthrough or similar as depicted by an arrow  301 . The higher pressure gas then enters the interior of the inlet pipe  111  through the gas-permeable wall. The pressure difference between the pressure of the higher pressure gas and the pressure of the reactive gas prevents the reactive gas from attaching to the wall of the inlet pipe  111 . 
       FIG. 4  shows an apparatus in accordance with yet further embodiments. The apparatus shown in  FIG. 4  generally corresponds to the structural features and operation of the apparatus shown in  FIGS. 1-3  except that in the apparatus shown in  FIG. 4  the outer chamber  140  is omitted. The outer tube  120  forms a volume outside of the reaction chamber  130 , and the in-feed line  101  extends from the pulsing valve  105  through said volume into the reaction chamber  130 . The higher pressure gas is passed into the outer tube  120  from the gas source  170  via the valve  106  and via a feedthrough or similar as depicted by an arrow  401 . The higher pressure gas enters the interior of the inlet pipe  111  through the gas-permeable wall. The pressure difference between the pressure of the higher pressure gas and the pressure of the reactive gas prevents the reactive gas from attaching to the wall of the inlet pipe  111 . The heater  160  is optionally integrated with a reaction chamber  130  wall. The apparatus shown in  FIG. 4  may optionally comprise the opening  123  that allows gas flow from the outer tube  120  into the reaction chamber  130  without passing an intermediate element. 
     In certain embodiments, the pressure difference over the inlet pipe  111  gas-permeable wall relates to a pulsing sequence or process via the control system  180 . 
       FIG. 5  shows an apparatus in accordance with certain embodiments comprising a three-way valve. The apparatus shown in  FIG. 5  generally corresponds to the structural features and operation of the apparatus shown in  FIGS. 1-4  except that in the apparatus shown in  FIG. 5  the valve  105  has been implemented as a three-way valve  505 , also known as such as an ALD valve. Further,  FIG. 5  shows a possible option of extending the inlet pipe  111  with the gas-permeable wall partly outside of the intermediate space  190 . Further,  FIG. 5  shows a possible option of extending the portion having the gas-permeable wall upstream of the valve  505 . Further,  FIG. 5  shows a possible option of using different surrounding fluids in different portions of the in-feed line  101 . 
     In addition to the outer tube  120  surrounding the inlet pipe  111  downstream the valve  505 , the in-feed line  101  comprises a second inlet pipe  112  with a gas permeable wall surrounded by a second outer tube  520  upstream of the valve  505 . Higher pressure gas is passed into the outer tube  120  from the gas source  170  via the valve  106  similarly as described by the preceding description and as depicted by an arrow  501 . The higher pressure gas enters the interior of the inlet pipe  111  through the gas-permeable wall. The pressure difference between the pressure of the higher pressure gas and the pressure of the reactive gas prevents, e.g., the reactive gas flowing within the inlet pipe  111  from attaching to the wall of the inlet pipe  111 . A second higher pressure gas (which may be the same gas as or different gas than the gas from source  170 ) is passed into the second outer tube  520  from a gas source  570  via a valve  506  as depicted by an arrow  502 . The higher pressure gas enters the interior of the second inlet pipe  112  through the gas-permeable wall. The three-way valve  505  comprises two inlets, and an outlet towards the reaction chamber  130 . The reactive chemical is passed to a first inlet of the valve  505  along the second inlet pipe  112  as depicted by arrow  551 . A second chemical is passed to a second inlet of the valve  505  as depicted by arrow  552 . The control system  180  controls which of the inlets is/are passed through to the inlet pipe  111  via the outlet. 
     In other embodiments, the incoming chemical may decompose in the pipes and therefore the role of flows  552  and  551  may be exchanged. 
     Yet in other embodiments, the flow  551  is carrying in the reactive chemical, but the incoming gas at  502  is replaced by evacuation, i.e., the outer tube  520  is connected to an outgoing gas line (to pump/waste/recovery). The gas from the inlet pipe  112  flows through the gas-permeable wall to the outer tube  520  and therefrom to waste when it does not go through the valve  505 . 
     The heating of the inlet pipe(s) and outer tube(s) can be implemented in a similar manner as in other embodiments. 
       FIG. 6  shows an apparatus in accordance with further embodiments comprising separate surrounding gas volumes. The apparatus shown in  FIG. 6  generally corresponds to the structural features and operation of the apparatus shown in  FIGS. 1-5 . However, instead of the outer tube  120  providing only a single volume surrounding the inlet pipe  111 , separate and successive gas volumes are provided. In certain embodiments, each volume has its separate gas inlet. For example, in the example shown in  FIG. 6  the volume surrounding the inlet pipe  111  is divided to two separate gas volumes  661  and  662  in the flow direction of the inlet pipe  111 , for example, by a partition wall  615 . 
     First fluid (which may be inactive gas) is passed into the volume  661  from the gas source  170  via valve  106 . The inlet pipe  111  is divided to two sections. The first section  111   a  is at the area of volume  661  and the second section  111   b  at the area of volume  662 . The first fluid enters the interior of the inlet pipe  111  from the volume  661  through a gas-permeable wall section  111   a.    
     Second fluid (which may be the same fluid as the first fluid or different fluid) is passed into the volume  662  from a gas source  670  via valve  606 . The second fluid enters the interior of the inlet pipe  111  from the volume  662  through a gas-permeable wall section  111   b.    
     In the example shown in  FIG. 6 , the number of surrounding volumes is two. However, in other embodiments, there may be more surrounding volumes than two. In certain embodiments, the surrounding volumes are controlled in terms of prevailing pressure. In certain embodiments, the surrounding volumes are controlled in terms of prevailing temperature. In certain embodiments, the surrounding volumes are controlled in terms of flow direction. In certain embodiments, the gases passed to each of the surrounding volumes are mutually different. During certain times and/or process steps, the flow direction of fluid through the gas-permeable wall sections may be opposite or mutually different. The said control is performed by the control means  180 , and/or the volumes may comprise their own control means. 
     In certain embodiments, each surrounding volume has its own heating means. As mentioned, the gas inlet(s) and heating means may be controlled by the control system  180 , or each volume may have its own control means. 
       FIG. 7  shows an apparatus in accordance with further embodiments. The apparatus shown in  FIG. 7  generally corresponds to the structural features and operation of the apparatus shown in  FIGS. 1-6  except that the apparatus shown in  FIG. 2  comprises an optional particle filter  714 . The particle filter  714  is added to the reaction chamber side end of the inlet pipe  111  to prevent particles from entering the reaction chamber  130 . 
       FIG. 7  also shows an optional outlet channel (waste or recovery line)  715  leading from the space between the inlet pipe  111  and the outer tube  120  to a pump (pump  150  or similar) for exhaust. In the example shown in  FIG. 7  the outlet channel begins at the reaction chamber end of the surrounding volume. The pressure within the outlet channel  715  may be controlled, e.g., by shapes or means that cause a directed gas flow, such as a cyclone separation flow. The pressure control in certain embodiments reduces or obviates the need of the filter  714 . The flow direction of gas in this and other embodiments may generally be controlled by the shape of the inlet pipe  111 , by the orientation of the holes or pores of the gas-permeable wall material, or by plasma, or by the surface structure of the inlet pipe  111 . 
       FIG. 8  shows an apparatus in accordance with yet further embodiments in which plasma may be optionally involved. The apparatus  800  shown in  FIG. 8  generally corresponds to the structural features and operation of the apparatus  100  shown in  FIGS. 1-7 . Accordingly, a reference is made to the preceding description. However, the apparatus  800  is specifically designed for plasma assisted deposition, for example plasma assisted ALD or similar technology in particular. 
     The apparatus  800  comprises a reaction chamber  130  and an in-feed line  101  to provide plasma or radicals to the reaction chamber  130 . The apparatus further comprises a valve  805  in the in-feed line  101  controlled by the control system  180 . The valve  805  may refer to several valves or means of controlling the incoming gas flow(s) having the same or different pressures and/or same or different temperatures and/or same or different gases or mixtures of gases. Further, the apparatus  800  optionally comprises a flow guiding unit  816  which may be a gas mixer, an ejector, a porous medium or their combination to guide the gases properly onto a vertical downward stream towards the substrate  110 . Further, the flow can be designed so that there is a fixed stream of gas, such as a gas flow as depicted by reference numeral  817  to the flow guiding unit  816 . In an embodiment, the valve  805  is connected directly to the flow guiding unit  816 . 
     The apparatus  800  further comprises a volume outside of the reaction chamber  130  and at least partly surrounding the in-feed line  101 . In the embodiment shown in  FIG. 8 , an intermediate space  190  formed between the reaction chamber  130  and an outer chamber  140  surrounds both the reaction chamber  130  and the in-feed line  101 . An outer tube  820  resides around the in-feed line  101 . The in-feed line  101  extends from the valve  805  into the reaction chamber  130 . In this portion from the valve  805  to the reaction chamber  130 , the in-feed line is in the form of an inlet pipe  811  with a gas-permeable wall. The reaction chamber  130  comprises an inlet opening  821  at its top part, and the inlet pipe  811  with the gas-permeable wall extends to the inlet opening  821 . However, in other embodiments the gas-permeable wall does not extend all the way to the inlet opening  821 , but it only extends towards the inlet opening  821 . In such embodiments, an edge of the reaction chamber  130  close to the inlet opening  821  may be a hot or heated edge to reduce sticking. 
     The inlet pipe  811  in certain embodiments is a porous pipe or a perforated pipe. The wall of the inlet pipe  811  in certain embodiments comprises a plurality of holes or gaps, in certain embodiments directional holes, and/or sections with gaps or slits. The pipe material used may be for example metal or ceramic. The outer tube  820  as well as the intermediate space  190  surround the inlet pipe  811 . However, in the example shown in  FIG. 8  the inlet pipe  811  with the gas-permeable wall is only partly in the intermediate space  190 . 
     The volume(s) at least partly surrounding the in-feed line  101  can be heated volume(s). In certain embodiments, the reaction chamber  130  (and the intermediate space  190 ) are heated by a heater  160  placed within the intermediate space  190 . The volume within the outer tube  820  (and inlet pipe  811 ) may be heated similarly as described in connection with  FIG. 1 . The outer tube  820  in an embodiment is provided with heat insulation. 
     Plasma is generated by a remote plasma generator (not shown) and it flows as a direct path within the inlet pipe  811  through the inlet opening  821  to the substrate  110 . An example of a plasma generator assembly on an ALD tool is shown, e.g., in WO 2012/136875 A1. 
     The reactive chemical/plasma that flows within the inlet pipe  811  is prevented from coming to contact or adhering to the (inner) wall of the inlet pipe  811  (or the coming into contact or adherence is reduced) by providing higher pressure fluid (or gas) to surround the inlet pipe  811 . Surrounding higher pressure gas is passed into the outer tube  820  via a feedthrough or valve or similar as depicted by an arrow  801 . The higher pressure gas enters the interior of the inlet pipe  811  through the gas-permeable wall. The pressure difference between the pressure of the higher pressure gas and the pressure of the reactive gas/plasma prevents the reactive gas from attaching to the wall of the inlet pipe  811 . The higher pressure gas passes through the wall of the inlet pipe  811  and mixes with the reactive gas. The mixture flows via the inlet pipe  811  through the inlet opening  821  into the reaction chamber  130  in which the substrate  110  is exposed to sequential self-saturating surface reactions as controlled by the control system  180 . The substrate  110  can be loaded into the reaction chamber  130  before processing and removed from the reaction chamber  130  after processing by lowering the reaction chamber  130  in the manner as presented in PCT/FI2017/050071, or by moving it through the side via an opening. The higher pressure gas can be different inert gas than the other inert gases or gases used in plasma generation. Limiting of plasma generation to designated regions can be accomplished by selecting pressures and gases depending on the embodiment. 
     The remaining reactants and reaction by-products (if any) are pumped towards a vacuum pump  150  via a fore-line  145 . 
     As presented in the foregoing, gas from the outer tube  820  may enter directly the reaction chamber  130  (as in  FIG. 4 ) and/or enter a waste or recovery line (as in  FIG. 7 ) and/or enter the intermediate space  190 . 
     The inlet pipe  811  and/or mixer  816  that receives incoming gas from valve  805  may additionally or instead contain at least partially patterned areas to eject an ejector flow. In certain embodiments, this flow is directed from top, side or from a selected angle to prevent the generated plasma, or gas flowing inside this or other porous pipe (or chamber) referred to in the instant application, from coming into contact with a solid portions of surrounding surfaces. 
     In certain embodiments, the apparatus  100 / 800  contains means to adjust and in some cases means to measure pressures and/or flows to adjust the pressure difference over the gas-permeable inlet pipe  111 / 811 , for example. Such means may include valves, mass flow controller(s), pressure sensors of gases before entering the inlet pipe  111 / 811  or the intermediate space  190  in between the reaction chamber  130  and a vacuum chamber (outer chamber  140 ) measuring the outgoing flow and/or pressure or the pressure in one of the following: inlet pipe  111 / 811 , inlet pipe  111 / 811  and outer tube  120 / 820 , and intermediate space  190 . 
     The control system  180  can be adapted to adjust the pressure around outer tube  120 / 820 . In some embodiments the same or independent control system can be configured to adjust the temperature in the space  190 , in the inside of the outer tube  120 / 820  or outside of the vacuum chamber  140 . The flow rate and level of vacuum can be adjusted by controlling the fore-line  145 /vacuum pump  150  by the control system  180 . The pressure control may in practice be performed, e.g., with such systems that are generally known as APC, Automatic Pressure Control. 
     In certain embodiments, more than one reactive gas is lead to the gas-permeable inlet pipe  111 / 811 , but they are prevented from absorbing on the wall of the inlet pipe  111 / 811  with the aid of the flow coming through the inlet pipe  111 / 811  wall, or further inhibited by a (decreased) temperature of the gas coming through the inlet pipe  111 / 811  wall. 
     In yet further embodiments, there are means to induce electromagnetic radiation to the space within the outer tube  120 / 820  outside the gas-permeable inlet pipe  111 / 811  or to the intermediate space  190 , which electromagnetic radiation interacts with the gas flowing within the inlet pipe  111 / 811 . Such radiation can be UV-light or microwave radiation, induced with similar elements as denoted by reference numerals  160  and/or  122 , or emitted from locations of  160  and/or  122 , when produced outside of the outer chamber (vacuum chamber)  140 . 
     Although not repeated in connection with all embodiments, the features presented in one or more embodiments as a general rule may be applied to all other embodiments. For example, the valves in different embodiments may be three-way valves although presented in the preceding only in connection with  FIG. 5 , etc. 
       FIG. 9  shows an apparatus in accordance with certain further embodiments. In these embodiments, the reaction chamber  130  has gas-permeable walls. The reaction chamber walls are formed of gas-passing pathways that may include pores. Accordingly, the reaction chamber  130  may be porous. There may be provided a multitude of gas-passing pathways providing a protective flow extending along the whole inner surface of the reaction chamber  130 . 
     The reaction chamber  130  is surrounded, at least partly, by a confined volume. The surrounding volume may be the intermediate space  190  formed between the gas-permeable wall of the reaction chamber  130  and an outer chamber  140  wall. In certain embodiments, such as shown in  FIG. 9 , the surrounding volume is defined by the gas-permeable wall of the reaction chamber  130  and an (optional) outer intermediate wall  920 , the outer intermediate wall  920  residing in between the gas-permeable wall of the reaction chamber  130  and the outer chamber  140  wall. In an embodiment, the wall  920  conforms to the shape of the reaction chamber wall  130 . 
     In certain embodiments, a system similar to that of  FIG. 9  is implemented without the outer chamber  140 . The possible heaters can be conveniently adapted in connection with the intermediate wall  920  (especially if this is used as an outer wall), and/or the apparatus can comprise elsewhere heating for the gas. If preferable for a high purity wafer coating the sample/substrate loading is made in the outer chamber  140 , rather than in ambient air and pressure. An opening in the reaction chamber  130  wall for loading can be implemented in various places.  FIG. 9  shows an example opening level  960  at which a reaction chamber  130  upper portion can be lifted or lower portion lowered for loading. 
     The apparatus is configured to provide fluid to surround and enter the reaction chamber  130  from the surrounding confined space through the gas-permeable wall of the reaction chamber  130 . In certain embodiments, such as shown in  FIG. 9 , the apparatus comprises the inlet pipe  111  with gas-permeable wall surrounded by the outer tube  120 . Higher pressure fluid may flow (or may be fed) via the outer tube  120  into the confined space in between the reaction chamber  130  wall and the wall  920 . In this context, the higher pressure fluid means fluid that has pressure higher than that inside of the reaction chamber  130 . Alternatively, higher pressure fluid may be fed into the confined space by its own in-feed line (without passing through the outer tube  120 ). This is also applicable in embodiments in which the outer tube  120  is missing and in embodiments in which the route from the outer tube  120  to the confined space is blocked by the wall  920  (in the area depicted by reference numeral  950 ). It is also not necessary in these embodiments that the inlet pipe  111  has gas-permeable walls. Otherwise the apparatus shown in  FIG. 9  operates as described in the preceding. 
       FIG. 10  shows an embodiment in which a substrate holder (or chuck)  1115  under the substrate  110  comprises at least one gas-permeable wall. The substrate holder  1115  comprises a hollow space inside of the substrate holder  1115 . Inactive gas is fed into the hollow space, e.g., via a channel  10  controlled by the control system  180 . The route of the channel  10  depends on the embodiment. The channel  10  may, for example, extend via the fore-line  145 . The substrate holder  1115  may be shaped like a Petri dish with edges to hold the substrate  110 , or it may be of any other shape adapted to hold the substrate  110 . The substrate holder  115  may be configured at least partially to prevent gas-based deposition on its selected surface(s). 
     In an embodiment, at least a surface of the substrate holder  1115  facing upwards or facing a substrate  110  (or substrates in case there are more than one) is gas-permeable. In certain embodiments, the substrate holder  1115  comprises side surfaces, and these are also gas-permeable. In certain embodiments, the whole substrate holder  1115 , i.e., each of the outer surfaces of the substrate holder  1115  are gas-permeable. 
     In certain embodiments, the substrate holder walls that are gas-permeable are formed of gas-passing pathways that may include pores. Accordingly, the substrate holder walls concerned may be porous. There may be provided a multitude of gas-passing pathways in each of the gas-permeable substrate holder wall. 
     Inactive gas with pressure higher than the pressure prevailing in the surroundings of the substrate holder  1115  passes from the hollow space through the gas-permeable walls to outside of the substrate holder  1115 . The passing through the gas-permeable wall(s) of the substrate holder  1115  establishes a protecting flow to prevent or reduce material growth on the outer surfaces of the substrate holder  1115 . The passing through a wall facing the substrate  110  prevents or reduces material growth on a backside of the substrate  110 . 
     The substrate holder  1115  may be gas-permeable without the need of other walls of the system (e.g., reaction chamber wall, inlet pipe wall) to be gas-permeable. 
     Instead of providing a separate substrate holder, the substrate holder may form part of the reaction chamber or form part of a reaction chamber structure. 
       FIG. 11  shows fluid channels within an inlet pipe in accordance with further embodiments. In these embodiments, the inlet pipe  111  (or outer tube  120 , or any other confined space) comprises within the inlet pipe  111  one or more separate fluid channels  11 . Separate herein means that any material flowing within the separate fluid channels  11  is in no fluid communication with the chemical flow in the inlet pipe  111 . As an example, the channel(s)  11  may be made of 3D printed material. In further embodiments, the channel  11  may be a welded pipe. In certain embodiments, the channel  11  has a spiral form. The channel(s)  11  may be air channel(s). The channel(s)  11  may be located on the inner surface of the inlet pipe  11  (or of a structure bounding a confined space). In certain embodiments, the channels  11  provide the inlet pipe  111  with a heating or a cooling effect by flowing fluid within the channel  11  having a temperature different from the temperature of chemical or reactive chemical flow in the inlet pipe. 
       FIG. 12  shows an apparatus in accordance with yet other embodiments. The apparatus shown in  FIG. 12  corresponds to the structural features and operation of the apparatus shown in the preceding, especially to those shown in  FIGS. 9 and 10 . In addition, the apparatus shown in  FIG. 12  comprises a fore-line structure having an inner pipe  1121  surrounded by an outer tube  1120 . The fore-line  145  extends from the reaction chamber  130  to or towards the pump  150 . In this portion, the inner pipe  1121  is in the form of a pipe with a gas-permeable wall. The portion having the gas-permeable wall can extend all the way from the reaction chamber  130  to the pump  150 , or a shorter distance. Fore-line structures usually contain at least one valve in between the pump and the reaction chamber, which is (are) omitted from the drawings. 
     The chemical(s) that flows within the fore-line  145  (within the inner pipe  1121 ) is prevented from coming to contact or adhering to the (inner) wall of the inner pipe  1121  (or the coming into contact or adherence is reduced) by providing higher pressure fluid (or gas) to surround the inner pipe  1121 . Especially in the pipe  1121 , it may be preferable to prevent a chemical reaction by increasing or decreasing the flowing fluid temperature, by controlling the temperature of the porous pipe  1121  or the incoming gas. Surrounding higher pressure gas is passed into the outer tube  1120  via a feedthrough or valve or similar in a similar manner as presented in the preceding e.g. in the context of describing passing higher pressure fluid into the inlet pipe  111 . For example, the higher pressure gas may be passed into the outer tube  1120  (formed of a gas-impermeable wall) from a gas source via a valve. The higher pressure gas enters the interior of the inner pipe  1121  through the gas-permeable wall. The pressure difference between the pressure of the higher pressure gas and the pressure of the chemical(s) flowing within the inner pipe  1121  prevents the said chemical(s) from attaching to the wall of the inner pipe  1121 . 
     In some embodiments, there is at least one valve before the pump  150 . The at least one valve may be within the portion of the fore-line  145  having the gas-permeable wall or downstream of that portion. A possible option of dividing the volume surrounding the inner pipe  1121  to two separate gas volumes (similar to those of  661  and  662  in  FIG. 6 ) in the flow direction of the inner pipe  1121 , for example, by a partition wall (similar to  615  in  FIG. 6 ) may also be realised. In addition or alternatively, other features or operations described in the context of the inlet pipe embodiments are also applicable here. Some parts of a typical ALD reactor have not been drawn in  FIG. 12  for the sake of clarity. 
     As indicated in the preceding, the pump fore-line  145  extending from the reaction chamber  130  to the pump  150  can contain one or more intervening parts.  FIG. 13  shows an intervening particle trap  1155  before the pump  150 . The pump fore-line  145  shown in  FIG. 13  has a similar structure compared to that shown in  FIG. 12 . Accordingly, the inner pipe  1121  is surrounded by an outer tube  1120 . The fore-line  145  extends from the reaction chamber  130  towards the pump  150 . In the portion between the reaction chamber  130  and the trap  1155 , the inner pipe  1121  is in the form of a pipe with a gas-permeable wall. 
     Conventionally traps have a second chemical coming in from a route other than a route coming from the reaction chamber  130  to generate solid products of the chemicals in the trap. In the embodiment shown in  FIG. 13 , a second chemical (e.g., water or water vapor in case the other reactive chemical is e.g. TMA, trimethylaluminum) is fed from a precursor container  1132  via a valve  1106  into the trap  1155  as controlled by the control system  180 . 
     The trap  1130  may also have in some embodiments an inner wall  1131  separating a volume which receives a flow from the reaction chamber  130  via the fore-line  145  from a surrounding volume on the other side of the inner wall  1131  receiving a flow from the valve  1106 . The said surrounding volume may be delimited by a trap (gas-impermeable) outer wall. 
     The inner wall  1131  or at least a portion of the inner wall  1131  is gas-permeable in certain embodiments. The flow from the container  1132  can be ON or OFF for the whole substrate processing process, part of the deposition or processing cycle, or controlled to be in a different state at different stages of the substrate processing process. For example, water vapor can be disposed through the porous wall (inner wall)  1131  during and immediately after the TMA pulses, but during other times inert gas can flow in with a smaller flow rate. 
     Otherwise the apparatus shown in  FIG. 13  corresponds to the structural features and operation of the apparatus shown in  FIG. 12 . 
     The following presents an example of working conditions within the disclosed apparatus or reactor:
         inlet gas flow of 0.001-20000 sccm, or 1-1000 sccm, for example 200 sccm; the inlet gas flow may include carrier gas which may be the same gas as the gas coming though the gas-permeable walls of the inlet pipe   inlet gas temperature of −60° C. to 1500° C., or 20 to 300° C., for example 100° C.; the desired temperature may be realized, e.g., with a tungsten heater on porous aluminum oxide   gas temperature in the intermediate space: from temperature 0° C. to 900° C., or 50-500° C., or 80-450° C., for example 100° C.   gas flow into the intermediate space: 0.001-10000 sccm, or 10-2000 sccm, or 50-500 sccm, or 100-200 sccm (there may be other means, such as a leakage towards, e.g., the pump  150  or a separate outlet line, to remove gas from the intermediate space (not shown))   gas flow in between the outer tube and the inner pipe (inlet pipe): 0.001-1000 sccm, or 0.1-100 sccm, or 1-10 sccm adjusted so that there is a pressure difference to enable gas flow to a desired direction across the inlet pipe and/or through the gas-permeable wall   gas flow in between the inner part of the reaction chamber and its exterior, being the intermediate space  190  or the confined space on the reaction chamber side of wall  920 : 0.001-1000 sccm, or 0.1-100 sccm, or 1-10 sccm adjusted so that there is a pressure difference to enable gas flow to a desired direction across the and/or through the gas-permeable wall in question   gas in between the outer tube and the inlet pipe having the temperature of −60° C. to 1000° C., or 80-800° C., or 10-300° C. depending on the chemicals used       

     In accordance with certain process examples, chemicals such as Cu(acac) 2  (Cupric acetylacetonate″C 10 H 16 CuO 4 ) are processed in the reaction chamber  130  at reaction temperatures &lt;100° C., such as 90° C., where the precursor is source in question is kept at a higher temperature, for example, a temperature &gt;100° C., such as 110° C., and the gas coming through the gas-permeable wall of the inlet pipe  111 / 811  decreases the total temperature of the incoming gas to such a temperature that it adjusts the reaction chamber  130  to the temperature of said 90° C. Other chemical for the deposition of Cu 2 O in the said ALD process can be water or O 2  for example. By using the presented embodiments, the temperature of one reactive gas may be increased, or reactive ions to ease the reaction may be created. 
     Another process example is such where, e.g., RuCp 2  precursor flows in the in-feed line  101  at a temperature of 85° C., for example, to prevent decomposition of the precursor in a precursor source container or in the valve  105 / 505 . The precursor is heated by the surrounding gas coming through the gas-permeable wall of the inlet pipe  111 / 811  to around 300° C., i.e., to the temperature of the reaction chamber  130 . The said process can be accompanied for example with O 2  or O 3 , which can be heated within the inlet pipe  111 / 811  to the temperature of 300° C. or even higher, enabling a decreased RuCp 2  temperature, respectively. In other example configurations, the RuCp 2  may have the source temperature of 140° C., where the pipe leading to the reaction chamber has a gradually increasing heat-gradient up to 350° C., the temperature of the reaction chamber. The reactions within the reaction chamber can be operated in more than 100° C. lower temperature when the reactive gases enter to a contact with the substrate with a different, heated, temperature pulse. 
     In certain embodiments, the temperature on the surface of the substrate  110  is controlled by controlling the temperature of gas entering the reaction chamber  130  by the surrounding gas entering the inlet pipe  111 / 811  through the gas-permeable wall. Such an apparatus or reactor comprises a first in-feed line with the presented gas-permeable wall arrangement and a second in-feed line also comprising the gas-permeable wall arrangement. The arrangement in the first in-feed line provides the reaction chamber  130  with gas having a first temperature, for example 100° C., and the arrangement in the second in-feed line provides the reaction chamber  130  with gas having a second temperature, for example 150° C. The temperature on the substrate  110  surface is controlled by the quantity of the gas flowing from the different in-feed lines (or different sources) at different times of the process or different times of the process or deposition sequence. In this way it is possible to provide different temperatures on the surface of the substrate  110  at different times (as different precursors may require different reaction temperatures). The temperature controlling method presented herein, inter alia, obviates the need for transferring the substrate between separate reaction chambers when different reaction temperatures are required. 
     In further embodiments, the disclosed apparatus with the gas-permeable wall in the inlet pipe  111 / 811  enables passivation or etching interior surface(s) of the reaction chamber  130 . During the passivation or etching, there may not be a wafer inside the reaction chamber. Various ways known as such in chemistry, such as RIE (Reactive ion etching), or ALE (Atomic layer etching) may be applied, depending, e.g., on the material(s) to be removed and the material under it. An etching process can be enhanced by chemistry created in the inlet pipe  111 / 811  with the gas-permeable wall by heat, chemical reaction(s) or by plasma, for example. 
     In certain embodiments, an atomic layer etching process is performed to remove SiCl x  from a silicon surface. In accordance with presented embodiments, the incoming gas into the reaction chamber is excited to remove SiCl x  from the surface. The incoming gas can be excited to an adequate energy level, for example to an energy level corresponding to Ar +  ion energy level conventionally used in etching processes. 
     In certain embodiments, the gas-permeable wall of any of the inlet pipe  111 / 811 , the reaction chamber  130 , or the substrate holder  1115 , comprises one or more gas channels within the wall material so as to provide ameliorated spreading of protective gas to out of the surface of the part in question. 
     In the disclosed apparatus, even one thermodynamically stable material, or multiple materials, can have a wide range of reactions with the aid of catalytic surfaces that are catalytic to gases inside the inlet pipe (or to at least one chemical, such as one flowing through the gas-permeable wall). Some of the gases may be further affected by plasma or electromagnetic radiation. Short-lived product(s) may be created. In general terms, an example of this is that gas A is pulsed to the inlet pipe. Gas B comes through the gas-permeable wall to meet A within the inlet pipe. 
     The gases A and B are selected so that they do not react on the substrate  110  (considering the state of the reaction, ALD for example), but A and B produce, in conditions within the inlet pipe, gas C (i.e., A+B→C). Gas C reacts on the substrate  110  surface as desired. Further, by a catalytic reaction, A and B* produce D in conditions within the inlet pipe (i.e., A+B*→D), a reaction which would not occur without, e.g., a catalyst. When appropriate, the particle filter (see filter  714  is  FIG. 7 ) can also be selected so that it removes at least partly, at least one of the chemicals mentioned in the preceding reactions. 
     When a pulsing valve is not immediately next to the reaction chamber and/or the pulsing valve is not a hot valve, the adsorption of various chemicals, such as water, occurs spontaneously, especially for metal surfaces. In certain embodiments, such an adsorption surface can be covered by a proper gas flow separating the chemicals from the walls of the pipe that they are traveling in. Furthermore, other possible places of contact due to, e.g., turbulence are constantly purged with hot fluid, for example. 
     Without limiting the scope and interpretation of the patent claims, certain technical effects of one or more of the example embodiments disclosed herein are listed in the following. A technical effect is providing minimized adherence of chemical on the infeed-line(s). Since the surrounding gas is pushing through the inlet pipe wall, gas contact of the reactive chemical with the inlet pipe wall is minimized. A further technical effect is providing heating or cooling of the reactive chemical within the inlet pipe as desired. A yet another technical effect is mixing of reactive gas with an inactive gas within the inlet pipe. A yet another technical effect is causing a reaction between surrounding reactive gas and the chemical flowing within the inlet pipe to produce a desired further compound required in the reaction chamber. A technical effect is the heating of the gas flowing in the in-feed line right after the valve (particularly, a pulsing valve in the in-feed line), or in some embodiments before the valve. A technical effect is enabling reaction(s) of material flowing into the reaction chamber with the aid of spontaneous chemical reaction(s) within the inlet pipe before the reaction chamber. 
     The foregoing description has provided by way of non-limiting examples of particular implementations and embodiments of the present disclosure a full and informative description of the best mode presently contemplated by the inventors for carrying out the disclosed embodiments. It is however clear to a person skilled in the art that the present disclosure is not restricted to details of the embodiments presented above, but that it can be implemented in other embodiments using equivalent means without deviating from the characteristics of the present disclosure. 
     Furthermore, some of the features of the above-disclosed embodiments of this present disclosure may be used to advantage without the corresponding use of other features. As such, the foregoing description should be considered as merely illustrative of the principles of the present disclosure, and not in limitation thereof. Hence, the scope of the disclosed embodiments is only restricted by the appended patent claims.