Abstract:
A system delivers radiation to a substrate with a radiation source to generate radiation having a source intensity distribution pattern; and a redistribution radiation guide adapted to receive the radiation from the radiation source and to direct the radiation from one region to different regions on the substrate so that the substrate intensity distribution pattern is different from the source pattern.

Description:
BACKGROUND 
   This invention relates to apparatus and methods to thermally process substrates. 
   In many semiconductor-manufacturing processes, substrates are thermally processed in a series of one or more phases. For example, some thermal processes include a pre-heating phase during which the substrate is heated to an initial temperature before the substrate is loaded completely into a processing chamber and processed with a prescribed heating cycle. To achieve the required device performance, yield, and process repeatability, the temperature of a substrate such as a semiconductor wafer is strictly controlled during processing. For example, semiconductor devices have layers that are tens of angstroms thick and this thickness uniformity must be held to within a few percent. Potential problems arising from a non-uniform substrate temperature include semiconductor crystal slips that can destroy devices through which the slip passes. Additionally, certain semiconductor processes, such as those to form an epitaxial layer, require a uniform temperature to obtain uniform resistivity. These requirements dictate that temperature variations across the substrate or wafer during processing be limited to a tight range. 
   To achieve the desired substrate temperature, certain process chambers use one or more high intensity heating elements, such as lamps, positioned over the substrate to be heated. Potential problems with the use of high intensity lamps as a heat source, particularly for larger diameter wafers include difficulties in maintaining a uniform temperature across the wafer. Further, temperature differences can arise during heating/cooling transients and during processing. The interior walls of typical lamp based systems are usually relatively cool and are not heated to a uniform equilibrium process temperature as in a conventional batch furnace. Different radial locations on the wafer surface receive different fractions of their incident radiation from each of the lamps and have different views of the relatively cool side walls. As a result, it may be difficult to ensure that the net radiant heat flux, and hence the equilibrium temperature may not be uniformly maintained on the wafer. 
   SUMMARY 
   In one aspect, a system delivers radiation to a substrate with a radiation source to generate radiation having a source intensity distribution pattern; and a redistribution radiation guide adapted to receive the radiation from the radiation source and to direct the radiation from one region to different regions on the substrate so that the substrate intensity distribution pattern is different from the source pattern. 
   Implementations of the above aspect may include one or more of the following. The redistribution radiation guide directs the radiation from one region to different regions by spreading out the source section. The radiation guide includes a plurality of spreading components for spreading a region of the radiation source to a larger region on the substrate. The spreading component of the radiation guide distributes a local concentration section of the radiation source over a large region on the substrate for a more uniform distribution of radiation source on the substrate. The redistribution radiation guide directs the radiation from one region to different regions by shifting the source section when the radiation guide is moving. The radiation guide comprises a plurality of shifting components for shifting a region of the radiation source to a different region on the substrate. The shifting component of the radiation guide spreads a local concentration section of the radiation source over a large region on the substrate for a more uniform distribution of radiation source on the substrate when the radiation guide is moving. The shifting components of the radiation guide shift a ring section of the radiation source to a ring section on the substrate, and shift a portion of the ring section of the radiation source progressively to a portion of a ring section on the substrate so that a ring portion of the source is directed to many different ring portions of the substrate when the radiation guide is moving. The ring section on the substrate is wider than the ring section of the radiation source to spread the radiation source over a large region. The radiation source comprises one or more lamps. The radiation is thermal radiation for heating the substrate. The radiation is visible light radiation for lighting the substrate. A substrate temperature sensor can be coupled to the substrate. The substrate temperature sensor can be a pyrometer or a thermocouple in contact with the substrate. A motor can be coupled to the radiation guide to move the radiation guide. A processor can be coupled to a substrate temperature sensor and to the motor. The motor can rotate the radiation guide, or can rock the thermal radiation guide in an oscillatory manner. The motor can rock the thermal radiation guide in more than one dimensions. The radiation source can be positioned substantially parallel to the substrate and the radiation guide can be positioned in a direct path between the radiation source and the substrate. The radiation guide can be a light pipe. The radiation source can be positioned a at first angle to the substrate and the radiation guide is positioned at a second angle to the substrate to direct radiation from the radiation source to the substrate. The radiation source can be positioned at a 90 degree angle to the substrate and the radiation guide is positioned at a 45 degree angle to the substrate. The radiation guide can be a surface to reflect radiation from the radiation source to the substrate. 
   In another aspect, a method for heating a semiconductor substrate includes generating thermal radiation using a radiation source; and sending the thermal radiation through an uniformity radiation guide to the substrate. 
   In yet another aspect, a system to process a substrate includes a chamber adapted to receive the substrate; a radiation source coupled to the chamber to generate radiation; and a uniformity radiation guide adapted to receive the radiation from the radiation source and to direct the radiation to different regions on the substrate with a substrate intensity distribution pattern different from the source pattern. 
   Implementations of the above aspect may include one or more of the following. The method includes measuring the substrate temperature to provide a closed-loop feedback control. A pyrometer can measure substrate temperature. The target region can be rotated. The target region can be randomly selected. The method includes receiving temperature from a temperature sensor; and actuating a motor to rotate the radiation guide and to sweep the thermal radiation over the substrate to maintain a uniform substrate temperature. 
   In another aspect, a system delivers radiation to a substrate with a radiation source to generate radiation; and a radiation guide adapted to direct the radiation from the radiation source to the substrate, the guide being rotated to reflect the radiation to one or more dispersed regions. 
   In yet another aspect, a system processes a substrate. The system includes a chamber adapted to receive the substrate; a radiation source coupled to the chamber to generate radiation; and a radiation guide adapted to direct the radiation from the radiation source to the substrate, the guide spreading the radiation to one or more dispersed regions. 
   Advantages of the system may include one or more of the following. The system avoids damage to a substrate and undesirable process variations by providing a precise temperature control of the substrate during fabrication or manufacturing. The system minimizes the number of components in the chamber. Thus, potential sources of particulate contamination in the chamber are reduced. The system allows the heating temperature to be rapidly raised or lowered. The control of heating temperature can be readily effected by controlling the electricity to be supplied to the heat source. Contamination is reduced since the substrate is heated without being brought into contact with the heat source. Energy consumption is reduced because only one heat source is reduced and the heat source enjoys high-energy efficiency. The system is smaller in size and less costly, compared with other heating furnaces such as resistive furnaces and high-frequency furnaces. The temperature of the substrate is accurately controlled. Further, the increased accuracy in substrate temperature determination is provided in an apparatus that is simple to assemble, reliable and inexpensive. 
   Other features and advantages will become apparent from the following description, including the drawings and the claims. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  shows a cross sectional view of one embodiment of a system to deliver radiation onto a substrate or wafer. 
       FIG. 2  shows a process for maintaining temperature uniformity based on data from a temperature sensor and motor actuations. 
       FIG. 3  shows a second embodiment of a system to uniformly deliver radiation such as heat onto the substrate. 
       FIG. 4  shows a third embodiment of a system to uniformly deliver radiation such as heat onto the substrate. 
       FIG. 5  shows a fourth embodiment of a system to uniformly deliver radiation such as heat onto the substrate. 
       FIG. 6  shows a fifth embodiment of a system to uniformly deliver radiation such as heat onto the substrate. 
       FIG. 7  shows a fifth embodiment of a system to uniformly deliver radiation such as heat onto the substrate. 
       FIG. 8  shows an exemplary an apparatus for liquid and vapor precursor delivery with uniformly heated substrates. 
   

   DESCRIPTION 
   In the following description, the temperature of a substrate is discussed. The term “substrate” broadly covers any object that is being processed in a thermal processing chamber and the temperature of which is being measured during processing. The term “substrate” includes, for example, semiconductor wafers, flat panel displays, and glass plates or disks. 
     FIG. 1  shows a cross sectional view of one embodiment of a system  100  to deliver radiation such as heat onto a substrate or wafer  110 . The wafer  110  may be any of a number of semiconductor materials such as silicon, silicon carbide, gallium arsenide, gallium nitride, for example. If desired, these semiconductor materials can be in combination with thin insulators and/or metal layers. The semiconductor wafer  110  is positioned in a reactor chamber (not shown) above a susceptor (not shown). 
   The system  100  includes a radiation source  102  that generates thermal radiation in one embodiment. Openings are provided near a seal between the radiation source  102  and the body of the radiation source  102  to permit air to flow around and over the radiation source  102 . In one implementation, the radiation source  102  is a heat lamp including ultraviolet (UV) discharge lamps such as mercury discharge lamps, metal halide visible discharge lamps, or halogen infrared incandescent lamps, for example. The wavelength range for the UV spectrum is from about 200 nanometers to about 400 nanometers, and the wavelength range for the visible spectrum is from about 400 nanometers to about 800 nanometers. 
   The thermal radiation is sent through a radiation guide  104  to the wafer  110 . In one implementation, the light guide  104  is substantially circular and covers the wafer  110 . The thermal radiation guide  104  directs thermal radiation from the heat source to the substrate. In one embodiment, the thermal radiation guide  104  has one or more openings to allow thermal radiation to pass through the radiation guide  104  and reach the substrate  110 . In another embodiment, the radiation guide  104  includes fiber optic cable bundles or light pipes to transmit radiation from the radiation source  102  to the substrate  110 . The light pipes deliver highly collimated radiation from the radiation source  102 . The light pipes can be made of sapphire with relatively small light scattering coefficients and with high transverse light rejection. The light pipes can be made of any appropriate heat-tolerant and corrosion-resistant material such as quartz that can transmit the sampled radiation to the pyrometer. Suitable quartz fiber light pipes, sapphire crystal light pipes, and light pipe/conduit couplers may be obtained from the Luxtron Corporation-Accufiber Division, 2775 Northwestern Parkway, Santa Clara, Calif. 95051-0903. 
   The radiation source  102  may be divided into a plurality of zones which are located in a radially symmetrical manner. The power supplied to the different zones can be individually adjusted to allow the radiative heating of different areas of substrate  110  to be precisely controlled. 
   A motor  106  moves the radiation guide  104  in a sweeping pattern to deliver the thermal radiation over the substrate  110 . In one embodiment, the motor  106  “rocks” or oscillates the thermal radiation guide  104  so that the radiation is swept back and forth over the substrate  110 . The rocking motion can also be performed in two-dimensional movements. The motor is controlled by a computer  120  using a suitable high voltage I/O motor controller board. 
   The computer  120  achieves the required level of temperature uniformity, reliable real-time, multi-point temperature measurements through a closed-loop temperature control with one or more substrate temperature sensors  108  for sensing substrate temperature. The substrate temperature sensor can be a pyrometer  110 , which is a non-contact temperature probe. The pyrometers are configured to measure substrate temperature based upon the radiation emitted from a substrate being heated by the radiation source  102 . The substrate temperature may be controlled within a desired range by the computer  120  that adjusts the radiation source  102  based upon signals received from one or more of the pyrometers. Additionally, contact probes (such as thermocouples) may be used to monitor substrate temperatures at low temperatures. 
     FIG. 2  shows a process  200  where code executable by the processor receives temperature from the temperature sensor  108 . While the substrate  110  is being processed, the pyrometers  108  detect the temperatures of the substrate  110  (step  202 ). By indirectly obtaining the temperature of the wafer  110 , the computer  120  controls the power supplied to the radiation source  102  so that the substrate  110  is maintained at a temperature required for purposes of processing the wafer (step  204 ). Depending on the local temperature of the substrate  110 , the power to the radiation source  102  may be varied to provide temperature uniformity across the entire substrate  110 . The system  100  uses feedback from the radiation source  102  to enhance substrate temperature uniformity. Once the local temperature of the substrate  110  is determined, the variation of substrate thickness with substrate radius may then be used as a guide to vary the power of the radiation source  102 . For example, where the grown layer is too thick, the power to the radiation source  102  is lowered to make the substrate temperature uniform. Further, the motor  106  is actuated to sweep the thermal radiation over the substrate  110  to maintain a uniform substrate temperature (step  206 ). 
     FIG. 3  shows a second embodiment  300  of a system to uniformly deliver radiation such as heat onto the substrate  310 . In this embodiment, a radiation source  302  is positioned substantially perpendicularly to the substrate  310  and a radiation guide  304  is positioned at an angle to the substrate to direct thermal radiation over the substrate  310 . In one implementation, the radiation source  302  is positioned at a 90 degree angle relative to the substrate  310  and the radiation guide  304  is positioned at a 45 degree angle to the substrate  310 . 
   The radiation guide  304  has a plurality of reflecting spots  312 . When the radiation guide  304  is rotated by a motor  311 , the reflecting spots  312  receive incident radiation beams from the radiation source  302  and redirects the radiation to the surface of the wafer  310 . The computer  320  receives substrate temperature from pyrometers  315  and  317 , and based on the temperature directs the rotation rate of the radiation guide  304  and the intensity of the radiation source  302  as necessary to ensure a uniform substrate temperature. As the radiation guide  304  rotates, radiation from the stationary radiation source or lamp  302  is redirected and is reflected onto the substrate  310 . 
     FIG. 4  shows a third embodiment  400  of a system to uniformly deliver radiation to the substrate  420 . In this embodiment, a first radiation source or lamp  402  is positioned approximately above a substrate  420 . The lamp  402  has a source light pattern. A plurality of first light pipes  404  receives radiation from the lamp  402  and delivers the radiation to a plurality of dispersed spots  406  on the substrate  420 . Because the light pipes deliver light in a shifted manner, the pattern rendered onto the substrate  420  differs from the source light pattern. Similarly, a second radiation source or lamp  412  is positioned approximately above the substrate  420 . A plurality of second light pipes  414  receives radiation from the lamp  412  and deliver the radiation to a plurality of dispersed spots  416  on the substrate  420 . In another implementation, the second light pipes  414  receive radiation from the first radiation source or lamp  402  and disperses the radiation in a different pattern than the pattern of the first radiation source  402  onto the substrate  420 . 
     FIG. 5  shows a fourth embodiment  500  of a system to spread radiation onto a substrate  110 . In  FIG. 5 , a radiation source is positioned above light pipes  511 - 516 . Each of the light pipes  511 - 516  is angled so as to shift or reposition the delivery of the radiation from the radiation source onto different spots  521 ,  523  and  525 . The pipe  511  generates a beam  501 , the pipe  512  generates a beam  502 .The pipe  513  generates a beam  503 , pipe  514  generates a beam  504 , pipe  515  generates a beam  505 , and pipe  516  generates a beam  506 . Further, due to the position of the light pipes  511 - 516 , beam  501  is delivered to spot  521 , while beam  502  is delivered to spot  523 , beam  503  is delivered to spot  525 , beam  504  is delivered to spot  521 , beam  505  is delivered to spot  523 , and beam  506  is delivered to spot  525 . Note that in this configuration, not all spots  521 - 526  on the substrate are illuminated due to the position of the light pipes  511 - 516 . 
     FIGS. 6A-6F  show a fifth exemplary embodiment  600  of a system to spread radiation onto a substrate  510 . In  FIG. 6 , a plurality of radiation sources are positioned above light pipes which are angled so as to shift or reposition the delivery of the radiation from the radiation sources onto a different spot on the substrate.  FIG. 6A  shows an exemplary light source  511  generating the beam  501 . The rotation pattern of a pipe is exemplified in path  601 , which represents zero degree of rotation, upon which the beam is delivered onto spot  511 A.  FIG. 6B  shows the pipe being rotated 60 degrees counter clockwise in path  602 , resulting in the illumination of spot  511 B with the non-moving light source  511 .  FIG. 6C  shows the generation of a beam  603  when the pipe is rotated 120 degrees in path  603 , resulting in the illumination of spot  511 C. Again, the light source  511  remains stationary.  FIGS. 6D ,  6 E and  6 F show the pipe being rotated 180 degrees, 240 degrees and 270 degrees in paths  604 ,  605  and  606  to generate beams  504 ,  505  and  506  which are delivered onto spots  511 D,  511 E and  511 F, respectively. 
   As shown in  FIGS. 6A-6F , with the source  511  stationary and the light pipe rotating, the spots  511 A- 511 F are rotated in a counter direction relative to the rotation direction of the light pipe. Thus, the source is not rotated, and the delivery of the beams is achieved accurately and with minimal mechanical support without tangling of electrical wires. 
     FIG. 7  shows a second embodiment of the apparatus of  FIGS. 5 and 6 . In this embodiment, a radiation source is positioned above light pipes  511 - 516 . Each of the light pipes  511 - 516  is angled so as to shift or reposition the delivery of the radiation from the radiation source onto pairs of spots  531 - 534 ,  532 - 535  and  533 - 536 . The pipe  511  generates beam  501 , pipe  512  generates beam  502 , pipe  513  generates beam  503 , pipe  514  generates beam  504 , pipe  515  generates the beam  505 , and pipe  516  generates beam  506 . Further, due to the position of the light pipes  511 - 516 , beam  501  is delivered to spot  531 , while beam  502  is delivered to spot  532 , beam  503  is delivered to spot  533 , beam  504  is delivered to spot  533 , beam  505  is delivered to spot  535 , and beam  506  is delivered to spot  536 . Note that in this configuration, the illuminated spots are spread and delivered to a larger range than the focused spots of FIG.  5 . 
   The above heating system can be used in an exemplary an apparatus for liquid and vapor precursor delivery using either the system  100  or the system  300 . As shown in  FIG. 8 , an apparatus  40  includes a chamber  44  such as a CVD chamber. The chamber  40  includes a chamber body that defines an evacuable enclosure for carrying out substrate processing. The chamber body has a plurality of ports including at least a substrate entry port that is selectively sealed by a slit valve and a side port through which a substrate support member can move. The apparatus  40  also includes a vapor precursor injector  46  connected to the chamber  44  and a liquid precursor injector  42  connected to the chamber  40 . 
   In the liquid precursor injector  42 , a precursor  60  is placed in a sealed container  61 . An inert gas  62 , such as argon, is injected into the container  61  through a tube  63  to increase the pressure in the container  61  to cause the copper precursor  60  to flow through a tube  64  when a valve  65  is opened. The liquid precursor  60  is metered by a liquid mass flow controller  66  and flows into a tube  67  and into a vaporizer  68 , which is attached to the CVD chamber  71 . The vaporizer  68  heats the liquid causing the precursor  60  to vaporize into a gas  69  and flow over a substrate  70 , which is heated to an appropriate temperature by a susceptor to cause the copper precursor  60  to decompose and deposit a copper layer on the substrate  70 . The CVD chamber  71  is sealed from the atmosphere with exhaust pumping  72  and allows the deposition to occur in a controlled partial vacuum. 
   In the vapor precursor injector  46 , a liquid precursor  88  is contained in a sealed container  89  which is surrounded by a temperature controlled jacket  100  and allows the precursor temperature to be controlled to within 0.1° C. A thermocouple (not shown) is immersed in the precursor  88  and an electronic control circuit (not shown) controls the temperature of the jacket  100 , which controls the temperature of the liquid precursor and thereby controls the precursor vapor pressure. The liquid precursor can be either heated or cooled to provide the proper vapor pressure required for a particular deposition process. A carrier gas  80  is allowed to flow through a gas mass flow controller  82  when valve  83  and either valve  92  or valve  95  but not both are opened. Also shown is one or more additional gas mass flow controllers  86  to allow additional gases  84  to also flow when valve  87  is opened, if desired. Additional gases  97  can also be injected into the vaporizer  68  through an inlet tube attached to valve  79 , which is attached to a gas mass flow controller  99 . Depending on its vapor pressure, a certain amount of precursor  88  will be carried by the carrier gases  80  and  84 , and exhausted through tube  93  when valve  92  is open. 
   After the substrate has been placed into the CVD chamber  71 , it is heated by the heat source  102  and the guide  104 , as discussed above. After the substrate has reached an appropriate temperature, valve  92  is closed and valve  95  is opened allowing the carrier gases  80  and  84  and the precursor vapor to enter the vaporizer  68  through the attached tube  96 . Such a valve arrangement prevents a burst of vapor into the chamber  71 . The precursor  88  is already a vapor and the vaporizer is only used as a showerhead to evenly distribute the precursor vapor over the substrate  70 . After a predetermined time, depending on the deposition rate of the copper and the thickness required for the initial copper deposition, valve  95  is closed and valve  92  is opened. The flow rate of the carrier gas can be accurately controlled to as little as 1 sccm per minute and the vapor pressure of the precursor can be reduced to a fraction of an atmosphere by cooling the precursor  88 . Such an arrangement allows for accurately controlling the copper deposition rate to less than 10 angstroms per minute if so desired. Upon completion of the deposition of the initial copper layer, the liquid source delivery system can be activated and further deposition can proceed at a more rapid rate. 
   The system allows the substrates to have temperature uniformity through reliable real-time, multi-point temperature measurements in a closed-loop temperature control. The control portion is implemented in a computer program executed on a programmable computer having a processor, a data storage system, volatile and non-volatile memory and/or storage elements, at least one input device and at least one output device. 
   Each computer program is tangibly stored in a machine-readable storage medium or device (e.g., program memory or magnetic disk) readable by a general or special purpose programmable computer, for configuring and controlling operation of a computer when the storage media or device is read by the computer to perform the processes described herein. The invention may also be considered to be embodied in a computer-readable storage medium, configured with a computer program, where the storage medium so configured causes a computer to operate in a specific and predefined manner to perform the functions described herein. 
   The present invention has been described in terms of several embodiments. The invention, however, is not limited to the embodiment depicted and described. For instance, the radiation source can be a radio frequency heater rather than a lamp. Hence, the scope of the invention is defined by the appended claims.