METHOD AND APPARATUS FOR CHEMICAL VAPOR DEPOSITION

Abstract: Method and an apparatus for the deposition of material on a substrate (7) through the method of chemical vapor deposition without degrading the substrate by thermal stress. The substrates are supported by a carrier (6). Heat is supplied to the carrier from the side opposite the substrate by one energy source (5) and to the side with the substrates by a second focused, or nearly focused, radiant energy source (12) located outside the process chamber (2, 4). This complimentary heating configuration permits thin, flat substrates to be heated quickly and efficiently to high temperature without inducing undesirable thermal stress.

Description: METHOD AND APPARATUS FOR CHEMICAL VAPOR DEPOSITION Field of the Invention The present invention relates to a method and an apparatus for depositing a layer of material onto a substrate, and more particularly, to the chemical vapor deposition of a material onto a single crystal substrate. Background of the Invention Chemical vapor for the deposition of a layer of material onto a substrate is a well-known art. One example of a substrate is a single crystal silicon slice used in the manufacture of semiconductor devices. Such slices are presently 75-100mm diameter and are expected to be produced in excess of 200mm diameter in the future. These silicon slices are approximately 0.5mm thick. Heating such substrates rapidly to chemical vapor process temperatures (900-1300°C) and cooling them to room temperature is a major technical problem for the semiconductor industry. Material deposited on a single crystal substrate may be epitaxial (having the same crystal orientation as the substrate) , polycrystalline (having many regions of different crystallographic orienta- tions) , or amorphous (having essentially no crystalline structure) . The invention described here applies specifi¬ cally to epitaxial single crystal silicon films depo¬ sited on a single crystal silicon substrate; however, the invention also applies to heating any thin, flat substrate to high temperature for the purpose of depositing a single crystal, polycrystalline or amorphous film. In the present art, substrates are placed on a carrier or susceptor which is heated to 900-1300°C. Process gases, continuously introduced into the process enclosure, react on the heated carrier and substrate, for the deposition of material upon the substrates, and byproducts exhausted from said enclosure. Process gases are then purged from the chamber, and the carrier with substrates is cooled in order to remove the substrates. The process chamber walls are maintained at a substantially lower temperature than the carrier to minimize deposits there. Three methods of heating have been used to ' heat the carrier: 1) induction heating with coils in'side or outside the chamber; 2) resistance heating with coils inside or. outside the chamber; and 3) radiant heating by* infrared lamps placed outside the chamber. With induction heating, the carrier or susceptor is heated by the inductive coupling of high frequency electromagnetic waves emanating from a coil located inside or outside the process chamber. With resistance heating, coils are heated by the resistance against the flow of electric current through the coils. The heater coils are normally placed on one side of the carrier and the substrates are placed on the other side. In both cases, thermal energy is transferred to the substrate by radiation, gaseous conduction, and solid-solid conduction. With radiant heating, substrates are placed on the carrier and are heated by a generally uniform, non-focused, radiant energy field created by heating lamps located outside the process chamber and radiating directly onto the substrates and their carrier. A problem with the induction and resistance heating schemes described here is that undesirable crystal defects still occur in both the substrate and OMPI the epitaxial silicon layer. These defects are caused by induced thermal stress. The thermal energy flux through the carrier and a substrate causes the substrate to bow and lose contact at its periphery. Loss of contact at the edge reduces the edge temperature further, thereby, increas¬ ing the radial temperature difference and the thermal energy flux in the substrate. When the stress, as evidenced by the bow, exceeds the elastic strength of the crystal, dislocations are generated and crystal slip occurs. Dislocations or slip in the silicon substrate and in the epitaxial layer are believed to be collec¬ tion points for impurities which can be the cause of diode leakage and/or emitter-collector shorts in the bipolar transistors that are ultimately manufactured from the substrate. In addition, for MOS devices, slip can cause electrical leakage currents which significantly deteriorate the performance of the devices. Thus, the reduction or elimination of dislo¬ cations in the epitaxially grown layer and in the substrate is important for reducing manufacturing defects, improving the performance and reliability of semiconductor devices or circuits, and reducing manu- facturing costs. On the other hand, the radiant heating method, with heating lamps located outside the process chamber, reduces thermal stresses in a substrate by heating the substrate directly as well as heating the carrier. However, while this method worked well for substrates up to 75-lOOmm in diameter, it has not eliminated slip in substrates lOOmm in diameter or larger. In radiantly heated systems, the substrates are significantly hotter than the carrier. Excessive temperature gradients occur where larger and heavier substrates touch the carrier; crystal slip can be generated near the point of contact. In addition, the substrate bows due to the high thermal flux through the substrate to the carrier to heat the colder carrier. This bow alone can be sufficient to cause slip, espec¬ ially in larger diameter substrates. Another disadvantage of radiant heating is that material can be transferred from the backside of the heated substrate to the carrier when chlorides are present in the process chamber. The transfer occurs from the hotter body to the cooler body. Radiant heating has the substrates at a higher temperature than the carrier so that material is transferred from the substrates to the carrier. This transfer may result in the release of certain undesirable elements into the process chamber to cause contamination of the substrates during the same heating process or subsequent processes. On the other hand, induction or resistance heating, has the carrier/susceptor at a higher temperature than the substrate. Material can be transferred from the carrier onto the backside of the substrate during processing. This backside material transfer seals the backs of the substrates. Such sealing is an advantage in manufacturing certain semiconductor devices. The present invention avoids or substantially mitigates the problems above. Substrates are heated with minimum amounts of temperature gradients to avoid stress. Crystal slip and dislocations in the sub¬ strates are thus avoided. Moreover, the present invention permits mass transfer between the carrier/ susceptor and the substrate to be controlled. This adds flexibility to chemical vapor deposition processes which, heretofore, has not existed. SUMMARY OF THE INVENTION The present invention provides for a method and apparatus for uniformly heating a thin, flat substrate to high temperatures for the purpose of fTRE__ O PI depositing a layer of material on the substrate. The material may be epitaxial, polycrystalline or amor¬ phous. The invention is generally directed toward a chemical vapor deposition apparatus comprising a substrate carrier for holding the substrates, a first means for heating said substrates through said sub¬ strate carrier, a second means for heating said sub¬ strates directly by focused radiant energy distributed substantially uniformly over said substrates, and a means for enclosing said carrier to provide control of the environment around said carrier and said substrates. For the second heating means, a focusing reflector for example, such as an elliptical reflector and a radiant lamp having most of its emission at wavelengths less than 10,000 Angstroms are used.. The present invention also provides "a method for depositing material on a substrate comprising: introducing at least one substrate on a carrier into a process enclosure, heating the substrate through the carrier, complementarily heating the substrate from at least one radiant energy source focused to distribute the radiant energy substantially uniformly over the wafer, introducing process gases into the process chamber whereby material is deposited onto the substrate by chemical vapor deposition, and exhausting process gases and unwanted effluents from the process chamber. Brief Description of the Drawings FIG. 1 is a cross-sectional side view of an embodiment of the present invention, a bell jar type chemical vapor deposition reactor; and FIG. 2 is a cross-sectional side view of another embodiment of the present invention, a barrel type chemical vapor deposition reactor. Detailed Description of the Preferred Embodiments Referring to FIG. 1, there is shown a repre¬ sentation of a preferred embodiment of this invention. A sealplate 2 supports a susceptor/carrier 6 on a pedestal 16 rotating about a center axis 19. The process gases enter the system through an inlet port 1 from a control console (not shown) and exits from one or more exhaust ports 17. The process chamber is defined by the seal plate 2 and a removable quartz vessel 4 with optional multiple windows 8, 9 and a re-makeable seal 3. If the quartz vessel 4 is trans¬ parent, windows are not required. The quartz vessel may be of a bell jar configuration, closed at one end with one sealplate, as shown, or it may be of a tube type configuration with two or more sealplates. The substrates 7 are placed on the sus¬ ceptor/carrier 6. Specially shaped cavities receive the substrates. These cavities are designed to mini¬ mize thermal gradients in the substrates and are found in present day induction and resistance heating systems.. A coil 5 may be either a multi-zone resis¬ tance heater or a high frequency induction coil. A coil cover 15 protects and separates the coil 5 from the carrier/susceptor 6. The process chamber 2, 4 may be operated at pressures from below 1 torr to above 7600 torr (10 atmospheres) absolute pressure by suit¬ able pumps (not shown) . Appropriately located fans 13, shown symbolically, cool portions of the system as required. Cooling channels within coil 5, may also be used to cool other portions of the system. All of the foregoing are known in the art. The energy from the coil 5 heats the car¬ rier/susceptor 6. The carrier/susceptor 6 may also be heated from below by radiant heating below by using the generally unfocused radiant energy fields taught in the prior art. In such a case, the coil 5 is eliminated and replaced by one or more unfocused radiant energy lamps. The present invention also provides comple¬ mentary energy from a radiant lamp 12 reflected and focused by a reflector 11 so that this energy is substantially uniformly distributed over the sus¬ ceptor/carrier 6 surface perpendicular to the axis 19. The energy spectrum of the radiant lamp 12 is selected to have most of its energy emitted at wave- lengths less than 10,000 Angstroms to minimize absorption by the quartz enclosure or windows and to assure absorption by the silicon. Xenon arc lamps such as those manufactured by Canrad-Hanovia of Newark, New Jersey, have the desired emission characteristics. These lamps typically have at least 50% of their emission energy at wavelengths below 10,000 Angstroms. The reflector 11 focuses the radiant energy so that the energy passes through the top window 8 of the bell jar enclosure 4. The focusing reflector 11 is elliptical and, together with the lamp 12, is located on the center axis 19 of the process chamber formed by the seal plate 2 and the quartz vessel 4. By moving the reflector 11 and lamp 12 along the axis 19 and varying the distance between the reflector 11 and lamp 12, the energy of the lamp 12 is focused so that the energy flux is substantially uniform over the substrates 7. As shown by the dotted beam lines 18, the reflector 11 focusing is determined so that the radiant energy is distributed uniformly over as large an area of the susceptor/carrier 6 as possible. This permits a maximum number of substrate wafers 7 to be processed at once. Elliptical reflectors are commercially available .from companies, such as Pichell Industries of Rancho California, California. Of course, these reflectors may be specially designed in accordance with the requirements of the particular system. A temperature sensor 10 is used to provide temperature control over the power supply to the coil 5 in-a feedback fashion. The temperature sensor 10 is designed to be.shielded or insensitive to the reflec- tion of light from the radiant source 12 off the polished surfaces of the substrate wafers 7. Thus, the sensor 10, which may be located within or without the chamber 4, may be shielded by focusing the sensor 10 upon the carrier/susceptor 6. The sensor 10 may directly measure the temperature of the substrates 7 by focusing upon the substrates; however, the sensor 10 must be insensitive to the radiation emitted by the lamp 12. This is done by using a sensor sensitive to wavelengths much different than the lamp wavelengths in order to measure the substrate temperature by the true -t block body radiation of the substrates 7. Temperature sensors as discussed are gener¬ ally available from manufacturers, such as Ircon, Inc., of S'kokie, Illinois. When the temperature of the substrates 7 are lower than desired, the energy from the coil 5 below the susceptor/carrier 6 is increased. For temperatures higher than desired, the energy output is lowered. In this manner, a steady state condition is achieved in the process environment. Additional reflectors 14, which are optional, surround the process chamber, as an example, for energy savings by returning energy escaping from the process chamber. in operation, the energy radiated to the substrate 7 from the carrier/susceptor 6 is partially balanced by the complementary radiation from the radiant lamp 12 with the focusing reflector 11. This configuration minimizes the net thermal flux through a substrate, thereby minimizing thermal stress. The radiant energy from the radiant lamp 12 and reflectors 11, 14 helps heat the substrates over their entire tiϋ*l_0 surfaces, to reduce radial thermal gradients in the substrates. Cooling of the quartz vessel 4 is adjusted to the optimum temperature to minimize deposits on the internal walls. By appropriately adjusting the complementary energy emitted from the lamp 12 relative to that emitted from the carrier/susceptor 6, slip-free heating for epitaxial silicon deposition are possible for wafers in excess of 200mm diameter. Such capability is not presently available in the semiconductor industry. With the configuration as described above and illustrated in FIG. 1, silicon wafers of 125mm diameter have had epitaxial layers of 10 micron thickness deposited upon them by a dichlorosilane (SiH 2 Cl 2 ) process at 1080°C following an HC1 etch at 1100°C (all temperatures are optical) . No slip or dislocation defects were found in the substrate or deposited layer. Susceptor energy flux was approximately 100 watts per square inch; complementary energy flux from the lamp was approximately 23 watts per square inch. Other tests show that silicon wafers up to 125mm diameter may be heated, to higher temperatures, in excess of 1160°C, for epitaxial silicon deposition with no crystal slip. The present invention is able to achieve the desired goal of heating the substrate wafers with a radial temperature difference of less than 25°C between the substrate center and its circumference. This difference is a theoretical calculation of the required temperature differential before deformation occurs in the substrate with resulting crystal dislocation. Up to now, such low radial temperature differences have not been attainable under the process time constraints of semiconductor manufacturing for large (greater than 100mm diameter) semiconductor substrate wafers. The present invention also allows the material transfer between a substrate and the susceptor/carrier to be controlled. By adjusting the energy fluxes from the coils 5 and the focused lamp or lamps, the relative temperature difference between the Co substrate 7 and the carrier/susceptor are set. This determines the direction of material transfer, a flexibility which has not heretofore existed in chemical vapor deposition processing. Besides the advantages of uniform heating and material transfer control, illustrated in FIGS. 1 and 2, the present invention permits the substrates to be heated quickly. Energy is used more efficiently because energy is reflected back onto the carrier/ susceptor for heating. Furthermore, when the system is operated at a reduced pressure, the radiant energy from the lamp (s) can be " adjusted to make up for the lower heat transfer efficiency from the carrier/ susceptor alone. FIG. 2 illustrates another embodiment of the present invention. Here the sealplate 22, the quartz vessel 29, single or multiple gas inlets 21 A,, B, the exhaust 37, the temperature sensor 30, the cooling fans 33, and the general reflector 34 serve the same purposes as discussed for the embodiment in FIG. 1. The apparatus in FIG. 2 is a barrel type reactor with a carrier/susceptor 26 in the general shape of a trun- cated cone or cylinder. The substrates 27 are placed in banks of rows on the external surface of the car¬ rier/susceptor 26. As shown in FIG. 2, the substrates 27 are arranged in three rows about the carrier/susceptor 26. The number, and arrangement of rows is dictated by the substrate diameter and by realtor size. Energy is supplied by coils 25 which may be induction-type or resistance heaters. The coils 25 are located within a coil cover 35 which may be optionally sealed to the sealplate 22. Sealing the coils 25 permits them to be operated at a different pressure from the process chamber formed by the vessel 29 and •______*____ • _ sealplate 22. The barrel-type carrier/susceptor 26 rotates about the center axis 39 of the enclosure. Such barrel type reactors have been used without the coils 25 in the prior art. Instead, radiant lamps are placed outside and around the quartz vessel 29; the unfocused radiation from the lamps have been directed inward toward the substrates. It was believed that the substrates would be bathed in a uniform energy flux for an even heating of the substrates. The present invention uses radiant lamps 22 as a complementary energy -source to the coils 25. Each lamp 22 and reflector 31 are arranged with respect to a particular row of substrates so that the lamp's focused energy is substantially uniformly distributed over the surface of a substrate in the row as the substrate passes before the bank of lamps 22, as indicated by the dotted beam lines 38. Banks of these lamps 22 surround the quartz vessel 29 about the center axis 39. Such an arrangement of focused heat lamps assures a much more uniform distribution of energy to the substrates 27 than possible in the prior art. Variations of the present invention are possible. For example, the lamp 12 in FIG. 1 may be replaced by a ring lamp positioned perpendicular to the center axis 19 and with its center on the center axis 19. Besides elliptical mirrors, other types of focusing optical devices may be used, including other types of mirrors, lenses, and various combinations of mirrors and lenses. Thus, while the invention has been particularly shown and described with reference to the preferred embodiments, it is understood by those skilled in the art that changes in form and details may be made therein without departing from the spirit of this invention. It is therefore intended that an exclusive right be granted to the invention as limited only by the metes and bounds of the appended, claims. OMPI

Claims: WHAT IS CLAIMED IS: 1. An apparatus for depositing a layer of material on one or more substrates, said apparatus comprising: a substrate carrier for holding said sub- 5 strates; a first means for heating said substrates through said substrate carrier; a second means for heating said carrier and substrates by focused radiant energy distributed 0 substantially uniformly over said substrates simul¬ taneously; and a means for enclosing said carrier to provide control of the environment around said carrier. 2. The apparatus of claim 1 wherein said ^5 second heating means comprises at least one radiant lamp having at least 50% of its energy at wavelengths shorter than 10,000 Angstroms. 3. The apparatus of claim 1 wherein said second heating means further comprises a reflector 0 associated with said radiant lamp in such a manner that said radiant energy is focused to distribute said energy substantially uniformly upon said wafers and carrier. 4. The apparatus of claim 3 wherein said 5 reflector is elliptical. 5. The apparatus of claim 4 wherein said substrate carrier is substantially perpendicular to a center axis of said enclosing means, and said reflector and said radiant lamp are positioned substantially 0 along said center axis. 6. The apparatus of claim 5 comprising reflective means positioned outside said enclosing means for directing radiant energy from said enclosing means back toward said enclosing means. 7. The apparatus of claim 3 wherein said substrate carrier holds said substrates substantially vertically in banks of rows, and said second heating means comprises a plurality of radiant energy sources and reflectors associated therewith, each radiant energy source and associated reflector disposed so that said radiant energy source is focused to distribute energy substantially uniformly upon a substrate of a predetermined row. 8. The apparatus of claim 7 wherein said substrates in each row are disposed around a vertical axis of said enclosing means, each row rotated with respect to said radiant energy sources and associated reflectors around said vertical axis such that each radiant energy source distributes energy substantially uniformly over substrates of a predetermined row. 9. The apparatus of claim 1 further com¬ prising a temperature sensor insensitive to reflected light from said radiant energy source coupled to said first heating means for temperature control of said substrates. 10. The apparatus of claim 1 further com¬ prising a temperature sensor placed so as to not receive reflected light from said radiant energy source coupled to said first heating means for temperature control of said substrates. 11. The apparatus of claim 1 wherein said first heating means heats said substrates and said OMPI substrate carrier from a side of said substrate carrier opposite said substrates. 12. The apparatus of claim 11 wherein said first heating means is an electrically conductive coil, inductively coupled to a high frequency power source. 13. The apparatus of claim 11 wherein said first heating means is an electrically conductive coil heated by the resistance to an electric current passing therethrough. 14. The apparatus of claim 11 wherein said first heating means is an unfocused radiant energy source. 15. A method for depositing material on a substrate comprising: introducing at least one substrate on a carrier into a process enclosure, heating said substrate through said carrier t complementarily heating said substrate from at least one radiant energy source focused to distribute said radiant energy substantially uniformly over said substrate, and introducing process gases into said process enclosure, whereby material is deposited onto said substrate by chemical vapor deposition. 16. The method of claim 15 wherein said complementary heating step is performed by at least one radiant energy lamp and an elliptical reflector. 17. The method of claim 16 wherein said radiant energy lamp emits at least 50% of its energy at wavelengths less than 10,000 Angstroms. 18. The method of claim 15 further comprising the step of monitoring said substrate temperature to provide control thereover. 19. The method of claim 18 wherein said temperature monitoring step comprises sensing energy radiated from within said process chamber at wave- lengths differing from wavelengths of energy substan¬ tially emitted by said lamp. 20. The method of claim 18 wherein the temperature monitoring step comprises sensing energy radiating from within said process chamber by avoiding energy reflected off said .substrate from said radiant energy sourc .

Inventors: HAMMOND MARTIN L, MCDIARMID JAMES, PFEFFERKORN GLENN A, HAMMOND, MARTIN, L., MCDIARMID, JAMES, PFEFFERKORN, GLENN, A.
Applicants: GEMINI RESEARCH INC, GEMINI RESEARCH, INC.
Application year: 1984
Main classification: C23C11
IPC codes: C23C16