Vertical hot wall CVD reactor.

BACKGROUND AND SUMMARY OF THE INVENTION

0001This invention relates to the chemical vapor deposition of thin film material layers on a substrate; and more particularly to a method and apparatus for carrying out such depositions, including the epitaxial deposition of silicon, for example, used in the fabrication of semiconductor electronic devices.

0002It has been qenerally accepted in the industry that semiconductor-prade monocrystalline silicon epitaxy, requires a "cold-wall" reactor desiqn, involvinq the use of RF energy to aenerate heat in susceptors whereon silicon slices or other substrates are supported; or the use of infrared lamps to focus heat on the substrates.

0003The use of a "hot wall" reactor has been considered unacceptable because of the inability to suppress homoaeneous qas phase reactions, and the unwanted deposition of silicon on reactor walls and other parts, followed by flaking and/or settling of such unwanted silicon in particulate form, thereby contaminatinq the epitaxial layers formed on the substrates.

0004Other considerations that weiqh heavily in the development of new reactor configurations are the need for deposition thickness uniformity across individual slices, and from slice to slice, crystalline quality, and pattern inteqrity. These are affected by the qas flow pattern and flow rates, the control and uniformity of heat input, the slice carrier confiquration, the deposition pressure and temperature, the composition of feed aases, and the composition of reactor parts.

OBJECTS OF THIS INVENTION

0005A primary object of this invention is to provide a "hot-wall" reactor confiouration that avoids or minimizes the above mentioned contamination problems, and thereby achieves high-quality epitaxial arowth at greatly improved throughput efficiencies compared with previously available systems.

0006Other advantaaes of the invention include a slice per hour throughput rate that is independent of slice diameter. The system is also more readily adapted for automated loadina and unloadinq of slices, than are prior systems.

0007Another ob.iect of the invention is to provide a method for the qrowth of electronic qrade epitaxial silicon films having greater uniformity and crystal intearity, resultina from the use of an improved qas flow pattern, in combination with a simplified substrate carrier motion, and the virtual elimination of thermal qradients from slice front to back surfaces.

0008One aspect of the invention is embodied in a "hot wall" reactor comprising a resistance-heated furnace element surrounding a process tube or envelope wherein a rotatable substrate carrier is positioned between a aas inlet system and a qas exhaust system.

0009The carrier includes a plurality of substrate supportina means, for enablina the center of each substrate to be placed at a point on the axis of rotation of the carrier. The aas inlet system includes a plurality of manifolds havinq ports for introducinq qas at separate locations near the carrier, to provide each substrate with a separate qas-flow pattern.

0010The qas exhaust system is preferably positioned to remove aases at separate locations near the carrier, such that qases having passed in contact with one substrate are not permitted to pass in contact with another substrate. A preferred exhaust system includes a plurality of manifolds positioned near the carrier, each manifold havina a plurality of exhaust ports spaced comparably with the spacinq of the substrate support means of said carrier system. This arranqement further enhances the separation of the qas flow patterns from each other.

0011An alternate exhaust configuration consists essentially of ports in the base plate, spaced on the opposite side of the carrier from the qas inlet manifolds. Although this embodiment is sliahtiy less desirable because of the reduced separation of qas flow patterns across each substrate, the concept of the invention is nevertheless fully illustrated.

0012The process tube surface, i.e. the inside reactor wall of the preferred emobdfment of the invention is made of a high purity refractory material selected for its ability to retain whatever spurious deposits may be formed thereon during operation of the reactor. For example, when silicon is beina deposited, pure silicon carbide is the preferred surface for interior reactor surfaces. This material is superior because any silicon deposited thereon remains in place, instead of flaking off to contaminate the substrates. Similarly, when depositing silicon, silicon carbide is the preferred material for construction of the substrate carrier, the gas inlet system, and the exhaust system, for the same reason.

0013When depositinq silicon nitride, the preferred material for construction of reactor parts and interior surfaces is silicon nitride. For depositinq silicon dioxide, the preferred construction material is ouartz. These materials have also been found superior in their ability to prevent flaking of spurious deposits.

0014The method of the invention is carried out in the above-described reactor. The substrates are located on the rotatable supports, and the carrier assembly is rotated while reaction gases are passed in contact with the substrates durinq a "hot wall" condition resulting from the heat flow from the furnace element surrounding the process tube.

0015When depositing epitaxial silicon on monocrystalline substrates, the reaction oases comprise hydrogen and trichlorosilane and/or other halosilanes. The hydroqen is passed separately through one or more inlet manifolds, while the halosilane is passed throuqh one or more other inlet manifolds. Separate introduction avoids premature interaction of the qases, prior to slice contact.

BRIEF DESCRIPTION OF THE DRAWINGS

0016<ul id="ul0001" list-style="none"><li>Fiqure I is a vertical cross section throuqh the center of a preferred embodiment of the reactor of the invention.</li><li>Fiqure 2 is a similar cross section of a portion of the reactor. showing the aas inlet and exhaust manifolds in qreater detail, including the qas flow patterns throuqh the substrate carrier support levels.</li><li>Fiqure 3 is a perspective view of the interior of the reactor, showina the arranaement of inlet and exhaust manifolds surroundinq the substrate carrier.</li></ul>

DESCRIPTION OF THE_PREFERRED EMBODIMENT

0017In the embodiment of Fiqure 1, a vertical cylindrical, resistance-heated furnace element 11 surrounds a first vertical process tube or bell jar 12, which surrounds an optional, second process tube 13, surroundinq the assembly of rotatable substrate carrier support members 14 located between inlet manifolds 15 and exhaust manifolds 16. Furnace element 11 is preferably suspended from above, usinq a lift mechanism for elevatina the furnace above the process tube or tubes, in order to provide access to the interior assembly for loading the substrates, and for facilitating maintenance.

0018In Figure 2 the cross section of a gas inlet manifold 15 and a gas exhaust manifold 16 are shown in greater detail, including inlet ports 17 and exhaust ports 18. The size of ports 17 is progressively larger in the downstream direction of flow, in order to compensate for the pressure drop, so that equal volumes of gases flow in contact with each substrate. Conversely, the size of ports 18 is proqressively smaller in the downstream direction of flow. to preserve a substantially separate flow pattern across each substrate, thermocouple 19 is used to control the furnace temperature.

0019Baseplate 20 is fitted against the lower end of bell jar 12 with seals 21. The water-cooled base plate is isolated from reactant gases by quartz layer 20a. Substrate carrier shaft 22 extends through the baseplate 20 and is fitted with seals that permit rotation of the carrier. Gas input and exhaust are also provided through the baseplate at ports 23 and 24, respectively.

0020In Figure 3,.the interior reactor assembly is seen to include inlet manifolds 15 partially surrounding one side of the carrier, while exhaust manifolds 16 partially surround the other side. Tube 25 is provided to house a thermocouple for temperature control.

0021Substrate carrier assembly 14 is removable as a unit, so that it can be readily interchangeable with other carrier assemblies. This facilitates automated loading and unloading of substrates, thereby increasing reactor throughput efficiency.

0022Suitable reactor dimensions include a furnace element with an 11 inch inside diameter, and a 17 inch outside diameter, 60 inches lonq, with a 20 inch flat temperature profile zone. The process tube is 54 inches long and 8 inch inside diameter. Such a reactor size is suitable for wafers of 100 mm diameter.

0023A typical process sequence with predicted flow rates are as follows: <ul id="ul0002" list-style="none"><li>1. Load silicon wafers, furnace and bell jar in up position at 800 degrees C.</li><li>2. Lower bell jar and purge system.</li><li>3. Lower furnace element.</li><li>4. Cycle furnace up to bake/etch temperature, e.q. 1200 degrees C.</li><li>5. Bake and etch wafers while rotatinq carrier at about 10 revolutions per minute.</li><li>6. Cycle furnace down to deposition temperature, e.g. 1120 degrees C.</li><li>7. Purge--deposit--purge while rotatinq wafer support system.</li><li>8. Cycle furnace to 800 degrees C.</li><li>9. Raise furnace leaving bell jar.</li><li>10. Cool bell jar to room temperature.</li><li>11. Raise bell jar.</li><li>12. Unload silicon wafers.</li></ul>

TYPICAL EPITAXY DEPOSITION CONDITIONS:

0024Hydrogen flow 0.8 to 6 liters per minute per wafer, e.g. 4 liters per minute.

0025Halosilane flow equal to 0.3 to 3 percent of hydroqen flow rate.

0026Process flows will vary as a function of wafer diameter crystal orientation of wafers, deposition temperature and deposition rate.

0027The composition of interior reactor walls and other interior surfaces is selected in order to prevent flaking of inadvertent deposits thereon, as previously mentioned. The primary reason that flakina is thereby prevented involves a matchinq of thermal expansion coefficients. That is, during thermal cycling of the reactor as a part of its routine operation, expansion and contraction of the reactor surfaces is thereby caused to equal the expansion and contraction of spurious deposits thereon, which prevents flaking.