Horizontal reactor for compound semiconductor growth

Described is a horizontal reactor for processing GaN based semiconductors which achieves high quality epitaxial growth because no dust is produced through use of a ferrofluidic power transmission or gas flow to rotate its susceptor, elements from thermal decomposition of ammonia gas are provided separately at high temperatures at a position proximate the substrate so that premature reaction between ammonia ions and the reactant gases is avoided, and the reactor is constructed to suppress thermal convection attributed to heat from the susceptor which otherwise hinders smooth epitaxial growth.

FIELD OF THE INVENTION
 The present invention is related to a reactor for processing
 semiconductors, and in particular to a horizontal reactor for GaN based
 semiconductors.
 BACKGROUND OF THE INVENTION
 Compound semiconductor products have been used in emitting diodes for
 displays, optical telecommunications equipment, laser diodes (LD) for
 compact/video discs (CD/VD), photoconductors, capacitors for high speed
 computers, capacitors for satellites, and the like. The use of compound
 semiconductor products is being extendeded to mobile telecommunications
 equipment, blue laser diodes for optical digital displays (ODD),
 capacitors for optical computers, and the like.
 Light emitting diodes (LED) used for color image, graphic display elements
 provide a full color display through a combination of the three basic
 colors, red, green and blue. Among these, blue LED is manufactured from
 III-V nitrides, AIN, GaN, InN, and the like, and have emitting wavelengths
 of about 450 nm. (Al.sub.x Ga.sub.1- x).sub.1- y In.sub.y N has a direct
 energy band structure in the range of (1.gtoreq.x .gtoreq.0) and
 (1.gtoreq.y.gtoreq.0), and has the advantage of adjusting the band gap
 from 2.0 eV up to 6.2 eV (wavelength range, 370-650 nm) with the
 variations in x and y variables providing the ability to realize various
 colors with a single material.
 Metal Organic Chemical Vapor Deposition (MOCVD) systems are generally used
 in processing III nitride materials. MOCVD systems are divided into two
 basic groups by the arrangement of the reactor types, horizontal reactors
 and vertical reactors.
 Vertical reactors are generally equipped with a rotating mechanism for
 susceptors and are inferior in terms of uniformity in epitaxial growth due
 to a speedy flow of source gases on the periphery of the substrate. In
 contrast, horizontal reactors are advantageous for obtaining uniformity
 due to laminar flow formation of source gases parallel with the substrate.
 In spite of this, conventional horizontal reactors are still weak in
 suppressing thermal convection resulting in limitations on the formation
 of a uniform epitaxial growth. Although horizontal reactors employing
 rotating suceptors for improving uniformity are known, they have the
 disadvantage of producing dust from gear friction and insufficient
 prevention of thermal convection even with the employment of such rotating
 mechanisms.
 Prior art publications for GaN based semiconductor processing techniques
 include T. Nakamori, Nikkei Electronics Asia, 6(1), 57(1997); M. Kamp,
 Compound Semiconductor, 2(5), 22 (1996); I. Bhat, Compound Semiconductor,
 2(5), 24(1996); S. Nakamura, Microelectronics, J., 25(8), 651 1994); and
 S. Strite and H. Morkoc, J. Vac. Sci. Technol., R10(4), 1237(1992).
 SUMMARY OF THE INVENTION
 An object of the invention is to provide an improved horizontal reactor for
 GaN based semiconductors which provide a solution to the above-stated
 problems in the art, and which achieve uniform epitaxial growth.
 The above and other objects are accomplished by providing a horizontal
 reactor for compound semiconductor growth which comprises a susceptor
 adapted to hold a substrate on which a thin film for a semi-conductor
 grows, and an inner cell having an upper wall, a base wall and side walls.
 The upper wall, base wall and side walls define a reactant gas passage
 having two open ends. The upper wall has an inclined portion deriving
 laminar flow for reactant gases in the mid section of the upper wall. The
 lower wall supports the susceptor in a position opposite to the inclined
 portion. The reactor further comprises an outer cell surrronding the inner
 cell, an ammonia supply means for supplying ammonia gas to the reactant
 gas passage, a reactant gas supply means communicating with a first end of
 the two ends of the reactant gas passage which supplies reactant gases
 except ammonia gas to the reactant gas passage, a reactant gas vent means
 communicating with the second end of the two ends of the reactant gas
 passage for exhausting reactant gases out of the reactant gas passage, an
 ammonia gas heating means for heating ammonia gas, and a susceptor heating
 means for heating the susceptor.
 Preferably, the reactor further comnprises a susceptor rotating means for
 rotating the susceptor.
 Preferably, the ammonia heating means and the susceptor heating means are
 RF (radio frequency) coil heaters. The susceptor has a rotating portion
 which holds the substrate and is rotated by the susceptor rotating means
 and a stationary portion which surrounds the rotating portion. The ammonia
 supply means has an ammonia supply tube, one end of which is open at a
 position adjacent the rotating portion of the susceptor. The ammonia
 supply tube is installed through the stationary portion of the susceptor
 so that it is heated as the stationary portion is heated.
 Preferably, a long groove extends around the substrate on an upper surface
 of the stationary portion of the susceptor. The end of the ammonia supply
 tube is connected to the groove.
 Preferably, the susceptor rotating means comprises a ferrofluidic power
 transmission which connects the susceptor to a susceptor driving motor.
 Preferably, the ammonia supply means has an ammonia supply tube, one end of
 which is open at a position of the base wall of the inner cell adjacent
 the susceptor. The ammonia heating means comprises an electric resistance
 heater which surrounds the ammonia supply tube and the susceptor heating
 means comprises an electric resistance heater positioned below the
 susceptor.
 Preferably, the inner cell has a tube-type injector which projects
 downwardly from the base wall of the inner cell and receives the ammonia
 supply tube. The tube-type injector has a long groove which extends
 perpendicular to the longitudinal axis of the inner cell at the portion of
 the injector at which the injector meets with the base wall of the inner
 cell.
 Preferably, the reactor further comprises a first gas supply means and a
 second gas supply means which supply gas to the susceptor. The susceptor
 has a susceptor block supported on the base wall of the inner cell, a
 central cylindrical portion and a rotating portion. The susceptor block is
 provided with a recess for receiving the rotating portion and the central
 cylindrical portion, a first gas supply tube through which flows the gas
 supplied from the first gas supply means, a second gas supply tube through
 which flows the gas supplied from the second gas supply means, and outlets
 for exhausting the gases. The central cylindrical portion is in the shape
 of a hollow cylinder having an open end fixed to the bottom of the recess,
 and is provided with a plurality of through holes. The rotating portion
 has a main body for holding the substrate and a hollow cylindrical portion
 extending downwards from the lower surface of the main body. The hollow
 cylindrical portion has a plurality of wings arranged on its outer
 periphery. The first gas supply tube is connected to the bottom of the
 recess so that gas supplied through the first gas supply tube fills the
 space defined by the bottom of the recess and the inside of the central
 cylindrical portion and flows into a gap between the central cylindrical
 portion and the hollow cylindrical portion of the rotating portion through
 the plurality of through holes so that the gas flow exerts a pressure
 against the surface of the hollow cylindrical portion to lift the rotating
 portion. The second gas supply tube is connected to the wall of the recess
 so that gas supplied through the second gas supply tube flows into a space
 between the hollow cylindrical portion of the rotating portion and the
 recess of the susceptor block so that the gas impacts against the wings to
 rotate the rotating portion.
 The horizontal reactor of the present invention can achieve high quality
 epitaxial growth for the following reasons:
 (1) No dust is produced by friction among gears because the present
 suceptor is rotated by a ferrofluidic power transmission or gas flow.
 (2) Elements from thermal decomposition of ammonia gas are provided
 separately and yield nitrogen ions at a temperature of approximately
 1,000.degree. C. and the decomposed ammonia gas is supplied at a position
 proximate the substrate so that premature reaction between ammonia ions
 and the reactant gases is avoided.
 (3) The inner cell is inclined above the suceptor and downwardly toward the
 gas outlet in order to suppress thermal convection attributed to heat from
 the suceptor which hinders smooth epitaxial growth.

DETAILED DESCRIPTION OF THE INVENTION
 FIGS. 1-11 depict the first embodiment of the invention. The horizontal
 reactor of the invention is primarily for use in MOCVD processes for
 epitaxial growth of compound semiconductors, but can also be used for
 other similar proceses.
 FIG. 1 shows a horizontal reactor 1 for GaN-based semiconductor growth.
 Reactor 1 has an outer cell 2, an inner cell 3 to induce laminar flow of
 the source gases, a reactant gas supply portion 9, a susceptor 6 to admit
 a substrate 17, a ferrofluidic power transmission 8 to rotate the
 susceptor, an RF heater 12 for heating the substrate, and a vent portion
 13 to exhaust the reacted gases from the reactor. Reactor 1 is connected
 to a loading chamber 15 via a gate valve 14.
 Outer cell 2 functions to maintain the pressure of the reactant gases and
 is made from a quartz tube to avoid being heated by RF heater 12 which is
 wound around the exterior of the outer cell. Outer cell 2 is fixed by a
 vacuum flange 10 which has a water cooling jacket.
 Inner cell 3 is made from a quartz tube to avoid being heated by RF heater
 12. One end of inner cell 3 is connected with reactant gases supply
 portion 9. Inner cell 3 includes a shower head 5 to spray reactant gases
 and an inclined portion 4 to suppress thermal convection. All reactant
 gases except ammonia gas flow through shower head 5 which is provided with
 uniformly distributed holes to spray the gases and mix them with the
 nitrogen ions yielded by thermal decomposition of ammonia gas just before
 reaching susceptor 6, and then allowed to flow over the substrate, whereby
 GaN epitaxial growth is formed on substrate 17 placed on susceptor 6 which
 has been placed in the mid section of inner cell 3. Substrate 17 may be
 rotated by susceptor 6 to improve the uniformity of epitaxial growth on
 the substrate as explained below.
 As high temperatures of over 1,000.degree. C. are required during epitaxial
 growth through a conventional MOCVD process, the reactant gas used
 (hydride gas) and the MO source do not settle down and instead float over
 heated substrate 17 due to thermal convection from the high temperatures.
 Accordingly, if thermal convection is not suppressed, epitaxial growth
 cannot form uniformly or it may not form at all. Inclined portion 4 is
 provided in the middle of inner cell 3 in order to eliminate thermal
 convection and to allow laminar flow to reach the substrate on which the
 GaN semiconductor growth process occurs, avoiding the adverse effects due
 to thermal convection from the high temperature of the susceptor. The
 inclined angle of inclined portion 4 is varied depending on the size of
 the substrate and drift velocity of the source gases, and is selected to
 form laminar flows above the substrate. By providing inclined portion 4
 opposite the susceptor, the flow of source gases collides with inclined
 portion 4 and goes downward to the substrate in spite of the heating of
 source gases by hot substrate 17. Therefore, the inclined portion 4 of the
 inner cell of the present invention makes it possible to induce source gas
 flow to be steadily focused onto the substrate thereby increasing the
 efficiency of the epitaxial growth and reducing the loss of sources
 adhered to the inner cell near the substrate.
 FIGS. 2-6 show the inner cell of the horizontal reactor for compound
 semiconductor processing pursuant to the present invention. The inner cell
 comprises a gas inlet 40 in the shape of a cylinder which admits the
 reactant gases supplied from gas supply portion 9 into the reacting space
 defined by the inner cell. Gas supply portion 9 supplies all reactant
 materials except ammonia ions. The inner cell also comprises a base wall
 45 having a supporter 46 supporting the susceptor, an upper wall 42 having
 inclined portion 4 located above the susceptor, and side walls 43 and 44
 connecting upper wall 42 and base wall 45. These walls constitute a
 rectangular channel for flow of all reactant gases. A diffusion area 41
 links gas inlet 40 with the channel. Reactant gases are sprayed through
 shower head 5 at a position where the channel begins to pass diffusion
 area 41. Supporter 46 projects outwards from around the middle part of
 base wall 45 and is provided with grooves 33 into which projections 48 of
 the susceptor are adapted to be inserted (further details are provided
 below). Inclined portion 4 of upper wall 42 is positioned opposite the
 substrate on the susceptor supported by supporter 46. The source
 (reactant) gases flow over the substrate and are then exhausted through
 the outlet end of the inner cell, which is positioned opposite gas inlet
 40.
 A gas such as hydrogen is allowed to flow in the space between inner cell 2
 and outer cell 3. The gas flow maintains the pressure of reactant gases
 inside inner cell 2. The hydrogen gas flowing out of the space meets and
 mixes with the reacted gases coming out of inner cell 2. All mixed gases
 are then exhausted from the reactor through vent portion 13 driven by a
 pump (not shown in the drawings). Accordingly, the pressure required for
 the reaction is kept constant and the source gases are supplied
 continuously into the reactor.
 FIGS. 7-10 depict susceptor 6 of the horizontal reactor for compound
 semiconductors of the present invention. Susceptor 6 comprises a rotating
 portion 30 to support as well as rotate substrate 17, and a stationary
 portion 31 surrounding the rotating portion 30. To the ends of stationary
 portion 31 are attached side walls 47. Each of the side walls 47 has a
 projection 48 adapted for insertion into groove 33 in supporter 46 of
 inner cell 3. Preferably, the gap between rotating portion 30 and
 stationary portion 31 is made as small as possible, for example about 1
 mm, which takes into consideration the ease of machining of suceptor 6. An
 ammonia gas supply tube 7 is positioned longitudinally through stationary
 portion 31. Ammonia gas supply tube 7 is connected to a long recess 50 by
 an inclined tube. Recess 50 is positioned at the end of stationary portion
 31, which is directed toward reactant gas supply portion 9 when stationary
 portion 31 is installed in inner cell 3. In this manner, ammonia ion is
 supplied to the inside of inner cell 3 through tube 7 and recess 50.
 FIG. 11 shows susceptor 6 assembled in the reactor in detail. Rotating
 portion 30 of susceptor 6 is rotated to improve the uniformity of
 epitaxial growth quality including the thickness of the epitaxial layer
 which grows on the substrate. Rotating portion 30 is connected with a
 ferrofluidic power transmission 8 driven by a motor 51. In this way,
 proper rotation and vacuum sealing are achieved. The rotating portion of
 susceptor 6 and substrate 17 laid thereon are positioned substantially
 flush with base wall 45 of inner cell 3. Rotating portion 30, stationary
 portion 31 and side walls 32 of susceptor 6 are made of graphite and
 coated with SiC (silicon carbide). Susceptor 6 is heated in its entirety
 with an RF induction heater which coils around the outer cell. As the
 susceptor is heated, the ammonia gas tube installed at stationary portion
 is also heated, ammonia gas is decomposed into nitrogen ions which are
 sprayed through recess 50. Recess 50 is made wider than the diameter of
 substrate 17 to make the nitrogen ion flow over the substrate uniform.
 Since recess 50 is positioned proximate to substrate 17, the nitrogen ion
 flow is formed directly over substrate 17 and consequently increases the
 density of nitrogen ions to satisfy GaN based epitaxial growth. Further,
 the stay time of nitrogen ions in the reaction space is shortened and
 restoration to ammonia gas is decreased. The flow of nitrogen ions is
 further forced toward the substrate by the flow pressure of the reactant
 gases exiting from shower head 5 and consequently the density of nitrogen
 ions onto the substrate is further increased.
 The disclosure up to now has been on the first embodiment of the horizontal
 reactor for processing compound semiconductors of the present invention.
 The reactor of the first embodiment has the merit of simple construction
 as the ammonia gas tube is integral with the susceptor. As the susceptor
 and ammonia gas are heated together at the same time with an RF induction
 heater wound around the outer cell, the necessity for installing heaters
 inside the outer cell is avoided.
 FIGS. 12-18 show the second embodiment of the horizontal reactor of the
 present invention. In the horizontal reactor shown in FIG. 12, the ammonia
 supply tube is not disposed inside the susceptor but connected to the
 reaction space inside the inner cell as a separate supply tube. The
 susceptor and the ammonia gas tube are heated separately by its own
 dedicated heater. In the first embodiment, both susceptor and ammonia gas
 tube are heated by one RF heater at the same time at the same temperature
 (for example, 800.degree. C.). In the second embodiment, the temperature
 for decomposition of ammonia gas is controlled at about 1000.degree. C.
 and the temperature of the susceptor is controlled at a suitable
 temperature below 1000.degree. C. by two separate heaters and more
 appropriate conditions for the reaction inside the inner cell can be
 obtained.
 The horizontal reactor of the second embodiment is provided in more detail
 with reference to FIGS. 12-18. For elements which are used in common with
 the first embodiment, the same reference numerals are applied and their
 details are omitted hereinbelow.
 In the horizontal reactor 100 shown in FIG. 12, ammonia gas supply portion
 110 and a base plate 120 for supporting susceptor 130 are fixed to a
 supporting plate 102 by bolts (not shown). Supporting plate 102 is shown
 projecting from the outer cell. Base plate 120 has grooves 120 to receive
 O-rings for creating a vacuum seal between supporting plate 102 and base
 plate 120.
 Susceptor 130 on which substrate 17 is laid, is connected to the axis of
 rotating mechanism 135 of the ferrofluidic motor and fixed to the base
 plate by mechanism 135. Ammonia gas supply portion 110 is positioned
 through a hole 122 provided in base plate 120 and is fixed to the base
 plate by a vacuum flange 111 for the ammonia gas supply portion. Vacuum
 flange 111 is provided with grooves 112 to receive O-rings for forming a
 vacuum seal between vacuum flange 111 and base plate 120.
 FIG. 13 illustrates the relationship between ammonia gas supply portion
 110, suceptor 130 and base plate 120 of the second embodiment of the
 invention. Ammonia gas supply portion 110 consists of an ammonia gas tube
 113, a tube-type heater surrounding the upper portion of the gas tube, a
 main body 115 surrounding the lower portion of the gas tube and a quick
 coupling seal 116 attached below main body 115 for vacuum sealing the
 ammonia gas tube from the surroundings. The main body has a feedthrough
 flange 117 attached to it and a water cooling jacket 118 within it to
 insulate quick coupling seal 116 from heat generated by the tube-type
 heater 114. The tube-type heater is connected to a heating tube support
 119 in a flange type connection at its lower end. Support 119 has a larger
 thickness and diameter than the tube-type heater. The heating tube support
 is connected with a power line (not shown) of the heating tube, and
 transfers power from the power line to the heating tube, and insulates the
 surroundings from the high temperature heating tube. The power line of the
 heating tube is connected to a power source (not shown) outside the
 reactor through feedthrough flange 117. The main body is fixed to vacuum
 flange 111 by welding and the vacuum flange is fixed to base plate 120 by
 bolts (not shown). Both the vacuum flange and the base plate are made of
 stainless steel.
 A PBN heater is used for heating tube 114. As it is possible to heat
 ammonia gas and the susceptor by separate heaters rather than one RF coil
 surrounding the outer cell, the outer cell can also be made of stainless
 steel.
 The susceptor is made of graphite and coated with SiC. The susceptor has a
 recess for laying substrate on it. The susceptor is surrounded by a
 molybdenum plate 131 at its periphery and on its bottom surface. A
 plate-type heater 132 is located under the molybdenum plate with a gap. A
 PBN heater is used for plate-type heater 132. The molybdenum plate allows
 uniform heating of susceptor 130 by dispersing heat from plate-type heater
 132. Heater 132 is surrounded by a reflecting plate 133 except at the
 portion facing the molybdenum plate. The reflecting plate efficiently
 focuses heat from the heater onto molybdenum plate 131 and avoids
 radiation to other portions of the reactor. The molybdenum plate is
 connected with the axis 134 of the rotating mechanism of ferrofluidic
 motor 135. The driving force to rotate the susceptor is transferred from
 motor 137 to molybdenum plate 131 through coupling 136, rotating mechanism
 135 and axis 134. Heater 132 is supported by a supporter 138 fixed to the
 base plate 120. Rotating mechanism 135 is fixed to an NPT connection 139
 by screws. Groove 140 is provided between the rotating mechanism and the
 NPT connection for receiving an O-ring for vacuum sealing. Water cooling
 jackets 141 are provided inside the base plate to protect O-rings from
 heat generated by the heater.
 Referring again to FIG. 12, ammonia gas tube 113 is inserted into a
 tube-type injector 146 projecting from base wall 145 of inner cell 103.
 The-tube type heater abuts with the end of tube-type injector 146.
 Tube-type injector 146 is provided with a long groove 148 lateral to inner
 cell 103 at a portion which merges with base wall 145. Such arrangement
 enables nitrogen ions to flow into the reaction space of inner cell 103
 with negligible leaks between the tube-type injector and tube-type heater
 114. Ammonia gas is heated up to approximately 1,000.degree. C. as it
 passes through tube-type heater 114 surrounding ammonia gas tube 113. As
 ammonia gas is heated, it decomposes to nitrogen ions which spray out of
 ammonia gas supply portion 110 and flow into the reaction space of the
 inner cell through tube-type injector 146. Nitrogen ions are mixed with
 reactant gases issuing from reactant gases supply portion 9, and the
 mixture forms a flow of source gases on substrate 17 as described for the
 first embodiment of the invention.
 Susceptor 130 is positioned through a hole 147 in base wall 145 of inner
 cell 103 so that molybdenum plate 131, base wall 145 and substrate 17 are
 flush with one another. The gap between hole 147 and molybdenum plate 131
 is tooled at about 1 mm depending on the ease of machining.
 FIGS. 14-18 illustrate the inner cell 103 of the reactor of the second
 embodiment. Inner cell 103 of the second embodiment differs from that of
 the first embodiment in that it has a tube-type injector 146 connected
 with ammonia supply tube 113 instead of supporter 46 of inner cell 3 as in
 the first embodiment, and hole 147 for receiving susceptor 130 is located
 in base wall 145.
 FIGS. 19-32 illustrate the third embodiment of the present invention. In
 the horozontal reactor for GaN semiconductor growth shown in FIG. 19,
 rotation of the susceptor is achieved by a gas flow through the susceptor.
 The gas is supplied from outside the reactor. The susceptor is heated by
 an RF heater 212 wound around the exterior of the outer cell as in the
 first embodiment.
 The details on the horizontal reactor for GaN semiconductor growth of the
 third embodiment of the invention are provided below with reference to
 FIGS. 19-32. Components in common with the first and second embodiments
 are indicated by the same two-digit reference numerals added by 200 and
 their specific details are omitted below.
 The horizontal reactor 200 for GaN semiconductor growth shown on FIG. 19
 differs from the second embodiment in that the rotation of susceptor 230
 is performed by flow of gas such as hydrogen gas supplied from outside
 reactor 200 through gas supply portions 210 and 212. Another difference is
 that the ammonia gas supply portion 110 is installed horizontal to
 reactant gases supply portion 209 with bolts, and heated ammonia gas
 supplied from ammonia gas supply portion 110 flows into the reaction space
 defined by inner cell 203 through a diffuser 216. Since the third
 embodiment does not employ a ferrofluidic power transmission, provisions
 for protection and installation of a ferrofluidic power transmission are
 not needed. In addition, as ammonia gas supply portion 110 is installed
 horizontally, there is no need to provide an opening in outer wall 202 for
 installing the ammonia gas supply portion. Consequently, the structure of
 the reactor becomes simple and easier to manufacture.
 FIGS. 20-23 show the inner cell 203 of the third embodiment. Inner cell 203
 has a slit 218 through which ammonia gas flowing out of diffuser 216,
 flows into the reaction space. Slit 218 is positioned near shower head 5.
 A susceptor receiving portion 220 for receiving susceptor 230 is provided
 between slit 206 and the exit for inner cell 203, and opposite inclined
 portion 4.
 Referring to FIG. 24, details on the rotating operation of susceptor 230 is
 provided. Susceptor 230 includes a susceptor block 260, a rotating portion
 262 and a central cylindrical portion 264, which are explained in more
 detail below with reference to FIGS. 25-27. Pressurized hydrogen gas is
 supplied from gas supply portion 212 through a gas supply tube 266
 connected to the bottom of central cylindrical portion 264. The hydrogen
 gas is ejected through holes 268 provided in the cylindrical wall of
 central cylindrical portion 264, and flows into the gap between central
 cylindrical portion 264 and a recess 270 of rotating portion 262 which
 surrounds central cylindrical portion 264. The hydrogen gas exerts a
 pressure on the surface of recess 270 so that the rotating portion is
 lifted from a resting postition, at which rotating portion 262 rested on a
 step 272 of susceptor block 260, to an operating position in which
 substrate 17 is laid on rotating portion 262 and flush with base wall 245
 and the upper surface of susceptor block 260. This lifting operation using
 hydrogen gas flow may be controlled by controlling the flow rate of the
 hydrogen gas through gas supply tube 266, with a mass flow controller
 (MFC, not shown).
 When rotating portion 262 is lifted to the operating position, hydrogen gas
 from gas supply portion 210 flows into the gap between susceptor block 260
 and rotating portion 262 through a gas supply tube 280. The introduced
 hydrogen gas impacts on wings 282 provied on the lower periphery of
 rotating portion 262 thereby moving the rotating portion. The rotating
 speed of rotating portion 262 may be controlled by controlling the flow
 rate of the hydrogen gas through gas supply tube 280 with an MFC (not
 shown). The in-coming hydrogen gas is exhausted through outlet holes 284
 and 286 provided on a step of susceptor block 260 and does not flow into
 the reaction space defined by inner wall 203 and susceptor 230. After
 completion of epitaxial thin film growth, gas flow rates through gas
 supply tubes 266 and 280 are controlled so that the movement of rotating
 portion 262 is stopped and the rotating portion 262 is lowered to the
 resting position on step 272 of susceptor block 260.
 Details on susceptor block 260 is provided with reference to FIGS. 25-27.
 Block 260 is generally a retangular cube made of graphite and coated with
 SiC. A recess 288 for receiving rotating portion 262 and central
 cylindrical portion 264 is provided around the center of the upper surface
 278 of the block. Recess 288 includes steps 272, 274 and 276
 concentrically arranged from upper surface 278 to the bottom 290 of recess
 288 and circular walls 292, 294, 296 and 298 between the steps. Each step
 is of a suitable size and in a suitable position to support rotating
 portion 262. The lower surface 306 of block 260 is provided with a hole
 302 extending longitudinal to the block for receiving gas supply tube 266,
 and a projection 308 surrounding hole 302. One end of hole 302 opens at a
 side surface of susceptor block 260 and the other end opens perpendicular
 to the longitudal axis of hole 302 at the center of bottom 290. When
 susceptor 230 is loaded into inner cell 203, projection 308 is fitted in a
 cut-out portion 311 provided in the susceptor receiving portion 220 of
 inner cell 203. A hole 300, extending longitudinal to the block, for
 receiving gas supply tube 280 is provided ajacent circular wall 294 of
 susceptor block 260. One end of hole 300 is opens at the side surface 310
 of susceptor block 260 and the other end opens in wall 294 of the recess.
 In addition, a hole 304 which extends longitudinal to the block, is
 provided at a position opposite hole 300 with respect to the centerline of
 susceptor block 260. One end of hole 304 opens at side surface 310 of
 susceptor block 260 and the other end opens at a position where wall 294
 and step 274 of the recess, meet. A quartz pipe (not shown) similar to gas
 supply tubes 266 and 280 is inserted into hole 304 and performs the role
 of supporting susceptor 230 together with gas supply tube 266 and 280 when
 susceptor 230 is loaded into or unloaded from reactor 200, and is adapted
 to receive a thermocouple (not shown) to measure the temperature of the
 susceptor.
 The details on the central cylindrical portion 264 of susceptor 230 is
 provided with reference to FIGS. 28 and 29. Central cylindrical portion
 264 is made of graphite and coated with SiC. Central cylindrical portion
 264 has a shape of a hollow cylinder, one end of which is blind and the
 other end of which is open. The open end of central cylindrical portion
 264 is fixed to bottom 290 of recess 288 with bolts and the like (not
 shown). A plurality of through holes 312 are uniformly distributed on the
 cylindrical wall of central cylindrical portion 264. Hydrogen gas supplied
 through gas supply tube 266, flows past the space defined by the inside of
 central cylindrical portion 264 and bottom 290 of recess 288 of susceptor
 block 260 and is exhausted through holes 312.
 Details on the rotating portion 262 of susceptor 230 is provided with
 reference to FIGS. 30-32. Rotating portion 262 is made of graphite and
 coated with SiC. Rotating portion 262 includes a main body 322, a recess
 324 provided on the upper surface of main body 322 for holding substrate
 17, and a hollow cylindrical portion 326 which extends downwardly from the
 lower surface of main body 322. The hollow space inside hollow cylindrical
 portion 326 defines recess 270 which surrounds central cylindrical portion
 264. The plurality of wings 282 are uniformly arranged on the outer
 periphery of hollow cylindrical portion 326.
 The horizontal reactor embodiments described herein eliminate thermal
 convection from source gases flowing over a susceptor and, at the same
 time, induces uniform laminar flow of the source gases over the substrate,
 which contribute to the production of a high quality epitaxial layer.
 Various modifications and alterations to the present invention may be
 appreciated based on a review of this disclosure. These changes and
 additions are intended to be within the scope and spirit of this invention
 as defined by the following claims.