FR2711274A1 - Apparatus for chemical vapor deposition. - Google Patents

Abstract

Disclosed is a chemical vapor deposition apparatus for crystal growth on a pellet disposed in a reaction chamber in which gaseous materials are supplied from an upper portion of the reaction chamber while the materials are supplied. in the gaseous state escape from the bottom of the chamber. According to the invention, it comprises a susceptor (2) on which is placed the pellet (4), a heater (5) arranged under the susceptor (2) to heat it and a detachable cylindrical member (7) arranged at the bottom of the reaction chamber (1) in order to cover parts under the susceptor (2) and to prevent gaseous matter from flowing around the parts under this susceptor (2). The invention applies in particular to semiconductors.

Description

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  The present invention relates to an apparatus for chemical vapor deposition (CVD) for crystal growth of compound or analog semiconductors using a chemical vapor phase reaction, particularly, it relates to an apparatus for the

  chemical vapor deposition of an organic metal (MOCVD).

  Fig. 11 is a sectional view showing a reaction chamber of a conventional fast rotating type MOCVD apparatus. In FIG. 11, a cylindrical reaction chamber 1 is made of SUS. A susceptor 2 of the disk type is placed in the reaction chamber 1. A plate 3

  for the pellets is mounted detachable on the susceptor 2.

  A semiconductor substrate 4, such as a GaAs substrate, is placed in a throat of the plate 3. A circular heater

  5 heats the susceptor 2 from its lower portion.

  A circular heat-shielding plate 6 is disposed on the heater 5. An electrode 7 is connected to the heater 5. The rotation axis 8 for the rotation of the susceptor 2 is fixed to the susceptor 2. A thermocouple 9 detects the temperature of the heater. Heater 5. First and second meshes 12, 13 uniformly disperse the gases introduced into the reaction chamber 1. An opening 10 is used when the tray 3 of the pellets is transported in the reaction chamber 1. A delivery tube 20a a carrier gas and gaseous material supply tubes 20b and 20c supply a carrier gas and gaseous materials into the reaction chamber 1 respectively. A needle valve 11 for adjusting the gas flow is attached to each of the tubes 20a, 20b and 20c. A rotary pump 16 is disposed downstream in an exhaust duct 1a of the reaction chamber 1 and the suction pressure of the gas in the reaction chamber 1 is adjusted by a pressure adjustment valve 15 which is arranged in upstream of the rotary pump 16. A filter 14 is arranged upstream of the pressure adjustment valve, which removes dust or the like of the gas in the chamber of

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  reaction 1 and sends the gas to the pressure adjustment valve 15. According to the CVD apparatus of the very rapid rotation type, the susceptor on which the pellets are placed is rotated at a fast speed while the gaseous materials are supplied, and these materials supplied in the gaseous state. gather in swirls in the center of the susceptor. Then, gaseous materials are uniformly dispersed from the susceptor center to its circumference. As a result, the uniformity of crystal growth between the pellets can be improved. We will now describe the operation during the

crystal growth.

  The platen 3 for the pellets on which the semiconductor device (GaAs substrate in this case) is disposed at a predetermined position is transported in the reaction chamber 1 through the opening of this chamber 1. The plate 3 is placed on the susceptor 2 in the reaction chamber 1. Hydrogen gas (H2), serving as a carrier gas, is introduced through the carrier gas supply tube 20a disposed in an upper part of the reaction chamber 1 and the pressure in the chamber of reaction 1 is

  adjusted to a desired pressure, for example 66.5 mbar.

  At this time, the carrier gas (H2) is uniformly dispersed by the first mesh 12 and is supplied in the chamber of

reaction 1.

  Then, the susceptor 2 is gradually rotated to reach a predetermined number of revolutions, for example, 1000 rpm. Then, the heater 5 is heated to a predetermined temperature, for example 700 C, while arsine (ASH3) as a Group V gaseous material is introduced through the gas supply pipe 20b into the reaction chamber 1 to prevent the thermal decomposition (mainly escaping As atoms) of the substrate 4. At this time, the heat produced by the heater 5 is reflected by the two plates 6 of

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  thermal shielding which are arranged under the heater, so the heat goes for the most part to the susceptor 2. At this time, the temperature is monitored by the thermocouple 9 in the reaction chamber 1. In addition, as the decomposition temperature AsH3 is more important than that of TMG (which will be described below) or the like, a relatively large amount of

  AsH3 to maintain its concentration on the substrate 4.

  Then, a gaseous material for crystal growth, such as TMG, is introduced through the pipe 20c for a desired period of time. Thus, AsH3 and TMG (trimethylgallium) are uniformly dispersed by the second mesh 13 disposed at the upper part of the

  reaction chamber 1 to reach the substrate 4 GaAs.

  Therefore, it improves the uniformity of the thickness and the carrier concentration of a GaAs film shot on the

substrate 4 in GaAs.

  Then, the delivery of the gaseous TMG is stopped and the heater 5 is stopped while supplying AsH3 to prevent As in the growing film of GaAs from escaping. When the temperature falls to a desired point, the supply of AsH3 is stopped and the number of turns of the susceptor 2 is gradually reduced until the rotation stops. Then, the plate 3 for the pellets has left the reaction chamber 1 through the opening 10 and the GaAs substrate 4 is obtained on which the GaAs film is drawn. Moreover, in the case of crystalline growth of GaAs, TMA (trimethylaluminum) is provided at the same time as

  TMG through gas supply pipe 20c.

  Since the conventional CVD apparatus is constituted as described above, the exhaust occurs at the bottom of the reaction chamber and the reaction gas arrives in a region below the susceptor where the temperature is low. As a result, as shown in FIG. 12, reaction products 17 produced by the thermal decomposition of the reaction gas are attached to the side wall of the reaction chamber 1, to the shielding plates

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  As a result, the heat radiation fluctuates i.e., drops, because of the attachment of the reaction products 17, and thus the temperature monitored seems to drop. In order to compensate for this, electric current is applied to heater 5. Accordingly, as shown in Fig. 13 (a), the actual growth temperature fluctuates during crystal growth and from one test to another. In particular, the growth temperature fluctuates greatly just after the maintenance. In addition, cleaning to remove the reaction products 17 from the above described parts of the chamber

  reaction 1 must be periodically performed.

  In addition, since the gaseous feed is controlled by the needle valve 11, the film thickness, carrier concentration, or the like become irregular in a region downstream of the gas flow, in the substrate 4 the reaction chamber. We

  will give a detailed description referring to the figure

  13. With regard to the thickness of the film, as the boundary layer becomes thin downstream of the wafer, as can be seen in FIG. 13 (b), there is accordingly a reduction in the thickness of the drawn film on the pellet. With regard to the carrier concentration, since a large amount of Group V atoms are provided with a high decomposition temperature, the concentration is less irregular in the substrate, but there is a consumption of Group III atoms and the concentration decreases downstream. As a result, the group V atom concentration appears to increase downstream as shown in Figure 13 (c). As described above, there is an irregularity in film thickness, carrier concentration, or the like. As a result, it decreases the uniformity of the product. Additionally, the reaction products are attached to the second mesh because of the thermal decomposition of the gaseous materials introduced by the pipes which are arranged at the upper part of the chamber.

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  reaction in this room, forcing the mesh to clog. As a result, the gaseous materials are not uniformly supplied to the substrate so that the thickness and the carrier concentration of the film pulled on the substrate become irregular. In addition, an interview to remove

  the reaction products must be carried out.

  On the other hand, since the decomposition temperature of the Group V gas material, such as AsH 3, is high as described above, the gas decomposes mainly on the substrate only. As a result, when the gaseous material and Group III atoms are supplied in an equivalent amount, the concentration of Group V atoms (As atoms in the case of arsine) which are provided for crystal growth on the substrate decreases. Therefore, a large amount of the Group V gaseous material must be introduced during the crystalline growth, which means that the efficiency of the gaseous materials supplied (material efficiency) for the

Crystalline growth is low.

  On the other hand, the patent application published in Japan N 248519/1986 and the published patent application in Japan N 126823/1985 reveal an apparatus comprising two exhaust ducts at a lower part of a reaction chamber, so that the flow of the reaction gas is accelerated under a susceptor to reduce the production of reaction products at the bottom of the reaction chamber. However, in this structure, the reaction gas is not completely prevented from passing under the susceptor and the film thickness, the carrier concentration and the like

  are irregular upstream and downstream of the gas flow.

  In addition, there is still the disadvantage above that the mesh disposed at an upper portion of the chamber of

reaction may be clogged.

  On the other hand, in the conventional example, in order to remove the reaction products which are deposited in the reaction chamber, the reaction chamber is heated to a prescribed temperature until the products of

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  reaction are sufficiently decomposed after the crystalline growth whereas only the carrier gas is supplied or in an evacuated atmosphere. However, according to this method, the maintenance time is extremely increased and this decreases the manufacturing efficiency. Still further, for example, as disclosed in Japanese Patent Application No. 277627/1992 and Japanese Patent Application Publication No. 126823/1985, a gas shower electrode ejecting gaseous materials is heated or the pipes supplying the gaseous substances are directly heated. However, in this structure, the gaseous materials are heated before being introduced into the reaction chamber, therefore the flow of the gaseous materials in the gas shower electrode or the gaseous supply pipes is not sufficiently heated. In addition, since the gaseous materials decompose in the gas shower electrode or the gaseous feed pipes, reaction products are formed therein.

attach.

  The object of the present invention is to provide a CVD apparatus in which the fluctuation of the growth temperature is reduced and the cycle of

  cleaning of parts in a reaction chamber is increased.

  Another object of the present invention is to provide a CVD apparatus capable of growth

crystalline very uniform.

  Another object of the present invention is to provide a CVD apparatus in which a mesh disposed under the pipes for introducing gaseous materials into a reaction chamber can be easily and quickly cleaned, and gaseous materials are found

  always uniformly supplied to a substrate.

  Another object of the present invention is to provide a CVD apparatus capable of improving material efficiency by accelerating the decomposition of a gaseous material.

  whose decomposition temperature is high.

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  According to a CVD apparatus of the present invention, an exhaust vent is formed at a lower portion of a reaction chamber and a detachable cylindrical member is disposed to surround parts below a heater. Thus, since the parts arranged under a susceptor are surrounded by the cylindrical member, the materials in the gaseous state can not pass around these parts. According to a CVD apparatus of the present invention, as an exhaust vent is formed in a side wall of a reaction chamber near a susceptor while gaseous materials are provided from the upper part of the reactor. the reaction chamber, the materials supplied in the gaseous state escape near the susceptor and they can not pass below it. In addition, as a carrier gas introduction pipe to prevent attachment of the products is provided to provide a carrier gas from the bottom of the reaction chamber to the rear surface of the susceptor, the gaseous materials can not flow around a region under

the susceptor.

  According to a CVD apparatus of the present invention, the gaseous materials are supplied from an upper part of a reaction chamber and the gaseous material is also supplied from an auxiliary pipe to a portion thereof. downstream of the flow of gaseous materials above, in a pellet disposed on a susceptor. Consequently, this reduces the irregularity of the boundary layers to

the surface of the pellet.

  According to a CVD apparatus of the present invention, a heatable mesh is disposed between the outlets of the gaseous material feed pipes in a reaction chamber and a pellet tray on a susceptor where a substrate is placed and the mesh is heated at the time of maintenance. Then, the products attached to the

  mesh can be quickly removed.

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  According to a CVD apparatus of the present invention, gaseous materials having different decomposition temperatures are provided individually by different pipes; the outlet of a gaseous material supply pipe which supplies the gaseous material having the highest decomposition temperature is disposed closer to a substrate than the outlet of the material supply pipe; a gaseous state which supplies the gaseous material with the lowest decomposition temperature; a heatable mesh is disposed under the outlets of the pipes above; and the gaseous material having the highest decomposition temperature is decomposed and is supplied to the substrate during crystal growth. Thus, the concentration of the atoms of the gaseous material having the highest decomposition temperature on the pellet is increased and the efficiency of the gaseous material is improved. In addition, two gases with different decomposition temperatures do not react before

to reach the pellet.

  The invention will be better understood and other purposes, features, details and advantages thereof

  will become clearer during the description

  explanatory text which will follow with reference to the accompanying schematic drawings given by way of example only, illustrating several embodiments of the invention and in which: FIG. 1 is a sectional view showing an apparatus for MOCVD according to a first embodiment of the present invention; Fig. 2 is a sectional view showing an apparatus for MOCVD according to a second embodiment of the present invention; Fig. 3 is a sectional view showing an apparatus for MOCVD according to a third embodiment of the present invention;

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  Fig. 4 is a sectional view showing an apparatus for MOCVD according to a fourth embodiment of the present invention; Fig. 5 is a sectional view showing an apparatus for MOCVD according to a fifth embodiment of the present invention; Fig. 6 is a sectional view showing an apparatus for MOCVD according to a sixth embodiment of the present invention; Fig. 7 is a plan view showing a structure of a second mesh of the MOCVD apparatus; Fig. 8 is a sectional view showing an apparatus for MOCVD according to a seventh embodiment of the present invention; Fig. 9 is a perspective view showing a structure of a porous ceramic heater used in the MOCVD apparatus according to an eighth embodiment of the present invention; Fig. 10 is a sectional view showing an apparatus for MOCVD according to ninth and tenth embodiments of the present invention; Figure 11 is a sectional view showing a MOCVD apparatus of the very fast rotation type according to the prior art; Fig. 12 is a sectional view explaining the problems of the prior art MOCVD apparatus; and Figs. 13 (a) -13 (c) are graphs explaining the problems posed by the art MOCVD apparatus.

prior.

  The first embodiment will be described below.

  Fig. 1 is a sectional view illustrating an apparatus for MOCVD according to a first embodiment of the present invention. In Figure 1, the same reference numerals as in the figures. 11 and 12 denote identical or corresponding parts. In addition, a number of exhaust vents lb are provided at the bottom of the chamber

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  1 and a pipe 1c for introducing hydrogen gas to a lower part of the axis of rotation 8. In addition, a detachable cylindrical member 17 (made of quartz, for example) is attached to the bottom of the the reaction chamber 1 in order to surround the pieces lying

under the heater 5.

  The operation of the apparatus during crystal growth will be described. Since the crystal growth process is the same as that described in the conventional example, only one operation which is characteristic of

  this embodiment will be described.

  As shown in FIG. 1, the flow of gas during crystal growth does not pass around the parts on the heater 5 because the thermal shielding plate 12 surrounds the periphery of the heater, the axis of rotation 8 and the like. In addition, since hydrogen gas (H 2), as the carrier gas, is supplied by the pipe 1c disposed at the bottom of the reaction chamber 1, the gaseous materials are better prevented from passing around the parts and thus the reaction products can not attach to the parts under the heater 5. Consequently, this reduces the fluctuation of the thermal radiation caused by the attachment of the reaction products and this also reduces the fluctuation the growth temperature during crystal growth, from one test to another. Although the pipe 1c is provided to supply the bottom gas from the reaction chamber 1 to the axis of rotation 8 in the vertical direction in FIG. 1, as the axis of rotation 8 rotates at a rapid rate during the growth. crystalline, the carrier gas supplied flows to the lower surface of the susceptor 2 along the axis of rotation 8

while turning.

  Moreover, since the outside of the cylindrical member 17 is mainly contaminated, only the member 17 has left the reaction chamber 1 after the crystalline growth 2711274 to be cleaned at the time of the maintenance, which is very simple. Still further, since the carrier gas introduced by the pipe 1c represents about one-sixth of the gaseous material and the carrier gas is supplied from the upper part of the reaction chamber 1, the flow of materials to the gaseous state provided on the substrate 4 during the

  Crystalline growth is not bad influence.

  The second embodiment will now be described, with FIG. 2 being a sectional view illustrating an apparatus for MOCVD according to a second embodiment of the present invention. In Figure 2, a number of exhaust vents ld are provided on the side wall of the reaction chamber 1, near the susceptor 2, along the periphery of the reaction chamber 1. At least two air vents 1d exhaust are arranged face to face on the side wall of the reaction chamber 1 or a number of exhaust vents ld are preferably radially disposed from the center of the plate 3, the flow of materials in the gaseous state can be uniformly provided on the plate 3. In addition, as for the first embodiment described above, the pipe 1c is arranged to introduce the hydrogen gas from the lower side of the rotation axis 8, in this second embodiment of the present invention. In addition, although an aperture 10 between and between the plate 3 of the chip is also provided in this second embodiment, it is not shown in the sectional view of FIG. apparatus described above in

  moment of crystalline growth will now be described.

  Since the crystalline growth process is the same as in the conventional example, only the operation which is characteristic of the second embodiment of the invention will be described.

present invention.

  Raw materials in the gaseous state flow mainly from the center of the plate 3 for

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  pellets to the periphery and then flow to the exhaust vents which are arranged on the side wall of the reaction chamber 1, as shown in Figure 2, while the carrier gas is introduced through the pipe arranged lc Under the susceptor 2, therefore, gaseous materials are better prevented from passing under susceptor 2. As a result, the reaction products can not

  attach to the parts under the heater 5.

  As a result, the fluctuation of the thermal radiation due to the fixing of the products is reduced and the fluctuation of the growth temperature during crystal growth and from one test to another is also reduced. On the other hand, in this case, since the reaction products are barely attached to the parts in the reaction chamber 1, maintenance, such as cleaning the parts and the interior of the reaction chamber, is not necessary.

  or its cycle can be considerably increased.

  Figure 3 is a sectional view illustrating an apparatus for MOCVD according to a third embodiment of the invention. In FIG. 3, an exhaust space 24 is formed on the inner peripheral surface of the chamber of

  reaction 1, downward, from the susceptor.

  The operation of the apparatus during crystal growth will now be described. Since the process of crystal growth is the same as that described for the conventional example, only the operation will be described.

  which is characteristic of this embodiment.

  The gases supplied by the carrier gas supply pipe 20a and the gaseous material supply pipes 20b and 20c flow from the center of the plate 3 towards its periphery and then flow uniformly from the

  periphery of the plate 3 towards the exhaust space 24.

  Then, the gases escape from the reaction chamber 1. At this moment, since the carrier gas is introduced through the pipe 1 disposed under the susceptor 2, the gaseous substances

  are even better prevented from passing under the susceptor 2.

  As a result, reaction products can not focus on

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  Thus, as in the second embodiment of the present invention, a fluctuation of the thermal radiation caused by the attachment of the reaction products is reduced and the fluctuation of the growth temperature during crystalline growth and growth. one trial to another is also reduced. Moreover, the maintenance as the cleaning of the parts and the interior of the reaction chamber is useless or its cycle is considerably increased. Moreover, since the gas escapes uniformly around the periphery of the plate 3, this improves the regularity of the boundary layers in the substrate 4. As a result, it is possible to obtain

uniform crystals.

  Fig. 4 is a sectional view illustrating an apparatus for MOCVD according to a fourth embodiment of the present invention. In Fig. 4, an auxiliary pipe of gaseous material 19, for introducing gaseous material from its end to the outer side of the substrate (the side of the side wall of the reaction chamber) , is disposed above the plate 3 close to it. Although there is only one pipe 19 shown in Figure 4, there are actually a number of pipes 19 in the reaction chamber 1. In addition, the other end of the pipe 19 is connected. to a boiling apparatus 21. To the bubbling apparatus 21 is provided the carrier gas (H 2 in this case) whose flow rate is controlled by a mass flow controller 22. Thus, a predetermined amount of gaseous material is produced. The rest of the structure is the same as in the example

conventional.

  The operation of the apparatus during crystal growth will now be described. According to this embodiment of the present invention, since the gaseous substances are supplied from the upper part of the reaction chamber 1 by each of the pipes 20b and 20c and also through the auxiliary pipe 19, the material to the gaseous state is also provided at the outer side of the pellet

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  (or downstream) o The boundary layer irregularity may occur. As a result, the uniformity of the drawn layer can be easily improved. For example, when forming a GaAs-drawn layer, its uniformity is improved by providing an appropriate amount of TMG through the pipe

auxiliary 19.

  Fig. 5 is a sectional view illustrating an apparatus for MOCVD according to a fifth embodiment of the present invention. While in the fourth embodiment described above, the gaseous material is produced by the bubbling apparatus 21 and is supplied to the auxiliary pipe 19, in this fifth embodiment, the materials in the state. gaseous are provided by the supply pipes of the necessary materials in the gaseous state and also by the auxiliary pipe 19 connected to the material supply pipe in the gaseous state by using a bypass pipe 23 as shown in FIG. In this case, the branch pipe 23 is connected to the gas supply pipe 20c and the needle valve 11 is placed in the middle. The other parts are identical to the third embodiment of the

present invention.

  According to the above described structure, desired gaseous materials can be supplied only by changing the piping without additionally providing a mechanism for producing gaseous materials as in the fourth embodiment, which structure is

very simple.

  Fig. 6 is a sectional view illustrating an apparatus for MOCVD according to a sixth embodiment of the present invention. In Fig. 6, a heating electrode of the mesh 25 is connected to the second mesh 26. By applying a voltage to the electrode 25, the second mesh 26 is heated. Fig. 7 is a view showing a detailed structure of the second mesh 26. As shown in Fig. 7, the second mesh 26 is formed by a resistance wire 26a comprising tungsten or the like and a film

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  insulator 26b comprising quartz or the like. The electrode 25

  is connected to both ends of the resistance wire 26a.

  Thus, the second mesh 26 is heated by application

a voltage at the electrode 25.

  The operation of the apparatus will now be described during crystal growth. Although the process for crystal growth is the same as in the conventional example, such as the second mesh 26 disposed between the plate 3 for the pellet on which the substrate 4 GaAs is placed and the pipes 20b and 20c to introduce the materials to the gaseous state in the reaction chamber 1 can be heated, it can be easily cleaned by performing

  the next operation after crystal growth.

  Indeed, initially the substrate 4 GaAs is placed on the plate 3 or nothing is put there. Then, the plate 3 is placed on the susceptor 2 in the reaction chamber. Next, hydrogen gas (H2) serving as a carrier gas is introduced into the pipe 20a which is arranged at the upper part of the reaction chamber 1. in this chamber 1 and the pressure in the reaction chamber 1 is

  set to a desired value, for example 66.5 mbar.

  Alternatively, the reaction chamber 1 is evacuated without

  introduce the carrier gas into the chamber 1.

  Then, a predetermined voltage is applied to the electrode 25 connected to the second mesh 26 and the second mesh 26 is heated to a temperature of 300 ° C. or

  more, to which the reaction products are decomposed.

  Thus, the second mesh 26 is cleaned for a desired period of time. As a result, the reaction products attached to the second mesh 26 are decomposed by heat and removed from the second mesh 26 and the decomposed reaction products are discharged through the exhaust vent 1a, outwardly of the chamber. reaction 1. At this time, although some of the decomposed reaction products can disperse and attach to the susceptor,

  if the tray 3 is placed on the susceptor 2a described above

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  above, the reaction products can not attach to the susceptor 2. As a result, when the crystalline growth is carried out again after the cleaning, the heat of the

  susceptor 2 can be efficiently transferred to tray 3.

  After cooling the second mesh 26, the plate 3 is out of the reaction chamber 1 to be

  prepared for the next crystalline growth.

  As described above, according to this sixth embodiment of the present invention, as the second heatable mesh for dispersing ejected gaseous materials is disposed under hoses 20b and 20c for supplying materials to the In the gaseous state, only the second mesh 26 is rapidly and selectively heated at the time of maintenance and cleaning in the reaction chamber can be quickly accomplished. In addition, it improves the uniformity of thickness and concentration in

  carriers of the film shot on the substrate 4.

  Fig. 8 is a sectional view illustrating an apparatus for MOCVD according to a seventh embodiment of the present invention. Although the second mesh 26 is heated while the carrier gas flows into the reaction chamber 1 or into an atmosphere discharged at the time of cleaning in the sixth embodiment described above, the second mesh 26 is heated while hydrogen gas (H2), serving as a carrier gas, is introduced together with an etching gas such as HC1, in this seventh embodiment of the present invention, which can be seen in FIG. 8 The structure is the same as

  for the sixth embodiment.

  In this seventh embodiment, since the second mesh 26 is cleaned while the etching gas is supplied, the mesh 26 can be even more effectively cleaned in comparison with the sixth embodiment of the invention.

present invention.

  Although HC1 is used as the etching gas in this embodiment, the attachment of crystals other than

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  GaAs and InP can be well suppressed by changing the gas

  of attack according to the attached products.

  Fig. 9 is a perspective view illustrating a porous ceramic heater employed in a MOCVD apparatus according to an eighth embodiment of the present invention.

  invention. Whereas in the sixth embodiment

  described above, the second mesh 26 is formed of a thread of the tungsten resistance wire 26a and the quartz insulating film 26b and that the heating electrode of the mesh is connected to both ends of the resistance wire 26a, The electrode 25 can be connected to a porous ceramic heater 30 shown in FIG. 9. In short, another structure can be used if the temperature can be high, the corrosion resistance is excellent and the materials to be

  the gaseous state can be transmitted.

  Fig. 10 is a sectional view illustrating an apparatus for MOCVD according to a ninth embodiment of the present invention. In Fig. 10, a third mesh 27, having the same structure as the second mesh 24 is disposed under the second mesh 26, and the heating electrode 25 is connected thereto. The outlets of a pipe 20d for supplying material in the gaseous state are classified between

  second stitch 26 and the third stitch 27.

  The operation of this device for MOCVD will be described. First, the GaAs substrate 4 is placed in a groove of the plate 3 and the plate 3 is placed on the susceptor 2 in the reaction chamber 1. Then hydrogen gas (H2) serving as carrier gas is provided by the pipe 20a which is disposed at the upper part of the reaction chamber 1, in the reaction chamber 1, and the pressure in the reaction chamber 1 is set at a

  desired pressure, for example 66.5 mbar.

  Then, the susceptor 2 is rotated and the heater 5 is heated while arsine (ASH3) is introduced as the gaseous group V material, through the material supply pipe 20b. the gaseous state, in the reaction chamber 1 in order to prevent decomposition at

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  the heat of the substrate 4 in GaAs. Thus, the GaAs substrate 4 is heated to a desired temperature, for example 700 C, by raising the temperature of the susceptor 2. At the same time, a voltage is applied to the electrode 25 connected to the second mesh 26 which is arranged under the pipe 20b for

  heat the second mesh 26 at around 100 to 300 C.

  Thus, AsH3 which passes through the second mesh 26 has already been heated and this accelerates the decomposition on the substrate 4 in GaAs, and therefore the As concentration on the GaAs substrate increases and the rate of material actually increases.

used increases.

  Then, a gaseous group III material such as TMG is introduced through the gas supply pipe 20d for crystal growth. AsH3 gas and TMG gas are uniformly dispersed by the second mesh 26 which is disposed under the pipe 20b to provide gas AsH3 and the third mesh 27 disposed under the pipe d to supply TMG gas, respectively, in order to reach the substrate 4 in GaAs . Thus, the uniformity of the thickness of the composition and the carrier concentration of the GaAs film shot on the GaAs substrate 4 is improved. In addition, since the gaseous TMG is provided by the pipe 20d whose outlets are placed under the second mesh 26, it can not happen that TMG gas decomposes before reaching the substrate 4 in GaAs and attaches to the third mesh 27 by

a reaction with AsH3.

  Then, the supply of gaseous TMG is stopped and the substrate 4 in GaAs is cooled by suppressing the heating of the heater 5 while supplying AsH3 gas. Then, the heating of the second mesh and the supply of AsH3 gas are stopped then the rotation of the susceptor 2 is stopped. Then, the plate 3 is out of the reaction chamber 1 and the substrate 4 is removed in GaAs on which one

been drawn from the crystals.

  In addition, in the case where the mesh 27 is plugged by the reaction products after a predetermined number of growth, as in the case of the sixth embodiment

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  of the present invention, a voltage is applied to the mesh heating electrode 25 which is connected to the third mesh 27 to clean the mesh. In addition, if necessary, the electrode 25 connected to the second mesh 26 may be heated by the application of a voltage. Thus, according to this ninth embodiment of the present invention, the second heatable mesh 26 is disposed under the pipe 20b to provide an AsH3 gas close thereto, the outlets of the pipe 20d to provide TMG gas are placed under the second mesh 26 and the third mesh 27 is disposed under the outlets of the pipe b. In addition, during crystal growth, the second mesh 26 is heated and AsH3 having a higher decomposition temperature than that of TMG and a lower decomposition efficiency than that of TMG is heated before being supplied to the substrate 4. In Accordingly, this accelerates the decomposition of AsH3 on the substrate 4. As a result, the concentration of the group V gas on the substrate 4 can be increased and the gaseous material content effectively used for the crystal growth is

also increased.

  On the other hand, the outlets of the pipe 20d supplying the material in the gaseous state to provide TMG in the decomposition temperature is lower than that of AsH3 are placed under the second mesh 26 and the third mesh 27 is disposed under the pipe outlets 20d, so it can not happen that TMG gas is decomposed and GaH3 gaseous previously heated by the second mesh 26 and react and

  attaches on the third mesh 27.

  An apparatus for MOCVD according to a tenth embodiment of the present invention will be described. Although the second mesh 26 is heated between 100 and 300 C during the crystal growth, to preheat AsH3 whose decomposition temperature is higher in the ninth embodiment of the present invention, the second mesh 26 can be heated to a high temperature of 700 C or more to decompose AsH3. In this case, even

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  if there is decomposition of ASH3, as the temperature of the second mesh 26 is sufficiently larger than the decomposition temperature of ASH3, the reaction products can not attach to the second mesh 26. Thus, this further improves the effective use of AsH3. On the other hand, by also heating the third mesh 27 to a temperature much higher than the decomposition temperature of the gaseous material, such as AsH 3 or TMG, this also improves the efficiency of use of the material at the same time. gaseous state that is provided by the pipe 20d to provide gaseous material such as TMG. In this case, however, the decomposed gaseous materials in the vicinity of the third mesh 27 could react with each other and their reaction products could attach to the side wall of the

reaction chamber 1.

  In addition, although GaAs crystals are drawn using AsH3 as the Group V gaseous material and TMG as the Group III gaseous material according to each of the above embodiments, the same effect as in the embodiments described above to be expected with respect to the crystal growth of another material such as AlGaAs, InP, InGaAsP, or AlGaInP. In addition, with respect to crystal growth other than crystal growth of III-V materials, the same effect can be expected by using two or more kinds of gaseous state materials with different temperatures.

different from decomposition.

  Furthermore, although the exhaust vent lb is arranged to allow the escape of gaseous materials from the bottom of the reaction chamber 1, in the vertical direction, according to the first embodiment of the invention. In the present invention, the exhaust vent may be arranged to allow the gaseous materials to escape to the bottom of the reaction chamber 1 in the horizontal direction.

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  As described above, according to the CVD apparatus of the present invention, since the parts arranged under the heater are covered with the cylindrical member, the reaction products can not attach to the parts surrounded by the cylinder. organ. As a result, it stabilizes the growth temperature and this facilitates the maintenance of the

reaction chamber.

  In addition, according to the CVD apparatus of the present invention, since gaseous materials escape around the susceptor, gaseous materials can not pass under the susceptor. Thus, the reaction products can not attach to the parts under the susceptor and therefore the growth temperature is stabilized and the maintenance of the

reaction chamber is facilitated.

  Still further, by supplying the carrier gas from the bottom of the reaction chamber to the rear surface of the susceptor, the gaseous materials are even better.

  prevented from passing under the susceptor.

  In addition, according to a CVD apparatus of the present invention, since the gaseous material is provided in an auxiliary manner to the downstream portion of the gaseous material flow, in the pellet disposed on the susceptor, the regularity of the boundary layers of the pellet is improved and a layer of high uniformity of film thickness, carrier concentration can be obtained

and the like.

  On the other hand, according to the CVD apparatus of the present invention, as the heatable mesh is disposed between the outlets of the pipes for introducing gaseous materials into the reaction chamber and the tray or susceptor where the substrate is placed. , the mesh can easily be cleaned and gaseous materials are always uniformly provided on the substrate, allowing

  to improve the uniformity of crystal growth.

  Additionally, according to the CVD apparatus of the present invention, the pipe for the introduction of gaseous material whose decomposition temperature

22 2711274

  is relatively high is disposed above the pipe for the introduction of the material in the gaseous state whose decomposition temperature is relatively low, the heatable mesh is provided under each zone and the gaseous state material whose temperature of decomposition is relatively high has already been heated or decomposed and

  supplied to the pellet. As a result, this improves the efficient use of the gaseous material at a high decomposition temperature.

23 2711274

Claims (13)

  1. Apparatus for chemical vapor deposition for crystal growth on a pellet disposed in a reaction chamber where gaseous materials are provided from an upper portion of the reaction chamber while the materials are gaseous state escape from the bottom of the reaction chamber, characterized in that it comprises: a susceptor (2) on which is placed the pellet (4); a heater (5) disposed under the susceptor (2) for heating it; and a detachable cylindrical member (17) disposed at the bottom of the reaction chamber (1) to cover parts under the susceptor (2) and to prevent gaseous materials   to flow around the rooms under the susceptor (2).   2. Apparatus for chemical vapor deposition for crystal growth on a pellet disposed in a reaction chamber while gaseous materials are provided from an upper portion of the reaction chamber, characterized in that it comprises: a susceptor (2) on which is placed the pellet (4); a heater (5) disposed under the susceptor (2) for heating it; and an exhaust vent (1d) disposed in a side wall of the reaction chamber (1) near the susceptor (2).   3. Apparatus according to claim 2, characterized in that it further comprises a number of exhaust pipes which are connected to said exhaust vent (ld), each pipe having a mechanism (18) for adjusting the pressure to adjust the exhaust pressure of the material in the gaseous state. 24 2711274   4. Apparatus according to claim 2, characterized in that the exhaust vent (ld) is formed between an inner side wall of the reaction chamber (1) and a partition wall formed over its entire inner periphery, at a predetermined interval; and in that gaseous materials escape out of the reaction chamber (1) by a gap (24) between the inner side wall and the separating wall of the reaction chamber (1). the reaction chamber.   5. Apparatus according to one of claims 1 or 2,   characterized in that it further comprises a carrier gas introduction pipe (1c) for introducing a carrier gas from the bottom of the reaction chamber (1) to a rear surface of the susceptor (2) to prevent gaseous materials from flowing to rooms under the susceptor (2).   6. Apparatus for chemical vapor deposition having a susceptor on which is placed a pellet, in a reaction chamber in which gaseous raw materials are supplied from an upper part of the reaction chamber and they flow from the center of the susceptor towards its periphery on the susceptor, characterized in that it comprises: a pipe (19) for supplying auxiliary material in the gaseous state to supply the material to the gaseous state in an auxiliary manner to a part downstream of the flow of gaseous materials, in a pellet (4) placed on the susceptor (2).   Apparatus according to claim 6, characterized in that it further comprises: a number of gaseous material supply pipes (20a, 20b, 20c) for supplying gaseous materials in two kinds of gaseous materials; and said auxiliary gaseous material supply pipe (19) diverging from the material supply pipe 2711274   in the gaseous state to provide the same kind of material to   the gaseous state provided by the auxiliary pipe (19).   8. Apparatus for chemical vapor deposition for crystal growth on a pellet disposed in a reaction chamber where gaseous materials are provided from an upper part of the reaction chamber, characterized in that it comprises: hoses (20a, 20b, 20c) for supplying gaseous materials for supplying gaseous materials in the reaction chamber (1).   a mesh (26) disposed under the outlets of the pipes   (20a, 20b, 20c) to uniformly disperse the supplied gas.   means (25) for heating the mesh to heat said mesh and remove attached reaction products   to the mesh (26) when cleaning the appliance.   9. Apparatus according to claim 8 characterized in that a feed gas for decomposing the reaction products is introduced at the same time as the carrier gas by the supply pipe material in the gaseous state while the mesh is heated.   10. Apparatus according to claim 8, characterized in that the aforementioned mesh is a porous ceramic heater (30) and said mesh is heated by application of a   voltage heater ceramic heater (30).   11. Apparatus for chemical vapor deposition for crystal growth on a pellet, disposed in a reaction chamber where gaseous materials are provided from an upper part of the reaction chamber, characterized in that it comprises: a first pipe (20b) for supplying material in the gaseous state, for supplying a first material in the gaseous state and having an outlet; a second pipe (20d) for supplying gaseous material to provide a second gaseous material having a lower decomposition temperature than that of the first gaseous material, said second pipe ( 20d) having an outlet disposed closer to the 26 2711274   pellet (4) that the outlet of the first pipe (20b) for supplying a material in the gaseous state; a first mesh (12) disposed under the first gaseous material supply pipe (20b) for uniformly spreading the first gaseous material provided by the pipe.   a second mesh (26) disposed under the second pipe (20d) for uniformly dispersing the second gaseous material provided by the pipe; and heating means (25) for heating the first and second meshes; the first gaseous material has been previously heated by heating the first mesh (12) during the crystal growth.   12. Apparatus for chemical vapor deposition for crystal growth on a pellet disposed in a reaction chamber o gaseous materials are provided from an upper portion of the reaction chamber, characterized in that comprises: a first gas supply pipe (20b) for supplying a first gaseous material and having an outlet; a second pipe (20d) for supplying gaseous material to provide a second gaseous material whose decomposition temperature is lower than that of the first gaseous material, said second pipe (20d) having an outlet disposed closer to the pellet (4) than the outlet of the first gas supply pipe (20b); a first mesh (12) disposed under the first pipe (20b) to uniformly disperse the first material to   the gaseous state provided by the pipes.   a second mesh (26) disposed under the second pipe (20d) for uniformly dispersing the second gaseous material provided by the pipe; and a heating mechanism (25) for heating the first and second meshes (12, 26); 2711274   the first gas-state material is decomposed by heating the first mesh (12) to a temperature greater than the decomposition temperature of the first gaseous material to be provided on the tablet (4) during crystalline growth . 13. Apparatus according to claim 11 or 12 characterized in that the reaction products attached to the second mesh (26) are removed by heating the second   mesh (26) when the appliance is cleaned.