Vapor-phase deposition apparatus

Abstract: A vapor-phase deposition apparatus comprises substrate-supporting unit (4, 10, 11) for supporting a substrate (3), heater (6) for heating substrate-supporting unit (4, 10, 11), and gas-supplying unit (9) for supplying gas for forming a thin film on the substrate (3) supported by the substrate-supporting unit (4, 10, 11). The substrate-supporting unit (4, 10, 11) includes a first member (4) to be heated to a predetermined temperature by the heater (6), a second member (10) for supporting a peripheral part of the substrate (3), and a support member (11) for supporting the second member (10) on the first member (4) and located outside a periphery of the substrate (3).

Description: The present invention relates to a vapor-phase deposition apparatus designed for use in manufacture of semiconductor devices or the like. Various vapor-phase deposition apparatuses are known which performs vapor-phase deposition to form semiconductor films or the like on a crystal substrate, thereby to manufacture semiconductor devices or the like. A typical vapor-phase deposition apparatus comprises a base plate, a reaction vessel secured to the base plate in airtight fashion, a shaft passing through the base plate into the vessel, a substrate holder located within the vessel and rotatably supported by the shaft, for holding a crystal substrate, and a heater located within the vessel, for heating the holder and a crystal substrate held by the holder. The reaction vessel has a gas-inlet port in the top, and a gas-outlet port in the bottom. Gases (e.g., feed gas, carrier gas, etc.) are supplied into the vessel through the gas-inlet port. Any gas that is left unreacted in the vessel is discharged through the gas-outlet port. In operation, the heater heats the crystal substrate, which is held by the holder, to a predetermined temperature. Then, feed gas (SiH 4 , SiH 2 Cℓ 2 , SiHCℓ 3 , SiCℓ 4 , Si 2 H 6 , or the like) are supplied into the reaction vessel through the gas-inlet port, along with carrier gas (H 2 or the like). In most cases, a device having a lamp, a highfrequency wave generator, or a electric resistor is utilized as heater to heat the substrate held by the holder to the predetermined temperature. Whatever heating device is used, it is necessary to heat the substrate uniformly. To this end, use can be made of a substrate holder having a recess in which to hold a crystal substrate, as is disclosed in Published Unexamined Japanese Patent Application No. 61-215289 and No. 62-4315. Even if heated while held by this holder, a substrate is heated more at its peripheral part than at the center part since the peripheral part contacts the holder. Consequently, it is very difficult to form a crystal film having a uniform thickness, on the substrate. Recently, it is increasingly demanded that a substrate be used in its entirety. In other words, it is desired that the peripheral part of a substrate should not be cut and discarded, in order to save material. Hence, there is a great demand for a technique of forming a crystal film having a uniform thickness on the substrate, and the difference in temperature between the peripheral part and center part of the substrate can no longer be ignored. Moreover, once the substrate warps due to the difference in temperature between the upper and lower surfaces of the substrate, the gap between the substrate and the surface of the holder changes. This changes the temperature distribution of the substrate. The change in the surface temperature distribution results in stress. The stress is great, in particularly when the substrate is made of single-crystal silicon. It causes transition of the single-crystal silicon, which is known as "slip." The slip deteriorates the characteristics of the semiconductor devices formed on the silicon substrate. The slip is a phenomenon that crystal molecules glide along crystal lattices and are deformed when the stress, caused by the non-uniform distribution of surface temperature of the substrate heated to a high temperature, increases above the yield point of the crystal substrate. As is known in the art, the higher the temperature of the crystal substrate, the lower the yield point of the substrate, and the higher the probability of slip. Also, the substrate must be cooled to a low temperature some time before it is placed on and removed from the holder. It would otherwise difficult to place the substrate on the holder, and to remove it from the holder. As has been pointed out, in the conventional vapor-phase deposition apparatus, the peripheral part of a substrate, which contacts the holder, is more heated than the center part which does not contact the holder. The non-uniform temperature distribution of the substrate inevitably makes it difficult to form a crystal film having a uniform thickness, on the substrate. Further, once the substrate warps due to the difference in temperature between the upper and lower surfaces of the substrate, the gap between the substrate and the surface of the holder changes, inevitably changing the surface temperature distribution of the substrate. The change of the surface temperature distribution results in two problems. First, it is impossible to form a crystal film having a uniform physical property such as carrier concentration. Second, the substrate has stress, which causes transition of the single-crystal silicon, such as slip, ultimately deteriorating the characteristics of the semiconductor devices formed on the silicon substrate. Moreover, the substrate must be cooled to a lower temperature some time before it is placed on and removed from the holder, in order to facilitate the placing and removal of the substrate. Needless to say, the cooling of the substrate is a bar to enhancement of throughput of the vapor-phase deposition apparatus. US-A-4535227 discloses a method for heating a semiconductor wafer by application of radiated light in which, when heating a semiconductor wafer by means of application of radiated light, a subsidiary heating device which is arranged in contact with the surface of a circumferential edge or a surface portion lying in the vicinity of the circumferential edge of the semiconductor wafer is employed to additionally heat or to preheat the circumferential portion of the wafer so as to make the temperature of the wafer uniform across the entire surface thereof. JP-A-58-7818 discloses a vapor-phase deposition apparatus having substrate supporting means for supporting a substrate and heating means for heating the substrate supporting means. The substrate supporting means includes a ring-shaped spacer supporting the periphery of the substrate. JP-A-5391076 discloses a vapor-deposition apparatus having substrate supporting means with substrate heating means. An object of the present invention is to provide a vapor-phase deposition apparatus which can impart a uniform surface-temperature distribution to a crystal substrate, causing no transition such as slip in the substrate and, thus, making it possible to form semiconductor devices on the substrate which have good characteristics. According to a first aspect of the invention, there is provided a vapor-phase deposition apparatus comprising: substrate-supporting means for supporting a substrate; heating means for heating the substrate-supporting means; and gas-supplying means for supplying gas for forming a thin film on the substrate supported by the substrate-supporting means, characterized in that said substrate-supporting means comprises: a disk-shaped first member having a diameter larger than that of said substrate and heated to a predetermined temperature by said heating means; a second member having an inner edge portion for supporting a peripheral part of the substrate and an outer edge portion located outside of said substrate; and a support member, located outside of the peripheral part of said substrate, for supporting said second member on said first member and for suppressing the heat conducting from the first member to the second member so that the substrate is uniformly heated by the radiation heat or the heat conducted by the gas. According to a second aspect of the invention, there is provided a vapor-phase deposition apparatus comprising: substrate-supporting means, including a body portion and a support portion mounted on said body portion, for supporting a peripheral part of a substrate having a first surface to be processed and a second surface opposite to the first surface; gas-supplying means for supplying gas to form a thin film on the first surface of the substrate supported by said substrate-supporting means; heating means, located at the side of the body portion remote from the substrate, for heating said substrate-supporting means and said substrate, said heating means causing a temperature distribution of the substrate in thickness direction thereof; and temperature-compensating means for compensating for a temperature fall at a support part of the substrate, which occurs when the substrate is heated by said substrate-heating means, characterized in that said temperature-compensating means comprises; a projection having a size determined such that the distance between said body portion and said support portion of said substrate-supporting means is shorter, at the position corresponding to the projection, than the distance between said body portion and the substrate, the projection extending from at least one of the body portion and the support portion at the position which corresponds to the peripheral part of the substrate. According to a third aspect of this invention, there is provided a vapor-phase deposition apparatus comprising: substrate-supporting means including a body portion and a support portion mounted on said body portion, for supporting a peripheral part of a substrate having a first surface to be processed and a second surface opposite to the first surface; gas-supplying means for supplying gas to form a thin film on the first surface of the substrate supported by said substrate-supporting means; heating means located at the side of the body portion remote from the substrate, for heating said substrate-supporting means and said substrate, said heating means causing a temperature distribution of the substrate in a thickness direction thereof; and temperature-compensating means for compensating for a temperature fall at a support part of the substrate, which occurs when the substrate is heated by said substrate-heating means, characterized in that said heating means comprises a first heater for heating the substrate and a second heater for heating the support portion supporting a part of the substrate, and in that said temperature-compensating means comprises temperature detectors for detecting the temperature of the central portion of the substrate and the temperature of the peripheral part thereof which is supported by said support portion, and temperature-controlling means for controlling the first and second heaters independently by output signals from the temperature detectors. The most prominent problem with a typical vapor-phase deposition apparatus is the slip occurring in the substrate, due to thermal stress resulting from the non-uniform distribution of surface temperature of the substrate. The inventors hereof repeated experiments and analyzed the results of the experiments, in order to ascertain the relation between the heat-transmission in and heat-radiation from substrates, one the one hand, and the stress developed in the substrates, one the other hand. Finally did they find that the stress due to the temperature difference between the upper and lower surfaces of a substrate was not immediate cause of the slip in the substrate. Rather, as they found, the temperature distribution in the radial direction of the substrate was not uniform because the substrate warped due to the temperature difference, and this non-uniform surface-temperature distribution was the very cause of the slip. Therefore, to prevent slip from occurring in a substrate, the temperature difference between the surfaces of the substrate is not necessarily reduced by heating both surfaces of the substrate by applying lamp heating thereto, though it has hitherto been thought necessary to reduce said temperature difference. To prevent slip, it is suffices to make the surface-temperature distribution uniform. Hence, the inventors hereof invented various methods of rendering the surface-temperature distribution uniform, no matter whether the surface-temperature distribution is not uniform due to the warping of the substrate, the heat transmission by a member supporting the substrate, or any other cause. This invention can be more fully understood from the following detailed description when taken in conjunction with the accompanying drawings, in which: Fig. 1 is a cross-sectional view illustrating a vapor-phase deposition apparatus according to the invention; Fig. 2 is an enlarged, cross-sectional view showing the substrate-supporting unit of the apparatus shown in Fig. 1 and a substrate supported by the unit; Fig. 3 is a graph representing the relation between the temperature T of the substrate and the distance d between the holder and the substrate; Fig. 4 is an enlarged, cross-sectional view of a first modification of the substrate-supporting unit shown in Fig. 2; Fig. 5 is an enlarged, cross-sectional view of a second modification of the substrate-supporting unit; Fig. 6 is a vertical sectional view illustrating a vapor-phase deposition apparatus according to the present invention; Fig. 7 is an enlarged, cross-sectional view of a third modification of the substrate-supporting unit; Figs. 8 and 9 are, respectively, an enlarged, cross-sectional view and a plan view of a fourth modification of the substrate-supporting unit shown in Fig. 2; Fig. 10 is an enlarged, cross-sectional view of the substrate-supporting unit employed in the invention; Fig. 11 is an enlarged, cross-sectional view of a first modification of the substrate-supporting unit illustrated in Fig. 10; Fig. 12 is an enlarged, cross-sectional view of a second modification of the substrate-supporting unit shown in Fig. 10; Fig. 13 is an enlarged, cross-sectional view of a third modification of the substrate-supporting unit shown in Fig. 10; Fig. 14 is an enlarged, cross-sectional view of a modification of the substrate-supporting unit shown in Fig. 7; Fig. 15 is an enlarged, cross-sectional view of a modification of the substrate-supporting unit illustrated in Fig. 11; Fig. 16 is an enlarged, cross-sectional view of a modification of the substrate-supporting unit shown in Fig. 14; Fig. 17 is an enlarged, cross-sectional view of a modification of the substrate-supporting unit shown in Fig. 15; Fig. 18 is an enlarged, cross-sectional view of a first modification of the substrate-supporting unit illustrated in Fig. 2; Fig. 19 is an enlarged, cross-sectional view of a second modification of the substrate-supporting unit shown in Fig. 2; Fig. 20 is a graph representing the relation between the total-slip length L of a substrate and the temperature difference ΔT between the substrate and a portion of the supporting member, said relation being one observed in the modifications illustrated in Figs. 18 and 19; Fig. 21 is a circuit diagram showing a device for independently controlling the temperature of the center part of a substrate and that of the peripheral part thereof; Fig. 22 is a graph showing the relation between the total-slip length L of a substrate and H2/H1, observed in the modifications illustrated in Figs. 18 and 19, where H1 is the distance between the substrate holder and the substrate-supporting member, and H2 is the distance between the substrate and the substrate holder; Fig. 23 is an enlarged, cross-sectional view showing another type of a substrate-supporting unit according to the present invention; Fig. 24 is an enlarged, cross-sectional view showing still another type of a substrate-supporting unit according to the present invention; Fig. 25 is a plan view showing another substrate-supporting unit according to the present invention; Fig. 26 is an enlarged, cross-sectional view illustrating another substrate-supporting unit used in the invention; Figs. 27A, 27B and 28 are enlarged, cross-sectional views showing the modifications of the substrate holders illustrated in Fig. 26. Fig. 29 is a cross-sectional view schematically showing a modified reaction vessel; Fig. 30 is a sectional view illustrating another type of vapor-phase deposition apparatus, according to the present invention; Fig. 31 is a sectional view showing another modified substrate-supporting unit; and Figs. 32 and 33 are schematic views of a vapor-phase deposition apparatus according to the invention, explaining how to transfer a substrate into, and out of, the reaction vessel of the apparatus. Embodiments of the invention will now be described with reference to the accompanying drawings. Fig. 1 illustrates a vapor-phase deposition apparatus according to the invention. As is shown in this figure, the apparatus comprises a base plate 1, a reaction vessel 2 secured to the base plate 1 in airtight fashion, a disc-shaped substrate holder 4 located within the vessel 2, for supporting a crystal substrate 3, a vertical shaft 5 passing through the base plate 1 into the vessel 2, a heater 6 provided in the vessel 2, for heating both the substrate 3 and the holder 4, a drive unit 8 located below the base plate 1, and a gas-supplying unit 9 located outside the vessel 1. The upper end of the shaft 5 is detachably connected to the substrate holder 4, and the lower end of the shaft 5 is connected to the drive unit 8. As Fig. 1 shows, the reaction vessel 2 has a gas-inlet port 2a, and the base plate 1 has a gas-outlet port 2b. The gas-supplying unit 9 is coupled to the gas-inlet port 2a, for supplying a feed gas and a carrier gas into the reaction vessel 2 through the gas-inlet port 2a. The gases left unreacted in the vessel 2 is discharged from the vessel 2 through the gas-outlet port 2b. The heater 6, which is placed right below the substrate holder 4, heats the holder 4. The holder 4, thus heated, heats the substrate 3 to a predetermined temperature. The feed gas is applied to the heated substrate 3 supplied through the port 2a, together with the carrier gas supplied also through the port 2a. As a result of this, vapor-phase deposition takes place on the upper surface of the substrate 3, forming a thin semiconductor film thereon. Fig. 2 is an enlarged, cross-sectional view showing the substrate 3 and the substrate holder 4, both illustrated in Fig. 1. As is evident from Fig. 2, three support posts 11 protrude upward from the peripheral edge of the holder 4, and a substrate-supporting member 10 is supported by the posts 11, with its peripheral edge contacting the support posts 11. The three posts 11 can be replaced by one support post, two sup port posts, or four or more support posts. Alternatively, it can be replaced by a ring-shaped wall fixed to the peripheral edge of the holder 4. The substrate-supporting member 10 has a center hole 10a having a diameter slightly less than that of the crystal substrate 3. The hole 10a is defined by a stepped portion of the substrate-supporting member 10. Only the peripheral part of the substrate 4 contacts this stepped portion, whereby the substrate 3 is supported the member 10, and the member 10 is connected to the holder 4 by the thin support posts 11 only. The member 10 and the posts 11 constitute long heat paths each having a small cross-sectional area. Hence, the heat which is transmitted from the holder 4 to the peripheral part of the substrate 3 through these heat paths is negligible, far less than the heat radiated from the holder 4 to the substrate 3 and than the heat conducted from the holder 4 to the substrate 3 via the gas (i.e., the carrier gas H 2 ) existing in the gap between the substrate 3 and the holder 4. Let us assume that the amount of heat radiated from the substrate 3 is equal to the amount of heat applied from the holder 4 to the substrate, by virtue of the law of conservation of heat. Then, the temperature T of the substrate 3 and the distance D between the substrate 3 and the holder 4 have the relationship shown in the graph of Fig. 3, provided the temperature of the holder 4 is maintained at a fixed value by means of the heater 6. As can be understood from Fig. 3, the temperature of the substrate 3 greatly changes with the distance D, as long as the distance D is equal to or less than 1 mm. When the distance D is greater than 1 mm, however, the temperature of the substrate 3 changes with the distance D, but not so much. It follows that the temperature of the substrate 3 will remain fairly uniform even if the substrate warps due to the temperature difference between the upper and lower surfaces of the substrate 3, provided that the distance D is set at more than 1 mm. Hence, in the apparatus shown in Fig. 2, the substrate 3 is spaced apart from the holder 4 by a distance of 5 mm, and the substrate-supporting member 10 is spaced apart from the holder 4 by a distance of 4 mm. The substrate holder 4 is uniformly heated by the heater 6, and the substrate 3 is uniformly heated by virtue of the heat radiated from the holder 4 and the heat conducted therefrom through the carrier gas existing in the gap between the substrate 3 and the holder 4. While the substrate 3 is heated, the drive unit 8 rotates the vertical shaft 5 at the speed of, for example, 10 rpm, thereby rotating the holder 4 and hence the substrate 3. The substrate-supporting member 10 is heated, also by virtue of the heat radiated from the holder 4 and the heat conducted therefrom through the carrier gas existing in the gap between the substrate 3 and the holder 4. Scarcely is it heated by the heat conduction from the holder 4 through the support posts 11. Hence, the member 10 is heated to substantially the same temperature as the crystal substrate 3, and the peripheral part of the substrate 3, which contacts the member 10, is heated neither more or less than any other part. In the apparatus shown in Fig. 2, the holder 4, the member 10, and support posts 11 are separate components and assembled together, constituting a substrate-supporting unit. Instead, these components can be formed integrally as is illustrated in Fig. 4, thus forming a substrate-supporting unit. The unit has a disc-shaped hollow 20 which has a diameter greater than that of the crystal substrate 3. Due to this, the heat path extending from the holder 4 to the substrate 3, formed of an annular portion 10 and a ring-shaped wall 11, is so long that only a negligibly small amount of heat is conducted from the holder 4 to the peripheral part of the substrate 3. Hence, the peripheral part of the substrate 3 is heated to substantially the same temperature as any other part. Fig. 5 illustrates a substrate-supporting unit, which is a second modification of the unit shown in Fig. 2. As is evident from Fig. 5, this modification is characterized in that the substrate-supporting member 10 has a thin portion 10a. Because of the thin portion 10a, each of the heat paths has a reduced cross-sectional area and, hence, conducts less heat from the holder 4 to the substrate 3, than does each heat path of the substrate-supporting unit illustrated in Fig. 2. Fig. 6 is a vertical sectional view illustrating a vapor-phase deposition apparatus according to the invention. This apparatus is characterized in two respects. First, a heater coil 7, which is wound around the vessel 2, is used in place of a heater located within the vessel 2. Second, the substrate-supporting member 10 and the ring-shaped wall 11 are made of material, such as glass or ceramics, which is hardly be heated by the coil unlike the material of the holder 4 which is used as susceptor. The peripheral part of the substrate 3, contacting the member 10, is therefore heated neither more or less than any other part. As a result, heat is distributed uniformly in the substrate 3. In the substrate-supporting units shown in Figs. 4, 5, and 6, the ring-shaped wall 11 can be replaced by, for example, three support posts. In this case, the annular portion or the substrate-supporting member 10 can be replaced by three components shaped like Japanese fans, secured to the three posts, respectively, and arranged in a circle. Fig. 7 illustrates a third modification of the substrate-supporting unit shown in Fig. 2. As is evident from Fig. 7, the substrate-supporting unit is characterized in two respects. First, the holder 4 and the ring-shaped wall 11 are integrally formed. Second, the substrate-supporting member 10 is made of material having a low thermal conductivity, such as glass or ceramics. Since the member 10 is made of such material, only a negligibly small amount of heat is conducted from the holder 4 to the peripheral part of the substrate 3 through the wall 11 and the member 10. Therefore, the heat distribution in the substrate 3 is substantially uniform. The ring-shaped wall 11 can, of course, be made of the same material as the member 10. Figs. 8 and 9 show a fourth modification of the substrate-supporting unit illustrated in Fig. 2, the former being an enlarged, cross-sectional view, and the latter being a plan view. This modification is identical to the unit shown in Fig. 2, except that three pointed protrusions 10c are formed on the stepped portion at the edge of the hole 10a of the member 10. Hence, the substrate 3 is set in three-point contact with the substrate-supporting member 10. This reduces the cross-sectional area of the heat path extending from the holder 4 to the peripheral part of the substrate 3. Therefore, the heat distribution in the substrate 3 is more uniform than in the case where the substrate 3 is supported by the unit of Fig. 2. Needless to say, the pointed protrusions 10c can be replaced by a thin annular wall 10c, in which case the substrate 3 is placed in line-contact with the substrate-supporting member 10. Fig. 10 is an enlarged, cross-sectional view of the substrate-supporting unit employed in the invention. As is shown in Fig. 10, the unit is made by forming a disc-shaped hollow 20 in a disc-shaped block 4. The unit has a center hole made in the top wall and having a diameter smaller than that of a crystal substrate 3. A stepped portion is formed at the edge of the center hole. The substrate is placed on the annular top portion, i.e., the substrate-supporting portion 4a, with its peripheral part resting on the stepped portion. Fig. 11 illustrates a first modification of the substrate-supporting unit illustrated in Fig. 10. This modified unit comprises a disc-shaped block having a circular recess 20 and an annular substrate-supporting member 10 secured to the top of the block, with its upper surface in the same plane as the top of the block. The substrate-supporting member 10 is made of material having a low thermal conductivity, such as glass or ceramics. The member 10 has an inside diameter which is smaller than that of a substrate 3, and has a stepped portion at its inner edge. The substrate 3 is supported by the member 10, with its peripheral part resting upon the stepped portion of the member 10. Fig. 12 shows a second modification of the substrate-supporting unit shown in Fig. 10. This unit different from the unit of Fig. 10, only in that the substrate-supporting portion 4a has a thin portion 4b. Because of the thin portion 4b, the heat path extending from the bottom portion to the peripheral part of the substrate 3 has a reduced cross-sectional area and, hence, conducts less heat than does the heat path of the substrate-supporting unit illustrated in Fig. 10. Fig. 13 is an enlarged, cross-sectional view of a third modification of the substrate-supporting unit shown in Fig. 10. This modification is identical to the unit of Fig. 10, except that an annular thin wall or a plurality of pointed protrusion 4c are integrally formed on the stepped portion. Hence, the substrate 3 is set in line-contact or point-contact with the substrate-supporting member 10. This reduces the cross-sectional area of the heat path extending from the bottom portion to the peripheral part of the substrate 3. Therefore, the heat distribution in the substrate 3 is more uniform than in the case where the substrate 3 is supported by the unit illustrated in Fig. 10. Fig. 14 shows a modification of the substrate-supporting units of Fig. 7, and Fig. 15 illustrates a modification of the substrate-supporting unit shown in Figs. 10 and 11. As can be understood from Figs. 14 and 15, these substrate-supporting units are identical to the units of Figs. 7 and 11, except that the substrate-supporting member 10 is made of a specific material as will be described later in detail. Both units of Figs. 14 and 15 have a disc-shaped hollow 20 which has a diameter greater than that of the crystal substrate 3. Due to this, the heat path extending from the bottom portion of the block 4 to the peripheral part of the substrate 3, formed of an annular wall 11 and the substrate-supporting member 10, is so long that only a negligibly small amount of heat is conducted from the holder 4 to the peripheral part of the substrate 3. Hence, the peripheral part of the substrate 3 is heated to substantially the same temperature as any other part. The heat conducted to the substrate 3 through the heat path is negligibly small, the substrate 3 is heated, virtually by only the heat radiated from the holder 4 and the heat conducted therefrom through the carrier gas existing in the gap between the substrate 3 and the holder 4. Means, other than the long heat path, is used in the modified units of Figs. 14 and 15 in order to reduce, even more, the temperature difference between the center and peripheral parts of the substrate 3. More specifically, the substrate-supporting member 10 is made of material having emissivity which is substantially equal to that of the substrate 3, or has surface roughness which is substantially equal to that of the substrate 3. As is known in the art, the emissivity of a member is inversely proportional to the surface roughness of the member. In other words, the less the surface roughness, the higher the emissivity; the greater the surface roughness, the lower the emissivity. To be more specific, if the substrate is made of silicon, the member 10 is made of the material having emissivity substantially equal to that of silicon, or has a surface roughness substantially equal to that of the substrate 3. As a result of this, the substrate 3 and the member 10 are heated to substantially the same temperature as the block 4 is heated by a heater 6 (not shown). There is but an extremely small temperature difference between the center and peripheral parts of the substrate 3. In other words, the substrate 3 has a uniform surface-temperature distribution. Alternatively, in order to impart a uniform surface-temperature distribution to the substrate, the substrate-supporting member 10 is made of material having substantially the same heat capacity per unit area as that of the substrate 3. In this instance, the substrate 3 has virtually no thermal stress, and hence the molecules of the substrate undergo virtually no slip. If the substrate-supporting member 10 had a heat capacity per unit area which is different from that of the substrate 3, the substrate 3 should have a non-uniform surface-temperature distribution, and should inevitably have a thermal stress, which would cause slip or glide of the substrate molecules. Fig. 16 shows a modification of the substrate-supporting unit illustrated in Fig. 14, and Fig. 17 shows a modification of the substrate-supporting unit shown in Fig. 15. The unit of Fig. 16 is characterized in that the annular wall 11 is made of material having low thermal conductivity. The unit of Fig. 17 is characterized in that the substrate-supporting member 10 consists of two components 10d and 10e. The first component 10d is made of material which has the same emissibility or the same heat capacity per unit area, as the substrate 3, and the second component 10e is made of material which has lower emissivity or less heat capacity per unit area, than that of the substrate 3. Hence, the wall 11 or component 10e conducts less heat to the peripheral part of the substrate 3 than in the unit illustrated in Fig. 14 or 15. In the substrate-supporting units illustrated in Figs. 14 to 17, it is most desirable that the member 10, which needs to have the same emissivity or the same heat capacity as the substrate 3, be made of the material identical to that of the substrate 3. Hence, if the substrate 3 is a silicon substrate, the member 10 should best be made of silicon. In other words, it suffices to support the substrate 4 by means of an annular dummy substrate of the same material as the substrate 3, such that the peripheral part of the substrate 3 contacts the inside edge of the dummy substrate. Fig. 18 shows a modification of the substrate-supporting unit illustrated in Fig. 2. Generally, in a vapor-phase deposition apparatus, the peripheral part of a substrate 3, which contacts an annular substrate-supporting member 10, is likely to be cooled due to the thermal resistance at the interface between the substrate 3 and the member 10. The substrate-supporting unit shown in Fig. 18 is designed to prevent the peripheral part from being cooled. More specifically, an annular wall 10f is formed integrally with a holder 4, protrude upwards therefrom, and is located right below the inside edge of the annular member 10. The inside edge of the member 10 is therefore heated more than any other part of the member 10, because of the heat radiated from the top of the annular wall 10f. It follows that the peripheral part of the substrate 3, which is placed on the inside edge of the member 10, is heated to the same temperature as any other part of the substrate 3. As a result, the substrate 10 has a surface-temperature distribution which is sufficiently uniform. Fig. 19 shows a second modification of the substrate-supporting unit illustrated in Fig. 2. This modification is also designed to prevent the peripheral part from being cooled. An annular wall 10g is integrally formed with a substrate-supporting member 10, and protrudes downwards from the inside edge of the member 10. The inside edge of the member 10 is heated more than any other part of the member 10, because of the heat radiated from the holder 4 is readily applied to the lower end of the annular wall 10g. Hence, the peripheral part of the substrate 3, which is placed on the inside edge of the member 10, is heated to the same temperature as any other part of the substrate 3. As a result, the substrate 10 has a surface-temperature distribution which is sufficiently uniform. The inventors made several substrate-supporting units of the types shown in Figs. 18 and 19, which had annular walls 10f and 10g having various heights H1, and used them in a vapor-phase deposition apparatus available to the inventors, thus heating substrates. Then, they recorded the temperatures to which the walls 10f and 10g were heated, against the heights of these annular walls. The results were as is shown in the graph of Fig. 20, which is graph representing the relation between the total-slip length L of a substrate (plotted on the Y axis) and the difference ΔT (plotted on the X axis) between the temperature (T1) of the substrate and the temperature (T2) of the annular wall 10f or 10g. As is evident from Fig. 20, when the temperature difference ΔT is less than 10°C, the slip is enormous. This is because the peripheral part of the substrate 3 is less heated than the other part due to the thermal resistance at the interface between the substrate 3 and the member 10, and the substrate 3 inevitably has a non-uniform temperature distribution. As is evident from Fig. 20, too, the slip is also prominent when the difference ΔT is greater than 200°C. This is because the peripheral part of the substrate 3 is excessively heated and more than the other part, despite of the thermal resistance at the interface between the substrate 3 and the member 10, and the substrate 3 inevitably has a non-uniform temperature distribution. As can be understood from Fig. 20, the slip can be minimized by heating the annular wall 10f or 10g to a temperature 10 to 200°C higher than that of the substrate 3, thereby imparting a more uniform temperature distribution to the substrate 3. There are two methods of heating the inner edge of the member 10 to a temperature 10 to 200°C higher than that of the substrate 3. The first method is to control the temperatures of the center and peripheral parts of the holder 4 independently. The second method is set the distance H1 (Figs. 18 and 19) between the annular wall 10f or 10g and the member 10 or the holder4, at a specific ratio to the distance H2 (Figs. 18 and 19) between the holder 4 and the substrate 3. The first method can be performed by means of the heating unit illustrated in Fig. 21. The heating unit comprises two heater coils 6a and 6b, two power supplies 8a and 8b connected to the coils 6a and 6b, respectively, and two temperature controllers 9a and 9b connected to the power supplies 8a and 8b, respectively. The controllers 9a and 9b have a radiation thermometer each. The thermometers incorporated in the controllers 9a and 9b detect the temperatures ambient to the center and peripheral parts of the substrate 3, respectively. The controllers 9a and 9b controls the power supplies 8a and 8b and, hence, the heater coils 6a and 6b, in accordance with the temperatures thus detected, such that the substrate 3 has a uniform surface-temperature distribution. When the spaces between heater coils 6a and 6b are located corresponding to outermost portions of the substrate 3, as is shown in Fig. 21, the substrate-supporting member 10 can be controlled to a desired temperature, thereby enabling the substrate 3 to have a uniform temperature distribution. The arrangement of the coils 6a and 6b is not limited to this. If each of them is further divided, and the number of spaces between the coils 6a and 6b and between divided portions of each coil is more than two, at least one of the spaces must be located corresponding to outermost portions of the substrate 3 to obtain the same effect. Other types of heating units can be employed to perform the first method of heating the annular wall 10f or 10g to a temperature 10 to 200°C higher than that of the substrate 3. For example, thermocouples can be used, instead of thermometers, for directly detecting the temperature of that portion of the member 10 which contacts the substrate 3, thus measuring the temperature of the peripheral part of the substrate 3. Further, four or more heater coils can be used, instead of three, thereby to heat the substrate more uniformly. Still further, only one heater coil can be used, which consists of portions, each having turns arranged at a different pitch and exhibiting a different heat-generating efficiency. The second method of heating the annular wall 10f or 10g to a temperature 10 to 200°C higher than that of the substrate 3 will now be explained in detail. To determine the most desirable ratio of the distance H2 between the holder 4 and the member 10 to the distance H1 of the annular wall 10f or 10g and the member 10 or the holder 4, the inventors studied the the relation between the total-slip length L of a substrate and the ratio, H2/H1, which was observed in the substrate-supporting units of the types shown in Figs. 18 and 19 they have made for experimental use. This relation was as is shown in the graph of Fig. 22, wherein the ratio H2/H1 is plotted on the X axis, and the total-slip length L is plotted on the Y axis. As can be understood from Fig. 22, the slip in the substrate 3 is enormous when the ratio H2/H1 is less than 2. This is because the peripheral part of the substrate 3 is less heated than the other part due to the thermal resistance at the interface between the substrate 3 and the member 10, and the substrate 3 inevitably has a non-uniform temperature distribution. Further, as is evident from Fig. 22, the slip is great also when the ratio H2/H1 is greater than 20. This is because the peripheral part of the substrate 3 is heated excessively and more than the other part, despite of the thermal resistance at the interface between the substrate 3 and the member 10, and the substrate 3 inevitably has a non-uniform temperature distribution. Hence, as can be understood from Fig. 22, the slip in the substrate 3 can be reduced to a minimum, by setting the ratio H2/H1 to a value ranging from 2 to 20, thereby to impart a uniform surface-temperature distribution to the substrate 3. Although not shown in the drawings, the substrate-supporting unit of Fig. 19 can be modified such that the annular wall 10g is more thick, extending over almost entire lower surface of the substrate-supporting member 10. As has been described, due to the thermal resistance at the interface between the substrate 3 and the member 10, the peripheral part of the substrate 3 may be less heated than the other part, and the substrate 3 may inevitably has a non-uniform temperature distribution. In this case, the substrate-supporting member 10, which is a thin member, also has a non-uniform temperature distribution and, hence, a thermal stress. Due to this thermal stress, the member 10, which is thin, warps, inevitably changing the distance between the substrate 3 and the holder 4 changes, and the surface-temperature distribution of the substrate 3 becomes even less uniform. Fig. 23 shows another type of a substrate-supporting unit according to the invention, which is designed to prevent the member 10 from warping in spite of the thermal stress. More specifically, this unit has an annular rib 10h integrally formed with the substrate-supporting member 10 and extending downward from the peripheral edge thereof. The rib 10h mechanically reinforce the substrate-supporting member 10, thus preventing the member 10 from warping. Fig. 24 illustrates another type of a substrate-supporting unit, designed also to prevent the member 10 from warping in spite of the thermal stress. As is shown in Fig. 24, the member 10 consists of two parts 10 which are made of the same material. Thus, the member 10, as a whole, is less likely to warp due to the thermal stress. In addition, owing to the thermal resistance at the joint between the parts 10j and 10k, the temperature fall at the peripheral part of the substrate 3, which contacts the member 10, can be decreased. Fig. 25 shows another substrate-supporting unit according to the present invention. This unit comprises a holder 4 and a substrate-supporting member 10 located above the holder 4. The member 10 is a disc and has a center hole 10a which has a shape similar to them of the substrate 3 and has a diameter slightly less than that of the substrate 3. The substrate 3 is supported by the member 10, with its peripheral part contacting the member 10. There are no gaps between the substrate 3 and the member 10, thus not allowing the feed gas flow into the space between the holder 4 and the lower surface of the substrate 3. Hence, no layer will be deposited on the lower surface of the substrate 3. Another apparatus according to the invention will be described, with reference to Fig. 26. The apparatus is characterized by the measures taken to heat a substrate 3 uniformly even if the substrate warps. The results of the experiments repeated by the inventors show that substrates warp at a curvature ranging from about 10mR to about 100mR, depending on the temperature to which the substrates are heated and also the emissibility which the substrates have. The apparatus of the invention is designed based on this finding. Fig. 26 shows a substrate holder 4 for use in the vapor-phase deposition apparatus according to the invention. As is evident from Fig. 26, the holder 4 has a circular recess 20 having a concave bottom. The concave bottom has a curvature within a range from about 10mR to about 100mR. Hence, when the substrate 3 placed on the holder 4 warps at a curvature falling in the same range, the gap between the substrate 3 and the bottom of the recess 20 is uniform. As a result of this, the same amount of heat is applied from the bottom of the recess 20 to any part of the substrate, whereby the substrate 3 has a uniform surface-temperature distribution, all the time a crystal layer is formed on the substrate 3 by means of vapor-phase deposition. The recess 20 horizontally extends into the peripheral portion of the holder 4 and, therefore, has a greater diameter than the substrate 3. Since the heat path formed of the peripheral portion of the holder 4 has a smaller cross-sectional area, the substrate 3 will have a relatively uniform surface-temperature distribution. Figs. 27A, 27B and 28 illustrate modifications of the substrate holders illustrated in Fig. 26. Another apparatus according to the invention will now be described, with reference to Fig. 29. Fig. 29 shows a modified reaction vessel 2 for a component of a vapor-phase deposition apparatus according to this invention. This vessel 2 is characterized in that its inner surface 2a is polished to a degree close to mirror-polish degree, thus having a small roughness. The inner surface 2a, therefore, has a low heat-emissivity. Due to the low heat-emissivity, the substrate 3 can have a uniform surface-temperature distribution. Alternatively, the reaction vessel 2 can be made of material which has a low heat-emissivity, or the inner surface 2a of the vessel 2 can be coated with a layer of material having a low heat-emissivity. In either case, the substrate 3 can have a uniform surface-temperature distribution. Fig. 30 illustrates a so-called horizontal vapor-deposition apparatus. The feed gas and the carrier gas are supplied into a reaction vessel 2 through a gas-inlet port 2a, and flow through the vessel horizontally to the right (Fig. 30). Fig. 31 (which embodies the invention) shows a modification of the substrate-supporting member 10 incorporated in the horizontal vapor-phase deposition apparatus illustrated in Fig. 30. The modified member 10 is designed to support a plurality of substrates 3. Figs. 32 and 33 are schematic views of a vapor-phase deposition apparatus according to the invention, and explain how to transfer a substrate into, and out of, the reaction vessel 2 of the apparatus. As is shown in Figs. 32 and 33, a substrate holder 4 is connection to the upper end of a shaft 5. Mounted on the holder 4 is a substrate-supporting member 10 which supports a substrate 3. The shaft 5 extends downwards through bellows 30 secured to the lower end of the vessel 2 in airtight fashion. The shaft 5 is coupled, at its lower end, to a drive unit 31. The drive unit 31 moves the shaft 5 up and down. A chamber 33 is located beside the reaction vessel 2 and connected thereto by means of a gate valve 32. A substrate tray 34 is provided in the chamber 33. The tray 34 is connected by a connection rod 36 to a tray-transferring unit 37. The unit 37 moves the rod 36 back and forth, in the directions of arrows A. Hence, the substrate tray 34 is horizontally moved, back and forth through the chamber 33, and into and out of the reaction vessel 2 through the gate valve 32. In operation, the member 10 supporting a substrate 3 is placed on the substrate tray 34. Then, the tray-transferring unit 37 is operated, thereby transferring the tray 34 into the reaction vessel 2 through the gate valve 32. Next, the member 10 is moved from the tray 34 onto the holder 4 which has been lowered to the bottom of the reaction vessel 2. Then, the unit 37 is operated, transferring the tray 34, now empty, from the vessel 2 to the chamber 33 through the gate valve 32. Thereafter, the drive unit 31 is operated, thus moving the shaft 5 upwards, and so moving the substrate holder 4. As a result of this, the substrate-supporting member 10 is moved up to a predetermined level within the reaction vessel 2, and the substrate 3 is subjected to vapor-phase deposition. Upon completion of the deposition, the drive unit 31 is operated, lowering the shaft 5. Hence, the holder 4, the member 10, and the substrate 3 are moved downwards altogether. The tray-transferring unit 37 is operated, transferring the tray 34 into the reaction vessel 2 through the gate valve 32. The member 10 is moved from the holder 4 onto the tray 34. The unit 37 is further operated, thus transferring the tray 34, now supporting the member 10 and, hence, the processed substrate 3, from the vessel 2 into the chamber 33 through the gate valve 32. The chamber 33 has an opening made in the top, which is closed by a cover 39. An O-ring 38 is inter posed between the cover 39 and the top of the chamber 33. The chamber 33 has an exhaust port 33a made in the bottom. Through this port 33, the unreacted gas is discharged from the chamber 33 in a controlled amount, whereby the pressure in the chamber 33 is adjusted to the best possible value. In the vapor-phase deposition apparatus shown in Figs. 32 and 33, the substrate 3 can be transferred into and out of the reaction vessel 2, while supported by the member 10. In other words, the substrate 3 need not be mounted onto or removed from the member 10. This helps to enhance the efficiency of vapor-phase deposition. The present invention is not limited to the embodiments and modifications -- all described above.

Claims: A vapor-phase deposition apparatus comprising: substrate-supporting means for supporting a substrate; heating means for heating the substrate-supporting means; and gas-supplying means for supplying gas for forming a thin film on the substrate supported by the substrate-supporting means, characterized in that said substrate-supporting means comprises: a disk-shaped first member (4) having a diameter larger than that of said substrate and heated to a predetermined temperature by said heating means (6,6a,6b,7); a second member (10) having an inner edge portion for supporting a peripheral part of the substrate (3) and an outer edge portion located outside of said substrate; and a support member (11), located outside of the peripheral part of said substrate, for supporting said second member (10) on said first member (4) and for suppressing the heat conducting from the first member (4) to the second member (10) so that the substrate is uniformly heated by the radiation heat or the heat conducted by the gas. The apparatus according to claim 1, characterized in that said second member (10) is made of the same material as said substrate (3). The apparatus according to claim 1, characterized in that said support member (11) spaces said first member (4) away from the substrate (3) by a distance of at least 1 mm. The apparatus according to claim 1, characterized by further comprising a reaction vessel (2) containing said substrate-supporting means and having an inner surface (2c) which has low heat-emissivity. The apparatus according to claim 1, characterized in that said support member (11) comprises at least three supporting posts disposed outside of the outermost peripheral part of the substrate. A vapor-phase deposition apparatus comprising: substrate-supporting means, including a body portion (4) and a support portion (10) mounted on said body portion, for supporting a peripheral part of a substrate (3) having a first surface to be processed and a second surface opposite to the first surface; gas-supplying means (9) for supplying gas to form a thin film on the first surface of the substrate supported by said substrate-supporting means; heating means (6a,6b), located at the side of the body portion (4) remote from the substrate, for heating said substrate-supporting means and said substrate, said heating means causing a temperature distribution of the substrate in thickness direction thereof; and temperature-compensating means (9a, 9b, 8a, 8b) for compensating for a temperature fall at a support part of the substrate (3), which occurs when the substrate (3) is heated by said substrate-heating means, characterized in that said temperature-compensating means comprises; a projection (10f, 10g) having a size determined such that the distance (H1) between said body portion (4) and said support portion (10) of said substrate-supporting means is shorter, at the position corresponding to the projection, than the distance (H2) between said body portion (4) and the substrate (3), the projection (10f,10g) extending from at least one of the body portion (4) and the support portion (10) at the position which corresponds to the peripheral part of the substrate (3). The apparatus according to claim 6, characterized in that said projection (10f,10g) has a height determined such that the ratio (H2/H1) of the distance (H2) between said body portion (4) and the substrate (3) to the distance (H1) between said body portion (4) and said support portion (10) ranges from 2 to 20. A vapor-phase deposition apparatus comprising: substrate-supporting means including a body portion (4) and a support portion (10) mounted on said body portion, for supporting a peripheral part of a substrate (3) having a first surface to be processed and a second surface opposite to the first surface; gas-supplying means (9) for supplying gas to form a thin film on the first surface of the substrate supported by said substrate-supporting means; heating means (6a,6b) located at the side of the body portion (4) remote from the substrate, for heating said substrate-supporting means and said substrate, said heating means causing a temperature distribution of the substrate in a thickness direction thereof; and temperature-compensating means (9a, 9b, 8a, 8b) for compensating for a temperature fall at a support part of the substrate (3), which occurs when the substrate (3) is heated by said substrate-heating means, characterized in that said heating means comprises a first heater (6a) for heating the substrate (3) and a second heater (6b) for heating the support portion (10) supporting a part of the substrate, and in that said temperature-compensating means comprises temperature detectors (9a,9b) for detecting the temperature of the central portion of the substrate (3) and the temperature of the peripheral part thereof which is supported by said support portion (10), and temperature-controlling means for controlling the first and second heaters independently by output signals from the temperature detectors. The apparatus according to claim 8, characterized in that said heating means includes a heater (6b) for heating said support portion (10) to a temperature 10°C to 200°C higher than the temperature of the substrate (3). The apparatus according to claim 8, characterized in that said heating means comprises a heater (6a) located at the side of the body portion (4) remote from said substrate. The apparatus according to claim 8, characterized in that said temperature-compensating means comprises temperature detectors (9a,9b) for detecting the temperature of the support portion (10) which contacts the substrate thus measuring the temperature of the peripheral part of the substrate, and temperature-controlling means for controlling the first and second heaters (6a,6b) independently by output signals from the temperature detectors (9a,9b).

Inventors: OHMINE TOSHIMITSU, SATO YUUSUKE, OHMINE, TOSHIMITSU, SATO, YUUSUKE, OHMINE, TOSHIMITSU, C/O INTELLECTUAL PROPERTY DIV., SATO, YUUSUKE, C/O INTELLECTUAL PROPERTY DIVISION
Applicants: TOSHIBA KK, KABUSHIKI KAISHA TOSHIBA
Application year: 1991
Main classification: C23C16
IPC codes: C23C16