Abstract:
A film-deposition apparatus simultaneously realizes high partial pressure of volatile components, great flow velocity and smooth deposition rate curve at lower gas consumption. The apparatus comprises a disk-like susceptor, a face member opposing the susceptor, an injector, a material gas introduction portion, and a gas exhaust portion. A wafer holder retains a substrate, and a supporting member of the susceptor retains the wafer holder. The susceptor revolves around its central axis and the substrate rotates by itself. The opposing face member is structured so that a fan-shaped recessed portion and a fan-shaped raised portion are formed alternately in a radial manner, by which the height of the flow channel changes in a circumferential direction. The apparatus provides film deposition equivalent to that attained under optimal conditions by a conventional apparatus at a smaller flow rate of the carrier gas, and increases a partial pressure of material gases of volatile components.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present invention relates to a vapor phase film deposition apparatus which forms a semiconductor film on a semiconductor or an oxide substrate and, in particular, relates to a rotation/revolution type vapor phase film-deposition apparatus which allows a substrate to rotate by itself or revolve around during film deposition. 
         [0003]    2. Description of the Related Art 
         [0004]    In general, it is considered that three factors are needed in keeping the high quality of film which is formed by a vapor phase film-deposition method. More specifically, they are a) film deposition pressure, b) flow velocity and c) curve of deposition rate. Hereinafter, a detailed description will be given regarding the influences of these factors on the quality of film. 
         [0005]    First, a) film deposition pressure is important in particular where a highly volatile component is contained in elements of film. A system where significant volatilization from the film occurs is subjected to such treatment in which a film deposition pressure is elevated to increase a partial pressure of the volatile component, thereby suppressing dissociation of the volatile component from the film to provide a film with fewer defects and higher quality. For example, in the case of III-V compound semiconductors, due to high volatility of an group V element of the Periodic Table, it is necessary to increase a partial pressure of the group V element in vapor phase in order to suppress dissociation of the volatile component from the film. Among other things, in a nitride system-based compound semiconductor, it is often preferred to carry out film deposition at a pressure close to a normal pressure due to high volatility of nitrogen. 
         [0006]    Next, with regard to b) flow velocity, the higher flow velocity is more desirable. Under normal film deposition conditions, a Reynolds number is not high enough to allow occurrence of turbulence. A higher flow velocity is preferable, if no turbulence occurs. A first reason thereof is that where the flow velocity is low, the interface of a film is deteriorated in quality. On general film deposition, various types of interface are formed on a film by changing compositions of the film or changing a doping material in the course of film deposition. Where the flow velocity is low, a material gas used in a film deposition layer prior to formation of interfaces is not fast exhausted. Thus, it is difficult to obtain a steep interface, resulting in a failure of keeping the interface in high quality. Another reason is that it takes a longer time from introduction of a source gas into a reactor to arrive at a substrate, by which precursors (raw material elements) are consumed at a higher percentage by vapor reactions. Thereby, the utilization efficiency of raw material is decreased. Still another reason is that where the flow velocity is low, it is difficult to control a random diffusion of raw material molecules by the flow velocity of gas, resulting in production of undesirable deposition at unintended parts (other than the substrate) inside the reactor, which may adversely influence the quality of film and reproducibility. 
         [0007]    In a range at which no turbulence will occur, a higher flow velocity enables to stably realize a higher quality of film and a higher quality of interface. When consideration is given to the flow velocity in association with the film deposition pressure at the same flow rate of the carrier gas, a higher film deposition pressure is advantageous in suppressing dissociation of volatile components but can be disadvantageous in terms of flow velocity, because the flow velocity becomes slower with an increase in pressure, causing the film in lower quality. These two factors are basically not compatible. It is, therefore, necessary to conduct such operation that searches an optimal film deposition pressure and flow velocity from a comprehensive point of view. 
         [0008]    Finally, consideration is given to c) the curve of deposition rate.  FIG. 10  is a cross sectional view which shows a general rotation/revolution type reactor structure. More accurately, this is an example of reactor which is often used in film deposition of III-V group compound semiconductors. A reactor  100  is constituted with a disk-like susceptor  20 , an opposing face member  110  which opposes the susceptor  20 , a material gas introduction portion  60  and a gas exhaust portion  38 . A substrate W is retained by a wafer holder  22 , and the wafer holder  22  is retained by a supporting member  26  of the susceptor  20 . The reactor  100  is centrosymmetric and structured so that the susceptor  20  revolves around its central axis and the substrate W rotates by itself at the same time. A mechanism for revolution and rotation as described above is publicly known. Further, the structure shown in  FIG. 10  is also provided with a separately supplying type gas injector  120 . The separately supplying-type gas injector  120  shown in  FIG. 10  is divided by a first injector member  122  and a second injector member  124  into a gas introduction portion made up of three layers, i.e. upper, middle and lower layers. And this gas injector is often used in such a manner that a source gas of a H2/N2/group V element is introduced from the upper layer, a source gas of a group III element is introduced from the middle layer and H2/N2/group V is introduced from the lower layer. In the present invention, a curve obtained by plotting a deposition rate at every position on the susceptor  20  and the substrate W in a radial direction of the rotation/revolution type reactor  10  is defined as a curve of deposition rate. 
         [0009]      FIG. 11  shows an ordinary curve of deposition rate obtained by the above-mentioned film deposition apparatus. This curve is dominated mainly by transport of raw material molecules. For example, in the case of III-V compound semiconductors, in most cases, film deposition is carried out, with a group V element being excessively supplied. Thus, only a group III element is handled as raw material molecules which dominate the deposition rate curve. A horizontal axis represents a distance from an injector end, whereas a longitudinal axis represents a deposition rate. A site at which deposition starts is substantially equal to an injector end where a source gas is introduced into a reactor from the separately supplying type injector. The deposition rate will increase from the site and soon decrease monotonously after the arrival at a peak. Regarding the position of the substrate, an uppermost upstream part of the substrate is usually arranged at a position slightly downstream from the peak of the curve of deposition rate. Next, the substrate is allowed to rotate by itself, by which a difference in deposition rate between upstream and downstream is eliminated to realize a relatively favorable uniformity of film thickness. In other words, the curve of deposition rate determines the uniformity of film thickness after rotation and revolution. In addition to the film thickness, chemical compositions of film, concentrations of dopants and others are greatly influenced by the deposition rate. Thus, the curve of deposition rate is quite important in terms of these characteristics and in-plane uniformity of the substrate. Therefore, the curve of deposition rate is regarded as one of the important factors which greatly influences the quality of film. 
         [0010]    A deeper consideration will be given to the curve of deposition rate. This time, consideration will be given to important factors which influence the distribution of deposition rate. In a method for rotation/revolution type film deposition, film deposition is carried out quite often in a so-called mass transport rate-determining mode in which mass transport mainly based on diffusion of raw material molecules determines the deposition rate under the flow field in a laminar flow mode. In this case, (1) the concentrations of raw material molecules in a gas, (2) the flow rate of carrier gas and (3) the height of flow channel are regarded as major factors which influence the distribution of deposition rate. In addition, in the present invention, a description of flow rate of carrier gas is used as a term which covers a total flow rate of all types of gases used in film deposition, in addition to simply as a carrier gas. Among the above-described factors of (1) to (3), regarding (1) the concentrations of raw material molecules, there is a simple relationship that the deposition rate is proportional to the concentrations of raw material molecules (refer to  FIG. 12  which shows the conversion of the curve of deposition rate when the concentrations of raw material molecules are changed). 
         [0011]    Next, in giving consideration to (2) flow rate of the carrier gas, in  FIG. 13 , a difference in the curve of deposition rate is shown when the flow rate of the carrier gas is changed. In addition, when the flow rate of the carrier gas is changed, all the other film deposition conditions are to be kept unchanged. In this drawing, if a) is taken as a curve of deposition rate when a certain flow rate of the carrier gas is given as F0, each of b) and c) shows a curve of deposition rate at a flow rate of the carrier gas which is respectively twice or triple higher than a). The above description appears, with an increase in carrier gas, the curve of deposition rate changes so as to shrink in a longitudinal direction and extend in a lateral direction. Quantitatively, when the flow rate is multiplied a times, the curve of deposition rate is substantially consistent so as to be multiplied by 1/a longitudinally and multiplied by square root α (√α) laterally. This is due to the fact that in the previously described laminar flow mode and also the mass transport limited mode, the deposition rate is proportional to an gradient of concentrations of raw material molecules in a direction perpendicular to a face of a substrate or of the susceptor and the distribution of concentrations of raw material molecules in a flow channel is substantially in accordance with a solution of the advective diffusion equation under a boundary condition that the concentrations of raw material molecules on the surface of the substrate or the susceptor are zero. Next, a relationship between the above-described flow rate of carrier gas and the curve of deposition rate is derived by the similar rule of the advective diffusion equation. 
         [0012]    Further, a description will be given for the influences of (3) the height of flow channel on the curve of deposition rate.  FIG. 14  shows the curves of deposition rate when the height of the flow channel is changed. When a) is taken as a curve of deposition rate given at a certain height of the flow channel of L0, each of b) and c) shows a curve of deposition rate at the height of the flow channel which is respectively twice or triple higher than the height of a). This is also subjected to the similar rule of the advective diffusion equation as the flow rate. When the height of the flow channel is multiplied by α, the curve of deposition rate is substantially consistent so as to be multiplied by 1/α longitudinally and multiplied by square root α (√α) laterally. 
         [0013]    With regard to the above description of (1) to (3) factors, consideration will be summarized as follows. With an increase in (2) the flow rate of carrier gas and also with an increase in (3) the height of flow channel, the curve of deposition rate is accordingly distributed in the shape that extends relatively in a radial direction, that is, in the shape that is relatively low inclination. Finally, an absolute value of the deposition rate is determined by (1) the concentrations of raw material molecules. 
         [0014]    In addition to the three factors of (1) to (3), hereinafter, consideration will be given for the influences of the film deposition pressure on the curve of deposition rate. According to the advective diffusion equation, where a ratio of flow velocity to diffusion coefficient is constant, the distribution of concentrations of raw material molecules in a flow channel is kept unchanged. When consideration is given to a case where only a pressure is changed at the same flow rate of the carrier gas, the flow velocity is inversely proportional to the pressure and the diffusion coefficient is also generally inversely proportional to the pressure. As a result, a ratio of the flow velocity to the diffusion coefficient is kept unchanged. Thus, when only the pressure is changed, substantially similar results are to be obtained. However, where chemical reactions in vapor phase cannot be disregarded, the chemical reactions proceed differently due to the flow velocity and pressure, which can lead to different results. 
         [0015]    Since roles of the three factors which dominate the curve of deposition rate are made apparent, from now on, consideration will be given to an ideal curve of deposition rate. As described previously, the three factors are changed to obtain a variety of curves of deposition rate, and these curves have their own advantages and disadvantages. In a relatively steep curve of deposition rate obtained when a carrier gas flow rate is lower or when the height of the flow channel is lower, most of the raw material molecules contained in a source gas will be exhausted until the source gas is discharged. Therefore, there is such an advantage that the utilization efficiency of raw material is high. On the other hand, there is such a disadvantage that a thicker deposition layer is inevitably formed on the susceptor upstream from the substrate. This upstream deposit may not only deteriorate the quality of film but also may contribute to unstable film deposition, thus resulting in a decrease in yield or an increase in maintenance frequency that lead to high costs. Further, there is a great difference in deposition rate between upstream and downstream. Therefore, it is more likely to make a difference in quality of film such as compositions or concentrations of dopants between the center of the substrate where film deposition is carried out always at the same deposition rate and a peripheral part of the substrate where film deposition is carried out alternately at slow and fast deposition rates, thus reducing the uniformity of film. 
         [0016]    When the flow rate of the carrier gas is greater or when the height of the flow channel is higher, conversely the distribution of deposition rate is smoother. In this case, although the utilization efficiency of raw material is relatively low, the adverse influences due to the upstream deposit will be reduced and the quality of film will become more uniform. As described above, there are advantages and disadvantages in any case. Thus, a comprehensive judgment is made to select an optimal curve of deposition rate in view of the points such as the quality of film and productivity. However, when only the quality of film or uniformity of film is taken into account, a smooth curve of deposition rate is more desirable. 
         [0017]    Here, reverting to the three factors described at the beginning of the specification, that is, a) film deposition pressure (in particular, a partial pressure of volatile components), b) flow velocity and c) curve of deposition rate, influences of these factors on the quality of film will be summarized. In order to obtain a good quality of film or uniformity of film, the higher a) the film deposition pressure becomes, the better the result will be; the higher b) the flow velocity becomes, the better the result will be; and the lower c) the curve of deposition rate becomes, the better the result will be. 
         [0018]    Now, in order to obtain a high flow velocity at a high film deposition pressure, with a flow rate of the carrier gas being fixed, the only way is to decrease the height of the flow channel. However, a decrease in height of the flow channel will make c) the distribution of deposition rate become steep, which is not desirable for the quality of film. On the other hand, in order to realize a smooth distribution of deposition rate in the above-described condition, the only way is to increase the flow rate of the carrier gas. However, an increase in only the flow rate of the carrier gas will decrease a percentage of material gases of volatile components, thereby resulting in a decreased partial pressure of the volatile components, which is not desirable. Finally, it is necessary to increase the material gas of the volatile components, along with the carrier gas. Since the material gas is expensive, it is in reality impossible to increase the material gas without any limitation. 
         [0019]    To the contrary, under a reduced pressure which realizes a high flow velocity, basically the only way is to decrease partial pressures of every gas. However, an increase in percentage of the material gas of volatile components in a carrier gas is able to realize a high partial pressure even under a reduced pressure. Hereinafter, consideration will be given to this possibility. As described previously, a supply flow rate of the material gas cannot be increased without any limitation but with a superior limitation. As a result, in order that the material gas is increased in partial pressure at a certain pressure and also at a predetermined material gas flow rate, it is necessary to decrease a carrier gas other than the material gas. In order to obtain a smooth curve of deposition rate at a smaller flow rate of the carrier gas, the height of the flow channel may be increased. However, when the height of the flow channel is increased at a smaller flow rate of the carrier gas, the flow velocity is synergistically decreased. Thus, the quality of film and productivity are significantly decreased even under a reduced pressure. 
       SUMMARY OF THE INVENTION 
       [0020]    From the above consideration, it is difficult to satisfy the three factors at the same time, that is, a high partial pressure of volatile components, a high flow velocity and a smooth distribution of deposition rate, with a flow rate of material gas kept at a realistic level, by using a conventional apparatus. It is almost impossible to satisfy these factors in particular in a large-sized apparatus for mass production. 
         [0021]    In view of the above-described problems with conventional technology, an object of the present invention is to provide a film deposition apparatus which is capable of realizing the three factors at the same time, that is, a high partial pressure of volatile components, a high flow velocity and a smooth curve of deposition rate, with lower gas consumption. 
         [0022]    The present invention is directed to a vapor phase film deposition apparatus having a disk-like susceptor which has a wafer holder for holding substrates for film deposition, a mechanism which allows the substrates to rotate by itself and revolve around, an opposing face which opposes a wafer holder to form flow channels, an introduction portion and a exhaust portion of a material gas of each flow channel in which recessed and raised profiles are formed on the opposing face so that a distance between the disk-like susceptor and the opposing face is changed in a direction at which the substrate revolves around. 
         [0023]    In one of the major aspect, a disk-like injector is provided at an introduction portion of the material gas and recessed and raised profiles are formed on the injector so as to correspond to the recessed and raised profiles formed on the opposing face. In another aspect, a method for film deposition is based on chemical vapor growth. Still another mode is such that a film to be formed is a compound semiconductor. 
         [0024]    Further, in another aspect, a part of the material gas contains an organic metal. In still another aspect, a member which constitutes the opposing face and the injector is made of any one of metal material, such as stainless steel, molybdenum; carbide, such as carbon, silicon carbide and tantalum carbide; nitride such as boron nitride and aluminum nitride, and oxide-based ceramic such as quartz and alumina or in combination thereof. The above-described object and other objects of the present invention as well as characteristics and advantages will be made apparent from a detailed description given hereinafter and attached drawings. 
         [0025]    According to the present invention, it is possible to realize film deposition equivalent to that obtained by using a conventional apparatus under optimal conditions at a smaller flow rate of the carrier gas. It is also possible to dramatically increase a partial pressure of material gases of volatile components as compared with a conventional case and, as a result, to form a film with higher quality than a conventional film. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0026]      FIG. 1  is a plan view which shows an opposing face member of the present invention. 
           [0027]      FIG. 2  is a cross sectional view taken along the line of A-A in  FIG. 1 . 
           [0028]      FIG. 3  is a plan view which shows another example of the opposing face member. 
           [0029]      FIG. 4  is a cross sectional view which shows another example of the opposing face member. 
           [0030]      FIG. 5  is an exploded perspective view which shows a reactor structure of the present invention. 
           [0031]      FIG. 6  is a cross sectional view which shows the reactor structure of the present invention. 
           [0032]      FIG. 7  is an exploded perspective view which shows an injector structure of the present invention. 
           [0033]      FIG. 8  is a drawing which shows a curve of deposition rate obtained in an experimental example of the present invention. 
           [0034]      FIG. 9  is a drawing which shows photoluminescence spectrum of a multiple quantum well obtained in the experimental example of the present invention. 
           [0035]      FIG. 10  is a cross sectional view which shows a reactor structure of a conventional rotation/revolution type film deposition apparatus. 
           [0036]      FIG. 11  is a drawing which shows a common curve of deposition rate and arrangement of a substrate which rotates by itself and also revolves around. 
           [0037]      FIG. 12  is a drawing which shows a change in curve of deposition rate when concentrations of raw material molecules are changed. 
           [0038]      FIG. 13  is a drawing which shows a change in curve of deposition rate when a flow rate of the carrier gas is changed. 
           [0039]      FIG. 14  is a drawing which shows a change in curve of deposition rate when height of the flow channel is changed. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0040]    Hereinafter, a detailed description will be given of the best mode for carrying out the present invention on the basis of examples. 
       Example 1 
       [0041]    First, a description will be given of a concept of the present invention with reference to  FIG. 1  and  FIG. 2 . The inventors have diligently studied to solve the above-described problems, they found a reactor structure that is able to realize a sufficient flow velocity at a lower consumption of carrier gas and also able to realize an optimal curve of deposition rate. A method thereof is to provide recessed and raised profiles on an opposing face to form flow channels which spread radially from the center of a reactor and which are separated from each other, thereby limiting the area contributing to film deposition to the flow channels. In conventional technologies, there have been a method in which an opposing face is formed in the shape of a cone and a method in which a step is disposed on its way to a flow channel (for example, Japanese Published Unexamined Patent Application No. 2005-5693 or the like). However, in both of these methods, the flow channels are constant in height when viewed from the circumference. Therefore, according to the technology disclosed in Japanese Published Unexamined Patent Application No. 2005-5693, it is an advantage that undesirable deposition at a region upstream from the substrate can be decreased. However, since the flow channels are constant in height at a substrate region in a circumferential direction, a curve of deposition rate at the substrate region is essentially not different from that obtained in a normal flow channel. Therefore, the structure is not free of the previously described problems, i.e. the three factors of the film deposition pressure, the flow velocity and the curve of deposition rate are associated with each other. In the present invention, the flow channels are changed in height in the circumferential direction. And, in this sense, the present invention is a completely different mode from a conventional apparatus and provided with the efficacy stated below. 
         [0042]    A concept of the present invention is shown in  FIG. 1  and  FIG. 2 .  FIG. 1  is a plan view of an opposing face member which constitutes a film deposition apparatus of the present invention.  FIG. 2  is a cross sectional view taken along the line of A-A in  FIG. 1 . A reactor structure of the film deposition apparatus is illustrated in  FIG. 5  and  FIG. 6 . Here, for the sake of describing a basic concept of the present invention, description will be given of only an opposing face member  30 . In addition, a reactor structure  10  itself is fundamentally similar to the reactor structure  100  of the above-described Background Art. The present invention has features with regard to the profile of the opposing face member  30  which is opposed to a susceptor  20 . The opposing face member  30  is provided with an opening  32  at the center from which a recessed portion  34  and a raised portion  36  are radially formed in alternative manner. The opposing face to the susceptor  20  is formed as described above, by which a source gas hardly flows into the raised portion  36  and the most gas flows into the recessed portion  34 . Therefore, film deposition is carried out fundamentally only at the recessed portion  34 . 
         [0043]    A description will be given of a concept of the present invention with reference to another example. Now, in a conventional structure (refer to  FIG. 10 ), optimal film deposition conditions are assumed to be attained from the height of the flow channel L0 in terms of a film deposition pressure, a flow velocity and a curve of deposition rate. The structure of the present invention is set so that an area ratio of the raised portion  36  to the recessed portion  34  is 1:1 and the height of the flow channel L at the channel portion  34  (refer to  FIG. 2 ) is the same as an optimal value L0 of the conventional structure. For the purpose of facilitating the understanding, it is assumed that no gas flows into the raised portion  36  and the gas only flows into the recessed portion  34 . In an actual structure, it is impossible to completely limit a film deposition area to the recessed portion  34 . However, since it is possible to easily realize a situation closer to the above, consideration may be given under the above assumption. The film deposition pressure can be controlled arbitrarily and, therefore, is set under the same conditions as those of the conventional structure. 
         [0044]    In order that the above described structure of the reactor is used to attain a favorable curve of deposition rate similar to a conventional curve of deposition rate, a flow velocity of the flow channel at a recessed portion may be made consistent with a conventional flow velocity. The structure of the present invention is half in a cross sectional area through which a gas flows as compared with the conventional structure. Thus, half a flow rate of the carrier gas suffices to obtain the same flow velocity. In other words, under the above-described condition, the height L0 of the flow channel and the flow velocity at the recessed portion  34  are also completely equivalent to the conventional optimal conditions, thus, always enabling to obtain an optimal curve of deposition rate. 
         [0045]    Next, consideration will be given to an absolute value of the deposition rate. In the structure of the present invention, a region contributing to film deposition is reduced to half as compared with the conventional structure, which has the effect of reducing an absolute value of the deposition rate to half. On the other hand, since a carrier gas is reduced to half, the concentration of raw materials in the gas are increased twice, which has the effect of increasing the deposition rate twice. As a result, these effects counterbalance each other, by which an absolute value of the deposition rate is made equivalent to a conventional absolute value. That is, raw material molecules are fed in the same quantity to obtain a deposition rate similar to a conventional deposition rate, but the utilization efficiency of raw materials will not be decreased. 
         [0046]    From the description given so far, it is apparent that adoption of the structure of the present invention enables to realize a state which is identical with a conventional optimal condition at half a quantity of a carrier gas used by the conventional structure. Only this fact is able to reduce a quantity of the used carrier gas and also greatly advantageous in reducing the production cost. In fact, the present invention has another important advantage. In decreasing a flow rate of the carrier gas, the flow rate of material gases of volatile components is kept the same as a conventional flow rate, by which a percentage of material gases of volatile components in the carrier gas will increase accordingly. Therefore, it is possible to greatly increase a partial pressure of material gases of the volatile components as compared with a conventional case. In this case, a further description will be given by referring to III-V group semiconductors. With regard to film deposition conditions of the present invention, a ratio of a group V element to a group III element as one of the most important parameters of film deposition is set the same as a conventional ratio. Since the group III element may be supplied in the same quantity as a conventional quantity, a material gas of the group V element may be also supplied in the same quantity. On the other hand, since the flow rate of the carrier gas is reduced to half as compared with a conventional flow rate, a percentage of the material gas of group V element in a flow rate of all supplied gases is increased twice. As a result, a partial pressure of the material gas of the group V element is also increased twice. This high partial pressure is effective in suppressing dissociation of atoms of the group V element from a film, thus making it possible to obtain a film in higher quality than a conventional film. 
         [0047]    As described so far, according to the method of the present invention, it is possible to realize film deposition which is equivalent to that realized under optimal conditions by a conventional apparatus at a smaller flow rate of the carrier gas. It is also possible to dramatically increase a partial pressure of material gases of volatile components as compared with a conventional case and, therefore, possible to form a film in higher quality than a conventional film. 
         [0048]    As described previously, in the actual structure, the film deposition area cannot be exclusively limited to the recessed portion  34 . A height ratio of the raised portion  36  to the recessed portion  34  and an area ratio thereof are appropriately selected, thus making it possible to obtain effects of the present invention sufficiently. Further, a side wall  35  of the flow channel which is a side face of the raised portion slightly influences a flow pattern, the influence of which is, however, limited. If the influence of the side wall  35  is desired to be corrected, the correction can be made by slightly adjusting gas conditions, because the correction relates to a flow velocity. 
         [0049]    Finally, consideration will be given to temporal transition of the deposition rate. In the present invention, during revolution of the substrate, gas passes alternately through a film deposition region which is the recessed portion  34  and a region free of film deposition which is the raised portion  36 . Therefore, when temporal transition of the deposition rate is taken into account, the temporal transition is considered to be formed in a rectangular shape or in a pulse manner. Whether this poses a problem or not is, as a matter of course, a concern. In this connection, there has been recently reported a method for film deposition in which raw materials are supplied in a pulse manner such as pulse MOCVD (C. Bayram et, al. Proc. of SPIE Vol. 7222 722212-1 or others). This method provides results better than those obtained by a usual method for film deposition. With the above description taken into account, it may be safe in saying that no fundamental problem is posed in terms of temporal transition of the deposition rate in a rectangular shape or in a pulse manner. Further, with regard to influences of the deposition rate in a pulse manner on the uniformity of film, this deposition rate will not affect the uniformity, because the deposition rate in a pulse manner is similarly found everywhere on the substrate. That is, as with a conventional method, it may be safe in saying that the uniformity is dominated after all only by the curve of deposition rate. From the consideration given so far, it can be concluded that temporal transition of the deposition rate in a pulse manner will not be disadvantageous in every respect. 
         [0050]    As described so far, the present invention is completely free of conventional disadvantages and at the same time is provided with a great advantage that the film is greatly improved in quality and gas consumption is greatly reduced due to a high partial pressure of material gas. 
         [0051]    Next, a detailed description will be given of the structure of the film deposition apparatus of the present invention with reference to  FIG. 3  to  FIG. 7 .  FIG. 3  is a plan view which shows another example of the opposing face member.  FIG. 4  is a cross sectional view which shows another example of the opposing face member.  FIG. 5  is an exploded perspective view which shows a reactor structure of the present invention.  FIG. 6  is a cross sectional view which shows the reactor structure of the present invention.  FIG. 7  is an exploded perspective view which shows an injector structure of the present invention. As shown in  FIG. 5  and  FIG. 6 , it is acceptable that the structure other than the opposing face member  30  and the injector  40  is identical with a conventional structure. Regarding the profile of the opposing face which is an essential part of the present invention, design parameters include a planar shape and a cross sectional profile of the opposing face, an area ratio and a height ratio of recessed portion to raised portion, and the number of divisions of flow channels. 
         [0052]      FIG. 1  is a plan view which shows an example of the recessed portion  34  formed in a fan shape. Similar effects can be obtained in a rectangular shape or in combination thereof. It is acceptable that deposition conditions and others are taken into account to select an appropriate shape dependent on respective film deposition conditions. An opposing face member  70  shown in  FIG. 3  illustrates a recessed portion  74  is formed in a profile that combines a rectangular portion  74 A with a fan-shaped portion  74 B. Further,  FIG. 2  shows a cross sectional shape of the recessed portion which is rectangular as an example. Of course, it is apparent that a trapezoid, a triangle or a curved face such as sine curve can provide similar effects. In view of attaining a smoother flow field, a profile including a curved face may be preferred.  FIG. 4  shows an example of the recessed and raised profiles, cross section of which is a trapezoid and in which a fillet  75  is provided at the edge. 
         [0053]    Next, with regard to an area ratio of the recessed portion  34  to the raised portion  36 , the smaller the area ratio of the recessed portion  34  is, the higher the effect of reducing the carrier gas and thus the effect of increasing a partial pressure of material gases of volatile components become. However, an excessively small area of the recessed portion  34  will result in longer passage time of the gas through the raised portion  36  which does not contribute to growth. This may be disadvantageous in forming a very thin layer depending on the case. Although relating to the rotation/revolution speeds, a permissible area ratio of the recessed portion  34  may be about 20% to 80%. 
         [0054]    With regard to a height ratio of the recessed portion  34  to the raised portion  36 , the susceptor rotates by itself and also revolves around, whereas the opposing face remains stationary, by which a clearance is required between the raised portion  36  and the susceptor  20 . Of course, a higher ratio of the height of the flow channel at the recessed portion  34  to that at the raised portion  36  (distance between the susceptor and the opposing face) will accordingly provide greater effects of the invention. However, even a slight difference in height will exert some effects. If actually satisfactory effects are to be obtained, the height ratio of the raised portion to the recessed portion is desirably about 1:2. In order to increase the height ratio, the smaller the distance between the raised portion  36  and the susceptor  20  is, the greater the effect will become. However, an excessively small distance results in a higher risk that the susceptor  20  may be in contact with the raised portion  36  of the opposing face due to thermal deformation of the susceptor  20  or the others. Therefore, the clearance between the raised portion  36  and the susceptor  20  may be required to be at least about 1 mm. The height of the flow channel at the recessed portion  34  is required to be consistent with an optimal condition of a conventional type. The height of the flow channel actually used in a rotation/revolution type reactor varies from 5 mm to 40 mm. If the height of the recessed portion  34  is selected to be 40 mm, effects will be provided by even setting the height of the raised portion  36  to be about 20 mm. Further, if the height of the recessed portion is set to be 5 mm, the height of the raised portion  36  is decreased to be 2.5 mm or less, preferably about 1 mm. With the above description taken into account, it is desirable that the height of the raised portion  36  is selected to be 1 mm to 20 mm and the height of the recessed portion  34  is selected to be 5 mm to 40 mm depending on other conditions. 
         [0055]    The last design parameter of the profile of the opposing face is the number of divisions of the flow channels. The larger the number of divisions is, the smaller the bias in a circumferential direction becomes. Thus, in light of this, the larger the number of divisions is, the better the result will be. However, when the number of divisions is increased to make excessively small the width of the flow channel at the recessed portion, the side wall  35  of the flow channel becomes more influential. Although this will not instantly pose a problem, there is inevitably found a great divergence from data obtained by a conventional method. With the above description taken into account, the number of divisions may be appropriately in a range of 3 to 30, which is, however, not very accurate. A large-size reactor used for mass production is able to utilize the data obtained by a conventional method, as it is, within this range, although depending on the size of the reactor. Where the number of divisions is smaller than 3, an area per raised portion is increased, resulting in an excessively long time of a gas passing through. Further, where the number is larger than 30, the width of the flow channel is excessively narrow, by which a side wall face of the flow channel exerts prominent influences on gas streams in view of fluid dynamics. 
         [0056]    In addition to the profile of the opposing face, it is desirable to change the profile of the injector in accordance with recessed and raised profiles of the opposing face. In this case as well, a description will be given by referring to III-V compound semiconductors. The injector frequently used in this field has such functions that group V and III elements of the Periodic Table are mixed adjacent to the substrate as much as possible and, then, the injector is kept at a low temperature, thereby suppressing precursor reactions of raw material molecules. In a conventional apparatus, as shown in  FIG. 10 , an injector  120  is fundamentally constituted with a first injector member  122  and a second injector member  124 , each of which is in a simple disk-like shape. On the other hand, in the present invention, for the purpose of preventing the occurrence of turbulence, as shown in  FIG. 5  or  FIG. 7 , it is preferred that flows inside the injector are also divided so as to continue to flow channels on the opposing face. 
         [0057]    More specifically, as shown in  FIG. 5  and  FIG. 7 , in this example, a first injector member  42  and a second injector member  50  which constitute a separately supplying type injector  40  are a surface profile similar to that of an opposing face member shown in  FIG. 3 . The first injector member  42  is such that a fan-shaped recessed portion  44  and a fan-shaped raised portion  46  are radially formed in an alternative manner and provided at the center with a gas introduction port  48  in which a through hole  48 A is formed. The second injector member  50  is configured that a fan-shaped recessed portion  52  and a fan-shaped raised portion  54  are radially formed in an alternative manner and provided at the center with a gas introduction port  56  in which a through hole  56 A is formed. 
         [0058]    The above-described structure is provided, by which an injector member is able to have a larger area which is in contact with a lower face. Next, the contact portion is used as a heat sink, thus making it possible to keep the injector at a lower temperature than a conventional apparatus. Technology in Japanese Published Unexamined Patent Application No. 2011-155046 discloses that an injector is brought into contact with a lower face and cooled. In the above-described invention, a contact portion thereof is formed in a cylindrical shape, thereby preventing occurrence of turbulence. However, the effect is not sufficient. The structure of the present invention is able to have a sufficiently great contact area and also prevent occurrence of turbulence and, therefore, definitely advantageous. 
         [0059]    A description has been so far given of the structure which is provided with the injector  40 . The present invention shall not be, however, limited to the use of an injector. Frequently, no injector is used on film deposition of arsenic-based or phosphorous-based compound semiconductors. It is apparent that a concept of the present invention in which recessed and raised portions are formed on an opposing face and divided into a plurality of flow channels can be used in this case as well and effects of the invention can be obtained. 
         [0060]    Further, in the drawings used in the above description, there is shown a so-called face down type apparatus in which the surface of the substrate faces downward in a perpendicular direction. Under ordinary film deposition conditions, gravitational influences are slight. Thus, it is self-evident that the effects of the present invention can be obtained also in a so-called face up apparatus in which the surface of substrate faces upward. Therefore, the present invention shall not be limited to a face down type apparatus. 
         [0061]    A material used to constitute the opposing face member  30  and the injector  40  of the present invention may basically include any material, as long as it is able to meet the degree of the purity as well as heat resistance and corrosion resistance to the ambient environment. More specifically, there are included metal material such as stainless steel, molybdenum; carbide such as carbon, silicon carbide and tantalum carbide; nitride such as boron nitride, silicon nitride and aluminum nitride, and oxide-based ceramic such as quartz and alumina which are generally used on film deposition of semiconductors or oxides. And, any material may be selected appropriately from them. 
       Experimental Example 1 
     Curve of Deposition Rate of Gallium Nitride Film 
       [0062]    Next, an example will be introduced in which the present invention is applied to the deposition of a gallium nitride film, then compared with a conventional method. First, a description will be given of an example prepared by the conventional method for comparison. In the conventional example, a reactor has a cross-sectional structure shown in  FIG. 10 . The apparatus was used to set conditions in consideration of quality of film, utilization efficiency of raw materials, consumption of carrier gas and flow velocity, finding that an optimal film deposition pressure was 25 kPa, a height of the flow channel was 14 mm, and a flow rate of the carrier gas was 120 SLM. On the other hand, in the structure of the present invention, as an opposing face member, there was adopted an opposing face having a rectangular cross section as shown in  FIG. 1  and  FIG. 2  to give a flow channel divided into 12 portions. Each pair of the recessed portion  34  and the raised portion  36  had 15 degree angle therebetween and was provided with periodicity of 30 degrees. Therefore, each pair was formed in a symmetrical shape for 12 times. A distance between the recessed portion  34  and the susceptor  20  remains 14 mm, that is, an optimal value of the conventional structure, and a distance between the raised portion  36  and the susceptor  20  was 4 mm. Carbon was used as a material of the opposing face member. 
         [0063]    Further, corresponding to the conventional structure, an injector is of a three-layer flow. A flow channel made up of three layers was 4 mm per layer in height, and each partition plate therebetween for dividing them was 1 mm in thickness, a total of 14 mm which was equivalent to the height of the flow channel at an opposing face portion. Regarding these three layers, each of the lower two flow channels was shaped to be divided into 12 portions so as to continue to a flow channel on the opposing face, while the upper layer was free of division and shaped to flow evenly at 360 degrees. In addition, the injector is made of molybdenum. The structure was shown in  FIG. 5  and  FIG. 6 .  FIG. 5  is a perspective view in which the structure was disassembled into components.  FIG. 6  is a cross sectional view in which the structure was assembled. A right half part of the cross sectional view shows a flow channel of the recessed portion, while a left half part thereof shows a flow channel of the raised portion. 
         [0064]    The Table 1 below showed the gas conditions on film deposition of the gallium nitride film. In the conventional example, the conditions for a total flow rate of the carrier gas being 120 SLM, in the examples of the present invention, given were experimental conditions, that is, a total flow rate of 120 SLM equivalent to that of the conventional example, 60 SLM; that is, half the above total flow rate; and 35 SLM at which a curve of deposition rate similar to that of the conventional example was consequently obtained. 
         [0000]    
       
         
               
               
               
               
               
             
               
               
               
               
               
               
               
               
             
               
               
               
               
               
               
               
               
             
           
               
                   
                 TABLE 1 
               
             
             
               
                   
                   
               
               
                   
                   
                 Carrier gas flow rate 
                 Flow 
                 Partial 
               
               
                   
                 Growth 
                 (SLM) 
                 rate of 
                 pressure 
               
             
          
           
               
                   
                 Structure of 
                 pressure 
                   
                   
                 Total 
                 TMGa 
                 of 
               
               
                   
                 apparatus 
                 (kPa) 
                 H 2   
                 NH 3   
                 flow rate 
                 (sccm) 
                 NH 3  (kPa) 
               
               
                   
                   
               
             
          
           
               
                 a) 
                 Conventional 
                 25 
                 96 
                 24 
                 120 
                 100 
                 5 
               
               
                   
                 type 
               
               
                 b) 
                 Present 
                 25 
                 96 
                 24 
                 120 
                 100 
                 5 
               
               
                   
                 invention 
               
               
                   
                 type 
               
               
                 c) 
                 Present 
                 25 
                 36 
                 24 
                 60 
                 100 
                 10 
               
               
                   
                 invention 
               
               
                   
                 type 
               
               
                 d) 
                 Present 
                 25 
                 11 
                 24 
                 35 
                 100 
                 17.1 
               
               
                   
                 invention 
               
               
                   
                 type 
               
               
                   
               
             
          
         
       
     
         [0065]      FIG. 8  shows the curves of deposition rate obtained from the results of film deposition under respective conditions. They are the results obtained on film deposition carried out at 5 rpm only by revolution but without rotation by itself. Where the structure of the present invention is used at a carrier gas flow rate of 120 SLM which is equivalent to that of the conventional structure, the curve of deposition rate extends in a lateral direction and shrinks in a longitudinal direction. This mode represents an excessively great flow velocity, which is well in line with the theory considered at the beginning of the specification. A decrease in flow rate of the carrier gas allowed the curve of deposition rate to be steep, thereby yielding a result close to that obtained by the curve of deposition rate of the conventional example at a 35 SLM flow rate of the carrier gas. In the structure of the present invention, the flow channel in a cross sectional area is about 64% of the conventional structure. Thus, it appears unusual that a similar curve of deposition rate was obtained at a flow rate of 35 SLM which was about 29% of the flow rate of the conventional structure. However, when a diffusion coefficient is taken into account, this should be a reasonable result. In the example of the present invention, the ratio of NH 3  in a carrier gas is increased. Since NH 3  has much greater in molecular weight than hydrogen, it has much smaller in diffusion coefficient than hydrogen according to Grahams&#39; law. The curve of deposition rate is dominated by the convection diffusion equation and, therefore, will vary not only by the flow velocity but also by the diffusion coefficient. In this experimental example, it is considered that a curve of deposition rate similar to a conventional one can be obtained at a smaller flow rate of the carrier gas than expected, due to a decrease in practical diffusion coefficient of the carrier gas. 
         [0066]    As described so far, according to the present invention, in order to obtain a curve of deposition rate similar to a conventional one, it is possible to reduce the carrier gas by 70% or more. Further, as apparent from the Table 1, the partial pressure of NH 3  is increased from conventional 5 kPa to 17.1 kPa, which is triple higher or more. Therefore, dissociation of nitrogen atoms from the surface of a film is suppressed to obtain a film in higher quality. 
       Experimental Example 2 
     Photoluminescence Characteristics of Multiple Quantum Well 
       [0067]    Next, the conventional type apparatus described in Example 1 and the present invention-type apparatus were used to prepare a multiple quantum well of InGaN/GaN, thereby evaluating them by referring to photo luminescence spectra. The respective film deposition conditions are shown in the Table 2 below. 
         [0000]    
       
         
               
               
               
               
               
             
               
               
               
               
               
               
               
               
               
               
             
           
               
                   
                 TABLE 2 
               
             
             
               
                   
                   
               
               
                   
                   
                 Carrier gas flow 
                 Flow rate of group III 
                 Partial 
               
               
                   
                 Growth 
                 rate (SLM) 
                 element (sccm) 
                 pressure 
               
             
          
           
               
                   
                 Structure of 
                 pressure 
                   
                   
                 Total 
                 TEG 
                 TEGa 
                 TMIn 
                 of NH 3   
               
               
                   
                 apparatus 
                 (kPa) 
                 N 2   
                 NH 3   
                 flow rate 
                 (barrier) 
                 (well) 
                 (well) 
                 (kPa) 
               
               
                   
               
               
                 a) 
                 Conventional 
                 30 
                 26 
                 24 
                 50 
                 500 
                 185 
                 200 
                 14.4 
               
               
                   
                 type 
               
               
                 b) 
                 Present 
                 30 
                 10 
                 21 
                 31 
                 416 
                 154 
                 200 
                 20.3 
               
               
                   
                 invention type 
               
               
                   
               
             
          
         
       
     
         [0068]    Under these film deposition conditions, a 4-inch size substrate was used to carry out film deposition by allowing the substrate to revolve at around 5 rpm and rotate by itself at 15 rpm.  FIG. 9  shows photo luminescence spectra obtained by the multiple quantum well. It is apparent from this drawing that the multiple quantum well prepared by the structure of the present invention has higher peak of strength by about 15% and smaller full width at half maximum (FWHM). Of course, a film with steeper in peak and thus greater strength is in higher quality. Thus, improvement in quality of the multiple quantum well may be due to a higher partial pressure of NH 3  by about 40% as shown in the Table 2. This can be realized because the use of the structure of the present invention enables to decrease a total flow rate of the carrier gas. Further, it is possible to decrease the consumption of a group III element, in addition to consumption of gas, which provides a great contribution to a reduction in the costs of film deposition. 
         [0069]    In addition, the present invention shall not be limited to the above-described examples but may be modified in various ways within a scope not departing from the gist of the present invention, including, for example, the following. 
         [0070]    (1) The shape and dimensions shown in the previously described examples are one example. The present invention may be modified in design, if necessary, within its scope and provides the same effects. 
         [0071]    (2) A material which constitutes the opposing face member  30  and the injector  40  shown in the previously described examples is one example. The present invention may be modified in design, if necessary, within its scope and provides the same effects. 
         [0072]    (3) In the previously described examples, the injector  40  is to be used. This is, however, one example, and the injector may be installed if necessary. The structure of the injector  40  is also one example, and the present invention may be modified in design if necessary. 
         [0073]    (4) In the previously described examples, the face-down type apparatus has the surface of the substrate facing downward. However, the present invention is also applicable to a face-up type apparatus in which the surface of the substrate faces upward. 
         [0074]    According to the present invention, it is possible to realize the film deposition equivalent to that realized under optimal conditions by using a conventional apparatus at a smaller flow rate of the carrier gas. It is also possible to dramatically increase a partial pressure of material gases of volatile components as compared with a conventional case. This enables to form a film which is in higher quality than a conventional film. Therefore, the present invention is also applicable to a rotation/revolution type vapor phase film-deposition apparatus and in particular applicable to the film deposition of compound semiconductor films and oxide films. 
       DESCRIPTION OF REFERENCE NUMERALS 
       [0000]    
       
           10 : reactor structure 
           20 : disk-like susceptor 
           22 : wafer holder 
           24 : isothermal plate 
           26 : supporting member 
           30 : opposing face member 
           30 A: opposing face 
           32 : opening 
           34 : recessed portion 
           34 A: recessed portion opposing face 
           35 : side wall 
           36 : raised portion 
           36 A: raised portion opposing face 
           38 : gas exhaust portion 
           40 : injector 
           42 : first injector member 
           44 : recessed portion 
           46 : raised portion 
           48 : gas introduction portion 
           48 A: through hole 
           50 : second injector member 
           52 : recessed portion 
           54 : raised portion 
           56 : gas introduction portion 
           56 A: through hole 
           60 : gas introduction portion 
           70 : opposing face member 
           72 : opening 
           74 : recessed portion 
           74 A: rectangular portion 
           74 B: fan-shaped portion 
           75 : inclined face 
           76 : raised portion 
           100 : reactor structure 
           110 : opposing face member 
           110 A: opposing face 
           120 : injector 
           122 : first injector member 
           124 : second injector member 
         W: substrate