Abstract:
A chemical vapor deposition reactor for depositing a thin film on at least a substrate through a reaction between a vertical input reagent gas flow and the at least a substrate is provided, in which a vertical output reagent gas flow is produced after the reaction. The reactor includes a vertical tube, at least a reaction chamber located inside the vertical tube, an input flow baffle located on the at least a reaction chamber, and at least a gas exit installed on the at least a reaction chamber for exhausting the vertical input reagent gas flow and the vertical output reagent gas flow. In addition, the substrate is located at the bottom of the at least a reaction chamber. The provided reactors allow the achievement of more efficient heating process, lower gas consumption and higher growth uniformity than the conventional reactors.

Description:
This application claims priority to Application No. 092100278 filed in China on Jan. 7, 2003. 
   FIELD OF THE INVENTION 
   This invention relates to a reactor, and more particularly to a chemical vapor deposition reactor. 
   BACKGROUND OF THE INVENTION 
   Chemical vapor deposition is a thin film deposition technique about using a method of depositing a solid product onto a chip surface from reactants by a chemical reaction in a reactor. The reactants are usually gas reactants. After decades of developments, the chemical vapor deposition has become the most important and the main deposition method in the semiconductor manufacturing process for depositing a thin film on the semiconductor elements, such as conductors, semiconductors, and dielectric materials. 
   The key equipment of the facilities for the chemical vapor deposition is the reactor, and a thin film is deposed onto a substrate therein. However, according to the relevant application, scopes, the designs for chemical vapor deposition reactors might be various. A Hydrogen Vapor Phase Epitaxy reactor, HVPE reactor, is one of the popular chemical vapor decomposition reactors. 
   The conventional HVPE reactors for growing the compound semiconductors of IV and III–V groups of the periodical table and their alloys are well-known in the industry. These reactors can be divided into three main groups according to their geometrical features. The three main groups are respectively HVPE reactors with horizontal geometry of gas flow (HG HVPE reactors), HVPE reactors with vertical geometry of gas flow (VG HVPE reactors), and HVPE reactors with closed shower head (SH HVPE reactors). 
   Please refer to  FIG. 1 , which shows a structural diagram of a prior HG HVPE reactor. As shown in  FIG. 1 , the HG HVPE reactor includes a horizontal tube  11 , a horizontal reagent gas flow  12 , a substrate  13 , and a gas heater  14 . A hydride thin film is deposited on the substrate  13  through a reaction of the horizontal reagent gas flow  12  in the HG HVPE reactor. The relevant structures and features of HG HVPE reactors are disclosed in U.S. Pat. Nos. 6,176,925, 6,177,292, 6,179,913 and 6,350,666. 
   The disadvantages of above-mentioned HG HVPE reactors include: 1. It&#39;s difficult to obtain a high efficiency of gas utilization and high growth uniformity of the thin film simultaneously. 2. In order to avoid the temperature gradients inside the horizontal tube  11 , a big gas heater  14  with high power consumption is always necessary. 3. Because it is difficult to control the temperature difference between the inside walls of the horizontal tube  11  and the substrate  13 , a deposition material is always formed on the inside walls of the HG HVPE reactor. 4. Because of the long thermal relaxation time and the changes of the gas flow rate, a Quantum Well structure, QW structure, is unable grown. 5. It is difficult to control and model the growth processes of the thin film due to the low symmetry of the HG HVPE reactor. 
   Please refer to  FIG. 2 , which shows a structural diagram of a prior VG HVPE reactor. As shown in  FIG. 2 , the VG HVPE reactor includes a vertical tube  21 , a vertical reagent gas flow  22 , a substrate  23 , and a gas heater  24 . A hydride thin film is deposited on the substrate  23  through a reaction of the vertical reagent gas flow  22  in the VG HVPE reactor. The relevant structures and features of VG HVPE reactors are disclosed in U.S. Pat. Nos. 5,980,632 and 6,086,673. 
   The disadvantages of above-mentioned VG HVPE reactors include: 1. The growth uniformity of the thin film is not yet ideal enough. 2. In order to avoid the temperature gradients inside the vertical tube  21 , a big gas heater  24  with high power consumption is still necessary. 3. Because it is still difficult to control the temperature difference between the inside walls of the vertical tube  21  and the substrate  23 , a deposition material is always formed on the inside walls of the VG HVPE reactor. 4. Because of the long thermal relaxation time and the changes of the gas flow rate, a Quantum Well structure, QW structure, is either unable grown. 
   Please refer to  FIG. 3 , which shows a structural diagram of a prior SH HVPE reactor. As shown in  FIG. 3 , the SH HVPE reactor includes a horizontal tube  31 , a vertical reagent gas flow  32 , a substrate  33 , a gas heater  34 , and a shower-type head  35 . A hydride thin film is deposited on the substrate  33  through a reaction of the vertical reagent gas flow  32  in the SH HVPE reactor. The SR HVPE reactor further includes a horizontal gas flow  36  as a buffer gas. The relevant structures and features of SH HVPE reactors are disclosed in U.S. Pat. No. 4,574,093. 
   The disadvantages of above-mentioned SH HVPE reactors include: 1. The shower-type head  35  is a non-technological design, so that the shower-type head  35  is difficultly fabricated. 2. Because it is difficult to control the temperature difference between the inside walls of horizontal tube  31  and the substrate  33 , deposition materials are always formed on the inside walls of the SH HVPE reactor and the shower-type head  35 . 
   As above-mentioned, a HVPE reactor with the abilities of high efficiency of gas utilization and high growth uniformity of thin film being able to avoid the erroneous deposition is worthy for the relevant industries. 
   Because of the technical defects described above, the applicant keeps on carving unflaggingly to develop a “CHEMICAL VAPOR DEPOSITION REACTOR”. 
   SUMMARY OF THE INVENTION 
   In accordance with one aspect of the present invention, a reactor is provided for depositing a thin film on a substrate through a reaction between an input gas and the substrate. A output gas is produced after the reaction. The reactor includes a vertical tube, at least a reaction chamber located inside the vertical tube, a plurality of baffles staggeredly arranged along the inside walls of the vertical tube, a plurality of heaters connected to the vertical tube for controlling a temperature difference between the substrate and walls of the reactor and improving a distribution of the input gas, a gas exit installed on the at least a reaction chamber for exhausting the reacted gas and an extended diffusion layer formed from a bottom of the reaction chamber to the gas exit. In addition, the substrate is located at the bottom of the at least a reaction chamber. 
   Preferably, the reactor is a hydride vapor deposition reactor. 
   Preferably, the gas exit is installed on a side wall of the at least a reaction chamber. 
   Preferably, the reactor is made of a material selected from a group consisting of steel, quartz, sapphire, and ceramics. 
   Preferably, the input gas is a mixture of HCl, GaCl, NH 3 , and Ar gases. 
   Preferably, the substrate is a sapphire substrate. 
   Preferably, the thin film is one compound semiconductor selected from a group consisting of IV group and their alloys, III–V groups and their alloys, and GaN. 
   Preferably, the reacted gas is a mixture of HCl, GaCl, Cl 2  NH 3 , and H 2  gases. 
   Preferably, the extended diffusion layer is used for increasing a utility rate of the input gas and a deposition unity. 
   Preferably, the plurality of heaters include a first gas heater and a second gas heater. 
   Preferably, the first gas heater is one of an external side wall gas heater and an internal side wall gas heater. 
   Preferably, the second gas heater is an external bottom gas heater. 
   Preferably, the second gas heater includes an input gas tube and a heater. 
   Preferably, the reaction chamber is a cylindrical chamber. 
   Preferably, the extended diffusion layer is used for transmitting the input gas to the substrate. 
   In accordance with another aspect of the present invention, a hydride vapor deposition reactor is provided for depositing a thin film on a substrate through a reaction between an input gas and the substrate. A reacted gas is produced after the reaction. The reactor includes a vertical tube with two side wall gas heaters and a bottom gas heater, a baffle staggeredly located on an inside wall of the vertical tube for extending routes of the input gas, a reaction chamber located inside the vertical tube a second baffle located on a top of the reaction chamber, and a gas exit installed on a side wall of the reaction chamber for exhausting the reacted gas. 
   Preferably, the thin film is one compound semiconductor selected from a group consisting of III–V groups and their alloys, IV groups and their alloys, and GaN. 
   Preferably, the two side wall gas heaters are a first gas heater and a second gas heater respectively located on external side walls of the vertical tube. 
   Preferably, the vertical tube further includes a Ga tank. 
   The above contents and advantages of the present invention will become more readily apparent to those ordinarily skilled in the art after reviewing the following detailed descriptions and accompanying drawings, in which: 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  shows a structural diagram of a prior HG HVPE reactor; 
       FIG. 2  shows a structural diagram of a prior VG HVPE reactor; 
       FIG. 3  shows a structural diagram of a prior SH HVPE reactor; 
       FIG. 4  shows a structural diagram of the HVPE reactor according to a preferred embodiment I of the present invention; 
       FIG. 5  shows a structural diagram of the HVPE reactor according to a preferred embodiment II of the present invention; 
       FIG. 6  shows a structural diagram of the HVPE reactor according to a preferred embodiment III of the present invention; 
       FIG. 7  shows a structural diagram of the HVPE reactor according to a preferred embodiment IV of the present invention; 
       FIG. 8  shows a structural diagram of the HVPE reactor according to a preferred embodiment V of the present invention; and 
       FIG. 9  shows a structural diagram of the HVPE reactor according to a preferred embodiment VI of the present invention. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
   The present invention will now be described more specifically with reference to the following embodiments. It is to be noted that the following descriptions of preferred embodiments of this invention are presented herein for purpose of illustration and description only; it is not intended to be exhaustive or to be limited to the precise form disclosed. 
   The present invention provides HVPE reactors with opposite direction flow geometries and extended diffusion layers. A quantum well structure can be formed on a semiconductor material in the HVPE reactor of the present invention. 
   Please refer to  FIG. 4 , which shows a structural diagram of a HVPE reactor according to the preferred embodiment I of the present invention. As shown in  FIG. 4 , the HVPE reactor includes a vertical tube  41 , a first gas heater  45 , a second gas heater  46 , a reaction chamber  47 , the diaphragm  49 , and the gas exist slit  410 . The reaction chamber  47  has a containing portion  48 . And, a substrate  43  for being deposited thereon is positioned at the lower part of the containing portion  48 . 
   The first gas heater  45  is positioned on the external side wall of the vertical tube  41 , and the second gas heater  46  is positioned at the external bottom wall of the vertical tube  41 . The reaction chamber  47  is located inside the vertical tube  41  and is a cylindrical reaction chamber. The diaphragm  49  is positioned on the top of the reaction chamber  47 , and the gas exist slit  410  is located on the internal side wail of the reaction chamber  47  with a particular distance from the substrate  43 . An extended diffusion layer  411  is formed between the gas exist slit  410  and the bottom of the reaction chamber  47 . The reaction chamber  47  is made of a material selected from a group consisting of steel, quartz, sapphire, and ceramics. The substrate  43  is a sapphire substrate. 
   The HVPE reactor of the preferred embodiment I of the present invention is used for depositing the thin film  412  on the substrate  43  by a reaction between the input reagent gas  42  and the substrate  43 . And, a reacted gas  44  is produced after the reaction. The reacted gas  44  can be exhausted through the gas exist slit  410 . 
   The input reagent gas  42  is a mixture of HCl, GaCl, NH 3 , and Ar gases. The thin film  412  is a compound semiconductor selected from a group consisting of III–V groups and their alloys, IV group and their alloys, and GaN. The reacted gas  44  is a mixture of HCl, GaCl, NH 3 , Ar, and H 2  gases. And, the second gas heater  46  is used for controlling the temperature difference between the substrate  43  and the internal side walls of the HVPE reactor. 
   On the other hand, the substrate  43  is not directly reacted with the input reagent gas  42 . The reaction is performed during the diffusion process of the input reagent gas  42  in the extended diffusion layer  411 . Meanwhile, the input reagent gas  42  is still in a gas state during the diffusion process. Because the second gas heater  46  can be used to control the temperature difference between the internal side walls of the HVPE reactor and the substrate  43 , no deposition will be formed on the internal side walls of the HVPE reactor. 
   Therefore, the advantages of the reactor according to the preferred embodiment I includes that it is not necessary to seal up the first gas heater  45  and the second gas heater  46 , because they are not directly exposed to the input reagent gas  42  and the reacted gas  44 . As above, the HVPE reactor of the present invention has a significantly smaller volume than those of the prior reactors. 
   Please refer to  FIG. 5 , which shows a structural diagram of a HVPE reactor according to the preferred embodiment II of the present invention. As shown in  FIG. 5 , the HVPE reactor includes a vertical tube  51 , a first gas heater  55 , a second gas heater  56 , a reaction chamber  57 , the diaphragm  59 , and the gas exist slit  510 . The reaction chamber  57  includes a containing portion  58 . And, a substrate  53  for being deposited thereon is positioned at the lower part of the containing portion  58 . 
   The first gas heater  55  is positioned in the vertical tube  51 . The second gas heater  56  is positioned at the external bottom wall of the vertical tube  51 . The reaction chamber  57  is located inside the vertical tube  51  and is a cylindrical reaction chamber. The diaphragm  59  is positioned on the top of the reaction chamber  57 , and the gas exist slit  510  is located on the side wall of the reaction chamber  57  with a particular distance from the substrate  53 . An extended diffusion layer  511  is formed from the gas exist slit  510  to the bottom of the reaction chamber  57 . The reaction chamber  57  is made of a material selected from a group consisting of steel, quartz, sapphire, and ceramics. The substrate  53  is a sapphire substrate. 
   The HVPE reactor of the preferred embodiment II is used for depositing a thin film  512  on the substrate  53  by a reaction between the input reagent gas  52  and the substrate  53 . And, the reacted gas  54  is produced after the reaction. The reacted gas  54  can be exhausted through the gas exist slit  510 . 
   The input reagent gas  52  is a mixture of HCl, GaCl, NH 3 , and Ar gases. The thin film  512  is a compound semiconductor selected from a group consisting of III–V groups and their alloys, IV group and their alloys, and GaN. The reacted gas  54  is a mixture of HCl, GaCl, NH 3 , Ar, and H 2  gases. And, the second gas heater  56  is used for controlling the temperature difference between the substrate  53  and the side walls of the HVPE reactor. 
   On the other hand, the substrate  53  is not directly reacted with the input reagent gas  52 . The reaction is performed during the diffusion process of the input reagent gas  52  in the extended diffusion layer  511 . Meanwhile, the input reagent gas  52  is still in a gas state during the diffusion process. Because the second gas heater  56  can be used to control the temperature difference between the side walls of the HVPE reactor and the substrate  53 , no deposition will be formed on the internal side walls of the HVPE reactor. 
   The first gas heater  55  is directly exposed to the reacted gas  54 , so that it is necessary to seal up the first gas heater  55  of the HVPE reactor of the preferred embodiment II of the present invention. Furthermore, the HVPE reactor according to the preferred embodiment II is more sensitive to the temperature change than the HVPE reactor of the preferred embodiment I. 
   Please refer to  FIG. 6 , which shows a structural diagram of a HVPE reactor according to the preferred embodiment III of the present invention. As shown in  FIG. 6 , the HVPE reactor includes a vertical tube  61 , a first gas heater  65 , a second gas heater  66 , a reaction chamber  67 , the diaphragm  69 , and the gas exist slit  610 . The reaction chamber  67  includes a containing portion  68 . And, a substrate  63  for being deposited thereon is positioned at the lower part of the containing portion  68 . 
   The first gas heater  65  is positioned on the internal side wall of the vertical tube  61 . The second gas heater  66  is positioned at the external bottom wall of the vertical tube  61 . The reaction chamber  67  is located inside the vertical tube  61  and is a cylindrical reaction chamber. The diaphragm  69  is positioned on the top of the reaction chamber  67 , and the gas exist slit  610  is located on the side wall of the reaction chamber  67  with a particular distance from the substrate  63 . An extended diffusion layer  611  is formed from the gas exist slit  610  to the bottom of the reaction chamber  67 . The reaction chamber  67  is made of a material selected from a group consisting of steel, quartz, sapphire, and ceramics. The substrate  63  is a sapphire substrate. 
   Particularly, the second gas heater  66  includes an input gas tube  612  and an internal heater  613 . The input reagent gas  614  is heated by the internal heater  613  while being flown through the input gas tube  612 . A reacted gas  615  is formed after the heated input reagent gas flow  614  reacts with the substrate  63 . The input reagent gas  614  and the reacted gas  615  are oppositely directed and thermally coupled. Because the temperature of the substrate  63  directly depends on the heated input reagent gas  614 , the temperature of the substrate  63  can be changed quickly. 
   In addition, the HVPE reactor of the preferred embodiment III of the present invention is used for depositing a thin film  616  on the substrate  63  by a reaction between the input reagent gas  62  and the substrate  63 . A reacted gas  64  is produced after the reaction. The reacted gas flow  64  can be exhausted through the gas exist slit  610 . 
   The input reagent gas  62  is a mixture of HCl, GaCl, NH 3 , and Ar gases. The thin film  616  is a compound semiconductor selected from a group consisting of III–V groups and their alloys, IV group and their alloys, and GaN. The reacted gas  64  is a mixture of HCl, GaCl, NH 3 , Ar, and H 2  gases. 
   In the preferred embodiment III, the substrate  63  is not directly reacted with the input reagent gas  62 . The reaction is performed during the diffusion process of the input reagent gas  62  in the extended diffusion layer  611 . The input reagent gas  62  is still in a gas state during the diffusion process. The second gas heater  66  is used for controlling the temperature difference between the substrate  63  and the side walls of the reactor, so that no deposition will be formed on the internal side walls of the HVPE reactor. 
   The reactors of the preferred embodiments I, II, and III of the present invention are used for depositing a thin film on single substrate, so that they are not suitable for the mass production. On the other hand, the following reactors of the preferred embodiments IV and V of the present invention are suitable for the mass production of the substrates with thin films. 
   Please refer to  FIG. 7 , which shows a structural diagram of a HVPE reactor according to the preferred embodiment IV of the present invention. As shown in  FIG. 7 , the HVPE reactor includes a vertical tube  71 , a first gas heater  75 , a second gas heater  76 , a reaction chamber  77 , the diaphragm  79 , and the gas exist slit  710 . The reaction chamber  77  includes a containing portion  78 . And, the substrates  73  for being deposited thereon are positioned at the lower part of the containing portion  78 . 
   The first gas heater  75  is positioned at the external side wall of the vertical tube  71 , and the second gas heater  76  is positioned on the external bottom wall of the vertical tube  71 . The reaction chamber  77  is located inside the vertical tube  71  and is a cylindrical reaction chamber. The diaphragm  79  is positioned on the top of the reaction chamber  77 , and the gas exist slit  710  is located on the side wall of the reaction chamber  77  with a particular distance from the substrates  73 . An extended diffusion layer  711  is formed from the gas exist slit  710  to the bottom of the reaction chamber  77 . The reaction chamber  77  is made of a material selected from a group consisting of steel, quartz, sapphire, and ceramics. The substrates  73  are sapphire substrates. 
   The HVPE reactor of the preferred embodiment IV is used for depositing the thin film  712  on each of the substrates  73  by reactions between the input reagent gas  72  and the substrates  73 . A reacted gas  74  is produced after the reaction. The reacted gas  74  can be exhausted through the gas exist slit  710 . 
   The input reagent gas  72  is a mixture of HCl, GaCl, NH 3 , and Ar gases. The thin film  712  is a compound semiconductor selected from a group consisting of III–V groups and their alloys, IV group and their alloys, and GaN. The reacted gas  74  is a mixture of HCl, GaCl, NH 3 , Ar, and H 2  gases. 
   In the preferred embodiment IV, the substrates  73  are not directly reacted with the blowing of the input reagent gas  72 . The reactions are performed during the diffusion process of the input reagent gas  72  in the extended diffusion layer  711 . The input reagent gas  72  is still in a gas state during the diffusion process. The second gas heater  76  is used for controlling the temperature difference between the substrates  73  and the side walls of the HVPE reactor, so that no deposition will be formed on the internal side walls of the HVPE reactor. 
   Please refer to  FIG. 8 , which shows a structural diagram of a HVPE reactor according to the preferred embodiment V of the present invention. As shown in  FIG. 8 , the HVPE reactor includes a vertical tube  81 , a plurality of first gas heaters  85 , a plurality of second gas heaters  86 , a plurality of reaction chambers  87 , the diaphragms  89 , and the gas exist slits  810 . Each of the reaction chambers  87  includes a containing portion  88 . And, each of the substrates  83  for being deposited thereon is positioned at the lower part of each containing portion  88 . 
   The first gas heaters  85  are positioned on the external side walls of the vertical tubes  81  respectively, and the second gas heaters  86  are positioned at the external bottom walls of the vertical tubes  81 . The reaction chambers  87  are respectively located inside the vertical tubes  81  and are cylindrical reaction chambers. The diaphragm  89  is positioned on a top of the reaction chamber  87 , and each gas exist slit  810  is located on the internal side wall of the reaction chamber  87  with a particular distance from the substrate  83 . A plurality of extended diffusion layers  811  are respectively formed from the gas exist slits  810  to the bottoms of the reaction chambers  87 . The reaction chambers  87  are made of a material selected from a group consisting of steel, quartz, sapphire, and ceramics. The substrates  83  are sapphire substrates. 
   The HVPE reactor of the preferred embodiment V of the present invention is used for respectively depositing the thin film  812  on the substrate  83  by a reaction between the input reagent gas  82  and the substrate  83 , and, the reacted gas  84  is produced after the reaction. The reacted gas  84  can be exhausted through the gas exist slit  810 . 
   The input reagent gas  82  is a mixture of HCl, GaCl, NH 3 , and Ar gases. The thin film  812  is a compound semiconductor selected from a group consisting of III–V groups and their alloys, IV group and their alloys, and GaN. The output reagent gas  84  is a mixture of HCl, GaCl, NH 3 , Ar, and H 2  gases. 
   In the preferred embodiment V, the substrates  83  are not directly reacted with the input reagent gas  82 . The reaction is performed during the diffusion process of the input reagent gas  82  in the extended diffusion layers  811 . And, the input reagent gas  82  is still in a gas state during the diffusion process. The second gas heater  86  is used for controlling the temperature difference between the substrate  83  and the side walls of the HVPE reactor, so that no deposition will be formed on the internal side walls of the HVPE reactor. 
   The reactors of the preferred embodiments I, II, III, IV, and V are the main designs of the HVPE reactors in the present invention. The following reactor of the preferred embodiment VI is an extended reactor of the preferred embodiment I. 
   Please refer to  FIG. 9 , which shows a structural diagram of a HVPE reactor according to the preferred embodiment VI of the present invention. As shown in  FIG. 9 , the HVPE reactor includes a vertical tube  91 , a first gas heater  95 , a second gas heater  914 , a third gas heater  96 , a reaction chamber  97 , the second diaphragm  99 , the first diaphragms  912 , the gas exist slit  910 , the Ga tank  913 , and the water cooled flange  915 . The reaction chamber  97  includes a containing portion  98 . And, the substrate  93  for being deposited thereon is positioned at the lower part of the containing portion  98 . 
   The first gas heater  95  is positioned on one external side wall of the vertical tube  91 , the second gas heater  914  is positioned on another external side wall of the vertical tube  91 , and the third gas heater  96  is positioned at the external bottom wall of the vertical tube  91 . The reaction chamber  97  is located inside the vertical tube  91  and is a cylindrical reaction chamber. The second diaphragm  99  is positioned on the top of the reaction chamber  97  and upon the first diaphragms  912  staggeredly arranged along the side wall of the vertical tube  91 . The gas exist slit  910  is located on the internal side wall of the reaction chamber  97  with a particular distance from the substrate  93 . An extended diffusion layer  911  is formed from the gas exist slit  910  to the bottom of the reaction chamber  97 . The reaction chamber  97  is made of a material selected from a group consisting of steel, quartz, sapphire, and ceramics. The substrate  93  is a sapphire substrate. 
   The HVPE reactor of the preferred embodiment VI of the present invention is used for depositing the thin film  916  on the substrate  93  by a reaction between the input reagent gas and the substrate  93 . The reacted gas  94  is produced after the reaction. The reacted gas  94  can be exhausted through the gas exit slit  910 . 
   The input reagent gas is a mixture of a first gas containing NH 3  and Ar gases and a second gas containing HCl and GaCl gases. The thin film  916  is a compound semiconductor selected from a group consisting of III–V groups and their alloys, IV group and their alloys, and GaN. The reacted gas  94  is a mixture of HCl, GaCl, NH 3 , Ar, and Ha gases. The first diaphragm  912  is for extending the flowing routes of the first gas  92  and the reacted gas  94 , and enhancing the thermal interaction between the first gas  92  and the reacted gas  94 . Furthermore, it is possible that the volume of the reactor can be effectively reduced by the design of first diaphragms  912 . 
   In the preferred embodiment VI, the substrate  93  is not directly reacted with the input reagent gas. The reaction is performed during the diffusion process of the input reagent gas in the extended diffusion layer  911 . The input reagent gas is still in a gas state during the diffusion process. The third gas heater  96  is used for controlling the temperature difference between the substrate  93  and the side walls of the HVPE reactor, so that no deposition will be formed on the internal side walls of the HVPE reactor. 
   As above-mentioned, the features of the HVPE reactors provided by the present invention include:
         1. The reactor has a design of an input reagent gas flow and a reacted gas flow being oppositely directed and thermally coupled. The design makes the effect of the gas heating improved effectively and allows a reactor with a smaller volume. Besides, with the ability of quick responding to the changes of the temperature and the reagent gas flowing rate, the HVPE reactors are potentially suitable for the growth of quantum well structures.   2. With the design of an extended diffusion layer, the input reagent gas flow can be reacted with the substrate in a gas state during the diffusion process, so that it is possible to enhance the utilization efficiency of the reagents and obtain a good growth uniformity of the thin film.   3. The external bottom gas heater of the HVPE reactors according to the present invention allows the control of the temperature difference between the substrate and the internal side wall of the reactor, so that no deposition is formed on the internal side walls of the HVPE reactor.   4. The reaction chamber of the present invention is a cylindrical chamber with high symmetry, so that it is easy to control the model of the deposition processes.       

   Thus, the advantages of the HVPE reactors provided by the present invention can be summarized as follows:
         1. Good deposition uniformity.   2. High efficiency of gas reagent utilization.   3. Compact design.   4. Easily controlling and modeling the deposition processes due to the high symmetry.   5. Possibility of using low power heater.   6. Possibility of growing a QW structure.   7. Possibility of suppressing the deposition on side walls of the reactor.       

   While the invention has been described in terms of what is presently considered to be the most practical and preferred embodiment, it is to be understood that the invention needs not be limited to the disclosed embodiment. On the contrary, it is intended, to cover various modifications and similar arrangements included within the spirit and scope of the appended claims which are to be accorded with the broadest interpretation so as to encompass all such modifications and similar structures.