Abstract:
An apparatus  101  for depositing a thin-film onto a surface of a substrate  113  using precursor gases G 1 , G 2  is disclosed. The apparatus  101  comprises i) a supporting device  111  for holding the substrate  113 ; and ii) a spinner  105  positioned adjacent to the supporting device  111 . Specifically, the spinner  105  includes a hub  106  for connecting to a motor, and one or more blades  201  connected to the hub  106 . In particular, the one or more blades  201  are operative to rotate around the hub  106  on a plane to drive a fluid flow of the precursor gases G 1 , G 2 , so as to distribute the precursor gases G 1 , G 2  across the surface of the substrate  113.

Description:
FIELD OF THIS INVENTION 
       [0001]    The present invention relates to an apparatus for thin-film deposition, in which precursor gases are introduced into the apparatus to deposit a thin-film onto a surface of a substrate. 
       BACKGROUND OF THE INVENTION 
       [0002]    Thin-film deposition techniques are generally used to deposit a semiconductor material onto a substrate for manufacturing integrated circuit devices or optoelectronic devices. For instance, MOCVD is a method of depositing a semiconductor material such as gallium nitride (GaN) on a substrate. The MOCVD method is performed in a reactor with a temperature-controlled environment to activate the deposition of precursor gases on a heated substrate arranged in the reactor whilst reducing the parasitic deposition of the precursor gases on unwanted areas such as on the chamber walls, which are cooler. A first precursor gas includes a Group III element such as gallium (Ga), while a second precursor gas includes a Group V element such as nitrogen (N). These precursor gases are introduced into the reactor to deposit a compound semiconductor such as GaN on a planar surface of the heated substrate. Purging gases such as nitrogen (N 2 ) and hydrogen (H 2 ) are also introduced into the reactor to minimise the deposition of the precursor gases on the unwanted areas within the reactor. Carrier gases such as N 2  and H 2  are used during the MOCVD operation to move the precursor gases towards the heated substrate. 
         [0003]    Typically, the precursor gases are introduced into the reactor in a direction perpendicular or parallel to the planar surface of the heated substrate. In order to ensure that the precursor gases chemically react on the major planar surface of the heated substrate to form the compound semiconductor, these precursor gases have to be close to each other on top of the substrate surface. One problem that arises when the precursor gases are close to each other when they are introduced into the reactor is that an undesirable mutual gas phase reaction takes place which compromises the efficiency of the precursors and consequently the quality of the compound semiconductor deposited on the substrate. 
         [0004]    Thus, it is an object of this invention to address the limitation associated with the conventional way of introducing precursor gases into a reactor among thin-film deposition techniques, and particularly among chemical vapour deposition (CVD) techniques. 
       SUMMARY OF THE INVENTION 
       [0005]    A first aspect of this invention is an apparatus for depositing a thin film onto a surface of a substrate using precursor gases. The apparatus comprises: i) a supporting device configured to hold the substrate; and ii) a spinner positioned adjacent to the supporting device. Specifically, the spinner has a hub for connecting to a motor, and one or more blades connected to the hub. In particular, the one or more blades are operative to rotate around the hub on a plane to drive a fluid flow of the precursor gases, so as to distribute the precursor gases across the surface of the substrate. 
         [0006]    By providing the spinner having one or more blades that are operative to rotate around the hub, a uniform distribution of the precursor gases can be provided across the substrate surface. Otherwise, the distribution of the precursor gases may be localized at particular regions on the substrate surface. Advantageously therefore, embodiments of the first aspect of the invention may ensure a reasonably high quality of the thin-film as deposited on the surface of the substrate. 
         [0007]    Some optional features of the invention are defined in the dependent claims. 
         [0008]    For example, the blade of the spinner may have a drive face inclined at an oblique angle to the plane for driving the distribution of the precursor gases across the surface of the substrate. This may assist in speeding up the deposition process. 
         [0009]    In addition, the hub of the spinner may include a hub inlet through which one of the precursor gases is introduced into an interior of the hub, and each of the one or more blades may also have a blade outlet through which the precursor gas is dispensed from an interior of the respective blade, wherein the interiors of the hub and the blade are in mutual fluid communication. In this way, the spinner may further act as a gas distributor to direct the precursor gas to the substrate surface. 
         [0010]    Optionally, each of the one or more blades is an airfoil to generate an additional force for drive the precursor gases towards the substrate surface. 
         [0011]    A second aspect of the invention is an apparatus for depositing a thin-film onto a surface of a substrate using precursor gases. Specifically, the apparatus comprises: i) a supporting device configured to support the substrate; ii) a plurality of sets of gas supplies, each set of the gas supplies being configured to supply precursor gases; and iii) a gas distributor configured to direct the precursor gases to the surface of the substrate. Specifically, the gas distributor has a plurality of sets of compartments, each set of compartments being configured to receive the precursor gases from the respective set of gas supplies, and each compartment having apertures through which the received precursor gases flow from the gas distributor towards the supporting device. In particular, the plurality of sets of gas supplies are operative to supply at least one of the precursor gases at controllable flow rates. Further, the apertures at each compartment of the gas distributor are evenly distributed. One of the sets of compartments has a larger volume at the centre of the gas distributor, and a smaller volume at the edge of the gas distributor, compared with the respective other set of compartments. By controlling the relative gas flow ratio between the first and second sets of compartments, thickness uniformity of the deposited thin-film can be tuned and improved. 
         [0012]    A third aspect of the invention is an apparatus is similar to the second aspect of the invention. By contrast, however, the plurality of sets of compartments of the gas distributor have a same volume. One of the sets of compartments has more apertures at the centre of the gas distributor, and fewer apertures at the edge of the gas distributor, compared with the respective other set of compartments. By controlling the relative gas flow ratio between the first and second set of compartments, thickness uniformity of the deposited thin-film can be tuned and improved. 
         [0013]    By improving the thickness uniformity of the thin-film as deposited on the substrate, embodiments of the second aspect of the invention may ensure a reasonably high quality of the thin-film as deposited on the substrate surface. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0014]    Embodiments of the invention will now be described, by way of example only, with reference to the drawings in which: 
           [0015]      FIG. 1  shows an MOCVD reactor having a gas distributor and a spinner according to its first embodiment of the invention; 
           [0016]      FIG. 2  is an isometric view of the first embodiment of the spinner when in use; 
           [0017]      FIG. 3   a  and  FIG. 3   b  are respective top and bottom views of the spinner of  FIG. 2 ; 
           [0018]      FIG. 4  is a cross-sectional view of a blade of the spinner of  FIG. 2  and shows an air-flow around the blade; 
           [0019]      FIG. 5  shows a blade of the spinner of  FIG. 2  including an inner partition; 
           [0020]      FIG. 6  shows the spinner of  FIG. 2  including a water channel; 
           [0021]      FIG. 7   a  and  FIG. 7   b  are respective top and bottom views of the spinner of  FIG. 6 ; 
           [0022]      FIG. 8  is an isometric view of a spinner according to a second embodiment of the invention; 
           [0023]      FIG. 9   a  and  FIG. 9   b  are respective top and bottom views of the spinner of  FIG. 8 ; 
           [0024]      FIG. 10   a  and  FIG. 10   b  are respective top and bottom views of a spinner according to a third embodiment of the invention; 
           [0025]      FIG. 11  shows a different configuration of a blade of the spinner of  FIG. 2 ; 
           [0026]      FIG. 12  shows a gas distributor according to its first embodiment of the invention; 
           [0027]      FIG. 13  shows a gas distributor according to its second embodiment of the invention; 
           [0028]      FIG. 14  shows susceptors for use in the MOCVD reactor of  FIG. 1  to support substrates. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0029]      FIG. 1  shows an MOCVD reactor  101  having a gas distributor  103  that is connected to one or more gas supplies, a spinner  105  according to a first embodiment for introducing one or more gases into the MOCVD reactor  101 , a gas inlet  107  that is connected to one or more gas supplies, a feedthrough  109  that connects the gas inlet  107  to the spinner  105 , and a susceptor  111  on which substrates  113  are placed. 
         [0030]    Specifically, the feedthrough  109  is connected to a hub  106  of the spinner  105 . Various channels providing mutual fluid communication are also included within the spinner  105 , the gas inlet  107 , and the feedthrough  109 , so that gases can flow from the gas inlet  107  through the feedthrough  109  to the spinner  105 , and subsequently from the spinner  105  into the MOCVD reactor  101 . The gas inlet  107  also includes a motor for driving the feedthrough  109 . When the motor is operated to drive the feedthrough  109 , the feedthrough  109  in turn drives the hub  106  of the spinner  105  to rotate the spinner  105 . 
         [0031]    During operation of the MOCVD reactor  101 , the substrates  113  are heated by a heater and rotate along with the susceptor  111 . A first precursor gas G 1  is introduced into the MOCVD reactor  101  via the spinner  105 , while a second precursor gas G 2  and purging gases G 3  are introduced via the gas distributor  103 . In particular, the precursor gases G 1 , G 2  and the purging gases G 3  are introduced into the MOCVD reactor  101  in a downward direction generally perpendicular to planar surfaces of the substrates  113 . 
         [0032]    The first precursor gas G 1  is an organometallic gas comprising a Group III element such as gallium (Ga). Examples of the first precursor gas G 1  are trimethylgallium (TMG), trimethylindium (TMI), trimethyaluminium (TMA) and their mixture. The second precursor gas G 2  is an organometallic gas comprising a Group V element such as nitrogen (N). An example of the second precursor gas G 2  is ammonia gas (NH 3 ). The purging gases G 3  assist the first and second precursor gases G 1 , G 2  to move towards the substrates  113  that are placed on the susceptor  111 . The purging gases G 3  also assist to expel the precursor gases G 1 , G 2  from the interior of the MOCVD reactor  101  to minimise contamination of its internal walls. Examples of the purging gases G 3  include nitrogen gas (N 2 ) and hydrogen gas (H 2 ). It should be appreciated that the purging gases G 3  may also be carrier gases for transporting the precursor gases G 1 , G 2  to the major planar surfaces of the substrates  113 . 
         [0033]    The spinner  105  is rotated during the operation of the MOCVD reactor  101 . The rotation of the spinner  105  accordingly changes the direction in which the precursor gases G 1 , G 2  and the purging gases G 3  proceed towards the planar surfaces of the substrates  113 , from the original downward direction generally perpendicular to the planar surfaces of the substrates  113  to a direction that is generally parallel to the planar surfaces of the substrates  113 . The rotation of the spinner  105  thus provides a uniform distribution of the precursor gases G 1 , G 2  across the planar surfaces of the substrates  113 . Without the rotation of the spinner  105 , the distribution of the precursor gases G 1 , G 2  may be localized at particular regions on the planar surfaces of the substrates  113 . Additionally, the precursor gases G 1 , G 2  may be separated from each other as much as possible before they are introduced into the MOCVD reactor  101  whilst ensuring that the precursor gases G 1 , G 2  are both present when they are just above the planar surfaces of the substrates  113  to form the compound semiconductor. Advantageously, undesirable gas phase reactions between the precursor gases G 1 , G 2  may be reduced as the precursor gases G 1 , G 2  move toward the substrates  113  in the MOCVD reactor  101 . 
         [0034]    Although  FIG. 1  shows that first precursor gas G 1  is introduced into the MOCVD reactor  101  through the spinner  105  instead of through the gas distributor  103 , it should nevertheless be appreciated that other ways of introducing the precursor gases and the purging gases G 1 -G 3  into the MOCVD reactor  101  are also feasible. For instance, the second precursor gas G 2  may be introduced into the MOCVD reactor  101  through the spinner  105 , with the first precursor gas G 1  and the purging gases G 3  being introduced through the gas distributor  103 . Alternatively, both the first and second precursor gases G 1 , G 2  may be both introduced into the MOCVD reactor  101  through the spinner  105 , with the purging gases G 3  being solely introduced through the gas distributor  103 . Yet another way involves introducing all the precursors and purging gases G 1 -G 3  through the gas distributor  103  into the MOCVD reactor  101 , with no gas being introduced through the spinner  105 . In this particular instance, the spinner  105  may be a solid structure. In addition, the purging gases may not be needed if the gas distributor  103  introduces at least one of the first and second precursor gases G 1 , G 2  into the MOCVD reactor  101 . 
         [0035]      FIG. 2  is an isometric view of the spinner  105  when in use. The spinner  105  includes four elongate blades  201   a - d  connected to the hub  106 . It can be seen from  FIG. 2  that each of the elongate blades  201   a - d  defines a generally thin and flat structure. In particular, the blades  201   a - d  are mutually diverging and orthogonally spaced around the hub  106 . The blades  201   a - d  also include respective blade channels  203   a - d  having inlets  207   a - d  through which a gas can be introduced and outlets  209   a - d  located at the base of the blades  201   a - d  through which the introduced gas can exit. 
         [0036]    The feedthrough  109  also includes a gas channel  205  having an inlet through which a gas can be introduced from a gas supply and an outlet through which the introduced gas can exit. The exited gas from the feedthrough  109  then enters the hub  106  through a hub inlet  208 . Since the hub  106  of the spinner  105  is generally hollow, there is thus a fluid communication through the gas channel  205  of the feedthrough  109 , the hub  106 , and the blade channels  203   a - d  of the blades  201   a - d . This accordingly allows the first precursor gas G 1  to flow unimpeded from the feedthrough  109  to the blades  201   a - d  through the hub  106  of the spinner  105 , before being introduced into the MOCVD reactor  101 . 
         [0037]    From  FIG. 2 , it can also be seen that the thickness of the blades  201   a - d  generally decreases and tapers towards respective edge portions  211   a - d  to form corresponding wedge portions. However, it should be appreciated that it is merely preferable but not essential that each of the blades  201   a - d  include a corresponding wedge portion. Alternatively, an elongated structure having flat parallel faces may instead be used to construct each of the blades  201   a - d.    
         [0038]    The spinner  105  is configured to rotate on a plane in a circumferential direction around the hub  106 , whereby the wedge portions  211   a - d  define leading edges of the blades  201   a - d  and their corresponding opposite edges define trailing edges of the blades  201   a - d  during rotation. Accordingly, the blades  201   a - d  of the spinner  105  are configured to rotate in an anti-clockwise circumferential direction around the hub  106  when viewed from the top of the spinner  105  in  FIG. 2 . 
         [0039]      FIG. 3   a  and  FIG. 3   b  are top and bottom views of the spinner  105  of  FIG. 2  respectively. It can be seen from  FIG. 3   a  that the hub  106  includes the hub inlet  208  for connecting with the gas channel  205  of the feedthrough  109  in such a way as to allow fluid communication. However, the underside of the hub  106  is completely sealed as shown in  FIG. 3   b  so that the first precursor gas G 1  flows from the hub  106  to each of the blades  201   a - d  of the spinner  105 . 
         [0040]      FIG. 4  is a cross-sectional view of a particular blade  201   a  of the spinner  105  of  FIG. 2  when viewed along line B-B′ as indicated in  FIG. 3   b . It is seen that the underside of the blade  201   a  is inclined at an oblique angle to the plane on which the blade  201   a  rotates. Accordingly, the inclined underside of the blade  201   a  provides a driving force on the fluid gases during rotation, whereby the fluid gases are made to flow from the leading edge to the trailing edge of the blade  201   a . A laminar fluid flow is therefore generated along the top and bottom surfaces of the blade  201   a  from the leading edge to the trailing edge as the blade  201   a  rotates. More specifically, the underside of the blade  201   a  is inclined at different angles to form a kink  401 . This increases the corresponding volume of the blade channel  203   a.    
         [0041]    It should be appreciated that the other three blades  201   b - d  of the spinner  105  is also identical to the blade  201   a  shown in  FIG. 4 . Thus, laminar fluid flows are similarly generated along the top and bottom surfaces of these blades  201   b - d  from the respective leading edges to the trailing edges as they rotate. 
         [0042]    Although the precursor gases G 1 , G 2  and the purging gases G 3  are introduced into the MOCVD reactor  101  in the downward direction that is generally perpendicular to the planar surfaces of the substrates  113  during operation, the driving forces provided by the structure of the blades  201   a - d  alter the flow direction of the precursor gases G 1 , G 2  and the purging gases G 3  to create a laminar gas flow next to the top and bottom surfaces of the blades  201   a - d  when the spinner  105  rotates. This ensures that the precursor gases G 1 , G 2  meet to chemically react on top of the wafer surface, even though they are separated far from each other when they are introduced into the MOCVD reactor  101 . By separating the precursor gases G 1 , G 2  far from each other, any undesirable gas phase reaction between them may be significantly reduced. This advantageously improves the precursor efficiency and the quality of the compound semiconductor deposited on the substrate  113 . 
         [0043]    Optionally, each of the blades  201   a - d  may include an inner partition.  FIG. 5  shows a cross-sectional view of the blade  201   a  with an inner partition  501  arranged along a length of the blade  201   a , which thereby divides the blade channel  203   a  into first and second compartments  505 ,  507 . The inner partition  501  specifically includes a slit opening  503  along the length of the blade  201   a  through which the first precursor gas G 1  can flow from the first compartment  505  to the second compartment  507 , before the first precursor gas G 1  subsequently exits the second compartment  507  from the outlet  209   a  into the MOCVD reactor  101 . 
         [0044]    Without the inner partition  501  in each of the blades  201   a - d , most of the first precursor gas G 1  may tend to be introduced into the MOCVD reactor  101  through the proximal ends of the blades  201   a - d  nearest to the hub  106  compared with their distal ends furthest from the hub  106 . This consequently leads to an uneven distribution of the first precursor gas G 1  in the MOCVD reactor  101  along each length of the blades  201   a - d.    
         [0045]    By providing the inner partition  501  in each of the blades  201   a - d , the slit opening  503  which is significantly smaller than the outlet  209   a -prevents most of the first precursor gas G 1  from exiting the blades  201   a - d  through their proximal ends and ensures that sufficient amount of the first precursor gas G 1  exits through the distal ends of the blades  201   a - d . This accordingly ensures a more even distribution of the first precursor G 1  in the MOCVD reactor  101  along the length of the blades  201   a - d.    
         [0046]    Referring to  FIG. 5 , it is also seen that the surfaces of the blade  201   a  are inclined at respective angles α, β and γ with respect to the plane on which the blade  201   a  rotates. Preferably, that the range of a may be between 10-60°, the range of β between 5-45°, and the range of γ between 45-135°. 
         [0047]    Optionally, the spinner  105  and the feedthrough  109  may further include a water channel  220  arranged within the interiors of the hub  106  and the blades  201   a - d  for cooling the spinner  105  during use, as shown in  FIG. 6 . The water channel  220  includes a water inlet  222  through which cooling water can be introduced into the water channel  220  from a water supply, and a water outlet  224  through which the cooling water can be discharged from the water channel  220  and returned to the water supply for re-cooling. Advantageously, the water channel  220  adapts the spinner  105  for compatibility in high-temperature MOCVD processes. 
         [0048]      FIG. 7   a  and  FIG. 7   b  are top and bottom views of the spinner  105  of  FIG. 6  respectively. It can be seen from  FIG. 7   a  that both the water inlet  222  and the water outlet  224  of the water channel  220  are positioned at the hub  106 . Like the hub  106  of the spinner  105  without the water channel  220 , the underside of the hub  106  is completely sealed as seen from  FIG. 3   b  so that the first precursor gas G 1  flows from the hub  106  to each of the blades  201   a - d  of the spinner  105 . 
         [0049]      FIG. 8  shows a spinner  600  according to a second embodiment of the invention. The spinner  600  is largely similar to the spinner  105  of the first embodiment. For instance, the spinner  600  includes a hub  606  for operative connection to a motor. The spinner  600  also includes four elongate blades  601   a - d  connected to the hub  606 , which are mutually diverging and angularly spaced orthogonally around the hub  606 . The blades  601   a - d  also include respective edge portions defining wedge portions, and the blades  601   a - d  are configured to rotate such that these wedge portions form corresponding leading edges. 
         [0050]    However, the hub  606  of the spinner  600  in the second embodiment comprises four hub inlets  608   a - d  for fluid communication with respective gas channels  605   a - d  of a similar feedthrough  609 , instead of comprising just a single hub inlet  208  in the case of the spinner  105  according to the first embodiment. Moreover, there is no fluid communication among different blade channels of the blades  601   a - d . Thus, the feedthrough  609  may be connected to different gas supplies for supplying different fluid gases into the MOCVD reactor  101 . For instance, both the first and second precursor gases G 1 , G 2  may be introduced into the MOCVD reactor  101  through adjacent blades  601   a - d  of the spinner  600 . Alternatively, the precursor gases G 1 , G 2 , and the purging gases G 3  may all be introduced into the MOCVD reactor  101  through the blades  601   a - d  of the spinner  600 . 
         [0051]      FIG. 9   a  and  FIG. 9   b  are respective top and bottom views of the spinner  600  of  FIG. 8 . It is seen from  FIG. 9   a  that the hub  606  includes the respective hub inlets  608   a - d  for connecting with the corresponding gas channels  605   a - d  of the feedthrough  609  in such a way as to allow fluid communication. Like the hub  106  of the spinner  105  according to the first embodiment, the underside of the hub  606  is completely sealed as seen from  FIG. 9   b  so that the precursor gases G 1 , G 2  and/or the purging gases G 3  flow from the hub  606  to each of the blades  601   a - d  of the spinner  600 . 
         [0052]    Of course, it should be appreciated that the feedthrough  609  may be connected to a single gas supply that supplies any one of the precursor gases G 1 , G 2  and the purging gases G 3  to the MOCVD reactor  101 . 
         [0053]      FIG. 10   a  and  FIG. 10   b  are respective top and bottom views of a spinner  800  according to a third embodiment of the invention. The spinner  800  of the third embodiment is also largely similar to the spinner  105 ,  600  of the first and second embodiments. For instance, the spinner  800  includes four elongate blades  801   a - d  connected to a hub  806 . In particular, the blades  801   a - d  are mutually diverging and orthogonally spaced angularly around the hub  806  about which the blades  801   a - d  rotate. The blades  801   a - d  also include blade channels with respective outlets  809   a - d  at the base of the blades  201   a - d  through which any introduced gas can exit. 
         [0054]    In contrast with the spinners  105 ,  600  of the first and second embodiments, it can be seen from  FIG. 10   b  that the respective outlets  809   a - d  of the blades  801   a - d  are arranged mid-way between the leading and trailing edges of the blades  801   a - d  as they rotate, instead of being arranged at the trailing edges of the blades  801   a - d  as in the spinners  105 ,  600  according to the first and second embodiments. Furthermore, two parallel rows of outlets are provided between the respective leading and trailing edges of the blades  801   a - d.    
         [0055]      FIG. 11  shows a different configuration of a blade  1101  of the spinner  105 . The blade  1101  is similar to the previous blade  201   a  as earlier described, except in respect of its outlets  1103  through which the precursor gas or the purging gas can flow into the MOCVD reactor  101 . In the configuration of the previous blade  201   a , the outlet  209   a  is located at the base of the blade  201   a . Thus, the precursor gas or purging gas can be directed towards the substrate surface. In contrast with the previous blade  201   a , however, the outlets  1103  of the blade  1101  are arranged at its side. Accordingly, the precursor gas or the purging gas is discharged in a direction that is generally parallel to the substrate surface. Such a configuration of the blade may thereby reduce fluid disturbance when the MOCVD reactor  101  is in use, compared with that of the previous blade  201   a.    
         [0056]      FIG. 12  shows a plan view of an embodiment of a gas distributor  1200 , which is usable in the MOCVD reactor  101 . The gas distributor  1200  is configured to direct the precursor gases G 1 , G 2  and/or the purging gases G 3  towards the substrate surface in the MOCVD reactor  101 . In particular, the interior of the gas distributor  1200  is partitioned into various sets of compartments  1202   a - b ,  1204   a - b ,  1206   a - b ,  1208   a - b  with seals provided between different sets of the compartments  1202   a - b ,  1204   a - b ,  1206   a - b ,  1208   a - b  to prevent mutual fluid communication. In addition, the gas distributor  1200  has apertures  1201  which are evenly distributed at the base of the compartments  1202   a - b ,  1204   a - b ,  1206   a - b ,  1208   a - b  through which the fluid gases can pass through. 
         [0057]    However, the interior of the gas distributor  1200  is not partitioned evenly, and therefore, the compartments  1202   a - b ,  1204   a - b ,  1206   a - b ,  1208   a - b  have different internal volumes. In particular, the gas distributor  1200  is partitioned in such a way that the compartments  1202   a ,  1204   a ,  1206   a ,  1208   a  have a larger concentration of apertures  1201  at their outer edges compared with the adjacent compartments  1202   b ,  1204   b ,  1206   b ,  1208   b . The compartments  1202   a ,  1204   a ,  1206   a ,  1208   a  also have a smaller concentration of apertures  1201  at their centres compared with the adjacent compartments  1202   b ,  1204   b ,  1206   b ,  1208   b.    
         [0058]    In use, the various sets of compartments  1202   a - b ,  1204   a - b ,  1206   a - b ,  1208   a - b  are connected to separate gas supplies to receive various fluid gases. Specifically, the compartments  1202   a - b  receive the first precursor gas G 1 , the compartments  1204   a - b  receive the second precursor gas G 2 , and the compartments  1206   a - b ,  1208   a - b  receive the purging gases G 3 . More specifically, two separate sets of gas supplies are provided—a first set for supplying the first and second precursor gases G 1 , G 2  and the purging gases G 3  to the compartments  1202   a ,  1204   a ,  1206   a  and  1208   a  respectively, and a second set for supplying the first and second precursor gases G 1 , G 2  and the purging gases G 3  to the compartments  1202   b ,  1204   b ,  1206   b  and  1208   b  respectively. 
         [0059]    If the thickness of the film deposited on the substrate  113  is thicker at its centre than at its outer edge, the flow rate of the gas supply connected to the compartment  1202   a —which receives the first precursor gas G 1 —may be increased relative to the flow rate of the gas supply connected to the corresponding compartment  1202   b . This is because the deposit growth of the semiconductor component on the substrate  113  is most sensitive to the distribution of the first precursor gas G 1  in the MOCVD reactor  101 . Since the compartment  1202   a  has a larger concentration of apertures  1201  at its outer edge compared with the corresponding compartment  1202   b , the gas distributor  1200  is thus able to compensate the non-uniformity of the thickness of the deposited film on the substrate  113 . 
         [0060]    However, if the thickness of the deposited film is thicker at its outer edge than at its centre of the substrate  113 , the flow rate of the gas supply connected to the compartment  1202   b  may be increased relative to the flow rate of the gas supply connected to the compartment  1202   a . Since the compartment  1202   b  has a larger concentration of apertures  1201  at its centre compared with the corresponding compartment  1202   a , the gas distributor  1200  is thus able to compensate the non-uniformity of the thickness of the deposited film on the substrate  113 . 
         [0061]    It should be appreciated that the flow rates of each of the first and second set of gas supplies connected to the compartments  1202   a - b ,  1204   a - b ,  1206   a - b ,  1208   a - b  may be appropriately adjusted so that the gas distributor  1200  better ensures the thickness uniformity of the deposited substrate film, and advantageously improves the quality of the deposited film on the substrate. 
         [0062]      FIG. 13  shows another gas distributor  1300  according to a second embodiment. Like the previous gas distributor  1200 , the interior of the gas distributor  1200  is partitioned into various sets of compartments  1302   a - b ,  1304   a - b ,  1306   a - b ,  1308   a - b  with seals provided between different sets of the compartments  1302   a - b ,  1304   a - b ,  1306   a - b ,  1308   a - b  to prevent fluid communication. 
         [0063]    In use, the various sets of compartments  1302   a - b ,  1304   a - b ,  1306   a - b ,  1308   a - b  are connected to separate gas supplies to receive various gases. Specifically, the compartments  1302   a - b  receive the first precursor gas G 1 , the compartments  1304   a - b  receive the second precursor gas G 2 , and the compartments  1306   a - b ,  1308   a - b  receive the purging gases G 3 . More specifically, two separate sets of gas supplies are provided—a first set for supplying the first and second precursor gases G 1 , G 2  and the purging gases G 3  to the compartments  1302   a ,  1304   a ,  1306   a  and  1308   a  respectively, and a second set for supplying the first and second precursor gases G 1 , G 2  and the purging gases G 3  to the compartments  1302   b ,  1304   b ,  1306   b  and  1308   b  respectively. 
         [0064]    However, unlike the previous gas distributor  1200 , the compartments  1302   a - b ,  1304   a - b  of the present gas distributor  1300  have the same internal volume. The compartments  1306   a - b  and the compartments  1308   a - b  also have the same volume. Moreover, the apertures  1301  at the base of each of the compartments  1302   a - b ,  1304   a - b  are not evenly distributed. Instead, there is a higher concentration of apertures  1301  at the outer edges of the compartments  1302   a ,  1304   a  compared with the outer edges of the corresponding compartments  1302   b ,  1304   b . There is also a higher concentration of apertures  1301  at the centres of the compartments  1302   b ,  1304   b  compared with the centres of the corresponding compartments  1302   a ,  1304   a.    
         [0065]    If the thickness of the deposited film is thicker at its centre than at its outer edge, the flow rate of the gas supply connected to the compartment  1302   a  may be increased relative to the flow rate of the gas supply connected to the compartment  1302   b . Since the compartment  1302   a  has a larger concentration of apertures  1301  at its outer edge compared with the corresponding compartment  1302   b , the gas distributor  1200  is thus able to compensate the non-uniformity of the thickness of the deposited film on the substrate  113 . 
         [0066]    However, if the thickness of the deposited film is thicker at its outer edge than at its centre, the flow rate of the gas supply connected to the compartments  1302   b  may be increased relative to the flow rate of the gas supply connected to the compartment  1302   a . Since the compartment  1302   b  has a larger concentration of apertures  1301  at its centre compared with the corresponding compartment  1302   a , the gas distributor  1300  is thus able to compensate for the non-uniformity of the thickness of the deposited film on the substrate  113 . 
         [0067]    It should be appreciated that each of the flow rates of the first and second set of gas supplies connected to the compartments  1302   a - b ,  1304   a - b  may be appropriately controlled so that the gas distributor  1300  better ensures the thickness uniformity of the deposited substrate film, and advantageously improves the quality of the deposited film. 
         [0068]      FIG. 14  shows the three susceptors  1401  that are usable in the MOCVD reactor  101  of  FIG. 1 . Each susceptor  1401  carries a number of substrates  113  and rotates when in use. By rotating the susceptors  1401 , any difference in the thickness of the film deposited on the substrates  113  can be compensated, thereby improving the uniformity of the thickness of the deposited film. This further improves the quality of the deposited film on the substrates  113 . 
         [0069]    It should be appreciated that other variations of the components of the MOCVD reactor  101  may be included without departing from the scope and spirit of this invention. For instance, although it has been described that embodiments of the spinner each has four mutually divergent blades that are angularly spaced orthogonally around the spinner hub, other embodiments of the spinner may instead either just have a single blade, or they may have any number of blades. In addition, although GaN has been described as the thin-film material deposited on the surfaces of the substrates  113 , other material forming the Group III/V compound group such as Gallium Arsenide (GaAs) or those forming the Group II/VI compound group such as Zinc Oxide (ZnO) may also be used. Furthermore, different embodiments of the spinner and the gas distributor herein described may also be used in other deposition techniques such as chemical vapour deposition (CVD), atomic layer deposition (ALD), and hydride vapour phase epitaxy (HVPE).