Abstract:
A gallium nitride substrate is originally grown above a silicon substrate. The present invention easily separates the gallium nitride substrate from the silicon substrate. And the separation is done with a simple etching so that the cost is low.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention relates to a manufacturing method; more particularly, relates to obtaining a gallium nitride (GaN) substrate easily separated from a silicon (Si) substrate. 
       DESCRIPTION OF THE RELATED ARTS 
       [0002]    GaN materials have been attracted for short wavelength light-emitting diodes (LED), laser diodes, high-power electronic devices, etc. The technique for growing the GaN material is applied on sapphire substrate or silicon carbide (SiC) substrate nowadays. However, the sapphire substrate is not conductive and has a poor heat dissipation so that the efficiency of GaN based devices is hard to be improved greatly. And, regarding the SiC substrate, it is too expensive to meet financial benefits. Hence, a new trend is to grow GaN material on a Si substrate, a gallium arsenide (GaAs), etc.; and this technique is a main technique to obtain a large-size GaN material or GaN substrate. 
         [0003]    However, the crystal types, the lattice arrangements, the lattice lengths and the thermal expansion coefficients between GaN and Si are different, although cost can be greatly reduced by growing the GaN material on a Si substrate. Therefore, when growing GaN, many lattice defects happen to the GaN material obtained and its critical thickness is thin. But, in order to be used as a GaN substrate, the GaN material must have few lattice defects to grow thicker. Consequently, a few prior arts are used to reduce lattice defects with selective growing methods for GaN material to grow on Si substrates. 
         [0004]    As shown in  FIG. 3A  to  FIG. 3C , a first prior art is proclaimed by S. Tanaka, etc., where GaN is grown on a Si substrate. A silicon oxide (SiO 2 ) layer  32  is deposited on a Si substrate  31  at first. Then, a periodic ridge structure of SiO 2  mask  33  is obtained from the SiO 2  layer  32  by an etching of a lithography with exposing a surface of silicon crystals outside. Then a GaN bulk layer  34  is grown on the surface of silicon crystals. Because GaN can not be grown on a SiO 2  surface, GaN is grown on two lateral surfaces of SiO 2  masks  33  to obtain GaN crystals with few lattice defects. Yet, a shortcoming still exists. That is, because lattices of GaN and Si do not match, the GaN material puts much stress on the Si substrate so that it is hard to grow a thick GaN layer to fabricate a GaN substrate with a big size. 
         [0005]    As shown in  FIG. 4A  and  FIG. 4B , a second prior art is proclaimed by T. M. Katona, etc. A Si substrate is etched into a Si ridge structure to obtain a stripe patterned silicon substrate  41  at first. Then a GaN bulk layer  42  is grown on an upper surface of the stripe patterned silicon substrate  41  together with being grown on the lateral surfaces. One of its drawbacks include that GaN crystals can even be grown at the bottom of the Si ridge structure providing few selections for crystal growth. The same shortcoming for the first prior art is also included in the drawbacks of the second prior art. The GaN material puts much stress on the Si substrate too so that a break in the GaN crystal may occurs when fabricating a GaN bulk layer of a big size. 
         [0006]    The above two prior arts both fabricate GaN substrates, but not GaN substrates of big sizes. Hence, the prior arts do not fulfill users&#39; requests on actual use. 
       SUMMARY OF THE INVENTION 
       [0007]    The main purpose of the present invention is to separate a GaN substrate from a Si substrate with a saved cost through etching a dielectric layer. 
         [0008]    To achieve the above purpose, the present invention is a method for manufacturing single crystalline GaN material substrate, comprising steps of: (a) obtaining a Si substrate; (b) overlaying a dielectric layer on the Si substrate; (c) overlaying a Si crystal layer on the dielectric layer; (d) overlaying a mask layer on the Si crystal layer; (e) processing a lithography to the mask layer to form a patterned mask layer; (f) etching the Si crystal layer until stopping at the dielectric layer to form a Si crystal island; (g) removing the patterned mask layer; (h) growing a GaN material on the Si crystal island to form a structure of a GaN substrate; and (i) applying an etching solution to the structure of the GaN substrate to separate the GaN substrate from the Si substrate to etching the dielectric layer, where the dielectric layer is made with SiO 2  or silicon nitride (SiN); the mask layer is made of a polymer, SiO 2  or SiN; the etching in step (f) is a wet etching or a dry etching; the GaN material in step (h) is GaN, aluminum gallium nitride (AlGaN), indium gallium nitride (InGaN) or aluminum gallium indium nitride (AlGaInN); and the etching solution is made with SiO 2 , hydrofluoric acid (HF) or phosphoric acid (H 3 PO 4 ). Accordingly, a novel method for manufacturing single crystalline GaN material substrate is obtained. 
     
     
       BRIEF DESCRIPTIONS OF THE DRAWINGS 
         [0009]    The present invention will be better understood from the following detailed description of the preferred embodiment according to the present invention, taken in conjunction with the accompanying drawings, in which 
           [0010]      FIG. 1  is the view showing the flow chart of the preferred embodiment according to the present invention; 
           [0011]      FIG. 2A  to  FIG. 2I  are the views showing the structures in step (a) to step (i); 
           [0012]      FIG. 3A  to  FIG. 3C  are the views showing the structures of the first prior art; and 
           [0013]      FIG. 4A  and  FIG. 4B  are the views showing the structures of the second prior art. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0014]    The following description of the preferred embodiment is provided to understand the features and the structures of the present invention. 
         [0015]    Please refer to  FIG. 1  and  FIG. 2A  to  FIG. 2I , which are a view showing a flow chart and views showing structures in step (a) to step (i) of a preferred embodiment according to the present invention. As shown in the figures, the present invention is a method for manufacturing single crystalline gallium nitride (GaN) material substrate, comprising the following steps: 
         [0016]    (a) Obtaining a Si substrate  11 : A silicon (Si) substrate  21  is obtained. 
         [0017]    (b) Overlaying a dielectric layer on the Si substrate  12 : A dielectric layer  22  is overlaid on the Si substrate  21 , where the dielectric layer  22  is made of silicon oxide (SiO 2 ) or silicon nitride (SiN). At first, an ion-implantation of oxygen atoms having high energy is implanted into the Si substrate  21  at a default depth; then a rapid temperature annealing is processed to combine the oxygen atoms and original silicon atoms of the Si substrate  21  to obtain the dielectric layer  22 . 
         [0018]    (c) Overlaying a Si crystal layer on the dielectric layer  13 : A Si crystal layer  23  is overlaid on the dielectric layer  22 . 
         [0019]    (d) Overlaying a mask layer on the Si crystal layer  14 : A mask layer  24  is overlaid on the Si crystal layer  23 , where the mask layer  24  is made of a polymer, SiO 2  or SiN. 
         [0020]    (e) Forming a patterned mask layer  15 : The mask layer  24  is processed with a lithography to form a patterned mask layer  24   a , where the lithography is a photolithography, an electron-beam lithography or a focus-ion-beam lithography. 
         [0021]    (f) Forming a Si crystal island  16 : The Si crystal layer  23  is processed with an etching to form a Si crystal island  23   a ; and the etching is stopped at the dielectric layer  22 , where the etching is a dry etching or a wet etching. 
         [0022]    (g) Removing the mask layer  17 : The patterned mask layer  24   a  is removed. 
         [0023]    (h) Forming a GaN substrate  18 : A GaN material is grown on the Si crystal island  23   a  to form a structure of a GaN substrate  24 , where the GaN material is GaN, aluminum gallium nitride (AlGaN), indium gallium nitride (InGaN) or aluminum gallium indium nitride (AlGaInN); and the GaN material is grown on the Si crystal island  23   a  through a molecular beam epitaxy, a metalorganic vapor phase epitaxy or a hydride vapor phase epitaxy. 
         [0024]    (i) Separating the GaN substrate from the Si substrate  19 : An etching solution is applied to the structure of the GaN substrate  25  to etch the dielectric layer  22  so that the GaN substrate  25  is separated from the Si substrate  21 . Therein, the etching solution is made with SiO 2  etching solution, hydrofluoric acid (HF) or phosphoric acid (H 3 PO 4 ). 
         [0025]    To sum up, the present invention is a method for manufacturing single crystalline gallium nitride material substrate, where a separation procedure is greatly simplified with a saved cost through a simple etching. 
         [0026]    The preferred embodiment herein disclosed is not intended to unnecessarily limit the scope of the invention. Therefore, simple modifications or variation is belonging to the equivalent of the scope of the claims and the instructions disclosed herein for a patent are all within the scope of the present invention.