Abstract:
In a method of manufacturing a semiconductor device, trench sections are formed on a side of one of opposing surface portions of a substrate. At least a part of each of the trench sections is covered by a power supply metal layer which is formed on the one surface portion of the substrate. The substrate is fixed to a support such that the one surface of the substrate fits to the support. A chip is separated from the substrate using the trench sections. A conductive film is formed on side surface portions of the chip and the other surface portion of the chip. Then, the chip is separated from the support.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    The present invention relates to a method of manufacturing a semiconductor device that has side wall metal layers.  
           [0003]    2. Description of the Related Art  
           [0004]    Most semiconductor devices used for mobile-communication and satellite-communication are available in the form of high-speed, high-performance small MMICs. The MMIC is composed of active elements such as field effect transistors and bipolar transistors and passive elements such as capacitors and inductors. In such an MMIC, radiation of heat generated from elements and connection to the ground potential are important for the high circuit performance. In the MMIC using a GaAs semiconductor substrate, a metal ground layer is formed on the back surface of the substrate and the elements are formed on the front surface of the substrate.  
           [0005]    As disclosed in Japanese Laid Open Patent Application (JP-A-Heisei 7-5832), a surface pattern is connected to a metal ground layer by side wall metal layers provided on the side walls of a chip or via-holes formed to penetrate the substrate. The metal ground layer functions as a so-called “plated heat sinks” (hereinafter, to be referred to as “PHS”) to radiate heat generated by the active elements. The via-holes and device-separating trenches can be easily formed in the MMIC using such a GaAs substrate by means of reactive ion etching using a sulfuric acid-based etchant or chlorine-based etchant.  
           [0006]    In recent years, researches and development have been conducted to provide electronic devices or light-emitting devices that use nitride-based III-V group compound semiconductor (GaN-based semiconductor) composed mainly of GaN. The GaN-based semiconductor are superior to the conventional GaAs-based field effect transistors in saturation electron mobility and a break-down voltage, and the GaN-based semiconductor would be effective for a high frequency field effect transistor and a high power field effect transistor. Such GaN-based semiconductor is usually grown on a sapphire substrate or a SiC substrate by means of chemical vapor deposition (CVD) or molecular beam epitaxy (MBE).  
           [0007]    Conventionally, trenches are formed by a scriber or a dicing saw in the surface of the substrate which is a chemically stable substrate such as a sapphire substrate or a SiC substrate, and the substrate is broken using the trenches, as disclosed in Japanese Laid Open Patent Application (JP-A-Heisei 11-126923). By this method, the sapphire substrate can be separated into chips, but it is difficult to form metal layers on side walls of the chip.  
           [0008]    It may be possible to form a metal ground layer on the surface of the substrate and to carry out mechanical dicing from the back of the substrate such that the metal ground layer is exposed. In this case, however, side walls of the metal ground layer are exposed only. For this reason, there would be a case that the power cannot be stably supplied from the metal ground layer due to dirt or scars in a metal plating process. In such a case, side wall metal layers would fail to have a uniform thickness or a desired shape. As a result, the MMIC cannot provide desired characteristics, and the product yield of the MMIC would be inevitably low.  
           [0009]    In conjunction with the above description, a method of manufacturing a semiconductor device is disclosed in Japanese Laid Open Patent Application (JP-A-Showa 63-276276). In this reference, a semiconductor substrate is adhered to a support plate. The semiconductor substrate has a source electrode, a drain electrode and a gate electrode through an insulating film in a front surface and an electrode layer at a back surface. The insulating film in a scribe region of the semiconductor substrate is selectively removed and then the semiconductor substrate is selectively etched using the remained insulting film as a mask so that the electrode layer is exposed. A metal layer is formed to connect the source electrode and the electrode layer and the semiconductor substrate is separated.  
           [0010]    Also, a microwave monolithic integrated circuit is disclosed in Japanese Laid Open Patent Application (JP-A-Heisei 3-58534). In this reference, a plurality of microwave monolithic integrated circuits are formed on a main surface of a semi-insulative compound substrate. Via-holes are formed between the adjacent integrated circuits to penetrate the substrate. A ground conductor of the integrated circuit is led to a back surface of the substrate through the via-hole. The substrate is separated into the integrated circuits by breaking the semiconductor along the via-holes.  
           [0011]    Also, a method of manufacturing a semiconductor device is disclosed in Japanese Laid Open Patent Application (JP-A-Heisei 6-5880). In this reference, a high frequency, large output FET, a gate electrode ( 2 ), a source electrode ( 3 ), and a drain electrode ( 4 ) are formed on the main surface of a semi-insulative GaAs substrate ( 1 ) and covered by an insulating film ( 5 ). After the main surface of the semi-insulative GaAs substrate ( 1 ) is fixed to a support plate  12  by using wax ( 13 ), the substrate is made thin at the back side to have the thickness of several tens of micrometers. Next, a protection film ( 14 ) is deposited on the back surface of the thinned substrate. Via-holes ( 7 ) are formed using as a mask a protection film pattern ( 14   a ) which has been aligned with the source electrode. The protection film pattern is removed and a metal layer ( 8 ) is formed on the entire back surface of the substrate and then a heat radiation electrode ( 9 ) is formed by a gold (Au) plating method.  
           [0012]    Also, a method of manufacturing a compound semiconductor device is disclosed in Japanese Laid Open Patent Application (JP-A-Heisei 6-338522). In this reference, a plurality of circuit elements are formed on a main surface of a semi-insulative substrate. The main surface of the substrate is etched so as to form grooves for separating the substrate into chips. The substrate is adhered to a support plate at the side of main surface. The back surface side of the substrate is grinded until the grooves are exposed. A metal layer is deposited on the entire back surface of the substrate so as to allow the chips to be held. The substrate is peeled from the support plate and the metal layer is cut to dice the substrate into the chips.  
           [0013]    Also, a method of manufacturing a semiconductor device is disclosed in Japanese Laid Open Patent Application (JP-A-Heisei 7-66384). In this reference, an active element is formed on the main surface of a semiconductor substrate. A via-hole opening mask for a ground electrode of the active element and a heat radiation hole opening mask in a region directly below the active element are on the back surface of the substrate such that the via-hole opening mask is larger than the heat radiation hole opening mask in size. The back surface of the substrate is etched using the via-hole opening mask and the heat radiation hole opening mask until the ground electrode of the active element is exposed. At this time, a heat radiation hole does not penetrate the substrate. A metal layer is formed on the back surface of the substrate.  
         SUMMARY OF THE INVENTION  
         [0014]    Therefore, an object of the present invention is to provide means for forming side wall metal layers on a semiconductor element made from a substrate that can hardly be processed by chemical reactions, thereby to improve the characteristics of an MMIC and raise the yield thereof.  
           [0015]    In an aspect of the present invention, a method of manufacturing a semiconductor device is attained by (a) forming trench sections on a side of one of opposing surface portions of a substrate, wherein at least a part of each of the trench sections is covered by a power supply metal layer which is formed on the one surface portion of the substrate; by (b) fixing the substrate to a support such that the one surface of the substrate fits to the support; by (c) separating a chip from the substrate using the trench sections; by (d) forming a conductive film on side surface portions of the chip and the other surface portion of the chip; and by (e) separating the chip from the support.  
           [0016]    Here, the (a) forming step may include cutting the surface portion of the substrate to form the trench sections. In this case, the (c) separating step may be attained by cutting the substrate from the other surface portion of the substrate to the trench section. Alternatively, the (c) separating step may be attained by grinding the other surface portion of the substrate; and by cutting the grinded substrate from the other surface portion to the trench section.  
           [0017]    Also, the (a) forming step may be attained by cutting the one surface portion of the substrate to form first trench portions; by forming the power supply metal layer to cover the one surface portion of the substrate and a surface of each of the first trench portions; and by cutting the first trench portions to form second trench sections so that the trench sections are formed. In this case, the (c) separating step may be attained by grinding the other surface portion of the substrate such that the second trench portions are exposed  
           [0018]    Also, the (a) forming step may be attained by forming a peripheral film in a peripheral portion of the chip on the one surface portion of the substrate to form the trench sections. In this case, the (c) separating step may be attained by cutting the substrate from the other surface portion of the substrate to the trench sections. Alternatively, the (c) separating step may be attained by grinding the other surface portion of the substrate; and by cutting the grinded substrate from the other surface portion of the substrate to the trench section.  
           [0019]    Also, the (a) forming step may be attained by forming a peripheral film in a peripheral portion of the chip on the one surface portion of the substrate to form first trench portions; by forming the power supply metal layer to cover the one surface portion of the substrate and a surface of each of the first trench portions; and by cutting the first trench portions to form second trench sections so that the trench sections are formed. In this case, the (c) separating step may be attained by grinding the other surface portion of the substrate such that the second trench portions are exposed.  
           [0020]    Also, the (b) fixing step may further include filling a material soluble to a solvent in the trench section.  
           [0021]    Also, when the conductive film includes a first conductive film and a second conductive film, the (d) forming step may be attained by (f) forming the first conductive film on side surface portions of the chip and the other surface portion of the chip; and by (g) forming the second conductive film on the first conductive film. In this case, the first conductive film may be formed by a sputtering method or a vapor deposition method, and the second conductive film may be formed by a plating method. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0022]    [0022]FIGS. 1A to  1 F are cross-sectional views showing a method of manufacturing a semiconductor device, according to a first embodiment of the present invention;  
         [0023]    [0023]FIGS. 2A to  2 E are cross-sectional views showing a method of manufacturing a semiconductor device, according to a second embodiment of the present invention;  
         [0024]    [0024]FIGS. 3A to  3 F are cross-sectional views showing a method of manufacturing a semiconductor device, according to a third embodiment of the present invention; and  
         [0025]    [0025]FIGS. 4A to  4 E are cross-sectional views for explaining a method of manufacturing a semiconductor device, according to a fourth embodiment of the present invention. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0026]    Hereinafter, a method of manufacturing a semiconductor device of the present invention will be described with reference to the attached drawings. Nonetheless, the present invention is not limited to the embodiments described below.  
         [0027]    [0027]FIGS. 1A to  1 F are cross-sectional views showing a semiconductor device in a manufacturing according to the first embodiment of the present invention. Referring to FIGS. 1A to  1 F, the components identical or similar are designated at the same reference numerals. Once described in detail, each component will not be described again or will be described briefly.  
         [0028]    As shown in FIG. 1A, a substrate  1  made of sapphire is prepared. Components such as field effect transistors (not shown), transmission lines (not shown) and capacitors (not shown) are formed on the substrate  1 . Device separating trenches  2  are made in the first main surface  1   a  of the substrate  1  by use of a mechanical apparatus such as a dicing saw. The trenches  2  have a depth of about 20 to 150 μm and a width of about 100 to 400 μm.  
         [0029]    Next, a metal layer  3  is formed on the region including the trenches  2  by use of a known film-forming method such as sputtering or vapor deposition. The metal layer  3  is made of electrically conductive metal such as Platinum (Pt) or gold (Au) and used for supplying power in a metal plating process. Then, a photoresist layer  4  soluble to organic solvents is applied to cover the metal layer  3  in the trenches  2  so that the substrate surface becomes flat.  
         [0030]    Next, as shown in FIG. 1B, the substrate  1  is bonded or fixed to a support  5  such as a quartz substrate, a sapphire substrate or an Si substrate by use of wax  6  such that the first main surface  1   a  is contact the support  5 . Subsequently, the substrate  1  is subjected to a mechanical polishing process to polish or grind the second main surface of the substrate  1   b , until the substrate becomes thin to the extent shown by the broken line in FIG. 1B, but not exposing the trenches  2 .  
         [0031]    Next, as shown in FIG. 1C, trenches  7  are cut by a dicing saw from the second main surface  1   b  of the thinned substrate  1 . The trenches  7  thus cut reach the trenches  2  at least. The trenches  7  may be deep to reach the photoresist  4  as shown in FIG. 1C.  
         [0032]    Thereafter, as shown in FIG. 1D, the photoresist  4  exposed in the process of forming the trenches  7  is washed away with an organic solvent. In this way, the surface  3   a  of the metal layer  3  in each trench  2  is exposed.  
         [0033]    Next, as shown in FIG. 1E, a lower metal layer  8  is formed on the second main surface  1   b  of the substrate  1  to cover the surfaces of the trenches  7 . The lower metal layer  8  is made of an electrically conductive metal such as Platinum (Pt) or gold (Au). As a result, the metal layer  8  is formed such that the metal layer  8  extends from the second main surface  1   b  of the substrate  1  to the exposed surface  3   a  of the metal layer  3 .  
         [0034]    The lower metal layer  8  can be formed by a film-forming method such as a sputtering method or a vapor deposition method. If the sputtering method is employed, the sputtered particles will easily reach the interior of each trench  2  formed in the first main surface  1   a  of the substrate  1 . This facilitates the forming of a metal film that continuously extends from the lower metal layer  8  provided on the second main surface  1   b  of the substrate  1  to the exposed surface  3   a  of the metal layer  3 .  
         [0035]    Then, a gold film of 20 μm to 50 μm in thick is plated to reach the metal layer  3  by using the lower metal layer  8 . Thus, the side wall metal layers  9  and a PHS layer or ground layer  10  are formed.  
         [0036]    Finally, as shown in FIG. 1F, the wax  6  is solved, and the support  5  is removed. Thus, a chip, i.e., a semiconductor device having side wall metal layers and the PHS layer is manufactured.  
         [0037]    It should be noted that the grinding process is carried out but it is not always necessary.  
         [0038]    In the first embodiment described above, the trenches  2  are formed in the first main surface  1   a  of the substrate  1 , and the trenches  7  in the second main surface  1   b  of the substrate  101 . Alternatively, a second trench may be formed in the substrate to extend from the trench formed in the first main surface  1   a  of the substrate  1 .  
         [0039]    A method of manufacturing a semiconductor device using the alternative method of forming trenches according to the second embodiment of the invention will be described with reference to FIGS. 2A to  2 E. In FIGS. 2A to  2 E, the components identical or similar are designated at the same reference numerals. Once described in detail, each component will not be described again or will be described briefly.  
         [0040]    [0040]FIG. 2A to  2 E are cross-sectional views showing the semiconductor device in the manufacturing method in the second embodiment of the present invention.  
         [0041]    As shown in FIG. 2A, a substrate  101  made of sapphire is prepared. The components such as field effect transistors (not shown), transmission lines (not shown) and capacitors (not shown) are formed on the first main surface  101   a  of the substrate  101 . First device-separating trenches  102   a  are formed in the first main surface  101   a  of the substrate  101  by use of a mechanical device such as a dicing saw. The first trenches  102   a  have a depth of about 20 to 150 μm and a width of about 100 to 400 μm.  
         [0042]    Subsequently, a metal layer  103  is formed on at least the region including the trenches  102   a  by use of a known film-forming method such as a sputtering method or a vapor deposition method. The metal layer  103  is made of an electrically conductive metal such as Platinum (Pt) and gold (Au) and used to supply the power in the plating process. Subsequently, second device-separating trenches  102   b  are cut in the substrate  101 , to extend from the first trenches  102   a  to the inside of the substrate  101 . Then, a photoresist layer  104  soluble to organic solvents is applied to fill the first trenches  102   a  and the second trenches  102   b.    
         [0043]    Next, as shown in FIG. 2B, the substrate  101  is bonded or fixed to a support  105  such as a quartz substrate, a sapphire substrate or an Si substrate at the first main surface  101   a  by use of wax  106 . Subsequently, the substrate  101  is subjected to a mechanical polishing process to polish or grind the second main surface  101   b  of the substrate  101 , until the substrate  101  becomes thin to the extent shown by the broken line FIG. 2B. Thus, the second trenches  102   b  are exposed.  
         [0044]    Next, as shown in FIG. 2C, the photoresist  104  exposed in the process of rendering the substrate  101  thin is washed away with an organic solvent. In this way, the surface  102   c  of the metal layer  103  in each first trench  102   a  and the second trench  102   b  are exposed.  
         [0045]    Next, as shown in FIG. 2D, a lower metal layer  108  is formed on the second main surface  101   b  of the substrate  101  to cover the second trenches  102   b  and the exposed surface  102   c  of the metal layer  103 . The lower metal layer  108  is made of an electrically conductive metal such as Platinum (Pt) or gold (Au). The lower metal layer  108  is formed such that the lower metal layer  108  extends from the second main surface  101   b  of the substrate  101  to the exposed surface  102   c  of the metal layer  103 .  
         [0046]    The lower metal layer  108  can be formed by a film-forming method such as a sputtering method or a vapor deposition method. If the sputtering method is employed, the sputtered particles will easily move into the trenches  102   a  and  102   b  made in the first main surface  101   a  of the substrate  101 . This facilitates the forming of the lower metal layer  108  that continuously extends from the lower metal layer  108  provided on the second main surface  101   b  of the substrate  101  to the exposed surface  102   c  of the metal layer  103 .  
         [0047]    Then, a gold film of 20 μm to 50 μm in thick is plated to reach the metal layer  103 , by using the lower metal layer  108 . The side wall metal layers  109  and a PHS layer or ground layer  110  as the upper metal layer are formed.  
         [0048]    Finally, as shown in FIG. 2E, the wax  106  is solved, and the support  105  is removed. Thus, a chip, i.e., a semiconductor device is manufactured.  
         [0049]    In the second embodiment, the metal layer  103  is formed after the first device-separating trenches  102   a  have been made. Alternatively, the metal film  103  may be formed after the second device-separating trenches  102   b  have been made.  
         [0050]    If this alternative process is employed, the metal layer  103  is already formed on the side walls of each trench  102   b  when the lower metal layer  108  is formed. Therefore, it is possible to form a metal film that continuously extends from the second main surface  101   b  of the substrate  101  to the exposed surface  102   c  of the metal layer  103 . Thus, the side wall metal layers  109  and the PHS layer  110  can be later formed in higher uniformity than otherwise.  
         [0051]    In the first and second embodiments, the substrate  1  or  101  is processed and the device-separating trenches  2  or  102  are formed: Alternatively, projections may be formed on the first main surface of the substrate and the spaces between the projections may be used as device-separating trenches.  
         [0052]    [0052]FIGS. 3A to  3 F are cross-sectional views showing a semiconductor device in the manufacturing method employing this alternative method of making trenches in the third embodiment of the present invention. The third embodiment will be described with reference FIGS. 3A to  3 F. In FIGS. 3A to  3 F, the components identical or similar are designated at the same reference numerals. Once described in detail, each component will not be described again or will be described briefly.  
         [0053]    As shown in FIG. 3A, a substrate  201  made of sapphire is prepared. Field effect transistors (not shown), transmission lines (not shown) and capacitors (not shown) are formed in the substrate  1 . A thick gold layer is plated on a peripheral region surrounding the chip region (not shown) that is provided in the first main surface  201   a  of the substrate  201 . The gold layer is processed to form a plurality of projections  211 . The space between any two adjacent projections  211  is used as a first device-separating trench  212 . The projections  211  are about 20 μm to 50 μm in tall. The gap between any two adjacent projections  211  (i.e., the width of the trench  212 ) is about 100 μm to 400 μm. A metal layer  203  is formed on the region including the first device-separating trenches  212  by use of a known method such as a sputtering method or a vapor deposition method. The metal layer  203  is made of an electrically conductive metal such as platinum or gold and is used to supply the power in the metal plating process. Then, a photoresist layer  204  soluble to organic solvents is applied to fill the first device-separating trenches  212 .  
         [0054]    Next, as shown in FIG. 3B, the substrate  201  is bonded or fixed to a support  205  such as a quartz substrate, a sapphire substrate or an Si substrate at the first main surface  201   a  by use of wax  206 . Subsequently, the substrate  201  is subjected to a mechanical polishing process to polish or grind the back surface or second main surface  201   b  of the substrate, until the substrate  201  becomes thin to the extent shown by the broken line in FIG. 3B.  
         [0055]    Next, as shown in FIG. 3C, second device-separating trenches  207  are formed in the second main surface  201   b  of the substrate  201  by use of a mechanical device such as a dicing saw. The second trenches  207  are at least so deep as to reach the first device-separating trenches  212 . In the third embodiment, the second trenches  207  are just as deep, reaching the photoresist  204 , as is shown in FIG. 3C.  
         [0056]    Next, as shown in FIG. 3D, those parts of the photoresist layer  204  exposed when the second trenches  207  are formed, are solved with an organic solvent and removed. The surfaces  212   a  of the first trenches  212  made of the metal layer  203  are exposed.  
         [0057]    Next, as shown in FIG. 3E, a lower metal layer  208  is formed on the entire second main surface  201   b  including the second trenches  207  of the substrate  201  by a film-forming method. The lower metal layer  208  is made of an electrically conductive metal such as platinum or gold. The lower metal layer  208  covers the surfaces  212   a  of the first device-separating trenches  212  of the metal layer  203 .  
         [0058]    The lower metal layer  208  can be formed by a film-forming method such as a sputtering method or a vapor deposition method. If the sputtering method is employed, the sputtered particles will easily move into the second trenches  207  and to the exposed surface  212   a  of the metal layer  203 . This facilitates the forming of a metal film that continuously extends from the second main surface  201   b  of the substrate  201  to the metal layer  203 .  
         [0059]    Subsequently, a gold layer having the thickness of 20 μm to 50 μm is plated as an upper metal layer to reach the metal layer  203 , thereby forming side wall metal layers  209  and a PHS layer or ground layer  210   
         [0060]    Finally, as shown in FIG. 3F, the wax  206  is solved, and the support  205  is removed. Thus, a chip, i.e., a semiconductor device is manufactured.  
         [0061]    In the third embodiment, the metal layer  203  is formed after the projections  211  have been formed. Alternatively, the metal layer used to supply power in the plating process for forming the projections  211  can be used as the metal layer  203 . The process of forming the metal layer  203  can be omitted to simplify the method of manufacturing a semiconductor device.  
         [0062]    In the third embodiment, the projections  211  are provided on the first main surface  201   a  of the substrate  201 , and the gap between any two adjacent projections  211  is used as a first device-separating trench  212 . Further, the second device-separating trenches  207  are formed in the second main surface  201   b  of the substrate  201 . Alternatively, the second device-separating trenches may be formed in the bottom of one first device-separating trench  212 , i.e., a gap between two projections  211 .  
         [0063]    A method of manufacturing a semiconductor device, using this alternative method of making trenches according to the fourth embodiment of the present invention will be described with reference to FIGS. 4A to  4 E. In FIGS. 4A to  4 E, the components identical or similar are designated at the same reference numerals. Once described in detail, each component will not be described again or will be described briefly.  
         [0064]    As shown in FIG. 4A, a substrate  301  made of sapphire is prepared. Components such as field effect transistors (not shown), transmission lines (not shown), capacitors (not shown) and specific patterns are formed in the substrate  1 . A thick gold layer is plated on a peripheral region surrounding the chip region (not shown) that is provided in the first main surface  301   a  of the substrate  301 . The gold layer is processed to form a plurality of projections  311 . The space between any two adjacent projections  311  is used as a first device-separating trench  312 . The projections  311  are about 20 μm to 50 μm in tall. The gap between any two adjacent projections  311  (i.e., the width of the trench  312 ) is about 100 μm to 400 μm.  
         [0065]    A metal layer  303  is formed on the region including the first device-separating trenches  312  by use of a known method such as a sputtering method or a vapor deposition method. The metal layer  303  is made of an electrically conductive metal such as platinum or gold, and used to supply the power in the metal plating process.  
         [0066]    Then, second device-separating trenches  302  are made in the bottoms of first device-separating trenches  312 . Thereafter, a photoresist layer  304  soluble to organic solvents is applied to fill the first device-separating trenches  312  and the second device-separating trenches  302 .  
         [0067]    Next, as shown in FIG. 4B, the substrate  301  is bonded or fixed to a support  305  such as a quartz substrate, a sapphire substrate or an Si substrate at the first main surface  301   a  by use of wax  306 . Subsequently, the substrate  301  is subjected to a mechanical polishing process to polish or grind the back surface or second main surface of the substrate  301 , until the substrate  301  becomes thin to the extent shown by the broken line in FIG. 4B.  
         [0068]    Next, as shown in FIG. 4C, those parts of the photoresist  304  exposed when the substrate  301  is made thinner is solved with an organic solvent and removed. The surfaces  312   a  of the first trenches  312  formed of the metal layer  303  are exposed.  
         [0069]    Next, as shown in FIG. 4D, a lower metal layer  308  is formed on the entire second main surface  301   b  of the substrate  301  by a film-forming method. The lower metal layer  308  is formed of an electrically conductive metal such as platinum or gold. The lower metal layer  308  is continuous to extend from the second main surface  301   b  of the substrate  301  to the metal layer  303 . The lower metal layer  308  can be formed by a film-forming method such as a sputtering method or a vapor deposition method. If the sputtering operation is employed, the sputtered particles will easily move into the second trenches  302  and to the exposed surface  312   a  of the metal layer  303 . This facilitates the forming of a metal film that continuously extends from the lower metal layer  308  on the second main surface  301   b  of the substrate  301  to the metal layer  303 .  
         [0070]    Next, as shown in FIG. 4D, a gold layer having the thickness of 20 μm to 50 μm as an upper metal layer is plated on the second main surface  301   b  and side walls of the substrate  301  to reach the metal layer  303 . Thus, side wall metal layers  309  and a PHS layer or ground layers  310  are formed.  
         [0071]    Finally, as shown in FIG. 4E, the wax  306  is solved, and the support  305  is removed. Thus, a chip, i.e., a semiconductor device is manufactured.  
         [0072]    In the fourth embodiment, the metal layer used to supply power in the plating process for forming the projections  311  can be used as the metal layer  303  in the same way as in the third embodiment. The process of forming the metal layer  303  can be omitted to simplify the method of manufacturing a semiconductor device.  
         [0073]    In this embodiment, the metal layer  303  is formed after the projections  311  have been formed. Alternatively, the metal layer  303  may be formed after the second trenches  302  have been made in the first trenches  312 . If this is the case, the metal layer  303  is already provided on the surfaces of the second trenches  302  before the lower metal layer  308  is formed. A metal layer extending from the second main surface  301   b  of the substrate  301  to the exposed surface  312   a  of the metal layer  303  can thus be formed on the second main surface  301   b  of the substrate  301 . This enhances the uniformity of the plating that will be performed later.  
         [0074]    In the third and fourth embodiments, the gaps between the projections  211  or  311  are used as the first device-separating trenches  212  or  312 . Hence, the metal layer  203  or  303 , which is provided in the first device-separating trenches  212  or  312 , contacts the surface of the substrate  201  or  301 . Therefore, the metal layer  203  or  303  has a better surface condition than in the first and second embodiments in which the device-separating trenches  2  or  102  are made by a mechanical process. It follows that the layer formed by a plating process on the metal layer  203  or  303  has higher uniformity than in the first and second embodiments.  
         [0075]    As has been described in detail, trenches are made in, or projections are provided on, the first main surface of a substrate having a semiconductor layer, in the method of manufacturing a semiconductor device according to the present invention. Thus, when the substrate is bonded to the support at the first main surface, and a gap is provided between the support and the metal layer formed in each trench.  
         [0076]    When the second trenches are made in the second main surface of the substrate and the lower metal layer is formed on the second main surface by a film-forming method such as sputtering, the lower metal layer is deposited on the side walls and exposed surface of the metal layer. A uniform layer can therefore be plated and can serve as side walls and a PHS layer or ground layer.  
         [0077]    A metal layer can be formed directly on that surface of the substrate which is not mechanically processed, particularly in the method in which projections are formed on the main surface of the substrate and a gap between any two adjacent projections is used as a device-separating trench. The metal layer therefore has a good surface condition. The layer plated on the metal layer has higher uniformity than in the case where the metal layer has not good surface condition.  
         [0078]    In the method in which projections are formed on the main surface of the substrate, the metal layer used for supplying power to form the projections by plating can be used. The process of forming the metal layer can be omitted. This simplifies the method of manufacturing a semiconductor device.