Patent Publication Number: US-9905666-B2

Title: Trench schottky rectifier device and method for manufacturing the same

Description:
This is a divisional application of co-pending, U.S. application Ser. No. 15/360,155, filed Nov. 23, 2016, which is a divisional of U.S. Pat. No. 9,536,976, filed Nov. 13, 2015, which is a divisional of U.S. Pat. No. 9,219,170, filed Oct. 29, 2014, which is a divisional of U.S. Pat. No. 8,890,279, filed Nov. 15, 2013, which is a divisional of U.S. Pat. No. 8,618,626, filed Oct. 12, 2010, the subject matter of which is incorporated herein by reference. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to a trench Schottky rectifier device and related manufacturing method, and more particularly to a trench Schottky rectifier device with embedded doped regions. 
     BACKGROUND OF THE INVENTION 
     A Schottky diode is a unipolar device using electrons as carriers, which is characterized by high switching speed and low forward voltage drop. However, the Schottky diodes have limitation of relatively high reverse leakage current. The characteristics of the Schottky barrier are determined by the metal work function of the metal electrode, the band gap of the intrinsic semiconductor, the type and concentration of dopants in the semiconductor layer, and other factors. In contrast to the Schottky diode, a PN junction diode is a bipolar device that can pass more current than the Schottky diode. However, the PN junction diode has a forward voltage drop higher than that of the Schottky diode, and takes longer reverse recovery time due to a slow and random recombination of electrons and holes during the recovery period. 
     A Schottky rectifier device has been described in U.S. Pat. No. 6,710,418 to overcome the current leakage problem. Please refer to  FIG. 1 , a schematic diagram illustrating the Schottky rectifier device with insulation-filled trenches. The Schottky rectifier device  100  includes a heavily-doped N-type substrate  102 , a lightly-doped N-type epitaxial layer  104  overlying the substrate  102 , and a plurality of insulation-filled trenches  114  extending from the top surface of the epitaxial layer  104 . There are two P-type silicon strips  108  on sidewalls of each trench  114 . An anode electrode  110  is provided on the top surface of the epitaxial layer  104  and a cathode electrode  116  is provided on the bottom surface of the substrate  102 . The anode electrode  110  forms a Schottky contact with the underlying epitaxial layer  104 , and is in contact with the P-type silicon strips  108 . 
     In the Schottky rectifier device  100 , the Schottky contact between the anode electrode  110  and the epitaxial layer  104  results in low forward voltage drop. Furthermore, the P-type strips  108  can prevent the low accumulation threshold to reduce the current leakage problem of the Schottky rectifier device  100 . However, the P-type strips  108  occupy some areas of the Schottky contact, and thus the size of the Schottky rectifier device  100  should be enlarged to keep the equivalent area of the Schottky contact to prevent increasing the forward voltage drop and consuming more power. Therefore, an improved Schottky rectifier device with low current leakage but without increasing the size thereof is desired. There is a need of providing the improved Schottky rectifier device in order to obviate the drawbacks encountered from the prior art. 
     SUMMARY OF THE INVENTION 
     The present invention provides a trench Schottky rectifier device having low forward voltage drop and low reverse leakage current. 
     The present invention also provides a method for manufacturing a trench Schottky rectifier device having low forward voltage drop and low reverse leakage current. 
     In accordance with an aspect of the present invention, the trench Schottky rectifier device includes a substrate of a first conductivity type; a plurality of trenches formed in the substrate; and an insulating layer formed on sidewalls of the trenches. The trenches are filled with conductive structure. An electrode overlies the conductive structure and the substrate to form a Schottky contact between the electrode and the substrate. There are a plurality of doped regions of a second conductivity type formed in the substrate and located under the trenches. Each doped region and the substrate will form a PN junction to pinch off current flowing toward the Schottky contact in a reverse bias mode. 
     In accordance with another aspect of the present invention, a method for fabricating a trench Schottky rectifier device is provided. At first, a plurality of trenched are formed in a substrate of a first conductivity type. An insulating layer is formed on sidewalls of the trenches. Then, an ion implantation procedure is performed through the trenches to form a plurality of doped regions of a second conductivity type under the trenches. Subsequently, the trenches are filled with conductive structure such as poly-silicon structure or tungsten structure. At last, an electrode overlying the conductive structure and the substrate is formed. Thus, a Schottky contact appears between the electrode and the substrate. Each doped region and the substrate will form a PN junction to pinch off current flowing toward the Schottky contact to suppress the current leakage in a reverse bias mode. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above objects and advantages of the present invention will become more readily apparent to those ordinarily skilled in the art after reviewing the following detailed description and accompanying drawings, in which: 
         FIG. 1  (prior art) is a cross-sectional view schematically illustrating the conventional Schottky rectifier device; 
         FIG. 2  is a cross-sectional view illustrating a preferred embodiment of a trench Schottky rectifier device according to the present invention; 
         FIGS. 3A-3H  schematically illustrate the manufacturing method for forming the trench Schottky rectifier device of  FIG. 2 ; 
         FIG. 4  is a cross-sectional view illustrating another preferred embodiment of a trench Schottky rectifier device according to the present invention; 
         FIGS. 5A-5G  schematically illustrate the manufacturing method for forming the trench Schottky rectifier device of  FIG. 4 ; 
         FIG. 6  is a cross-sectional view illustrating a further preferred embodiment of a trench Schottky rectifier device according to the present invention; and 
         FIGS. 7A-7J  schematically illustrate the manufacturing method for forming the trench Schottky rectifier device of  FIG. 6 . 
     
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     The present invention will now be described more specifically with reference to the following embodiments. It is to be understood that other embodiment may be utilized and structural changes may be made without departing from the scope of the present invention. Also, it is to be understood that the phraseology and terminology used herein are for the purpose of description and should not be regarded as limiting. The use of “including,” “comprising,” or “having” and variations thereof herein is meant to encompass the items listed thereafter and equivalents thereof as well as additional items. Unless limited otherwise, the terms “connected,” “coupled,” and “mounted,” and variations thereof herein are used broadly and encompass direct and indirect connections, couplings, and mountings. 
     Please to  FIG. 2 , a cross-sectional view illustrating a preferred embodiment of a trench Schottky rectifier device according to the present invention. Please note that the article “a” or “an” may be used for some elements, but the number of the elements is not limited to “one”. The amount may vary with different applications. As shown in  FIG. 2 , the trench Schottky rectifier device  2  includes a substrate  20 , a plurality of trenches  21 , doped regions  22 , polysilicon structure  23 , oxide layers  210 ,  213 ,  24 , an adhesion layer and an electrode  26 . The substrate  20  includes a heavily-doped N-type silicon layer  201  and a lightly-doped N-type epitaxial layer  202 . The plurality of trenches  21  are formed in the epitaxial layer  202  and extending from the top surface of the epitaxial layer  202 . The sidewalls of the trenches  21  are covered with the oxide layers  213  and the trenches  21  are filled with the polysilicon structure  23  which protrudes from the top surface of the epitaxial layer  202 . The doped regions  22  of P-type conductivity are formed in the epitaxial layer  202  and located under the trenches  21 , and in contact with the polysilicon structure  23  at bottoms of the trenches  21 . 
     An isolation layer including the oxide layers  210  and  24  is provided to cover a portion of the epitaxial layer  202  at an inactive area of the trench Schottky rectifier device  2  and separate the trench Schottky rectifier device  2  from other devices. The electrode  26  is provided on the oxide layer  24 , the exposed epitaxial layer  202 , and the protruding polysilicon structure  23 . The electrode  26  is made of metal material, for example Al, Al alloy or other suitable metal material. An adhesion layer  25  made of Ti or TiN may be provided between the electrode  26  and the substrate  20  to enhance the bonding of the electrode  26  to the substrate  20 . According to the described structure, Schottky contacts are formed on the interface between the metal electrode  26  (or the adhesion layer  25 ) and the epitaxial layer  202 . 
     In a forward bias mode, the Schottky contacts between the metal layer  25  and the epitaxial layer  202  bring low forward voltage drop and consume less power. Furthermore, the P-type doped regions  22  and the lightly-doped N-type epitaxial layer  202  form PN junctions. In a reverse bias mode, depletion regions of the PN junctions are widened and the carrier density therein is very small. Hence, the widened depletion regions of neighboring PN junctions will hinder and pinch off the current flow under the Schottky contacts. Based on the pinch-off effect, the reverse current leakage is thus suppressed. It is to be noted that the P-type doped regions  22  are located under the trenches  21  and do not occupy the area of the Schottky contacts. Hence, it is not necessary to enlarge the size of the trench Schottky rectifier device  2  to compensate for the reduced area of the Schottky contacts. 
       FIGS. 3A-3H  illustrate a manufacturing method for forming the trench Schottky rectifier device of  FIG. 2  according to the present invention. As shown in  FIG. 3A , a stack structure including a substrate  20 , a mask oxide layer  210  and a first patterned photoresist layer  211  with a trench pattern is provided. The substrate  20  includes a heavily-doped N-type silicon layer  201  and a lightly-doped N-type epitaxial layer  202 . The mask oxide layer  210  on the substrate  20  is grown by thermal oxidation or deposition. The mask oxide layer  210  is then subjected to an etching step to partially remove the mask oxide layer  210  to expose a portion of the lightly-doped N-type epitaxial layer  202  according to the trench pattern. 
     In  FIG. 3B , the first patterned photoresist layer  211  is stripped off. Then, the epitaxial layer  202  is etched through openings of the mask oxide layer  210  to form the trenches  21  in the epitaxial layer  202 . An O 2  based thermal procedure is performed to form a thin sacrificial oxide layers  212  on sidewalls and bottoms of the trenches  21 . P-type dopants such as B ions or BF 2  are then implanted into the epitaxial layer  202  through the bottoms of the trenches  21  to form the doped regions  22  under the trenches  21 . The doped regions  22  play an important role in suppressing the leakage current as described above. 
     In  FIG. 3C , the thin sacrificial oxide layer  212  has been removed and gate oxide layers (insulating layers)  213  are formed to cover the sidewalls and the bottoms of the trenches  21 . It is to be noted that after removing the thin sacrificial oxide layers  212 , the smoothness of the surfaces of the trenches  21  are improved. The oxide layers  213  on the bottoms of the trenches  21  are further etched off to expose the doped regions  22 . 
       FIG. 3D  shows that the trenches  21  are filled with a polysilicon structure  23 . In an embodiment, a polysilicon layer is first grown to cover the structure of  FIG. 3C  by a chemical vapor deposition (CVD) procedure, and then the polysilicon layer is subjected to an etch-back procedure to remove a portion of the polysilicon layer out of the trenches  21 . It is to be noted that the polysilicon structure  23  may be a polysilicon layer with or without dopants. If an ion implantation procedure is performed after the formation of the polysilicon layer to introduce dopants such as B ions into the polysilicon layer, a thermal drive-in step or an annealing step is optionally performed to allow better diffusion of the dopants or activate the dopants. 
     In  FIG. 3E , an oxide layer  24  and a second patterned photoresist layer  214  defining the device area of the trench Schottky rectifier device  2  are sequentially formed on the structure of  FIG. 3D . The oxide layer  24 , for example, is formed from tetraethyl orthosilicate (TEOS) by a low pressure CVD (LPCVD) procedure with high deposition rate. Then, the oxide layers  24  and  210  are partially etched according to the second patterned photoresist layer  214  to expose portions of the top surface of the epitaxial layer  202  and the polysilicon structure  23 .  FIG. 3F  shows the obtained structure in which the second patterned photoresist layer  214  has been stripped off, the resultant structure is obtained as shown in  FIG. 3F . The combination of the oxide layers  210  and  24  may be considered as an isolation layer covering the inactive area of the trench Schottky rectifier device  2  to separate the trench Schottky rectifier device  2  from other devices. 
     At last, the electrode  26  is formed on the obtained structure. The adhesion layer  25  may be formed prior to the formation of the electrode  26  to enhance the bonding of the electrode  26  to the substrate  20 . The electrode  26  and the adhesion layer  25  may be formed, but not limited to, as follows. At first, a metal sputtering procedure is performed on the structure of  FIG. 3G  to form the adhesion layer  25 . Therefore, the whole wafer is blanketed by the adhesion layer  25 . In an embodiment, the adhesion layer  25  is made of Ti or TiN. Subsequently, another metal sputtering procedure is performed on the adhesion layer  25  to form the electrode metal layer  26  overlying the adhesion layer  25 . In an embodiment, the electrode metal layer  26  is made of Al or Al alloy. A rapid thermal processing (RTP) procedure may be performed after the electrode metal layer  26  is formed, so as to correct the defects resulting from the metal sputtering procedure. Then, a third patterned photoresist layer  216  is formed over the electrode metal layer  26 . Portions of the electrode metal layer and the adhesion layer  25  are etched off to form the electrode  26  according to the third patterned photoresist layer  216 . After the third patterned photoresist layer  216  is stripped off, a sintering process may be performed to enhance adhesion of the metal layer  25  to the substrate  20 , the polysilicon structure  23  and the oxide layer  24 . It is to be noted that the sintering procedure may be performed after each metal sputtering process. The resultant structure of the trench Schottky rectifier device  2  has been described with reference to  FIG. 2 . Although there are trenches  21  and doped regions  22  in the inactive area of the trench Schottky rectifier device  2  of  FIG. 2 , they are not essential components according to the present invention. 
       FIG. 4  is a cross-sectional view illustrating another preferred embodiment of a trench Schottky rectifier device according to the present invention. The trench Schottky rectifier device  3  includes a substrate  30 , a plurality of trenches  31 , doped regions  32 , metal structure  35 , oxide layers  310 ,  313 , an adhesion layer  34  and an electrode  36 . The substrate  30  includes a heavily-doped N-type silicon layer  301  and a lightly-doped N-type epitaxial layer  302 . The plurality of trenches  31  are formed in the epitaxial layer  302  and extending from the top surface of the epitaxial layer  302 . The sidewalls of the trenches  31  are covered with the oxide layers  313  and the trenches  31  are filled with the metal structure  35 . The metal structure  35  may be made of W or other suitable metal. The doped regions  32  of P-type conductivity are formed in the epitaxial layer  302  and located under the trenches  31 . The bottoms of the metal structure  35  are in contact with the doped regions  32 . 
     The oxide layer  310  is provided to cover an inactive area of the trench Schottky rectifier device  3  and separate the trench Schottky rectifier device  3  from other devices. An electrode  36  is provided on the oxide layer  310 , the exposed epitaxial layer  302 , and the metal structure  35 . The electrode  36  is made of metal material, for example Al, Al alloy or other suitable metal material. An adhesion layer  34  made of Ti or TiN may be provided between the electrode  36  and the substrate  30  to enhance the bonding of the electrode  36  to the substrate  30 . In particular, the adhesion layer  34  covers the epitaxial layer  302  and the oxide layers  310 ,  313 . According to the described structure, Schottky contacts are formed on the interface between the metal electrode  36  (or the adhesion layer  34 ) and the epitaxial layer  302 . 
     In a forward bias mode, the Schottky contacts between the metal layer  36  and the epitaxial layer  302  have advantage of less power consumption. Furthermore, PN junctions consisting of the P-type doped regions  32  and the lightly-doped N-type epitaxial layer  302  can hinder and pinch off the current flow under the Schottky contacts as explained with reference to  FIG. 2 . Based on the pinch-off effect, the reverse current leakage is thus suppressed. The embedded doped regions  32  do not narrow the Schottky contacts. Hence, it is not necessary to enlarge the size of the trench Schottky rectifier device  3  to compensate for the reduced area of the Schottky contacts. 
       FIGS. 5A-5G  illustrate a manufacturing method for forming the trench Schottky rectifier device of  FIG. 4  according to the present invention. As shown in  FIG. 5A , a stack structure including a substrate  30 , a mask oxide layer  310  and a first patterned photoresist layer  311  with a trench pattern is provided. The substrate  30  includes a heavily-doped N-type silicon layer  301  and a lightly-doped N-type epitaxial layer  302 . The mask oxide layer  310  on the substrate  30  is grown by thermal oxidation or deposition. The mask oxide layer  310  is then subjected to an etching step to partially remove the mask oxide layer  310  to expose a portion of the lightly-doped N-type epitaxial layer  302  according to the trench pattern. 
     In  FIG. 5B , the first patterned photoresist layer  311  is stripped off. Then, the epitaxial layer  302  is etched through openings of the mask oxide layer  310  to form the trenches  31  in the epitaxial layer  302 . An O2 based thermal procedure is performed to form thin sacrificial oxide layers  312  on sidewalls and bottoms of the trenches  31 . P-type dopants such as B ions or BF 2  are then implanted into the epitaxial layer  302  through the bottoms of the trenches  31  to form the doped regions  32  under the trenches  31 . The doped regions  32  and the epitaxial layer  302  will form PN junctions whose depletion regions can pinch off the leakage current in the reverse bias mode. 
     In  FIG. 5C , the thin sacrificial oxide layers  312  has been removed and gate oxide layers (insulating layers)  313  are formed to cover the sidewalls and the bottoms of the trenches  31 . The removal of the thin sacrificial oxide layers  312  improves the smoothness of the surfaces of the trenches  31 . The oxide layers  313  on the bottoms of the trenches  31  are further etched off to expose the doped regions  32 . 
     In  FIG. 5D , a hard mask layer  33 , for example a silicon nitride layer, is formed by a CVD procedure to cover the structure of  FIG. 5C . A second patterned photoresist layer  314  for defining device area of the trench Schottky rectifier device  3  is formed on the hard mask layer  33  and in the trenches  31 . Then, the uncovered hard mask layer  33  are removed by a dry etching step, and the exposed mask layer  310  is also removed by another dry etching step to expose the top surface of the epitaxial layer  302  at the device area.  FIG. 5E  shows the obtained structure in which the second patterned photoresist layer  314  has been stripped off. 
     In  FIG. 5F , the remaining hard mask layer  33  is removed, and an adhesion layer  34  made of Ti or TiN is optionally formed on the surfaces of the oxide layers  310  and  313  by a sputtering procedure to enhance the bonding of the electrode  36  to the epitaxial layer  302  and the oxide layers  310 . The adhesion layer  34  may be subjected to a rapid thermal nitridation (RTN) process to enhance the bonding effect. Subsequently, the trenches  31  are filled with the metal structure  35 , for example, made of W. In an embodiment, a metal layer such as a W layer is formed to cover the adhesion layer  34  by a CVD procedure, and then the metal layer is subjected to an etch-back procedure to remove a portion of the metal layer out of the trenches  31 . 
     At last, the electrode  36  is formed on the obtained structure. In an embodiment, a metal sputtering procedure is performed on the structure of  FIG. 5F  to form the metal layer  36  overlying the adhesion layer  34  and the metal structure  35 . In an embodiment, the metal layer  36  is made of Al or Al alloy. A rapid thermal processing (RTP) step can be performed after the metal layer  36  is formed, so as to correct the defects resulting from the metal sputtering procedure. Then, a third patterned photoresist layer  316  is formed over the metal layer  36  ( FIG. 5G ). Portions of the metal layer  36  and the adhesion layer  34  are etched off to form the electrode  36  according to the third patterned photoresist layer  316 . After the third patterned photoresist layer  316  is stripped off, a sintering procedure may be performed to enhance adhesion of the metal layer  36  (and the adhesion layer  34 ) to the substrate  30 , the metal structure  35  and the oxide layer  310 . It is to be noted that the sintering procedure may be performed after each metal sputtering procedure. The resultant structure of the trench Schottky rectifier device  3  has been described with reference to  FIG. 4 . Similarly, the trenches  31  and doped regions  32  in the inactive area of the trench Schottky rectifier device  3  of  FIG. 4  are not essential components according to the present invention. 
       FIG. 6  is a cross-sectional view illustrating a further preferred embodiment of a trench Schottky rectifier device according to the present invention. Similar to the trench Schottky rectifier device  3  of  FIG. 4 , the trench Schottky rectifier device  4  includes a substrate  40  (including a heavily-doped N-type silicon layer  401  and a lightly-doped N-type epitaxial layer  402 ), a plurality of trenches  41 , doped regions  42 , metal structure  45 , oxide layers  410 ,  413 , an adhesion layer  44  and an electrode  46 . The relevant components are not described verbosely again. In addition, the trench Schottky rectifier device  4  includes a guard ring  405  in the edge area of the substrate  40  for improving latchup immunity of the device and preventing interference between adjacent devices. The guard ring  405  may be of P-type conductivity when the substrate  40  is a N-type substrate. 
     In a forward bias mode, the trench Schottky rectifier device  4  has low forward voltage drop because of the Schottky contacts. Furthermore, in a reverse bias mode, the reverse current leakage is suppressed because of the widened depletion regions of the PN junctions consisting the P-type doped regions  42  and the N-Type epitaxial layer  402 . It is to be noted that the P-type doped regions  42  are located under the trenches  41  and do not affect the area of the Schottky contacts. 
       FIGS. 7A-7H  illustrate a manufacturing method for forming the trench Schottky rectifier device of  FIG. 6  according to the present invention. As shown in  FIG. 7A , a stack structure including a substrate  40 , a mask layer  408  and a first patterned photoresist layer  409  defining the guard ring  405  is provided. The substrate  40  includes a heavily-doped N-type silicon layer  401  and a lightly-doped N-type epitaxial layer  402 . The mask layer  408  on the substrate  40  is grown by thermal oxidation or deposition, and then subjected to an etching step to partially remove the mask layer  408  to expose a portion of the lightly-doped N-type epitaxial layer  402 . 
     In  FIG. 7B , the first patterned photoresist layer  409  has been stripped off. Then, an etching step is performed through the opening of the mask layer  408  to form a depression in the epitaxial layer  402 . Subsequently, an ion implantation procedure is performed by using the remaining mask layer  408  as a mask to introduce dopants in to the edge area of the epitaxial layer  402 , and thus the guard ring  405  is formed along the surface of the epitaxial layer  402  in the edge area. The dopants may include B ions or BF 2 , and a thermal drive-in step or an annealing step is optionally performed to allow better diffusion of the dopants or activate the dopants.  FIG. 7C  shows the obtained structure in which the mask layer  408  has been removed. 
     The subsequent steps are similar to those as described with reference to  FIGS. 5A-5G . In  FIG. 7D , the mask oxide layer  410  and a second patterned photoresist layer  411  with a trench pattern is provided. The mask oxide layer  410  is then subjected to an etching step to expose a portion of the lightly-doped N-type epitaxial layer  402  according to the trench pattern. 
     In  FIG. 7E , the second patterned photoresist layer  411  is removed. Then, the epitaxial layer  402  is etched through openings of the mask oxide layer  410  to form the trenches  41  in the epitaxial layer  402 . An O 2  based thermal procedure is performed to form the thin sacrificial oxide layer  412  on sidewalls and bottoms of the trenches  41 . P-type dopants such as B ions or BF 2  are then implanted into the epitaxial layer  402  through the bottoms of the trenches  41  to form the doped regions  42  under the trenches  41 . The doped regions  42  and the epitaxial layer  402  will form PN junctions whose depletion regions can pinch off the leakage current in the reverse bias mode. 
     In  FIG. 7F , the thin sacrificial oxide layer  412  has been removed to improve the smoothness of the surfaces of the trenches  41  and another oxide layers  413  are formed to cover the surfaces of the trenches  41 . The oxide layers  413  on the bottoms of the trenches  41  are further etched off to expose the doped regions  42 . 
     In  FIG. 7G , a hard mask layer  43 , for example a silicon nitride layer, is formed by a CVD procedure to cover the structure of  FIG. 7F . A third patterned photoresist layer  414  for defining device area of the trench Schottky rectifier device  4  is formed on the hard mask layer  43  and in the trenches  41 . Then, the uncovered hard mask layer  43  and the underlying mask oxide layer  410  are dry-etched off to expose the top surface of the epitaxial layer  402  at the device area.  FIG. 7H  shows the obtained structure in which the third patterned photoresist layer  414  has been stripped off. 
     In  FIG. 7I , the remaining hard mask layer  43  is removed, and an adhesion layer  44  made of Ti or TiN is optionally formed on the surfaces of the oxide layers  410  and  413  by a sputtering process to enhance the bonding of the electrode  46  to the epitaxial layer  402  and the oxide layers  410 . The adhesion layer  44  may be subjected to a rapid thermal nitridation (RTN) process to enhance the bonding effect. Subsequently, the trenches  41  are filled with metal structure  45 , for example, formed by a CVD procedure along with an etch-back procedure. 
     At last, the electrode  46  is formed on the resulting structure, as shown in  FIG. 7J . In an embodiment, a metal sputtering procedure is performed on the structure of  FIG. 7I  to form the metal layer  46  overlying the adhesion layer  44  and the metal structure  45 . In an embodiment, the metal layer  46  is made of Al or Al alloy. A rapid thermal processing (RTP) step can be performed to correct the defects resulting from the metal sputtering procedure. Then, a fourth patterned photoresist layer  416  is formed over the metal layer  46  to define the electrode  46 . The resultant structure of the trench Schottky rectifier device  4  has been described with reference to  FIG. 6 . 
     According to the present invention, the trench Schottky rectifier device has low forward voltage drop and rapid switching speed in the forward bias mode. Furthermore, better than the conventional Schottky rectifier device, the Schottky rectifier device according to the present invention has low reverse leakage current in the reverse bias mode due to the pinch off effect as described above. The embedded doped regions  22 ,  32  and  42  do not reduce the effective area of the Schottky contacts because they are located under the trenches  21 ,  31  and  41 . Hence, the present invention overcome the problems of the prior arts and is highly competitive. 
     While the invention has been described in terms of what is presently considered to be the most practical and preferred embodiments, 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.