TWI594443B - Shottcky diode structure and method for forming the same - Google Patents

Description

Schottky diode structure and formation method of Schottky diode structure

The present invention relates to a Schottky diode structure and a method of forming a Schottky diode structure.

Schottky Diode is a Schottky Contact that uses a metal to contact a semiconductor substrate. Since there are no minority carriers in the metal, the characteristics of the Schottky diode are the majority of its current system. Produced by the movement of carriers (ie electrons). Most carriers are injected into the conduction band of the metal by the semiconductor passing through the junction. Since the process does not involve the combination of the majority carrier and the minority carrier (random reaction and takes a long time), the Schottky diode stops conducting. The speed will be faster than the PN junction diode, and the low turn-on voltage drop of the Schottky diode. These characteristics allow the Schottky diode to quickly switch between conduction and non-conduction. It does not cause excessive time delays and is therefore widely used in electronic devices.

In order to further enhance the performance of the Schottky diode, the Schottky diode system is improved by the semiconductor substrate because the switching speed of the Schottky diode is related to the barrier of the Xiaoji contact. The doping concentration reduces the energy barrier of the Xiaoji contact to increase its switching speed. However, the doping concentration that can be achieved by the current semiconductor material doping technology is difficult to further increase. Therefore, how to reduce the barrier height of the Xiaoji contact is an important issue that is currently required.

In view of this, the present invention proposes a Schottky diode structure and a method of forming a Schottky diode structure.

In one embodiment, the Schottky diode structure includes a semiconductor substrate, an epitaxial layer, a first metal germanide layer, a second metal germanide layer, a first metal layer, and a second metal layer. The semiconductor substrate and the epitaxial layer have the same conductivity type. The semiconductor substrate comprises an upper surface and a lower surface. The epitaxial layer covers the upper surface and is formed with a plurality of convex portions and a plurality of concave portions. The top surface and the upper surface of each convex portion have a first vertical distance, and the bottom surface and the upper portion of each concave portion There is a second vertical distance between the surfaces, the first vertical distance being in the range of 0.1 μm to 50 μm and the second vertical distance being in the range of 0.099 μm to 49.99 μm. The first metal telluride layer and the second metal telluride layer are respectively formed on the epitaxial layer and the lower surface of the semiconductor substrate. The first metal layer and the second metal layer respectively contact the first metal telluride layer and the second metal germanide layer.

In one embodiment, the lower surface of the semiconductor substrate is also formed with a plurality of convex portions and a plurality of concave portions.

In an embodiment, the top surface of the convex portion formed on the lower surface has a third vertical distance between the top surface and the upper surface, and the plurality of concave portions formed on the lower surface and the upper surface have a fourth vertical distance. The ratio of the four vertical distances to the third vertical distance is in the range of 0.99 to 0.99999.

In one embodiment, the material of the semiconductor substrate comprises germanium, gallium nitride or tantalum carbide.

In one embodiment, the ratio of the aforementioned second vertical distance to the first vertical distance is between 0.99 and 0.9998.

In one embodiment, the aforementioned third vertical distance is in the range of 1 μm to 1000 μm, and the fourth vertical distance is in the range of 0.99 μm to 999.99 μm.

In one embodiment, the distance between two adjacent convex portions of the epitaxial layer, the distance between two adjacent concave portions located in the epitaxial layer, and the distance between two adjacent convex portions on the lower surface of the semiconductor substrate And the distance between two adjacent recesses on the lower surface is in the range of 0.01 μm to 20 μm.

In one embodiment, the method for forming a Schottky diode structure includes forming an epitaxial layer on an upper surface of a semiconductor substrate; etching the epitaxial layer to form a plurality of protrusions and a plurality of recesses, and top surfaces of the protrusions Having a first vertical distance from the upper surface, each recess having a second vertical distance from the upper surface, the first vertical distance being between 0.1 μm and 50 μm, and the second vertical distance being between 0.099 μm and Between the range of 49.99 μm; forming a first metal telluride layer on the epitaxial layer; forming a first metal layer contacting the first metal telluride layer; forming a second metal germanide layer on the lower surface of the semiconductor substrate; and forming a The second metal layer contacts the second metal telluride layer.

In one embodiment, before forming the second metal layer on the lower surface of the semiconductor substrate, the lower surface of the semiconductor substrate is etched to form a plurality of protrusions and a plurality of recesses on the lower surface.

In one embodiment, the top surface formed on the lower surface has a third vertical distance between the top surface and the upper surface, and the plurality of recesses formed on the lower surface have a fourth vertical distance from the upper surface. In the step of etching the lower surface of the semiconductor substrate, the wet etching process and the dry etching process are performed so that the third vertical distance is in the range of 1 μm to 1000 μm, and the fourth vertical distance is in the range of 0.99 μm to 999.99 μm. between.

In summary, according to an embodiment of the Schottky diode structure of the present invention, the epitaxial layer has convex portions and concave portions such that the Schottky contact system is non-flat and enhances contact between the metal telluride layer and the metal layer. The area, in this way, reduces the contact resistance of the Shoji contact and thus the performance of the Schottky diode. Moreover, the manufacturing cost of the process can be reduced by forming the recesses and protrusions by the etching process instead of by the reticle.

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a schematic cross-sectional view showing an embodiment of a Schottky diode structure in accordance with the present invention. Referring to FIG. 1 , the Schottky diode includes a semiconductor substrate 11 , an epitaxial layer 12 , and two metal telluride layers (referred to as a first metal telluride layer 15 and a second metal germanide layer 16 respectively for convenience of description). And two metal layers (referred to as first metal layer 13 and second metal layer 14 for convenience of description). The first metal telluride layer 15 and the second metal germanide layer 16 are formed on the epitaxial layer 12 and the semiconductor substrate 11, respectively. The first metal layer 13 covers the epitaxial layer 12, the epitaxial layer 12 covers the semiconductor substrate 11, and the semiconductor substrate 11 covers the second metal layer 14.

The semiconductor substrate 11 includes an upper surface 111 and a lower surface 112, and the epitaxial layer 12 covers the upper surface 111 of the semiconductor substrate 11. The first metal telluride layer 15 is on the surface of the epitaxial layer 12, and the first metal layer 13 covers the epitaxial layer 12 to contact the first metal telluride layer 15 to form a Schottky contact. As shown in FIG. 1 , the Schottky contact between the first metal telluride layer 15 and the first metal layer 13 is non-flat. In detail, the epitaxial layer 12 is formed with a plurality of convex portions 121 and a plurality of concave portions 122. The first metal telluride layer 15 has a corresponding concavo-convex shape, and the top surface 1211 of each convex portion 121 contacts the first metal layer 13. The side surface 1212 of each convex portion 121 also contacts the first metal layer 13, and each concave portion 122 contacts the first portion. Metal layer 13. The first metal telluride layer 15 in the epitaxial layer 12 contacts the first metal layer 13 in the horizontal direction and the vertical direction of the semiconductor substrate 11 to increase the first metal germanide layer 15 and the first layer, compared to the flat Schottky contact. The area of the base contact between the metal layers 13 further enhances the performance of the Schottky diode.

As shown in FIG. 1 , the top surface 1211 of each convex portion 121 has a first vertical distance d1 from the upper surface 111 of the semiconductor substrate 11 , and the bottom surface 1221 of each concave portion 122 and the upper surface 111 of the semiconductor substrate 11 have a first Two vertical distances d2. Here, the difference between the first vertical distance d1 and the second vertical distance d2 (ie, The depth of each recess 122 is indicated. If the depth is deeper, the larger the surface area of each side surface 1212 is, the larger the contact area between the first metal telluride layer 15 and the first metal layer 13 is. However, the too deep recess 122 causes the second vertical distance d2 to become too small, which may result in other undesirable effects of the Schottky diode. Accordingly, the first vertical distance d1 is in the range of 0.1 μm to 50 μm, and the second vertical distance d2 is in the range of 0.099 μm to 49.99 μm, that is, the ratio of the second vertical distance d2 to the first vertical distance d1. Preferably between 0.99 and 0.9998 (ie, That is, the depth of each recess 122 is in the range of 0.001 μm to 0.01 μm, that is, between 0.02% and 1% of the first vertical distance d1 (ie, ). In the foregoing embodiment, when the first vertical distance d1 is 0.1 μm, the breakdown voltage of the Schottky diode can reach 20 V; when the first vertical distance d1 is 50 μm, the Schottky diode The breakdown voltage can reach 10 kV. Based on this, the Schottky diode can have a breakdown voltage that meets the needs of the product and at the same time has better performance.

As shown in FIG. 1, the second metal telluride layer 16 is located on the lower surface 112 of the semiconductor substrate 11, and the second metal layer 14 contacts the second metal telluride layer 16 to form an ohmic contact. In some implementations, the ohmic contact between the second metal telluride layer 16 and the second metal layer 14 is also non-planar. In detail, the lower surface 112 of the semiconductor substrate 11 is also formed with a plurality of convex portions 113 and a plurality of concave portions 114, so that the second metal telluride layer 16 has corresponding concave and convex shapes, and the top surface 1131 of each convex portion 113 contacts the second metal layer. 14. The bottom surface 1141 of each recess 114 contacts the second metal layer 14, and the side surface 1132 of each convex portion 113 also contacts the second metal layer 14, that is, the second metal telluride layer 16 is horizontally and vertically. Contacting the second metal layer 14 in the two-dimensional direction increases the contact area between the second metal telluride layer 16 and the second metal layer 14, thereby reducing the contact resistance between the second metal telluride layer 16 and the second metal layer 14. And improve the performance of the Schottky diode.

Moreover, as shown in FIG. 1, the top surface 1131 of each convex portion 113 and the upper surface 111 of the semiconductor substrate 11 have a third vertical distance d3, and between the bottom surface 1141 of each concave portion 114 and the upper surface 111 of the semiconductor substrate 11. There is a fourth vertical distance d4. Here, the difference between the third vertical distance d3 and the fourth vertical distance d4 (ie, The depth of each recess 114 is indicated. If the depth is deeper, the larger the surface area of each side surface 1132 is, the larger the contact area between the second metal telluride layer 16 and the second metal layer 14 is. And the ratio of the fourth vertical distance d4 to the third vertical distance d3 is preferably between 0.99 and 0.99999 (ie, ), that is, the depth of each recess 114 is between 0.001% and 1% of the third vertical distance d3 (ie, ). In some embodiments, the third vertical distance d3 may be in the range of 1 μm to 1000 μm, and the second vertical distance d2 may be in the range of 0.99 μm to 999.99 μm. Here, the depth of each concave portion 114 is 0.01 μm.

In some embodiments, the spacing between the adjacent two recesses 122, the spacing between the adjacent two recesses 114, the spacing between the adjacent two convex portions 121, and between the adjacent two convex portions 113 The spacing is between 0.01 μm and 20 μm.

In the present embodiment, the epitaxial layer 12 is homoepitaxial, that is, the epitaxial layer 12 has the same conductivity type as the semiconductor substrate 11, for example, the semiconductor substrate 11 includes germanium and the conductive type is For example, the N-type material may include a heavily doped N-type germanium, and the epitaxial layer 12 may comprise a lightly doped N-type germanium. In other embodiments, the material of the semiconductor substrate 11 and the epitaxial layer 12 may also include gallium nitride (GaN) or tantalum carbide (SiC). The material of the first metal layer 13 and the second metal layer 14 may be selected from any electrically conductive metal such as Ti, Ni, Ag, Al, and the like. The material of the two metal telluride layers 15, 16 may comprise titanium (Titanium), nickel (nickel) and platinum (Platinum).

In this embodiment, as shown in FIG. 1 , the convex portions 113 and 121 and the concave portions 114 and 122 are cylindrical, so that both the Schottky contact and the ohmic contact are wave-shaped, but the invention is not limited thereto, and is implemented in other embodiments. In the aspect, please refer to FIG. 2 to FIG. 4 . As shown in FIG. 2 , the shapes of the convex portions 113 and 121 and the concave portions 114 and 122 may also be a square cylinder. As shown in FIGS. 3 and 4, the convex portions 113 and 121 and the concave portions 114 and 122 may have a shape of a cone.

5 to 12 are exploded views of an embodiment of the method for forming a Schottky diode of FIG. 1. First, as shown in FIGS. 5 and 6, an epitaxial layer 12 is formed on the upper surface 111 of the semiconductor substrate 11, and the thicknesses of the epitaxial layer 12 and the semiconductor substrate 11 are a first vertical distance d1 and a third vertical distance d3, respectively. Next, as shown in FIG. 7, the epitaxial layer 12 is subjected to an etching process to form a plurality of convex portions 121 and concave portions 122 on the surface of the epitaxial layer 12 to form an uneven surface. Also, the etching process is controlled such that the first vertical distance d1 is in the range of 0.1 μm to 50 μm, and the second vertical distance d2 is in the range of 0.099 μm to 49.99 μm. In some embodiments, in the step of etching the epitaxial layer 12, the plurality of convex portions 121 and the recesses 122 are formed by an isotropic etching wet etching process, provided that the depth of each of the concave portions 122 is deep. Between 0.02% and 1% of the first vertical distance d1, for example, the depth of each recess 122 is only 0.005% of the first vertical distance d1. At this time, each recess 122 may be further dry-etched. To increase the depth of the recess 122.

Then, a metal such as titanium, nickel, and platinum is doped on the surface of the epitaxial layer 12 by a diffusion method or ion implantation to form a first metal in a surface region of the epitaxial layer 12. The telluride layer 15 is as shown in FIG. Next, as shown in FIG. 9, a deposition process is performed to form the first metal layer 13 on the epitaxial layer 12. After the first metal layer 13 is formed, the first metal layer 13 is filled in each of the concave portions 122 to contact the surfaces of the convex portions 121 and the concave portions 122, that is, the top surface 1211 of the convex portion 121, the side surface 1212 of the convex portion 121, and the concave portion 122. The bottom surface 1221.

In some embodiments, before forming the second metal layer 14, as shown in FIG. 10, the other surface of the semiconductor substrate 11, that is, the lower surface 112 is etched to form a plurality of convex portions 113 and a plurality of concave portions on the lower surface 112. 114 forms another non-flat surface. Also, the etching time is controlled such that the ratio of the third vertical distance d3 to the fourth vertical distance d4 is in the range of 0.99 to 0.99999. Similarly, the ratio of the third vertical distance d3 to the fourth vertical distance d4 may be in the range of 0.99 to 0.99999 by the wet etching process and the dry etching process, and the wet etching process and the dry etching process are detailed in the front. This will not be repeated here.

Next, as shown in FIG. 11, the lower surface 112 of the semiconductor substrate 11 is doped with a metal by diffusion or ion implantation to form a second metal germanide layer 16 on the lower surface 112.

Finally, after forming the plurality of convex portions 113 and the plurality of concave portions 114, as shown in FIG. 12, a deposition process is performed on the lower surface 112 of the semiconductor substrate 11 to form the second metal layer 14. The second metal layer 14 is filled in each of the concave portions 114 to contact the surfaces of the convex portions 113 and the concave portions 114, that is, the top surface 1131 of the convex portion 113, the side surface 1132 of the convex portion 113, and the bottom surface 1141 of the concave portion 114.

In some embodiments, the first metal layer 13 and the second metal layer 14 may be formed by a chemical vapor deposition (CVD) or a physical vapor deposition (PVD) of a deposition process. . Moreover, in some embodiments, in order to increase the contact area between the first metal telluride layer 15 and the first metal layer 13, and the contact area between the second metal telluride layer 16 and the second metal layer 14 Further, each surface of each of the convex portion 121 and the concave portion 122 may be a curved surface by using an etching technique or a physical processing technique, as shown in FIG. 1 , compared with the convex portions 113, 121 and the concave portion in FIGS. 2 to 4 . 114, 122, the top surface 1131 of the convex portion 113 in FIG. 1, the side surface 1132 of the convex portion 113, the top surface 1211 of the convex portion 121, the side surface 1212 of the convex portion 121, the bottom surface 1141 of the concave portion 114, and the bottom surface 1221 of the concave portion 122 are both A curved surface has a large contact area between the first metal telluride layer 15 and the first metal layer 13 and between the second metal telluride layer 16 and the second metal layer 14.

In summary, according to an embodiment of the Schottky diode of the present invention, the epitaxial layer has convex portions and concave portions such that the Schottky contact system is non-flat and the contact area between the metal telluride layer and the metal layer is increased. In this way, the contact resistance of the Xiaoji contact is lowered to improve the performance of the Schottky diode. Moreover, the manufacturing cost of the process can be reduced by forming the recesses and protrusions by the etching process instead of by the reticle.

The present invention has been disclosed in the above embodiments, and it is not intended to limit the present invention. Any one of ordinary skill in the art can make some modifications and refinements without departing from the spirit and scope of the present invention. The scope of the invention is defined by the scope of the appended patent application.

11‧‧‧Semiconductor substrate
111‧‧‧Upper surface
112‧‧‧ lower surface
113‧‧‧ convex
1131‧‧‧ top surface
1132‧‧‧ side
114‧‧‧ recess
1141‧‧‧ bottom
12‧‧‧ epitaxial layer
121‧‧‧ convex
1211‧‧‧ top surface
1212‧‧‧ side
122‧‧‧ recess
1221‧‧‧ bottom
13‧‧‧First metal layer
14‧‧‧Second metal layer
15‧‧‧First metal telluride layer
16‧‧‧Second metal telluride layer
D1‧‧‧first vertical distance
D2‧‧‧second vertical distance
D3‧‧‧ third vertical distance
D4‧‧‧ fourth vertical distance

Fig. 1 is a schematic cross-sectional view showing a first embodiment of a Schottky diode structure according to the present invention. Fig. 2 is a schematic cross-sectional view showing a second embodiment of the Schottky diode structure according to the present invention. Fig. 3 is a schematic cross-sectional view showing a third embodiment of the Schottky diode structure according to the present invention. Fig. 4 is a schematic cross-sectional view showing a fourth embodiment of the Schottky diode structure according to the present invention. Fig. 5 is an exploded perspective view (I) of an embodiment of a method for forming a Schottky diode structure according to the present invention. Fig. 6 is an exploded perspective view (2) of an embodiment of a method for forming a Schottky diode structure according to the present invention. Fig. 7 is an exploded perspective view (III) of an embodiment of a method for forming a Schottky diode structure according to the present invention. Fig. 8 is an exploded perspective view (4) of an embodiment of a method for forming a Schottky diode structure according to the present invention. Fig. 9 is an exploded perspective view (5) of an embodiment of a method for forming a Schottky diode structure according to the present invention. Fig. 10 is an exploded perspective view (6) of an embodiment of a method for forming a Schottky diode structure according to the present invention. [Fig. 11] Fig. 11 is an exploded view (7) of an embodiment of a method for forming a Schottky diode structure according to the present invention. Fig. 12 is an exploded perspective view (8) of an embodiment of a method for forming a Schottky diode structure according to the present invention.

11‧‧‧Semiconductor substrate

111‧‧‧Upper surface

112‧‧‧ lower surface

113‧‧‧ convex

1131‧‧‧ top surface

1132‧‧‧ side

114‧‧‧ recess

1141‧‧‧ bottom

12‧‧‧ epitaxial layer

121‧‧‧ convex

1211‧‧‧ top surface

1212‧‧‧ side

122‧‧‧ recess

1221‧‧‧ bottom

13‧‧‧First metal layer

14‧‧‧Second metal layer

15‧‧‧First metal telluride layer

16‧‧‧Second metal telluride layer

D1‧‧‧first vertical distance

D2‧‧‧second vertical distance

D3‧‧‧ third vertical distance

D4‧‧‧ fourth vertical distance

Claims (10)

A Schottky diode structure comprising: a semiconductor substrate having a conductivity type, the semiconductor substrate comprising an upper surface and a lower surface; an epitaxial layer having the conductivity type, the epitaxial layer covering the upper surface and Forming a plurality of convex portions and a plurality of concave portions, each of the convex portions having a first vertical distance between the top surface and the upper surface, and a second vertical distance between the bottom surface of each of the concave portions and the upper surface, the first The vertical distance is in the range of 0.1 μm to 50 μm, and the second vertical distance is in the range of 0.099 μm to 49.99 μm; a first metal telluride layer is formed on the epitaxial layer; a first metal layer, Contacting the first metal telluride layer; a second metal telluride layer formed on the lower surface of the semiconductor substrate; and a second metal layer contacting the second metal telluride layer. The Schottky diode structure of claim 1, wherein the lower surface of the semiconductor substrate is also formed with a plurality of convex portions and a plurality of concave portions. The Schottky diode structure of claim 2, wherein a top surface of the convex portions formed on the lower surface has a third vertical distance from the upper surface, and a plurality of recesses formed on the lower surface There is a fourth vertical distance from the upper surface, and the ratio of the fourth vertical distance to the third vertical distance is between 0.99 and 0.99999. The Schottky diode structure of claim 3, wherein the material of the semiconductor substrate comprises germanium, gallium nitride or tantalum carbide. The Schottky diode structure of claim 3, wherein the third vertical distance is in the range of 1 μm to 1000 μm, and the fourth vertical distance is in the range of 0.99 μm to 999.99 μm. The Schottky diode structure according to claim 3, wherein a distance between two adjacent convex portions of the epitaxial layer and a distance between two adjacent concave portions of the epitaxial layer are located on the lower surface The distance between the adjacent two convex portions and the distance between the adjacent two concave portions on the lower surface are in the range of 0.01 μm to 20 μm. The Schottky diode structure of claim 1, wherein the ratio of the second vertical distance to the first vertical distance is between 0.99 and 0.9998. A method for forming a Schottky diode structure includes: forming an epitaxial layer on an upper surface of a semiconductor substrate, the epitaxial layer and the semiconductor substrate having the same conductivity type; etching the epitaxial layer to form a plurality a convex portion and a plurality of concave portions, wherein a top vertical distance between the top surface of each convex portion and the upper surface has a second vertical distance between the concave portion and the upper surface, the first vertical distance being 0.1 Between μm and 50 μm, the second vertical distance is in the range of 0.099 μm to 49.99 μm; forming a first metal telluride layer on the epitaxial layer; forming a first metal layer contacting the first metal a second metal telluride layer is formed on a lower surface of one of the semiconductor substrates; and a second metal layer is formed to contact the second metal germanide layer. The method for forming a Schottky diode structure according to claim 8, wherein the lower surface is etched to form a plurality of convex portions and a plurality of concave portions before the step of forming the second metal layer on the lower surface is performed surface. The method for forming a Schottky diode structure according to claim 8, wherein a top surface of the convex portions formed on the lower surface and the upper surface have a third vertical distance formed on the lower surface And a fourth vertical distance between the plurality of recesses and the upper surface, in the step of etching the lower surface of the semiconductor substrate, performing a wet etching process and a dry etching process to make the third vertical distance between 1 μm and 1000 μm Between the ranges, and the fourth vertical distance is in the range of 0.99 μm to 999.99 μm.