Diode including a plurality of Schottky contacts

Abstract

In a general aspect, the diodes (100, 200) include substrates (102, 202), semiconductor layers (104, 204) of a first conductivity type disposed on the substrates and including drift regions (120, 220), shield regions (110a, 110b, 210a, 210b) of a second conductivity type disposed in the semiconductor layers adjacent to the drift regions, first Schottky materials (132a, 132b, 236a, 236b) disposed on a part of the shield regions and a first part of the drift regions and defining first Schottky contacts (142a, 142b, 246a, 246b) with the drift regions, and second Schottky materials (130, 232a, 232b) disposed on a second part of the drift regions adjacent to the first Schottky materials and defining second Schottky contacts (240, 242a, 242b) with the drift regions. The barrier height of the first Schottky contact is lower than the barrier height of the second Schottky contact.

Description

Technical Field

[0001] (Cross - Reference to Related Applications) This application is a continuation of U.S. Patent Application No. 17 / 805,824, filed on June 7, 2022, and claims the benefit of its priority, the entire disclosure of which is incorporated herein by reference in its entirety.

[0002] (Field of the Invention) This specification relates to diodes including a plurality of Schottky contacts having different respective barrier heights.

Background Art

[0003] Semiconductor materials used to manufacture high - power semiconductor devices, such as silicon (Si), silicon carbide (SiC), gallium nitride (GaN), are affected by the presence of high electric fields during the operation of related semiconductor devices that can operate at 400 volts (V), 600 V, 1200 V, or higher. Schottky diodes utilizing such power semiconductor materials (e.g., SiC) can experience leakage currents approaching or exceeding acceptable operating limits due to such high electric fields under reverse - bias conditions. This is partly due to the fact that there is a trade - off between the forward - operating characteristics of the Schottky diode and its reverse - bias leakage current. That is, by improving the forward - operating characteristics of the Schottky diode, such as reducing the conduction loss by reducing the forward voltage drop (Vf), the leakage current of the diode increases. Thus, in previous approaches, in order to reduce the conduction loss in the on - state (e.g., reduce Vf), designers had to sacrifice the reverse - direction characteristics of the diode, which can result in leakage currents exceeding acceptable values. Conversely, in previous approaches, in order to improve the reverse characteristics of the diode (e.g., reduce leakage), designers had to sacrifice the forward - operating characteristics of the diode.

Summary of the Invention

[0004] In some aspects, the techniques described herein relate to a diode that includes a substrate of a first conductivity type, a semiconductor layer of the first conductivity type disposed on the substrate, the semiconductor layer including a drift region of the diode, a shield region of a second conductivity type disposed within the semiconductor layer adjacent to an upper portion of the drift region, a first Schottky material disposed on at least a portion of the shield region and a first portion of the upper portion of the drift region, the first Schottky material defining a first Schottky contact with the drift region, a second Schottky material disposed on a second portion of the drift region, the second Schottky material being adjacent to the first Schottky material, the second Schottky material defining a second Schottky contact with the drift region, the first Schottky contact having a first barrier height, the second Schottky contact having a second barrier height, and the first barrier height being lower than the second barrier height.

[0005] In some aspects, the techniques described herein relate to a diode that further includes a third Schottky material disposed on a third portion of the drift region, the third Schottky material defining a third Schottky contact with the drift region, the third Schottky material being adjacent to the second Schottky material, the second Schottky material being disposed between the first Schottky material and the third Schottky material, and the third Schottky contact having a third barrier height that is higher than the second barrier height.

[0006] In some aspects, the techniques described herein relate to a diode, wherein the first conductivity type is n-type and the second conductivity type is p-type.

[0007] In some aspects, the techniques described herein relate to a diode, wherein the substrate is a silicon carbide substrate, the semiconductor layer is an epitaxial silicon carbide layer, and the substrate has a doping concentration higher than the doping concentration of the epitaxial silicon carbide layer.

[0008] In some aspects, the techniques described herein relate to a diode, at least a portion of the shield region is a first portion of the shield region, the diode is disposed in a second portion of the shield region, and further includes a metal that defines an ohmic contact to the shield region.

[0009] In some aspects, the techniques described herein relate to a diode, and the metal disposed in the second portion of the shield region includes one of a first Schottky material or a second Schottky material.

[0010] In some aspects, the techniques described herein relate to a diode, and the metal disposed in the second portion of the shield region includes at least one of a metal silicide or a deposited metal.

[0011] In some aspects, the techniques described herein relate to a diode, the diode comprising a substrate of a first conductivity type, a semiconductor layer of the first conductivity type disposed on the substrate, a first shield region of a second conductivity type disposed within the semiconductor layer, and a second shield region of the second conductivity type disposed within the semiconductor layer, the second shield region being laterally spaced from the first shield region, a drift region of the diode being disposed within the semiconductor layer and at least partially disposed between the first shield region and the second shield region, a first portion disposed on at least a part of the first shield region and a first part of the drift region and defining a first Schottky contact with the drift region, a second portion disposed on at least a part of the second shield region and a second part of the drift region and defining a second Schottky contact with the drift region, a first Schottky material layer having the first portion and the second portion, a second Schottky material layer disposed on a third part of the drift region, the second Schottky material layer being at least partially disposed between the first portion of the first Schottky material layer and the second portion of the first Schottky material layer and defining a third Schottky contact with the drift region, the first Schottky contact and the second Schottky contact having a first barrier height, the third Schottky contact having a second barrier height, and the first barrier height being lower than the second barrier height.

[0012] In some aspects, the techniques described herein relate to a diode, the diode being disposed in a fourth portion of a drift region and defining a fourth Schottky contact with the drift region, a first portion, wherein a first portion of a third Schottky material layer is disposed between a first portion of a first Schottky material layer and a second Schottky material layer, and a second portion disposed in a fifth portion of the drift region and defining a fifth Schottky contact with the drift region, wherein a second portion of the third Schottky material layer is disposed between a second portion of the first Schottky material layer and the second Schottky material layer, further comprising a third Schottky material layer having the first portion and the second portion, and the fourth Schottky contact and the fifth Schottky contact have a third barrier height, the third barrier height being lower than the second barrier height and higher than the first barrier height.

[0013] In some aspects, the techniques described herein relate to a diode, the first conductivity type being n-type and the second conductivity type being p-type.

[0014] In some aspects, the techniques described herein relate to a diode, the substrate being a silicon carbide substrate, the semiconductor layer being an epitaxial silicon carbide layer, and the substrate having a doping concentration higher than the doping concentration of the epitaxial silicon carbide layer.

[0015] In some aspects, the techniques described herein relate to a diode, at least a part of the first shield region being a first portion of the first shield region, the diode being disposed in a second portion of the first shield region and further comprising a metal defining an ohmic contact to the first shield region.

[0016] In some aspects, the techniques described herein relate to a diode, the metal disposed in the second portion of the first shield region comprising one of the first Schottky material of the first Schottky material layer or the second Schottky material of the second Schottky material layer.

[0017] In some aspects, the techniques described herein relate to a diode, and the metal disposed in the second portion of the first shield region includes at least one of a metal silicide or a deposited metal.

[0018] In some aspects, the techniques described herein relate to a diode, at least a portion of the second shield region is the first portion of the second shield region, the diode is disposed in the second portion of the second shield region, and further includes a metal that defines an ohmic contact to the second shield region.

[0019] In some aspects, the techniques described herein relate to a method for forming a diode, the method comprising: forming a first conductivity type semiconductor layer disposed on a substrate of the first conductivity type, the semiconductor layer including a drift region of the diode; forming a second conductivity type shield region in the semiconductor layer adjacent to the drift region; depositing and patterning a first Schottky material on at least a portion of the shield region and a first portion of the upper part of the drift region, the first Schottky material defining a first Schottky contact with the drift region; depositing and patterning a second Schottky material disposed in a second portion of the drift region, the second Schottky material being adjacent to the first Schottky material, the second Schottky material defining a second Schottky contact with the drift region, wherein the first Schottky contact has a first barrier height, the second Schottky contact has a second barrier height, and the first barrier height is lower than the second barrier height.

[0020] In some embodiments, the techniques described herein relate to a method that further includes depositing and patterning a third Schottky material in a third portion of the drift region, the third Schottky material defining a third Schottky contact with the drift region, the third Schottky material being adjacent to a second Schottky material, the second Schottky material being disposed between the first Schottky material and the third Schottky material, and the third Schottky contact having a third barrier height that is higher than the second barrier height.

[0021] In some embodiments, the techniques described herein relate to a method, and forming a semiconductor layer includes forming an epitaxial semiconductor layer having a doping concentration lower than the doping concentration of the substrate.

[0022] In some embodiments, the techniques described herein relate to a method, at least a portion of the shield region being a first portion of the shield region, the method further including depositing and patterning a metal layer in a second portion of the shield region, the metal layer defining an ohmic contact to the shield region.

[0023] In some embodiments, the techniques described herein relate to a method, and the metal layer includes one of a first Schottky material or a second Schottky material.

Brief Description of the Drawings

[0024]

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[0025] In drawings that are not necessarily drawn to scale, the same reference numerals in different figures may indicate the same and / or similar components (elements, structures, etc.). The drawings generally illustrate, by way of example and not limitation, various implementation forms discussed in the present disclosure. Reference numerals shown in one drawing may not be repeated for the same and / or similar elements in related drawings. Reference numerals repeated in multiple drawings may not be specifically discussed for each of those drawings, but are provided for the context between related drawings. Also, when multiple examples of an element are shown, not all of the same elements in the drawing are necessarily specifically referred to by one reference numeral.

DETAILED DESCRIPTION OF THE INVENTION

[0026] The present disclosure is directed to diodes (e.g., Schottky diodes) including Schottky contacts, and related methods of manufacturing such diodes. In the approach described herein, different materials having different work functions are used to form a Schottky interface with a lower semiconductor material (e.g., in a drift region of a diode). That is, a plurality of Schottky contacts having different barrier heights can be included in the Schottky interface (e.g., Schottky contacts) of a diode. In other words, in the approach described herein, the Schottky contacts of a diode can include a plurality of auxiliary contacts having different barrier heights that together form the Schottky contacts of the diode. By placing the lower-barrier auxiliary contact portion of the Schottky contact in a part of the drift region of the diode having a lower electric field, the effective turn-on voltage or forward voltage drop V f of the diode can be reduced (thus, on-state losses) without significantly affecting the reverse blocking ability of the diode (e.g., without significantly increasing the reverse bias leakage current). In some implementations, both the forward operating characteristics and the reverse operating characteristics of the Schottky diode can be improved.

[0027] FIG. 1 is a cross-sectional view of a diode 100 including Schottky contacts having different barrier heights according to one implementation. In some implementations, the diode 100 may have a linear (stripe) cell layout with the same structure and dimensions, for example, within and / or outside a page. In some implementations, the diode 100 may be of a cell type such as the example shown in FIG. 3. The diode 100 shows a cross-section of a single diode cell perpendicular to the stripe of the linear cell layout, which can be interconnected with other diode stripes or diode cells to form a larger diode (e.g., by electrically connecting respective anodes to each other and by electrically connecting respective cathodes to each other). Depending on the specific implementation, the element spacing, size, and arrangement of the diode 100 may vary.

[0028] As shown in FIG. 1, the diode 100 includes a substrate 102 and a semiconductor layer 104 (semiconductor region). The substrate 102 and the semiconductor layer 104 may be of a first conductivity type, for example, n-type conductivity. The substrate 102 may have a doping concentration higher than that of the semiconductor layer 104. In some implementations, the semiconductor layer 104 may be an epitaxial semiconductor layer or may include a plurality of epitaxial semiconductor layers having different doping concentrations. That is, looking at FIG. 1, the upper part of the semiconductor layer 104 may have a doping concentration higher than that of the lower part of the semiconductor layer 104. In some implementations, the substrate 102 and the semiconductor layer 104 may include silicon carbide or other semiconductor materials.

[0029] Diode 100 includes shield regions 110a and 110b disposed within semiconductor layer 104. Shield regions 110a and 110b are disposed adjacent to drift region 120 of diode 100, and drift region 120 is disposed between shield region 110a and shield region 110b. Shield regions 110a and 110b of diode 100 have a second conductivity type opposite to the first conductivity type, for example, p-type conductivity. In some implementations, the first conductivity type and the second conductivity type can be reversed.

[0030] Diode 100 also includes a first Schottky material 130 (first Schottky material layer) that defines a Schottky contact 140 with drift region 120, and a second Schottky material (second Schottky material layer) that includes portions 132a and 132b that respectively define Schottky contacts 142a and 142b with drift region 120. That is, as shown in FIG. 1, portion 132a is disposed in a part of shield region 110a and a first part of drift region 120, portion 132b is disposed in a part of shield region 110b and a second part of drift region 120, and first Schottky material 130 is disposed in a third part of drift region 120 between (and in contact with) portion 132a and portion 132b. In this example, first Schottky material 130 can have a work function higher than the work function of the second Schottky material layer. Accordingly, Schottky contact 140 will have a barrier height greater than the barrier heights of Schottky contacts 142a and 142b. In an exemplary implementation, each Schottky material can respectively include one or more of a metal, an alloy, a silicide, a semiconductor material, or other materials having an appropriate work function to define a Schottky barrier with a semiconductor material.

[0031] As shown in FIG. 1, the Schottky material 130 and the Schottky contact 140 have a width W1. In an exemplary implementation, the width W1 can be selected based on the electric field distribution (e.g., the electric field distribution under reverse bias conditions) on the surface of the drift region 120 so as to achieve a desired relationship between the on-state operating characteristics and the off-state operating characteristics of the diode 100. In the following description, references to the electric field and the electric field distribution refer to the electric field and the electric field distribution under reverse bias conditions, respectively, unless otherwise specified.

[0032] In this example, as W1 changes (increases or decreases), the associated surface area of the drift region 120 where the Schottky material 130 is disposed (the area of the Schottky contact 140) changes (increases or decreases, respectively). Similarly, as W1 changes, the respective surface areas of the drift region 120 where the portions 132a and 132b are disposed (and the respective areas of the Schottky contacts 142a and 142b) also change accordingly. That is, when W1 is increased, the respective surface areas of the drift region 120 where the portions 132a and 132b are disposed decrease, and when W1 is reduced, the respective surface areas of the drift region 120 where the portions 132a and 132b are disposed increase.

[0033] In the diode 100, the electric field (e.g., immediately below the Schottky contacts 140, 142a, and 142b (e.g., within 5 nanometers or less)) in the drift region 120 is highest at the midpoint between the shield region 110a and the shield region 110b, and decreases (e.g., having a bell-shaped curve distribution) towards the shield region 110a and the shield region 110b, respectively, as it moves away from the midpoint along the surface of the drift region 120. Therefore, the Schottky material 130 in the diode 100 is disposed in a part of the drift region 120 having the highest electric field for the diode 100, and the portions 132a and 132b are disposed in areas of the drift region 120 having a lower electric field.

[0034] In this example, since the Schottky contact 140 has a higher barrier height than the Schottky contacts 142a and 142b, the trade-off between the forward operating characteristics and the reverse operating characteristics of the diode 100 can be improved compared to, for example, using only the Schottky material 130 or only the second Schottky material of the portions 132a and 132b. For example, in the diode 100, the width W1 of the Schottky material 130 can be adjusted such that the leakage current density (e.g., the total leakage current through a specific device portion divided by the area of that portion) of each of the Schottky contact 140, the Schottky contact 142a, and the Schottky contact 142b is the same or substantially the same (e.g., having the same design goal), whereby the total leakage current of the diode 100 is reduced compared to a diode implemented using only the second Schottky material (of the portions 132a and 132b) having a lower barrier height. Further, in the diode 100, the lower barrier heights of the Schottky contacts 132a and 132b will reduce the Vf of the diode 100 (e.g., reduce the on-state conduction loss) compared to a diode implemented using only the Schottky material 130 having a higher barrier height. Therefore, the implementation form of the diode 100 can achieve an improved trade-off between the on-state operating characteristics and the off-state operating characteristics of the Schottky diode.

[0035] Also, as shown in FIG. 1, the diode 100 includes a metal including portions 134a and 134b. The portions 134a and 134b form an ohmic contact 144a with the shield region 110a and an ohmic contact 144b with the shield region 110b, respectively. In some implementations, the portions 134a and 134b can include one of the Schottky materials of the diode 100. In some implementations, the portions 134a and 134b can include different metals that can be deposited, annealed, and / or silicided to form the ohmic contacts 144a and 144b.

[0036] FIG. 2 is a cross-sectional view of another diode 200 including Schottky contacts having different barrier heights according to one implementation. Similar to diode 100, in some implementations, diode 200 may have a design layout of linear (stripe) or linear cells, for example, within and / or outside a page. In some implementations, the cell layout of diode 200 may be a cell type (e.g., a diode cell using a square, hexagon, etc.), such as the example shown in FIG. 3. Diode 200 shows a single diode stripe or a single diode cell, which can be interconnected with other diode stripes or diode cells to form a larger diode. Depending on the specific implementation, the element spacing, size, and arrangement of diode 200 may vary.

[0037] As shown in FIG. 2, diode 200 includes a substrate 202 and a semiconductor layer 204 (semiconductor region). Substrate 202 and semiconductor layer 204 may be of a first conductivity type, for example, n-type conductivity. Substrate 202 may have a doping concentration higher than that of semiconductor layer 204. In some implementations, semiconductor layer 204 may be an epitaxial semiconductor layer or may include a plurality of epitaxial semiconductor layers having different doping concentrations. That is, looking at FIG. 2, the upper part of semiconductor layer 204 may have a doping concentration higher than that of the lower part of semiconductor layer 204. In some implementations, substrate 202 and semiconductor layer 204 may include silicon carbide or other semiconductor materials.

[0038] Diode 200 includes a shield region 210a and a shield region 210b disposed within semiconductor layer 204. Shield region 210a and shield region 210b are disposed adjacent to the drift region 220 of diode 200, and drift region 220 is disposed between shield region 210a and shield region 210b. The shield region 210a and the shield region 210b of diode 200 are of a second conductivity type opposite to the first conductivity type, for example, p-type conductivity. In some implementations, the first conductivity type and the second conductivity type may be reversed.

[0039] Similar to diode 100, diode 200 includes a first Schottky material 230 (first Schottky material layer) that defines a Schottky contact 240 with the drift region 220, and a second Schottky material (second Schottky material layer) that includes portions 232a and 232b that respectively define Schottky contacts 242a and 242b with the drift region 220. Diode 200 further includes a third Schottky material (third Schottky material layer) that includes portions 236a and 236b that respectively define Schottky contacts 246a and 246b with the drift region 220. In this example, the first Schottky material 230 may have a work function higher than the work function of the second Schottky material layer, and the second Schottky material, such as portions 232a and 232b, may have a work function higher than the work function of the third Schottky material layer, such as portions 236a and 236b. Accordingly, the Schottky contact 240 has a barrier height higher than the respective barrier heights of the Schottky contacts 242a, 242b, 246a, and 246b, and the Schottky contacts 242a and 242b will have a barrier height higher than the barrier heights of the Schottky contacts 246a and 246b. In some implementations, additional Schottky material layers having different work functions (e.g., lower work functions) may be included.

[0040] As shown in FIG. 2, the Schottky material 230 and the Schottky contact 240 have a width W1, and the Schottky material 230, portions 232a and 232b together have a width W2. In an exemplary implementation, the widths W1 and W2 may be selected based on the electric field distribution (e.g., the electric field distribution under reverse bias conditions) at the surface of the drift region 220 to achieve a desired relationship between the on-state operating characteristics and the off-state operating characteristics of the diode 200.

[0041] In this example, as W1 changes (widens or narrows), the associated surface area of the drift region 220 where the Schottky material 230 is disposed (the area of the Schottky contact 240) changes (increases or decreases respectively). Similarly, as W1 changes, the respective surface areas of the drift region 220 where the portions 232a, 232b, 236a, and 236b are disposed (and the respective areas of the Schottky contacts 242a, 242b, 246a, and 246b) also change accordingly. That is, when W1 is increased, the surface area of the drift region 220 where the portions 232a, 232b, 236a, and 236b are disposed decreases, and when W1 is reduced, the surface area of the drift region 220 where the portions 232a, 232b, 236a, and 236b are disposed increases. Also, as W2 changes, the respective surface areas of the drift region 220 where the portions 236a and 236b are disposed (and the respective areas of the Schottky contacts 246a and 246b) also change accordingly. That is, when W2 is increased, the surface area of the drift region 220 where the portions 236a and 236b are disposed decreases, and when W2 is reduced, the surface area of the drift region 220 where the portions 236a and 236b are disposed increases.

[0042] In the diode 200, similar to the diode 100, the electric field within the drift region 220 (e.g., just below the Schottky contacts 240, 242a, 242b, 246a, and 246b) is highest at the midpoint between the shield region 210a and the shield region 210b, and decreases (e.g., has a bell-shaped curve distribution) towards the shield region 210a and the shield region 210b respectively as it moves away from the midpoint along the surface of the drift region 220. Accordingly, the Schottky material 230 within the diode 200 is disposed in a part of the drift region 220 that has the highest electric field for the diode 200, while the portions 232a, 232b, 236a, and 236b are disposed in areas of the drift region 220 that have a lower electric field.

[0043] The Schottky contact 240, in this example, has a higher barrier height than the Schottky contacts 242a and 242b, and the Schottky contacts 242a and 242b have a higher barrier height than the Schottky contacts 246a and 246b. Thus, the trade-off between the forward operating characteristics and the reverse operating characteristics of the diode 200 can be improved compared to, for example, the case of using only the Schottky material 230, only the second Schottky material of the portions 232a and 232b, or only the third Schottky material of the portions 236a and 236b. For example, in the diode 200, the widths W1 and W2 can be adjusted such that the respective effective leakage current densities (e.g., the total leakage current through a specific device area divided by the area) of the Schottky contacts 240, 242a, 242b, 246a, and 246b are the same or substantially the same (e.g., having the same design goal). Thereby, the total leakage current of the diode 200 is reduced compared to a diode implemented using only the second Schottky material (of the portions 232a and 232b) or only the third Schottky material (of the portions 236a and 236b) having a lower barrier height. Further, in the diode 200, the lower barrier heights of the Schottky contacts 232a, 232b, 236a, and 236 reduce the Vf of the diode 200 (e.g., reduce the on-state conduction loss) compared to a diode implemented using only the Schottky material 230 having a higher barrier height. Therefore, the implementation form of the diode 200 can achieve an improved trade-off between the on-state operating characteristics and the off-state operating characteristics of the Schottky diode. In some implementation forms of the diode 200, the leakage current density through the Schottky contacts 242a, 242b, 246a, and 246b can be less than the current density through the Schottky contact 240 while still providing a better trade-off between the on-state characteristics and the off-state characteristics.

[0044] Also, as shown in FIG. 2, the diode 200 includes a metal including portions 234a and 234b. The portions 234a and 234b form ohmic contacts 244a with the shield region 210a and ohmic contacts 244b with the shield region 210b, respectively. In some implementations, the portions 234a and 234b may include one of three different Schottky materials of the diode 200. In some implementations, the portions 234a and 234b may include different metals that can be deposited, annealed, and / or silicided to form the ohmic contacts 244a and 244b.

[0045] FIG. 3 is a (planar) view looking down from above another diode 300 including Schottky contacts having different barrier heights according to one implementation. The view of the diode 300 shown in FIG. 3 is part of a diode having a cell-type design. For the sake of explanation, the diode 300 is shown without a metallization layer, such as pad metal, Schottky material, and / or ohmic contact metal, so as not to obscure the underlying structure.

[0046] In the example of FIG. 3, the diode 300 includes hexagonal cells, each cell including a shield region 310. The drift region 320 of the diode 300 is disposed between the hexagonal shield regions 310 having intersections of the drift region 320 therebetween, for example, as segments, streets, etc. That is, a hexagonal drift region portion surrounds each shield region 310. In the diode 300, the highest electric field occurs at these intersections of the drift region portion 320 shown as region 340 in FIG. 3. The diode 300 also includes an ohmic contact region 334 disposed within the shield region 310. In this example, the first Schottky material may be disposed in the region 340, and the second Schottky material may be disposed in the remaining portion of the drift region 320 and a part of the shield region 310. The ohmic contacts within the ohmic contact region 334 may be formed using one of the two Schottky materials or another metal as described above with respect to FIGS. 1 and 2.

[0047] In diode 300, the first Schottky material forms a Schottky contact in the remaining portion of drift region 320 that has a higher barrier height (in region 340) than the Schottky contact formed of the second Schottky material. The width W1 of region 340 (similar to width W1 of diode 100) can be varied to achieve the desired operating characteristics of diode 300. For example, increasing W1 of diode 300 decreases the area of drift region 320 of diode 300 where the second Schottky material is disposed, and decreasing W1 of diode 300 increases the area of drift region 320 of diode 300 where the second Schottky material is disposed. In some implementations, the width W1 of region 340 can be selected such that the leakage current density through each of regions 340 is the same as, or substantially the same as (e.g., has the same design goal as), the respective leakage current density through each of the segments of drift region 320 between each of regions 340. In some implementations, the width W1 of region 340 can be selected such that the leakage current density through each of regions 340 is lower than the respective leakage current density through each of the segments of drift region 320 between each of regions 340. Further, in some implementations, additional Schottky material can be used in region 340 as described with respect to diode 200 of FIG. 2.

[0048] FIG. 4 is a cross-sectional view of the doping profile of a diode portion 400 (e.g., half of a cell of a diode having a stripe or cell of a linear / stripe design) including Schottky contacts having different barrier heights so as to be used to implement the diodes described herein. In an exemplary implementation, the diode portion 400 can be mirrored to the right and / or left to create a complete and / or additional diode stripe or cell. The legend of FIG. 4 shows the relative doping concentration of the conductivity type (e.g., p-type conductivity) in the shield region 410 of the diode portion 400, and the doping concentration increases in the direction of the arrow. In this example, the relative doping concentration of the conductivity type (e.g., n-type conductivity) in the drift region 420 (and under the shield region 410) is not specifically shown. Such doping concentrations both depend on the particular implementation.

[0049] As shown in FIG. 4, the diode portion 400 includes a semiconductor layer 404 of a first conductivity type (e.g., n-type conductivity) and a shield region 410 of a second conductivity type (e.g., p-type conductivity). In some implementations, these conductivity types can be reversed. The first Schottky material 430 is disposed in a first portion of the drift region 420 of the diode portion 400, and since the diode portion 400 is a half-diode segment or cell, the first Schottky material 430 has a width of 0.5W1, e.g., half of the width W1 of FIG. 1. The second Schottky material 432 is disposed in a second portion of the drift region 420 and a part of the shield region 410. Similar to the diode 100 of FIG. 1, the first Schottky material 430 forms a Schottky contact with the drift region 420 having a barrier height greater than the barrier height of the Schottky contact with the drift region 420 formed by the second Schottky material 432. Note that in FIG. 4, the metal defining the ohmic contact with the shield region 410 is omitted.

[0050] In FIG. 4, the distance in arbitrary units (A.U.) is shown on the x-axis, and the depth in A.U. is shown on the y-axis. The distance and depth in FIG. 4 are shown for reference and may vary depending on the specific implementation. In the example of FIG. 4, the distance along the x-axis indicates the left-right distance along the diode portion 400, corresponding to the distance in the graph of the electric field distribution of the diode portion 400 shown in FIG. 5. The depth in FIG. 4 indicates the depth of the semiconductor layer 404, which can be a part of the epitaxial semiconductor layer as described herein.

[0051] FIGS. 5 to 7 are graphs showing the operating characteristics of diode implementation forms including Schottky contacts with different barrier heights, such as the implementation form of the diode 100 in FIG. 1 (e.g., using the diode portion 400). However, the aspects of FIGS. 5 to 7 described below are similarly applicable to other diodes, such as the exemplary diode implementation forms described herein. Specifically, FIG. 5 is a graph 500 showing the electric field distribution along the semiconductor surface under the Schottky contact of the implementation form of the diode portion 400 in FIG. 4 (or the diode 100 in FIG. 1) under reverse bias conditions. FIG. 6 is a graph showing the IV curve (e.g., forward operating characteristics) of the implementation form of the diode in FIG. 1, for example, based on the diode portion 400, compared with a conventional diode implementation form. FIG. 7 is a graph showing the forward voltage drop of the diode implementation form shown in FIG. 6.

[0052] Referring to FIG. 5, an electric field distribution 510 for an implementation form of the diode portion 400 under reverse bias conditions is shown. The applied reverse bias voltage varies depending on a specific device implementation form (e.g., the voltage rating of the diode) and operating conditions. In some implementation forms, the reverse bias voltage can be 500 volts (V) or more. The electric field distribution 510 shown in FIG. 5 shows the electric field within the diode portion 400 just below the upper surface of the semiconductor layer 404 (e.g., 5 nm below the upper surface) along the semiconductor surface under the Schottky contact. As described above, the distance along the x-axis in FIG. 5 corresponds to the distance along the x-axis in FIG. 4 of the diode portion 400 using the same A.U. scale. The electric field is shown in A.U. on the y-axis as a function of distance. As shown in FIG. 5, the electric field within the shield region 410 remains negligible until approaching the interface between the shield region 410 and the drift region 420 where the increase in the electric field begins. After the initial stage increase in the electric field at the interface between the shield region 410 and the drift region 420, the electric field continues to increase and reaches a peak at the right end of the graph 500 corresponding to the highest electric field point. For example, the peak electric field shown in FIG. 5 corresponds to the peak of the electric field at the center of the Schottky contact 140 of the diode 100 (e.g., the center of the drift region 120).

[0053] Based on this electric field distribution, a width W1 (0.5W1 in FIG. 5) can be selected. For example, in some implementation forms, the width W1 can be selected such that the interface between the first Schottky material 430 and the second Schottky material 432 is located at a distance along the x-axis where the electric field is 25 percent less than the peak electric field. In such implementation forms, the leakage current can be significantly reduced (e.g., 5 to 10 times) compared to similar-sized diodes implemented using only Schottky materials with lower barrier height Schottky contacts such as the second Schottky material 432.

[0054] Referring to FIG. 6, a graph 600 showing the IV curves (forward operating characteristics) of various Schottky diode implementation forms is shown. In graph 600, the voltage (forward voltage) is shown in A.U. along the x-axis, and the current is shown in A.U. along the y-axis. In graph 600, trace 610 shows the IV curve of a Schottky diode that includes only a single Schottky material with a high barrier height, such as the Schottky material 130 of diode 100. That is, trace 610 shows the on-state operation of the implementation form of diode 100 where the width W1 extends over the entire upper part of the drift region 120 (for example, there is no Schottky contact formed of a second Schottky material with a lower barrier, and portions 132a and 132b are omitted).

[0055] In FIG. 6, traces 620, 630, 640, 650, 660, and 670 show the forward operating characteristics of the implementation form of diode 100 when the width W1 decreases (as shown in FIG. 1) and the area of the drift region 120 (portions 132a and 132b) where Schottky materials with lower barrier heights are disposed increases. As shown in FIG. 6, as W1 decreases, the current for a given forward voltage increases, demonstrating the advantage of the method described herein of using multiple Schottky contacts with different barrier heights to improve the trade-off between forward and reverse operating characteristics.

[0056] Referring to FIG. 7, graph 700 shows the forward voltage drop V (at a constant forward current density) with respect to the width W1 of the implementation form of diode 100, such as the implementation forms shown by traces 620 - 680 in FIG. 6. f In FIG. 7, the width W1 is shown in A.U. along the x-axis, and the corresponding V f values are shown in A.U. on the y-axis. As shown in FIG. 7, as W1 decreases, V f also decreases. In graph 700, points 740 and 760 correspond to traces 640 and 660 in FIG. 6, respectively. In some implementation forms, compared to the diode implementation form shown by trace 610 (for example, a diode that includes only a Schottky material with a high barrier height), V is about 4 - 10 percentf The reduction of V can be achieved. f Such a reduction of V allows the overall size of the Schottky diode to be reduced so as to achieve a desired forward operating current density, and the total manufacturing cost can be reduced.

[0057] FIG. 8 is a cross-sectional view showing a method for forming Schottky and ohmic contacts of the diode portion 400 of FIG. 4. As shown in FIG. 8, a Schottky material 832 (a Schottky material with a lower barrier height) can be deposited on the diode portion 400 and patterned. After patterning the Schottky material 832, a Schottky material 830 (a Schottky material with a higher barrier height) can be formed and patterned, and the Schottky material 832 also forms an ohmic contact to the shield region 410. In some implementations, different metals can be used to form the ohmic contact to the shield region 410.

[0058] FIG. 9 is a cross-sectional view showing another method for forming Schottky and ohmic contacts of the diode portion 400 of FIG. 4. As shown in FIG. 8, a Schottky material 930 (a Schottky material with a higher barrier height) can be deposited on the diode portion 400 and patterned. After patterning the Schottky material 930, a Schottky material 932 (a Schottky material with a higher barrier height) can be formed and patterned. In this example, the Schottky material 930 forms an ohmic contact to the shield region 410, and the Schottky material 932 is formed above the Schottky material 930 and includes a portion of the Schottky material 930 used to form the ohmic contact. In some implementations, different metals can be used to form the ohmic contact to the shield region 410.

[0059] FIG. 10 is a cross-sectional view showing yet another method for forming a Schottky contact and an ohmic contact of the diode portion 400 of FIG. 4. As shown in FIG. 10, a Schottky material 1030 (Schottky material with a higher barrier height) can be deposited and patterned on the diode portion 400. After patterning the Schottky material 830, a Schottky material 1032 (Schottky material with a lower barrier height) can be formed and patterned, and the Schottky material 1032 also forms an ohmic contact to the shield region 410. In some implementations, different metals can be used to form an ohmic contact to the shield region 410.

[0060] FIG. 11 is a flowchart showing a method 1100 for manufacturing a Schottky diode having Schottky contacts of different barrier heights, such as the diode of FIGS. 1-4. More or fewer operations than shown may be performed. Two or more operations may be performed in a different order unless otherwise specified.

[0061] In operation 1105, method 100 includes forming a semiconductor layer of a first conductivity type disposed on a substrate of the first conductivity type. The semiconductor layer can be an epitaxial layer having a doping concentration lower than that of the substrate. The semiconductor layer can include a drift region of a Schottky diode. In operation 1110, method 1100 includes forming a shield region of a second conductivity type within the semiconductor layer adjacent to the drift region. In operation 1115, method 1100 includes depositing a first Schottky material on at least a portion of the shield region and a first portion of the drift region and patterning it using, for example, photolithography techniques. The first Schottky material can define a first Schottky contact with the drift region. In operation 1120, method 1100 includes depositing and patterning a second Schottky material disposed on a second portion of the drift region, the second Schottky material being adjacent to the first Schottky material, and the second Schottky material defining a second Schottky contact with the drift region. In an exemplary implementation, the first Schottky contact can have a first barrier height, the second Schottky contact can have a second barrier height, and the first barrier height can be lower than the second barrier height.

[0062] As operation 1125, method 1100 includes depositing and patterning a third Schottky material on a third portion of the drift region. The third Schottky material can define a third Schottky contact with the drift region and can be adjacent to the second Schottky material. The second Schottky material can be disposed between the first Schottky material and the third Schottky material. The third Schottky contact can have a third barrier height greater than the second barrier height.

[0063] At least a part of the shield region of operation 1115 may be the first part of the shield region, and method 1100 may include depositing and patterning a metal layer on the second part of the shield region in block 1130, and the metal layer may define an ohmic contact to the shield region. In some implementations, the metal layer may include one of a first Schottky material, a second Schottky material, or a third Schottky material.

[0064] In the foregoing description, when an element such as a layer, region, substrate, or component is referred to as being on, connected to, electrically connected to, coupled to, or electrically coupled to another element, it is to be understood that this can be directly disposed on, connected to, or coupled to the other element, or one or more intervening elements may be present. On the other hand, when an element is referred to as being directly on, directly connected to, or directly coupled to another element or layer, no intervening element or layer is present. Although the terms directly on, directly connected, or directly coupled may not be used throughout the detailed description of the present invention, elements illustrated as being directly on, directly connected, or directly coupled may be referred to as such. The claims of the present application (if included) may be amended to recite the exemplary relationships described herein or shown in the drawings.

[0065] As used herein and in the claims, the singular forms may include the plural forms unless the context clearly dictates otherwise from the perspective of a particular case. Terms indicating spatial relativity (e.g., throughout, above, upper, below, lower side, beneath, sub-) are intended to encompass different orientations of the device during use or operation in addition to the orientation depicted in the drawings. In some implementations, the relative terms above and below can each include vertically above and vertically below, respectively. In some implementations, the term adjacent can include adjacent laterally or adjacent horizontally.

[0066] Some implementations may be implemented using various semiconductor processing and / or packaging techniques. Some implementations may be implemented using various types of semiconductor processing techniques associated with semiconductor substrates including, but not limited to, for example, silicon (Si), gallium arsenide (GaAs), gallium nitride (GaN), silicon carbide (SiC), and / or the like.

[0067] The specific features of the described implementations have been illustrated as described herein, but here, one of ordinary skill in the art will envision many modifications, substitutions, changes, and equivalents. Therefore, it will be understood that the appended claims are intended to cover all such modifications and changes that fall within the scope of the implementations. These are presented by way of example only and not limitation, and it should be understood that various changes may be made in form and detail. Any part of the apparatus and / or method described herein may be combined in any combination, except mutually exclusive combinations. The implementations described herein may include various combinations and / or sub-combinations of functions, components, and / or features of the different implementations described.

[0068] The specific features of the described implementations have been illustrated as described herein, but here, one of ordinary skill in the art will envision many modifications, substitutions, changes, and equivalents. Therefore, it will be understood that the appended claims are intended to cover all such modifications and changes that are included within the scope of the embodiments.

Claims

1. A diode (100, 200), comprising: A substrate (102, 202) of a first conductivity type; A semiconductor layer (104, 204) of the first conductivity type disposed on the substrate (102, 202), the semiconductor layer (104, 204) including a drift region (120, 220) of the diode (100, 200); A shield region (110a, 110b, 210a, 210b) of a second conductivity type disposed in the semiconductor layer (104, 204) adjacent to an upper portion of the drift region (120, 220); A first Schottky material (132a, 132b, 236a, 236b) disposed on at least a part of the shield region (110a, 110b, 210a, 210b) and a first part of the upper portion of the drift region (120, 220), the first Schottky material (132a, 132b, 236a, 236b) defining a first Schottky contact (142a, 142b, 246a, 246b) with the drift region (120, 220); A second Schottky material (130, 232a, 232b) disposed on a second part of the drift region (120, 220), the second Schottky material (130, 232a, 232b) being adjacent to the first Schottky material (132a, 132b, 236a, 236b), the second Schottky material (130, 232a, 232b) defining a second Schottky contact (140, 242a, 242b) with the drift region (120, 220); The first Schottky contact (142a, 142b, 246a, 246b) has a first barrier height, the second Schottky contact (140, 242a, 242b) has a second barrier height, and the first barrier height is lower than the second barrier height. Diode (100, 200).

2. Further comprising a third Schottky material (230) disposed in a third portion of the drift region (220), the third Schottky material (230) defining a third Schottky contact (240) with the drift region (220), the third Schottky material (230) being adjacent to the second Schottky materials (232a, 232b), the second Schottky materials (232a, 232b) being disposed between the first Schottky (236a, 236b) material and the third Schottky material (230), the third Schottky contact (240) having a third barrier height higher than the second barrier height, the diode (200) according to claim 1.

3. The first conductivity type is n-type, The second conductivity type is p-type, the diode (100, 200) according to claim 1.

4. The substrate (102, 202) is a silicon carbide substrate, The semiconductor layer (104, 204) is an epitaxial silicon carbide layer, The substrate (102, 202) has a doping concentration higher than the doping concentration of the epitaxial silicon carbide layer, the diode (100, 200) according to claim 1.

5. At least a part of the shield regions (110a, 110b, 210a, 210b) is a first portion (110a, 110b, 210a, 210b) of the shield regions, the diode (100, 200) being Disposed in a second portion of the shield regions (110a, 110b, 210a, 210b), and further comprising a metal (134a, 134b, 234a, 234b) defining an ohmic contact (144a, 144b, 244a, 244b) with the shield regions (110a, 110b, 210a, 210b), the diode (100, 200) according to claim 1.

6. The metal (134a, 134b, 234a, 234b) disposed in the second portion of the shield region (110a, 110b, 210a, 210b) is the first Schottky material, or the diode (100, 200) according to claim 5, comprising one of the second Schottky materials.

7. The metal (134a, 134b, 234a, 234b) disposed in the second portion of the shield region (110a, 110b, 210a, 210b) is metal silicide, or the diode (100, 200) according to claim 5, comprising at least one of deposited metals.

8. A diode (100, 200), comprising a substrate (102, 202) of a first conductivity type, a semiconductor layer (104, 204) of the first conductivity type disposed on the substrate (102, 202), a first shield region (110a, 210a) of a second conductivity type disposed in the semiconductor layer (104, 204), a second shield region (110b, 210b) of the second conductivity type disposed in the semiconductor layer (104, 204), wherein the second shield region (110b, 210b) is laterally spaced from the first shield region (110a, 210a), and a drift region (120, 220) of the diode (100, 200) is disposed in the semiconductor layer (104, 204) and is at least partially disposed between the first shield region (110a, 210a) and the second shield region (110b, 210b), the second shield region (110b, 210b), a first Schottky material layer, comprising It is disposed on at least a part of the first shield region (110a, 210a) and a first part of the drift region (120, 220), and defines a first Schottky contact (142a, 246a) with the drift region (120, 220). A first part (132a, 236a), It is disposed on at least a part of the second shield region (110b, 210b) and a second part of the drift region (120, 220), and defines a second Schottky contact (142b, 246b) with the drift region (120, 220). A second part (132b, 236b), and a first Schottky material layer having A second Schottky material layer (130, 230) disposed on a third part of the drift region (120, 220), wherein the second Schottky material layer (130, 230) is the first part of the first Schottky material layer (132a, 236a). And a second Schottky material layer (130, 230) that is at least partially disposed between the second part (132b, 236b) of the first Schottky material layer and defines a third Schottky contact (140, 240) with the drift region (120, 220). including, The first Schottky contact (142a, 246a) and the second Schottky contact (142b, 246b) have a first barrier height, the third Schottky contact (130, 240) has a second barrier height, and the first barrier height is lower than the second barrier height. Diode (100, 200).

9. A third Schottky material layer, It is disposed on a fourth part of the drift region (220), and is a first part (232a) that defines a fourth Schottky contact (242a) with the drift region (220), and the first part (232a) of the third Schottky material layer is the first part (236a) of the first Schottky material layer. And a first part (232a) disposed between the second Schottky material layer (230) and disposed in a fifth portion of the drift region (220), and defining a fifth Schottky contact (242b) with the drift region (220), a second portion (232b), wherein the second portion (232b) of the third Schottky material layer is disposed between the second portion (236b) of the first Schottky material layer and the second Schottky material layer (230), and further comprising a second portion (232b). The fourth Schottky contact (242a) and the fifth Schottky contact (242b) have a third barrier height, and the third barrier height is lower than the second barrier height and higher than the first barrier height. The diode (200) according to claim 8.

10. The first conductivity type is n-type. The second conductivity type is p-type. The diode (100, 200) according to claim 8.

11. The substrate (102, 202) is a silicon carbide substrate. The semiconductor layer (104, 204) is an epitaxial silicon carbide layer. The substrate (102, 202) has a doping concentration higher than the doping concentration of the epitaxial silicon carbide layer. The diode (100, 200) according to claim 8.

12. At least a part of the first shield region (110a, 210a) is a first part of the first shield region (110a, 210a), and the diode (100, 200) is disposed in a second portion of the first shield region (110a, 210a), and further comprising a metal (134a, 234a) defining an ohmic contact (144a, 244a) with the first shield region (110a, 210a). The diode (100, 200) according to claim 8.

13. The metal (134a, 234a) disposed in the second portion of the first shield region (110a, 210a) is The first Schottky material of the first Schottky material layer, or The diode (100, 200) according to claim 12, comprising one of the second Schottky materials of the second Schottky material layer.

14. The metal (134a, 234a) disposed in the second portion of the first shield region (110a, 210a) is Metal silicide, or The diode (100, 200) according to claim 12, comprising at least one of deposited metals.

15. At least a part of the second shield region (110b, 210b) is the first part of the second shield region (110b, 210b), and the diode (100, 200) is Disposed in the second portion of the second shield region (110b, 210b), and further comprising a metal (134b, 234b) that defines an ohmic contact (144b, 244b) with respect to the second shield region (110b, 210b). The diode (100, 200) according to claim 8.

16. A method (1100) for forming a diode (100, 200), the method (1100) comprising: Forming (1105) the first conductivity type semiconductor layer (104, 204) disposed on the first conductivity type substrate (102, 202), the semiconductor layer (104, 204) including the drift region (120, 220) of the diode (100, 200), and Forming (1110) a second conductivity type shield region (110a, 110b, 210a, 210b) in the semiconductor layer (104, 204) adjacent to the drift region (120, 220), and Depositing and patterning a first Schottky material (132a, 132b, 236a, 236b) on at least a part of the shield regions (110a, 110b, 210a, 210b) and a first part of the drift regions (120, 220) (1115), wherein the first Schottky material (132a, 132b, 236a, 236b) defines a first Schottky contact (142a, 142b, 242a, 242b) with the drift regions (120, 220), Depositing and patterning a second Schottky material (130, 232a, 232b) disposed in a second part of the drift regions (120, 220) (1120), wherein the second Schottky material (130, 232a, 232b) is adjacent to the first Schottky material (132a, 132b, 236a, 236b), and the second Schottky material (130, 232a, 232b) defines a second Schottky contact (140, 242a, 242b) with the drift regions (120, 220), including this, The first Schottky contact (142a, 142b, 242a, 242b) has a first barrier height, the second Schottky contact (140, 242a, 242b) has a second barrier height, and the first barrier height is lower than the second barrier height, method (1100).

17. Further including depositing and patterning a third Schottky material (230) on a third part of the drift region (220) (1125), wherein the third Schottky material (230) defines a third Schottky contact (240) with the drift region (220), the third Schottky material (230) is adjacent to the second Schottky material (232a, 232b), the second Schottky material (232a, 232b) is disposed between the first Schottky material (236a, 236b) and the third Schottky material (230), and the third Schottky contact (240) has a third barrier height higher than the second barrier height, the method (1100) according to claim 16.

18. Forming the semiconductor layer (104, 204) includes forming an epitaxial semiconductor layer having a doping concentration lower than the doping concentration of the substrate (102, 202), the method (1100) according to claim 16.

19. At least a part of the shield region (110a, 110b, 210a, 210b) is a first part of the shield region (110a, 110b, 210a, 210b), and the method (1100) comprises Depositing and patterning a metal layer (134a, 134b, 234a, 234b) on a second part of the shield region (110a, 110b, 210a, 210b) (1130), the metal layer (134a, 134b, 234a, 234b) defining an ohmic contact (144a, 144b, 244a, 244b) with the shield region (110a, 110b, 210a, 210b), further comprising the method (1100) according to claim 16.

20. The metal layer (134a, 134b, 234a, 234b) Includes one of the first Schottky material, or One of the second Schottky materials, the method (1100) according to claim 19.

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