Semiconductor devices with low barrier height Schottky contacts

Abstract

Schottky diodes according to several embodiments include a silicon carbide drift layer having a first conductivity type and a junction shield region within the drift layer. The junction shield region has a second conductivity type opposite to the first conductivity type. The Schottky diode further includes an anode contact on the silicon carbide drift layer. The anode contact comprises a high-melting-point metal nitride and forms a Schottky junction with the drift layer and an ohmic contact with the junction shield region.

Description

[Technical Field]

[0001] This disclosure relates to semiconductor device structures, and more particularly to power semiconductor devices including silicon carbide Schottky diodes and metal-oxide semiconductor field-effect transistors (MOSFETs). [Background technology]

[0002] Narrow-bandgap semiconductor materials such as silicon (Si) and gallium arsenide (GaAs) are widely used in semiconductor devices for low-power applications, and in the case of Si, for low-frequency applications. However, these semiconductor materials may not be suitable for high-power and / or high-frequency applications due to their relatively small bandgap (1.12 eV for Si and 1.42 eV for GaAs at room temperature) and relatively low breakdown voltage.

[0003] Interest in high-power, high-temperature, and / or high-frequency applications and devices is concentrated on broad-bandgap semiconductor materials such as silicon carbide (3.2 eV for 4H-SiC at room temperature) and group III nitrides (e.g., 3.36 eV for GaN at room temperature). These materials may have higher field breakdown strengths and higher electron saturation velocities than GaAs and Si.

[0004] One important application of broad-bandgap semiconductors such as silicon carbide is the Schottky diode.

[0005] A Schottky diode, also known as a Schottky barrier diode, is a semiconductor diode formed by a junction between a semiconductor and a metal. In a Schottky diode, the junction between the metal and the semiconductor (unlike a semiconductor-to-semiconductor junction in a conventional PN junction diode) creates the Schottky barrier. The metal side acts as the anode of the diode, and the n-type semiconductor acts as the cathode. If a forward voltage sufficient to overcome the Schottky barrier at the metal-to-semiconductor junction is applied, current flows forward through the device. If a reverse voltage is applied, a depletion region is formed in the semiconductor, hindering the flow of current.

[0006] Compared to conventional PN junction diodes, Schottky diodes have a smaller forward voltage drop and extremely fast switching operation.

[0007] A key difference between PN junction diodes and Schottky diodes is the reverse recovery time (t). rr This is the time it takes for the diode to switch from a conductive state (forward bias) to a non-conductive state (reverse bias). In the conductive state, a conventional PN junction diode introduces minority carriers into the diffusion region on the N side of the junction, where they diffuse and then recombine with majority carriers. The reverse recovery time of a PN junction is mainly limited by the diffusion capacitance of minority carriers accumulated in the diffusion region during the conductive state.

[0008] In contrast, Schottky diodes are unipolar or "majority carrier" devices that do not rely on the input of minority carriers. Rather, in the conducting state, majority carriers (electrons in the case of an n-type semiconductor layer) are input to the entire junction. Therefore, when switching a Schottky diode from a conducting state to a non-conducting state, there is no need for the time required for the input carriers to recombine. Rather, the switching speed of a Schottky diode is limited only by the junction capacitance of the device.

[0009] Silicon carbide Schottky diodes are ideal rectifiers for advanced power electronics applications above 650V because they offer significantly lower leakage current and capacitance than silicon-based Schottky diodes, resulting in faster switching speeds.

[0010] For example, in power boost converters, SiC Schottky diodes may need to carry surge currents approximately 10 to 15 times the device's rated current over short periods of a few milliseconds. So-called merged PN-Schottky (MPS) diodes facilitate this by merging the PN junction island into the Schottky diode. As a result, under high forward currents, the PN junction between the island and the drift layer can be turned on, enabling conduction modulation of the drift layer and allowing surge currents to flow at lower voltages than conventional Schottky diodes. [Overview of the Initiative] [Means for solving the problem]

[0011] Schottky diodes according to several embodiments include a silicon carbide drift layer having a first conductivity type and a junction shielding region within the drift layer. The junction shielding region has a second conductivity type opposite to the first conductivity type. The Schottky diode further includes an anode contact on the silicon carbide drift layer. The anode contact comprises a refractory metal nitride and forms a Schottky junction with the drift layer and an ohmic contact with the junction shielding region.

[0012] The Schottky barrier height for the drift layer at the anode junction may be less than about 1.2 eV, and in some embodiments, less than about 1 eV. The anode junction may contain (Mo) nitride. The molecular ratio x of nitrogen at the anode junction is greater than about 0.5, and in some embodiments, may be about 1.0 to 1.6.

[0013] The thickness of the anode contact may be at least about 50 nm, and in some embodiments, the thickness of the anode contact is about 50 nm to 300 nm. The level of residual stress at the time of deposition on the drift layer of the anode contact may be less than about 500 MPa.

[0014] The anode junction may include a plurality of high-melting-point metal nitride portions and a plurality of non-high-melting-point metal nitride portions arranged in an alternating pattern along the surface of the drift layer. The non-high-melting-point metal nitride portions may form a Schottky barrier junction with the drift layer having a Schottky barrier height higher than the Schottky barrier height formed by the high-melting-point metal nitride portions with the drift layer.

[0015] The Schottky diode may further include multiple junction shield regions within the drift layer, and the high-melting-point metal nitride portion is positioned on top of the junction shield regions, forming ohmic contact with each of them.

[0016] The non-high melting point metal nitride portion may be in contact with the drift layer between adjacent bonding shield regions. The non-high melting point metal nitride portion may contain Ti and / or TiW.

[0017] The anode junction may include alternating first and second regions along the surface of the drift layer, wherein the first region has a first Schottky barrier height to the drift layer that is higher than the second Schottky barrier height to the drift layer of the second region.

[0018] The first area is MoN x It may include, and the second region is MoN y It may include x > y.

[0019] The nitrogen concentration at the anode contact may vary horizontally between the first region and the second region. In some embodiments, the nitrogen concentration at the anode contact may vary smoothly between the first region and the second region. In some embodiments, the nitrogen concentration at the anode contact may vary stepwise between the first region and the second region.

[0020] The Schottky diode may further include a plurality of trenches on the upper surface of the drift layer, and the anode contact may include a plurality of high melting point metal nitride portions within the trenches and a metal layer on the upper surface of the drift layer, and the metal layer contacts the high melting point metal nitride portions.

[0021] The metal layer forms a first Schottky junction with the drift layer, the high melting point metal nitride portions form a second Schottky junction with the drift layer, and the first Schottky junction has a higher Schottky barrier height than the second Schottky junction.

[0022] The Schottky diode may further include a plurality of junction shield regions within the drift layer, the junction shield regions are disposed under each of the trenches, and the high melting point metal nitride regions form ohmic contacts to each of the junction shield regions.

[0023] The high melting point metal nitride region may include MoN x and the metal layer may include molybdenum, titanium, and / or tungsten.

[0024] The Schottky diode may further include a plurality of silicide regions on the drift layer between the drift layer and the anode contact. The silicide regions may include MoSi.

[0025] The Schottky diode may further include a plurality of junction shield regions within the drift layer, the plurality of silicide regions are disposed on each of the plurality of junction shield regions, and form ohmic contacts to the junction shield regions.

[0026] The silicide regions may be located within each trench in the drift layer, and the junction shield regions are located below the trenches. The anode junctions may extend within the trenches.

[0027] A method for forming a Schottky diode includes the steps of: forming a drift layer on a substrate, wherein the drift layer and the substrate contain silicon carbide and may have a first conductivity type; forming a junction shield region on the surface of the drift layer, wherein the junction shield region has a second conductivity type opposite to the first conductivity type; and forming an anode contact on the drift layer, wherein the anode contact contains a high-melting-point metal nitride and the anode contact forms a Schottky junction with the drift layer. [Brief explanation of the drawing]

[0028] [Figure 1] This is a diagram of a conventional Schottky diode. [Figure 2] This figure shows a Schottky diode in several embodiments. [Figure 3] This graph shows the forward current as a function of the anode voltage (VA) of Schottky contacts formed with titanium (curve 302), molybdenum (curves 304a, 304b), and MoNx (curve 306). [Figure 4] This graph shows the deposition rate of the MoNx layer (by sputtering) as a function of the fraction of N2 in the sputtering chamber relative to the N2 / Ar gas mixture in the chamber. [Figure 5] This graph shows the effect of the fraction of N2 in the sputtering chamber on the residual stress of the MoNx layer in the N2 / Ar gas mixture within the chamber. [Figure 6A] This figure shows the operation for forming the active region of a Schottky diode structure according to several embodiments. [Figure 6B] This figure shows the operation for forming the active region of a Schottky diode structure according to several embodiments. [Figure 6C] This figure shows the operation for forming the active region of a Schottky diode structure according to several embodiments. [Figure 6D] This figure shows the operation for forming the active region of a Schottky diode structure according to several embodiments. [Figure 7] This figure shows the active region of a SiC Schottky diode according to further examples. [Figure 8] This figure shows a SiC Schottky diode according to several embodiments, in which the anode contact includes a non-MoNx layer formed on the surface of the epitaxial layer. [Figure 9] This figure shows the active region of a Schottky diode structure according to several embodiments, with an anode contact provided. [Figure 10] This figure shows the active region of a Schottky diode in several embodiments. [Figure 11] This figure shows a SiC Schottky diode according to several embodiments, in which the anode contact includes a MoNx layer formed on the surface of the epitaxial layer. [Figure 12] This figure shows the operation for forming a Schottky diode according to several embodiments. [Figure 13A] This figure shows the process of forming a semiconductor device according to several embodiments. [Figure 13B] This figure shows the process of forming a semiconductor device according to several embodiments. [Figure 14A] This figure shows the process of forming a semiconductor device according to several embodiments. [Figure 14B] This figure shows the process of forming a semiconductor device according to several embodiments. [Figure 14C] This figure shows the process of forming a semiconductor device according to several embodiments. [Modes for carrying out the invention]

[0029] Here, an embodiment of the concept of the present invention will be described with reference to the attached drawings.

[0030] Silicon carbide (SiC) Schottky diodes are suitable for use in advanced power electronics above 650V because they offer significantly lower leakage current and capacitance than silicon Schottky diodes, enabling high-speed switching. In power boost converters, SiC Schottky diodes need to handle surge currents approximately 10 to 15 times the rated current in short periods of a few milliseconds. So-called MPS (Merged PN-Schottky) diodes achieve this by merging the PN junction island into the Schottky diode, allowing the PN junction to turn on at high forward currents. This enables conduction modulation of the drift layer, allowing the device to conduct surge currents at lower voltages than conventional Schottky diodes.

[0031] Figure 1 shows a cross-section of a portion of the MPS Schottky diode 10. The Schottky diode 10 includes an active area 15A and an edge termination area 15B (also called the junction termination region or simply the termination region) located outside the active area.

[0032] An n-silicon carbide epitaxial layer 14 is formed on a silicon carbide substrate 12. The silicon carbide epitaxial layer 14 and the silicon carbide substrate may contain the 2H, 4H, 6H, 3C, or 15R polytype of silicon carbide, where "polytype" refers to the way in which the atoms of the material are arranged in the crystal lattice. In this context, "n-" refers to the conductivity type of the silicon carbide material, indicating that the silicon carbide material is doped to a low concentration of n-type dopant. In semiconductor substrates, semiconductor layers, or semiconductor regions, it is possible to dope the material with impurities that cause an excess of positively charged (p-type) or negatively charged (n-type) charge carriers, which defines the conductivity type of the material. The symbols "+" or "-" are used to indicate that a particular region or layer of a semiconductor material is doped to a higher or lower concentration than another region or layer. For example, materials labeled "n-" have a lower concentration of n-type dopant than the n-type layer, and are doped at a lower concentration, while materials labeled "n+" have a higher concentration of n-type dopant than the n-type layer, and are doped at a higher concentration.

[0033] A metal anode contact 26 is formed on the surface of the silicon carbide epitaxial layer 14 facing the substrate 12. The anode contact 26 is typically made of titanium or titanium-tungsten and forms a Schottky barrier junction SJ with the silicon carbide epitaxial layer 14.

[0034] A metal coating layer 20 is formed on the anode contact. The metal coating layer 20 may contain gold, which can facilitate wire bonding to the diode 10 or the formation of other contacts.

[0035] Multiple p+ junction shield regions 24 are formed on the surface of the silicon carbide epitaxial layer 14. The p+ junction shield regions 24 may be formed by ion implantation to form a pn junction (PNJ) with the silicon carbide epitaxial layer 14. The anode contact 26 forms ohmic contact with the p+ junction shield regions 24.

[0036] A cathode-ohmic contact 22 is formed on the back side of the substrate 12.

[0037] Although the description concerns a device including an n-type epitaxial layer 14 and a p-type junction shield region 24, it will be understood that in some embodiments, the conductivity types may be reversed, i.e., a p-type epitaxial layer and an n-type shield region.

[0038] The Schottky barrier junction SJ between the anode contact 26 and the silicon carbide epitaxial layer 14 is formed on the exposed region 28 of the silicon carbide epitaxial layer 14 between the p+ junction shield regions 24 and has a lower Schottky barrier height (or barrier energy) than the PN junction PNJ between the p+ junction shield regions 24 and the silicon carbide epitaxial layer 14. For example, if the anode contact 26 contains titanium, the anode contact 26 has a Schottky barrier height of approximately 1.20 to 1.26 eV. This allows the Schottky barrier junction SJ to turn on before the PN junction PNJ in the forward bias (conductive) state. Conversely, in the reverse bias (non-conductive) state, the Schottky barrier junction SJ is shielded from the high electric field by the depletion region formed at the interface between the PN junction PNJ and the silicon carbide epitaxial layer 14.

[0039] In the edge termination area 15B, multiple floating guard rings 32 (also called equipotential rings or field rings) are formed in each region 31 of the surface of the silicon carbide epitaxial layer 14. The guard rings 32 may include p+ regions injected into the silicon carbide epitaxial layer 14. A silicon nitride passivation layer 25 is formed on the edge termination area 15B. A protective layer (not shown) of a material such as polyimide may be formed on the silicon nitride passivation layer 25.

[0040] At low current densities, forward current flows across the Schottky barrier junction. The Schottky barrier height (PHIbn or SBH) limits the conductivity of the n-type region of the device at low current densities. Although the Schottky barrier height of metal contacts on silicon carbide formed from metals such as titanium and titanium-tungsten is very low, devices formed using such contacts can still experience undesirably high voltage drops across the Schottky barrier junction at low current densities.

[0041] Reducing the barrier height by using different materials as Schottky contact metals can potentially reduce the voltage drop between n-type regions and thus improve the overall efficiency of the device.

[0042] Accordingly, some embodiments described herein provide silicon carbide-based Schottky diodes having a low Schottky barrier height, or more simply, a Schottky contact with a low barrier height. In this context, a low Schottky barrier height refers to a Schottky barrier height of less than about 1.2 eV for the Schottky contact with silicon carbide. Specifically, high melting point metal nitride materials such as molybdenum nitride may be used to form an anode contact with a low Schottky barrier height. Other high melting point metal nitride materials that may be used include, for example, tungsten nitride and tantalum nitride. Specifically, molybdenum nitride (MoN x ) exhibits a Schottky barrier height of approximately 0.8 eV to 1.2 eV on 4H-SiC. MoN x When used as a Schottky barrier metal, the low SBH reduces the voltage drop across the junction at low current densities. Device power consumption is also reduced proportionally, which can improve device efficiency.

[0043] Figure 2 shows a 100A SiC-based MPS Schottky diode. Diode 100A includes an n-type silicon carbide substrate 12, on which an n-type silicon carbide epitaxial layer 14 is formed. Epitaxial layer 14 functions as the drift layer of diode 100A. Diode 100A includes a plurality of junction shield regions 24 on the surface of the epitaxial layer.

[0044] An anode contact 110 is formed on the epitaxial layer 14 in the active region 115A of diode 100A. Anode contact 110 includes a layer of a high melting point metal nitride such as MoN x which forms a low-barrier-height Schottky junction SJ with the exposed portion of the epitaxial layer 14 between the junction shield regions 24. The thickness of the layer of high melting point metal nitride may be at least about 0.05 microns and may be within the range of about 0.05 to 0.30 microns. The molar ratio of nitrogen (indicated by the subscript x) in the high melting point metal nitride layer may be greater than about 0.5 and may range from about 1.0 to about 1.6 in some embodiments.

[0045] The nitrogen content of the high melting point metal nitride layer may affect the Schottky barrier height of anode contact 110. Specifically, the Schottky barrier height of anode contact 110 formed of MoN x may decrease as the nitrogen fraction x in the MoN x layer increases. For example, Figure 3 is a graph of the forward current as a function of the anode voltage (V x ) of Schottky contacts formed of titanium (curve 302), molybdenum (curves 304a, 304b), and MoN A (curve 306). The Schottky barrier height of the MoNx Schottky contact was 0.82 eV, whereas the Schottky barrier height of the Mo Schottky contact was about 1 eV and the Schottky barrier height of the Ti Schottky contact was 1.2 eV. Thus, as seen in Figure 3, the MoN x Schottky contact has a lower anode voltage V AAt low current densities of less than approximately 0.5V, it showed significantly higher current than Mo or Ti Schottky contacts.

[0046] Therefore, it is sometimes desirable to increase the nitrogen fraction x in high-melting-point metal nitrides as much as possible. However, doing so results in design trade-offs because the nitrogen fraction x in high-melting-point metal nitrides also affects the material properties of the layer, such as residual stress within the layer. The nitrogen fraction x in high-melting-point metal nitrides can also affect manufacturing parameters such as the deposition rate of the material.

[0047] For example, Figure 4 is a graph showing the deposition rate of a MoNx layer (by sputtering) as a function of the fraction of N2 in the sputtering chamber relative to the N2 / Ar gas mixture in the chamber. As shown in Figure 4, as the ratio increases, (the amount of N in the chamber increases, and therefore the amount of deposited MoNx increases). x As the nitrogen fraction x in the layer increases, the deposition rate of the material decreases.

[0048] Figure 5 shows the fraction of N2 in the sputtering chamber relative to the N2 / Ar gas mixture in the chamber. x This graph shows the effect on the residual stress of the layers. As shown in Figure 5, when N2 is not used (Mo layer, or MoN at x=0) x (Equivalent to a layer), the resulting film has a positive (tensile) stress of approximately 1500 MPa. If the fraction of N2 in the sputtering chamber relative to the N2 / Ar gas mixture is approximately 0.31, the residual stress of the film is negligible. If the fraction of N2 in the sputtering chamber relative to the N2 / Ar gas mixture is approximately 0.79, the residual stress of the film is approximately -1000 MPa, which is a compressive stress. In general, a low stress in the deposited film is desirable to reduce the possibility of cracking or other defect formation.

[0049] Other process factors may also affect the barrier height at the MoNx-SiC interface. For example, it has been reported that the Schottky barrier height at the MoNx-SiC interface is inversely proportional to the deposition temperature. However, it has also been reported that the Schottky barrier height at the MoNx-SiC interface is directly proportional to the deposition temperature. Therefore, it is thought that the barrier height at the MoNx-SiC interface may depend on multiple process conditions.

[0050] The operation for forming the active region of a Schottky diode structure 100A according to several embodiments is shown in Figures 6A to 6D. Referring to Figure 6A, a silicon carbide substrate 12 is provided. The silicon carbide substrate 12 may have 2H, 4H, 6H, 3C, and / or 15R polytypes. <0001> The silicon carbide substrate 12 may have an off-axis orientation of about 1 to 3 degrees from the crystal direction. The silicon carbide substrate 12 may be doped with an n-type dopant such as nitrogen and / or phosphorus. The silicon carbide epitaxial layer 14 is grown on the silicon carbide substrate 12 by epitaxial growth. The silicon carbide epitaxial layer 14 may be doped with an n-type dopant at a low concentration and have n conductivity.

[0051] Referring to Figure 6B, an injection mask 62 is formed on the silicon carbide epitaxial layer, and p-type dopant ions 64 are injected into the silicon carbide epitaxial layer 14 to form a junction shield region 24.

[0052] Referring to Figure 6C, MoN is on the silicon carbide epitaxial layer 14. xA film of a high-melting-point metal nitride is deposited to form the anode junction 110. The high-melting-point metal nitride may be deposited, for example, by sputtering a high-melting-point metal such as Mo onto the silicon carbide epitaxial layer 14 in an atmosphere containing nitrogen (N2) and argon (Ar). Specifically, the level of nitrogen in the atmosphere may be selected so that the high-melting-point metal nitride film has a desired nitrogen fraction such that the Schottky barrier height of the anode junction 110 to the silicon carbide epitaxial layer 14 is less than about 1 eV. The level of nitrogen in the atmosphere may also be selected considering the effect that the resulting nitrogen level in the high-melting-point metal nitride film has on the amount and type of stress (e.g., compressive stress or tensile stress) in the film.

[0053] Referring to Figure 6D, a metal overlay 120 is formed on the anode contact 110. The metal overlay 120 may contain a material such as gold that allows for the formation of a wire bond thereon. The metal overlay 120 may be provided with one or more other metals and / or metal layers, such as barrier layers or adhesive layers.

[0054] In Schottky barrier diodes with high-melting-point metal nitride anode contacts, the Schottky barrier height at the metal-semiconductor junction is reduced, potentially lowering the forward voltage drop during forward conduction and improving efficiency. However, such devices may be prone to leakage current under reverse blocking conditions. To mitigate this problem, some embodiments provide anode contacts with alternating regions of high and low Schottky barrier height, where the low-Schottky barrier height regions are located near or above the junction shield region 24, which in turn protects the low-Schottky barrier height regions under reverse blocking conditions.

[0055] For example, Figure 7 shows the active region of a SiC Schottky diode 100B according to a further embodiment. In the embodiment shown in Figure 7, the anode contact 110B has an alternating arrangement of high-melting-point metal nitride portions 135 and non-high-melting-point metal nitride portions 125 that are in contact with the epitaxial layer 14 between the high-melting-point metal nitride portions 135. The non-high-melting-point metal nitride layer 125 may contain a metal such as Ti or TiW that forms a Schottky barrier junction in the epitaxial layer 14 having a Schottky barrier junction that is higher than that of the high-melting-point metal nitride portions 135B.

[0056] The high-melting-point metal nitride portion 135B is positioned on top of the junction shield region 24, and the non-high-melting-point metal nitride layer 125 is positioned in the area between the junction shield regions 24. In this arrangement, the high-melting-point metal nitride portion 135B increases the current at a low forward voltage, thereby improving operating efficiency while being protected from high reverse blocking voltage by the junction shield region 24. The non-high-melting-point metal nitride layer 125 of the anode contact 110B is provided in the portion of the anode contact 110 between the junction shield regions 24 (the portion not protected by the junction shield region 24).

[0057] Figure 8 shows a SiC Schottky diode 100C in which the anode contact 110C includes a non-high melting point metal nitride layer 140 formed on the surface of the epitaxial layer 14. The high melting point metal nitride region 135C is located in a thin trench of the epitaxial layer 14 above the junction shield region 24 and is in contact with the non-high melting point metal nitride layer 140. Similar to the embodiment shown in Figure 7, the high melting point metal nitride portion 135C increases the current at a low forward voltage, thereby improving operating efficiency while being protected from a high reverse blocking voltage by the junction shield region 24. The vertical thickness of the high melting point metal nitride portion 135C may be about 0.3 to 0.5 microns.

[0058] The non-high melting point metal nitride layer 140 of the anode contact 110C is provided in the portion of the anode contact 110 between the bonding shield regions 24 (therefore, it is not as protected by the bonding shield regions 24 as the high melting point metal nitride portion 135C). Non-MoNx The layer 140 may contain a material such as Ti or TiW, and may form a Schottky junction with an epitaxial layer 14 having a Schottky barrier height higher than that of the high-melting-point metal nitride in the high-melting-point metal nitride region 135C.

[0059] Figure 9 shows the active region of the Schottky diode structure 100D, which is provided with an anode contact 110D. The anode contact 110D is a MoN diode whose nitrogen content changes throughout the entire active region. x It is formed from high-melting-point metal nitrides such as the above. Specifically, the anode junction 110D includes a first region 112 of high-melting-point metal nitride with a high nitrogen content and a second region 114 of high-melting-point metal nitride with a low nitrogen content. The first region 112 is located on the junction shield region 24, and the second region 114 is located on the epitaxial layer 14 in the region between the junction shield regions 24. Because the first region 112 has a high nitrogen concentration, it may have a lower Schottky barrier height than the second region 114, which has a lower nitrogen concentration.

[0060] The nitrogen concentration gradient between the first region 112 and the second region 114 may be smooth, as shown by the gradient shading in Figure 9, or it may be stepped in one or more steps.

[0061] Figure 10 shows the active region of a Schottky diode 100E according to several embodiments. The Schottky diode 100E includes an anode contact 110E formed of a high melting point metal nitride. Within the anode contact 110E, on the junction shield region 24, MoSi is present as a planar silicide ohmic contact with the junction shield region 24. X High-melting-point metal silicide regions 130 are formed. The planar arrangement shown in Figure 10 may have a lower shielding effect than the trench arrangement shown in Figure 8. However, the planar arrangement may have a simpler manufacturing process because it does not require the formation of trenches.

[0062] The embodiment shown in Figure 10 utilizes the ohmic characteristics of the silicide contact for p+ silicon carbide in the bonding shield region 24 and the rectifying characteristics of the high-melting-point metal nitride contact for n-type silicon carbide in the epitaxial layer 14. The contact between the high-melting-point metal nitride portion and the silicide portion 130 of the anode contact 110E is a metallic contact, i.e., an ohmic and non-rectifying contact.

[0063] Figure 11 shows a SiC Schottky diode 100F in which the anode junction 110F includes a high-melting-point metal nitride layer formed on the surface of the epitaxial layer 14. Within the trench 134 in the epitaxial layer 14, a high-melting-point metal silicide (e.g., MoSi) is formed on the junction shield region 24. X A region 132 is provided. The silicide region 132 is in contact with the anode contact 110F. The silicide portion 132 forms ohmic contact with the junction shield region 24. The high-melting-point metal nitride of the anode contact 110C forms a Schottky barrier junction with the epitaxial layer 14 between the trenches 134. The high-melting-point metal nitride of the anode contact 110dC may extend into the trenches 134, as shown in Figure 11.

[0064] Figure 12 shows the operation of forming a Schottky diode according to several embodiments. Referring to Figure 12, the operation includes the steps of forming a drift layer on a substrate, wherein the drift layer and the substrate contain silicon carbide and have a first conductivity type (block 1202); forming a junction shield region on the surface of the drift layer, wherein the junction shield region has a second conductivity type opposite to the first conductivity type (block 1204); and forming an anode contact on the drift layer, wherein the anode contact contains a high melting point metal nitride such as MoNx, and the anode contact forms a Schottky junction with the drift layer.

[0065] Figures 13A and 13B illustrate the process of forming a semiconductor device according to several embodiments. Specifically, Figures 13A and 13B illustrate the process of forming a device structure 100B as shown in Figure 7, where the anode contact 110B includes a non-high melting point metal nitride layer 125 and a plurality of high melting point metal nitride portions 135. The non-high melting point metal nitride portion 125 may contain a metal such as Ti or TiW that forms a Schottky barrier junction in the epitaxial layer 14 having a Schottky barrier junction higher than that of the high melting point metal nitride portion 135B.

[0066] Referring to Figure 13A, a mask 210 is formed on the epitaxial layer 14, and the mask 210 has a pattern of openings 212 that expose the portion of the epitaxial layer 14 where the bonding shield region 24 is formed. MoN is applied to the mask 210 and the exposed portion of the epitaxial layer 14. x A blanket layer of high-melting-point metal nitrides is deposited. The mask 210 is peeled off, leaving multiple high-melting-point metal nitride portions 135 on the epitaxial layer 14. Next, a layer 125 of non-high-melting-point metal nitrides such as tungsten and / or titanium is deposited on the structure. The layer 125 is in contact with the epitaxial layer 14 between the high-melting-point metal nitride portions 135, forming Schottky contacts with the epitaxial layer 14.

[0067] Figures 14A to 14C show the operation of forming a semiconductor device according to several embodiments. Specifically, Figures 14A to 14C show the operation of forming a device structure 100D as shown in Figure 9, where the anode contact 110B is MoN, where the nitrogen content changes throughout the active region. x It is formed from high-melting-point metal nitrides such as the above. Specifically, as shown in Figure 9, the anode junction 110D includes a first region 112 of high-melting-point metal nitride with a high nitrogen content and a second region 114 of high-melting-point metal nitride with a low nitrogen content.

[0068] Referring to Figure 14A, a mask 210 is formed on the epitaxial layer 14. The mask 210 has a pattern of openings 212 that expose the portion of the epitaxial layer 14 where the bonding shield region 24 is formed. MoN is applied to the mask 210 and the exposed portion of the epitaxial layer 14. x A blanket layer of high-melting-point metal nitrides is deposited. The mask 210 is peeled off, leaving multiple high-melting-point metal nitride portions 220 on the epitaxial layer 14. Next, a non-nitride high-melting-point metal layer 230, such as Mo, is deposited on the structure. The layer 230 is in contact with the epitaxial layer 14 between the high-melting-point metal nitride portions 220.

[0069] Referring to Figure 14B, the structure is then heated 240 to a temperature sufficient to partially alloy layer 230 and the high-melting-point metal nitride portion 220. Referring to Figure 14C, the heat treatment causes some of the nitrogen in the high-melting-point metal nitride portion 220 to diffuse into layer 230, resulting in the formation of a first region 112 of high-melting-point metal nitride with a high nitrogen content and a second region 114 of high-melting-point metal nitride with a low nitrogen content. The first region 112 is located above the bonding shield region 24, and the second region 114 is located above the epitaxial layer 14 in the region between the bonding shield regions 24. Because the first region 112 has a higher nitrogen concentration, it may have a lower Schottky barrier height than the second region 114, which has a lower nitrogen concentration. Due to diffusion, the nitrogen concentration of the layers may smoothly gradient between the first region 112 and the second region 114.

[0070] In this specification, ordinal numbers such as first, second, third, etc., may be used to describe various elements, but it will be understood that these elements should not be limited by these terms. These terms are used solely to distinguish one element from another. For example, without departing from the scope of this disclosure, the first element may be called the second element, and similarly, the second element may be called the first element.

[0071] Furthermore, as shown in the drawings, relative terms such as “below” or “bottom” and “up” or “top” may be used to describe the relationship between one element and another. It is understood that relative terms are intended to encompass different orientations of the device in addition to the orientations illustrated in the drawings. For example, if the device is turned over in one of the drawings, a feature described as being on the “below” an element will be oriented on the “up” an element. Thus, the exemplary term “below” can describe both below and above orientations, depending on the particular orientation of the device. Similarly, if the device is turned over in one of the drawings, an element described as being “below” or “directly below” another element will be oriented above those other elements. Thus, the exemplary terms “below” or “directly below” can describe both above and below orientations.

[0072] The terms used in the description of this disclosure are for the sole purpose of describing specific embodiments and do not limit the disclosure. Where used in the description of this disclosure and the appended claims, the singular forms "an" and "the" also include the plural form unless otherwise specified in the context. Furthermore, where used herein, the terms "and / or" are understood to refer to and encompass any possible combination of one or more of the related enumerated items. In addition, where used herein, the terms "comprises" and "comprising" specify the presence of the described steps, actions, features, elements, and / or components, but do not preclude the presence or addition of one or more other steps, actions, features, elements, components, and / or groups thereof.

[0073] The embodiments of this disclosure are described herein with reference to cross-sectional views, which are schematic illustrations of ideal embodiments of this disclosure. Therefore, deformations from the illustrated shapes are expected, for example, as a result of manufacturing techniques and / or tolerances. Accordingly, the embodiments of this disclosure are not limited to specific shapes of the areas shown herein, but include, for example, deviations of shape due to manufacturing. The areas shown in the drawings are schematic in nature, and their shapes are not intended to represent the actual shapes of areas of the device, nor are they intended to limit the scope of this disclosure unless expressly stated otherwise. Furthermore, in the following drawings, lines that appear straight, horizontal, or vertical for schematic reasons are often inclined, curved, non-horizontal, or non-vertical. Furthermore, the thickness of elements is schematic in nature.

[0074] Unless otherwise defined, all terms used in the embodiments of this disclosure, including technical and scientific terms, have the same meaning as commonly understood by those skilled in the art and are not necessarily limited to any specific definition known at the time of this disclosure. These terms may include subsequently created synonyms. Furthermore, terms defined in commonly used dictionaries, etc., should be interpreted as having the meaning consistent with their meaning in the context of this specification and the art.

[0075] While embodiments of the concept of the present invention have been described in considerable detail with reference to their specific configurations, other versions are possible. Therefore, the spirit and scope of the present invention should not be limited to the specific embodiments described above.

Claims

1. A silicon carbide drift layer having a first conductivity type, A bonding shield region within the drift layer having a second conductivity type opposite to the first conductivity type, an anode contact on the silicon carbide drift layer, comprising a high melting point metal nitride, forming a Schottky junction with the drift layer and forming ohmic contact with the junction shield region. Schottky diodes, including [specific component].

2. The Schottky diode according to claim 1, wherein the Schottky barrier height of the anode contact with respect to the drift layer is less than about 1.2 eV.

3. The Schottky diode according to claim 1, wherein the Schottky barrier height of the anode contact with respect to the drift layer is less than about 1 eV.

4. The Schottky diode according to claim 1, wherein the anode contact contains molybdenum (Mo) nitride.

5. The Schottky diode according to claim 1, wherein the molecular ratio x of nitrogen at the anode contact is greater than approximately 0.

5.

6. The Schottky diode according to claim 1, wherein the molecular ratio x of nitrogen at the anode contact is approximately 1.0 to 1.

6.

7. The Schottky diode according to claim 1, wherein the thickness of the anode contact is at least about 50 nm.

8. The Schottky diode according to claim 1, wherein the thickness of the anode contact is approximately 80 nm to 300 nm.

9. The Schottky diode according to claim 1, wherein the level of residual stress at the time of deposition of the anode contact on the drift layer is less than approximately 500 MPa.

10. The Schottky diode according to claim 1, wherein the anode contact includes a plurality of high-melting-point metal nitride portions and a plurality of non-high-melting-point metal nitride portions arranged in an alternating pattern along the surface of the drift layer, and the non-high-melting-point metal nitride portions form a Schottky barrier junction with the drift layer having a Schottky barrier height higher than the Schottky barrier height formed by the high-melting-point metal nitride portions with the drift layer.

11. The Schottky diode according to claim 10, further comprising a plurality of junction shield regions within the drift layer, wherein the high melting point metal nitride portion is positioned on the junction shield regions and forms ohmic contact with each of the junction shield regions.

12. The Schottky diode according to claim 11, wherein the non-high melting point metal nitride portion is in contact with the drift layer between adjacent junction shield regions.

13. The Schottky diode according to claim 12, wherein the non-high melting point metal nitride portion includes Ti and / or TiW.

14. The Schottky diode according to claim 1, wherein the anode contact includes alternating first and second regions along the surface of the drift layer, and the first region has a first Schottky barrier height to the drift layer that is higher than the second Schottky barrier height of the second region to the drift layer.

15. The Schottky diode according to claim 14, wherein the first region includes MoNx and the second region includes MoNy, and x > y.

16. The Schottky diode according to claim 15, wherein the nitrogen concentration at the anode contact is gradient laterally between the first region and the second region.

17. The Schottky diode according to claim 16, wherein the nitrogen concentration at the anode contact has a smooth gradient between the first region and the second region.

18. The Schottky diode according to claim 16, wherein the nitrogen concentration at the anode contact is stepped between the first region and the second region.

19. The Schottky diode according to claim 1, further comprising a plurality of trenches on the upper surface of the drift layer, wherein the anode contact includes a plurality of high-melting-point metal nitride portions within the trenches and a metal layer on the upper surface of the drift layer, the metal layer being in contact with the high-melting-point metal nitride portions.

20. The Schottky diode according to claim 19, wherein the metal layer forms a first Schottky junction with the drift layer, the high-melting-point metal nitride portion forms a second Schottky junction with the drift layer, and the first Schottky junction has a higher Schottky barrier height than the second Schottky junction.

21. The Schottky diode according to claim 19, further comprising a plurality of junction shield regions within the drift layer, wherein the junction shield regions are located beneath each of the trenches, and the high melting point metal nitride region forms ohmic contact with each of the junction shield regions.

22. The Schottky diode according to claim 19, wherein the high melting point metal nitride region comprises MoNx, and the metal layer comprises molybdenum, titanium, and / or tungsten.

23. The Schottky diode according to claim 1, further comprising a plurality of silicide regions on the drift layer between the drift layer and the anode contact.

24. The Schottky diode according to claim 23, wherein the silicide region includes MoSi.

25. The Schottky diode according to claim 23, further comprising a plurality of junction shield regions within the drift layer, wherein the plurality of silicide regions are arranged on each of the plurality of junction shield regions to form ohmic contact with the junction shield regions.

26. The Schottky diode according to claim 25, wherein the silicide region is provided in each trench within the drift layer, and the junction shield region is located below the trench.

27. The Schottky diode according to claim 26, wherein the anode contact extends into the trench.

28. A method for forming a Schottky diode, A step of forming a drift layer on a substrate, wherein the drift layer and the substrate contain silicon carbide and have a first conductivity type, A step of forming a bonding shield region on the surface of the drift layer, wherein the bonding shield region has a second conductivity type opposite to the first conductivity type. A step of forming an anode contact on the drift layer, wherein the anode contact comprises a high melting point metal nitride, and the anode contact forms a Schottky junction with the drift layer. Methods that include...

29. The aforementioned high melting point metal nitride is MoN ｘ The method according to claim 28, including the method described in claim 28.

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