Semiconductor device and method for manufacturing a semiconductor device

Abstract

Semiconductor device (1) comprising: a semiconductor material (100, 120, 180, 200) having a band gap greater than 2 eV and less than 10 eV and comprising SiC, and a contact layer (130) which is in contact with the semiconductor material (100, 120, 180, 200), wherein the contact layer (130) comprises a metal nitride, a nitrogen content of the metal nitride is 10 to 45 at.% and the metal nitride comprises a metal from the group consisting of molybdenum, titanium and tantalum, a non-ohmic contact is formed between the semiconductor material (100, 120, 180, 200) and the contact layer (130).

Description

BACKGROUND

[0001] Schottky diodes featuring a metal-semiconductor junction are commonly used for blocking devices. SiC Schottky diodes, in particular, are increasingly finding application in the field of power electronics.

[0002] The publication Jin-Ping Ao et al. “Schottky contacts of refractory metal nitrides on gallium nitride using reactive sputtering”, Vacuum, 84, 2010, 1439 - 1443 describes the formation of Schottky contacts on GaN.

[0003] It is an object of the invention to provide an improved semiconductor device having a metal-semiconductor junction. Furthermore, it is an object to provide a method for manufacturing such a semiconductor device.

[0004] According to the invention, the objects are achieved by the teaching of the independent patent claims. Further embodiments are defined in the dependent claims. SUMMARY

[0005] According to one embodiment, a semiconductor device comprises a semiconductor material with a band gap greater than 2 eV and less than 10 eV, and a contact layer in contact with the semiconductor material, wherein the contact layer comprises a metal nitride. A non-ohmic contact is formed between the semiconductor material and the contact layer.

[0006] According to another embodiment, a semiconductor device comprises a semiconductor body including a semiconductor material with a band gap greater than 2 eV and less than 10 eV, and a contact layer in contact with a first surface of the semiconductor body. The contact layer comprises a metal nitride. The contact layer is electrically connected to a first load terminal, and a non-ohmic contact is formed between the semiconductor body and the contact layer. A second surface of the semiconductor body is electrically connected to a second load terminal, the second surface being opposite the first surface.

[0007] According to another embodiment, a semiconductor device comprises a semiconductor body comprising a semiconductor material with a band gap greater than 2 eV and less than 10 eV, and a contact layer in contact with a first surface of the semiconductor body. The contact layer comprises a metal nitride. The contact layer is electrically connected to a first load terminal. A non-ohmic contact exists between the semiconductor body and the contact layer. A second surface of the semiconductor body is electrically connected to a second load terminal, the second surface being opposite the first surface. BRIEF DESCRIPTION OF THE ILLUSTRATIONS

[0008] The accompanying drawings are included to provide a further understanding of embodiments of the invention and are incorporated in and constitute a part of this disclosure. The drawings illustrate embodiments of the present invention and, together with the description, serve to explain the principles. Other embodiments of the invention and many of the intended advantages will be readily appreciated as they become better understood by reference to the following detailed description. The elements of the drawings are not necessarily to scale relative to one another. Like reference characters indicate similar parts, accordingly. Fig. 1A shows a cross-sectional view of an exemplary semiconductor device according to an embodiment. Fig. 1B shows a cross-sectional view of a semiconductor device according to another embodiment. Fig. 1C shows a cross-sectional view of a semiconductor device according to another embodiment. Fig. 1D shows a cross-sectional view of a semiconductor device according to another embodiment. Fig. Figure 2A shows an example of a current-voltage characteristic of an ohmic contact. Fig. Figure 2B shows a cross-sectional view of a blocking contact. Fig. Figure 3 shows an energy band diagram of a Schottky contact. Fig. 4 shows an example of a reaction chamber that can be used to manufacture the semiconductor device according to an embodiment. DETAILED DESCRIPTION

[0009] In the following detailed description, reference is made to the accompanying drawings, which form a part of the disclosure, and in which is shown, for purposes of illustration, specific embodiments in which the invention may be practiced. In this context, directional terminology such as "top," "bottom," "front," "back," "front," "rear," etc., will be used with reference to the orientation of the figures just described. Since components of embodiments of the invention can be positioned in a number of different orientations, the directional terminology is used for purposes of illustration and is in no way limiting. It is to be understood that other embodiments may be utilized and structural or logical changes may be made without departing from the scope defined by the claims.

[0010] The description of the embodiments is not limiting. In particular, elements of the embodiments described below can be combined with elements of different embodiments.

[0011] The terms "wafer," "substrate," or "semiconductor substrate" used in the following description may encompass any semiconductor-based structure having a semiconductor surface. Wafer and structure are understood to include silicon, silicon-on-insulator (SOI), silicon-on-sapphire (SOS), doped and undoped semiconductors, epitaxial layers of silicon supported by a base semiconductor substrate, and other semiconductor structures. The semiconductor need not be silicon-based. The semiconductor may also be silicon-germanium, germanium, or gallium arsenide. According to other embodiments, silicon carbide (SiC) or gallium nitride (GaN) may form the semiconductor substrate material.

[0012] The figures and the description illustrate relative doping concentrations by indicating “-” or “+” next to the doping type “n” or “p”. For example, “n - ” a doping concentration that is lower than the doping concentration of an “n” doping region, while an “n +"-doping region has a higher doping concentration than an "n"-doping region. Doping regions of the same relative doping concentration do not necessarily have the same absolute doping concentration. For example, two different "n"-doping regions can have the same or different absolute doping concentrations. In the figures and the description, for ease of understanding, the doped regions are often referred to as "p"- or "n"-doped. As is clearly understood, this designation is not intended to be limiting in any way. The doping type can be arbitrary as long as the described functionality is achieved. Furthermore, in all embodiments, the doping types can be reversed.

[0013] The terms "coupled" and / or "electrically coupled" used in this description are not intended to imply that the elements must be directly coupled together—intermediate elements may be provided between the "coupled" or "electrically coupled" elements. The term "electrically connected" is intended to describe a low-resistance electrical connection between the electrically connected elements.

[0014] The terms "have," "contain," "comprise," "have," and similar terms used herein are open terms that indicate the presence of identified elements or characteristics, but do not exclude additional elements or characteristics. The indefinite and definite articles are intended to include both the plural and the singular, unless the context clearly indicates otherwise.

[0015] The terms "lateral" and "horizontal," as used in this description, are intended to describe an orientation parallel to a first surface of a semiconductor substrate or semiconductor body. This can be, for example, the surface of a wafer or a die or chip.

[0016] The term "vertical" as used in the present description is intended to indicate an orientation that is arranged perpendicular to the first surface of the semiconductor substrate or the semiconductor body.

[0017] Fig. 1A shows a cross-sectional view of a semiconductor device 1 according to an embodiment. Fig. The semiconductor device 1 shown in FIG. 1A comprises a semiconductor material 100 and a contact layer 130 in contact with the semiconductor material 100. As explained below, the contact layer 130 comprises a metal nitride, and a non-ohmic contact is formed between the semiconductor material 100 and the contact layer 130. A band gap of the semiconductor material 100 is greater than 2 eV and less than 10 eV, e.g., less than 6 eV. According to another embodiment, the band gap of the semiconductor material is greater than 0.9 or 1 eV and less than 10 eV.

[0018] The semiconductor material 100 can be a semiconductor body 101 with one or more doped regions or layers on both sides. The doped region can be created by various methods, such as ion implantation, diffusion, and epitaxial growth of the doped layer. For example, the semiconductor material can be a material with a band gap greater than 1 eV. The semiconductor material comprises silicon carbide.

[0019] The semiconductor body 101 may, for example, be heavily n-doped and comprise an n-doped region with a lower dopant level, wherein the region may be arranged on a first surface 110 of the semiconductor body. The contact layer 130 may comprise a combination of a stoichiometric compound with a non-stoichiometric compound including the metal and nitrogen. For example, the contact layer 130 may comprise a mixture of M x N ywith different values ​​of x and y, where M denotes the metal. The metal nitride layer can, for example, be a mixture of MN and M x N y or from MN2 and M x N y Generally, x in these formulas can be 1, and y can be a real number satisfying 0 < y < 3. Alternatively, y can be 1, and x can be a real number satisfying 0 < x < 3. The metal is selected from the group consisting of molybdenum, titanium, and tantalum. The metal nitride can also comprise two metals, such as MoTiN.

[0020] The contact layer 130 may be electrically connected to an anode terminal. Furthermore, the semiconductor device 1 may include a backside metallization 160 that forms an ohmic contact with the semiconductor body 101. The backside metallization 160 is positioned on a second surface 115 of the semiconductor body 101, opposite the first surface 110. The backside metallization 160 may be electrically connected to a cathode terminal. The terms "ohmic contact," "Schottky contact," and "blocking contact" are explained further below with reference to the Fig. 2A and Fig. 2B.

[0021] Fig. 1B shows a further embodiment of a semiconductor device 1. The Fig. The semiconductor device 1 illustrated in Figure 1B comprises a semiconductor material 200, e.g., a semiconductor body 201, and a contact layer 130 in contact with the semiconductor material. The contact layer 130 comprises a metal nitride, and a non-ohmic contact is formed between the semiconductor material 200 and the contact layer 130. In general, the semiconductor material 200 may be a semiconductor body 201 having further doped regions. For example, these doped regions may be adjacent to a first surface 210 or a second surface 215 of the semiconductor body 201. Unlike the semiconductor material 200 illustrated in Figure 1B, Fig. 1A, the semiconductor device 1 of the Fig. 1B also has a doped region 180 of the second conductivity type. For example, the semiconductor material 200 n - -doped and the doped region 180 can be p +-doped. The doped region 180 can be arranged on the first surface 210 of the semiconductor body 201, and regions of the semiconductor material 200, which, for example, - -doped, may be present on the first surface 210. The contact layer 130 may be in contact with the semiconductor material 200 and the doped regions 180. The Fig. 1B also has a strongly n +-doped region 170 on the second surface of the semiconductor body 201. The semiconductor device further comprises a backside metallization layer 160 that forms an ohmic contact with the doped layer 170. The backside metallization layer 160 may be electrically connected to a cathode terminal. The contact layer 130 may be electrically connected to an anode terminal. The semiconductor material may comprise any of the materials mentioned above. For example, the semiconductor material may be silicon carbide.

[0022] The Fig. The semiconductor device shown in Figure 1B may implement a junction barrier Schottky (JBS) diode with p + implanted regions 180. If a reverse voltage is applied to the semiconductor device, depletion regions located at an interface between the n - -range 200 and the p +-region 180, absorbs a leakage current that may originate from the Schottky contact of the device. Consequently, such a junction barrier Schottky diode has a reduced leakage current. Such a JBS can be suitably used in switching power supplies.

[0023] According to a further embodiment, the semiconductor device 1 may implement a merged PIN Schottky diode (MPS). Fig. Figure 1C shows a cross-sectional view of such a merged PIN Schottky diode. The MPS has similar components to the JBS, with these components being designated by the same reference numerals as the corresponding components of the JBS. In particular, the p + -Areas 185 of the MPS are suitable for forward operation of minority carriers in the n - -area 400. For example, the p + -Areas 185 are highly endowed, approximately in the range 10 19 up to 10 20 cm-3 .

[0024] Fig. 1D shows another example of a semiconductor device. As illustrated, the semiconductor device 1 comprises a semiconductor body 101 comprising a semiconductor material with a band gap greater than 2 eV and less than 10 eV, a contact layer 130 in contact with a first surface 110 of the semiconductor body 101, wherein the contact layer 130 comprises a metal nitride. The contact layer 130 is electrically connected to a first load terminal 240. A non-ohmic contact is formed between the semiconductor body 101 and the contact layer 130. A second surface 115 of the semiconductor body 101 is electrically connected to a second load terminal 250. The second surface 115 is opposite the first surface 110.

[0025] The contact layer 130 may, for example, be in contact with the doped region 120. According to a further embodiment, the semiconductor body 101 may be highly n + -doped and of n-conductivity type. The doped region 120 may be n-conductivity type with a low concentration of n-type dopants.

[0026] For example, the Fig. The semiconductor device shown in Figure 1D may implement a Schottky diode or a semiconductor device related to a Schottky diode. In this case, the first load terminal 240 may be an anode terminal, and the second load terminal 250 may be a cathode terminal. Depending on the different implementations of the semiconductor device, the first load terminal 240 may be a source terminal and the second load terminal 250 may be a drain terminal, e.g., in the case of a MOSFET (metal oxide semiconductor field-effect transistor) or JFET (junction field-effect transistor). According to another example, the first load terminal 240 may be an emitter terminal and the second load terminal 250 may be a collector terminal, e.g., in the case of an IGBT (insulated gate bipolar transistor).

[0027] The semiconductor device may include an active region 181 and a junction termination region 182. In the active region 181, the contact layer 130 is in contact with the semiconductor body 101. The junction termination region 182 differs from the active region 181 in terms of function and structure. In particular, in the active region 181, a load terminal of the semiconductor device, e.g., the anode terminal, is electrically connected to the semiconductor body for the purpose of conducting current. In contrast, the junction termination region serves for edge termination to reduce an electric field peak in the outer region of the semiconductor device 1. Typical structural elements of the junction termination region include one or more elements made of field plates, ring structures such as floating guard rings or ring segments, junction termination extension (JTE) structures, and variation of lateral doping (VLD) structures.

[0028] Fig. Figure 2A shows an example of the current-voltage characteristic of an ohmic contact. As shown, the current is approximately proportional to the applied voltage. The ratio of voltage to current determines the resistance of the contact.

[0029] On the other hand, in a non-ohmic contact, the current follows, as in Fig. 2B, is not proportional to the voltage. As shown in the left part of the Fig. 2B, for example, almost no current can flow, regardless of the applied negative voltage. However, if a positive voltage is applied, the current can increase in a non-linear manner. Any type of current-voltage characteristic in which the current behaves non-linearly with the applied voltage can be considered to form a non-ohmic contact. For example, the contact can be a blocking contact, such as a pn junction or a Schottky junction, in which only a small current, i.e., the reverse saturation current, flows if a small reverse voltage is applied. If a larger reverse voltage is applied, a breakdown current can also flow.

[0030] In the context of this application, the term “non-ohmic contact” refers to any contact that has a non-linear current-voltage characteristic.

[0031] According to a further modification, the term "blocking contact" includes any contact through which little or no current flows when a reverse voltage is applied, the current being not proportional to the applied voltage.

[0032] Fig. Figure 3 shows an example of an energy band diagram of a blocking metal-semiconductor junction. The right side of the Fig. Figure 3 shows the energy band diagram within the semiconductor material, where W C characterizes the energy level of the conduction band, W V denotes the energy level of the valence band and W F characterizes the Fermi level of the semiconductor material. The difference ΔW between energy level W C of the conduction band and the energy level W V of the valence band indicates the band gap of the semiconductor material. The left area of ​​the energy band diagram of Fig. 3 shows the work function qx φ Mof the metal. If the metal and the semiconductor material form a junction, a potential barrier is created at the interface between the Fermi level of the metal W F and the valence band of the semiconductor material. The height of the potential barrier q × φ B is also called the “Schottky barrier” of contact.

[0033] In general, Schottky contacts with a wide bandgap semiconductor material exhibit a large forward voltage drop due to the work function and Schottky barrier of the contact metal used. According to the described embodiment, the height of the Schottky barrier can be adjusted by selecting a contact layer including a metal nitride. In particular, by varying the nitrogen content of the metal nitride, the work function of the metal can be appropriately adjusted. Consequently, the Schottky barrier and thus the forward voltage drop can be adjusted by adjusting the nitrogen content of the metal nitride. The nitrogen content of the metal nitride is greater than 10 at% and less than 45 at%. For example, the nitrogen content can be determined using Auger ion spectroscopy, secondary ion mass spectroscopy (SIMS), or X-ray photoelectron spectroscopy (XPS).

[0034] The semiconductor device may be a semiconductor component selected from the group consisting of a Schottky diode, a merged pn Schottky diode, a JFET, a MESFET, an integrated freewheeling diode, a rectifier, an inverter, and a power supply.

[0035] Fig.4 shows a reaction chamber of a sputtering system in which the contact layer comprising a metal nitride can be formed. A semiconductor substrate 430 can be placed on a rotatable plate 440. A sputtering target 410 can be attached to a support element 415. The target can comprise the metal that forms the metal nitride. The target is selected from a metal selected from the group consisting of molybdenum, titanium, and tantalum. Furthermore, the target 410 can comprise a combination of such metals. The chamber 400 has a gas inlet 420 through which a plasma-forming inert gas such as argon is introduced into the reaction chamber. Nitrogen (N2) can also be introduced via the inlet 420. After a plasma is ignited, nitrogen is present as a reactive gas that reacts with the atoms of the target 410. An electric field and a magnetic field can be applied in the sputtering system.Further details of the sputtering process are known to the person skilled in the art.

[0036] According to one embodiment, the nitrogen content in the deposited metal nitride layer can be determined by adjusting the partial pressure of nitrogen. It has been shown that this can change the work function of the contact layer. For example, the barrier height of Mo x N y Metal in contact with a silicon carbide layer can be 0.94 eV to 1.12 eV. For example, the total pressure within the sputtering system is 4 to 15 mTorr. The partial pressure of nitrogen (N2 / (N2+Ar)) can range from 0.1 to 1.0.

Claims

[1] A semiconductor device (1) comprising: a semiconductor material (100, 120, 180, 200) having a band gap greater than 2 eV and less than 10 eV and comprising SiC, and a contact layer (130) which is in contact with the semiconductor material (100, 120, 180, 200), wherein the contact layer (130) comprises a metal nitride, a nitrogen content of the metal nitride is 10 to 45 at.% and the metal nitride comprises a metal from the group consisting of molybdenum, titanium and tantalum, a non-ohmic contact is formed between the semiconductor material (100, 120, 180, 200) and the contact layer (130). [2] The semiconductor device (1) according to claim 1, wherein the metal nitride comprises a combination of a stoichiometric compound with a non-stoichiometric compound including the metal and nitrogen. [3] A semiconductor device (1) according to claim 1 or 2, wherein a Schottky contact is formed between the semiconductor material (100, 120, 200) and the contact layer (130). [4] Semiconductor device (1) according to one of the preceding claims, wherein a blocking contact is formed between the semiconductor material (100, 120, 200) and the contact layer (130). [5] An electrical component comprising the semiconductor device (1) according to any one of the preceding claims, wherein the electrical component is a component selected from the group consisting of a Schottky diode, a fused pn Schottky diode, a JFET, a MESFET, an integrated freewheeling diode, a rectifier, an inverter, and a power supply. [6] A semiconductor device (1) comprising: a semiconductor body (101, 201) comprising a semiconductor material having a band gap greater than 2 eV and less than 10 eV and comprising SiC; and a contact layer (130) which is in contact with a first surface (110) of the semiconductor body (101, 201), wherein the contact layer (130) comprises a metal nitride, a nitrogen content of the metal nitride is 10 to 45 at.% and the metal nitride comprises a metal from the group consisting of molybdenum, titanium and tantalum, and the contact layer (130) is electrically connected to a first load terminal (240), a non-ohmic contact formed between the semiconductor body (101, 201) and the contact layer (130), a second surface (115) of the semiconductor body electrically connected to a second load terminal (250), the second surface (115) being opposite the first surface (110). [7] A semiconductor device (1) according to claim 6, further comprising a doped region (180) in contact with the contact layer (130), the doped region (180) being embedded in the semiconductor body (201) and having a conductivity type opposite to the conductivity type of the semiconductor body (201). [8] A method of manufacturing a semiconductor device (1), comprising: Forming a contact layer (130) in contact with a semiconductor material (100, 120, 180, 200) comprising SiC, wherein a non-ohmic contact is formed between the semiconductor material (100, 120, 180, 200) and the contact layer (130), wherein the semiconductor material (100, 120, 180, 200) has a band gap greater than 2 eV and less than 10 eV, the contact layer (130) comprises a metal nitride comprising a metal from the group consisting of molybdenum, titanium and tantalum, wherein forming the contact layer (130) comprises selecting a composition ratio of the metal nitride, whereby a work function of the contact layer (130) is adjusted and a nitrogen content of the metal nitride is 10 to 45 at%. [9] The method of claim 8, wherein the contact layer (130) is formed by a reactive sputtering process using nitrogen as a reactant. [10] The method of claim 9, wherein a partial pressure of nitrogen during the reactive sputtering process is adjusted such that the metal nitride has a mixed phase of MN and M2N, where M denotes a metal. [11] The method according to claim 10, wherein a ratio of the nitrogen partial pressure and the total pressure during the sputtering process is in a range of 0.1 to 1.

0. [12] The method of claim 10 or 11, wherein the partial pressure of the nitrogen during the reactive sputtering process is adjusted to determine the work function of the contact layer (130).

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