Semiconductor device, method for manufacturing the same

Abstract

To easily correct the position of leads in semiconductor devices. [Solution] In the photoelectron spectrum on the Si side (center), there is no significant difference for (5) to (8), which correspond to a region deeper than the center of the Ni silicide layer. However, in (1) to (4), which are shallower and within 50 nm from the surface, in Example (b), the Ni in the photoelectron spectrum... x In comparative example (a), a region of localized high intensity (small peak) is observed at higher energies than the main peak corresponding to Si, whereas these small peaks are not visible in comparative example (a). The energy in this region corresponds to SiO2 and SiO2. x This corresponds to (x<2). In other words, in Example (b), silicon oxide is formed at these depths, whereas in Comparative Example (a), such silicon oxide is not formed.

Description

Technical Field

[0001] Embodiments of the present disclosure relate to a semiconductor device using an electrode that makes an ohmic contact with silicon carbide (SiC), and a method for manufacturing the same.

Background Art

[0002] Since silicon carbide (SiC) has a wider bandgap than silicon or the like, it is extremely promising as a material for power devices and the like. Using this, MOSFETs (Metal Oxide Semiconductor Field Effect Transistors) and Schottky barrier diodes (SBDs) using their Schottky junctions have been realized.

[0003] When forming such elements, current can be passed through SiC via an electrode formed on SiC, which is a semiconductor material. As electrodes in this case, there are two types: a Schottky electrode having rectifying properties in the current-voltage characteristics (I-V characteristics) with SiC, and an ohmic electrode having no rectifying properties and low contact resistance. Generally, these electrodes are made of a metal material, and it is known that various materials can be used for n-type SiC and p-type SiC, respectively.

[0004] Among these, the ohmic electrode for n-type SiC is widely used as an electrode for MOSFETs, SBDs, etc. As a material for an electrode having good ohmic properties (no rectifying properties in the I-V characteristics and low contact resistance) with n-type SiC, nickel (Ni) is known. However, as described in Patent Document 1, it is not between Ni and n-type SiC that has good ohmic properties, but precisely between Ni silicide (Ni x Si y ) and n-type SiC that is formed by heat-treating after forming Ni on the SiC surface and by a chemical reaction between Ni and SiC.

[0005] This allows for the production of SiC Schottky diodes by forming Ni silicide across the entire back surface of an n-type SiC substrate to create an ohmic electrode with low contact resistance on the back surface, and forming a Schottky electrode on the front surface. [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] Japanese Patent Publication No. 2012-190829 [Overview of the Initiative] [Problems that the invention aims to solve]

[0007] When manufacturing semiconductor devices, various processes may be performed on wafers with Ni silicide formed on them, as described above. For example, one such process is the removal of the oxide film (silicon oxide film) from the wafer surface. This process is generally carried out by wet etching using hydrofluoric acid (HF).

[0008] Unlike silicon oxide films, Ni silicide is not uniformly removed by hydrofluoric acid, but it can be partially etched, sometimes resulting in residue. Even if this residue does not adversely affect the Ni silicide contact itself, it can become a foreign substance and adversely affect other parts, such as the Schottky electrode.

[0009] Therefore, there was a need for semiconductor devices that used Ni silicide thin films, which are less likely to generate residues when treated with hydrofluoric acid.

[0010] This disclosure has been made in view of the aforementioned problems and aims to provide a semiconductor device and a method for manufacturing the same that solve the above problems. [Means for solving the problem]

[0011] This disclosure has the following structure in order to solve the above-mentioned problems. The semiconductor device of this disclosure comprises a nickel (Ni) silicide layer formed on the surface of a silicon carbide (SiC) substrate by a reaction between nickel (Ni) and SiC, characterized in that, in the Ni silicide layer, in a surface region with a depth of 50 nm or less in terms of silicon oxide film in depth profiling analysis by X-ray photoelectron spectroscopy from the surface opposite to the SiC substrate, a silicon (Si) oxide is formed in the Ni silicide at a certain depth in a compositional analysis of depth. In the aforementioned surface region, the ratio of the Si composition to the total composition of Ni and Si may be 25% or more. The Si composition in the surface region may be higher than the Si composition in the deeper regions of the Ni silicide layer. A method for manufacturing the semiconductor device, comprising: a film formation step of forming a Ni layer made of Ni on the SiC substrate; a heat treatment step of heating the SiC substrate on which the Ni layer is formed to react Ni and Si at the interface between the Ni layer and the SiC substrate; and an unreacted Ni layer removal step of removing the surface side of the Ni layer that remains in an unreacted state with Si after the heat treatment step to obtain the Ni silicide layer. In the aforementioned film formation process, the Ni layer with a thickness of 50 nm to 200 nm is formed. In the heat treatment step, the SiC substrate on which the Ni layer is formed may be heated at a temperature of 900°C to 975°C for a time of 30 seconds to 4 minutes. [Effects of the Invention]

[0012] As described above, this disclosure makes it possible to obtain a semiconductor device using a Ni silicide thin film that is less likely to generate residue due to hydrofluoric acid treatment. [Brief explanation of the drawing]

[0013] [Figure 1] This is a cross-sectional view showing a process for manufacturing a semiconductor device according to an embodiment of the present disclosure. [Figure 2]Optical photographs of the surfaces after exposing the Ni silicide layer patterns of Comparative Example (a) and Example (b) to hydrofluoric acid. [Figure 3] Detection results for each area of foreign matter after hydrofluoric acid treatment in Comparative Example (a) and Example (b). [Figure 4] Si and Ni composition distributions in the depth direction of the Comparative Example and the Example measured by XPS. [Figure 5] Shows the photoelectron spectra of the Ni side (left side) and Si side (center) for each depth, and the measurement points (right side) in the depth direction composition distributions of Si and Ni, measured by XPS, in Comparative Example (a) and Example (b).

Embodiments for Carrying Out the Invention

[0014] Hereinafter, a semiconductor device, which is an embodiment of the present disclosure, will be described. FIG. 1 is a process cross-sectional view showing a simplified manufacturing process of this semiconductor device, and here, only the process of forming a Ni silicide layer (thin film) is described. For example, when this semiconductor device is a Schottky diode, a Schottky electrode is formed on the surface opposite to the surface (the upper surface in the figure) on which this Ni silicide layer is formed. Since this process is the same as well-known ones, the description is omitted. The same applies when this semiconductor device is other than a Schottky diode.

[0015] In FIG. 1(a), a Ni layer 20 is uniformly formed (film forming process) on a clean SiC substrate 10 made of n-type SiC. This film formation is performed, for example, by sputtering, and the substrate temperature is room temperature. The thickness of the Ni layer 20 is set to 50 nm to 200 nm so that a Ni silicide with a sufficient thickness can be formed using this.

[0016] Next, a heat treatment for causing a silicide reaction is performed on the structure of FIG. 1(a) (heat treatment step). This heat treatment is carried out in an air atmosphere at a temperature of 900° C. or higher as the temperature for causing the above reaction. As a result, as shown in FIG. 1(b), a Ni silicide layer 30 is formed at the interface between the SiC substrate 10 and the Ni layer 20 by the reaction between Ni and Si.

[0017] After the Ni silicide layer 30 is formed as shown in FIG. 1(b) and the outermost surface becomes the unreacted Ni layer 20 (unreacted Ni layer 20A) of Si and Ni, as shown in FIG. 1(c), the unreacted Ni layer 20A is selectively etched and removed (unreacted Ni layer removal step). Here, there is a mixed solution of sulfuric acid (H2SO4) and hydrogen peroxide water (H2O2) as a solution that can etch the unreacted Ni layer 20A without adversely affecting the SiC substrate 10 and the Ni silicide layer 30. As a result, a structure in which the Ni silicide layer 30 is formed on the surface of the SiC substrate 10 is obtained.

[0018] Thereafter, a Schottky electrode is formed on the opposite surface as described above, and a wiring layer or the like composed of another low-resistance metal material (for example, a stacked structure of Ti / Ni / Au) is formed on the Ni silicide layer 30, whereby a desired semiconductor device can be obtained.

[0019] Here, the inventor has found that by adjusting the formation conditions of the Ni silicide layer 30 in the above heat treatment step, the composition distribution and the like in the thickness direction of the Ni silicide layer 30 can be adjusted, and thereby the residue formed when the Ni silicide layer 30 is exposed to hydrofluoric acid can be reduced. This point will be described below.

[0020] In the following, the formation conditions (heat treatment conditions) for the comparative example Ni silicide layer 30 were set to a temperature of 980°C and a treatment time of 120 sec, while the heat treatment conditions for the example were set to a temperature of 960°C and a treatment time of 120 sec. For heat treatment conditions that yield a Ni silicide layer 30 with similar properties, a temperature of 900°C to 975°C and a treatment time of 30 sec to 4 min are preferred, particularly a temperature of 950°C to 970°C and a treatment time of 1 min to 3 min. Such heat treatments include RTA (Rapid Thermal Annealing) using a halogen lamp or laser annealing.

[0021] Figure 2 shows optical photographs of the surfaces of the Ni silicide layer patterns N of Comparative Example (a) and Example (b) after exposure to hydrofluoric acid. In Comparative Example (a), foreign matter (residue) R can be visually confirmed, whereas no foreign matter can be confirmed in Example (b).

[0022] Figure 3 shows the detection results for each area of ​​foreign matter after the hydrofluoric acid treatment described above, using a wafer defect inspection device, for Comparative Example (a) and Example (b). Corresponding to the results in Figure 2, in Example (b), the area was 500 μm². 2 It is clear that the above-mentioned foreign matter has been reduced. In other words, the residue is significantly reduced in this embodiment.

[0023] Figure 4 shows the results of X-ray photoelectron spectroscopy (XPS) analysis of the Ni silicide layer 30 in the comparative example and the example, in the depth direction. The compositional distribution of Ni and Si in the depth direction is particularly shown. The depth direction distribution was measured by sputter etching the sample from the surface with Ar ions, and the horizontal axis represents the depth (thickness) in terms of SiO2.

[0024] In Figure 4, the right side (depth of 450 nm or more) corresponds to the SiC substrate 10, and the left side (depth of 0 nm) corresponds to the surface of the Ni silicide layer 30 in the state shown in Figure 1(c). The region with a depth of approximately 150 nm corresponds to the central part of the thickness direction of the Ni silicide layer 30. In this region, the composition of Ni and Si is the same between the comparative example and the example, with a Si / Ni composition ratio of approximately 1 / 3. This corresponds to the fact that this Ni silicide mainly consists of Ni3Si.

[0025] On the other hand, the compositional distribution differs between the comparative example and the example on the SiC substrate 10 side (right side) and the surface side (left side). Here, the region on the surface side (left side) is what affects the aforementioned residue. In this region, the Si composition ratio is higher in the example compared to the comparative example.

[0026] To investigate this point in more detail, photoelectron spectra obtained by XPS were examined at eight representative depths. Here, the photoelectron spectra measured were those in the energy range corresponding to electrons contributing to bonding with Si on the Ni side (Ni2p3 / 2) and electrons contributing to bonding with Ni on the Si side (Si2p). Figure 5 shows these results for Comparative Example (a) and Example (b), and on the far right, the measured depths ((1) to (8)) are shown in the composition distribution (Comparative Example (a), Example (b)) in Figure 4. The depths increase from the surface in the order of (1) to (8). In Figure 5, for both Comparative Example (a) and Example (b), the photoelectron spectra corresponding to the electrons on the Ni side are shown on the left, the photoelectron spectra corresponding to the electrons on the Si side are shown in the center, and the composition distribution is shown on the right. The photoelectron spectra are shown from bottom to top for the depths (1) to (8).

[0027] In Figure 5, the photoelectron spectra corresponding to electrons on the Ni side (left side) show no significant difference between Comparative Example (a) and Example (b) at any depth. In the photoelectron spectra on the Si side (center), there is no significant difference for (5) to (8), which correspond to regions deeper than the center of the Ni silicide layer (on the SiC substrate side). However, in (1) to (4), which are shallower and within 50 nm from the surface, Example (b) shows a difference in the Ni photoelectron spectra. x In comparative example (a), a region of locally high intensity (small peak) is visible at a higher energy level (left side in the figure) than the main peak corresponding to Si, whereas these small peaks are not visible in comparative example (a). The energy in this region corresponds to SiO2 and SiO2. x This corresponds to (x<2). In other words, in Example (b), silicon oxide is formed at these depths, whereas in Comparative Example (a), such silicon oxide is not formed.

[0028] The reduction in residue in the examples reflects the compositional distribution within the Ni silicide layer. Specifically, a Ni silicide layer formed to partially contain silicon oxide within a region (surface region) with a depth of 50 nm (in terms of Si oxide film) from the surface is preferable from the viewpoint of reducing residue. Analysis revealed that the composition of the silicon oxide was in the range of 0.1% to 5% (molar ratio) in the Ni silicide at the depth where the silicon oxide was present, and it was located at a depth of 50 nm from the surface of the Ni silicide layer. Although silicon oxide is an insulator and its presence may reduce the electrical conductivity of the Ni silicide layer, in this case, the composition of silicon oxide was small, so there was no significant difference in the electrical resistance of the Ni silicide layer between the examples and the comparative example. Therefore, this Ni silicide layer can be used as an electrode.

[0029] Furthermore, the results in Figures 4 and 5 (right side) show that in Example (b), the Ni / Si composition ratio decreases particularly as you approach the surface, and the Si composition ratio within the surface region is higher in Example (b) than the 25% corresponding to the Ni3Si case. In other words, this Ni and Si composition distribution is also considered to contribute to the reduction of the residue.

[0030] The above-described Ni silicide layer 30 does not generate residue (foreign matter) even during hydrofluoric acid treatment, making it particularly effective in semiconductor devices such as Schottky diodes, where it is used as an ohmic contact electrode. Furthermore, even when a manufacturing method other than the one described above is used, similar characteristics can be obtained if the Si oxide layer is formed in the same manner as described above and has the same Si and Ni composition distribution as described above.

[0031] Furthermore, in the above example, the Ni silicide layer was used as an ohmic contact electrode for an n-type SiC substrate, but a similar Ni silicide layer can also be formed on SiC other than n-type. In this case as well, it is clear that the above configuration is effective. [Explanation of Symbols]

[0032] 10 SiC substrates 20 Ni layers 20A Unreacted Ni layer 30 Ni silicide layer N Ni silicide layer pattern R Foreign matter (residue)

Claims

1. A semiconductor device comprising a nickel (Ni) silicide layer formed on the surface of a silicon carbide (SiC) substrate by a reaction between nickel (Ni) and SiC, A semiconductor device characterized in that, in the Ni silicide layer, in a surface region with a depth of 50 nm or less in terms of silicon oxide film as measured by depth profiling analysis by X-ray photoelectron spectroscopy from the surface opposite to the SiC substrate, a silicon (Si) oxide is formed in the Ni silicide at a certain depth in a plane as measured by depth profiling analysis.

2. The semiconductor device according to claim 1, characterized in that, in the surface region, the ratio of the Si composition to the total composition of Ni and Si is 25% or more.

3. The semiconductor device according to claim 2, characterized in that the composition of Si in the surface region is higher than the composition of Si in the Ni silicide layer in a region deeper than the surface region.

4. A method for manufacturing a semiconductor device according to claim 1 or 2, A film deposition step of forming a Ni layer made of Ni on the SiC substrate, A heat treatment step in which the SiC substrate on which the Ni layer is formed is heated to react Ni and Si at the interface between the Ni layer and the SiC substrate, A step to remove the unreacted Ni layer to obtain the Ni silicide layer by removing the surface Ni layer that remains in an unreacted state with Si after the heat treatment step, A method for manufacturing a semiconductor device, characterized by comprising the following:

5. In the aforementioned film formation process, the Ni layer having a thickness of 50 nm to 200 nm is formed. The method for manufacturing a semiconductor device according to claim 4, characterized in that, in the heat treatment step, the SiC substrate on which the Ni layer is formed is heated at a temperature of 900°C to 975°C for a time of 30 seconds to 4 minutes.

Images