SEMICONDUCTOR DEVICE AND METHOD FOR MANUFACTURING SAME

A semiconductor device that may include a silicon carbide substrate, a silicon layer disposed on the silicon carbide substrate, and a gate oxide layer disposed on the silicon layer. The silicon layer may be implanted within the silicon carbide substrate. The silicon layer may comprise a thickness of 100 angstroms 5000 angstroms. The silicon layer may contain less than one percent carbon, or may contain a certain percentage of carbon that decreases as a distance from the surface of the silicon carbide substrate increases.

TECHNICAL FIELD

The present disclosure relates generally to semiconductor substrates for electronic devices, and more specifically to silicon carbide substrates and a gate oxide layer with the silicon carbide substrate.

SUMMARY

According to an aspect of one or more examples, there is provided a method of fabricating a semiconductor device. The method may include forming a silicon layer on a surface of a silicon carbide substrate, and forming a gate oxide layer over the silicon layer. The silicon layer may comprise a thickness of 100 angstroms to 5000 angstroms. The silicon layer may contain less than one percent carbon, or may contain a certain percentage of carbon that decreases as a distance from the surface of the silicon carbide substrate increases. The step of forming the gate oxide layer may include oxidizing silicon from the silicon layer to form the gate oxide layer of silicon dioxide.

According to another aspect of one or more examples, there is provided a method of fabricating a semiconductor device. The method may include implanting silicon into a silicon carbide substrate to form a first silicon rich layer, forming a second silicon layer over the first silicon layer using epitaxial growth, and forming a gate oxide layer on the second silicon layer. Silicon rich means that the percent of silicon is greater than the percent of carbon, e.g., the silicon percentage could be twenty-five percent higher than the carbon percentage. In some example, a higher percentage of silicon may be better than a lower percentage of silicon, for example the higher percentage of silicon may reduce the number of defects. The first silicon layer and the second silicon layer may together comprise a thickness of 100 angstroms to 5000 angstroms. The second silicon layer may contain less than one percent carbon, or may contain a certain percentage of carbon that decreases as a distance from the surface of the silicon carbide substrate increases. The step of forming the gate oxide layer may include oxidizing silicon from the second silicon layer to form the gate oxide layer of silicon dioxide.

According to another aspect of one or more examples, there is provided a method of fabricating a semiconductor device. The method may include forming a first silicon layer on a surface of the silicon carbide substrate, polishing the first silicon layer, forming a second silicon layer over the first silicon layer, and forming a gate oxide layer over the second silicon layer. The first silicon layer and the second silicon layer together may comprise a thickness of 100 angstroms to 5000 angstroms. The second silicon layer may contain less than one percent carbon, or may contain a certain percentage of carbon that decreases as a distance from the surface of the silicon carbide substrate increases. The step of forming the gate oxide layer may include oxidizing silicon from the second silicon layer to form the gate oxide layer of silicon dioxide.

According to another aspect of one or more examples, there is provided a semiconductor device that may include a silicon carbide substrate, a silicon layer disposed on the silicon carbide substrate, and a gate oxide layer disposed on the silicon layer. The silicon layer may be implanted within the silicon carbide substrate. The silicon layer may comprise a thickness of 100 angstroms to 5000 angstroms. The silicon layer may contain less than one percent carbon, or may contain a certain percentage of carbon that decreases as a distance from the surface of the silicon carbide substrate increases.

DETAILED DESCRIPTION OF VARIOUS EXAMPLES

Reference will now be made in detail to the following various examples, which are illustrated in the accompanying drawings, wherein like reference numerals refer to like elements throughout. The following examples may be in various forms without being limited to the examples set forth herein.

FIGS.1A-1Cshows a silicon carbide substrate and a method of manufacturing the silicon carbide substrate according to one or more examples. Silicon carbide is often used as a substrate to create many semiconductor devices, and may result in reduced switching losses, higher power density, improved heat dissipation, and increased bandwidth as compared with other materials. Some semiconductor devices, such as metal-oxide-semiconductor field-effect transistors (MOSFETs) include a gate oxide layer that is a dielectric layer that separates the silicon carbide substrate from a gate electrode, which may be made of metal or other conductive material.

When forming the gate oxide layer on a silicon carbide substrate, the interface between the silicon carbide substrate and the gate oxide layer (for example, a gate oxide layer made of silicon dioxide) may be very rough. The rough interface between the gate oxide layer and the silicon carbide substrate may degrade carrier mobility in the silicon carbide substrate, which may limit device performance. In order to at least partially resolve this difficulty, and referring toFIG.1A, a layer of silicon (Si)30may be grown or deposited on a surface of a silicon carbide (SiC) substrate20. According to one or more examples, the silicon layer30may be approximately 100 angstroms to 5000 angstroms thick, though other thicknesses may be used depending on the application. For example, the amount of silicon used to create the silicon layer30may depend on the thickness of the gate oxide layer to be formed on the silicon layer30. As shown inFIG.1B, a gate oxide layer40may be formed on the silicon layer30. For example, the gate oxide layer40may be a layer of silicon dioxide, which may be formed or grown by a thermal oxidation process of the silicon layer30. According to an example shown inFIG.1C, a very thin layer of silicon30, or no silicon, may remain between the silicon carbide substrate20and the gate oxide layer40, when gate oxide layer40is comprised of silicon dioxide.

FIG.2shows a graph demonstrating potential carbon concentration of silicon layer30according to one or more examples. As shown in the graph inFIG.2, the vertical axis indicates the percentage of carbon contained in silicon layer30and silicon carbide substrate20, and the horizontal access indicates the depth from the top surface of the silicon layer30. Thus, the silicon layer30presents a graded silicon carbide layer, as the percentage of carbon in the silicon layer30decreases as a distance from the surface of the silicon carbide substrate increases. At the point where the silicon layer interfaces with the silicon carbide substrate, the percentage carbon increases to indicate a fixed carbon percentage in the silicon carbide substrate. According to an example demonstrated by the graph ofFIG.2, the carbon percentage in the silicon layer may be approximately zero at the top of the silicon layer30, and may increase as the distance from the silicon carbide substrate decreases, i.e. as the distance from the top of the silicon layer30increases. As shown in the example inFIG.2, the percentage of carbon in the silicon layer may increase approximately linearly until reaching the silicon carbide substrate, at which point the carbon percentage may become constant. Alternatively, the percentage of carbon may increase non-linearly in the silicon layer.

A method of manufacturing a silicon layer on a silicon carbide substrate is herein enabled according to one or more examples.FIGS.3A-3Cshow a silicon carbide substrate and a method of manufacturing the silicon carbide substrate according to one or more examples. InFIG.3A, a first silicon rich layer70may be implanted within an upper portion of a silicon carbide substrate20. Silicon rich means that the percent of silicon is greater than the percent of carbon, e.g., the silicon percentage could be twenty-five percent higher than the carbon percentage, without limitation. According to an example, the implanted depth of the implanted first silicon rich layer70may be approximately 100 angstroms to 5000 angstroms thick, though other thicknesses may be used. First silicon rich layer70may be formed by implanting silicon into the silicon carbide substrate20. As shown inFIG.3B, after the first silicon rich layer70is implanted within the upper portion of the silicon carbide substrate20, a second silicon layer80may be formed by using epitaxial growth on the implanted first silicon rich layer70. By implanting the first silicon rich layer70, there is a sufficient amount of silicon on top of the silicon carbide substrate20to obtain a better quality second silicon layer80, i.e. the silicon layer80may have fewer defects than may happen in the absence of the first silicon rich layer70. For example, the second silicon layer80may be a single crystalline layer. As shown inFIG.3C, after the second silicon layer80is formed, a gate oxide layer90may be formed on the second silicon layer80. For example, the gate oxide layer90may be a layer of silicon dioxide, which may be formed or grown by a thermal oxidation process of the second silicon layer80. Once the gate oxide layer90is formed, a portion of the second silicon layer80may remain between the implanted first silicon rich layer70and the gate oxide layer90, or there may be no portion of the second silicon layer80remaining after the gate oxide layer90is formed. The second silicon layer80may include less than one percent carbon, or alternatively the carbon percentage in the second silicon layer80may be approximately zero at the top of the second silicon layer80, and the carbon percentage may increase as the distance from the silicon carbide substrate20decreases. In other words, the percentage of carbon in the second silicon layer80may decrease as a distance from the silicon carbide substrate20increases. This can be accomplished during epitaxial growth, for example, by gradually reducing the percentage of carbon incorporation.

A method of manufacturing a silicon carbide substrate is herein enabled according to one or more examples.FIGS.4A-4Dshow a silicon carbide substrate and a method of manufacturing the silicon carbide substrate according to one or more examples. InFIG.4A, a layer of silicon30may be grown or deposited on a surface of a silicon carbide substrate20. When the silicon layer30is grown, the silicon layer30may have different types of defects. The silicon layer30may be polished to remove a portion of the silicon layer as shown inFIG.4B, which polishing may remove portions of the silicon layer30containing some of the defects. After the silicon layer30is polished, additional silicon may be grown or deposited on the existing silicon layer30as shown inFIG.4C. The silicon layer30may then be polished again to remove a portion of the silicon layer30that may contain defects. This process of growing or depositing silicon and polishing the silicon layer30may be repeated until a silicon layer30of sufficient quality is obtained. For example, the process may be repeated until a single crystalline silicon layer30is obtained. In one example, the additional silicon may contain less than one percent carbon. In one example, a percentage of carbon in the additional silicon decreases as a distance from the surface of the silicon carbide substrate increases. Once a sufficient silicon layer30is obtained, a gate oxide layer40may be formed on the silicon layer30as shown inFIG.4D. For example, the gate oxide layer40may be a layer of silicon dioxide, which may be formed or grown by a thermal oxidation process of the silicon layer30. According to an example, when the gate oxide layer40is formed, a layer of silicon30may remain between the silicon carbide substrate20and the gate oxide layer40. According to an example, a very thin layer of silicon, or no silicon, may remain between the silicon carbide substrate20and the gate oxide layer40.

Various examples have been disclosed herein, in connection with the above description and the drawings. It will be understood that it would be unduly repetitious to literally describe and illustrate every combination and sub-combination of these examples. Accordingly, all examples may be combined in any way and/or combination, and the present specification, including the drawings, shall be construed to constitute a complete written description of all combinations and sub-combinations of the examples described herein, and of the manner and process of making and using them, and shall support claims to any such combination or sub-combination.