Method of manufacturing an insulation layer on silicon carbide

Abstract

A method of manufacturing an insulation layer on silicon carbide includes first preparing a surface of the silicon carbide, then forming a first part of the insulation layer on the surface at a temperature lower than 400 Celsius. Finally, a second part of the insulation layer is formed by depositing a dielectric film on the first part. The surface of the silicon carbide is illuminated by a light at a wavelength below and/or equal to 450 nm during and/or after the formation of the first part of the insulation layer.

Claims

1. A method of manufacturing an insulation layer on silicon carbide (SiC), comprising: preparing a surface of the silicon carbide (SiC); forming a first part of the insulation layer (700, 901, 951) on the prepared surface of the silicon carbide (SiC) at a temperature less than 400 Celsius, the first part of the insulation layer being silicon oxide; forming a second part of the insulation layer by depositing a dielectric film on the first part of the insulation layer; and illuminating the prepared surface of the silicon carbide (SiC) with light at a wavelength no greater than 450 nanometers during the formation of the first part (700, 901, 951) of the insulation layer using a light source (LS), wherein the light source (LS) comprises one or more of a lamp (La), a laser (LX), a light emitting diode, and a plasma, wherein the silicon oxide of the first part (700, 901, 951) of the insulation layer is formed by exposing the prepared surface of the silicon carbide (SiC) to ozone (O3), and the ozone is generated at least partly from oxygen (O2) by the light which illuminates the prepared surface of the silicon carbide (SiC), and wherein nitrogen oxides are provided together with the oxygen (O2).

2. The method of claim 1, wherein the wavelength of the light is no greater than 380 nm.

3. The method of claim 1, wherein the light source (LS) emits the light with a density of photons on the prepared surface of the silicon carbide (SiC) that is greater than a density of carbon atoms on the prepared surface of the silicon carbide (SiC).

4. A method of manufacturing an insulation layer on silicon carbide (SiC), comprising: preparing a surface of the silicon carbide (SiC); forming a first part of the insulation layer (700, 901, 951) on the prepared surface of the silicon carbide (SiC) at a temperature less than 400 Celsius, the first part of the insulation layer being silicon oxide; forming a second part of the insulation layer by depositing a dielectric film on the first part of the insulation layer; and illuminating the prepared surface of the silicon carbide (SiC) with light at a wavelength no greater than 450 nanometers after the formation of the first part (700, 901, 951) of the insulation layer using a light source (LS), wherein the light illuminates the prepared surface of the silicon carbide (SiC) between the formation of the first (700, 901, 951) part of the insulation layer and the second part of the insulation layer using an atmosphere containing at least hydrogen.

5. The method of claim 4, wherein that the hydrogen comprises one or more of hydrogen molecules, hydrogen ions, and hydrogen radicals.

6. The method of claim 5, wherein the hydrogen ions, the hydrogen radicals, or both the hydrogen ions and the hydrogen radical are provided using one or both of a plasma and a catalytic decomposition.

7. The method of claim 6, wherein the light generated by the plasma is the light source (LS) that illuminates the first part (700, 901, 951) of the insulation layer.

Description

FIGURES

(1) Example embodiments of the invention are described below referring to figures showing the example aspects of the invention.

(2) FIG. 1 shows a flowchart of example aspects of an inventive method of manufacturing;

(3) FIG. 2 shows a cross-section of the semiconductor device showing the preparation of the surface;

(4) FIG. 3 shows a cross-section of the semiconductor device showing forming of the silicon oxide layer;

(5) FIG. 4 shows an alternative method of forming the silicon oxide layer;

(6) FIG. 5 shows the deposition of the dielectric film;

(7) FIG. 6 shows flowchart of example aspects of the inventive method with additional steps;

(8) FIG. 7 shows a first example embodiment after the inventive method;

(9) FIG. 8 shows a second example embodiment after the inventive method;

(10) FIG. 9 shows a third example embodiment after the inventive method;

(11) FIG. 10 shows a fourth example embodiment after the inventive method and

(12) FIG. 11 shows a fifth example embodiment after the inventive method.

DESCRIPTION OF THE FIGURES

(13) Reference will now be made to embodiments of the invention, one or more examples of which are shown in the drawings. Each embodiment is provided by way of explanation of the invention, and not as a limitation of the invention. For example, features illustrated or described as part of one embodiment can be combined with another embodiment to yield still another embodiment. It is intended that the present invention include these and other modifications and variations to the embodiments described herein.

(14) FIG. 1 shows a flowchart of manufacturing an insulating layer on the surface of the silicon carbide. The first step 300 is to prepare the surface of the silicon carbide for the further steps. This preparation is usually the removal of: (1) the native oxide; or (2) the silicon oxide formed during the carbon cap removal process for post-implantation; or (3) the sacrificial oxide which was damaged by ion bombardment during RIE and subsequently oxidized, on the silicon carbide. This can be achieved for example by using hydrofluoric acid. The symbol HF is used for this and it is normally dissolved in water. Alternative chemicals may be used for removing the residual oxidation layer but hydrofluoric acid is well proven. The etching away of this oxide layer may be achieved by HF dissolved in water or by the hydrofluoric acid in a vapor. Other chemicals of course may also be used.

(15) In step 301, the forming of the first part of the insulation layer on the silicon carbide is performed. As explained above and later below, this first part of the insulation layer is a silicon oxide film which is between 0.5 nanometer and 10 nanometers. This film could be grown below 400 Celsius, preferably between 0 Celsius and 45 Celsius. Ozone or O.sub.2 plasma may be used or chemicals the examples of which are as following. 68% HNO.sub.3 at room temperature (neither heating nor cooling) for 60 minutes, or 68% HNO.sub.3 at 100-121 Celsius for 30 minutes is an example. Both temperature range and duration range may be larger. When chemicals are used to grow the silicon oxide, rinsing by water, especially deionized water, and drying the substrate normally follow. During the formation of the first part of the insulation layer, the surface of the silicon carbide is illuminated by a light with a wavelength of 450 nm or shorter by a light source which may contain lamps, lasers or LEDs emitting such light. The light may generate the ozone from oxygen. Alternatively, the illumination takes place between step 301 and 302 for example in an ambient of hydrogen.

(16) In step 302, the dielectric film is deposited on this first part of the insulation layer. The dielectric film may be, for example, aluminum oxide, aluminum nitride, aluminum oxide nitride, hafnium oxide, hafnium aluminum oxide, hafnium silicide, zirconium oxide, zirconium silicide, titanium oxide, lanthanum oxide, silicon nitride, silicon oxide nitride or silicon oxide again. So by having the first part of the insulation layer, which is the silicon oxide film, and also the dielectric film, a good insulation is achieved for controlling the current flowing from source to drain by an electric field which is controlled over the gate electrode 13, 23. The advantage of atomic layer deposition is its excellent controllability of stoichiometry and thickness, including its uniformity. The gate insulator must be thin and uniform with high quality. Atomic layer deposition method may satisfy these requirements. On the other hand, chemical vapor deposition, which is sometimes enhanced by plasma, has an advantage of depositing closely packed film with relatively low cost. It is desirable for the surface protective film. The deposition temperature is typically 400 Celsius, or more widely, in the range of 150 Celsius-450 Celsius, to keep the excess hydrogen within.

(17) In FIG. 2, shows how the residual oxidation layer 400 on the silicon carbide SiC is removed by using hydrofluoric acid HF. This could be in combination with using photoresist defining those areas on the surface of the silicon carbide which should be cleaned by the hydrofluoric acid HF. Photolithography with photoresist is the usual way to pattern semiconductor devices from above. Edging and metallization are applied as needed. For simplicity photolithography is not shown in the figures. Again, this step is performed at a temperature between 0 Celsius and 45 Celsius, preferably at room temperature of 20 Celsius or 21 Celsius.

(18) FIG. 3 shows the forming of the silicon oxide layer SiO.sub.2 on the silicon carbide SiC. The thickness of the silicon oxide layer SiO.sub.2 is designated by the letter d. In the example shown in FIG. 5, the silicon oxide layer SiO.sub.2 is formed by using ozone O.sub.3. This is also done at a temperature below 400 Celsius. According to example aspects of the invention, this is supported by illuminating the surface by a light at a wavelength of 450 nm or shorter.

(19) FIG. 4 shows an alternative for forming the silicon oxide layer SiO.sub.2 with the thickness d on the silicon carbide SiC. Here a chemical solution CS is used for forming the silicon oxide layer SiO.sub.2. Examples for this chemical solution are mentioned as following. A solution could be used which includes nitric acid or hydrogen peroxide or sulfuric acid or hydro fluoric acid or ozone or acetic acid or boiling water or ammonium hydride or any combination thereof. This alternative is also realized at a temperature below 400 Celsius. This is then followed by the above described illumination.

(20) FIG. 5 shows the next step, mainly the deposition of the second part of the insulation layer or dielectric film Di on the silicon oxide layer SiO2 with the thickness d on the surface of the silicon carbide substrate SiC. The dielectric film Di is made of those elements mentioned above and may be deposited by atomic layer deposition or chemical vapor deposition or any other means of depositing such a dielectric film.

(21) Especially forming of the first thin silicon oxide film is done at temperatures below 400 Celsius preferably at room temperature from 0 Celsius to 45 Celsius. Thermal stress between the thin silicon oxide and the silicon carbide may be avoided in this way. The silicon oxide provides excellent interface quality by the following process of dielectric film coating. The dielectric film also complements the thin oxide with having high permittivity and insulating capability. These features increase the reliability and controllability of this gate structure.

(22) FIG. 6 shows a second flowchart of manufacturing the insulating layer on the silicon carbide. In step 800, the cleaning of the surface of the silicon carbide is performed. In step 801, a chemical solution is used for forming the first part of the insulating layer, namely the silicon oxide film. After the formation of the silicon oxide, rinsing by water, especially deionized water, and drying the substrate normally follow. This could be also achieved by using ozone or O.sub.2 plasma at temperatures below 400 Celsius preferably at room temperature. Here, the illumination according to example aspects of the invention takes place.

(23) In step 802, the dielectric film is deposited. This is done using atomic layer deposition or chemical vapor deposition or any other means of depositing such a dielectric layer. It is for example possible to use electrodeposition.

(24) In step 803, an annealing of this structure having the silicon oxide layer and the dielectric film is performed at least at 50 Kelvin higher than the deposition of the dielectric layer. A typical annealing temperature is 450 Celsius for a film deposited at 350 Celsius. The annealing step release excess hydrogen from the deposited film, and the part of the hydrogen reaches the interface of the thin silicon oxide and the silicon carbide. The hydrogen improves the film quality of the thin silicon oxide by terminating the dangling bonds in the oxide, and also improves the quality of the interface by terminating the dangling bonds at the surface of the silicon carbide.

(25) After that, in step 804, further steps of making the semiconductor device with the inventive insulating layer are performed. This is for example the metallization on the dielectric layer in order to have a complete gate structure. In some cases, one of these further steps, for example a sintering process of the metal electrode, may also play the role of the annealing step 803 if the process condition satisfies the requirement. In other words, one annealing step in the further steps can play two or more roles including termination of dangling bonds in the thin oxide and the surface of the silicon carbide in step 803. This means no additional cost is required for the annealing step 803.

(26) FIG. 7 shows a first example embodiment of the above described method. A lamp La emitting ultraviolet light at and/or below 450 nm is used as a light source (LS). The lamp La illuminates the surface of the silicon carbide SiC with the first part of the insulation layer 700. This layer 700 is formed by using oxygen O.sub.2 and ozone O.sub.3. Ozone is manufactured using the light of the lamp La. Alternatively, a gaseous nitride oxide, e.g. nitrous oxide (N.sub.2O), may be added to oxygen, which is expected to improve the interface quality between the formed silicon oxide and the silicon carbide.

(27) FIG. 8 shows a second example embodiment of the above described method. As a light source LS, a laser module LX is used with several laser diodes. Their emitted light is scattered using the optics O which may be an element with several holes in it. Alternatively, an optics for scanning the surface of the silicon carbide may be employed.

(28) FIG. 9 shows a third example embodiment of the above described method, wherein a light is illuminated in an atmosphere containing hydrogen and hydrogen radicals using catalytic decomposition after the formation of the first part of the insulation layer as a silicon oxide film. A silicon carbide substrate 900 with a silicon oxide film 901 as the first part of the insulation layer is located in a reaction chamber which is isolated from outside with a wall 905. The chamber has an evacuation system which properly controls the pressure inside the chamber as well as safely isolates hydrogen contained atmosphere from outside. Hydrogen (H.sub.2) gas is introduced from gas inlets 906 and the pressure is controlled at 3 Pa, though the pressure value may be lower or higher to optimize the reaction. In the atmosphere, other inert gases, like N.sub.2, Ar, Xe, etc., may also exist together.

(29) Inside the chamber underneath the gas inlets 906, linear ultraviolet (UV) lamps 907 perpendicular to the plane of FIG. 9 are arranged. The wavelength of the UV lamp is typically 172 nm in case of xenon excimer lamp, but other types of linear light sources whose peak wavelength is shorter than 450 nm are also applicable.

(30) Further underneath the UV lamps 907, linear tungsten wires 910 perpendicular to the plane of FIG. 9 are arranged. The diameter of these tungsten wires 910 is typically 0.5 mm, but can be narrower or wider. The tungsten wires 910 may be electrically heated. When the wire temperature is around 1500 C.-2100 C., the wires 910 catalytically decompose hydrogen and generate radicals of hydrogen atoms (H*) and hydrogen molecules (H.sub.2*).

(31) These radicals, together with undecomposed H.sub.2 molecules, penetrate into the matrix of the silicon oxide 901. Within the silicon oxide 901, the residual carbon atoms are disconnected from the matrix by the photon energy of the light illuminated by the UV lamps 907. The penetrated hydrogen radicals (H*, H.sub.2*) and hydrogen molecule (H.sub.2) react with these carbon atoms, transform to methane (CH.sub.4), and go out of the matrix as relatively small-sized molecules comparing with the networks in the matrix. This reaction may also take place without tungsten wires 910 which means no radical generation but only hydrogen molecules (H.sub.2) supplied, but the existence of the wires 910 generating hydrogen radicals accelerate the reaction. In addition, the silicon substrate 900 may be heated from underneath to accelerate the emission of the generated methane gas.

(32) FIG. 10 shows a fourth example embodiment of the above described method, which is similar with FIG. 9 but hydrogen ions may also be introduced using plasma. A silicon carbide substrate 950 with a silicon oxide film 951 as the first part of the insulation layer is located in a reaction chamber which is isolated from outside with a wall 955. The chamber also has an evacuation system which properly controls the pressure inside the chamber, and H.sub.2 gas is introduced from gas inlets 956 and the pressure is controlled at 100 Pa, though the pressure value may be lower or higher to optimize the reaction. In the atmosphere, other inert gases, like nitrogen (N.sub.2), argon (Ar), xenon (Xe), etc., may also exist together. Linear ultraviolet (UV) lamps 957 perpendicular to the plane of FIG. 10 are arranged similarly with FIG. 9 inside the chamber underneath the gas inlets 956.

(33) Further underneath the UV lamps 957, copper antennas 960 which are linear copper rods perpendicular to the plane of FIG. 10 and whose diameter is typically 3 mm. Each of the copper rods 960 is covered with a quartz tube 961 which shares the same circular center and whose outer diameter is typically 15 mm with 1-mm thick wall. The quartz tubes 961 isolate the copper antennas 960 from the hydrogen-contained atmosphere in the reaction chamber. When very high-frequency power of typically 2.45 GHz with 200 W is applied to each of the antennas 960, microwave energy radially propagates from the antenna 960 towards the quartz tube 961 and microwave plasma is induced outside the surface of the quartz tube 961. The plasma generates hydrogen ions (H.sup.+ and H.sub.2.sup.+) and radicals (H* and H.sub.2*) out of hydrogen molecules (H.sub.2).

(34) Similarly with the embodiment described for FIG. 9, these ions, radicals, and undecomposed H.sub.2 molecules penetrate into the matrix of the silicon oxide 951 and transform to methane (CH.sub.4) together with the residual carbon atoms which are disconnected from the matrix by being illuminated by the UV lamps 957. The presence of ions even accelerates the reaction.

(35) FIG. 11 shows a fifth example embodiment of the above described method, which is similar with FIG. 10 but even without the UV lamps. In this case UV light emission from the hydrogen plasma works as the light source and is used to disconnect the residual carbon atoms in the matrix of the silicon oxide film 951. When some kind of inert gas, typically argon (Ar), is mixed with hydrogen, UV light emission is enhanced and the disconnection of the residual carbon atoms is accelerated.

(36) Modifications and variations can be made to the embodiments illustrated or described herein without departing from the scope and spirit of the invention as set forth in the appended claims.

REFERENCE NUMERALS

(37) 300 Preparing a surface of the SiC 301 Forming first part of the insulation layer 302 Depositing dielectric film on first part 400 native oxide layer d thickness of silicon oxide layer 800 Cleaning 801 Dipping in chemical solution with the surface illuminated by UV light 802 Depositing dielectric film 803 annealing 804 further steps La lamp LS light source Oxygen Ozone 700 first part of the insulation layer SiC silicon carbide LX laser module Optics 900 silicon carbide substrate 901 silicon oxide film 905 wall of the reaction chamber 906 H2 gas inlet 907 UV lamp 910 tungsten wire 950 silicon carbide substrate 951 silicon oxide film 955 wall of the reaction chamber 956 H2 gas inlet 957 UV lamp 960 copper antenna 961 Quartz tube