CN108735607A - Manufacturing method of groove MOSFET device based on microwave plasma oxidation - Google Patents

Abstract

A method for manufacturing a grooved MOSFET device based on microwave plasma oxidation, comprising: after etching the grooved gate, using microwave plasma to oxidize silicon carbide on the surface of the grooved gate to silicon dioxide to form a grooved gate oxide layer , wherein the step of forming the grooved gate oxide layer includes: placing the silicon carbide substrate after the grooved gate is etched in a microwave plasma generating device; feeding oxygen-containing gas to generate oxygen plasma; oxygen plasma and carbonization Silicon reacts to form silicon dioxide with a predetermined thickness; stop feeding oxygen-containing gas, and the reaction ends; the reaction temperature between oxygen plasma and silicon carbide is 500-900°C, and the reaction pressure is 400-1000mTorr. The invention can significantly improve the oxidation efficiency of silicon carbide, improve the interface quality, and form a uniform gate dielectric layer.

Description

Fabrication Method of Groove MOSFET Device Based on Microwave Plasma Oxidation

technical field

The invention belongs to the technical field of semiconductors, and in particular relates to a method for manufacturing a groove MOSFET device based on microwave plasma oxidation.

Background technique

Silicon carbide (SiC) is the third-generation semiconductor-wide bandgap semiconductor material. It has the advantages of large bandgap width, high critical breakdown field strength, and high thermal conductivity. It is an ideal material for making high-voltage and high-power semiconductor devices. SiC power Electronic devices are at the heart of next-generation high-efficiency power electronics technology. Compared with Si MOSFETs, SiC MOSFETs have smaller on-resistance, higher switching voltage, higher application frequency, and better temperature performance, and are especially suitable for power switching applications. The integrated manufacturing process of SiC MOSFET devices, especially the gate dielectric process, is a current research hotspot.

SiC is the only compound semiconductor that can thermally grow _SiO2 , which makes SiC realize all Si MOS device structures. The thermal oxidation of SiC requires a higher oxidation temperature than Si, and the oxidation temperature is as high as 1300 °C. The current mainstream SiC oxidation process is mainly an oxidation furnace using resistance heating. The main principle is based on the reaction between silicon carbide and oxygen molecules. However, this method of oxidation with oxygen molecules is likely to cause residual carbon clusters and Si-OC bonds at the interface. , C dangling bonds and oxygen vacancies and other defects, the quality of the interface is degraded, resulting in a decrease in mobility, as shown in Figure 1. Especially at such a high temperature, in addition to oxidation, the interface will also cause interface damage and reduce oxidation efficiency.

In recent years, researchers have proposed a method of using plasma to oxidize SiC at low temperature, which improves the interface quality to a certain extent. However, the oxidation efficiency of this method is low, especially in the case of needing to obtain a thicker _SiO2 layer, the oxidation time is longer, and at the interface of SiC and _SiO2 , SiC and _SiO2 will still be in a thermodynamic equilibrium state, As a result, the interface quality is not ideal.

In addition, experiments have shown that the oxidation rate of silicon carbide in different crystal orientations varies greatly. On the Si surface, the oxidation rate of the plane perpendicular to the a-axis is even 3-5 times that of the plane perpendicular to the c-axis. If a thermal oxidation process is used to form the gate oxide of the UMOS structure, the thickness of the oxide layer on the sidewall will be 3-5 times that of the bottom, as shown in Figure 2, which makes the device cannot be turned on normally under forward bias.

Because the channel is a vertical channel formed from the sidewall, in order to enable the device to be turned on normally, it is necessary to provide a higher gate voltage VG. However, since the rate of SiO ₂ grown by thermal oxidation on the sidewall is several times that of the bottom oxidation rate, this makes the channel region on the sidewall fail to reach the threshold value when the gate voltage of the device reaches the maximum safe operating voltage of the gate oxide. Voltage, the device cannot be turned on, and the forward characteristics cannot be obtained. If the gate voltage continues to increase, the stability of the bottom gate oxide will deteriorate, causing the bottom oxide layer to break down in advance, and the device cannot work normally. Therefore, forming a low interface state and a uniform gate oxide layer is the key to fabricating trench MOSFET devices.

Contents of the invention

In order to solve the problems in the prior art, the present invention proposes a method for manufacturing a groove MOSFET device based on microwave plasma oxidation, which can form a low interface state and a uniform gate oxide layer.

In order to achieve the above object, the present invention adopts the following technical solutions:

A method of manufacturing a groove MOSFET device based on microwave plasma oxidation, comprising:

After the groove gate is etched, the silicon carbide on the surface of the groove gate is oxidized to silicon dioxide by microwave plasma to form a groove gate oxide layer,

The step of forming the groove gate oxide layer includes:

placing the silicon carbide substrate after groove gate etching in a microwave plasma generator;

Introduce oxygen-containing gas to generate oxygen plasma;

Oxygen plasma reacts with silicon carbide to form silicon dioxide of predetermined thickness;

Stop feeding the oxygen-containing gas, and the reaction ends;

Wherein, the reaction temperature between oxygen plasma and silicon carbide is 500-900° C., and the reaction pressure is 400-1000 mTorr.

Preferably, the oxygen plasma is heated up to the reaction temperature at a rate of 0.5-2 °C/s.

Preferably, the input power of the microwave plasma generator is 800-2000W, and the microwave frequency is 2.4-2.5GHz.

Preferably, the plasma discharge time is 400-1000s.

Preferably, the oxygen-containing gas is pure oxygen, or a mixed gas of oxygen and inert gas, and the oxygen content in the mixed gas is preferably 30-99 vol.%.

Preferably, the silicon dioxide formed has a thickness of 1-60 nm.

Preferably, the method further comprises the step of venting the carbon monoxide produced.

Preferably, nitrogen gas is introduced after the reaction is completed, and the temperature is cooled under a nitrogen atmosphere.

Compared with the prior art, the present invention has the following beneficial effects:

The invention can significantly improve the oxidation efficiency of silicon carbide, form a low-damage surface, improve surface roughness, reduce carbon residue at the interface, reduce dangling bonds at the interface, and reduce electronic defects in silicon oxide, thereby increasing the effective mobility. , especially the effective mobility under high electric field.

The invention can form a uniform gate dielectric layer, so that the thickness of the oxide layer on the side wall is equivalent to the thickness of the bottom oxide layer. Under a certain gate voltage, the device can be turned on normally, and normal forward characteristics can be obtained, preventing premature breakdown of the bottom gate oxide layer. , to take advantage of the recessed gate MOSFET device.

Description of drawings

Figure 1 is a schematic diagram of SiC/SiO ₂ interface defects;

Figure 2 is a groove MOSFET device formed by a conventional thermal oxidation process;

Figure 3A is the interface of thermodynamic non-equilibrium under ideal conditions;

Figure 3B is the interface of the thermodynamic equilibrium state under conventional oxidation conditions;

Figure 4 shows the reaction kinetic barriers of SiC under different oxidation conditions;

Fig. 5 is the preparation flowchart of groove MOSFET device in the embodiment of the present invention;

Fig. 6 is the SiC/SiO ₂ interface in the embodiment of the present invention;

FIG. 7 is a groove gate oxide layer in an embodiment of the present invention;

Fig. 8 is a comparison diagram of the interface state density in the examples of the present invention and the comparative examples.

Detailed ways

In order to make the object, technical solution and advantages of the present invention clearer, the present invention will be further described in detail below in conjunction with specific embodiments and with reference to the accompanying drawings.

When performing an oxidation process on SiC to form _SiO2 , it is ideal to obtain a thermodynamically non-equilibrium interface, as shown in Figure 3A. However, under the actual conventional oxidation conditions, only a thermodynamically balanced interface can be obtained, as shown in Figure 3B. In this case, carbon residues are likely to be generated, which on the one hand causes gate dielectric leakage, and on the other hand forms the scattering center of the interface, thereby It affects the mobility of silicon carbide, which in turn leads to a decrease in the output current of the device and induces reliability problems. Although the low-temperature plasma oxidation process can improve the interface quality to a certain extent, the interface between SiC and SiO ₂ is actually still in a state of thermodynamic equilibrium due to the long oxidation time.

The inventor has found through a large number of experimental studies that the process of silicon carbide oxidation to form silicon oxide can be regarded as the reaction diffusion process of carbon. The chemical reaction process of the body is equivalent. In this case, there will still be a gradient distribution of carbon at the SiC/SiO ₂ interface within a certain range. Although researchers have tried to perform plasma oxidation of silicon carbide at high temperature, the quality of the SiC/SiO ₂ interface has not been significantly improved due to the difficulty in controlling the plasma oxidation reaction conditions after the temperature rises.

For this reason, the present invention proposes a new silicon carbide oxidation method based on microwave plasma. By optimizing the conditions of plasma oxidation, better oxidation efficiency is obtained and interface quality is significantly improved. A high-efficiency and low-loss oxidation process manufacturing method based on microwave plasma proposed by the present invention is based on microwave plasma, which makes oxygen molecules plasma oxygen free radicals or oxygen plasma, thereby replacing oxygen molecules and reacting with the surface of silicon carbide. Reduce the corresponding temperature and surface oxygen concentration, thereby inhibiting the formation of C-related defects and corrosion pits on the SiC surface, reducing surface damage, and obtaining a relatively flat surface, thereby improving the carrier mobility of MOSFET devices under high temperature and high field.

The present invention mainly ionizes molecular oxygen in a specific temperature and pressure range to make it form oxygen plasma or oxygen free radical formed by homolysis. Under the oxidation conditions of the present invention, oxygen plasma or oxygen radicals have significant chemical activity and smaller size compared to oxygen molecules. When the interface oxidation occurs, while obtaining the oxide layer, because it has a smaller size, it does not need to interact more with the lattice during the diffusion process to oxidize the carbon residue generated by the reaction at the interface, Volatile carbon monoxide is formed, which is removed during the reaction.

The present invention utilizes the atomic heat capacity of free radicals or plasma at the same time. The heat generated in this process is not easy to be released during the reaction process, and can only be dissipated in the form of radiation, so the energy loss of the reaction is effectively saved, and in In this process, the non-dissipative reaction energy is all converted into the supply of chemical bonds, so that no carbon remains.

As shown in Fig. 4, the present invention changes the ratio of atomic oxygen and molecular oxygen by optimizing and adjusting the reaction conditions such as the content of the incoming gas, the pressure of the reaction chamber, and the heating rate of the plasma, so that the ratio of atomic oxygen is far greater than the ratio of molecular oxygen , so as to adjust the potential barrier of reaction kinetics, adjust the reaction pressure to change the kinetic potential barrier, and then change the microstructure at the interface by changing the reaction kinetic potential barrier. The microstructure here includes the surface bonding of atoms, the number of defects in the oxide, and the roughness of the surface. The bonding on the surface of the oxide will affect the Coulomb scattering center, thereby affecting the low-field carrier mobility in the channel, and affecting the subthreshold swing of the MOS field effect transistor. The change of the second kinetic potential barrier can change the interface and transfer to the average distribution of atoms in the middle. The more uniform distribution will help reduce the phonon scattering in the channel, thereby changing the mobility in the middle electric field state.

By adjusting the kinetic barrier, a relatively smooth interface can be effectively reduced. The rough scattering caused by roughness is of great help to improve the electron mobility in the high electric field state, which will directly affect the output current characteristics of the device. . In addition, by adjusting the kinetic barrier, the number of defects in the gate oxide can be fully reduced, which can effectively improve reliability, reduce the flat-band voltage caused by the gate voltage, the instability of the threshold voltage, and effectively reduce the long-range Coulomb scattering. .

On the basis of above-mentioned research, a kind of silicon carbide oxidation method based on microwave plasma that the present invention proposes comprises:

Provide a silicon carbide substrate;

placing the silicon carbide substrate in a microwave plasma generating device;

Introduce oxygen-containing gas to generate oxygen plasma;

Oxygen plasma reacts with silicon carbide to form silicon dioxide of predetermined thickness;

Stop feeding the oxygen-containing gas, and the reaction ends.

The microwave plasma oxidation of SiC includes the following processes: the transport of oxygen radicals or oxygen ions to the surface of the oxide layer; the diffusion of oxygen radicals or oxygen ions through the oxide layer to the reaction interface; at the interface, silicon carbide and oxygen radicals or oxygen ions The reaction; the reaction gas (CO) diffuses to the outside through the oxide layer; the reaction gas is excluded at the surface of the oxide layer.

In an embodiment of the present invention, the reaction temperature between oxygen plasma and silicon carbide is 500-900° C., the temperature of the plasma is raised to the reaction temperature at a rate of 0.5-2° C./s, and the reaction pressure is 400-1000 mTorr.

In an embodiment of the present invention, the input power of the microwave plasma generator is 800-2000W, and the microwave frequency is 2.4-2.5GHz. The plasma discharge time can be 400-1000s.

Under the above conditions, the diameter, density, duration and excitation position of the plasma fireball can be effectively controlled, so as to achieve ideal oxidation conditions. The inventor has found through many tests that under the oxidation conditions of the present invention, the chemical reaction rate of the plasma is far greater than the diffusion effect of carbon, and the isotropic properties of the generated silicon oxide are excellent, especially in the preparation of thicker silicon oxide. layer, the effect is more prominent.

As shown in Figure 5, based on the above-mentioned silicon carbide oxidation method, the present invention proposes a method for manufacturing a grooved MOSFET device based on microwave plasma oxidation, including:

After the groove gate is etched, the silicon carbide on the surface of the groove gate is oxidized to silicon dioxide by microwave plasma to form a groove gate oxide layer,

Wherein, the step of forming the groove gate oxide layer includes:

placing the silicon carbide substrate after groove gate etching in a microwave plasma generator;

Introduce oxygen-containing gas to generate oxygen plasma;

Oxygen plasma reacts with silicon carbide to form silicon dioxide of predetermined thickness;

Stop feeding the oxygen-containing gas, and the reaction ends;

Wherein, the reaction temperature between oxygen plasma and silicon carbide is 500-900° C., and the reaction pressure is 400-1000 mTorr.

In an embodiment of the present invention, the oxygen-containing gas is pure oxygen, or a mixed gas of oxygen and an inert gas, and the oxygen content in the mixed gas is 30-99 vol.%.

The thickness of the oxide layer in the present invention can be adjusted flexibly. In some embodiments of the present invention, the thickness of the formed silicon dioxide is 1-60 nm.

In an embodiment of the present invention, the method further includes the step of venting the generated carbon monoxide.

In some embodiments of the present invention, nitrogen gas is introduced after the reaction, and the temperature is cooled under nitrogen atmosphere.

Example 1

As shown in Figure 6, the fabrication method of a recessed MOSFET device generally includes the following steps:

(1) cleaning the substrate;

(2) Forming a P-base implantation mask and ion implantation on the substrate;

(3) Form N-plus mask and ion implantation;

(4) Forming the P-base and removing the corresponding mask;

(5) Forming N-plus and removing the corresponding mask;

(6) Forming a P-plus mask and ion implantation;

(7) High temperature activation annealing;

(8) Forming P-plus and removing the corresponding mask;

(9) forming a groove gate etching mask;

(10) Groove gate etching;

(11) forming a groove gate oxide layer;

(12) making a polysilicon gate electrode;

(13) making the source electrode;

(14) making the drain electrode;

(15) making interlayer media;

(16) Make the cover metal.

In this embodiment, a microwave plasma oxidation method is used when forming the grooved gate oxide layer, and the specific steps are as follows:

The microwave input power of the microwave plasma generating device is set to 1000w, and the adjustable range of the microwave frequency for exciting the microwave plasma is 2.4-2.5GHz. Under the atmosphere of 800mTorr and pure oxygen, the initial temperature of the sample stage is set to 100°C, and the plasma is heated up at a rate of 1.5°C/s until the set microwave plasma oxidation temperature is 800°C, and the plasma discharge time is 800s , carry out plasma oxidation, the thickness of the oxide layer is about 40nm, after the oxidation is completed, change the pure oxygen to pure nitrogen, and cool down in the nitrogen atmosphere.

As can be seen from Figure 7, the interface of SiC/ _SiO2 formed by the plasma oxidation process of the present invention is relatively clear, the surface roughness is low, the oxide layer is less damaged, the surface is flat, the oxidation rate of the side wall and the bottom is consistent, and the isotropy is good .

In the comparative example of the present invention, the silicon carbide bottom was placed in a high-temperature oxidation furnace, and conventional high-temperature oxidation was performed at 1200°C. It can be seen from Figure 8 that the interface state density obtained by using the plasma oxidation process in the embodiment of the present invention is obvious. Lower than conventional high temperature oxidation.

Compared with conventional high-temperature oxidation or low-temperature plasma oxidation methods, the oxidation reaction efficiency of the present invention can be increased by 20%-50%, C-related defects can be reduced by more than 20%, and the formation rate of corrosion pits on the SiC surface can be reduced to less than 10%.

The specific embodiments described above have further described the purpose, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above descriptions are only specific embodiments of the present invention, and are not intended to limit the present invention. Within the spirit and principles of the present invention, any modifications, equivalent replacements, improvements, etc., shall be included in the protection scope of the present invention.

Claims (8)

1. a kind of manufacturing method of the groove MOSFET element based on microwave plasma oxidation, including：

Notched gates etching after, using microwave plasma by the Oxidation of SiC on notched gates surface be silica, formed it is recessed Slot gate oxide,

Wherein the step of formation groove gate oxide, includes：

Silicon carbide substrates after progress notched gates etching are placed in microwave plasma generation device；

It is passed through oxygen-containing gas, generates oxygen plasma；

Oxygen plasma generates the silica of predetermined thickness with silicon carbide reactor；

Stopping is passed through oxygen-containing gas, and reaction terminates；

Wherein, the reaction temperature of oxygen plasma and silicon carbide is 500-900 DEG C, reaction pressure 400-1000mTorr.

2. manufacturing method according to claim 1, wherein oxygen plasma is warming up to described with the speed of 0.5-2 DEG C/s Reaction temperature.

3. manufacturing method according to claim 1, wherein the input power of the microwave plasma generation device is 800-2000W, microwave frequency 2.4-2.5GHz.

4. manufacturing method according to claim 1, wherein the plasma discharge time is 400-1000s.

5. manufacturing method according to claim 1, wherein the oxygen-containing gas is pure oxygen or is oxygen and indifferent gas The gaseous mixture of body, oxygen content is preferably 30-99vol.% in the gaseous mixture.

6. manufacturing method according to claim 1, wherein the thickness of the silica of generation is 1-60nm.

7. manufacturing method according to claim 1, wherein the method further includes the step for the carbon monoxide that discharge generates Suddenly.

8. manufacturing method according to claim 1, wherein be passed through nitrogen after reaction, under nitrogen atmosphere cooling drop Temperature.