JP2013157539A - Silicon carbide semiconductor device manufacturing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To inhibit increase caused by a heat treatment performed in a post-process, in low interface state density which is obtained by performing wet oxidation + hydrogen POA on (000-1) plane and (11-20) plane of a silicon carbide semiconductor thereby to achieve high channel mobility.SOLUTION: A silicon carbide semiconductor device manufacturing method comprises: a first process of forming a gate insulation film on (000-1) plane or (11-20) plane of a silicon carbide semiconductor in a process including thermal oxidation in a gas containing oxygen and moisture; and a second process of performing a heat treatment in a hydrogen-containing atmosphere after forming the gate insulation film. A temperature of the heat treatment in the hydrogen-containing atmosphere after formation of the gate insulation film in the second process is set equal to or higher than a heat treatment temperature in processes performed after the second process.

Description

  The present invention relates to a method for manufacturing a semiconductor device using a silicon carbide substrate, and more particularly to a method for manufacturing a silicon carbide semiconductor device characterized by a heat treatment step after forming a gate insulating film.

  Since semiconductor devices such as MOSFETs using silicon carbide can be switched at a higher speed than bipolar transistors, research and development of next-generation semiconductor devices using silicon carbide substrates have been promoted in recent years. Silicon carbide can form an insulating film by thermal oxidation like silicon, but has a characteristic that the channel mobility at the MOS interface differs depending on the crystal plane and the oxidation method.

The (000-1) plane or the (11-20) plane, which is a typical plane of a silicon carbide substrate, exhibits higher channel mobility than the (0001) plane when oxidized in a wet atmosphere, reduces on-resistance, and consumes. This is advantageous in reducing power.
Note that there is an interface state density as an index for alternatively evaluating the channel mobility, and it is generally known that the channel mobility tends to increase as the interface state density decreases.

  With respect to a method for manufacturing a semiconductor device using such a silicon carbide substrate, the following Patent Document 1 discloses that the (000-1) plane of the silicon carbide substrate is thermally oxidized in a wet atmosphere in order to reduce the interface state density. Thus, a method for obtaining a high channel mobility is shown. Specifically, after oxidation for forming a gate insulating film, annealing is performed in a hydrogen or water vapor atmosphere.

Japanese Patent No. 4374437

  Interface state of MOS interface obtained by oxidizing (000-1) and (11-20) surfaces of silicon carbide substrate in wet atmosphere and heat-treating in hydrogen-containing atmosphere as POA (Post Oxidation Annealing) It is known that the density is increased by heat treatment at a later step, for example, heat treatment at about 800 ° C. to 1000 ° C. for forming a metal ohmic contact, and the MOS interface characteristics are deteriorated.

It is said that the interface state density is reduced by wet atmosphere oxidation or hydrogen POA because hydrogen or hydroxyl groups terminate the interface state, but the ambient temperature rises due to the heat treatment in the subsequent process. Therefore, it is presumed that the interface state density increases due to elimination of the terminal hydrogen or hydroxyl group, and the MOS interface characteristics deteriorate.
Since the MOS interface characteristic deterioration due to this heat treatment does not occur in the MOS device fabricated on the silicon carbide (0001) surface, the MOS on the silicon carbide (000-1) surface or the (11-20) surface and the (0001) surface. Devices require different devices in the device process.

  In view of this, the present invention is based on the fact that a good MOS interface characteristic obtained by oxidizing a (000-1) surface or (11-20) surface of a silicon carbide semiconductor in a wet atmosphere and hydrogen POA is obtained by a heat treatment applied in a later step. It is an object of the present invention to provide a method for manufacturing a semiconductor device that suppresses deterioration due to an increase in level density.

In order to solve the above problems, in the method for manufacturing a silicon carbide semiconductor device of the present invention, the temperature of the hydrogen POA after forming the gate insulating film is set to be equal to or higher than the maximum temperature of the heat treatment applied in the subsequent process. Specifically, the following technical measures were taken. That is,
(1) The silicon carbide semiconductor (000-1) or (11-20) plane is subjected to thermal oxidation in a gas containing at least oxygen and moisture on the (000-1) plane or (11-20) plane. ) Surface or (11-20) surface, and a silicon carbide semiconductor comprising a first step of forming a gate insulating film so as to be in contact with the surface and a second step of heat-treating in an atmosphere containing hydrogen after forming the gate insulating film In the device manufacturing method, in the second step, a heat treatment temperature when performing heat treatment in an atmosphere containing hydrogen after forming the gate insulating film is equal to or higher than a heat treatment temperature in a step performed after the second step. did.

(2) A step performed after the second step includes a third step of removing a part of the insulating film formed in the first step and forming an opening, and at least a part of the opening. A fourth step of depositing a contact metal on the substrate, and a fifth step of performing a heat treatment for forming a reaction layer of the contact metal and silicon carbide,
The heat treatment temperature in the atmosphere containing hydrogen after forming the gate insulating film in the second step was set to be equal to or higher than the heat treatment temperature for forming the contact metal and silicon carbide reaction layer in the fifth step.

(3) The temperature of the heat treatment in the atmosphere containing hydrogen after forming the gate insulating film in the second step is in the range of 900 ° C. to 1100 ° C., and the contact metal and silicon carbide in the fifth step The temperature of the heat treatment for forming the reaction layer was in the range of 800 ° C. or higher and 1000 ° C. or lower.

(4) The off angle from the (000-1) plane or the (11-20) plane of the silicon carbide semiconductor was set to 0 degree to 8 degrees.

(5) The first step of forming the gate insulating film is a step in which thermal oxidation is performed in dry oxygen not containing moisture and then thermal oxidation in a gas containing moisture is combined.

(6) The first step of forming the gate insulating film is a step in which after the insulating film is deposited, thermal oxidation in a gas containing moisture is combined.

  Thus, according to the method for manufacturing a silicon carbide semiconductor device of the present invention, when the gate oxide film is formed by wet oxidation and hydrogen POA, the temperature of the hydrogen POA is subjected to various heat treatments such as ohmic contact annealing performed in a subsequent process. By setting the temperature higher than the maximum temperature, it is possible to suppress the desorption of hydrogen that has terminated the interface state during the gate oxidation due to the temperature rise accompanying the heat treatment in the subsequent process, and high channel mobility can be realized.

Diagram showing the configuration of the MOS capacitor used in the experimental example The figure which shows the distribution of the interface state density obtained by measuring the MOS capacitor of the above experimental example and the MOS capacitor of the comparative example Sectional drawing for demonstrating the manufacturing process of MOSFET by this invention The figure which shows the gate voltage dependence of the field effect channel mobility obtained by measuring MOSFET produced by this invention, and MOSFET of a comparative example

First, in order to verify how much deterioration of the MOS interface characteristics is suppressed according to the present invention, the MOS capacitor is required to have the highest temperature in the heat treatment in the process after the gate oxide film is formed. An experimental example in which annealing at an atmosphere and temperature assuming contact annealing is performed will be described with reference to FIGS.
FIG. 1 is a diagram showing the configuration of the MOS capacitor used in this experiment.

This MOS capacitor is manufactured as follows.
(1) Step 1
First, an n-type epitaxial film 2 having a donor density of about 1E + 16 cm ⁻³ is grown by 5 to 10 μm on an n-type 4H—SiC (000-1) substrate 1 (0 to 8 degrees off substrate from the (000-1) plane). Note that the 4H—SiC substrate alone or the 4H—SiC substrate and the epitaxial film are collectively referred to as a 4H—SiC semiconductor.

(2) Step 2
After the 4H—SiC semiconductor is cleaned, wet oxidation at 1000 ° C. is performed for 30 minutes to form the insulating film 3 having a thickness of 50 nm. Subsequently, heat treatment is performed for 30 minutes in a hydrogen atmosphere as POA. The POA temperature was set at three levels of 1100 ° C., 1000 ° C., and 900 ° C. In the POA atmosphere, hydrogen may be diluted with an inert gas.

(3) Process 3
Next, after cooling to room temperature, annealing is performed under atmospheric conditions and temperature conditions assuming ohmic contact annealing for forming a reaction layer of contact metal and silicon carbide.
That is, annealing is performed in an atmosphere of inert gas or a mixed gas of inert gas and hydrogen at 900 ° C. for 2 minutes.
The mixed gas of inert gas and hydrogen is a mixed gas of nitrogen, helium, or argon and hydrogen, and the hydrogen concentration in the mixed gas of inert gas and hydrogen is preferably 1% or more and 4% or less. Particularly preferably, the hydrogen concentration in the mixed gas of inert gas and hydrogen is 4%.

(4) Step 4
On the insulating film 3, a dot-shaped aluminum gate electrode 4 was deposited at room temperature, and a MOS capacitor composed of an aluminum back electrode 5 in which aluminum was deposited on the entire back surface was fabricated.

Here, in order to verify the effect of preventing deterioration of the MOS interface according to this experimental example, as a comparative example, in step 2, the POA in the hydrogen atmosphere was set to 800 ° C., which is lower than the annealing temperature of 900 ° C. assuming ohmic contact annealing. A MOS capacitor was fabricated.
The completed MOS capacitor was measured with a C-V meter 6 to examine the influence of the POA temperature in the hydrogen atmosphere on the interface state density.

FIG. 2 is a diagram showing the interface state density distribution obtained from the measurement results of the MOS capacitor according to this experimental example shown in FIG. 1 and the MOS capacitor manufactured for comparison.
As shown in FIG. 2, in FIG. 2, (a) a MOS capacitor fabricated at 900 ° C. with a hydrogen POA (gray diamond plot), compared to a MOS capacitor fabricated at 800 ° C. with a hydrogen POA (black triangle plot). ), (B) MOS capacitor (gray square plot) fabricated at 1000 ° C., and (c) MOS capacitor fabricated at 1100 ° C. (circle plot), the increase in interface state density is smaller. It was confirmed that the deterioration of the MOS interface was suppressed.

  In this way, by setting the hydrogen POA temperature to be equal to or higher than the temperature of the heat treatment performed in the subsequent step, it is possible to suppress an increase in the low interface state density obtained by wet oxidation + hydrogen POA due to the heat treatment performed in the subsequent step. It could be confirmed.

  Next, an embodiment of the present invention will be described with reference to FIGS.

FIGS. 3A to 3I are cross-sectional views for explaining steps 1 to 9 in manufacturing a MOSFET on a silicon carbide (000-1) surface according to this embodiment.
(1) Step 1
First, as shown in FIG. 3A, on a p-type 4H—SiC (000-1) substrate 7 (0 to 8 degrees off substrate from the (000-1) plane), a p-type with an acceptor density of 1E + 16 cm ⁻³ . Epitaxial film 8 is grown.

(2) Step 2
As shown in FIG. 3B, a SiO ₂ film having a thickness of 1 μm is deposited on the surface of the p-type epitaxial film 8 by low pressure CVD, and a mask 9 is formed by patterning by photolithography.
Thereafter, for example, phosphorus ions 10 are ion-implanted at a substrate temperature of 500 ° C., in multiple stages with an acceleration energy of 40 keV to 250 keV, and an implantation amount of 2E + 20 cm ⁻³ .

(3) Process 3
As shown in FIG. 3C, the mask 9 is removed, a 1 μm thick SiO ₂ film is deposited on the surface by low pressure CVD, and a mask 11 is formed by patterning by photolithography.
Thereafter, for example, aluminum ions 12 are ion-implanted at a substrate temperature of 500 ° C., in multiple stages of acceleration energy of 40 keV to 200 keV, and with an implantation amount of 2E + 20 cm ⁻³ .

(4) Step 4
As shown in FIG. 3D, the mask 11 is removed and activation annealing is performed at 1600 ° C. for 5 minutes in an argon atmosphere to form the drain region 13, the source region 14, and the ground region 15.

(5) Process 5
As shown in FIG. 3E, a field oxide film 16 having a thickness of 0.5 μm is deposited by low pressure CVD, and a part of the field oxide film 16 is removed by photolithography and wet etching to form an active region 17. To do.

(6) Step 6
As shown in FIG. 3F, after wet oxidation at 1000 ° C. for 30 minutes to form a gate insulating film 18 having a thickness of 50 nm, heat treatment is performed as POA in a hydrogen atmosphere at 1000 ° C. for 30 minutes. In the POA atmosphere, hydrogen may be diluted with an inert gas.
Thereafter, on the gate insulating film 18, polycrystalline silicon is deposited with a thickness of 0.3 μm by the low pressure CVD method, and the gate electrode 19 is formed by patterning by photolithography.

(7) Step 7
As shown in FIG. 3 (g), contact holes are formed on the drain region 13, the source region 14, and the ground region 15 by photolithography and hydrofluoric acid etching, and 10 nm thick aluminum and 60 nm nickel are further formed thereon. The contact metal 20 is formed by vapor deposition and patterning by lift-off.

(8) Step 8
As shown in FIG. 3 (h), the ohmic contact annealing is performed by annealing at 950 ° C. for 2 minutes in an atmosphere of an inert gas or a mixed gas of inert gas and hydrogen, and the contact metal 20 and the silicon carbide reaction layer 21 are formed. Form.
The mixed gas of inert gas and hydrogen is a mixed gas of nitrogen, helium or argon and hydrogen, and the hydrogen concentration in the mixed gas of inert gas and hydrogen is preferably 1% or more and 4% or less. Particularly preferably, the hydrogen concentration in the mixed gas of inert gas and hydrogen is 4%.

(9) Step 9
As shown in FIG. 3 (i), 300 nm of aluminum is vapor-deposited on the surface, pad electrode 22 is formed on gate electrode 19 and reaction layer 21 by photolithography and phosphoric acid etching, and aluminum is vapor-deposited on the back surface to a thickness of 100 nm. 23 is formed.

Further, as a comparative example, a MOSFET in which POA in a hydrogen atmosphere was set to 800 ° C. in step 6 (f) was manufactured.
4 is manufactured by changing the temperature condition of the silicon carbide MOSFET manufactured by the silicon carbide MOSFET manufacturing method shown in FIG. 3 and the POA in the hydrogen atmosphere in the step 6 (f) in FIG. 3 to 800 ° C. It is a figure which shows the gate voltage dependence of the channel mobility of the made silicon carbide MOSFET.

In FIG. 4, the channel mobility (solid line) of hydrogen POA 1000 ° C. in (a) shows a high value of about 70 cm ² / Vs at maximum, whereas the channel mobility (800) of hydrogen POA 800 ° C. in (b) The broken line is a low value of about 50 cm ² / Vs slightly at the maximum.
From this, the decrease in channel mobility occurs when hydrogen that has terminated the interface state is desorbed by ohmic contact annealing, and the hydrogen POA 800 ° C. is subjected to ohmic contact annealing at a temperature higher than the POA temperature. Thus, it can be easily confirmed that desorption of hydrogen occurs.

  On the other hand, when the POA temperature is 1000 ° C., the channel mobility is less deteriorated, and hydrogen is desorbed from the interface state during the ohmic contact annealing by maintaining the hydrogen POA at a higher temperature than the ohmic contact annealing. It turns out that it can suppress.

In this embodiment, the temperature of the POA is set to 1000 ° C., but the temperature of the POA may be equal to or higher than the temperature of the ohmic contact annealing performed in a later step, and is preferably set to 900 ° C. to 1100 ° C.
On the other hand, the temperature of the ohmic contact annealing is preferably a high temperature in order to obtain a good ohmic contact, and on the other hand, a low temperature is better in order to suppress the deterioration of the MOS interface. -1000 degreeC is preferable.

  From the above, when the ohmic contact annealing temperature is 800 ° C. to 1000 ° C., the POA temperature is in the range of 900 ° C. to 1100 ° C., and if it is selected to be higher than the ohmic contact annealing temperature, high channel mobility is provided. A high-performance silicon carbide MOSFET can be manufactured.

  In the above embodiment, the ohmic contact annealing, which generally requires the highest temperature in the heat treatment in the process after the hydrogen POA, has been described as an example. However, the present invention is not limited to this. Rather, in the manufacturing method of the semiconductor device, the temperature of the hydrogen POA is applied in a later step, including the formation temperature of polysilicon, the heat treatment temperature for reducing resistance, the heat treatment temperature for planarizing the interlayer insulating film, etc. The same effect can be obtained by setting the temperature to the maximum temperature of various heat treatments.

  In the above embodiment, a (000-1) substrate (0-8 ° off substrate) with a crystal structure of 4H—SiC was used, but the same effect can be obtained with a (11-20) substrate with a crystal structure of 4H—SiC. can get.

  As described above, the present invention has been described by taking an example of a method of manufacturing a lateral MOSFET as a silicon carbide MOSFET. Thus, similar effects can be achieved. Therefore, the present invention can be applied to various semiconductor device manufacturing methods without departing from the scope of the invention described in the claims.

1 n-type 4H-SiC (000-1) substrate 2 n-type epitaxial film 3 insulating film 4 aluminum gate electrode 5 aluminum back electrode 6 CV meter 7 p-type 4H-SiC (000-1) substrate 8 p-type epitaxial film 9 Mask 10 Phosphorus ion 11 Mask 12 Aluminum ion 13 Drain region 14 Source region 15 Ground region 16 Field oxide film 17 Active region 18 Gate insulating film 19 Gate electrode 20 Contact metal 21 Reaction layer 22 Pad electrode 23 Back electrode

Claims (6)

The (000-1) plane of the silicon carbide semiconductor or the (000-20) plane of the silicon carbide semiconductor in a process including thermal oxidation in a gas containing at least oxygen and moisture on the (000-1) plane or the (11-20) plane of the silicon carbide semiconductor A first step of forming a gate insulating film in contact with the (11-20) plane;
In the method for manufacturing a silicon carbide semiconductor device, including the second step of performing a heat treatment in an atmosphere containing hydrogen after forming the gate insulating film,
In the second step, the heat treatment temperature in the heat treatment in the hydrogen-containing atmosphere after the gate insulating film is formed is equal to or higher than the heat treatment temperature in the step performed after the second step. A method for manufacturing a silicon carbide semiconductor device. A step performed after the second step includes a third step of removing a part of the insulating film formed in the first step and forming an opening, and a contact metal in at least a part of the opening. And a fifth step of performing a heat treatment to form a reaction layer of the contact metal and silicon carbide,
The heat treatment temperature in the atmosphere containing hydrogen after forming the gate insulating film in the second step is equal to or higher than the heat treatment temperature for forming the reaction layer of the contact metal and silicon carbide in the fifth step. A method for manufacturing a silicon carbide semiconductor device according to claim 1.   The temperature of the heat treatment in the atmosphere containing hydrogen after forming the gate insulating film in the second step is in the range of 900 ° C. or higher and 1100 ° C. or lower, and the reaction layer of the contact metal and silicon carbide in the fifth step The method of manufacturing a silicon carbide semiconductor device according to claim 2, wherein the temperature of the heat treatment for forming the silicon carbide is in the range of 800 ° C. or higher and 1000 ° C. or lower.   The silicon carbide semiconductor according to any one of claims 1 to 3, wherein an off angle from the (000-1) plane or the (11-20) plane of the silicon carbide semiconductor is 0 to 8 degrees. Device manufacturing method.   The first step of forming the gate insulating film is a step of combining thermal oxidation in a gas containing moisture after performing thermal oxidation in dry oxygen not containing moisture. Item 5. A method for manufacturing a silicon carbide semiconductor device according to any one of Items 1 to 4.   44. The first step of forming the gate insulating film is a step of combining thermal oxidation in a gas containing moisture after depositing the insulating film. A method for producing a silicon carbide semiconductor device according to claim 1.

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