JP2008244056A - Manufacturing method of silicon carbide semiconductor device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain the manufacturing method of a silicon carbide semiconductor device equipped with a Schottky electrode having stabilized characteristics. <P>SOLUTION: The front surface side of an N<SP>-</SP>low concentration layer 2, in which the Schottky electrode is formed, is arranged so as to be contacted with the susceptor 11 of a heat treatment device through a thermal oxidation film 5. Namely, the lamination structure of an N<SP>+</SP>high concentration substrate 1 and the N<SP>-</SP>low concentration layer 2 is arranged under a state that the whole surface of the thermal oxidation film 5 is contacted with the susceptor 11. Under this state of arrangement, an ohmic electrode 7 formed of a metal is formed on the rear surface of the N<SP>+</SP>high concentration substrate 1. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a method for manufacturing a silicon carbide semiconductor device using silicon carbide as a material and having a Schottky electrode.

  In a conventional silicon carbide semiconductor device having a Schottky electrode, such as a Schottky barrier diode, the main steps of the manufacturing method for forming the electrode are as follows. That is, after the entire silicon carbide layer (silicon carbide semiconductor substrate) is oxidized, the oxide film on the back surface is removed and a metal film is deposited, and this is heat-treated to form an ohmic electrode, and then a Schottky electrode is formed. It was.

  Such a manufacturing method is disclosed in Patent Document 1, for example. In this manufacturing method, a high-temperature heat treatment of at least 900 ° C. is necessary to form an ohmic electrode on the back surface. Therefore, in order to prevent the performance deterioration of the Schottky barrier by such high-temperature heat treatment, the Schottky electrode is always formed after the ohmic electrode is formed.

JP 2006-202883 A (paragraph [0044], FIG. 6)

  In such a conventional method for manufacturing a silicon carbide semiconductor device, since the oxidation rate is generally slow on the (0001) plane where the Schottky electrode is formed, the silicon carbide semiconductor layer on which the Schottky electrode is directly formed is protected. A thermal oxide film such as a silicon dioxide film formed as a film is thin, and the Schottky electrode formation surface of the silicon carbide semiconductor layer is likely to be contaminated with a metal element in a process such as a heat treatment when forming an ohmic electrode. For this reason, there has been a problem that characteristic abnormality of the silicon carbide semiconductor device is likely to occur.

  The present invention has been made to solve the above-described problems, and an object of the present invention is to obtain a method for manufacturing a silicon carbide semiconductor device having a Schottky electrode having stable characteristics.

  According to a first aspect of the present invention, there is provided a method for manufacturing a silicon carbide semiconductor device comprising: (a) a step of forming an insulating film on the entire main surface of the silicon carbide semiconductor substrate; and (b) an entire surface of the insulating film. And placing the silicon carbide semiconductor substrate on a susceptor and forming an ohmic electrode made of metal on the other main surface of the silicon carbide semiconductor substrate in this arrangement, and (c) at least the insulating film Forming a Schottky electrode on the exposed surface after removing a part of the silicon carbide semiconductor substrate to expose at least a part of the one main surface.

  According to a second aspect of the present invention, there is provided a silicon carbide semiconductor device manufacturing method comprising: (a) a step of forming a first insulating film on the entire main surface of the silicon carbide semiconductor substrate; and (b) the first Forming a second insulating film on the insulating film; and (c) the silicon carbide semiconductor in a state in which the first and second insulating films are formed on one main surface of the silicon carbide semiconductor substrate. Forming an ohmic electrode made of metal on the other main surface of the substrate; and (d) removing at least a part of the first and second insulating films to at least one of the one main surface of the silicon carbide semiconductor substrate. Forming a Schottky electrode on the exposed surface after exposing the portion.

  The step (b) in the method for manufacturing a silicon carbide semiconductor device according to claim 1 includes the step of bringing the entire surface of the insulating film into contact with the silicon carbide semiconductor substrate on the susceptor and placing the other main surface of the silicon carbide semiconductor substrate on the susceptor. An ohmic electrode made of metal is formed thereon.

  For this reason, metal atoms scattered during the formation of the ohmic electrode do not reach the surface of the insulating film, and do not reach the region on the one main surface side of the silicon carbide semiconductor substrate. As a result, when a Schottky electrode is formed on one main surface of the silicon carbide semiconductor substrate, good Schottky characteristics can be obtained, and a silicon carbide semiconductor device having an ohmic electrode with good characteristics can be obtained. Play.

  Step (c) of the method for manufacturing a silicon carbide semiconductor device according to claim 2 of the present invention includes the step of forming the silicon carbide with the first and second insulating films formed on one main surface of the silicon carbide semiconductor substrate. An ohmic electrode made of metal is formed on the other main surface of the semiconductor substrate.

  Therefore, even if metal contamination is caused during the formation of the ohmic electrode in step (c), the metal atoms remain on the surfaces and inside of the first and second insulating films, and the region on the one main surface side of the silicon carbide semiconductor substrate. Never reach. As a result, it is possible to obtain a silicon carbide semiconductor device having a Schottky electrode with good characteristics and little variation.

<Embodiment 1>
1 to 3 are sectional views showing main steps of the method for manufacturing the silicon carbide semiconductor device according to the first embodiment of the present invention. Hereinafter, a method for manufacturing the silicon carbide semiconductor device according to the first embodiment will be described with reference to these drawings.

  First, the structure shown in FIG. 1 is obtained through the existing steps (for example, the steps shown in FIGS. 4 to 6 of Patent Document 1 (excluding the formation of the ohmic electrode 2)).

As shown in FIG. 1, an N ⁻ low concentration layer 2 made of a silicon carbide semiconductor is formed on the surface of a low resistance N ⁺ high concentration substrate 1, and the N ⁺ high concentration substrate 1 and A laminated structure (silicon carbide semiconductor substrate) composed of the N ⁻ low concentration layer 2 is obtained. Then, a P-type implantation region 3 serving as a guard ring region is selectively formed in the surface of the N ⁻ low concentration layer 2 in order to obtain a breakdown voltage structure.

Thereafter, a thermal oxide film 5 serving as a protective film is formed on the surface of N ⁻ low concentration layer 2 including P-type implantation region 3 (on one main surface of the silicon carbide semiconductor substrate). In this case, the thermal oxide film 5 means a silicon dioxide film.

Next, as shown in FIG. 2, the surface of the ohmic electrode 7 formed of a metal film faces upward, that is, the surface side (the lower side in the figure) of the N-low concentration layer 2 where the Schottky electrode is formed is thermally oxidized. The film 5 is disposed so as to be in contact with the susceptor 11 of the heat treatment apparatus. That is, the stacked structure of the N ⁺ high concentration substrate 1 and the N ⁻ low concentration layer 2 is disposed in a state where the entire surface of the thermal oxide film 5 is in contact with the susceptor 11.

The susceptor 11 means a general susceptor that holds a wafer. For example, a carbon product coated with SiC can be considered. In the manufacturing method of the first embodiment, the entire surface of the thermal oxide film 5 formed on the surface to be kept clean (the Schottky electrode contact surface of the N ⁻ low concentration layer 2) is brought into contact with the susceptor 11 to keep it clean. Is the purpose. It is desirable that the surface material of the susceptor 11 does not contaminate the wafer during heat treatment because impurities are mixed or contaminated.

Then, in this arrangement state, ohmic electrode 7 made of metal is formed on the back surface of N ⁺ high concentration substrate 1 (upper side in FIG. 2, the other front surface of the silicon carbide semiconductor substrate). Thereafter, the back surface of the N ⁺ high concentration substrate 1 and the ohmic electrode 7 are brought into ohmic contact by forming the ohmic electrode 7 by heat treatment in an inert gas atmosphere such as Ar.

Thereafter, as shown in FIG. 3, a part of the thermal oxide film 5 is removed to provide an opening, and a part of the surface of the N ⁻ low concentration layer 2 including the P-type implantation region 3 is exposed. At this time, all of the thermal oxide film 5 may be removed to expose the entire surface of the N ⁻ low concentration layer 2. Then, a Schottky electrode 8 is formed on the exposed surface of the N ⁻ low concentration layer 2 including the P-type implantation region 3. Thereafter, an Al electrode, a passivation film, and the like are formed as necessary to complete the silicon carbide semiconductor device having the Schottky electrode 8.

Thus, in the method for manufacturing the silicon carbide semiconductor device of the first embodiment, as shown in FIG. 2, the surface side of N ⁻ low concentration layer 2 on which the Schottky electrode is formed (one main surface side of the silicon carbide semiconductor substrate) The ohmic electrode 7 is formed in such a state that the entire surface of the thermal oxide film 5 formed in (1) is in contact with the susceptor 11 of the heat treatment apparatus. For this reason, the metal atoms scattered in the heat treatment apparatus during the formation of the ohmic electrode 7 do not reach the surface of the thermal oxide film 5, and do not reach the N ⁻ low concentration layer 2.

As a result, N ^- low concentration layer 2 on the surface, in the case of forming the Schottky electrode can be obtained a good Schottky characteristic is not affected by the metal atoms occurring during the formation of the ohmic electrode 7, good characteristics A silicon carbide semiconductor device having an ohmic electrode can be obtained.

<Embodiment 2>
4 to 10 are sectional views showing a method for manufacturing the silicon carbide semiconductor device according to the second embodiment of the present invention. Hereinafter, the procedure of the method for manufacturing the silicon carbide semiconductor device of the second embodiment will be described with reference to these drawings.

First, as shown in FIG. 4, the low-resistance N ⁺ high concentration substrate 1 on the low concentration of N ^- to form a low concentration layer 2, N ⁺ high concentration substrate 1 and N ^- laminate consisting of the low concentration layer 2 A structure (silicon carbide semiconductor substrate) is obtained.

Then, as shown in FIG. 5, a photoresist 4 having an opening 4a having a predetermined pattern is formed on the N ⁻ low concentration layer 2 by using a photolithography technique. Next, after performing ion implantation of Al (aluminum) or B (boron) from the top, the photoresist 4 is removed, and further, a heat treatment at 1500 ° C. or higher is performed, whereby a P-type implantation region that exhibits a guard ring effect. 3 is formed selectively.

Thereafter, as shown in FIG. 6, a thermal oxidation process is performed to form a thermal oxide film 5a on the N ⁻ low concentration layer 2 including the P-type implantation region 3 (on one main surface of the silicon carbide semiconductor substrate), Thermal oxide film 5b is formed on N ⁺ high concentration substrate 1 (the lower side in the figure, on the other main surface of the silicon carbide semiconductor substrate).

  Further, as shown in FIG. 6, a protective insulating film 6a is formed on the thermal oxide film 5a and a protective insulating film 6b is formed on the thermal oxide film 5b by using a CVD method or a PVD method. As the protective insulating films 6a and 6b, for example, a silicon dioxide film or a silicon nitride film having a property of hardly transmitting metal atoms can be considered. Note that FIG. 6 illustrates the step of forming the protective insulating films 6a and 6b together, but only the protective insulating film 6a can be selectively formed.

  Since the silicon dioxide film is the most common insulating film in the semiconductor industry, the protective insulating films 6a and 6b can be easily formed by using the silicon dioxide film.

  Furthermore, as a silicon dioxide film used as the protective insulating films 6a and 6b, a PSG (Phospho-Silicate Glass) film containing phosphorus can be used. In this case, there is an effect that a gettering effect for high Na (sodium) can be further expected. It is generally known that Na is a material (contamination source) that is likely to be generated in the entire process of the method for manufacturing a silicon carbide semiconductor device.

  Further, by using silicon nitride films as the protective insulating films 6a and 6b, it is possible to exert an effect capable of preventing the entry of metal atoms including Na.

Subsequently, as shown in FIG. 7, to expose the N ⁺ high concentration substrate 1 by removing the N ⁺ high backside of concentration substrate 1 of the thermal oxide film 5b and the protective insulating film 6b. Thereafter, a Ni film is formed under the N ⁺ high concentration substrate 1 by a sputtering method, and a heat treatment at 1000 ° C. is performed in an Ar atmosphere. As a result, ohmic electrode 7 is formed on the back surface of N ⁺ high concentration substrate 1 (the other main surface of the silicon carbide semiconductor substrate).

Thereafter, as shown in FIG. 8, a part of the thermal oxide film 5a and the protective insulating film 6a is removed to provide an opening 12, and a part of the surface of the N ⁻ low concentration layer 2 including the P-type implantation region 3 is formed. Expose. At this time, all of the thermal oxide film 5a and the protective insulating film 6a may be removed to expose the entire surface of the N ⁻ low concentration layer 2.

Next, as shown in FIG. 9, a Schottky electrode 8 is formed from the exposed surface of the N ⁻ low concentration layer 2 (including a part of the P-type implantation region 3) to a part of the protective insulating film 6a. An Al electrode 9 is formed on the electrode 8. The Schottky electrode 8 and the Al electrode 9 are formed by a method such as sputtering or electron beam evaporation.

  Finally, as shown in FIG. 10, after an insulating film such as polyimide is deposited on the entire surface, the central portion of the Al electrode 9 is opened to form the passivation film 10.

Thus, in the method for manufacturing the silicon carbide semiconductor device of the second embodiment, when forming ohmic electrode 7 on the back surface of N ⁺ high concentration substrate 1, thermal oxide film 5 a and protective film are formed on N ⁻ low concentration layer 2. It is protected by the insulating film 6a. That is, a total film thickness of about 100 nm to several μm can be ensured by the thermal oxide film 5a (film thickness of about several tens of nm) and the protective insulating film 6a.

  Further, the protective insulating film 6a is formed of a silicon dioxide film or a silicon nitride film having a property that it is difficult for metal atoms to pass therethrough.

Thus, N ^- low concentration layer 2 over a sufficient thickness, and can be covered with a protective film for a Schottky electrode (thermal oxide film 5a and the protective insulating film 6a) having transmitted was difficulty nature of the metal atom . Therefore, also the production process halfway (mainly during the formation of the ohmic electrode 7) as receiving the metal contamination, metal atoms N remains on the surface and inside of the Schottky electrode protective film ^- to reach the low concentration layer 2 no, N ^- can be kept low concentration layer 2 clean. As a result, a silicon carbide semiconductor device having a Schottky electrode with good characteristics and little variation can be obtained.

<Embodiment 3>
11 and 12 are cross sectional views showing the main steps of the method for manufacturing the silicon carbide semiconductor device according to the third embodiment of the present invention. Hereinafter, a method for manufacturing a silicon carbide semiconductor device according to the third embodiment will be described with reference to these drawings.

  First, the structure shown in FIG. 11 is obtained through the steps of the second embodiment shown in FIGS. 4 to 7 (except for the step of forming the ohmic electrode 7).

  Next, as shown in FIG. 12, the surface of the ohmic electrode 7 faces upward, that is, the surface side (lower side in the figure) of the N− low concentration layer 2 where the Schottky electrode is formed is the thermal oxide film 5a and the protective insulating film. It arrange | positions so that the susceptor 11 of a heat processing apparatus may be contacted via 6a. In other words, the protective insulating film 6 a is arranged so that the entire surface thereof is in contact with the susceptor 11.

Then, as shown in FIG. 12, the ohmic electrode 7 is formed on the back surface of the N ⁺ high concentration substrate 1 in the above state. Thereafter, the back surface of the N ⁺ high concentration substrate 1 and the ohmic electrode 7 are brought into ohmic contact by forming the ohmic electrode 7 by heat treatment in an inert gas atmosphere such as Ar.

Thereafter, the thermal oxide film 5a and the protective insulating film 6a are opened through the same steps as in the first embodiment shown in FIG. 3 (only the thermal oxide film 5 is replaced with the thermal oxide film 5a and the protective insulating film 6a). A Schottky electrode 8 is formed on the exposed surface of the N ⁻ low concentration layer 2 including the P-type implantation region 3 exposed by this. Thereafter, an Al electrode, a passivation film, and the like are formed as necessary to complete the silicon carbide semiconductor device having the Schottky electrode 8.

Thus, in the method for manufacturing the silicon carbide semiconductor device of the third embodiment, as shown in FIG. 12, the surface side of the N− low concentration layer 2 where the Schottky electrode is formed has the thermal oxide film 5a and the protective insulating film 6a. The ohmic electrode 7 is formed in a state of being disposed so as to be in contact with the susceptor 11 of the heat treatment apparatus. For this reason, metal atoms scattered in the heat treatment apparatus do not reach the surfaces of the thermal oxide film 5a and the protective insulating film 6a, and do not reach the N ⁻ low concentration layer 2.

  As a result, the method of manufacturing the silicon carbide semiconductor device of the third embodiment is similar to that of the first embodiment, and the silicon carbide semiconductor having an ohmic electrode with good characteristics that is not affected by the metal atoms generated when the ohmic electrode 7 is formed. A device can be obtained.

Furthermore, the method for manufacturing the silicon carbide semiconductor device of the third embodiment has the property that it has a sufficient film thickness on one main surface of the N ⁻ low concentration layer 2 and is difficult to transmit metal atoms, as in the second embodiment. By covering with a protective film (thermal oxide film 5a and protective insulating film 6a) having the above, a silicon carbide semiconductor device having a Schottky electrode with good characteristics and little variation can be obtained.

It is sectional drawing which shows the manufacturing process of the manufacturing method of the silicon carbide semiconductor device which is Embodiment 1 to this invention. 5 is a cross sectional view showing a manufacturing step of the method for manufacturing the silicon carbide semiconductor device of Embodiment 1. FIG. 5 is a cross sectional view showing a manufacturing step of the method for manufacturing the silicon carbide semiconductor device of Embodiment 1. FIG. It is sectional drawing which shows the manufacturing process of the manufacturing method of the silicon carbide semiconductor device which is Embodiment 2 in this invention. FIG. 12 is a cross sectional view showing a manufacturing step of the method for manufacturing the silicon carbide semiconductor device of the second embodiment. FIG. 12 is a cross sectional view showing a manufacturing step of the method for manufacturing the silicon carbide semiconductor device of the second embodiment. FIG. 12 is a cross sectional view showing a manufacturing step of the method for manufacturing the silicon carbide semiconductor device of the second embodiment. FIG. 12 is a cross sectional view showing a manufacturing step of the method for manufacturing the silicon carbide semiconductor device of the second embodiment. FIG. 12 is a cross sectional view showing a manufacturing step of the method for manufacturing the silicon carbide semiconductor device of the second embodiment. FIG. 12 is a cross sectional view showing a manufacturing step of the method for manufacturing the silicon carbide semiconductor device of the second embodiment. It is sectional drawing which shows the manufacturing process of the manufacturing method of the silicon carbide semiconductor device which is Embodiment 3 in this invention. FIG. 14 is a cross sectional view showing a manufacturing step of the method for manufacturing the silicon carbide semiconductor device of Embodiment 3.

Explanation of symbols

1 N ⁺ high concentration substrate, 2 N ^- low concentration layer, 5, 5a, 5b thermal oxide film, 6a, 6b protective insulating film, 7 ohmic electrode, 8 Schottky electrode.

Claims (6)

(a) forming an insulating film on the entire surface of the one main surface of the silicon carbide semiconductor substrate;
(b) placing the silicon carbide semiconductor substrate on a susceptor in contact with the entire surface of the insulating film, and forming an ohmic electrode made of metal on the other main surface of the silicon carbide semiconductor substrate in this arrangement; ,
(c) removing at least a portion of the insulating film to expose at least a portion of one main surface of the silicon carbide semiconductor substrate, and then forming a Schottky electrode on the exposed surface;
A method for manufacturing a silicon carbide semiconductor device comprising: (a) forming a first insulating film over the entire main surface of the silicon carbide semiconductor substrate;
(b) forming a second insulating film on the first insulating film;
(c) forming an ohmic electrode made of a metal on the other main surface of the silicon carbide semiconductor substrate in a state where the first and second insulating films are formed on the one main surface of the silicon carbide semiconductor substrate. When,
(d) removing at least a portion of the first and second insulating films to expose at least a portion of one main surface of the silicon carbide semiconductor substrate, and then forming a Schottky electrode on the exposed surface. With
A method for manufacturing a silicon carbide semiconductor device. A method for manufacturing a silicon carbide semiconductor device according to claim 1,
The insulating film includes first and second insulating films stacked,
A method for manufacturing a silicon carbide semiconductor device. A method for manufacturing a silicon carbide semiconductor device according to claim 2 or 3,
The second insulating film includes a silicon dioxide film;
A method for manufacturing a silicon carbide semiconductor device. A method for manufacturing a silicon carbide semiconductor device according to claim 4,
The silicon dioxide film includes a PSG (Phospho-Silicate Glass) film containing phosphorus,
A method for manufacturing a silicon carbide semiconductor device. A method for manufacturing a silicon carbide semiconductor device according to claim 2 or 3,
The second insulating film includes a silicon nitride film;
A method for manufacturing a silicon carbide semiconductor device.

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