JP2011146622A - Method of manufacturing silicon carbide semiconductor device - Google Patents

Abstract

A silicon carbide semiconductor device including an ohmic electrode having a good ohmic contact while preventing oxidation of a nickel silicide layer is obtained.
A nickel layer 4 having a thickness of about 100 nm is formed on one main surface of a silicon layer 3 by a sputtering method, and further having a thickness of 300 to 500 nm as an oxidation protection layer on one main surface of the nickel layer 4. The titanium nitride layer 5 is formed by a sputtering method. Thereafter, a high temperature annealing process at 400 to 700 ° C. is performed for 5 minutes, whereby the silicon layer 3 and the nickel layer 4 are reacted to form the nickel silicide layer 6.
[Selection] Figure 4

Description

  The present invention relates to a method for manufacturing a silicon carbide semiconductor device, and more particularly to a method for manufacturing a silicon carbide semiconductor device having an ohmic electrode in ohmic contact with a main surface of a silicon carbide substrate.

  Conventionally, when an electrode such as nickel (Ni) is formed on a silicon carbide (SiC) semiconductor layer, a silicide process in which heat treatment is performed at about 800 to 1000 ° C. is applied to form a low-resistance ohmic contact. is doing. By performing this heat treatment, nickel and silicon (Si) in SiC react to form nickel silicide.

  However, in the conventional method of forming an ohmic electrode on SiC, excess carbon is deposited at the interface between the nickel layer and the silicide layer when nickel silicide is formed, and this carbon causes peeling of the nickel layer. As a method for reducing the carbon deposition, for example, as disclosed in Patent Document 1, a silicon layer is interposed between the nickel layer and the SiC layer to perform heat treatment, and only the silicon layer reacts with the nickel layer. A method for preventing the deposition of carbon is employed.

JP 2000-106350 A

In the conventional method described above in which the silicon layer is interposed between the nickel layer and the SiC layer and the heat treatment is performed, the silicide process is performed in an inert gas atmosphere. Oxygen is released from the manufacturing apparatus itself, and oxygen is present in an inert gas atmosphere. Nickel silicide is oxidized by the oxygen to form a silicon oxide film (SiO ₂ ) which is an insulating film. As a result, there is a problem that the resistance of nickel silicide partially increases, causing variation in ohmic resistance and degrading the device characteristics.

  The present invention has been made to solve the above problems, and an object thereof is to obtain a silicon carbide semiconductor device having an ohmic electrode having a good ohmic contact while preventing oxidation of a nickel silicide layer. And

  A first aspect of a method for manufacturing a silicon carbide semiconductor device according to the present invention includes a first main electrode provided on a first main surface of a silicon carbide substrate, and a second main surface of the silicon carbide substrate. A silicon carbide semiconductor device manufacturing method in which a main current flows in a thickness direction of the silicon carbide substrate, the step (a) of preparing the silicon carbide substrate, and the carbonization A step (b) of forming a silicon layer on the first main surface of the silicon substrate; a step (c) of successively forming a nickel layer and an oxidation protective layer on the silicon layer in order from the silicon layer side; A step of heat-treating the silicon carbide substrate on which the oxidation protection layer is formed at a predetermined temperature to cause the nickel layer and the silicon layer to react to form a nickel silicide layer to form the first main electrode ( d) and after the formation of the nickel silicide layer, It includes a step (e) of removing of the protective layer, after removal of the oxide protective layer, and (f) forming a second main electrode to the second on the main surface.

  A second aspect of the method for manufacturing a silicon carbide semiconductor device according to the present invention includes a first main electrode provided on a first main surface of a silicon carbide substrate, and a second main surface of the silicon carbide substrate. A silicon carbide semiconductor device manufacturing method in which a main current flows in a thickness direction of the silicon carbide substrate, the step (a) of preparing the silicon carbide substrate, and the carbonization A step (b) of forming a silicon layer on the first main surface of the silicon substrate, a step (c) of sequentially forming a nickel layer, a gold layer and an oxidation protective layer on the silicon layer from the silicon layer side; A step of heat-treating the silicon carbide substrate on which the oxidation protection layer is formed at a predetermined temperature to cause the nickel layer and the silicon layer to react to form a nickel silicide layer to form the first main electrode ( d) and after the formation of the nickel silicide layer, the acid A step of removing the protective layer (e), after removal of the oxide protective layer, and a step (f) forming a second main electrode to the second on the main surface.

  According to the first aspect of the method for manufacturing a silicon carbide semiconductor device of the present invention, the nickel layer and the oxidation protective layer are formed on the silicon layer, and then the heat treatment is performed to react the nickel layer and the silicon layer, thereby forming the nickel silicide. Since the layer is formed, oxidation of the nickel layer and the nickel silicide layer can be prevented by the oxidation protective layer while preventing carbon from being deposited at the interface between the nickel layer and the silicide layer. By avoiding oxidation of the nickel silicide layer, variation in ohmic resistance of the ohmic electrode is prevented, and an ohmic electrode having good ohmic characteristics can be obtained. Further, by continuously forming the nickel layer and the oxidation protection layer, even if the silicon carbide substrate is once exposed to the atmosphere for heat treatment and the heat treatment is performed with moisture adsorbed on the oxidation protection layer, Reaction of nickel and nickel silicide can be prevented, and oxidation of the nickel silicide layer can be prevented.

  According to the second aspect of the method for manufacturing a silicon carbide semiconductor device of the present invention, a nickel layer, a gold layer, and an oxidation protective layer are formed on the silicon layer and then heat-treated to cause the nickel layer and the silicon layer to react. Thus, the nickel silicide layer is formed, so that oxidation of the nickel layer and the nickel silicide layer can be prevented by the oxidation protective layer while preventing carbon from being deposited at the interface between the nickel layer and the silicide layer. By avoiding oxidation of the nickel silicide layer, variation in ohmic resistance of the ohmic electrode is prevented, and an ohmic electrode having good ohmic characteristics can be obtained. Further, since the oxidation protective layer is formed on the gold layer, the nickel layer is prevented from being damaged as compared with the case where the oxidation protective layer is directly formed on the nickel layer.

It is sectional drawing explaining the manufacturing method of the silicon carbide semiconductor device of Embodiment 1 which concerns on this invention. It is sectional drawing explaining the manufacturing method of the silicon carbide semiconductor device of Embodiment 1 which concerns on this invention. It is sectional drawing explaining the manufacturing method of the silicon carbide semiconductor device of Embodiment 1 which concerns on this invention. It is sectional drawing explaining the manufacturing method of the silicon carbide semiconductor device of Embodiment 1 which concerns on this invention. It is sectional drawing explaining the manufacturing method of the silicon carbide semiconductor device of Embodiment 1 which concerns on this invention. It is sectional drawing explaining the manufacturing method of the silicon carbide semiconductor device of Embodiment 1 which concerns on this invention. It is sectional drawing explaining the manufacturing method of the silicon carbide semiconductor device of Embodiment 2 which concerns on this invention. It is sectional drawing explaining the manufacturing method of the silicon carbide semiconductor device of Embodiment 2 which concerns on this invention. It is sectional drawing explaining the manufacturing method of the silicon carbide semiconductor device of Embodiment 2 which concerns on this invention. It is sectional drawing explaining the manufacturing method of the silicon carbide semiconductor device of Embodiment 2 which concerns on this invention. It is sectional drawing explaining the manufacturing method of the silicon carbide semiconductor device of Embodiment 2 which concerns on this invention. It is sectional drawing explaining the manufacturing method of the silicon carbide semiconductor device of Embodiment 2 which concerns on this invention. It is a figure which shows the other example of application of this invention.

  Hereinafter, as an embodiment according to the present invention, a manufacturing method of a SiC Schottky barrier diode will be described as an example.

<Embodiment 1>
A method for manufacturing a silicon carbide semiconductor device according to the first embodiment of the present invention will be described with reference to FIGS. 1 to 6 which are cross-sectional views sequentially showing the manufacturing steps.

First, in the process shown in FIG. 1, a drift layer 1 having a thickness of 5 to 15 μm containing N-type impurities at a relatively low concentration (N ⁻ ) and a thickness containing N-type impurities at a relatively high concentration (N ⁺ ). A SiC substrate SB (silicon carbide substrate) composed of a drift layer 2 having a thickness of 300 to 400 μm is prepared.

  The SiC substrate SB is formed by, for example, a method in which the drift layer 1 is formed by epitaxial growth on one main surface of an SiC substrate containing N-type impurities at a relatively high concentration, and the remaining SiC substrate portion is used as the drift layer 2. Obtainable.

  Next, in the step shown in FIG. 2, for example, a 100 nm-thickness is formed on the first main surface of the SiC substrate SB, that is, one main surface of the drift layer 2 (the main surface opposite to the side in contact with the drift layer 1). The silicon layer 3 is formed by a CVD method using, for example, silane gas as a source gas.

  Next, in the step shown in FIG. 3, a nickel layer 4 having a thickness of about 100 nm is formed on one main surface of the silicon layer 3 (the main surface opposite to the side in contact with the drift layer 2) by a sputtering method.

  Further, a titanium nitride (TiN) layer 5 having a thickness of 300 to 500 nm is formed by sputtering as one oxidation protective layer on one main surface of nickel layer 4 (the main surface opposite to the side in contact with silicon layer 3). .

  Here, in the formation of the nickel layer 4 and the titanium nitride layer 5, the same sputtering apparatus is used, and when the titanium nitride layer 5 is formed following the nickel layer 4, the SiC substrate SB on which the nickel layer 4 is formed. Since the film is continuously formed without being exposed to the atmosphere, moisture in the atmosphere is not adsorbed or oxidized on the nickel layer 4.

  In addition, in the sputtering apparatus used here, it has the structure which can replace | exchange a sputtering target, without breaking the vacuum in an apparatus, and after forming the nickel layer 4, the used nickel target is replaced | exchanged for a titanium target. Then, the titanium nitride layer 5 is formed by performing sputtering while flowing nitrogen gas into the apparatus.

  Thereafter, in the step shown in FIG. 4, high temperature annealing at 400 to 700 ° C. is performed for 5 minutes, whereby the silicon layer 3 and the nickel layer 4 react to form the nickel silicide layer 6 as an ohmic electrode.

  In addition, by making the thickness of the silicon layer 3 and the nickel layer 4 the same, the silicon layer 3 and the nickel layer 4 are almost all reacted to form the nickel silicide layer 6.

  Here, in the present invention, as described above, since the titanium nitride layer 5 is continuously formed on the nickel layer 4 without breaking the vacuum, the SiC substrate SB is temporarily formed for high-temperature annealing. Even if it is exposed to the atmosphere and annealed with moisture adsorbed on the titanium nitride layer 5, it is possible to prevent moisture from reacting with nickel or nickel silicide and to prevent oxidation of the nickel silicide layer 6.

  Thus, carbon is deposited on the interface between the nickel layer and the silicide layer by forming the silicon layer 3 on the drift layer 2 and forming the titanium nitride layer 5 on the nickel layer 4 and then performing high-temperature annealing. The titanium nitride layer 5 that is difficult to oxidize serves as an oxidation protection layer while preventing the nickel layer 4 and the nickel silicide layer 6 from being oxidized.

  In addition, the oxidation of a lower layer can be reliably prevented by setting the thickness of the titanium nitride layer 5 to 300 to 500 nm.

  By avoiding the oxidation of the nickel silicide layer 6, variation in ohmic resistance of the ohmic electrode is prevented, and an ohmic electrode having good ohmic characteristics can be obtained.

  Next, in the step shown in FIG. 5, the titanium nitride layer 5 is removed by, for example, sputter etching (physical etching using an inert gas). Note that dry etching may be used to remove the titanium nitride layer 5.

  Thereafter, a titanium layer 7 having a thickness of 200 nm is vacuum-deposited as a Schottky electrode on the second main surface of SiC substrate SB and one main surface of drift layer 1 (the main surface opposite to the side in contact with drift layer 2). Then, an aluminum (Al) layer 8 having a thickness of 3 μm is formed on the titanium layer 7 as a wiring electrode. In addition, after the formation of the titanium layer 7, a heat treatment at about 600 ° C. may be performed in order to stabilize the height (φB) of the Schottky barrier.

Thereafter, in the step shown in FIG. 6, a nickel layer 9 having a thickness of about 700 nm is formed on one main surface of the nickel silicide layer 6 (the main surface opposite to the side in contact with the drift layer 2) by, for example, vacuum deposition. Further, a gold (Au) layer 10 having a thickness of 200 nm is formed on the nickel layer 9 by a vacuum deposition method. Through the above steps, the SiC Schottky barrier diode 100 having a good ohmic electrode having a contact resistance of 10 ⁻⁶ Ωcm ² is completed.

<Embodiment 2>
A method for manufacturing the silicon carbide semiconductor device according to the second embodiment of the present invention will be described with reference to FIGS. 7 to 12 which are sectional views sequentially showing the manufacturing steps.

First, in the step shown in FIG. 7, a drift layer 1 having a thickness of 5 to 15 μm containing N-type impurities at a relatively low concentration (N ⁻ ) and a thickness containing N-type impurities at a relatively high concentration (N ⁺ ). A SiC substrate SB composed of a drift layer 2 having a thickness of 300 to 400 μm is prepared.

  Next, in the step shown in FIG. 8, for example, a silicon layer 3 having a thickness of 100 nm is formed on the back surface of the SiC substrate SB, that is, on one main surface of the drift layer 2 (main surface opposite to the side in contact with the drift layer 1). For example, it is formed by a CVD method using silane gas as a source gas.

  Thereafter, a nickel layer 4A having a thickness of about 700 nm is formed by sputtering on one main surface of the silicon layer 3 (the main surface opposite to the side in contact with the drift layer 2).

  Next, in the process shown in FIG. 9, a gold layer 10 having a thickness of about 200 nm is formed on one main surface of the nickel layer 4A (the main surface opposite to the side in contact with the silicon layer 3) by vacuum deposition. .

  Next, in the step shown in FIG. 10, a titanium nitride layer 5 having a thickness of 300 to 500 nm is formed as an oxidation protection layer on one main surface of the gold layer 10 (the main surface opposite to the side in contact with the nickel layer 4A). And formed by sputtering.

  Thereafter, in the process shown in FIG. 11, a high temperature annealing process at 400 to 700 ° C. is performed for 5 minutes, whereby the silicon layer 3 and the nickel layer 4A react to form the nickel silicide layer 6 as an ohmic electrode.

  The nickel layer 4A has a thickness of about 700 nm. Even if the nickel layer 4A reacts with the silicon layer 3 having a thickness of about 100 nm, the unreacted nickel layer 4A remains on the nickel silicide layer 6. Here, the reason why the nickel layer 4A is formed thick to leave the unreacted nickel layer 4A is that if the nickel silicide layer 6 and the gold layer 10 are in direct contact with each other, the contact resistance increases. This is for reducing the contact resistance by bringing the gold layer 10 into contact therewith.

  Note that the thickness of the nickel layer 4A is not limited to 700 nm, but may be any thickness as long as it is thicker than the silicon layer 3 and remains unreacted even if all reacts with the silicon layer 3. The thickness may be 2 to 7 times that of the silicon layer 3.

  Thereafter, the titanium nitride layer 5 is removed by, for example, sputter etching. Note that dry etching may be used to remove the titanium nitride layer 5.

  In this way, the silicon layer 3 is formed on the drift layer 2 and the titanium nitride layer 5 is formed on the nickel layer 4A via the gold layer 10, and then the high temperature annealing is performed, so that the nickel layer, the silicide layer, It is possible to prevent the nickel layer 4A and the nickel silicide layer 6 from being oxidized while the titanium nitride layer 5 that is difficult to oxidize serves as an oxidation protection layer while preventing carbon from being deposited on the interface.

  Further, since the titanium nitride layer 5 is formed on the gold layer 10, the nickel layer 4A is prevented from being damaged as compared with the case where the titanium nitride layer 5 is directly formed on the nickel layer 4A. That is, since the titanium nitride layer 5 is formed by a sputtering method, when the titanium nitride layer 5 is directly formed on the nickel layer 4A, the nickel layer 4A is damaged during the formation of the titanium nitride layer 5, and the titanium nitride layer 5 The nickel layer 4A is also damaged by sputter etching when 5 is removed. However, in the manufacturing method of the present embodiment, since the titanium nitride layer 5 is formed on the nickel layer 4A via the gold layer 10, it is avoided that the nickel layer 4A is damaged.

  Further, since the gold layer 10 is formed on the nickel layer 4A by a vacuum deposition method, it can be formed with good adhesion without damaging the nickel layer 4A.

  Next, in the step shown in FIG. 12, a titanium layer 7 having a thickness of 200 nm as a Schottky electrode is formed on one main surface of the drift layer 1 (the main surface opposite to the side in contact with the drift layer 2) by vacuum deposition. Then, an aluminum (Al) layer 8 having a thickness of 3 μm is formed on the titanium layer 7 as a wiring electrode. In addition, after the formation of the titanium layer 7, a heat treatment at about 600 ° C. may be performed in order to stabilize the height (φB) of the Schottky barrier.

Through the above steps, a SiC Schottky barrier diode 200 having a good ohmic electrode with a contact resistance of 10 ⁻⁶ Ωcm ² is completed.

<Modification>
In the first and second embodiments described above, the example in which the titanium nitride layer is used as the oxidation protection layer for preventing the oxidation of the nickel silicide layer 6 has been described. However, the present invention is not limited to this, and the oxidation start Tantalum nitride (TaN), zirconium nitride (ZrN), aluminum nitride (AlN), boron nitride (BN), chromium nitride (CrN), niobium nitride (NbN), etc. with a temperature of 600 ° C. or higher and very high oxidation resistance Nitride may be used.

  Further, carbides such as titanium carbide (TiC), tungsten carbide (WC), and vanadium carbide (VC) that have high hardness and can maintain the uniformity of the silicide surface even during high-temperature annealing at 400 ° C. or higher may be used. .

Also, boricides such as titanium boride (TiB), tungsten boride (WB ₂ ) and zirconium boride (ZrB), which have a thermal expansion coefficient close to that of SiC and can suppress wafer warpage during annealing, are used. May be.

  The nitride described above can be formed by sputtering each metal sputter target in a nitrogen atmosphere, and the above-described carbide can be formed by sputtering each metal sputter target in a methane gas atmosphere. The resulting boride can be formed by an ion plating method.

<Other application examples>
In the first and second embodiments described above, the example in which the manufacturing method according to the present invention is applied to the manufacture of an SiC Schottky barrier diode has been described. However, the manufacturing method according to the present invention can be used to manufacture other SiC devices. Needless to say, the present invention can be applied to, for example, a vertical double diffusion structure MOSFET (DMOSFET).

FIG. 13 shows an example of the configuration of the DMOSFET. In the DMOSFET shown in FIG. 13, the drain electrode 28 is formed on the second main surface of the SiC substrate, that is, one main surface of the SiC drift layer 22 containing N-type impurities at a relatively high concentration (N ⁺ ). On the other main surface of the drift layer 22, an SiC drift layer 21 containing an N-type impurity at a relatively low concentration (N ⁻ ) is formed. A plurality of body regions 23 containing P-type impurities are selectively formed in the upper layer portion of the drift layer 21, and N-type impurities are relatively concentrated (N ⁺ ) in the surface of the body region 23. A source region 24 is formed.

  A gate insulating film 25 is formed on the first main surface of the SiC substrate, that is, on one main surface of the drift layer 21 so as to extend over between the source regions 24 of the adjacent body regions 23. A gate electrode 26 is formed on 25. A channel is formed in the surface of the body region 23 immediately below the gate insulating film 25 during the operation of the DMOSFET.

  The gate insulating film 25 is formed between the source regions 24 and on the edge of each source region 24, but the source electrode 27 is formed on the source region 24 and the body region 23 where the gate insulating film 25 is not formed. Is formed.

  In the DMOSFET having such a configuration, the manufacturing method according to the present invention can be applied when the source electrode 27 is formed of silicide.

  3 silicon layer, 4 nickel layer, 5 titanium nitride layer, 6,6A nickel silicide layer, 10 gold layer, SB SiC substrate.

Claims (14)

A thickness of the silicon carbide substrate, comprising: a first main electrode provided on a first main surface of the silicon carbide substrate; and a second main electrode provided on a second main surface of the silicon carbide substrate. A method for manufacturing a silicon carbide semiconductor device in which a main current flows in a direction,
(a) preparing the silicon carbide substrate;
(b) forming a silicon layer on the first main surface of the silicon carbide substrate;
(c) continuously forming a nickel layer and an oxidation protective layer on the silicon layer in order from the silicon layer side;
(d) The silicon carbide substrate on which the oxidation protection layer is formed is heat-treated at a predetermined temperature, the nickel layer and the silicon layer are reacted to form a nickel silicide layer, and the first main electrode is formed. Forming, and
(e) removing the oxidation protection layer after forming the nickel silicide layer;
(f) forming the second main electrode on the second main surface after removing the oxidation protection layer, and a method for manufacturing a silicon carbide semiconductor device. A thickness of the silicon carbide substrate, comprising: a first main electrode provided on a first main surface of the silicon carbide substrate; and a second main electrode provided on a second main surface of the silicon carbide substrate. A method for manufacturing a silicon carbide semiconductor device in which a main current flows in a direction,
(a) preparing the silicon carbide substrate;
(b) forming a silicon layer on the first main surface of the silicon carbide substrate;
(c) forming a nickel layer, a gold layer and an oxidation protective layer on the silicon layer sequentially from the silicon layer side;
(d) The silicon carbide substrate on which the oxidation protection layer is formed is heat-treated at a predetermined temperature, the nickel layer and the silicon layer are reacted to form a nickel silicide layer, and the first main electrode is formed. Forming, and
(e) removing the oxidation protection layer after forming the nickel silicide layer;
(f) forming the second main electrode on the second main surface after removing the oxidation protection layer, and a method for manufacturing a silicon carbide semiconductor device.   The method for manufacturing a silicon carbide semiconductor device according to claim 1, wherein the step (c) includes a step of forming the oxidation protection layer with a nitride.   The method for manufacturing a silicon carbide semiconductor device according to claim 3, comprising a step of forming the nitride with a thickness of 300 to 500 nm.   The method for manufacturing a silicon carbide semiconductor device according to claim 3, comprising a step of forming any one of nitrides selected from TiN, TaN, ZrN, AlN, BN, CrN, and NbN as the nitride.   The method for manufacturing a silicon carbide semiconductor device according to claim 1, wherein the step (d) includes a step of heat-treating the silicon carbide substrate at 400 to 700 ° C. as the predetermined temperature.   The method of manufacturing a silicon carbide semiconductor device according to claim 1, wherein the step (c) includes a step of forming the oxidation protection layer with a carbide.   The method for manufacturing a silicon carbide semiconductor device according to claim 7, comprising a step of forming any carbide selected from TiC, WC, and VC as the carbide.   The method for manufacturing a silicon carbide semiconductor device according to claim 1, wherein the step (c) includes a step of forming the oxidation protection layer with a boride. The method for manufacturing a silicon carbide semiconductor device according to claim 9, comprising a step of forming any boride selected from TiB, WB ₂ and ZrB as the boride. The step (d)
The method for manufacturing a silicon carbide semiconductor device according to claim 1, comprising a step of forming the nickel layer with a thickness comparable to that of the silicon layer. The step (d)
The method for manufacturing a silicon carbide semiconductor device according to claim 1, comprising a step of forming the nickel layer to a thickness two to seven times that of the silicon layer. The step (a)
A first silicon carbide drift layer containing a relatively high concentration of semiconductor impurities;
Preparing a silicon carbide substrate configured by laminating a second silicon carbide drift layer containing the semiconductor impurity at a relatively low concentration;
3. The silicon carbide semiconductor according to claim 1, wherein said first main surface is a main surface of said first silicon carbide drift layer opposite to a side in contact with said second silicon carbide drift layer. Device manufacturing method. The step (a)
A first silicon carbide drift layer containing a relatively high concentration of semiconductor impurities;
Preparing a silicon carbide substrate configured by laminating a second silicon carbide drift layer containing the semiconductor impurity at a relatively low concentration;
3. The silicon carbide semiconductor according to claim 1, wherein said first main surface is a main surface of said second silicon carbide drift layer opposite to a side in contact with said first silicon carbide drift layer. Device manufacturing method.

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