Method of manufacturing semiconductor device, and semiconductor device

Abstract

To provide a method of manufacturing a semiconductor device, which can form an electrode brought into Ohmic contact with the back side of a substrate by low resistance, while suppressing heat damage on a device structure provided on the front side of the substrate made of a gallium oxide-based semiconductor, and the semiconductor device manufactured by the method.SOLUTION: A method of manufacturing a semiconductor device includes the steps of: forming a device structure on the front side of a substrate 10 made of a gallium oxide-based semiconductor; forming a base electrode 31 on the back surface of the substrate 10 after the formation of the device structure; forming a melting layer 32 by applying laser anneal to the back surface of the substrate 10 from above the base electrode 31; and forming a back electrode on the surface of the base electrode after the formation of the melting layer.SELECTED DRAWING: Figure 3

Description

Technical Field

[0001] The present invention relates to a method for manufacturing a semiconductor device and a semiconductor device.

Background Art

[0002] Conventionally, as a method for forming an electrode that makes an ohmic contact with a substrate made of a gallium oxide-based semiconductor, a method is known in which a Ti film is used for a layer in contact with the substrate of the electrode, and an annealing treatment at about 450 °C is performed after the formation of the electrode (see, for example, Patent Document 1).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] However, in order to prevent contamination of the semiconductor manufacturing apparatus by the metal constituting the electrode, when forming an electrode on the back side of the substrate after providing a device structure on the front side of the substrate, if the electrode is formed on the back side of the substrate by the above method, the device structure on the front side of the substrate may be damaged by heat during the annealing treatment, and the device characteristics may deteriorate.

[0005] An object of the present invention is to provide a method for manufacturing a semiconductor device capable of forming an electrode that makes an ohmic contact with low resistance on the back side of a substrate while suppressing heat damage to a device structure provided on the front side of the substrate made of a gallium oxide-based semiconductor, and a semiconductor device manufactured by the method.

Means for Solving the Problems

[0006] One aspect of the present invention provides the following method for manufacturing a semiconductor device and a semiconductor device in order to achieve the above object.

[0007] [1] A step of forming a device structure including a surface electrode on the front side of a substrate made of a gallium oxide-based semiconductor; a step of forming an underlying electrode on the back surface of the substrate after forming the device structure; a step of performing laser annealing on the back surface of the substrate from above the underlying electrode to form a molten layer composed of a molten portion near the interface between the substrate and the underlying electrode between the substrate and the underlying electrode; and a step of forming a back surface electrode on the surface of the underlying electrode after forming the molten layer, wherein the underlying electrode is made of any one of an Al film, a Ti film, a Ni film, and an Al alloy film, a laminated film in which two or more of the Al film, the Ti film, the Ni film, and the Al alloy film are laminated in an arbitrary order, or a Si film, a method for manufacturing a semiconductor device. [2] The laser annealing is performed under the following conditions: the wavelength of the laser is less than 1050 nm, the output of the laser is 6.0 W or less, and the irradiation amount of the laser per unit area is 4.0 J / cm 2 The method for manufacturing a semiconductor device according to [1] above, which is performed under the following conditions. [3] The method for manufacturing a semiconductor device according to [1] or [2] above, wherein the underlying electrode contains Al. [4] In the molten layer, portions with a high concentration of elements contained in the underlying electrode are scattered in an island shape. The method for manufacturing a semiconductor device according to [1] or [2] above. [5] A semiconductor device comprising a substrate made of a gallium oxide-based semiconductor, a device structure including a surface electrode provided on the front side of the substrate, an underlying electrode provided on the back surface of the substrate, a molten layer provided between the substrate and the underlying electrode and composed of a molten portion of the substrate and the underlying electrode, and a back surface electrode provided on the surface of the underlying electrode, wherein the underlying electrode is made of any one of an Al film, a Ti film, a Ni film, and an Al alloy film, a laminated film in which two or more of the Al film, the Ti film, the Ni film, and the Al alloy film are laminated in an arbitrary order, or a Si film. [6] The semiconductor device according to [5] above, wherein the underlying electrode contains an Al film. [7] In the molten layer, portions with a high concentration of elements contained in the underlying electrode are scattered in an island shape. The semiconductor device according to [5] or [6] above. [Effect of the Invention]

[0008] According to the present invention, there is provided a method for manufacturing a semiconductor device capable of forming an electrode that makes ohmic contact with low resistance on the back side of a substrate while suppressing thermal damage to a device structure provided on the front side of a substrate made of a gallium oxide-based semiconductor, and a semiconductor device manufactured by the method.

Brief Description of the Drawings

[0009]

Figure 1

Figure 2

Figure 3

Figure 4

Embodiments for Carrying Out the Invention

[0010] FIG. 1 is a vertical cross-sectional view of a semiconductor device 1 according to an embodiment of the present invention. The semiconductor device 1 includes a substrate 10 made of a gallium oxide-based semiconductor, a device structure including a surface electrode 21 provided on the front side of the substrate 10, a base electrode 31 provided on the surface of the back side of the substrate 10, a molten layer 32 provided between the substrate 10 and the base electrode 31 and composed of a molten portion of the substrate 10 and the base electrode 31, and a back surface electrode 33 provided on the surface of the base electrode 31.

[0011] The substrate 10 is a single crystal substrate of a gallium oxide-based semiconductor. The gallium oxide-based semiconductor is Ga 2 O 3 , or Ga to which one or both of Al and In are added 2 O 3 , and ideally (Ga x Al y In (1-x-y)) 2 O 3 has a composition represented by (0 < x ≤ 1, 0 ≤ y < 1, 0 < x + y ≤ 1). Ga 2 O 3 When Al is added to it, the bandgap widens, and when In is added, the bandgap narrows. Note that the crystal of the above-mentioned gallium oxide-based semiconductor typically has a β-type crystal structure.

[0012] The plane orientation of the main surface of the substrate 10 is not particularly limited, and for example, it is (001) or (-201).

[0013] The base electrode 31 is made of any one of an Al film, a Ti film, a Ni film, and an Al alloy film, a laminated film in which two or more of an Al film, a Ti film, a Ni film, and an Al alloy film are laminated in an arbitrary order, or a Si film. It has been confirmed that when any of these films is used, the resistance between the substrate 10 and the base electrode 31 is smaller than when a Cu film is used. The thickness of the base electrode 31 is, for example, 1 to 500 nm.

[0014] The molten layer 32 is a layer composed of a portion melted by laser annealing of the substrate 10 and the base electrode 31 in the vicinity of the interface between the substrate 10 and the base electrode 31.

[0015] As a result of forming the molten layer 32, the resistance between the substrate 10 and the base electrode 31 is reduced. As a result, the resistance between the substrate 10 and the back electrode 33 is reduced, and the loss of the forward current flowing through the semiconductor device 1 is reduced.

[0016] When the base electrode 31 is made of a metal film such as an Al film, it is considered that the resistance between the substrate 10 and the base electrode 31 is reduced because the resistance of the molten layer 32 is small. When the base electrode 31 is made of a Si film, it is considered that the Si contained in the molten layer 32 and the Si diffused from the molten layer 32 to the substrate 10 act as donors in the gallium oxide-based semiconductor, so that the resistance between the substrate 10 and the base electrode 31 is reduced.

[0017] In the melting layer 32, it has been confirmed that there may be island-shaped spots where the concentration of the elements (Al, Ti, Ni, or Si) contained in the base electrode is high, and this configuration may reduce the resistance between the substrate 10 and the base electrode 31 more significantly.

[0018] When using a film containing Al such as an Al film or a Ni - Al - Ti alloy film as the base electrode 31, that is, when the base electrode 31 contains Al, the resistance between the substrate 10 and the base electrode 31 can be reduced more effectively.

[0019] This is considered to be one of the reasons that the light absorption rate of Al in the ultraviolet region is lower than that of other metals. When performing laser annealing, if the temperature at the interface between the substrate 10 and the base electrode 31 becomes too high, the resistance between the substrate 10 and the base electrode 31 cannot be effectively reduced. Therefore, it is known that it is necessary to suppress the energy applied by laser irradiation compared to laser annealing performed on substrates made of other materials such as SiC. Since the base electrode 31 containing Al has a low light absorption rate in the high - energy ultraviolet region, it is easy to control the temperature at the interface between the substrate 10 and the base electrode 31 in the lower direction during laser irradiation, and the resistance between the substrate 10 and the base electrode 31 can be effectively reduced.

[0020] The configuration of the back electrode 33 is not particularly limited. For example, it is composed of a Ti / Ni / Au laminated film or a Ti / Ni / Ag laminated film.

[0021] The semiconductor device 1 is a Schottky barrier diode, and includes, as a device structure on the front side of the substrate 10, a surface electrode 21 as an anode electrode that makes Schottky contact with the substrate 10, a guard ring 22 provided near the surface of the substrate 10, and an insulating film 23 provided on the surface of the substrate 10 to form a field plate structure. Also, a protective film made of polyimide or the like covering this device structure may be provided.

[0022] The surface electrode 21 is composed of, for example, a first layer 211 made of Ni with a thickness of 50 nm that contacts the substrate 10, a second layer 212 which is a laminate of a Ti film with a thickness of 10 nm and a Pt film with a thickness of 20 nm laminated on the first layer 211, and a third layer 213 which is a laminate of a Ti film with a thickness of 200 nm and an Al film with a thickness of 3000 nm that covers the outside of the first layer 211 and the second layer 212.

[0023] The guard ring 22 is, for example, an annular region formed at a position where a part overlaps with the surface electrode 21 by ion-implanting N into the surface of the substrate 10. It can relieve the electric field concentration at the end of the surface electrode 21 and improve the breakdown voltage of the semiconductor device 1 which is a Schottky barrier diode.

[0024] The insulating film 23 is composed of, for example, a laminate of a first layer 231 made of SiO 2 and a second layer 232 made of SiO 2 The insulating film 23 is provided around the contact surface between the substrate 10 and the surface electrode 21, and the edge of the surface electrode 21 rides on the insulating film 23 to form a field plate structure. This field plate structure can also relieve the electric field concentration at the end of the surface electrode 21 and improve the breakdown voltage of the semiconductor device 1 which is a Schottky barrier diode.

[0025] When, as in the conventional method, an annealing treatment at approximately 450 °C is performed using an electric furnace after forming the back electrode 33 in order to make an ohmic contact between the substrate 10 and the back electrode 33, deterioration of device characteristics occurs.

[0026] Specifically, in the semiconductor device 1 which is a Schottky barrier diode, the state of the interface between the first layer 211 made of Ni and the substrate 10 changes and the Schottky barrier decreases, a protective film made of, for example, polyimide (not shown) is damaged, elements such as Si contained in the insulating film 23 made of SiO 2 that function as dopants in gallium oxide diffuse into the gallium oxide, and there is a risk of problems such as adverse effects on device characteristics.

[0027] As described above, in the embodiment of the present invention, in order to reduce the resistance between the substrate 10 and the back surface electrode 33, after the formation of the device structure, an annealing process in an electric furnace is not performed, and the molten layer 32 is formed by laser annealing. According to laser annealing, since only the surface layer of the substrate 10 and the base electrode 31 are locally heated, deterioration of the device structure on the front side of the substrate 10 due to heat can be suppressed.

[0028] Furthermore, according to the method of forming the molten layer 32 by laser annealing, the resistance between the substrate 10 and the back surface electrode 33 can be made smaller than in the conventional method of performing an annealing process at approximately 450°C using an electric furnace after forming the back surface electrode 33 made of Ti.

[0029] The semiconductor device 1, which is the above-described Schottky barrier diode, is an example of the semiconductor device according to the present invention. The semiconductor device according to the present invention is a vertical semiconductor device having electrodes on the front and back sides of the substrate, and includes a substrate 10 made of a gallium oxide-based semiconductor, a device structure including a surface electrode 21 provided on the front side of the substrate 10, a base electrode 31 made of Al, Ti, Ni, or Si provided on the back surface of the substrate 10, a molten layer 32 formed of a molten portion of the substrate 10 and the base electrode 31 provided between the substrate 10 and the base electrode 31, and a back surface electrode 33 provided on the surface of the base electrode 31. The configuration of the device structure provided on the front side of the substrate 10 is not limited.

[0030] The semiconductor device according to the present invention may be, in addition to the Schottky barrier diode, a power device such as a MOS-based switching element or a bipolar transistor. In any case, by forming the molten layer 32 by laser annealing, the resistance between the substrate 10 and the back surface electrode 33 can be made smaller.

[0031] Figs. 2(a) to (c), Figs. 3(a) and (b) are vertical cross-sectional views showing an example of the manufacturing process of the semiconductor device 1. Hereinafter, an example of the flow of the manufacturing process will be described with reference to these figures.

[0032] First, as shown in FIGS. 2(a) and 2(b), a substrate 10 is prepared, and a device structure including a surface electrode 21, a guard ring 22, and an insulating film 23 is formed on one side thereof (referred to as the front side). This device structure can be formed by a known method.

[0033] Thereafter, the back surface of the substrate 10 (the surface on the side where the back surface electrode 33 is to be formed) is ground using a back grinder or the like.

[0034] If the back surface of the substrate 10 after grinding is too rough, it becomes difficult to reduce the resistance between the back surface electrode 33 and the substrate 10 even when the molten layer 32 is formed. For example, when the surface roughness Sa (ISO25178) of the back surface of the substrate 10 after grinding is 0.5 to 300 nm and the surface roughness Ra (JIS B0601) is 0.5 to 350 nm, it has been confirmed that the resistance between the back surface electrode 33 and the substrate 10 is reduced by forming the molten layer 32.

[0035] After grinding, the back surface of the substrate 10 is cleaned with a hydrofluoric acid-based chemical solution or an organic solvent such as acetone or IPA.

[0036] Next, as shown in FIG. 2(c), a base electrode 31 is formed on the back surface of the substrate 10 by vapor deposition or the like. The base electrode 31 is usually formed over the entire surface of the back surface of the substrate 10.

[0037] Next, as shown in FIG. 3(a), laser annealing is performed on the back surface of the substrate 10 from above the base electrode 31 to form a molten layer 32 composed of a melted portion near the interface between the substrate 10 and the base electrode 31 between the substrate 10 and the base electrode 31.

[0038] In this laser annealing, for example, the laser irradiation spot on the surface of the base electrode 31 is circular with a diameter of about 20 to 60 μm, and this irradiation spot is scanned while being moved for each pulse to irradiate the entire surface of the base electrode 31 with the laser.

[0039] As described above, if the temperature at the interface between the substrate 10 and the base electrode 31 becomes too high, the resistance between the substrate 10 and the base electrode 31 cannot be effectively reduced. Therefore, it is necessary to suppress the energy applied by laser irradiation as compared with laser annealing performed on a substrate made of another material such as SiC.

[0040] The wavelength of the laser is preferably less than 1050 nm. In this case, in order to suppress the energy applied by laser irradiation, the output of the laser is 6.0 W or less, and the irradiation amount of the laser per unit area is 4.0 J / cm 2 It is preferably as follows.

[0041] It has been confirmed that when the output of the laser and the irradiation amount of the laser per unit area exceed the above ranges, the resistance between the substrate 10 and the base electrode 31 may become larger than when it is within the above ranges.

[0042] Also, the output of the laser and the irradiation amount of the laser per unit area may be values that can form a molten layer within the above ranges. However, in order to more effectively reduce the resistance between the substrate 10 and the base electrode 31, the output of the laser is preferably 0.125 W or more, and the irradiation amount of the laser per unit area is 0.78 J / cm 2 It is preferably as follows.

[0043] After the formation of the molten layer 32, the surface of the base electrode 31 is cleaned with a hydrofluoric acid-based chemical solution or an organic solvent such as acetone or IPA.

[0044] Next, as shown in FIG. 3(b), a back electrode 33 is formed on the surface of the base electrode 31 by vapor deposition or the like to obtain the semiconductor device 1. Thereafter, a protective film made of polyimide or the like may be formed so as to cover the device structure on the front side of the substrate 10.

[0045] FIG. 4 is a cross-sectional SEM (scanning electron microscope) photograph of the substrate 10 in a state where a molten layer 32 is formed between the substrate 10 and the base electrode 31 by laser annealing. The substrate 10 according to FIG. 4 is β-Ga 2 O3 It is a substrate, and the underlying electrode 31 is an Al film.

[0046] Although it is difficult to visually recognize in this photograph, a thin underlying electrode 31 remains on the substrate 10. The black film on the underlying electrode 31 and the film thereon are a carbon film and a Pt film for preventing charge-up in SEM observation.

[0047] When EDX (Energy Dispersive X-ray Spectroscopy) mapping analysis was performed within the range included in this cross-sectional SEM photograph, in the region where the molten layer 32 was formed near the surface on the back side of the substrate 10, it was confirmed that a dark-colored region 320 included in the convexly bulged portion contained a large amount of Al. That is, in the molten layer 32, it was found that portions with a high concentration of Al contained in the underlying electrode 31 were scattered in an island-like manner.

[0048] (Effects of the Embodiment) According to the above-described embodiment of the present invention, by forming the molten layer 32 between the substrate 10 and the underlying electrode 31 using laser annealing and forming the back surface electrode 33 on the underlying electrode 31, it is possible to suppress thermal damage to the device structure on the front side of the substrate 10 while reducing the resistance between the substrate 10 and the back surface electrode 33. As a result, it is possible to reduce the loss of the forward current flowing through the semiconductor device 1 while suppressing deterioration of the device characteristics due to thermal damage to the device structure.

[0049] Although the embodiments of the present invention have been described above, the present invention is not limited to the above-described embodiments, and various modifications can be made without departing from the gist of the invention. Also, the components of the above-described embodiments can be arbitrarily combined without departing from the gist of the invention.

[0050] Also, the above-described embodiments do not limit the invention according to the claims. It should be noted that not all combinations of the features described in the embodiments are essential means for solving the problems of the invention.

Explanation of Reference Numerals

[0051] 1…Semiconductor device, 10…Substrate, 21…Surface electrode, 31…Underlying electrode, 32…Fused layer, 33…Back electrode

Claims

1. Forming a device structure including a surface electrode on the front side of a substrate made of a gallium oxide-based semiconductor; After forming the device structure, forming a base electrode on the back surface of the substrate; Performing laser annealing on the back surface of the substrate from above the base electrode to form a molten layer composed of a molten portion near the interface between the substrate and the base electrode between the substrate and the base electrode; After forming the molten layer, forming a back surface electrode on the surface of the base electrode; comprising: The base electrode is made of any one of an Al film, a Ti film, a Ni film, and an Al alloy film, a laminated film formed by laminating two or more of an Al film, a Ti film, a Ni film, and an Al alloy film in any order, or a Si film; A method for manufacturing a semiconductor device.

2. The laser annealing is carried out under the following conditions: the wavelength of the laser is less than 1050 nm, the output of the laser is 6.0 W or less, and the laser irradiation dose per unit area is 4.0 J / cm ２ 2 or less. The method for manufacturing a semiconductor device according to Claim 1.

3. The base electrode contains Al; The method for manufacturing a semiconductor device according to Claim 1 or 2.

4. In the molten layer, portions with a high concentration of elements contained in the base electrode are scattered in an island shape; The method for manufacturing a semiconductor device according to Claim 1 or 2.

5. A substrate made of a gallium oxide-based semiconductor; A device structure including a surface electrode provided on the front side of the substrate; A base electrode provided on the back surface of the substrate; A molten layer provided between the substrate and the base electrode and composed of a molten portion of the substrate and the base electrode; A back surface electrode provided on the surface of the base electrode; comprising: The base electrode is made of any one of an Al film, a Ti film, a Ni film, and an Al alloy film, a laminated film formed by laminating two or more of an Al film, a Ti film, a Ni film, and an Al alloy film in any order, or a Si film; A semiconductor device.

6. The base electrode contains an Al film; The semiconductor device according to Claim 5.

7. In the molten layer, portions with a high concentration of elements contained in the base electrode are scattered in an island shape; The semiconductor device according to Claim 5 or 6.

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