Semiconductor device manufacturing method and semiconductor device

Abstract

Provided is a semiconductor device manufacturing method including: a step for forming a device structure on a front side of a substrate 10 composed of a gallium oxide–based semiconductor; a step for forming a base electrode 31 on a rear-side surface of the substrate 10 after forming the device structure; a step for forming a molten layer 32 by performing laser annealing on the rear-side surface of the substrate 10 from above the base electrode 31; and a step for forming a rear-surface electrode on a front surface of the base electrode after forming the molten layer.

Description

Semiconductor device manufacturing method and semiconductor device

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

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

[0003] Japanese Patent Application Laid-Open No. 2022-65153

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

[0005] An object of the present invention is to provide a method for manufacturing a semiconductor device that can form an electrode that makes 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.

[0006] In order to achieve the above object, one aspect of the present invention provides the following semiconductor device manufacturing method and semiconductor device.

[0007] [1] A method for manufacturing a semiconductor device, comprising the steps of: forming a device structure including a front surface electrode on the front side of a substrate made of a gallium oxide-based semiconductor; forming an underlayer electrode on the back surface of the substrate after forming the device structure; performing laser annealing on the back surface of the substrate from above the underlayer electrode to form a melt layer between the substrate and the underlayer electrode, the melt layer being a melted portion near the interface between the substrate and the underlayer electrode; and forming a back surface electrode on the surface of the underlayer electrode after forming the melt layer, wherein the underlayer electrode is one of an Al film, a Ti film, a Ni film, and an Al alloy film, or a stacked film formed by stacking two or more of the Al film, the Ti film, the Ni film, and the Al alloy film in any order, or a Si film. [2] The laser annealing is performed using a laser having a wavelength of less than 1050 nm, a laser output of 6.0 W or less, and a laser irradiation amount per unit area of ​​4.0 J / cm. ２ A method for manufacturing a semiconductor device according to [1] above, carried out under the following conditions: [3] The method for manufacturing a semiconductor device according to [1] or [2] above, wherein the base electrode contains Al; [4] The method for manufacturing a semiconductor device according to [1] or [2] above, wherein the melting layer has island-like scattered portions of an element contained in the base electrode; [5] A semiconductor device comprising: a substrate made of a gallium oxide-based semiconductor; a device structure including a front electrode provided on the front side of the substrate; a base electrode provided on the back side of the substrate; a melting layer provided between the substrate and the base electrode and consisting of melted portions of the substrate and the base electrode; and a back electrode provided on the surface of the base electrode, wherein the base electrode is made of any of an Al film, a Ti film, a Ni film, and an Al alloy film, or a stacked film formed by stacking 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; [6] The semiconductor device according to [5] above, wherein the base electrode contains an Al film. [7] The semiconductor device according to [5] or [6] above, wherein the melting layer has island-like scattered portions where the element contained in the base electrode has a high concentration.

[0008] According to the present invention, it is possible to provide a method for manufacturing a semiconductor device that can form an electrode that makes 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 a substrate made of a gallium oxide-based semiconductor, and a semiconductor device manufactured by the method.

[0009] FIG. 1 is a vertical cross-sectional view of a semiconductor device according to an embodiment of the present invention. FIG. 2A is a vertical cross-sectional view showing an example of a manufacturing process for a semiconductor device according to an embodiment of the present invention. FIG. 2B is a vertical cross-sectional view showing an example of a manufacturing process for a semiconductor device according to an embodiment of the present invention. FIG. 2C is a vertical cross-sectional view showing an example of a manufacturing process for a semiconductor device according to an embodiment of the present invention. FIG. 3A is a vertical cross-sectional view showing an example of a manufacturing process for a semiconductor device according to an embodiment of the present invention. FIG. 3B is a vertical cross-sectional view showing an example of a manufacturing process for a semiconductor device according to an embodiment of the present invention. FIG. 4 is a cross-sectional SEM (scanning electron microscope) photograph of a substrate in a state in which a molten layer has been formed between the substrate and an underlying electrode by laser annealing.

[0010] 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 front surface electrode 21 provided on the front side of the substrate 10, a base electrode 31 provided on the back surface of the substrate 10, a melt layer 32 provided between the substrate 10 and the base electrode 31 and consisting of melted portions 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 semiconductor. ２ O ３ , or Ga doped with one or both of Al and In ２ O ３ and ideally (Ga ｘ Al ｙ In （１－ｘ－ｙ） ) ２ O ３ (0<x≦1, 0≦y<1, 0<x+y≦1). ２ O ３The band gap widens when Al is added to the gallium oxide-based semiconductor, and narrows when In is added to the gallium oxide-based semiconductor. The crystals of the gallium oxide-based semiconductor typically have a β-type crystal structure.

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

[0013] The base electrode 31 is made of an Al film, a Ti film, a Ni film, 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 any 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 melt layer 32 is a layer made of a portion of the substrate 10 and the base electrode 31 near the interface between the substrate 10 and the base electrode 31 that has been melted by laser annealing.

[0015] As a result of the formation of 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 base electrode 31 is made of a metal film such as an Al film, it is believed that the resistance between substrate 10 and base electrode 31 is reduced because the resistance of melt layer 32 is low. When base electrode 31 is made of a Si film, it is believed that the resistance between substrate 10 and base electrode 31 is reduced because Si contained in melt layer 32 and Si diffused from melt layer 32 to substrate 10 act as donors in the gallium oxide-based semiconductor.

[0017] It has been confirmed that in the molten layer 32, there may be scattered island-like areas with high concentrations of elements (Al, Ti, Ni, or Si) contained in the base electrode, and this configuration may further reduce the resistance between the substrate 10 and the base electrode 31.

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

[0019] One of the reasons for this is thought to be that Al has a lower absorbance rate for light in the ultraviolet region than other metals. When laser annealing is performed, 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 the energy applied by laser irradiation needs to be reduced compared to laser annealing performed on substrates made of other materials, such as SiC. Because the base electrode 31 containing Al has a low absorbance rate for light 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 during laser irradiation to a lower level, 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, but may be, for example, a Ti / Ni / Au laminated film or a Ti / Ni / Ag laminated film.

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

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

[0023] The guard ring 22 is, for example, a ring-shaped region formed at a position that overlaps partially with the surface electrode 21 by ion implanting N into the surface of the substrate 10, and can alleviate 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 made of, for example, SiO ２ and a first layer 231 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 up onto the insulating film 23 to form a field plate structure. This field plate structure also alleviates electric field concentration at the edge of the surface electrode 21, and can improve the breakdown voltage of the semiconductor device 1, which is a Schottky barrier diode.

[0025] When an annealing process is performed at approximately 450° C. in an electric furnace after the formation of the back electrode 33 in order to bring the substrate 10 into ohmic contact with the back electrode 33 as in the conventional method, the device characteristics are deteriorated.

[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, the Schottky barrier lowers, a protective film made of polyimide or the like (not shown) is damaged, and SiO ２ However, there is a risk that elements that function as dopants in gallium oxide, such as Si contained in the insulating film 23, may diffuse into the gallium oxide, adversely affecting the 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 electrode 33, the molten layer 32 is formed by laser annealing rather than performing annealing in an electric furnace after the device structure is formed. Laser annealing locally heats almost only the surface layer of the substrate 10 and the base electrode 31, thereby suppressing thermal degradation of the device structure on the front side of the substrate 10.

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

[0029] The semiconductor device 1, which is a Schottky barrier diode, is one example of a 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 a substrate, and is provided with a substrate 10 made of a gallium oxide-based semiconductor, a device structure including a front 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 side of the substrate 10, a molten layer 32 provided between the substrate 10 and the base electrode 31 and consisting of a molten portion of the substrate 10 and the base electrode 31, and a back 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 a Schottky barrier diode or a power device such as a MOS switching element or a bipolar transistor. In either case, the resistance between the substrate 10 and the back electrode 33 can be reduced by forming a molten layer 32 by laser annealing.

[0031] 2A to 2C, 3A, and 3B are vertical cross-sectional views showing an example of a manufacturing process for the semiconductor device 1. An example of the flow of the manufacturing process will be described below with reference to these figures.

[0032] 2A and 2B, 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 (front side) of the substrate 10. This device structure can be formed by a known method.

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

[0034] If the rear surface of substrate 10 after grinding is too rough, it becomes difficult to reduce the resistance between back surface electrode 33 and substrate 10 even if melting layer 32 is formed. For example, when the surface roughness Sa (ISO 25178) of the rear surface of 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 forming melting layer 32 reduces the resistance between back surface electrode 33 and substrate 10.

[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] 2C, a base electrode 31 is formed by vapor deposition or the like on the rear surface of the substrate 10. The base electrode 31 is usually formed over the entire rear surface of the substrate 10.

[0037] Next, as shown in Figure 3A, laser annealing is performed on the back surface of the substrate 10 from above the base electrode 31, and a molten layer 32 consisting of a molten portion near the interface between the substrate 10 and the base electrode 31 is formed 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 moved and scanned 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, and therefore, it is necessary to reduce the energy applied by laser irradiation compared to laser annealing performed on substrates made of other materials 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 the laser irradiation, the laser output is set to 6.0 W or less and the laser irradiation amount per unit area is set to 4.0 J / cm. ２ It is preferable that:

[0041] It has been confirmed that if the laser output and the laser irradiation amount per unit area exceed the above range, the resistance between the substrate 10 and the base electrode 31 may be higher than when they are within the above range.

[0042] The laser output and the laser irradiation amount per unit area may be within the above ranges as long as they are values ​​that allow the formation of a molten layer. However, in order to more effectively reduce the resistance between the substrate 10 and the base electrode 31, the laser output is preferably 0.125 W or more, and the laser irradiation amount per unit area is preferably 0.78 J / cm. ２ It is preferable that this is equal to or greater than this.

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

[0044] 3B , 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] 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 underlying electrode 31 by laser annealing. ２ O ３ The substrate is a substrate, and the base electrode 31 is an Al film.

[0046] Although it is difficult to see in this photograph, a thin base electrode 31 remains on the substrate 10. The black film on the base electrode 31 and the film above it are a carbon film and a Pt film to prevent charge-up during SEM observation.

[0047] An EDX (energy dispersive X-ray spectroscopy) mapping analysis was performed on the area included in this cross-sectional SEM photograph, and it was confirmed that a large amount of Al was contained in a dark colored region 320 included in a convexly bulging portion in the region where molten layer 32 was formed near the surface on the back side of substrate 10. In other words, it was found that in molten layer 32, parts with a high concentration of Al that were contained in base electrode 31 were scattered in an island-like pattern.

[0048] Effect of the Embodiment According to the above-described embodiment of the present invention, by using laser annealing to form the molten layer 32 between the substrate 10 and the base electrode 31 and forming the back electrode 33 on the base electrode 31, it is possible to reduce the resistance between the substrate 10 and the back electrode 33 while suppressing heat damage to the device structure on the front side of the substrate 10. 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 caused by heat 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 spirit and scope of the invention. Furthermore, the components of the above-described embodiments can be combined in any manner without departing from the spirit and scope of the invention.

[0050] Furthermore, the above-described embodiments do not limit the scope of the invention as claimed, and it should be noted that not all of the combinations of features described in the embodiments are necessarily essential to the means for solving the problems of the invention.

[0051] Provided are a method for manufacturing a semiconductor device that can form an electrode that makes 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.

[0052] DESCRIPTION OF SYMBOLS 1... semiconductor device, 10... substrate, 21... surface electrode, 31... base electrode, 32... melting layer, 33... rear electrode

Claims

1. A method for manufacturing a semiconductor device comprising the steps of: forming a device structure including a front surface electrode on a front side of a substrate made of a gallium oxide 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 consisting of a molten portion near the interface between the substrate and the base electrode between the substrate and the base electrode; and after forming the molten layer, forming a back surface electrode on the surface of the base electrode, wherein the base electrode is made of any of an Al film, a Ti film, a Ni film, and an Al alloy film, or a laminate film obtained by stacking 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.

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

3. The method for manufacturing a semiconductor device according to claim 1 or 2, wherein the base electrode contains Al.

4. The method for manufacturing a semiconductor device according to claim 1 or 2, wherein the melt layer has island-like scattered portions where the element contained in the base electrode has a high concentration.

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

6. The semiconductor device according to claim 5, wherein the base electrode includes an Al film.

7. The semiconductor device according to claim 5 or 6, wherein the melting layer has island-like scattered portions where the element contained in the base electrode has a high concentration.

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