JP2004158702A - Method for manufacturing semiconductor device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a semiconductor device manufacturing method for forming a thin impurity dopeed layer whose characteristics are satisfactory on a silicon cover guide substrate or a semiconductor layer formed on the silicon cover guide substrate whose conductive type is the same as that of the silicon cover guide substrate, and for easily forming an ohmic electrode on the impurity doped layer. <P>SOLUTION: The laser doping of impurity is carried out from the upper face of a first conductive 4H-SiC substrate or a first conductivity semiconductor layer formed on the first conductivity 4H-SiC substrate to form a second impurity doped layer, the heat treatment of the impurity doped layer is carried out at a temperature for improving the disturbed crystal structure due to the laser doping of impurity, a metallic thin film in a predetermined size is formed at a predetermined position on the impurity doped layer, and a laser is emitted from the upper face of the metallic thin film to form an ohmic electrode. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a semiconductor device manufacturing method and a semiconductor device.
[0002]
[Prior art]
Conventionally, a semiconductor material sensor may be used as an ultraviolet sensor for detecting ultraviolet light having a predetermined wavelength.
Such an ultraviolet sensor includes, for example, a layer forming a pn junction on a silicon carbide substrate, and ohmic electrodes provided on an upper portion of the layer forming the pn junction and on a lower portion of the silicon carbide substrate. Then, when ultraviolet light having a predetermined wavelength (ultraviolet light having a wavelength shorter than the wavelength corresponding to the band gap of silicon carbide and having a predetermined wavelength region) is irradiated from above the layer forming the pn junction to the light detection region, A voltage is generated between the ohmic electrodes. As a result, it is detected that ultraviolet light having a predetermined wavelength has been irradiated (for example, see Patent Document 1).
[0003]
Incidentally, in order to provide a layer forming a pn junction on a silicon carbide substrate, for example, an n-type epitaxial layer is formed on an n-type silicon carbide substrate provided with an n-type epitaxial layer, and the n-type epitaxial layer is formed. A thin impurity-doped layer doped with an impurity (such as Al) is formed on the upper surface of the epitaxial layer. The impurity-doped layer functions as a p-type layer, thereby forming a pn junction between the n-type layer and the p-type layer. In doping an impurity into the n-type layer, an ion implantation method or a crystal growth method is generally used.
When forming an ohmic electrode above the impurity-doped layer, a heat treatment is performed after depositing a metal thin film of a predetermined size at a predetermined position on the upper surface of the impurity-doped layer.
[0004]
[Patent Document 1]
JP-A-5-67803
[Problems to be solved by the invention]
When doping an impurity on the n-type layer, a heat treatment is generally performed to improve the crystal structure after doping the impurity and activate the doped impurity. If an ion implantation method or a crystal growth method is used for doping an impurity, it is necessary to perform a heat treatment at a relatively high temperature after forming the impurity doped layer. For example, in the ion implantation method, heat treatment is performed at a high temperature of about 1600 to 1700 ° C.
However, by performing the heat treatment at a high temperature, the surface of the impurity-doped layer may be roughened and the distribution of the impurities may be disturbed. This may cause various problems in using the device, such as an increase in reverse leakage current.
[0006]
In addition, when forming an ohmic electrode on a thin impurity-doped layer, when a metal thin film is deposited and heat-treated, components of the metal thin film sometimes penetrate the impurity-doped layer and penetrate the impurity-doped layer.
Therefore, the present invention provides a thin impurity-doped layer having good characteristics on a silicon carbide substrate or on a semiconductor layer of the same conductivity type as a silicon carbide substrate provided on a silicon carbide substrate, and on the impurity-doped layer, It is an object to provide a method for manufacturing a semiconductor device in which an ohmic electrode is easily formed.
[0007]
[Means for Solving the Problems]
As a means for solving the above object, a first invention of the present invention is a method for manufacturing a semiconductor device as described in claim 1.
In the method of manufacturing a semiconductor device according to claim 1, the second conductive type is formed on the first conductive type 4H-SiC substrate or on the first conductive type semiconductor layer provided on the first conductive type 4H-SiC substrate. Forming a conductive type impurity doped layer; providing a metal thin film of a predetermined size at a predetermined position on the impurity doped layer; and irradiating a laser from above the metal thin film to form an ohmic electrode. ing.
According to a second aspect of the present invention, there is provided a semiconductor device manufacturing method according to the second aspect.
The method of manufacturing a semiconductor device according to claim 2, wherein the second conductive layer is formed on the first conductive type 4H-SiC substrate or on the first conductive type semiconductor layer provided on the first conductive type 4H-SiC substrate. Forming a conductive type impurity-doped layer, providing a metal thin film of a predetermined size at a predetermined position on the impurity-doped layer, and heat-treating the metal thin film to form an ohmic electrode; The thickness of the impurity-doped layer below the electrode is thicker than other impurity-doped layers to the extent that it can withstand heat treatment when forming an ohmic electrode.
One of the first conductivity type and the second conductivity type is an n-type, and the other is a p-type.
According to the method for manufacturing a semiconductor device according to claim 1, the thin impurity-doped layer provided on the silicon carbide substrate or on the semiconductor layer of the same conductivity type as the silicon carbide substrate provided on the silicon carbide substrate is provided. An ohmic electrode can be easily formed thereon.
[0008]
According to a third aspect of the present invention, there is provided a semiconductor device manufacturing method according to the third aspect.
The method of manufacturing a semiconductor device according to claim 3, wherein the second conductive layer is formed on the first conductive type 4H-SiC substrate or on the first conductive type semiconductor layer provided on the first conductive type 4H-SiC substrate. Forming a conductive type impurity-doped layer; and heat-treating the impurity-doped layer at a temperature sufficient to improve a crystal structure disturbed by laser doping of the impurity and activate the impurity.
Here, generally, after doping with impurities, a heat treatment is performed to improve the crystal structure disturbed by the doping and activate the impurities. When doping is performed by an ion implantation method, a heat treatment at 1600 to 1700 ° C. is required. However, when the doping is performed by a laser doping method as in the third invention, a heat treatment at 1000 to 1200 ° C. is sufficient. This is because some of the impurities doped by the laser doping method have already been activated without heat treatment.
According to the semiconductor device manufacturing method of the third aspect, the thin impurity doped layer having good characteristics is provided on the silicon carbide substrate or on the semiconductor layer of the same conductivity type as the silicon carbide substrate provided on the silicon carbide substrate. be able to.
[0009]
According to a fourth aspect of the present invention, there is provided a semiconductor device manufacturing method as described in claim 4.
According to a fourth aspect of the present invention, in the method of manufacturing a semiconductor device, the second conductivity type is a p-type, and the impurity is a metal of a Group 3B element.
According to the semiconductor manufacturing method of the fourth aspect, a semiconductor device having good characteristics can be manufactured using the n-type silicon carbide substrate.
[0010]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, first and second embodiments of the present invention will be described. In the first and second embodiments, a case will be described in which the semiconductor manufacturing method of the present invention is applied as a method of manufacturing an ultraviolet sensor 1 that detects ultraviolet light having a predetermined wavelength (around 308 nm).
First, the principle of monitoring the optimum combustion state of a boiler or the like using the ultraviolet sensor 1 will be described.
When heavy oil, coal, and the like are burned in a boiler, the combustion exhaust gas contains OH ⁻ (hydroxyl group) generated by incomplete combustion. Since OH ⁻ contains information on O (oxygen) contained in the exhaust gas, it is possible to determine whether the amount of oxygen is excessive or insufficient for optimal combustion of fuel by detecting OH ⁻ .
By the way, when burned, OH ⁻ emits light at a wavelength near 308 nm in the ultraviolet region. Therefore, an ultraviolet sensor satisfying the following conditions (1) and (2) is useful for detecting OH ⁻ .
Condition (1): As it can be measured even in a bright environment, it does not react to light in the visible light region, but reacts to light near the wavelength of 308 nm in the ultraviolet region.
Condition (2) The heat-resistant temperature is at least 400 ° C. because it is installed near the area where heavy oil and coal are burning.
[0011]
Therefore, SiC is used as the material of the substrate. Generally, since the SiC substrate has better heat resistance than the Si substrate, the maximum operating temperature of the Si substrate is about 150 ° C., whereas the maximum operating temperature of the SiC substrate is about 400 to 500 ° C. Therefore, for example, when the ultraviolet sensor 1 is used at a high temperature to monitor the optimal combustion state of a boiler or the like, it is effective to use a SiC substrate, and the above condition (2) can be satisfied.
[0012]
The band gap of 4H-SiC is 3.2 eV among SiC as a material of the substrate, and it reacts to light having a wavelength of 280 to 320 nm in an ultraviolet region. Therefore, when ultraviolet light having a wavelength in this range is irradiated, electrons and holes are generated by photoexcitation of the pn junction provided in the ultraviolet sensor 1, and the electrons are separated into n regions and the holes are separated into p regions. You. Then, the n region is negatively charged and the p region is positively charged, and a potential difference is generated between the ohmic electrodes provided respectively. By detecting this potential difference, it is possible to detect OH ⁻ , so that the above condition (1) can be satisfied. Therefore, it is appropriate to select a 4H-SiC substrate in order to configure an ultraviolet sensor satisfying both the above conditions (1) and (2).
[0013]
First Embodiment (Laser irradiation is performed after deposition of a metal thin film for an electrode.)
First, the configuration of the ultraviolet sensor 1 according to the first embodiment will be described with reference to FIG.
For example, an n-type layer 50 is provided on the n-type 4H-SiC substrate 60. A thin (100 nm (± 50 nm)) p-type layer 30 is provided above the n-type layer 50. An upper ohmic electrode 10 of a Ti / Al thin film is provided on a part of the upper surface of the p-type layer 30. A region where the upper ohmic electrode 10 is not provided on the upper surface of the p-type layer 30 is covered with an insulating film 20 that transmits light. Further, a lower ohmic electrode 70 of, for example, a Ni thin film is provided below the n-type 4H-SiC substrate 60. The photodetection regions A and B when the ultraviolet light is irradiated are regions where the insulating film 20 is provided on the p-type layer 30 excluding the portion where the upper ohmic electrode 10 is formed.
[0014]
Next, the method of manufacturing the ultraviolet sensor 1 having the above configuration, which is a feature of the present invention, will be described in detail.
Procedure (1) On the n-type layer 50, for example, Al is laser-doped to form a p-type layer 30 (thickness: 100 nm ± nm).
Laser doping is performed using a doping apparatus 80 as shown in FIG. An n-type 4H-SiC substrate (sample 83 shown in FIG. 3) is set on a sample stage 82 in an atmosphere of trimethylaluminum (TMA; concentration: 450 ppm, gas pressure: 100 Torr (1 to 200 Torr, preferably 100 Torr)) diluted with hydrogen. I do. Then, using a KrF excimer laser device 84, the surface of the sample 83 is irradiated with a KrF excimer laser (wavelength: 248 nm, pulse width: 20 ns) (energy density: 0.6 to 1.0 J, irradiation pulse number: 2000 to 8000 pulses), Doping with Al. FIG. 4 shows the Al concentration characteristics after Al doping, in which the horizontal axis represents the depth [nm] from the surface of the sample 83 and the vertical axis represents the Al concentration [/ cm ³ ].
[0015]
-Procedure (2) Next, the surface of the p-type layer 30 is heat-treated at 1000 to 1200C.
By performing such a heat treatment, a crystal structure which is disordered by doping with an impurity can be improved. Thereby, for example, the reverse leakage current when used as the ultraviolet sensor 1 is reduced, and the rising characteristic of the forward current is improved. In addition, the doped impurities are activated. This makes it possible to detect weak light, increase the sensitivity of the ultraviolet sensor, and obtain good characteristics.
The heat treatment performed after the formation of the p-type layer 30 requires a temperature of about 1600 to 1700 ° C. when impurity doping is performed by ion implantation and about 2500 ° C. when impurity doping is performed by crystal growth.
According to the semiconductor device manufacturing method of the present invention, after doping impurities by laser doping to form the p-type layer 30, heat treatment may be performed at a relatively low temperature of 1000 to 1200C. Since the heat treatment is performed at a relatively low temperature, the possibility that the surface of the p-type layer 30 is roughened and the distribution of impurities is disturbed is low. Further, in order for the depletion layer 40 to efficiently absorb ultraviolet light of a predetermined wavelength, the p-type layer 30 needs to be thin (100 nm ± 50 nm). A good p-type layer 30 can be formed.
[0016]
Procedure (3) Next, a Ti / Al ohmic electrode 10 is formed on the p-type layer 30.
First, a Ti thin film (preferably 5 to 30 nm, preferably 10 nm) is deposited on the p-type layer 30 on which the ohmic electrode 10 is formed.
Next, an Al thin film (200 nm ± 100 nm) is deposited on the Ti thin film.
Then, a KrF excimer laser is irradiated under the conditions of an energy density of 0.4 to 0.8 J / cm ² , a repetition frequency of 1 to 10 Hz, and an irradiation pulse number of 1 to 100, so that an alloy layer is formed between the metal thin film and the 4H-SiC substrate. To form an ohmic electrode.
By irradiating the metal thin film formed on the p-type layer 30 with a laser without performing a heat treatment as in the related art, the possibility of the components of the metal thin film penetrating into the p-type layer 30 is low and the metal thin film is easily formed. The ohmic electrode 10 can be formed on the substrate.
[0017]
Second Embodiment (Heat treatment is performed after deposition of a metal thin film for an electrode.)
Next, the configuration of the ultraviolet sensor 1a according to the second embodiment will be described with reference to FIG.
For example, an n-type layer 50 is provided on the n-type 4H-SiC substrate 60. Above the n-type layer 50, a thin p-type layer 30a is provided. An upper ohmic electrode 10 of a Ti / Al thin film is provided on a part of the upper surface of the p-type layer 30a. A region where the upper ohmic electrode 10 is not provided on the upper surface of the p-type layer 30a is covered with an insulating film 20a that transmits light. Further, a lower ohmic electrode 70 of, for example, a Ni thin film is provided below the n-type 4H-SiC substrate 60. The photodetection regions A and B when the ultraviolet light is irradiated are regions where the insulating film 20a is provided on the p-type layer 30a except for the portion where the upper ohmic electrode 10 is formed.
The difference in configuration from the first embodiment is that in the second embodiment, the thickness d1 of the p-type layer 30a in the region where the ohmic electrode 10 is not formed on the top is 100 nm (± 50 nm), The point that the thickness d2 of the p-type layer 30a in the region where the electrode 10 is formed on the upper portion is 200 nm to 250 nm. That is, the thickness of the p-type layer 30a under the ohmic electrode 10 is thicker than other regions.
In addition, the shape of the insulating film 20a is a shape that covers the side portion of the ohmic electrode 10 formed in a protruding state.
[0018]
The method of manufacturing the ultraviolet sensor 1a according to the second embodiment, which is a feature of the present invention, will be described in detail.
Procedure (1) ′ In order to form the p-type layer 30 a on the n-type layer 50, for example, Al is doped as an impurity from the surface of the n-type layer 50 by 200 nm to 250 nm using an ion implantation method.
Procedure (2) ′ Next, the surface of the p-type layer 30a is heat-treated at 1600 ° C.
Procedure (3) ′ Next, the ohmic electrode 10 is formed at a predetermined position on the p-type layer 30a. First, a Ti thin film (preferably 5 to 30 nm, preferably 10 nm) is deposited on the p-type layer 30 on which the ohmic electrode 10 is formed. Next, an Al thin film (200 nm ± 100 nm) is deposited on the Ti thin film. Then, the Ti / Al ohmic electrode 10 is formed on the p-type layer 30a by performing a heat treatment (about 1000 ° C.) on the formed metal thin film.
Procedure (4) Then, the portion of the ohmic electrode 10 formed in the procedure (3) ′ on the upper surface of the p-type layer 30a is masked, and the other portion is etched and thinned by ion sputtering or the like (thickness 100 nm ( ± 50 nm)).
Thus, when the ohmic electrode 10 is formed, even if the metal thin film formed on the p-type layer 30a in step (3) ′ is heat-treated, the p-type layer 30a under the electrode is formed to be partially thick. Therefore, the possibility that the component of the metal thin film permeates into the p-type layer 30a is low, and the ohmic electrode 10 can be easily formed. Since the portion where the ohmic electrode 10 is not formed is thinned in the procedure (4), the p-type layer 30a is thin in the photodetection regions A and B and does not affect the sensitivity of the device to ultraviolet light.
[0019]
Operation of Ultraviolet Sensor 1 The operation of the ultraviolet sensors 1 and 1a of the first and second embodiments configured as described above will be described.
A pn junction is formed between the n-type layer 50 and the p-type layer 30 of the ultraviolet sensor 1 shown in FIG. 1, and the holes in the p-type layer 30 and the charges of the electrons in the n-type layer 50 are canceled out. Is present in the depletion layer 40. Therefore, for example, when the light detection regions A and B are irradiated with light having a wavelength of about 308 nm in the ultraviolet region (wavelength of light emitted when OH ⁻ is burned), electrons and holes in the depletion layer 40 are converted into electrons by photoexcitation. Is separated into an n region (n-type layer 50) and holes are separated into a p region (p-type layer 30). Then, the n-type layer 50 is negatively charged and the p-type layer 30 is positively charged, and a potential difference is generated between the ohmic electrodes provided respectively. OH ⁻ can be detected by detecting this potential difference.
As shown in FIG. 5, the sensitivity to the wavelength of the ultraviolet light received by the ultraviolet sensor 1 using the 4H-SiC substrate as in the first embodiment has a peak near 300 nm. Thereby, light near the wavelength of 308 nm can be sufficiently detected.
[0020]
The semiconductor device manufacturing method of the present invention is not limited to the configuration, appearance, connection, application, operation, and the like described in the present embodiment, and various changes, additions, and deletions are possible without changing the gist of the present invention. is there.
Although the case where the n-type layer 50 is provided on the n-type 4H-SiC substrate 60 has been described in the first and second embodiments, the n-type layer 50 may not be provided.
In the first and second embodiments, Al is doped as an impurity. However, the impurity may not be Al. For example, when the 4H-SiC substrate is an n-type, it may be an element belonging to Group 3B (for example, B) other than Al.
[0021]
【The invention's effect】
As described above, according to the semiconductor manufacturing method of the first and second aspects, the semiconductor device is provided on the silicon carbide substrate or on the semiconductor layer of the same conductivity type as the silicon carbide substrate provided on the silicon carbide substrate. An ohmic electrode can be easily formed on the thin impurity-doped layer.
According to the semiconductor manufacturing method of the third aspect, a thin impurity-doped layer having good characteristics is formed on a silicon carbide substrate or on a semiconductor layer of the same conductivity type as a silicon carbide substrate provided on the silicon carbide substrate. Can be provided.
According to the semiconductor manufacturing method of the fourth aspect, a semiconductor device having good characteristics can be manufactured using an n-type silicon carbide substrate.
[Brief description of the drawings]
FIG. 1 is a schematic diagram illustrating a configuration of an ultraviolet sensor 1 according to a first embodiment of the present invention.
FIG. 2 is a schematic diagram illustrating a configuration of an ultraviolet sensor 1a according to a second embodiment of the present invention.
FIG. 3 is a schematic explanatory view of a laser doping apparatus 80.
FIG. 4 is a graph showing the concentration of doped Al versus the depth from the surface after doping Al as an impurity.
FIG. 5 is a graph showing the sensitivities of the ultraviolet sensors 1, 1a corresponding to the ultraviolet light applied to the ultraviolet sensors 1, 1a.
[Explanation of symbols]
1, 1a UV sensor 10 Upper ohmic electrode 20, 20a Insulating film 30, 30a P-type layer 40 Depletion layer 50 N-type layer 60 n-type 4H-SiC substrate 70 Lower ohmic electrode 80 Laser doping device A, B Photodetection region

Claims (4)

Forming a second conductivity type impurity-doped layer on the first conductivity type 4H-SiC substrate or on the first conductivity type semiconductor layer provided on the first conductivity type 4H-SiC substrate;
Providing a metal thin film of a predetermined size at a predetermined position on the impurity-doped layer, and irradiating a laser from the upper surface of the metal thin film to form an ohmic electrode,
Semiconductor device manufacturing method. Forming a second conductivity type impurity-doped layer on the first conductivity type 4H-SiC substrate or on the first conductivity type semiconductor layer provided on the first conductivity type 4H-SiC substrate;
Providing a metal thin film of a predetermined size at a predetermined position on the impurity-doped layer, heat-treating the metal thin film to form an ohmic electrode,
The thickness of the impurity-doped layer below the ohmic electrode, compared to other impurity-doped layers, is thick enough to withstand the heat treatment,
Semiconductor device manufacturing method. Laser doping of impurities from the upper surface of the 4H-SiC substrate of the first conductivity type or the upper surface of the semiconductor layer of the first conductivity type provided on the 4H-SiC substrate of the first conductivity type, to thereby form an impurity doped layer of the second conductivity type. Forming a
Heat-treating the impurity-doped layer at a temperature that improves the crystal structure disturbed by laser-doping the impurity.
Semiconductor device manufacturing method. A method for manufacturing a semiconductor device according to claim 1,
The method according to claim 1, wherein the second conductivity type is a p-type, and the impurity is a metal of a Group 3B element.

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