JP2004335815A - Manufacturing method of silicon carbide schottky barrier diode - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To easily obtain an SiC Schottky barrier diode, small in the leakage current of a Schottky electrode and excellent in element characteristics. <P>SOLUTION: The manufacturing method of the SiC Schottky barrier diode is provided with an n-type silicon carbide substrate 1, an n-type silicon carbide epitaxial growth layer 2, the Schottky electrode 5 and a p-type terminal structure 3, and comprises an ion pouring process for effecting ion pouring of p-type impurities into the forming region of the terminal structure 3, and a laser activating anneal process for activating the p-type impurities poured through the ion pouring by providing a protective film 4 for preventing the transmission of laser beam on the forming region of the Schottky electrode 5 and irradiating the laser beam against the whole surface of a wafer. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a method for manufacturing a silicon carbide Schottky barrier diode.
[0002]
[Prior art]
A Schottky barrier diode using silicon carbide (SiC), which is a wide-gap semiconductor, as a constituent material has a dielectric breakdown voltage approximately one digit higher than that of silicon (Si), which is a general constituent material of SiC. Since it has excellent physical properties of twice the electron saturation drift speed, it is promising as an element that can control high power at high frequency.
[0003]
However, in high-frequency operation using high power, electric field concentration occurs at the periphery of the Schottky electrode when a reverse voltage is applied, and the element may be broken at a voltage lower than the originally expected withstand voltage by using SiC as a constituent material. In order to alleviate the electric field concentration on the peripheral portion and secure the withstand voltage, a termination structure called a so-called guard ring is formed on the peripheral portion of the Schottky electrode to improve the withstand voltage of the element.
[0004]
In such a termination structure, a p-type impurity is ion-implanted into the n-type SiC epitaxial growth layer at the periphery of the Schottky electrode, and then a heat treatment is performed at a high temperature of 1500 ° C. or more to electrically activate the ion-implanted p-type impurity. The n-type SiC epitaxial growth layer was formed by forming a p-type region of a conductivity type opposite to that of the n-type SiC epitaxial growth layer. However, the treatment performed at an extremely high temperature of 1500 ° C. or more during the impurity activation annealing causes damage to the SiC crystal surface, and when a reverse breakdown voltage is applied to the SiC Schottky barrier diode, the damage from the Schottky electrode through the damage occurs. Of the device characteristics such that the leakage current increases.
[0005]
In the conventional method of manufacturing a SiC Schottky barrier diode disclosed in Patent Document 1, laser activation annealing is performed instead of the high-temperature heat treatment that causes the above-described problem. This is because laser activation annealing has the same level of electrical activation of impurities at a lower temperature than conventional heat treatment.
[0006]
[Patent Document 1]
JP 2002-289550 A
[Problems to be solved by the invention]
In the case of a SiC Schottky barrier diode, laser activation annealing for the purpose of electrically activating ion-implanted impurities may be performed only in the termination structure formation region, and laser irradiation is performed on the SiC surface in the Schottky electrode formation region. Not only is activation annealing unnecessary, but rather it causes crystal surface roughness. However, when laser activation annealing is locally performed only in the region where the termination structure is formed, the throughput is extremely reduced, and a new problem that the element cannot be easily manufactured has arisen. On the other hand, if the entire surface of the wafer is uniformly laser-activated and annealed, the SiC surface in the Schottky electrode formation region, which does not need to be annealed, is also irradiated with the laser, thus causing the above-described crystal surface roughness.
[0008]
SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and has as its object to easily manufacture a SiC Schottky barrier diode having good element characteristics with small leakage current from a Schottky electrode. And
[0009]
[Means for Solving the Problems]
The method for manufacturing a silicon carbide Schottky barrier diode according to the present invention includes an n-type silicon carbide substrate, an n-type silicon carbide epitaxial growth layer formed on the n-type silicon carbide substrate, and an n-type silicon carbide epitaxial growth layer. A method for manufacturing a silicon carbide Schottky barrier diode, comprising: a provided Schottky electrode; and a p-type termination structure provided in the n-type silicon carbide epitaxial growth layer at the periphery of the Schottky electrode. An ion implantation step of implanting a p-type impurity into the formation region of the termination structure; and a protection film for preventing transmission of laser light on the formation region of the Schottky electrode, and irradiating the entire surface of the wafer with the laser light. A laser activation annealing step of activating the ion-implanted p-type impurity.
[0010]
BEST MODE FOR CARRYING OUT THE INVENTION
Embodiment 1 FIG.
A method for manufacturing the SiC Schottky barrier diode according to the first embodiment will be described with reference to FIGS. Here, FIG. 1 is a view showing a step of performing laser activation annealing on the p-type termination structure during the manufacturing process of the SiC Schottky barrier diode, and FIG. 2 is a view showing the SiC Schottky after the formation of the Schottky electrode and the back surface ohmic electrode. FIG. 3 is a diagram illustrating a barrier diode. In the figure, 1 denotes an n-type SiC substrate, 2 denotes an n-type SiC epitaxial growth layer, 3 denotes a p-type termination structure, 4 denotes a protective film, 5 denotes a Schottky electrode, and 6 denotes an n-type back ohmic electrode.
[0011]
Hereinafter, a method for manufacturing the SiC Schottky barrier diode of the first embodiment will be described. First, an n-type SiC epitaxial growth layer 2 is crystal-grown on an n-type SiC substrate 1. Subsequently, in order to form the p-type termination structure 3, a p-type impurity is ion-implanted into the n-type SiC epitaxial growth layer 2 at a peripheral portion of a region where the Schottky electrode 5 is formed in a later step. As the ion species in the ion implantation, a p-type impurity of a conductivity type opposite to that of the n-type SiC substrate 1, for example, aluminum ion is preferable. When the SiC substrate 1 is of a p-type, an n-type impurity of the opposite conductivity type may be implanted into the SiC substrate 1.
[0012]
In the above-described ion implantation, a region other than the formation region of the p-type termination structure 3 is covered with a resist or the like so that an ion implantation mask is provided so that only the formation region of the p-type termination structure 3 can be selectively ion-implanted.
[0013]
After removing the above-described ion implantation mask, a protective film 4 is formed in a region where a Schottky electrode 5 will be formed in a later step. The material and the thickness of the protective film 4 are selected so that the reflectance, the absorptivity or the transmittance has a desired value with respect to the wavelength of the laser to be irradiated. As a film type of the protective film 4, for example, a silicon nitride film (Si ₃ N ₄ ) is preferable. Further, a resist film made of a material and a film thickness that can realize the above-described respective set values may be used.
[0014]
As a laser light source at the time of laser activation annealing, for example, a XeCl excimer laser having a wavelength of 308 nm, a KrF laser having a wavelength of 248 nm, or an Ar ion laser having a wavelength of 488 nm is suitable. This is because the SiC crystal can be effectively annealed by laser light having a laser wavelength higher than the band gap energy of the SiC crystal.
[0015]
When irradiating laser light, the wafer is kept at room temperature or at a temperature of 100 ° C. to 1000 ° C. Laser irradiation is performed once or a plurality of times to electrically activate impurities implanted in the SiC crystal.
[0016]
Subsequently, after removing the protective film 4, a Schottky electrode 5 made of a metal such as titanium (Ti) is formed on the surface of the n-type SiC epitaxial growth layer 2, and the back side of the n-type SiC substrate 1, that is, n-type SiC epitaxial growth. An n-type back ohmic electrode 6 made of a metal such as nickel (Ni) is formed on the surface opposite to the side on which the layer 2 is formed (FIG. 2).
[0017]
When a reverse voltage is applied to the SiC Schottky barrier diode, the electric field concentration at the peripheral portion of the Schottky electrode 5 is reduced by the p-type termination structure 3 into which impurities are implanted, and as a result, the breakdown voltage of the SiC Schottky barrier diode is reduced. improves.
[0018]
In the SiC Schottky barrier diode according to the present embodiment, protection for effectively preventing laser light even at the time of laser activation annealing in which laser irradiation is performed on the entire surface of the wafer on the surface of n-type SiC epitaxial growth layer 2 located under Schottky electrode 5. Due to the presence of the film 4, the degree of temperature rise in such a region is significantly lower than that in the region of the p-type termination structure 3, so that damage to the SiC crystal surface due to the temperature rise is significantly reduced as compared to the case without the protective film 4. it can. Therefore, during the operation of the SiC Schottky barrier diode, the leak current from Schottky electrode 5 caused by crystal surface damage can be significantly reduced. Furthermore, contamination and damage to the crystal surface which may occur when the SiC crystal surface in the region where the Schottky electrode 5 is formed is exposed can be prevented. In other words, the laser irradiation can be scanned over the entire surface of the wafer without inducing the roughening of the surface of the SiC crystal in the region where the Schottky electrode 5 is to be formed. Can be improved.
[0019]
In the above-described ion implantation, the impurity to be implanted may be boron (B) ions. In addition, when performing ion implantation by covering the entire surface of the SiC surface with an oxide film or the like during ion implantation, contamination and damage to the SiC surface during ion implantation can be effectively prevented.
[0020]
As described above, according to the method for manufacturing a SiC Schottky barrier diode of the present embodiment, a protective film that does not transmit laser light is formed in a region corresponding to a Schottky electrode during laser activation annealing, and the entire surface of the wafer is irradiated with laser. Therefore, it is possible to easily manufacture a SiC Schottky barrier diode having good element characteristics with a small leakage current from the Schottky electrode.
[0021]
Embodiment 2 FIG.
FIG. 3 shows a method of manufacturing the SiC Schottky barrier diode according to the second embodiment. In the method of manufacturing the SiC Schottky barrier diode according to the present embodiment, protective film 4a provided in the region where Schottky electrode 5 is formed has both functions of a protective mask during laser irradiation and an ion implantation mask during ion implantation. As a result, as shown in FIG. 3, laser activation annealing and ion implantation are performed simultaneously or alternately.
[0022]
When the protective film 4a having a plurality of functions described above is applied, it is not necessary to form separate protective films one by one in the ion implantation step and the laser activation annealing step. Therefore, for example, when impurity ion implantation is performed a plurality of times at different acceleration energies to obtain an impurity concentration up to a desired depth, a single step of simultaneously or alternately continuously performing ion implantation and laser activation annealing is performed. Can be performed using only the protective film 4a, so that the entire process can be simplified.
[0023]
As described above, in the method of manufacturing the SiC Schottky barrier diode according to the second embodiment, the ion implantation of impurities into the formation region of the p-type termination structure and the laser activation annealing can be continuously performed. In addition to the effects described above, the overall process can be simplified and the activation rate of ion-implanted impurities can be improved.
[0024]
Embodiment 3 FIG.
FIG. 4 shows a method of manufacturing the SiC Schottky barrier diode according to the third embodiment. In the method of manufacturing a SiC Schottky barrier diode according to the present embodiment, first protective film 4 is formed separately in the region where Schottky electrode 5 is formed, and second protective film 7 is separately formed in the region where p-type termination structure 3 is formed. . Here, the material and thickness of each protective film are selected so that the first protective film 4 and the second protective film 7 have different reflectances, transmittances, or absorptances with respect to an irradiated laser. .
[0025]
When the above-described protective film configuration is applied, the temperature distribution generated by the same laser irradiation between the formation region of the Schottky electrode 5 and the formation region of the p-type termination structure 3 due to the unique properties of the respective protective films 4 and 7 It can be changed intentionally. Therefore, the region where the p-type termination structure 3 is formed reaches an annealing temperature sufficient for electrically activating the ion-implanted impurities, while the temperature near the surface of the n-type SiC epitaxial growth layer 2 in the region where the Schottky electrode 5 is formed is Since the temperature can be set to be lower than that of the p-type terminal structure 3 into which the impurity is implanted, a good impurity activation rate in the region where the p-type terminal structure 3 is formed is maintained, and at the same time, the region where the Schottky electrode 5 is formed is formed. Roughness of the SiC crystal surface can be effectively prevented. Therefore, the leakage current from the Schottky electrode during the operation of the SiC Schottky barrier diode can be significantly reduced.
[0026]
As described above, according to the method for manufacturing a SiC Schottky barrier diode of the third embodiment, a SiC Schottky barrier diode having good element characteristics can be manufactured more easily than the manufacturing method of the first or second embodiment. effective.
[0027]
【The invention's effect】
The method for manufacturing a silicon carbide Schottky barrier diode according to the present invention includes an n-type silicon carbide substrate, an n-type silicon carbide epitaxial growth layer formed on the n-type silicon carbide substrate, and an n-type silicon carbide epitaxial growth layer. A method for manufacturing a silicon carbide Schottky barrier diode, comprising: a provided Schottky electrode; and a p-type termination structure provided in the n-type silicon carbide epitaxial growth layer at the periphery of the Schottky electrode. An ion implantation step of implanting a p-type impurity into the formation region of the termination structure; and a protection film for preventing transmission of laser light on the formation region of the Schottky electrode, and irradiating the entire surface of the wafer with the laser light. A laser activation annealing step of activating the ion-implanted p-type impurity. The SiC Schottky barrier diode having a small excellent device characteristics leakage current from can be easily manufactured.
[Brief description of the drawings]
FIG. 1 is a diagram showing a step of performing laser activation annealing on a p-type termination structure during a manufacturing process of a SiC Schottky barrier diode according to a first embodiment.
FIG. 2 is a diagram showing a SiC Schottky barrier diode after a Schottky electrode and a back ohmic electrode are formed.
FIG. 3 is a diagram illustrating a part of a manufacturing process of the SiC Schottky barrier diode according to the second embodiment.
FIG. 4 is a diagram showing a part of the manufacturing process of the SiC Schottky barrier diode of the third embodiment.
[Explanation of symbols]
1 n-type SiC substrate, 2 n-type SiC epitaxial growth layer, 3 p-type termination structure, 4, 4a protective film (first protective film), 5 Schottky electrode, 6 n-type back ohmic electrode, 7 second protective film.

Claims (4)

an n-type silicon carbide substrate, an n-type silicon carbide epitaxial growth layer formed on the n-type silicon carbide substrate, a Schottky electrode provided on the n-type silicon carbide epitaxial growth layer, and a peripheral portion of the Schottky electrode A p-type termination structure provided in the n-type silicon carbide epitaxial growth layer of the above, comprising:
An ion implantation step of implanting p-type impurities into the formation region of the termination structure;
A laser activation annealing step of providing a protective film on the formation region of the Schottky electrode for preventing transmission of laser light, and irradiating the entire surface of the wafer with laser light to activate the ion-implanted p-type impurities;
A method for manufacturing a silicon carbide Schottky barrier diode comprising: 2. The method for manufacturing a silicon carbide Schottky barrier diode according to claim 1, wherein said protective film is also used as an ion implantation mask at the time of ion implantation. An ion implantation mask is composed of a first protective film, a second protective film is formed on a region where the Schottky electrode is formed, and the laser activation annealing is performed, and the first protective film and the second protective film are 2. The method for manufacturing a silicon carbide Schottky barrier diode according to claim 1, wherein the silicon carbide Schottky barrier diode has different reflectance, transmittance, or absorptance with respect to laser light. 3. The method of manufacturing a silicon carbide Schottky barrier diode according to claim 1, wherein said protective film is made of a silicon nitride film.

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