JP4506100B2 - Method for manufacturing silicon carbide Schottky barrier diode - Google Patents

Description

[0001]
BACKGROUND 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 higher by about one digit than silicon (Si), which is a general constituent material of SiC, and about 2 Since it has an excellent physical property of double electron saturation drift velocity, it is promising as an element capable of controlling high frequency and high power.
[0003]
However, in high-frequency operation with high power, electric field concentration occurs at the peripheral portion of the Schottky electrode when a reverse voltage is applied, and the element may be destroyed at a voltage lower than the originally expected breakdown voltage by using SiC as a constituent material. In order to alleviate such electric field concentration on the peripheral portion and ensure a breakdown voltage, a termination structure called a so-called guard ring is formed on the peripheral portion of the Schottky electrode to improve the breakdown voltage of the element.
[0004]
In such a termination structure, p-type impurities are ion-implanted into the n-type SiC epitaxial growth layer at the periphery of the Schottky electrode, and then heat-treated at a high temperature of 1500 ° C. or more to electrically activate the ion-implanted p-type impurities. The n-type SiC epitaxial growth layer is formed by forming a p-type region having a reverse conductivity type. However, the SiC crystal surface is damaged by the process performed at an extremely high temperature of 1500 ° C. or higher during the impurity activation annealing, and when reverse breakdown voltage is applied to the SiC Schottky barrier diode, the damage is caused from the Schottky electrode through the damage. There was a problem in device characteristics that the leakage current of the device increased.
[0005]
In the conventional method for manufacturing a SiC Schottky barrier diode disclosed in Patent Document 1, laser activation annealing is performed instead of high-temperature heat treatment that causes the above-described problems. This is because laser activation annealing provides the same level of electrical activation effect of impurities at a lower temperature than conventional heat treatment.
[0006]
[Patent Document 1]
JP 2002-289550 A [0007]
[Problems to be solved by the invention]
In the case of a SiC Schottky barrier diode, laser activation annealing for the purpose of electrical activation of ion-implanted impurities may be performed only in the region where the termination structure is formed, and the SiC surface in the region where the Schottky electrode is formed is irradiated with laser. The activation annealing by is not necessary at all, but on the contrary, it causes crystal surface roughness. However, if laser activation annealing is performed locally only in the region where the termination structure is formed, the throughput is drastically reduced and a new problem arises that the device cannot be easily manufactured. On the other hand, when the laser activation annealing is uniformly performed on the entire surface of the wafer, the SiC surface of the Schottky electrode formation region that originally does not need to be annealed is also irradiated with the laser, causing the above-described crystal surface roughness.
[0008]
The present invention has been made to solve the above-described problems, and an object of the present invention is to easily manufacture a SiC Schottky barrier diode having good device characteristics with a small leakage current from a Schottky electrode. And
[0009]
[Means for Solving the Problems]
A 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 of manufacturing a silicon carbide Schottky barrier diode comprising: a Schottky electrode provided; and a p-type termination structure provided in the n-type silicon carbide epitaxial growth layer at a peripheral portion of the Schottky electrode, an ion implantation step of implanting p-type impurity region for forming the above termination structure, after the ion implantation step, a protective film for preventing transmission of the laser beam on the formation region of the Schottky electrode, the p-type laser activation Annie to activate the p-type impurity implanted the ions by applying a laser beam to form a region of the termination structure And step comprises removing the protective film after the laser activation annealing step, a step of forming the Schottky electrode after the step of removing the protective film.
[0010]
DETAILED DESCRIPTION OF THE INVENTION
Embodiment 1 FIG.
A method for manufacturing the SiC Schottky barrier diode of the first embodiment will be described with reference to FIGS. Here, FIG. 1 is a diagram 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 diagram showing the SiC Schottky after forming the Schottky electrode and the back ohmic electrode. It is a figure which shows a barrier diode. In the figure, 1 is an n-type SiC substrate, 2 is an n-type SiC epitaxial growth layer, 3 is a p-type termination structure, 4 is a protective film, 5 is a Schottky electrode, and 6 is 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, the n-type SiC epitaxial growth layer 2 is crystal-grown on the n-type SiC substrate 1. Subsequently, in order to form the p-type termination structure 3, p-type impurities are ion-implanted into the n-type SiC epitaxial growth layer 2 in the peripheral portion of the region where the Schottky electrode 5 is formed in a later step. As an ion species in the ion implantation, a p-type impurity having a reverse conductivity type with respect to the n-type SiC substrate 1, for example, aluminum ions is preferable. If SiC substrate 1 is p-type, reverse conductivity type n-type impurities may be ion-implanted into SiC substrate 1.
[0012]
In the above-described ion implantation, an ion implantation mask is provided by covering regions other than the formation region of the p-type termination structure 3 with a resist or the like so that only the formation region of the p-type termination structure 3 can be selectively implanted.
[0013]
After removing the ion implantation mask, a protective film 4 is formed in a region where the Schottky electrode 5 is to be formed in a later step. The material and film thickness of the protective film 4 are selected so that the reflectance, absorption rate, or transmittance becomes 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 suitable. Further, a resist film made of a material and a film thickness that can realize each of the above set values may be used.
[0014]
As a laser light source at the time of laser activation annealing, for example, a XeCl excimer laser with a wavelength of 308 nm, a KrF laser with a wavelength of 248 nm, or an Ar ion laser with 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 with 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 into 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 relaxed by the p-type termination structure 3 into which impurities are ion-implanted. 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, the surface of the n-type SiC epitaxial growth layer 2 located on the lower surface of the Schottky electrode 5 is a protection that effectively prevents laser light even during laser activation annealing in which laser irradiation is performed on the entire surface of the wafer. Due to the presence of the film 4, the degree of temperature increase in such a region is significantly lower than that in the region of the p-type termination structure 3, so that the damage on the SiC crystal surface due to the temperature increase is significantly reduced compared to the case without the protective film 4. it can. Therefore, the leakage current from the Schottky electrode 5 generated through crystal surface damage during the SiC Schottky barrier diode operation can be greatly reduced. Furthermore, contamination and damage of the crystal surface that may occur when the SiC crystal surface in the Schottky electrode 5 formation region is exposed can be prevented. That is, the laser irradiation scan can be performed on the entire surface of the wafer without inducing the SiC crystal surface roughness in the Schottky electrode 5 formation region, so that the workability and throughput of the laser irradiation can be improved while maintaining the element characteristics well. It can be improved.
[0019]
In the above-described ion implantation, the impurity to be implanted may be boron (B) ions. Further, when the ion implantation is performed by covering the entire surface of the SiC surface with an oxide film or the like, contamination and damage of the SiC surface during the ion implantation can be effectively prevented.
[0020]
As described above, according to the manufacturing method of the SiC Schottky barrier diode of the present embodiment, a protective film that does not transmit laser light is formed in a region corresponding to the Schottky electrode during laser activation annealing, and laser irradiation is performed on the entire wafer surface. As a result, a SiC Schottky barrier diode having good device characteristics with a small leakage current from the Schottky electrode can be easily manufactured.
[0021]
Embodiment 2. FIG.
A method for manufacturing the SiC Schottky barrier diode of the second embodiment is shown in FIG. In the manufacturing method of the SiC Schottky barrier diode of the present embodiment, the protective film 4a provided in the formation region of the Schottky electrode 5 functions as both a protective mask at the time of laser irradiation and an ion implantation mask at the time of ion implantation. Thus, 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 process and the laser activation annealing process. Thus, for example, when performing impurity ion implantation a plurality of times with different acceleration energies to obtain an impurity concentration up to a desired depth, a single process is performed in which ion implantation and laser activation annealing are performed simultaneously or alternately. Therefore, the entire process can be simplified.
[0023]
As described above, in the manufacturing method of the SiC Schottky barrier diode according to the second embodiment, the impurity ion implantation into the formation region of the p-type termination structure and the laser activation annealing can be continuously performed. In addition to the above effect, further simplification of the whole process and improvement of the activation rate of the ion implantation impurity can be achieved.
[0024]
Embodiment 3 FIG.
FIG. 4 shows a method for manufacturing the SiC Schottky barrier diode of the third embodiment. In the method for manufacturing the SiC Schottky barrier diode according to the present embodiment, the first protective film 4 is separately formed in the formation region of the Schottky electrode 5 and the second protective film 7 is separately formed in the formation region of the p-type termination structure 3. . Here, the first protective film 4 and the second protective film 7 are selected for the material, film thickness, and the like of each protective film so as to have different reflectance, transmittance, or absorption rate with respect to the irradiated laser. .
[0025]
When the protective film configuration as described above 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 is caused by the inherent properties of the protective films 4 and 7. It can be changed intentionally. Therefore, the formation region of the p-type termination structure 3 reaches an annealing temperature sufficient for the electrical activation of the ion-implanted impurities, while the temperature near the surface of the n-type SiC epitaxial growth layer 2 in the formation region of the Schottky electrode 5 is Since the temperature can be set to be lower than that of the impurity-implanted p-type termination structure 3, a good impurity activation rate in the formation region of the p-type termination structure 3 can be maintained, and at the same time, the formation region of the Schottky electrode 5 can be reduced. Roughening of the SiC crystal surface can be effectively prevented. Therefore, the leakage current from the Schottky electrode when the SiC Schottky barrier diode is operated can be greatly reduced.
[0026]
As described above, according to the manufacturing method of the SiC Schottky barrier diode of the third embodiment, it is possible to more easily manufacture the SiC Schottky barrier diode having good element characteristics as compared with the manufacturing method of the first or second embodiment. effective.
[0027]
【The invention's effect】
A 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 of manufacturing a silicon carbide Schottky barrier diode comprising: a Schottky electrode provided; and a p-type termination structure provided in the n-type silicon carbide epitaxial growth layer at a peripheral portion of the Schottky electrode, An ion implantation step of ion-implanting p-type impurities in the termination structure formation region, a protective film for preventing transmission of laser light on the Schottky electrode formation region, and irradiating the entire surface of the wafer with laser light; A laser activation annealing step for 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 the manufacturing process of the SiC Schottky barrier diode in the first embodiment.
FIG. 2 is a diagram showing a SiC Schottky barrier diode after formation of a Schottky electrode and a backside ohmic electrode.
3 is a diagram showing a part of the manufacturing process of the SiC Schottky barrier diode according to the second embodiment; FIG.
4 is a diagram showing a part of manufacturing process of the SiC Schottky barrier diode according to the third embodiment; FIG.
[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 (3)

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, and a method for manufacturing a silicon carbide Schottky barrier diode,
An ion implantation step of ion-implanting p-type impurities into the formation region of the p-type termination structure;
After the ion implantation step, a protective film for preventing transmission of laser light is provided on the formation region of the Schottky electrode, and the ion-implanted p-type impurity is activated by irradiating the entire surface of the wafer with the laser light. A laser activation annealing step,
Removing the protective film after the laser activation annealing step;
Forming the Schottky electrode after the step of removing the protective film;
A method for manufacturing a silicon carbide Schottky barrier diode comprising: In the laser activation annealing step, a second protective film having a reflectance, transmittance, or absorption rate different from that of the protective film is applied to the laser light before the laser light irradiation. The method for producing a silicon carbide Schottky barrier diode according to claim 1, further comprising a step of providing in the formation region. The process according to claim 1 Symbol placement of silicon carbide Schottky barrier diode, wherein the protective film is composed of silicon nitride film.

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