By a News Reporter-Staff News Editor at Electronics Newsweekly -- A patent by the inventors Yabuki, Norihito (Kanonji, JP); Torimi, Satoshi (Kanonji, JP); Nogami, Satoru (Kanonji, JP), filed on November 17, 2015, was published online on July 3, 2018, according to news reporting originating from Alexandria, Virginia, by VerticalNews correspondents.
Patent number 10014176 is assigned to Toyo Tanso Co. Ltd. (Osaka-shi, JP).
The following quote was obtained by the news editors from the background information supplied by the inventors: "SiC, which is superior to Si or the like in, for example, heat resistance and electrical characteristics, has attracted attention as a new semiconductor material.
"A semiconductor device made of SiC is manufactured by using a SiC substrate with a diameter of 4-inch or 6-inch, for example. A method for isolating the semiconductor element by using grooves preformed on the SiC substrate in which ion implantation, ion activation and electrode formation, and the like are performed thereon has been conventionally known as a method for manufacturing the plurality of semiconductor elements from one SiC substrate.
"The SiC substrate may have grooves for the purpose of embedding of a MOSFET gate, in addition to the purpose of isolation of the semiconductor element (see a trench gate MOSFET, NON-Patent Document 1).
"Here, the SiC substrate needs to be heat-treated for activating ions after implanting ions such as Al, or the like. The heat treatment (ion activation treatment) needs to be performed at a high temperature of 1500.degree. C. or more. However, when ion implantation treatment and ion activation treatment are performed on the SiC substrate, the surface of the SiC substrate is roughened.
"Therefore, a carbon cap method in which a surface roughness of the SiC substrate is prevented by forming a carbon cap on the SiC substrate is used. In the carbon cap method, a resist is applied on the surface of the SiC substrate and then the SiC substrate is rotated around a perpendicular line of the surface as a rotation shaft, which can make the resist uniform (spin coating process). Then, the carbon cap is formed by carbonizing the resist. Formation of the carbon cap can suppress the surface roughening of the SiC substrate which is occurred during ion activation treatment. After ion activation treatment, the treatment for removing the carbon cap is needed.
"NON-PATENT DOCUMENT 1: '1700V/3.5 m.OMEGA.cm.sup.2 V-groove trench MOSFETs with high threshold voltage', SiC and relevant semiconductor study group 22th conference proceedings, The Japan Society of Applied Physics, Dec. 9, 2013, p. 21-22"
In addition to the background information obtained for this patent, VerticalNews journalists also obtained the inventors' summary information for this patent: "Problems to be Solved by the Invention
"However, in a SiC substrate having grooves, a resist is not uniformly applied even in using a spin coating process because of the grooves as an obstacle. Therefore, in the substrate having the grooves, the surface of the SiC substrate is roughened by ion implantation and ion activation treatment even in using the carbon cap method. This may lead to a case that an appropriate semiconductor element cannot be manufactured. In the carbon cap method, since processes for forming and removing the carbon cap are needed, a step of manufacturing the semiconductor element is complicated.
"The present invention has been made in view of the circumstances described above, and a primary object of this invention is to provide a SiC substrate treatment method for, with respect to a SiC substrate having grooves formed thereon, activating ions while preventing occurrence of a surface roughness.
"Means for Solving the Problems and Effects Thereof
"Problems to be solved by the present invention are as described above, and next, means for solving the problems and effects thereof will be described.
"In an aspect of the present invention, provided is a SiC substrate treatment method for, with respect to a SiC substrate that has, on its surface, an ion implantation region in which ions are implanted and has grooves provided in a region including at least the ion implantation region, performing an ion activation treatment in which the SiC substrate is heated under Si vapor pressure thereby activating ions that are implanted in the SiC substrate while etching the surface of the SiC substrate.
"Accordingly, when the SiC substrate is heated under Si vapor pressure, unlike when using the spin coating process, the grooves are less likely to obstruct (since there is gas, such heat treatment acts uniformly even if the grooves are existing). Therefore, the ions can be activated while preventing a surface roughening (rather while planarizing) even in the SiC substrate having the grooves. Thus, a high-quality semiconductor element can be manufactured with the SiC substrate having the grooves. In the ion activation treatment of the present invention, unlike the spin coating process, a manufacturing step can be simplified since a step of forming and removing a carbon cap is unnecessary. Furthermore, the surface of the SiC substrate can be etched by performing the ion activation treatment of the present invention, which can also remove a region where implanted ions are insufficient, with the same treatment.
"In the SiC substrate treatment method, it is preferable that the grooves formed on the SiC substrate are grooves for isolating the SiC substrate.
"Accordingly, the plurality of high-quality semiconductor elements can be manufactured with the SiC substrate having the grooves.
"In the SiC substrate treatment method, an ion implantation treatment for implanting ions in a SiC substrate that has, on its surface, an epitaxial layer of a single crystal SiC and has the grooves provided at least on the epitaxial layer, is preferably performed prior to the ion activation treatment.
"Accordingly, since an ion distribution can be assumed depending on conditions of ion implantation, the surface of the SiC substrate can be removed only for necessary and sufficient amount.
"In the SiC substrate treatment method, it is preferable that the ion activation treatment is performed under Si and inert gas atmosphere at the pressure of 10 Pa or more and 100 kPa or less.
"Accordingly, since the rate of etching can be suppressed by increasing the pressure with inert gas, the amount of etching on the surface of the SiC substrate can be accurately controlled.
"In the SiC substrate treatment method, it is preferable that the ion activation treatment is performed at 10.sup.-7 Pa or more and 10.sup.-2 Pa or less.
"Accordingly, since the rate of etching can be increased by performing the ion activation treatment under high-vacuum, a treatment time can be reduced when the implanted ions are located at a deep position of the SiC substrate, for example.
"It is preferable that the ion activation treatment is performed under Si and inert gas atmosphere, at the pressure of 10.sup.-2 Pa or more and 10 Pa or less.
"Accordingly, since the rate of etching can be adjusted by adjusting an inert gas pressure, the amount of etching on the surface of the SiC substrate can be controlled to an appropriate amount.
"The SiC substrate treatment method is preferably configured as follows. That is, the ion activation treatment is performed in a state where the SiC substrate is positioned at an internal space of a heat treatment container. The heat treatment container includes a tantalum metal, and has a tantalum carbide layer provided on the internal space side of the tantalum metal, and a tantalum silicide layer provided on the side further toward the internal space than the tantalum carbide layer.
"Accordingly, since the pressure of Si within a storing container can be uniform, the etching on the surface of the SiC substrate can be uniformly performed."
URL and more information on this patent, see: Yabuki, Norihito; Torimi, Satoshi; Nogami, Satoru. SiC Substrate Treatment Method. U.S. Patent Number 10014176, filed November 17, 2015, and published online on July 3, 2018. Patent URL: http://patft.uspto.gov/netacgi/nph-Parser?Sect1=PTO1&Sect2=HITOFF&d=PALL&p=1&u=%2Fnetahtml%2FPTO%2Fsrchnum.htm&r=1&f=G&l=50&s1=10014176.PN.&OS=PN/10014176RS=PN/10014176
Keywords for this news article include: Asia, Japan, Business, Tantalum, Electronics, Heavy Metals, Semiconductor, Toyo Tanso Co. Ltd., Transition Elements.
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