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Patent Issued for Semiconductor Device and Production Method Therefor

February 19, 2014



By a News Reporter-Staff News Editor at Electronics Newsweekly -- From Alexandria, Virginia, VerticalNews journalists report that a patent by the inventors Kuramoto, Masafumi (Tokushima, JP); Ogawa, Satoru (Anan, JP); Niwa, Miki (Anan, JP), filed on January 22, 2010, was published online on February 4, 2014.

The patent's assignee for patent number 8642392 is Nichia Corporation (Anan-Shi, JP).

News editors obtained the following quote from the background information supplied by the inventors: "The present invention relates to a semiconductor device and a production method therefor, especially, a method for bonding a semiconductor element (hereinafter sometimes referred to as a 'die-attach method').

"Various bonding methods for mounting semiconductor elements such as transistors, ICs, and LSIs have been known. In addition, various bonding methods that are suitable with, among semiconductor elements, light emitting semiconductor elements such as light emitting diodes (hereinafter sometimes referred to as 'LEDs') and laser diodes (hereinafter sometimes referred to as 'LDs') have been know as well.

"Conventionally, die-attach methods for semiconductor elements are roughly classified into two categories, i.e., bonding methods that use epoxy resin adhesives (hereinafter referred to as 'resin bonding') and bonding methods that use eutectic metals having an eutectic point at a high temperature of 300.degree. C. or greater (hereinafter referred to as 'eutectic bonding') (see, for example, Patent Documents 1 and 2). Such die-attach methods are selected according to the similarity between the thermal expansion behaviors of a lead frame material and a substrate material on which a semiconductor element is to be mounted, as well as the reliability, cost, and like factors. For example, resin bonding is used for light emitting diodes for use in liquid-crystal back lights of small portable devices and like devices whose cost is given priority, and eutectic bonding is generally used for light emitting diodes for lighting purposes that are required to last a long time and for laser diodes that are required to be highly reliable.

"A resin for use in resin bonding is mostly a thermosetting resin such as an epoxy resin. A paste in which a powder of a conductive material such as silver is dispersed is also a type of resin for resin bonding. In resin bonding, a liquid epoxy resin is heated to 150 to 200.degree. C. for curing. Resin bonding is convenient in that curing can be readily accomplished at low temperatures of 150 to 200.degree. C. In particular, thermal degradation of the thermosetting resin and melting of the thermoplastic resin can be avoided in a general-purpose surface-mounted semiconductor device in which a lead frame is molded in advance.

"However, the heat generation due to the recent increase of light energy attained by light emitting diodes, laser diodes and like devices as well as the recent increase in input electricity, causes the resin itself that is used in resin bonding to deteriorate with time, resulting in problems such as discoloration and deterioration of the bonding strength. The glass transition temperature, which is an indicator in terms of temperature of the modulus of elasticity of a resin, is, because curing is performed at a low temperature, lower than the solder mounting temperature applied when a semiconductor device is mounted as an electronic component, and thus separation resulting from deterioration of the resin strength caused by thermal shock during solder mounting is likely to occur. Moreover, resin bonding that uses only an epoxy resin and resin bonding that uses a silver paste both have a problem in that, since they have poor thermal conductivity and insufficient heat releasability, light emitting diodes and the like become unilluminable.

"On the other hand, eutectic bonding that uses an alloy of gold and tin can solve the aforementioned problems of resin bonding.

"However, eutectic bonding requires heating to 300.degree. C. or greater when bonding, and is therefore not applicable to widely used resin packages of PPA (polyphthalamide) or the like since such packages cannot withstand high temperatures. In addition, even if silver plating, which has high reflectivity, is provided over the surface of a wiring board or a lead frame on which a light emitting diode is to be mounted, light extraction effect cannot be enhanced since eutectic metals have poor reflectivity.

"Patent Document 1: JP 2004-128330 A

"Patent Document 1: JP 2006-237141 A"

As a supplement to the background information on this patent, VerticalNews correspondents also obtained the inventors' summary information for this patent: "Therefore, with the foregoing in mind, it is an object of the present invention to provide a method for mounting a reliable semiconductor element and to provide a method for mounting a semiconductor element that has high heat releasability. Accordingly, a low-cost semiconductor device and a simple production method of a semiconductor device can be provided.

"The present invention relates to a method for producing a semiconductor device in which silver or silver oxide provided on a surface of a base and silver or silver oxide provided on a surface of a semiconductor element are bonded, and the method includes the steps of arranging the semiconductor element on the base such that silver or silver oxide provided on a surface of the semiconductor element is in contact with silver or silver oxide provided on a surface of the base, temporarily bonding the semiconductor element and the base by applying a pressure or an ultrasonic vibration to the semiconductor element or the base, and permanently bonding the semiconductor element and the base by applying heat having a temperature of 150 to 900.degree. C. to the semiconductor device and the base. It is thus possible to provide a method for producing a reliable semiconductor device since components that are likely to deteriorate are not used. Moreover, since the semiconductor element and the base are directly bonded, the thermal conductivity is high and the heat generated by the semiconductor element can be efficiently transferred to the base. Furthermore, the semiconductor element can be mounted without special equipment, so a simple production method for a semiconductor device can be provided.

"The temperature for the permanent bonding is preferably in a range of 150 to 400.degree. C., and more preferably in a range of 150 to 320.degree. C. This is because the bonding can be attained at relatively low temperatures. Moreover, this is because at those temperatures the semiconductor element is not destroyed, and the package in which the semiconductor element is mounted and the mounted base do not undergo thermal deformation.

"It is preferable to simultaneously perform the step of temporarily bonding and the step of permanently bonding. This is because the semiconductor element can be mounted in a simpler manner.

"The step of permanently bonding is performed preferably in air or in an oxygen atmosphere, thereby enabling the fusion reaction of silver to be further enhanced.

"The present invention relates to a semiconductor device having a die shear strength of 13 to 55 MPa in which silver or silver oxide provided on a surface of a base and silver or silver oxide provided on a surface of a semiconductor element are directly bonded. While a resin adhesive, a silver paste, a eutectic metal, or the like is present between the base and the semiconductor element in conventional bonding such as resin bonding and eutectic bonding, the base and the semiconductor element are directly bonded in the present invention. A eutectic component that uses an alloy of gold and tin or a component such as an epoxy resin or a silver paste is not present between the semiconductor element and the base, and it is thus possible to provide a reliable semiconductor device. In particular, a semiconductor device that has a high die shear strength and that is unlikely to undergo separation can be provided.

"A light emitting semiconductor element may be used for the semiconductor element. The light emitting semiconductor element and the base are directly bonded, and it is thus possible to provide a semiconductor device that does not undergo photodegradation. The present invention is applicable also to transistors, ICs, LSIs, capacitors, Zener diodes, and the like other than light emitting semiconductor elements such as light emitting diodes and laser diodes.

"The semiconductor element used may include a semiconductor layer disposed on a translucent inorganic substrate; the translucent inorganic substrate is provided with first silver on the side opposite the semiconductor layer and furnished with a buffering member bonded with the first silver; and the silver or silver oxide is provided on a surface of the buffering member. It is thus possible to enhance the efficiency of extracting light from the semiconductor device. Moreover, the separation at the interface of the translucent inorganic substrate and the first silver can be reduced, thereby enhancing the die shear strength.

"By adopting the above-described configuration, a low-cost reliable semiconductor device that does not include components that undergo deterioration and a production method therefor can be provided. Moreover, since the semiconductor element and the base can be directly bonded, a semiconductor device with high heat releasability can be provided. Furthermore, a simple production method for a semiconductor device can be provided."

For additional information on this patent, see: Kuramoto, Masafumi; Ogawa, Satoru; Niwa, Miki. Semiconductor Device and Production Method Therefor. U.S. Patent Number 8642392, filed January 22, 2010, and published online on February 4, 2014. Patent URL: http://patft.uspto.gov/netacgi/nph-Parser?Sect1=PTO2&Sect2=HITOFF&p=85&u=%2Fnetahtml%2FPTO%2Fsearch-bool.html&r=4214&f=G&l=50&co1=AND&d=PTXT&s1=20140204.PD.&OS=ISD/20140204&RS=ISD/20140204

Keywords for this news article include: Electronics, Laser Diodes, Semiconductor, Nichia Corporation, Light-emitting Diode.

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Source: Electronics Newsweekly


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