JPH03129823A - Lapping of semiconductor substrate - Google Patents

Abstract

PURPOSE:To enable a semiconductor substrate to be lapped in even thickness by a method wherein the first film comprising a surface protective organic matter is coated on one side main surface of the semiconductor substrate and after forming the second film of an inorganic matter on the first film, the semiconductor substrate is bonded onto a lapping jig. CONSTITUTION:A photoresist film 2 is coated on the element surface of a semiconductor substrate 1 and after baking and drying the photoresist film 2, a gold layer 3 is laminated and evaporated on the photoresist film 2. Next, the gold layer 3 is bonded onto the reference surface 4a of a heated lapping jig 4 through the intermediary of a wax layer 5. Successively, after cooling down the lapping jig 4 for setting the wax layer 5, the rear surface of the semiconductor substrate 1 is spin-ground to manufacture another semiconductor 1a in the thickness specified by the positions of stoppers 6. At this time, the semiconductor substrate 1 can be bonded onto the reference surface 4a of the lapping jig 4 in parallel with each other with high precision since the photoresist film 2 and the wax layer 5 are mutually isolated not to be mixed with each other as they are indirectly in contact with each other through the intermediary of the gold layer 3.

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial Application Field) The present invention relates to a method for lapping a semiconductor substrate, and more particularly to a method for lapping a semiconductor substrate to a uniform thickness.

(Conventional technology) In order to improve the performance of microwave communication systems, GaA
Field effect transistor (hereinafter referred to as FET) made of materials such as s
) is becoming essential. For example, FETs for high output power amplification (hereinafter abbreviated as power FETs) have a longer lifespan than electron tubes.
Because they have the advantage of being small and lightweight, their production and development are being actively pursued.

The life of a power FET is closely related to the operating layer temperature.
In order to keep the operating layer temperature low and extend the lifetime, it is effective to reduce the thermal resistance between the back surface of the chip, which serves as a heat sink, and the surface where the operating layer is located. For this reason, the thickness of the FET chip is made as thin as about 30 μm, and the back surface of the chip is plated with a thick layer of gold.

In order to manufacture an FET with a thickness of 30 μm, a process of thinly lapping the semiconductor substrate is essential.

This is because semiconductor substrates usually have a thickness of approximately 300 μm to 500 μm in consideration of handling properties.

Lapping usually involves forming a surface protection film made of organic material such as photoresist on the element side of the semiconductor substrate, which can be easily removed later, and then applying wax or the like to the element side of the semiconductor substrate as a reference surface of the lapping jig. This is done by pasting and polishing the back side of the semiconductor substrate. In this lapping process, it is difficult to attach the semiconductor substrate parallel to the reference surface of the lapping jig. For example, when attaching a 3'φ semiconductor substrate to the lapping jig, there is a variation in parallelism of about ±10 μ-. was. Therefore, the semiconductor substrate is not formed with a uniform thickness within the same substrate surface, and the thickness is approximately ±10μ.
There were variations in thickness.

That is, in addition to a portion with a desired thickness of 30 .mu.I within the same substrate surface, there were also a thick portion with a maximum thickness of 40 .mu.m and a thin portion with a minimum thickness of 20 .mu.m. Chips cut from thicker parts have higher thermal resistance and shorter lifespans. Additionally, chips cut from thin sections have the problem of causing large warpage and being susceptible to cracking.

The reason why it is difficult to attach the semiconductor substrate parallel to the reference plane of the lapping jig is that the surface protective film formed on the semiconductor substrate and the adhesive such as wax used to attach it to the lapping jig are both composed of organic substances. This is because the two are easily mixed together, and this mixture and wax have relatively high viscosity.

(Problems to be Solved by the Invention) According to the above-mentioned conventional lapping method, when attaching a semiconductor substrate to a lapping jig, it is important to make the parallelism of both parts highly accurate; There is a serious problem in that the film and the adhesive to the wrapping jig mix and the parallelism deteriorates.

The present invention has been made in order to improve the problems in the prior art described above, and is a lapping method in which the semiconductor substrate is lapped to a uniform thickness by attaching the semiconductor substrate parallel to the reference plane of the lapping jig. The purpose is to provide a method.

[Structure of the invention]

(Means for Solving Problem 11) A semiconductor substrate lapping method according to the present invention includes depositing a first film made of an organic material on one main surface of a semiconductor substrate for surface protection, and then After a second coating made of an inorganic material is laminated and formed on the coating, the semiconductor substrate is adhered and held on a lapping jig, and the other main surface of the semiconductor substrate is subjected to lapping.

(Function) The present invention can prevent the organic surface protective film formed on the semiconductor substrate from mixing with the adhesive such as wax used for attaching the semiconductor substrate to the lapping jig. Pasting is achieved while maintaining parallelism with high accuracy to the reference plane of the tool. This makes it possible to wrap the semiconductor substrate to a uniform thickness.

(Example) Hereinafter, one embodiment of the present invention will be described with reference to the drawings.

First, as shown in the cross-sectional view in FIG.
Apply photoresist wA2 such as
After baking and drying for 0 minutes, a gold layer 3 is deposited on the photoresist film 2 to a thickness of about 1,000 layers. Next, the gold layer 3 deposited on the upper surface of the semiconductor substrate 1 is pasted onto the reference surface 4a of the lapping jig 4 heated to 150° C. using the wax layer 5.

Next, as shown in FIG. 2, the lapping jig 4 is cooled to solidify the wax layer 5, and then the back surface of the semiconductor substrate 1 is rotary polished to form a semiconductor of a desired thickness at the position of the stopper 6. A substrate 1a is obtained.

In the above, the photoresist film 2 and the wax layer 5 are in contact with each other through the gold layer 3 and are separated from each other, and the two are not mixed. Therefore, the semiconductor substrate 1 is parallel to the reference surface 4a of the lapping jig with high precision. It can be pasted on. This variation in parallelism was kept within ±5μ in the case of a 3' diameter semiconductor substrate.

【Effect of the invention〕

As described above, according to the present invention, it is possible to prevent the surface protective film formed on the semiconductor substrate from mixing with the adhesive such as wax used for attaching it to the lapping jig. It can be attached parallel to the reference plane of the tool, and the semiconductor substrate can be wrapped to a uniform thickness.

In this example, photoresist A21350 (trade name, manufactured by Hoechst Co., Ltd.) was used as the surface protective film, but a photoresist having a similar effect, such as 1350J (
(trade name, manufactured by Hoechst), or other organic materials such as polyimide may be used.

In addition, after forming the surface protective film, gold is vapor-deposited in this example, but as long as the surface-protective film and wax or other adhesive do not mix, any material may be used.For example, a metal film such as aluminum may be vapor-deposited. Alternatively, an insulating film such as an oxide film may be formed by sputtering.

Furthermore, organic substances other than wax such as photoresist A can be used as an adhesive for attaching the semiconductor substrate to the lapping jig.
Z 1350 (trade name, manufactured by Hoechst) or the like may be used.

[Brief explanation of the drawing]

The drawings are for explaining a semiconductor substrate lapping method according to an embodiment of the present invention. Fig. 1 is a cross-sectional view of the semiconductor substrate attached to a lapping jig, and Fig. 2 is a cross-sectional view of the semiconductor substrate after lapping. FIG. 1, la... Semiconductor substrate 2... Photoresist film 3... Gold layer 4... Lapping jig 4a... Reference surface of lapping jig 5... Wax layer

Claims (1)

[Claims] A first film made of an organic material is applied to one main surface of the semiconductor substrate for surface protection, and then a second film made of an inorganic material is laminated and formed on the first film, and then the semiconductor substrate is wrapped. 1. A method for lapping a semiconductor substrate, which comprises lapping the other main surface of the semiconductor substrate by attaching and holding the semiconductor substrate to a jig.