RU2385218C1 - Method to separate solid-state plates with two-sided thin-film coat into crystals - Google Patents

Abstract

FIELD: process engineering.

SUBSTANCE: invention relates to electronics engineering and can be used to produce crystals of thermal transducers and thermometers. Proposed method comprises forming marks by diamond cutter on plate surface and separation by bending the plate. Note here that marks are formed on both sides of the plate. Marks arranged on plate side extended in separation, are formed to depth of 1.1 to 1.3 of coat thickness, while those on contracted side are formed to depth of 2.5 to 3.0 of coat thickness.

EFFECT: higher reliability and yield of ready crystals.

3 dwg

Description

The invention relates to the field of manufacture of electronic products, in particular, is intended for the separation of semiconductor wafers with a double-sided thin-film optical coating into crystals, which are used for the manufacture of temperature sensors and thermometers.

Known and widely used is the method of separating semiconductor wafers with a diamond disk with an external cutting edge (see V.P. Zaporizhsky, B.A. Lapshinov. Processing of semiconductor materials. M: Higher school, 1988, P.184, see p. 106 -111). For plates with a double-sided thin-film coating, through cutting is used in circles with a thickness of up to 100 μm, which provides almost 100% crystal yield.

But this method with high reliability of the separation of the plates into crystals has the disadvantages:

- crystals have chips up to 15-18 microns and a defective zone up to 0.1 mm along the sides (see V.P. Zaporizhsky. P.110), which is unacceptable for crystals with an optical coating;

- when cutting a plate into crystals, for example, 2 × 2 mm in size, the mechanical waste of the plate material by the cut value (~ 100 μm) is ~ 20%.

For the prototype, a method was selected for separating semiconductor wafers into crystals, in which the technological waste of the wafer material during separation is close to zero percent. The method consists in applying marks to the surface of the plate with a diamond blade tool with a depth of 10-20 μm, according to which thereafter, the crystals are divided into crystals by bending the plate with zero material consumption into the separation zone (see V.P. Zaporizhsky. P.86-95). The crystals obtained in this way from uncoated semiconductor wafers in a streamlined process do not contain cracks and chips along the sides.

The most common implementation of this method is the edge of a diamond tool (see V.P. Zaporizhsky. P.88), which is a tetrahedral or trihedral pyramid. This option involves the formation of risks on the surface of the plate in one pass of the tool (see V.P. Zaporizhsky. S.93) and with a large angle (up to 140 °) of triangular cross section risks, which reduces the optical coating area of the crystal. A dull tool allows you to get risks that do not contain chips and cracks.

There is a second variant of the method of forming shapes with faces of a four- or three-sided pyramid, when qualitative risks are formed by at least two tool passes (forward and backward strokes of the tool), since the first pass of the tool cannot produce high-quality, chip-free risks (see AS No. 1271301. A method of scribing semiconductor wafers and a cutter for its implementation. 1986). This option allows you to get a narrower risk, with a triangular angle of 90 °.

Both the first and second embodiments of the method of separation of crystals of semiconductor wafers with a double-sided thin-film coating provides a low yield of crystals, which does not exceed ~ 20% due to the difficulty of separating wafers with a double-sided thin-film coating by bending the plate.

Most thin-film optical coatings applied to silicon wafers by thermal methods have a coefficient of thermal linear expansion greater than that of silicon. Therefore, after coating and cooling, tensile stresses occur in the coating, and compression stresses occur in silicon (Fig. 1). If a plate with a coating and the applied risks with a depth greater than the thickness of the coating, try to divide into crystals by risk by bending, then for separation it will be necessary to apply loads on the plate several times larger than for a plate without coating, that is, when coating is applied, the plate is hardened and its strength increases dramatically. In fact, this is a low reliability of separation of a double-coated plate into crystals and a low percentage of suitable crystals due to separation not at risk.

The essence of the proposed method of separation into crystals of semiconductor wafers with a double-sided thin-film coating is that the new state of a semiconductor wafer with a double-sided thin-film coating is used for separation, namely, the presence of compression stresses in the wafer layer mating with the coating. An uncoated plate, when divided into crystals by bending, is stretched on the side with risks due to tensile stresses and is compressed on the opposite side due to compression stresses. The crack along which the crystal is separated propagates from the top of the risks to the opposite side of the plate under the action of tensile stresses due to the bending of the plate.

In a plate with a double-sided thin-film coating, in order to divide the plate at risk, it is necessary to create tensile stresses in the surface layer of the plate with risk greater than in the uncoated plate by the amount of compression stresses existing in it. The opposite side of the coated plate must be compressed during separation, and it is already in a compressed state from the coating. In order for the plate to bend for the compressed side, the stresses must exceed the required value.

The objective of the proposed method of separation into crystals of semiconductor wafers with a double-sided thin-film coating, including forming a pattern with a diamond blade tool and separation by bending the plate, is to ensure reliable separation of the plate with an increase in the number of suitable crystals.

The depth ranges of the notches are prescribed by the conditions for the subsequent separation of the plate.

The risk on the side of the plate stretched during bending is formed with a depth of 1.1 ÷ 1.3 of the coating thickness with the edge of the pyramid of the diamond tool. The top of the risks should be located in the plate material, only in this case, when the plate bends, a crack will propagate from it along which separation will occur, which ensures a minimum risk depth of -1.1 of the coating thickness. The maximum risk depth of -1.3 of the coating thickness ensures that risks are obtained with a minimum number of defects along its sides when forming a diamond tool edge. In this range of depths of the grooves, at the apex, the risks of compression stress present under the coating in the plate (Fig. 1) will be removed (see M. Frocht. Photoelasticity. State Publishing House of Technical and Theoretical Literature. Moscow-Leningrad. 1950, P.60 , Fig. 2.18). Compression stresses are created by the coating, the risk is removed by the coating and in the part of the plate that is left uncoated adjacent to the risk with a depth of 1.1–1.3 of the coating thickness, tensile stresses will arise (see FIG. 2).

On the compressible side when bending the coated plate, a risk is formed with a depth of 2.5 ÷ 3.0 of the coating thickness by two passes of the diamond pyramid face. The minimum risk depth 2.5 of the coating thickness is determined by the fact that the peak of this risk is located below the compression zone in the plate from the coating, and the depth of risk 3.0 of the coating thickness is already in the undeformed plate area from the coating. The entire range of depths of the notches on the side of the plate that is compressible during separation allows one to increase its reliability due to the fact that the compression deformations of this side of the plate are performed by converging the sides of the notches at constant stresses in the crystals.

The method is illustrated by the following drawings:

figure 1 shows the stress distribution in the wafer and the coating deposited on both sides of the silicon wafer and consisting of ZnS.

figure 2 shows a plate with a double-sided thin-film coating and with risks with different depths. The stress distribution in the plate and coating has not changed. There are no stresses in the area of the peaks. At the points of intersection of the sides of the marks with an intermediate layer between the plate and the coating, tensile stresses arise in the plate with a depth of their propagation of not more than 1.3 from the depth of the risks.

figure 3. Separation of a double-coated semiconductor wafer into crystals. The zone free of compressive stresses before bending the plate is limited by points 1, 2, 3, 4 - this is the zone of propagation of a crack during its bending.

The implementation of the method consists in the formation of grooves with a depth of 1.1 ÷ 1.3 from the coating thickness on the side of the plate stretched during subsequent bending and with a depth of 2.5 ÷ 3.0 from the coating thickness on the compressible side.

The separation of the plate occurs by bending the plate as a whole, but between the neighboring crystals, the plate material undergoes the greatest deformation in the zone from risks with a depth of 1.1 ÷ 1.3 of the coating thickness, where it stretches and the cracking of the separation occurs to risks with a depth of 2, 5 ÷ 3.0 of the thickness of the coating, where compression occurs. The crack propagation zone between the crystals is limited to t. 1, 2, 3, 4 and the lines connecting these points (Fig. 3) during the bending of the plate is deformed to a greater extent and with lower loads than the crystals themselves, which are already in a deformed state. The load for bending the entire plate with a double-sided thin-film coating does not exceed the load for separating the plate without coating. Reliability of separation is high ~ 100% suitable crystals.

Claims (1)

A method of dividing into crystals of semiconductor wafers with a double-sided thin-film coating, comprising forming a pattern with a diamond blade tool on the wafer surface and separating by bending the wafer, characterized in that the risks are formed on both sides of the wafer, and the risks located on the stretched side of the wafer form to a depth of 1.1 ÷ 1.3 of the coating thickness, and on the compressible side to a depth of 2.5 ÷ 3.0 of the coating thickness.

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