JPS61141780A - Modified adhesive - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention is directed to the preparation of improved thermosetting adhesives. This adhesive has many uses and can replace many existing thermosets with improved application and product properties. Thermosetting adhesives are useful in manufacturing silicon wafers used in semiconductor manufacturing. In particular, the present invention relates to improvements in adhesives utilized to secure silicon ingots to graphite cutting beams prior to slicing the silicon ingots into wafers for final manufacturing.

The manufacture of semiconductor substrates, usually silicon, for manufacturing semiconductor devices requires many tightly controlled chemical and mechanical steps. Whatever manufacturing and purification methods are required, the substrate material must first be produced in a very pure state; this material is then crystallized to give very large single crystals in the form of ingots. These ingots are then sawed or sliced into wafers which are lapped and polished on a lapping plate to provide a flat surface for the manufacture of polished electronic components.

[Prior Art] Slicing an ingot into wafers is a difficult process because the wafers must have a uniform thickness, must have a flat profile, and must be free of stress caused by slicing. This is a very important step. One factor necessary to accomplishing these requirements is that the ingot must be kept very stationary during the slicing operation. The method currently used is to bond and glue the ingot to a cutting beam, which is usually graphite with epoxy resin. Coat the graphite cutting beam with epoxy and place the silicon ingot on the beam. The epoxy is allowed to cure for 12-14 hours before slicing the ingot into wafers using a diamond saw. The wafer is removed from the cutting beam by breaking the epoxy adhesive bond.

[Problems to be Solved by the Invention] There are many problems associated with this step. Long curing times are required to minimize stress on the ingot due to exothermic curing of the resin. During cutting, the diamond saw becomes clogged with epoxy adhesive and must be cleaned periodically. These problems increase the overall time required for the process. Furthermore, the strong epoxy bond makes removal of the wafer from the cutting beam difficult. Small errors in resin formulation and/or application can result in many rejects.

It is an object of the present invention to provide an improved epoxy adhesive. It is further an object of the present invention that the improved epoxy system contains hollow microspheres, provides faster curing times without stress, provides cleaner slices, and supports a support beam when used to join semiconductor ingots to a cutting beam. Provides improved separation by separating joined parts from each other.

SUMMARY OF THE INVENTION It has been discovered in the present invention that a number of significant advantages are realized when hollow microspheres are incorporated into an epoxy resin adhesive. That is, the curing time was reduced, the cured adhesive was relatively stress free, and the cutting time of the final product was reduced and more easily achieved. Silicon ingots could be bonded to graphite silicon beams by epoxy resin containing up to 50% by volume of hollow microspheres. The bond strength required to provide an even and defect-free cut was retained, yet other properties were greatly improved. The resin cutting time could be reduced without inducing stress in the ingot. Bonding to the saw due to resin residue has been reduced. These advantages have provided substantial time and cost savings. The rejection rate of broken wafers was also reduced because the sliced wafers could be easily removed from the slicing beam. The ease of releasing the epoxy bond between the wafer and the beam is surprising since the bond between the ingot and the beam is very strong. Additionally, the lifespan of the diamond saw blade has been increased.

The adhesive consists of resin and hollow microspheres. The resin can be any curable organic polymeric system that is compatible with the hollow microspheres, and the hollow microspheres that are added to the resin system to form an improved adhesive can be of almost any composition as long as they do not degrade the resin. It can be of. A two-component epoxy resin is preferred; the ingot can be any required semiconductor material, but is usually silicon or doped silicon. The slicing beam can be any relatively inert material that provides solid support to the ingot, and graphite is commonly used.

The hollow microspheres are fused glass microspheres, such as those described in U.S. Pat. No. 3,365,315.3,838,998 or U.S. Pat.
340.3,030,215.3.699,050.4
, 059, 423.4, 063.916. Organic polymeric hollow microspheres are also useful; such materials are described, for example, in US Pat. No. 2,978,340 and 3,615,972. Hollow microspheres of various materials including glass and metals are disclosed in U.S. Pat.
344.787, and these materials are also useful. These eleven patents are referenced herein as describing materials useful in the present invention.

Hollow microspheres of particular interest are those with shells composed of alkali metal silicates and polysalts. These materials are described in US Pat. No. 3,795,777, incorporated herein by reference. The microspheres are prepared by spray drying a homogeneous solution of silicate and polysalt selected from the group of ammonia pentaborate, sodium pentaborate, and sodium hexametaphosphate, and then further drying to reduce the moisture content from about 10% to less than about 7%. is created by reducing it to The dimensions of the hollow microspheres can vary widely, but the diameter should be such that no substantial weakening of the epoxy bond appears. In general, hollow microspheres having an average diameter of 1 to 500 microns appear to be useful. The amount of microspheres to be used with the epoxy system also varies widely, with the upper limit being the amount that significantly reduces the epoxy bond strength.

Useful amounts of microspheres range from about 2% to about 35% of the amount of resin composition.
change until. The microspheres should not exceed substantially 50x the capacity of the adhesive system.

The product of the invention is initiated by mixing hollow microspheres with the resinous portion of the adhesive. This step can be performed at the time of filling the resin or immediately before using the adhesive. In a two-component system, the resin component is mixed with an appropriate amount of curing agent, approximately 4 to 6
Allow curing time between closing and closing.

EXAMPLES The following examples illustrate certain embodiments of the invention and the prior art. These examples are not given to establish the scope of the invention, but rather that scope is disclosed in the specification and claimed. Ratios are parts by weight (pbν) or weight % (χwt/1w) unless otherwise specified.
).

Example 1 This example illustrates bonding a silicon ingot to a graphite cutting beam by prior art methods. A commercially available epoxy resin containing resin, calcium carbonate, and silica thickener was prepared. Sufficient curing agent was added to give a curing time of 12-24 hours. The resin system was then spread onto the graphite beam and the ingot was placed on top. After 12-24 hours the ingot was cut with a diamond saw to give wafers. When the wafer was removed from the graphite beam, the epoxy bond exerted so much force that several wafer losses were experienced.

Example 2 This example illustrates bonding a silicon ingot to a graphite cutting beam by the improved method of the present invention. 30.9 parts of commercially available epoxy resin (56.9 parts by weight)
It was mixed with parts by weight of calcium carbonate and 1.9 parts by weight of fumed silica. This mixture was prepared using high shear. heating the homogeneous mixture to reduce clay; 10.
Three parts by weight of hollow silicate microspheres were blended into the resin mixture at low shear.

This resin mixture was then mixed with 11.3 parts by weight of amine curing agent to effect curing of the epoxy. This system was spread on a graphite cutting beam and a silicon ingot was placed on top. After 5 hours, the epoxy had cured, but no apparent distortion occurred in the silicon ingot. Cutting the ingot was easier as the epoxy scum did not get caught in the saw as frequently occurred when compared to the method of Example 1. Removal of the resulting silicon wafer was also easy and there was less waste as the epoxy bond appeared to come off more easily than observed in the method of Example 1.

Claims (1)

[Scope of Claims] 1. 65% to 98% (w/w) adhesive resin; and 2.
% to 35% (w/w) hollow microspheres. 2. The adhesive according to claim 1, wherein the hollow microspheres have an average diameter of 1 to 500 micrometers. 3. An adhesive according to claim 1, wherein the hollow microspheres are formed from a silicate glass melt or a synthetic organic polymer. 4. The adhesive of claim 1, wherein the hollow microspheres are formed from a homogeneous solution of an alkali metal silicate and a polysalt selected from the group consisting of ammonium pentaborate, sodium pentaborate, and sodium hexametaphosphate. 5. An adhesive according to claim 2, wherein the hollow microspheres are formed from a silicate glass melt or a synthetic organic polymer. 6. The adhesive of claim 2, wherein the hollow microspheres are formed from a homogeneous solution of an alkali metal silicate and a polysalt selected from the group consisting of ammonium pentaborate, sodium pentaborate, and sodium hexametaphosphate. 7. 65% to 98% (w/w) epoxy resin and 2
An adhesive according to claim 1 for use in bonding a silicon ingot containing % to 35% (w/w) hollow microspheres to a slicing beam. 8. The adhesive according to claim 7, wherein the hollow microspheres have an average diameter of 1 to 500 micrometers. 9. An adhesive according to claim 7, wherein the hollow microspheres are formed from a silicate glass melt or a synthetic organic polymer. 10. The adhesive of claim 7, wherein the hollow microspheres are formed from a homogeneous solution of an alkali metal silicate and a polysalt selected from the group consisting of ammonium pentaborate, sodium pentaborate, and sodium hexametaphosphate. 11. An adhesive according to claim 8, wherein the hollow microspheres are formed from a silicate glass melt or a synthetic organic polymer. 12. The adhesive of claim 8, wherein the hollow microspheres are formed from a homogeneous solution of an alkali metal silicate and a polysalt selected from the group consisting of ammonium pentaborate, sodium pentaborate, and sodium hexametaphosphate. 13. (a) mixing hollow microspheres with an average diameter of 1 to 500 micrometers with the resin portion of the epoxy adhesive; (b) mixing a sufficient amount of the hardener of the epoxy adhesive with the mixture of step (a); (c) spreading the mixed adhesive system over the graphite beam and/or silicon ingot; (d) bringing the graphite beam and silicon ingot into contact with each other; e) A method of bonding silicon ingots to graphite cutting beams consisting of curing the adhesive for 4-6 hours. 14. The method of claim 13, wherein the hollow microspheres are formed from silicate glass melts or synthetic organic polymers. 15. The method of claim 13, wherein the hollow microspheres are formed from a homogeneous solution of an alkali metal silicate and a polysalt selected from the group consisting of ammonium pentaborate, sodium pentaborate, and sodium hexametaphosphate.