JPS6393562A - Wafer holding method - Google Patents

Abstract

PURPOSE:To obtain a waxless holing method for increasing accuracy for flatness, by bringing a back of a plate-shaped holder having a recessed portion on its front surface into close contact with a holding member having a number of holes defined except a potion corresponding to the recessed portion through the holes by absorption by means of pressure reduction, disposing a wafer in the recess and securing it by a holder. CONSTITUTION:A back of a plate-shaped holder having a recessed portion on its front surface is brought into close contact with a holding member of a grinding machine having a number of holes defined except a portion corresponding to the recessed portion through the holes by absorption by means of pressure reduction. A wafer is disposed in the recessed portion and secured by a holder 10. With the arrangement, since the holder is secured to a carrier plate without using wax or the like, no bubble or wrinkle is produced and no recess and projection caused by the application of the wax is produced. In addition, no hole for absorption is defined to a portion corresponding to the recessed portion so that no recess and projection are produced in the recessed portion. Therefore, the wafer can be held without recesses and projections, whereby grinding can be effected with very high accuracy for flatness.

Description

[Detailed description of the invention] (Industrial application field) The present invention relates to a method for holding a wafer in a polishing machine.

(Prior Art) Wafers, such as silicon wafers used as substrates for ICs, LSIs, etc., must have at least one surface mirror-polished with extremely high flatness accuracy. In this mirror polishing process, it is necessary to hold the wafer with high precision on a rotating jig of a polishing machine.

Conventionally, a wax method and a waxless method have been used as methods for holding a wafer in a polishing machine.

The wax method can polish the wafer surface with high flatness accuracy, but since wax is used to secure the wafer to the polisher, it takes time to attach and detach the wafer, and it requires a lot of effort to clean after polishing. However, there are many problems such as contamination of the wafer by residual wax and deterioration of the working environment by the special solvent used during cleaning.

On the other hand, the waxless method has the advantage of easy attachment and removal of the wafer and high production efficiency, but it has been pointed out that the flatness accuracy of the wafer surface after polishing is inferior to that of the wax method.

The conventional waxless method will be explained below.

In the conventional waxless system, a plate-shaped holder 110 is used as shown in FIG. They are laminated and bonded together.On the back side of the reinforcing layer 113, there is an adhesive layer 122 protected by a release paper 121.
is provided. As will be described later, when the holder is held on the carrier plate of the polishing machine, the template is located on the lower side, so the holder is illustrated in the drawings so that the template on the front side is on the lower side.

The template 111 of such a holder 110 includes
A required number of holes 114 are provided for accommodating the wafer 16 to be polished, and together with the backing material 112, a recess 115 for holding the wafer is formed. During polishing, the wafer 16 is placed in this recess 115 (see FIG. 7 (bl)), and the back surface (the surface that will not be polished) is attached to the banking material 112 using a liquid such as water, and the wafer 16 is It is fixed to the holder 110.

A typical polishing machine used for polishing wafers has two parts that can be moved up and down like the lid of a shell. It is equipped with a movable surface plate (Pl/-), not shown). The surfaces of the carrier play 1-120 and the plate are precisely finished. The carrier plate 120 is a member for holding a wafer. As shown in FIG. 8, the holder 110 from which the release paper 121 has been removed is fixed to the surface of the gear rear plate 1-120 with adhesive N122. A band, which is an abrasive cloth, is attached to the lower plate. The wafer 16 is polished by rotating the carrier plate 20 while supplying slurry between both plates.

Such a conventional boulder is fixed to the carrier plate 120 by using an adhesive layer provided in advance on the back surface of the holder, as shown in the example, or by applying an adhesive or an adhesive to the back surface of the holder. Ta.

(Problems to be solved by the invention) When fixing a conventional holder to a carrier plate,
Bubbles or wrinkles may occur between the carrier plate and the holder, and the thickness of the adhesive layer or the coating thickness of the adhesive or adhesive may be inconsistent, resulting in unevenness on the fixed surface. These influence the wafer 16 on the front side of the backing material 112 of the holder 110 from the back side. For this reason, in wafer polishing using the waxless method, the finished planar accuracy of the wafer surface cannot exceed a certain limit (approximately 5 μm). Furthermore, if a holder with an adhesive layer or release paper is used, the structure of the holder becomes complicated and the holder becomes expensive. When using a holder without an adhesive layer, a step of applying an adhesive or an adhesive is required before fixing.

There are various definitions of plane accuracy, but in this specification, TTV (Total Th1ckness Va)
riation), that is, the difference in μm between the highest and lowest points of the unevenness existing on the wafer surface when the wafer after polishing is held on a vacuum suction plate.

In order to avoid the above-mentioned problems, it is conceivable to form a large number of holes on the entire surface of the carrier plate, and to vacuum the holder through the holes to fix the holder to the carrier plate.

However, in this method, it is inevitable that the holes cause unevenness in the backing material, and it is not possible to improve the planar accuracy.

The present invention solves the problems of the prior art described above, and its purpose is to provide a waxless wafer holding method that allows the surface of a polished wafer to have extremely high flatness accuracy. It's about doing.

(Means for Solving the Problems) The wafer holding method of the present invention is a method for holding a wafer in a polishing machine, in which the back surface of a plate-like holder having a recess on the surface is placed in a position corresponding to the recess. The wafer is attached to the holding member of the polishing machine, which has a large number of holes formed in the polishing machine, through the wire holes by vacuum suction, and a J7 is placed in the recess to hold the wafer in the holder. It includes sticking and hanging,
Thereby, objective I is achieved.

In the present invention, the back side of the holder that holds the wafer is brought into close contact with the carrier plate of the polishing machine, and is fixed to the carrier plate by reduced pressure or vacuum.

An example of a holder used in the present invention is shown in FIG. This holder 10 is provided with four recesses 15,
It has a template 11 on the front surface and a backing agent 12 on the back surface which are integrally laminated and adhered (see FIG. 5(a)).

Further, an example of a carrier plate used as a holding member of a polishing machine is shown in FIGS. 2 and 3.

A large number of holes 41 for vacuum suction are bored on the surface of this carrier plate 40. However, when the holder 10 is fixed to the carrier plate (see FIG. 4), a wire hole 41 is not provided in a portion 42 (indicated by a broken line in FIG. 2) corresponding to the recess of the holder. First, the four corresponding portions 42 are flat portions. The sizes of these corresponding portions 42 are slightly larger than the ends of the corresponding recesses 15 of the holder 10, but are set to a size that does not impair the suction of the recesses 15. A wire hole 41 is formed over the entire surface of the carrier plate 40 other than the corresponding portion 42 . The diameter of these holes 41 is preferably about 0.3 to 5 mm, preferably 0.5 to 2.5 mm+. If the diameter of the wire hole 41 is too small, it will be difficult to process, and if it is too large, it will be difficult to suction the holder 30.

The distribution density of the wire holes 41 and the degree of pressure reduction are appropriately determined depending on the number of recesses 15, their sizes, etc. so that the holder 10 does not fall off and is reliably held during polishing. If the hole diameter is approximately 0.3 to 5 mm, the average hole pitch may be 1 to 5 mm, and either uniform distribution or random distribution may be used.

The carrier plate 40 is connected to a decompression or vacuum device (not shown) such as a vacuum pump, and has a structure that allows vacuum suction while attached to the polishing machine. carrier plate 40
is preferably removable from the polishing machine together with the carrier to which it is fixed. Also, Boulder-10
For convenience when fixing the holder 10 and the carrier plate, it is preferable to provide positioning marks 31 and 43 on the holder 10 and the carrier plate, respectively.

The holder used in the present invention includes at least one tenbrae.
- and the backing material are preferably laminated and bonded together.

Examples of the material of this template include glass fiber reinforced epoxy resin, Bakelite, thermoplastic plastics, polyester resin, polyimide resin, polysulfone resin, polyparaphenylene oxide resin, hard polyurethane resin, and phenol resin.

The backing material is a holding material for holding the wafer.
It is laminated and glued together with the template. wafer 16
is placed in the recess 15 of the holder 10, and is fixed to the holder 10 by the surface tension of liquid such as water and the action of microbubbles on the surface of the backing material 12 (see FIG. 5(b)).
. Further, when a backing material having self-adhesiveness is used, the wafer 16 is fixed to the boulder due to its self-adhesiveness.

As the backing material, a foamed film or sheet made of urethane polymer, thermoplastic elastomer, synthetic rubber, etc. that can adsorb and hold the wafer can be used. Particularly suitable is a foam made of urethane polymer, manufactured by a wet coagulation method, whose surface layer has a fine foam structure, and whose thickness is 5.
It is as thin as possible with a thickness of 00 μm or less. A urethane-based film-like polymer with adhesive properties and a thickness of 100 mm.
Thicknesses smaller than μm are also preferably used.

Further, as a holder, a holder 10a having a reinforcing layer 13 disposed on the back side as shown in FIG. 6 can be used as necessary to reinforce and support the backing material. Materials for the reinforcing layer 13 include thermoplastic resins (e.g., ethylene polymers, propylene polymers, polyamide resins, polyester resins, polycarbonate resins, polyethylene terephthalate resins, polysulfone resins, polyimide resins, etc.), films or sheets of celluloid, etc. They are selected from among these, taking into consideration strength, flatness, thickness accuracy, etc., depending on the purpose. The thickness of the reinforcing material is preferably thin in view of ease of handling during polishing, workability, and finish, and is preferably 300 μm or less. 100μm
It is preferred to use a biaxially oriented polyester film.

(Example) Examples of the present invention will be described below.

Using the holder shown in Table 1 below, wafers were polished under the conditions shown in the table (Examples 1 to 4). In addition, the wafer was polished in the same manner as in Example 1, except that the holder was held using the conventional wanxless method (comparative example).
.

As shown in Table 1, these polishes were performed in two stages: secondary polishing and final polishing. Note that different combinations of polishing pads and slurries are used for these subsequent and final polishing, and in order to improve the rise of the polishing band, the polishing pads are seasoned beforehand before being used for polishing the wafer. did.

Each of the obtained specimens was evaporated and dried, and then the flatness accuracy was measured. The results are shown in Table 1.

(The following is a margin) As can be seen from Table 1, the flatness accuracy of the wafers obtained in Examples 1 to 4 was all 3 μm or less. On the other hand, in the comparative example using the conventional method, only a flatness accuracy of 5 μm or more was obtained.

(Effects of the Invention) As described above, in the wafer holding method of the present invention, the holder is fixed to the carrier plate without using wax, adhesive, adhesive, etc., so air bubbles and wrinkles are not generated. No unevenness occurs due to application of adhesive or the like. Also,
No suction hole is formed in the portion of the carrier plate that corresponds to the recess of the holder. Therefore, the holder is brought into close contact with the carrier plate, and no unevenness occurs in the recess. Therefore, according to the method of the present invention, the wafer to be polished can be held in the polisher without any unevenness, and the wafer can be polished with extremely high planar accuracy. Since the holder used in the present invention does not require adhesives, adhesives, etc., there is no need to use an expensive holder with an adhesive layer or release paper arranged in advance, or to apply an adhesive.

A-JJ-Tsu (2) Testimonials - Figure 1 is a plan view of an example of a holder used in the present invention;
Fig. 2 is a bottom view of an example of carrier play 1, Fig. 3 is a sectional view taken along the line m-m in Fig. 2, Fig. 4 is an explanatory diagram of the method of the present invention, and Fig. 5 fa) is a diagram of the present invention. Fig. 6 is a cross-sectional view of another example of the holder, and Fig. 7 (a) is a sectional view of a conventional holder. FIG. 7 is a cross-sectional view of a holder in which a wafer is held by the holder, and FIG. 8 is an explanatory diagram of a conventional holding method.

10.10a...Holter-111...Tembray 1
-112... Backing material, 15... Recess, 16.
...Wafer, 40...Carrier plate, 41...
Hole, 42... Partial base corresponding to the recess -H

Claims (1)

[Claims] 1. A method for holding a wafer in a polishing machine, in which the back surface of a plate-shaped holder having a recess on the surface is held by a polisher having a large number of holes formed in a portion other than the portion corresponding to the recess. A method for holding a wafer, which includes bringing the wafer into close contact with a holding member of a polishing machine by vacuum suction through the hole, and placing the wafer in the recess and fixing the wafer to the holder. 2. The holder is a laminate including a template having a hole forming the recess on the front side and a backing material on the back side, and the wafer placed in the recess is fixed to the backing material. A method according to claim 1. 3. The method according to claim 1 or 2, wherein the holding member of the polisher is a carrier plate of the polisher.