Wafer processing method for processing wafer having bumps formed thereon

A wafer processing method for processing a wafer (20) having bumps (B) formed on a front surface (21) comprises the steps of: holding on a table (51), a bump region-conforming member (40) that has an outer shape conforming only to a bump region (25) where said bumps are formed in the wafer; forming a resin layer (29) by applying resin around the bump region-conforming member up to a thickness equal to or greater than that of the bump region-conforming member; grinding the bump region-conforming member along with the resin layer to a predetermined thickness; removing the bump region-conforming member from the table to form a concave part (45) in the resin layer; applying a film (11) on the front surface of the wafer; and disposing the wafer in the concave part of the resin layer and holding the wafer on the table so that a back surface (22) of said wafer faces upward. After that, the back surface of the wafer can also be ground. As a result, a change in the size of the bumps can be easily accommodated without creating clearance.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority of Japanese Patent Application Number 2008-018927, filed on Jan. 30, 2008.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a wafer processing method for processing a wafer having a plurality of bumps formed on its front surface.

2. Description of the Related Art

In the field of semiconductor manufacturing, wafers tend to become larger year after year and the wafers are made thinner for increasing packing density. In order to make a semiconductor wafer thinner, a backgrinding process for grinding a back surface of the wafer is performed. In the backgrinding process, a surface protection film is applied to a front surface of the wafer for protecting chips formed on the front surface of the wafer.

After the backgrinding process is finished, a dicing film application device applies a dicing film to the back surface of the wafer, so that the wafer is integrated with a mount frame. Then, the surface protection film that has been applied to the front surface of the wafer is removed, and then, the wafer is diced into chips. Each chip formed by the dicing process is picked up and mounted on a lead frame.

FIG. 8is a cross-sectional view of a wafer before the backgrinding process in the conventional art. As illustrated inFIG. 8, bumps B as electrical contacts are formed on each chip C on the front surface of the wafer. Because of chips C and bumps B formed thereon, front surface21of wafer20is not flat. As can be seen fromFIG. 8, when surface protection film110is applied to front surface21of wafer20, a central region of wafer20is elevated from its peripheral region. In other words, a step is formed on the front surface protection film110.

As illustrated inFIG. 9, wafer20is turned upside down and mounted on a table51for grinding the back surface22of wafer20. Table51is provided with a suction section52that is slightly smaller than the outer shape of wafer20. Because surface protection film110is elevated in the central region, it is not in contact with suction section52in the peripheral region. Therefore, as illustrated in the figure, in the peripheral region, an annular clearance is formed between the surface protection film110and suction section52.

In this state, when back surface22of wafer20is ground, stress may be concentrated on the central region of wafer20and, as a result, bumps B located in the central region and/or wafer20itself may be damaged. Further, because the peripheral region of wafer20is not sucked by suction section52, the edge of wafer20may be broken during the backgrinding process. Still further, during the backgrinding process, shavings may be sucked through the annular clearance by suction section52and, as a result, suction section52may be clogged.

In order to solve these problems, Japanese Unexamined Patent Publication No. 2005-109433 discloses a technique for covering the front surface of the wafer by a cup-shaped protection member that is provided with a peripheral adhesive part adhering to the peripheral region of the wafer. When such protection member is used, the stress during the backgrinding process is distributed over the entire wafer, and therefore the above-mentioned problems can be avoided.

However, the protection member disclosed in Japanese Unexamined Patent Publication No. 2005-109433, which is a special-purpose product conforming only to the bumps of a particular size, is expensive and therefore the cost of the resultant semiconductor chip is increased. Considering the fact that this protection member is used only during the backgrinding process and eventually discarded, it is desirable to reduce the cost of the protection member as much as possible.

Further, because the protection member is the special-purpose product, even when the height of the bumps is changed only slightly, the protection member cannot protect the bumps properly. In this case, if the protection member is used as it is without modification, the problems such as the damage to the wafer and/or bumps, the breakage of the edge of the wafer, and the clogging of the suction section may occur again.

The present invention has been made in view of such circumstances and it is an object of the present invention to provide an inexpensive wafer processing method that can easily accommodate change of size of bumps without creating clearance between a wafer and a table.

SUMMARY OF THE INVENTION

In order to accomplish the above object, according to a first aspect, there is provided a wafer processing method for processing a wafer having bumps formed on its front surface, comprising the steps of: holding, on a table, a bump region-conforming member that has an outer shape conforming only to a bump region of said wafer where said bumps are formed; forming a resin layer by applying resin around said bump region-conforming member up to a thickness equal to or greater than that of said bump region-conforming member; grinding said bump region-conforming member along with said resin layer to a predetermined thickness; removing said bump region-conforming member from said table to form a concave part in said resin layer; applying a film on the front surface of said wafer; and disposing said wafer in said concave part of said resin layer and holding said wafer on said table so that a back surface of said wafer faces upward.

Thus, in the first aspect, when the wafer is held on the table, a peripheral region of the wafer is mounted on the resin layer. Therefore, no clearance is formed between the wafer and the table. Further, change of size of the bumps can be easily accommodated by changing the grinding amount of both the bump region-conforming member and the resin layer depending on the height of the bumps and, therefore, the need for preparing a special-purpose protection member can be eliminated.

According to a second aspect, in the first aspect, said predetermined thickness is equal to the distance between said front surface of said wafer and the top of said bumps.

Thus, in the second aspect, the clearance that may be created when the wafer is mounted on the table can be eliminated substantially completely.

According to a third aspect, in the first or second aspect, further, the back surface of said wafer is ground.

Thus, in the third aspect, during the backgrinding process, damage of the wafer and/or bumps, breakage of an edge of the wafer, and clogging of a suction section can be eliminated.

According to a fourth aspect, in any of the first to third aspects, said bump region-conforming member is made of another wafer that has a size identical to that of said wafer.

Thus, in the fourth aspect, cost of processing the wafer can be reduced to be inexpensive.

These and other objects, features and advantages of the present invention will be more apparent from the detailed description of the typical embodiments of the present invention illustrated in the accompanying drawings.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinafter, the embodiments of the present invention will be described in detail with reference to the accompanying drawings. Throughout the several views, like elements are designated by like reference numerals. For ease of understanding, the scale of these drawings is changed appropriately.

FIG. 1is a schematic diagram of a wafer processing apparatus for performing a wafer processing method according to the present invention. It is assumed that a silicon wafer20is supplied to wafer processing apparatus30illustrated inFIG. 1, wherein a plurality of chips C each comprising bumps B are formed on a front surface21of silicon wafer20. (SeeFIG. 2bdescribed later.) As can be seen fromFIG. 1, wafer processing apparatus30mainly includes: a film application section31for applying a surface protection film11on wafer20; and a backgrinding section32for grinding a back surface22of wafer20.

Backgrinding section32includes: a dummy member disposition unit33for disposing a dummy member40on a table51; a resin application unit34for applying resin around dummy member40to form a resin layer29; a dummy member grinding unit35for grinding dummy member40and resin layer29to a predetermined thickness; a dummy member removal unit36for removing ground dummy member40; and a backgrinding unit37for grinding back surface22of wafer20. Here, backgrinding unit37may also serve as dummy member grinding unit35.

FIGS. 2aand2bare top and cross-sectional views of the wafer, respectively. For the sake of simplicity, bumps B are not illustrated inFIG. 2a. As can be seen from these figures, the plurality of chips C are formed only in a central region25of front surface21of wafer20and bumps B are formed in each of chips C. Then, these chips C and bumps B are not formed in a peripheral region26of wafer20. Therefore, hereinafter, central region25is referred to as a bump region25.

First, as illustrated inFIG. 2a, in film application section31, surface protection film11is applied to the entire front surface21of wafer20. This surface protection film11protects chips C and bumps B on front surface21during the backgrinding process described below. As can be seen fromFIG. 2b, after surface protection film11is applied, a step is formed between bump region25and peripheral region26. Here, though not illustrated in the figures, it is to be noted that, in reality, surface protection film11is slightly concaved between bumps B.

FIGS. 3a-6aandFIGS. 3b-6bare top and cross-sectional views of table51in backgrinding section32, respectively. As illustrated in these figures, table51mainly has: a table peripheral section53; and a suction section52included in table peripheral section53. Table peripheral section53has an outer diameter slightly larger than the diameter of wafer20. Further, suction section52is connected to a vacuum source (not illustrated in the figures) and it has an outer diameter slightly smaller than the diameter of wafer20.

Then, dummy member disposition unit33is used to dispose dummy member40concentrically with suction section52(SeeFIGS. 3aand3b). As can be seen from the comparison betweenFIGS. 2aand3a, dummy member40has an outer shape slightly larger than that of bump region25of wafer20. Dummy member40is made of a material that can be ground by a grindstone32adescribed later, such as, for example, silicon or plastic.

In one embodiment, dummy member40is formed by cutting out, by laser, for example, a wafer that has a shape identical to wafer20. In such case, it is advantageous that the cost of processing wafer20described later can be reduced to be inexpensive.

Then, resin application unit34is used to apply resin such as, for example, thermoset resin around dummy member40. As can be seen fromFIGS. 4aand4b, the resin is applied so as to be flush with both a peripheral surface53aof table peripheral section53and a top surface of dummy member40.

At this time, a frame and the like (not illustrated in the figures) surrounding table peripheral section53may be used, or a sheet may be disposed on suction section52around dummy member40. Further, the resin may be applied beyond peripheral surface53aof table peripheral section53, or the resin may be applied beyond the top surface of dummy member40. Alternatively, a portion of the resin may be applied on the top surface of dummy member40. After the resin is applied, it is hardened by natural drying or heat treatment. As a result, resin layer29or in other words, a ring-shaped resin-made member is formed around dummy member40.

Then, suction section52is activated to suck the dummy member40and resin layer29an table51. Then, grindstone35aof dummy member grinding unit35grinds the top surface of dummy member40. (SeeFIGS. 5aand5b.) At this time, resin layer29is also ground together and, as a result, dummy member40and resin layer29are ground to a predetermined thickness. This predetermined thickness is approximately equal to the distance between front surface21of wafer20and the top of bumps B. In other words, this predetermined thickness is approximately equal to the step in front surface protection film11between bump region25and peripheral region26of wafer20.

Then, the suction effect of suction section52is deactivated. Then, dummy member removal unit36is used to remove ground dummy member40from resin layer29. (SeeFIGS. 6aand6b.) As a result, a concave part45comprised of the inner side surface of resin layer29and the top surface of suction section52is formed inside ring-shaped resin layer29. As a matter of course, the outer shape of concave part45corresponds to bump region25of wafer20.

After that, wafer20with surface protection film11applied thereto is conveyed from film application section31to backgrinding section32by a robot hand39and held on table51(SeeFIG. 1).FIG. 7is a cross-sectional view of the wafer disposed on table51in backgrinding section32. As illustrated inFIG. 7, in backgrinding section32, wafer20is disposed on table51so that its back surface22faces upward and sucked by suction section52.

As described above, resin layer29has been formed on table51. Therefore, when wafer20is disposed on table51, as illustrated inFIG. 7, this resin layer29is positioned between peripheral region26of wafer20and suction section52. At this time, bump region25of wafer20is sucked by suction section52, and peripheral region26of wafer20is mounted on resin layer29. Therefore, in the present invention, no annular clearance is formed between peripheral region26of wafer20and suction section52.

Then, grindstone32aof backgrinding section32is used to grind back surface22of wafer20. In the present invention, peripheral region26of wafer20is supported by resin layer29and, therefore, stress is not concentrated on bump region25of wafer20, so that bumps B and the like and/or wafer20can be prevented from being damaged. Further, in the present invention, no annular clearance is formed and, therefore, the edge of wafer20is not broken during the backgrinding process and suction section52is not clogged with shavings created as a result of the backgrinding.

These can be accomplished by forming ring-shaped resin layer29. Then, resin layer29can be formed of any resin that can be hardened by heat. Further, dummy member40can be made of typical wafer20. Thus, in the present invention, no special-purpose product has to be prepared for making dummy member40and, therefore, the manufacturing cost of the semiconductor chip can be reduced.

Further, when the size of bumps B in wafer20to be processed is changed, it suffices to change the grinding amount of resin layer29and dummy member40depending on the size of bumps B. Therefore, in the present invention, even when the size of bumps B is changed due to design change, such change can be easily accommodated.

While the present invention has been described with reference to the typical embodiments, those skilled in the art can understand that the changes described above and other various changes, omissions or additions can be made without departing from the scope of the present invention.