JP2015041652A - Cutting method of wafer laminate for image sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a cutting method of an image sensor wafer package which allows for clear cutting effectively by a simple dry technique, without using a dicing saw.SOLUTION: In a cutting method of a wafer laminate W for image sensor having a structure where a glass wafer 1 and a silicon wafer 2 are bonded via a resin layer 4 arranged to surround each photodiode forming region, a scribe line S consisting of a crack penetrating in the thickness direction is formed, by rolling a scribing wheel 10, while pressing, along a cutting line on the upper surface of the glass wafer. Subsequently, the wafer laminate is deflected by pressing a break bar 14 from the lower surface side of the silicon wafer along the scribe line, thus cutting the silicon wafer along with the glass wafer.

Description

  The present invention relates to a cutting method for separating a wafer laminate in which a wafer level package of a CMOS image sensor is patterned.

  In recent years, the use of CMOS image sensors has been rapidly increasing in various small electronic devices such as mobile phones, digital cameras, and optical mice where low power, high functionality, and high integration are important.

FIG. 5 is a sectional view schematically showing a configuration example of a wafer level package (chip size unit product) W1 of the CMOS image sensor. The wafer level package W1 has a laminated structure in which a (separated) glass wafer 1 and a (separated) silicon wafer 2 are bonded with a resin partition 4 interposed therebetween.
A photodiode region (sensing region) 3 is formed on the upper surface (joint surface side) of the silicon wafer 2, and the photodiode region 3 is provided by arranging the periphery so that the resin partition 4 surrounds in a lattice shape. The inner space is made airtight. Further, a metal pad 5 is formed on the upper surface of the silicon wafer 2 (outside the photodiode region 3), and a via (through hole) penetrating the silicon wafer 2 vertically below the portion where the metal pad 5 is formed. ) 6 is formed. The via 6 is filled with a conductive material 7 having excellent electrical conductivity, and a solder bump 8 is formed at the lower end of the via 6. The structure in which the via 6 is formed and the conductive material 7 is filled to make electrical connection is referred to as TSV (Through Silicon Via).
A PCB substrate or the like (not shown) on which a predetermined electric circuit is patterned is bonded to the lower surface of the solder bump 8 described above.

  As shown in FIGS. 6 and 7, the wafer level package W <b> 1 which is a chip-sized unit product is obtained by bonding a large-area glass wafer 1 as a base and a large-area silicon wafer 2 through a resin partition 4. On the wafer stack W, a large number of patterns are formed by being divided into a lattice pattern by dividing lines L extending in the XY direction, and the wafer stack W is divided along the scheduled cutting lines L. Thus, the wafer level package W1 having a chip size (separated) is obtained.

  By the way, dicing saws as shown in Patent Documents 1 to 4 have been used in the past, including those for CMOS image sensors, in the process of dividing a silicon wafer into a product of a wafer level package. The dicing saw includes a rotating blade that rotates at a high speed, and is configured to perform cutting while spraying a cutting fluid that cools the rotating blade and cleans cutting waste generated during cutting onto the rotating blade.

JP-A-5-090403 JP-A-6-244279 JP 2002-224929 A JP 2003-051464 A

  Since the above-mentioned dicing saw is divided by cutting using a rotating blade, a large amount of cutting waste is generated, and even if the cutting fluid is cleaned with cutting fluid, a part of the cutting fluid remains or is scattered during cutting. As a result, cutting scraps may adhere to the package surface, which is a major cause of deterioration in quality and yield. Further, since a mechanism and piping for supplying the cutting fluid and collecting the waste fluid are required, the apparatus becomes large. In addition, since the glass wafer is cut by cutting, small chipping (chips) often occurs on the cut surface, and a clean cut section cannot be obtained. Further, since the blade edge of the rotating blade rotating at high speed is formed in a sawtooth shape, the blade edge is likely to be worn or damaged, and the service life is short. Furthermore, the thickness of the rotating blade cannot be made very thin from the viewpoint of strength, and even if it has a small diameter, it is formed with a thickness of 60 μm or more. There were problems such as being one of the limiting factors.

  Accordingly, the present invention provides a method for dividing an image sensor wafer package that solves the above-described conventional problems and can be divided effectively and cleanly by a simple dry method without using a dicing saw. The purpose is to do.

  In order to achieve the above object, the present invention takes the following technical means. That is, the present invention has a structure in which a glass wafer and a silicon wafer in which a plurality of photodiode formation regions are patterned vertically and horizontally are bonded together via a resin layer disposed so as to surround each photodiode formation region. A method for dividing a wafer laminate for an image sensor having a thickness by rolling a scribing wheel having a cutting edge along a circumferential ridge line while pressing along a scheduled cutting line on the upper surface of the glass wafer. Forming a scribe line consisting of cracks penetrating in the direction, and then pressing a break bar along the scribe line from the lower surface side of the silicon wafer to further flex the wafer laminated body to further crack the glass wafer Infiltrate to cut glass wafer and silicon wafer It is way.

According to the present invention, since the crack of the glass wafer penetrates in the thickness direction and is divided when divided by the break bar, the material does not require a cutting width as in the case of cutting of a conventional dicing saw, Can be effectively used, and the occurrence of chipping and the like can be suppressed, so that it can be cut with a clean cut surface. Moreover, since no cutting waste is generated, it is possible to eliminate the deterioration of quality and the generation of defective products due to the attachment of the cutting waste.
In particular, in the present invention, the cutting fluid such as a conventional dicing saw is not used, and the cutting is performed in a dry environment. Therefore, the mechanism and piping for supplying the cutting fluid and collecting the waste fluid can be omitted, and the cutting is performed. Subsequent washing and drying steps can be omitted, and the apparatus can be configured compactly.

In the above-described dividing method, a cut groove may be formed in advance on the lower surface of the silicon wafer at a position behind the position of the scheduled cutting line on the upper surface of the glass wafer, and then the break bar may be pressed.
Thereby, the silicon wafer can be easily cut from the groove with a clean cut section when the glass wafer is cut by the break bar.
In the wafer stack in which the TSV is formed, the kerf processing step can be simplified by forming the kerf during the process of processing the via of the TSV.

The figure which shows the 1st step of the cutting method of this invention. The figure which shows the 2nd step of the cutting method of this invention. The figure which shows another Example of FIG. The figure which shows the scribing wheel used by this invention, and its holder part. Sectional drawing which shows an example of the wafer level package for CMOS image sensors. Sectional drawing which shows a part of wafer laminated body for CMOS image sensors used as a base material. FIG. 7 is a schematic plan view showing the CMOS image sensor wafer laminate of FIG. 6.

Hereinafter, details of the method for dividing a wafer laminate for an image sensor according to the present invention will be described with reference to the drawings.
FIG. 1 shows a partial cross section of a wafer laminate W for a CMOS image sensor to be processed, which is the first stage of the cutting method of the present invention. The structure of the wafer stack W is basically the same as that shown in FIGS.
That is, a large-area glass wafer 1 (for example, 8 inches in diameter) serving as a base and a silicon wafer 2 disposed on the lower surface side of the glass wafer 1 are bonded via a lattice-shaped resin partition 4.
A photodiode formation region (sensing region) 3 is provided on the upper surface (bonding surface side) of the silicon wafer 2. A photodiode array is formed in the photodiode formation region 3 and functions as a light receiving surface of the image sensor. A metal pad 5 is formed in the vicinity of the photodiode forming region 3, and a via (through hole) 6 penetrating the silicon wafer 2 vertically is formed immediately below the portion where the metal pad 5 is formed. . The via 6 is filled with a conductive material 7 having excellent electrical conductivity (TSV), and a solder bump 8 is formed at the lower end of the via 6. A PCB substrate or the like (not shown) on which a predetermined electric circuit is patterned is bonded to the lower surface of the solder bump 8 described above.
As shown in FIG. 7, the CMOS image sensor wafer laminated body W is divided into pieces by being cut along a grid-like cutting planned line L extending in the XY direction, and is a chip-sized unit product. A certain wafer level package W1 is taken out.

Next, a parting procedure will be described. When the wafer stack W is cut along the line L to be cut, first, a scribe consisting of cracks (cracks penetrating in the thickness direction) on the surface of the glass wafer 1 using a scribing wheel 10 as shown in FIG. Process the line.
The scribing wheel 10 is formed of a material having excellent tool characteristics such as cemented carbide or sintered diamond, and a cutting edge 10a is formed on a circumferential ridgeline (outer peripheral surface). Specifically, it is preferable to use one having a diameter of 1 to 6 mm, preferably 1.5 to 4 mm, and a cutting edge angle of 85 to 150 degrees, preferably 105 to 140 degrees. It is appropriately selected according to the type.
The scribing wheel 10 is rotatably supported by a holder 11 and is held by a scribe head (not shown) via an elevating mechanism 12. The scribe head is formed so as to be movable in the direction of the division line L above a base plate (not shown) on which the wafer stack W is horizontally placed.
As shown in FIG. 1, a scribe line S composed of cracks is formed on the glass wafer 1 by rolling the scribing wheel 10 while pressing the scribing wheel 10 along the planned dividing line on the surface of the glass wafer 1. The scribe line S is preferably formed as a crack that penetrates to about half the thickness of the glass wafer 1. The scribe line S is formed outside the resin partition 4 of the wafer level package W1.

  Next, the substrate (wafer stack W) is reversed in the second stage shown in FIG. 2, and along the both sides so that the scribe line S is sandwiched between the outer surface of the glass wafer 1 (the surface opposite to the bonding surface). A pair of left and right receiving bases 13, 13 are arranged, and a long break bar 14 is pressed toward the scribe line S from the outer surface side (surface opposite to the bonding surface) of the silicon wafer 2. In this case, the groove 15 is preferably processed in advance along the line L to be divided on the outer surface (the surface opposite to the bonding surface) of the silicon wafer 2 facing the scribe line S. For example, when the vias 6 are formed on the silicon wafer 2 of the wafer stack W by a groove processing technique such as RIE, the grooves 15 are efficiently formed by using the same processing technique. Can be processed.

By the pressing of the break bar 14, the glass wafer 1 and the silicon wafer 2 are bent in the direction opposite to the pressing direction, and the scribe line S of the glass wafer 1, that is, the crack penetrates the entire thickness, and the glass wafer 1 is divided. At the same time, the silicon wafer 2 is also divided along the groove 15, whereby the wafer level package W 1 separated into individual pieces is completely divided along the division line L.
In this division, the glass wafer 1 is divided by cracks forming the scribe line S penetrating in the thickness direction, so that occurrence of chipping as in the case of cutting of a conventional dicing saw can be suppressed. Can be cut with a clean cut surface. Further, since the groove 15 is provided in the silicon wafer 2 along the planned division line L in advance, the silicon wafer 2 can also be divided along the groove 15 in a clean divided section.
Since the thickness of the silicon wafer 2 is very thin (25 μm to 100 μm) in many cases (by grinding), even if the groove 15 as described above is not provided, the glass is deformed by pressing the break bar 14. The wafer 1 can be easily divided at the same time as the wafer 1 is divided. Therefore, the process of processing the groove 15 can be omitted.

  As described above, since the crack of the scribe line S of the glass wafer 1 penetrates in the thickness direction and is divided at the time of the break processing by the break bar 14, cutting as in the case of cutting by a conventional dicing saw is performed. The material can be used effectively without requiring a width. Moreover, since no cutting waste is generated, it is possible to eliminate the deterioration of quality and the generation of defective products due to the attachment of the cutting waste. In particular, in the present invention, the cutting fluid such as a conventional dicing saw is not used, and the cutting is performed in a dry environment. Therefore, the mechanism and piping for supplying the cutting fluid and collecting the waste fluid can be omitted, and the apparatus is compact. Can be configured.

  In the present invention, at the time of the break processing by the break bar 14, instead of the pair of left and right receiving bases 13 and 13 that receive the glass wafer 1, as shown in FIG. 3, the thickness that can be recessed to the extent that the crow wafer 1 is bent. The cushion material 16 having the above may be arranged in contact with the surface of the glass wafer 1.

  As mentioned above, although the typical Example of this invention was described, this invention is not necessarily specified to said embodiment, The objective is achieved and it corrects and changes suitably within the range which does not deviate from a claim. Is possible.

  The dividing method of the present invention can be used for dividing a wafer laminate in which a glass wafer and a silicon wafer are bonded together.

L Scheduled line S Scribe line W Wafer stack W1 Wafer level package 1 Glass wafer 2 Silicon wafer 10 Scribing wheel 10a Cutting edge 14 Break bar 15 Groove

Claims (3)

For an image sensor having a structure in which a glass wafer and a silicon wafer in which a plurality of photodiode formation regions are patterned vertically and horizontally are bonded together via a resin layer disposed so as to surround each photodiode formation region. A method for dividing a wafer stack,
A scribe line composed of cracks penetrating in the thickness direction is formed by rolling a scribing wheel having a cutting edge along a circumferential ridge line while pressing along a scheduled cutting line on the upper surface of the glass wafer,
Next, by pressing a break bar along the scribe line from the lower surface side of the silicon wafer, the wafer laminated body is bent to further penetrate the cracks of the glass wafer to divide the glass wafer and also divide the silicon wafer. A method for dividing a wafer laminate for an image sensor.   2. The image sensor according to claim 1, wherein a kerf is formed in advance on a lower surface of the silicon wafer at a position on the upper surface of the glass wafer behind the position of the line to be cut, and the break bar is pressed. Method for dividing a wafer laminate for use.   3. The method of dividing a wafer laminate for an image sensor according to claim 2, wherein a TSV is formed in the wafer laminate, and the kerf is also formed in a step of processing a via of the TSV.

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