JP2019009372A - Grinding method of wafer - Google Patents

Abstract

To easily cut a resin of a part squeezed-out from a wafer and grind the wafer.SOLUTION: A grinding method of a wafer, includes: a coating step of absorbing a convexoconcave due to a bump Wf by coating a surface Wa of the wafer W with a resin J by the resin; a semi-hardening step of irradiating the resin with an ultraviolet ray UV of an exposure light amount that the resin J coated to the wafer W is not completely hardened, and semi-hardening the resin J; a cutting step of cutting the resin J coated to the wafer W so as to be squeezed-out from a circumference Wc along the circumference Wc of the wafer W; a completion hardening step of completely hardening the resin J by irradiating the resin J with the ultraviolet ray UV again after the cutting step; and a grinding step of grinding a back surface Wb of the wafer W after the completion hardening step. Since the cutting step is executed after the resin J becomes the semi-hardening state, the resin J squeezed-out from the circumference Wc of the wafer W can be easily cut-off. After that, the resin J is completely hardened and the grinding of the wafer W is executed, and the wafer W can be ground at high quality.SELECTED DRAWING: Figure 3

Description

  The present invention relates to a wafer grinding method in which the surface of a wafer is coated with a resin for grinding.

  In recent years, as a technology for realizing miniaturization of semiconductor devices, a device substrate in which a plurality of metal protrusions called bumps are formed on a device surface and these bumps are directly bonded to an electrode formed on a wiring board. Mounting technology has been put to practical use. Some wafers with bumps formed on the surface have large bumps formed on the surface as a result of mounting a thick bump called a high bump.

  As a method for grinding a wafer having such a large unevenness on the surface, a method is known in which the surface of the wafer is ground without any unevenness by coating the surface of the wafer with a resin that is cured by ultraviolet rays ( For example, see Patent Documents 1 and 2).

JP 2013-175647 A JP 2012-160515 A

  However, when grinding a wafer whose surface is covered with resin, if the resin protrudes from the peripheral edge of the wafer, for example, when grinding thinly to a thickness of 100 μm or less, the grindstone removes the resin during grinding. It will get caught and the grindstone will be easily damaged. And when a grindstone breaks, the problem that grinding quality falls, such as the roughness of a grinding surface becoming large, arises.

  For this reason, it is necessary to cut and remove the resin protruding from the periphery of the wafer before grinding, but there is a problem that it is not easy to cut the resin when the resin is completely cured.

  The present invention has been considered in view of such a problem, and an object of the present invention is to easily cut the resin protruding from the edge of the wafer so as to grind the wafer.

  In order to solve the above-mentioned problems, the present invention provides a method for grinding a wafer having irregularities on the surface, the coating step of coating the surface of the wafer with a resin and absorbing the irregularities with the resin, After the execution, the resin coated on the wafer is irradiated with an exposure amount of ultraviolet light that does not completely cure, so that the resin is in a semi-cured state, and after the semi-curing process, the resin protrudes from the periphery of the wafer. A cutting step of cutting the coated resin along the periphery of the wafer with a cutting means, a complete curing step of completely curing the resin by irradiating the resin again with ultraviolet rays after the cutting step, A grinding step of holding the resin side on a holding table and grinding the wafer by grinding means after the complete curing step.

  According to the present invention, after the surface of the wafer is coated with the resin, the resin coated on the wafer is irradiated with an exposure amount of ultraviolet rays that is not completely cured to make the resin semi-cured, and the resin in the semi-cured state is Since the cutting means cuts along the periphery of the wafer, the resin protruding from the edge of the wafer can be easily cut. After that, the wafer is ground by again irradiating the resin with ultraviolet rays to completely cure the resin, so that the wafer can be ground with high quality without causing damage to the grindstone due to the entrainment of the resin. .

It is sectional drawing which shows the structure of a wafer. (A) is sectional drawing which shows the state which supplies resin to the resin table and is holding resin with the resin table. (B) is sectional drawing which shows the resin coating process which makes the wafer table and the resin table approach, and coat | covers resin on the surface of a wafer. It is sectional drawing which shows the semi-hardening process which irradiates the exposure amount of the ultraviolet-ray which the resin coat | covered with the wafer does not harden | cure completely, and makes resin semi-hardened. It is sectional drawing which shows the cutting process which cut | disconnects the resin which protruded from the periphery of the wafer along the periphery of a wafer with a cutting | disconnection means. It is sectional drawing which shows the complete curing process which irradiates ultraviolet rays to resin and hardens resin completely. It is sectional drawing which shows the grinding process which hold | maintains the resin side to a holding table, and is ground with a grinding means.

A wafer W shown in FIG. 1 is a silicon wafer having a predetermined thickness (for example, 300 μm), and a device such as an IC or LSI is provided on a surface Wa of a plurality of lattice-like regions partitioned by a plurality of division lines. Is formed. A plurality of bumps (projection electrodes) Wf are provided on the surface of the device. The bumps Wf are formed with a height of about 100 to 200 μm, for example. The back surface Wb of the wafer W is a surface to be ground when grinding is performed.
Hereinafter, each step of the wafer cutting method according to the present invention in which the front surface Wa of the wafer W is coated with resin and the back surface Wb is ground will be described.

(1) Resin coating process As shown to Fig.2 (a), resin J is prepared. At that time, the supply nozzle 21 is positioned above the central region of the protective sheet S sucked and held on the upper surface 10 a of the resin table 10, and the resin J sent from the resin supply source 22 is dropped from the supply nozzle 21. The resin J maintains a substantially hemispherical shape on the protective sheet S due to its surface tension. After an appropriate amount of resin J is supplied to the upper surface of the protective sheet S, the resin supply means including the supply nozzle 21 and the resin supply source 22 is retracted from above the resin table 10.

  The resin table 10 is formed of a transparent member such as glass that transmits ultraviolet rays. The resin table 10 has a hollow structure, and a plurality of UV lamps 11 are disposed therein. The uncured resin J is a solventless resin having a viscosity of, for example, about 500 to 5000 mPa, and has a property of being cured when irradiated with ultraviolet rays.

  After the preparation of the resin J is completed, the moving means 31 shown in FIG. 2B moves the wafer table 30 holding the wafer W above the resin table 10 so that the surface Wa of the wafer W is the protective sheet S. The wafer W is positioned so as to face the upper resin J. A suction source 32 is connected to the wafer table 30, and the wafer W is sucked and held on the lower surface of the wafer table 30 by the vacuum suction force of the suction source 32. Then, the apex of the bump Wf of the wafer W and the resin J come into contact with each other by lowering the wafer table 30.

  When the wafer table 30 is further lowered from the state shown in FIG. 2B, the resin J on the protective sheet S is pressed by the wafer W, and the resin J is directed radially outward on the surface Wa of the wafer W. And spread. Then, the wafer table 30 is lowered to a height position at which the resin J is sufficiently pushed to the base of the bump Wf of the wafer W, so that the resin J on the protective sheet S is spread on the surface Wa of the wafer W.

  The state in which the resin J between the surface Wa of the wafer W and the upper surface of the protective sheet S is not divided after the wafer table 30 is lowered to a height at which the resin J is sufficiently pushed to the base of the bump Wf of the wafer W. The wafer table 30 is repeatedly raised and lowered a plurality of times (for example, 4 to 7 times). As a result, the entire surface Wa of the wafer W is coated with the resin J, and a resin film that eliminates the unevenness of the bumps Wf is formed.

  When the coating of the resin J on the entire surface Wa of the wafer W is completed, the wafer table 30 releases the suction holding of the wafer W and retracts from above the resin table 10. At this time, the wafer W is placed on the resin table 10 via the protective sheet S and the resin J.

(2) Semi-curing step After performing the resin coating step, a semi-curing step for making the resin a semi-cured state is performed. In this semi-curing process, as shown in FIG. 3, the UV lamp 11 is turned on, and the resin J covered with the wafer W is irradiated with ultraviolet rays having an exposure amount that does not completely cure the resin J from below the protective sheet S. To do. Thereby, the resin J becomes a semi-cured state. When the resin J is in a semi-cured state, the UV lamp 11 is turned off.

(3) Cutting process After performing a semi-hardening process, the cutting process which cut | disconnects resin J which protruded from the periphery Wc of the wafer W is implemented. In this cutting step, as shown in FIG. 4, the cutting means 40 is moved above the resin table 10 to rotate the wafer W, while the wafer W is rotated, and the resin J covered and covered from the peripheral edge Wc of the wafer W is cut. Then, the wafer W is cut and removed along the periphery of the wafer W. When the cutting of the resin J is completed, the cutting means 40 is retracted from above the resin table 10. The cutting means 40 is not particularly limited as long as it can cut a laser, a blade, a cutter or other resin.

(4) Complete curing step After performing the cutting step, a complete curing step for completely curing the semi-cured resin J is performed. In this complete curing step, as shown in FIG. 5, the UV lamp 11 is turned on again, and ultraviolet rays UV are applied to the resin J from below the protective sheet S until the resin J is completely cured. When the resin J is completely cured, the UV lamp 11 is turned off.

(5) Grinding process After performing the complete curing process, a grinding process for grinding the back surface Wb of the wafer W is performed. As shown in FIG. 6, the grinding process is performed by transferring the wafer W onto the holding table 51. The wafer W is sucked and held on the holding table 51 on the resin J side with the back surface Wb facing upward. The holding table 51 is positioned below the grinding means 60 after holding the wafer W. The grinding means 60 includes a grinding wheel 61 having a plurality of grinding wheels 62 attached to the lower surface 61a.

  In the grinding process, the holding table 51 is rotated at a predetermined speed (for example, 300 rpm) and the grinding wheel 61 is gradually lowered while being rotated at a predetermined speed (for example, 1000 rpm) to grind the back surface Wb of the wafer W. Do. When the wafer W is thinned by grinding, the processed groove formed on the front surface Wa of the wafer W along the planned division line is exposed on the back surface Wb of the wafer W, so that the wafer W is divided along the planned division line. Is done.

  As described above, in the present embodiment, after the surface Wa of the wafer W is coated with the resin J, the resin J coated on the wafer W is irradiated with an ultraviolet ray UV having an exposure amount that does not completely cure, so that the resin J is coated. Since the semi-cured resin J is cut along the peripheral edge of the wafer W by the cutting means 40, the portion of the resin J protruding from the peripheral edge Wc of the wafer W can be easily cut. it can. After that, the resin J is again irradiated with ultraviolet rays UV to completely cure the resin J, and then the wafer W is ground so that the grinding wheel is not damaged by the entrainment of the resin J. And can be divided into chips. Since the resin J does not entrain during grinding, even when the wafer W is thinly ground to a thickness of 100 μm or less, for example, high quality grinding can be performed.

  In the present embodiment, in the resin coating step, the wafer table 30 is raised and lowered a plurality of times while maintaining the state in which the liquid resin J between the surface Wa of the wafer W and the upper surface of the protective sheet S is not divided. Since the resin J is repeatedly spread on the wafer W, the entire surface Wa of the wafer W can be uniformly coated with the resin J without generating bubbles in the resin J.

  The embodiment of the present invention is not limited to the above-described embodiment, and various changes, substitutions, and modifications may be made without departing from the spirit of the technical idea of the present invention.

  For example, in the above embodiment, the resin J that covers the surface Wa of the wafer W is irradiated with ultraviolet rays UV from the UV lamp 11 disposed inside the resin table 10. You may make it irradiate ultraviolet rays UV from the arrange | positioned UV lamp 11. FIG.

The conditions of the wafer W and the resin J were as follows.
Wafer diameter: 200mm
Wafer thickness: 700 μm
Wafer material: Silicon Bump thickness: 150μm
Resin: Polyethylene Resin thickness: 230 μm

And the ultraviolet irradiation conditions in the semi-curing process and the complete curing process were as shown in the table below.

The amount of light on the ultraviolet path was determined by the following formula.
UV light exposure (mJ / square cm) = UV illuminance (mW / square cm) × irradiation time (seconds)

  After the resin coating step, when the semi-curing step was performed under the above-described ultraviolet irradiation conditions, the resin layer made of the semi-cured resin J cured to a hardness that can be easily cut by the cutting means 40 is the surface of the wafer W. Formed in Wa.

  By carrying out the cutting step after the semi-curing step, the portion of the resin J protruding from the peripheral edge Wc of the wafer W could be easily cut and removed.

  After the cutting step, the complete curing step was performed under the above-described ultraviolet irradiation conditions. As a result, a completely cured resin layer without a portion protruding from the peripheral edge Wc of the wafer W was formed on the surface Wa of the wafer W.

10: resin table 11: UV lamp 21: supply nozzle 22: resin supply source 30: wafer table 31: moving means 32: suction source 40: cutting means 51: holding table 60: grinding means 61: grinding wheel 62: grinding Whetstone J: Resin S: Protective sheet UV: Ultraviolet W: Wafer Wa: Front surface Wb: Back surface Wc: Perimeter Wf: Bump

Claims (1)

A method for grinding a wafer having irregularities on its surface,
A coating step of coating the surface of the wafer with a resin and absorbing the irregularities with the resin;
A semi-curing step for making the resin semi-cured by irradiating an ultraviolet ray having an exposure amount that does not completely cure the resin coated on the wafer after the coating step;
After performing the semi-curing step, a cutting step of cutting the coated resin that protrudes from the periphery of the wafer along the periphery of the wafer with a cutting means;
After the cutting step, a complete curing step of completely curing the resin by irradiating the resin with ultraviolet rays again;
A grinding step of holding the resin side on a holding table and grinding the wafer by a grinding means after the complete curing step.

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