JP3291805B2 - Method for manufacturing solid-state imaging device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a solid-state imaging device for reducing image defects. The fields of use include CCD image sensors and linear sensors.

[0002]

2. Description of the Related Art In the manufacture of a conventional solid-state imaging device, the back surface of a wafer is ground before forming a color filter and an on-chip lens. Before forming the color filter and the on-chip lens, for example, as shown in FIG. 7, a gate insulating film 24 and a polysilicon film 2 as a transfer electrode are formed on a wafer 21.
5, the silicon oxide film 26 and the polysilicon film 27 are patterned at positions excluding the light receiving region a. Further, an SiO ₂ film 28 is formed over the entire surface, and the light shielding A
An l film 29 is formed to cover the charge transfer region b . Further, a SiN film 30 is deposited, and a flattening film 31 is formed thereon.

That is, a process as shown in a flowchart of FIG. 8 is performed on a wafer before forming a color filter and an on-chip lens.

[0004] First, as shown in FIG.
1 is coated with an acid-resistant resist 22 (Step 1)
1). Then, as shown in FIG.
Hard tape 23 is used to reduce the load when grinding the backside.
Is pasted (step 12). In this state, FIG.
As shown in (C), the back surface of the wafer 21 is ground and etched (step 13). The reason for performing the back surface grinding step is to form a Ti-Au film on the back surface in order to obtain a stable ground potential from the back surface, and to prevent the oxide film or silicon nitride film formed on the back surface of the wafer from being pelletized. This is to prevent peeling and generation of dust. Another reason is to prevent an oxide film or the like on the back surface from causing blinding of the dicing blade during dicing performed in a later step, thereby preventing the occurrence of excessive Si dust. The back surface grinding includes a creep field method and an in-feed method.

[0005] The backside etching is performed to remove the distortion during the backside grinding to improve the chip strength and to flatten the surface whose flatness has been impaired by the backside grinding. The method is as follows: hydrofluoric acid (HF): nitric acid (HNO ₃ ) = 1: 1
In addition, if the back surface is not etched, the following problems occur.

(1) The warpage of the wafer at the time of grinding the back surface causes defects such as dimensional variations (pattern non-uniformity) in the formation of the color filter and the on-chip microlens, and the quality is reduced.

(2) The back surface ground surface is rubbed by the color filter and the on-chip micro lens forming process apparatus, and Si dust frequently occurs, and image defects such as black scratches due to dust adhesion are likely to occur.

(3) The wafer edge hits the manufacturing apparatus, and the wafer is likely to be broken or chipped.

Next, as shown in FIG. 9D, the hard tape 23 is peeled off (Step 14). And FIG.
As shown in (E), the resist 22 is stripped using a stripper (step 15). Next, wafer cleaning is performed (step 16), and thereafter, a color filter and an on-chip lens are formed.

However, since the resist stripping step and the cleaning step after the backside grinding are wet steps, dust remains on the wafer surface. This dust adheres to the wafer surface before forming the color filter and the on-chip lens. If these dusts are formed thereon, image defects such as so-called black flaws occur. Therefore, the quality of the solid-state imaging device is remarkably poor, and there is a problem that the production yield is reduced.

As a method for solving the problem associated with the backside grinding of the wafer, it is conceivable to reduce the thickness of the wafer in advance and omit the backside grinding. However, in this case, the wafer is frequently cracked in the process, and the warpage of the wafer due to the heat treatment causes defects such as dimensional variation in the formation of the color filter and the on-chip microlens. It could not be adopted due to problems such as collapse.

The problem to be solved by the present invention is that what kind of means should be taken to create a solid-state imaging device that does not damage a color filter, an on-chip lens, and the like and has no dust attached? It is in the point.

[0013]

In order to solve such a problem, the present invention employs a method of manufacturing a solid-state imaging device as described below.

According to the first aspect of the present invention, at least an on-chip lens is formed on a semiconductor substrate on which a light receiving region and a charge transfer region are formed, and a surface protection tape is attached to the entire surface of the semiconductor substrate. And a step of grinding the back surface of the semiconductor substrate and a step of peeling off the surface protection tape.

The invention described in claim 2 of the present application is
The surface protection tape is a UV irradiation curing type tape or an adhesive tape containing a surfactant.

The invention according to claim 3 of the present application is characterized in that the surface protective tape is made to be acid-resistant.

[0017]

According to the first aspect of the present invention, since the surface protection tape is applied to the entire surface of the semiconductor substrate (wafer) after the formation of the on-chip lens, the surface protection tape buffers the load at the time of grinding the back surface of the substrate. In addition, it has the effect of preventing physical damage to the on-chip lens and the like. Further, since it can be continuously formed from the formation of the solid-state imaging device to the formation of the on-chip lens, there is no room for dust to adhere. For this reason, there is an effect of reducing image defects such as black scratches due to dust adhesion.

Further, in the invention according to claim 2 of the present application, in addition to the above-mentioned functions, the peeling of the surface protection tape becomes easy. The UV-irradiation-curable tape is cured by ultraviolet light, has an extremely low adhesive strength, and has an effect that there is no adhesive residue and it is easy to peel off. For this reason, peeling and cleaning are unnecessary, and indirect material costs and work man-hours can be reduced. Moreover, since the adhesive tape containing a surfactant surrounds the adhesive particles with the surfactant particles, the adhesive tape has an effect of easily removing the adhesive residue by water washing after peeling. By using these surface protection tapes, it is possible to avoid damaging the base (such as an on-chip lens) when the tape is peeled off.

Furthermore, the invention according to claim 3 of the present application has an effect of protecting the wafer surface from an acidic etching solution even if the back surface is etched after the back surface grinding of the semiconductor substrate because the surface protection tape has acid resistance. There is.

[0020]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The details of a method for manufacturing a solid-state imaging device according to the present invention will be described below with reference to the embodiments shown in the drawings. The same parts as those of the conventional device are denoted by the same reference numerals, and description thereof will be omitted.

In this embodiment, the present invention is applied to a CCD image pickup apparatus, and uses a wafer in which a large number of light receiving areas and an associated charge transfer area are formed in a chip area.

First, in this embodiment, as shown in FIG. 2, a wafer 21 on which a color filter 32 and an on-chip lens 33 are formed is prepared by a known manufacturing technique.

The process of the flowchart shown in FIG. 1 is performed on the wafer 21. Hereinafter, the steps will be described with reference to FIGS.

Wafer 2 formed up to on-chip lens
As shown in FIG. 3, an acid-resistant UV-irradiation-curable tape (hereinafter, referred to as a UV tape) 34 is stuck on the entire surface of Step 1 (Step 1). The UV tape 34 has a UV resin content and a cross-linking agent content as large as possible in order to reduce adhesive residue after peeling after UV irradiation, that is, a tape provided with an adhesive having a high cross-linking density.

Next, as shown in FIG. 4, after the back surface of the wafer 21 is ground by a known technique, the back surface is wet-etched (step 2).

Then, 500 to 100 is applied to the UV tape 34.
0 (mj / cm ² ) UV light
Is stripped (step 3), only the wafer 21 as shown in FIG. 6 is obtained. The peeling of the UV tape 34 is performed by UV
It is easy after the light irradiation, and the adhesive does not remain on the on-chip lens 33. In addition, 500-1000mj /
The UV light of cm ² does not cause a problem such as discoloration of the color filter.

The back-ground wafer 2 is thus polished.
1 is processed into a desired thickness and cut into chips by a dicing process in a later process.

According to this embodiment, the on-chip lens 33
U as a surface protection tape
By attaching the V-tape 34, the on-chip lens 33 can be protected from an etchant during back surface etching. Further, since the back surface grinding step is performed after the formation of the on-chip lens, it is possible to form the on-chip lens without dust adhered to the wafer surface. Therefore, a high-quality solid-state imaging device without image defects can be created.

Although the embodiment has been described above, the present invention is not limited to this, and various material changes and structural changes are possible. For example, in the above embodiment, the UV tape 34 was used as the surface protection tape,
In addition, it is also possible to use an adhesive tape containing a surfactant. In this adhesive tape, a surfactant is surrounded around the adhesive particles, and the adhesive can be easily removed by washing with water after peeling after back surface grinding. Therefore, the on-chip lens and the color filter are not damaged.

In the above embodiment, since the back surface was etched after the back surface was ground, an acid-resistant surface protection tape was used. However, in a process in which the back surface etching was not performed, the surface protection tape was not acid-resistant. May be.

Further, in the above-described embodiment, the present invention is applied with a color filter. However, the present invention can be applied to a solid-state imaging device having no color filter. be able to.

In addition, various design changes are possible within the scope of the configuration of the present invention.

[0033]

As is apparent from the above description, according to the first to third aspects of the present invention, the following effects can be obtained.

(A) Since the impact and load during back grinding are buffered by the surface protection tape, microlenses and color filters are not damaged, and good back grinding can be performed.

(B) Since dust adhesion can be prevented until the step of forming an on-chip lens on a semiconductor substrate, image defects such as black spots can be reduced.

(C) Since the peeling treatment of the surface protective tape is easy, the cost of indirect materials and the number of working steps can be reduced.

(D) If particles adhere to the surface of the on-chip lens, they can be removed together when the surface protection tape is peeled off, further improving the yield.

[Brief description of the drawings]

FIG. 1 is a flowchart showing an embodiment of the present invention.

FIG. 2 is a sectional view of a main part of a sample used in an example of the present invention.

FIG. 3 is an essential part cross sectional view showing a step of an embodiment of the present invention;

FIG. 4 is an essential part cross sectional view showing a step of an embodiment of the present invention;

FIG. 5 is an essential part cross sectional view showing a step of an embodiment of the present invention;

FIG. 6 is an essential part cross sectional view showing a step of an embodiment of the present invention;

FIG. 7 is a sectional view of a main part of a sample used in a conventional example.

FIG. 8 is a flowchart showing steps of a conventional example.

FIGS. 9A to 9E are cross-sectional views of relevant parts showing a conventional process.

[Explanation of symbols]

 21: Wafer 32: Color filter 33: On-chip lens 34: UV tape

Claims (3)

(57) [Claims] 1. A step of forming at least an on-chip lens on a semiconductor substrate on which a light receiving region and a charge transfer region are formed, a step of applying a surface protection tape to the entire surface of the semiconductor substrate, and grinding the back surface of the semiconductor substrate And a step of peeling off the surface protection tape. 2. The surface protection tape according to claim 1, wherein the surface protection tape is a UV irradiation curing type tape or an adhesive tape containing a surfactant.
A manufacturing method of the solid-state imaging device according to the above. 3. The method according to claim 1, wherein the surface protection tape has acid resistance.