JPH09115899A - Formation of protective film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To ensure the uniformity of wafer thickness in a surface after RGB process by forming a uniform protective film on the wafer. SOLUTION: After the peripheral part of a protective film material layer 12 spin-coated over a wafer 11 is removed to remove a swollen part 12a of the protective film material layer 12, the protective film material layer 12 is prebaked. The peripheral part of a resist film 13, formed on the wafer 11 in a state where it covers the protective film material layer 12, is removed in a state where the periphery of the protective film material layer 12 is exposed. The peripheral part of the protective film material layer 12 is etched and removed by etching process using the resist film 13 as a mask, and a swollen part 12b of the protective film material layer 2 formed by prebaking is removed. After the resist film 13 is removed, the protective film material layer 12 is hardened by baking to form a protective film 15 having a flat surface.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of forming a protective film on a wafer in a semiconductor device manufacturing process.

[0002]

2. Description of the Related Art In the process of manufacturing a semiconductor device, various protective films are formed on the element formation surface of a wafer. For example, in order to prevent malfunction of the device caused by α rays emitted from U (uranium) and Th (thorium) contained in the package material, the transmission of α rays such as polyimide on the passivation film is prevented. A protective film made of a possible material is formed as a buffer coat film. By forming this protective film, it is possible to prevent malfunction of the device by 1000 FIT (Fa
ilure Unit: Failure rate) can be kept below the guaranteed value. 1000FIT = 8.76 × 10 ^-3 bit / ye
ar (10 year warranty)

An example of the method of forming the protective film will be described below with reference to FIG. First, as shown in FIG. 2 (1), a protective film material layer 12 such as polyamic acid is formed on the entire surface of the wafer 11 by a spin coating method, and then, as shown in FIG. The layer 12 is pre-baked to scatter the solvent in the protective film material layer 12. Next, FIG. 2 (3)
As shown in FIG. 1, the wafer 1 is formed so as to cover the protective film material layer 12.
After forming the resist film 13 on the wafer 1, the rinse liquid is dropped on the peripheral portion of the rotated wafer 11 to remove the resist film 13 on the peripheral portion of the wafer 11. This prevents the peripheral edge of the resist film 13 from being peeled off as dust. Then, as shown in FIG. 2D, the opening 13a is formed in the resist film 13 by the lithography method.
And the pad opening 14 is formed in the protective film material layer 12 by etching using the resist film 13 as a mask, and the protective film material layer 12 on the edge portion of the wafer 11 is formed.
Is removed. Next, as shown in FIG. 2 (5), after removing the resist film (13), the protective film material layer 12 is cured by baking to form a protective film 15 made of polyimide.

[0004]

However, the method of forming the protective film has the following problems. That is,
As shown in FIG. 2A, the wafer 11 is formed by spin coating.
In the peripheral portion of the protective film material layer 12 applied above, a raised portion 12a having a larger film thickness than other protective film portions is formed. Further, in the next prebaking shown in FIG. 2B, the protective film material layer 12 is thermally shrunk and the swelling of the peripheral portion is emphasized. Therefore, Fig. 2 (4)
As shown in FIG. 5, even if the peripheral edge portion of the protective film material layer 12 is removed in the step of etching the protective film material layer using the resist film from which the peripheral edge portion has been removed as a mask, the raised portion 12a is completely removed. Is not removed and remains on the wafer 11. Then, the protective film 1 shown in FIG.
In No. 5, the film thickness becomes non-uniform on the wafer 11.

When the thickness of the protective film is not uniform as described above, it is impossible to press the entire surface of the wafer with a uniform pressure in the subsequent back grinding (hereinafter referred to as BGR) step. For this reason, a large pressure is applied to a portion where the thickness of the protective film is large, the edge portion of the wafer is scraped and thinned more than other portions, and one wafer cannot be formed to have a uniform thickness.

[0006]

A method of forming a protective film according to the present invention for solving the above problems comprises a second step of removing a peripheral portion of a protective film material layer spin-coated on a wafer, and the above-mentioned protective film. A third step of pre-baking the material layer, and a fourth step of removing the peripheral edge portion of the resist film formed on the wafer while covering the protective film material layer while exposing the peripheral edge of the protective film material layer. And a fifth step of etching away the peripheral portion of the protective film material layer by etching using the resist film as a mask, and a sixth step of forming a protective film formed by curing the protective film material layer by baking. It is characterized by having.

In the above-mentioned forming method, since the pre-baking is performed after removing the peripheral portion of the protective film material layer spin-coated on the entire surface of the wafer, the film thickness is larger than the other parts by spin-coating during the pre-baking. The raised portion of the formed protective film material layer is removed. Therefore, the swelling generated in the peripheral portion of the protective film material layer due to the prebaking is suppressed to a small level. Then, after the pre-baking, in order to etch away the peripheral portion of the protective film material layer by etching using the resist film formed in a state of exposing the peripheral edge of the protective film as a mask, the peripheral portion of the protective film material layer The bulge is completely removed, and the surface of the protective film material layer is flattened.

[0008]

FIG. 1 is a diagram showing an example of a method for forming a protective film of the present invention, and an embodiment of the present invention will be described below with reference to this diagram. Here, the wafer 11 on which the protective film is formed has a passivation film formed on one main surface (front surface) on which elements are formed. First, FIG.
In the first step shown in (1), the wafer 11 is placed on a wafer chuck (not shown) of the spin coater. At this time, the vacuum suction unit arranged at the rotation center of the spin coater is arranged at the center of the wafer 11 so that the wafer 11 is uniformly coated.

Then, by a spin coating method using the above spin coating apparatus, for example, a protective film material made of polyamic acid dissolved in a solvent is coated on the entire surface of the wafer 11, whereby the protective film material layer 12 is formed. Form. At this time, after the supply of the protective film material onto the rotated wafer 11 is stopped, the rotation speed is continuously changed from 1000 rpm to 600 rpm.
The wafer 11 is rotated while maintaining the range of 0 rpm.
As a result, the film thickness of the protective film material layer 12 is made substantially uniform within the surface of the wafer 11. However, in the peripheral portion of the protective film material layer 12 formed here, a raised portion 12a in which the protective film material layer 12 is thicker than other portions is formed. The raised portion 12a is formed along the peripheral edge of the protective film material layer 12 of the wafer 11 with a width of w = 1 to 3 mm, for example.

Next, in the second step shown in FIG. 1 (2) -a,
At the upper end of the wafer 11 in a state of being rotated following the above process, for example, N, N dimethylformamide or NMP (1-
A rinse solution that dissolves the protective film material, such as Methyl-2-pyrrolidinone, is dropped to remove the peripheral portion of the protective film material layer 12 on the wafer 11. Here, the peripheral portion of the protective film 15 is removed with a width such that the raised portion 12a formed on the peripheral portion of the protective film material layer 12 is removed. Thereafter, as shown in FIG. 1 (2) -b, the rotation speed of the wafer 11 is increased to increase the rinse liquid a.
Remove by shaking off. Here, by rotating the wafer 11 at a high speed, the protective film material layer 12 spreads non-uniformly in the peripheral direction of the wafer 11, and the protective film material layer 12 is formed.
The contour of the periphery of is disturbed.

Next, in a third step shown in FIG. 1C, the protective film material layer 12 is pre-baked, and the protective film material layer 12 is prebaked.
The solvent inside is scattered. Here, the protective film material layer 12 is thermally contracted, and a bulge portion 12b smaller than the bulge portion (12a) formed in the first step is formed in the peripheral portion of the protective film material layer 12.

Then, in a fourth step shown in FIG. 1 (4),
A resist film 13 covering the protective film material layer 12 is formed on the wafer 11 by spin coating. The resist film 13 is, for example, a positive type resist. Next, on the upper end of the wafer 11 which is continuously rotated,
A rinsing liquid that dissolves the resist film 13 before exposure is dropped,
As a result, the peripheral portion of the resist film 13 is removed.
Here, the peripheral edge of the resist film 13 is removed with a width that exposes the peripheral edge of the protective film material layer 12. afterwards,
The rotation speed of the wafer 11 is increased to remove the rinse liquid by shaking off. Here, since the viscosity of the protective film material layer 12 is increased due to the pre-baking, the spread of the protective film material layer 12 appears remarkably. There is no such thing.

Next, in the fifth step shown in FIG. 1 (5), for example, the exposure light b is formed on the portion where the pad opening is formed in the protective film.
The pattern exposure is performed on the resist film 13 in the state of irradiating. Next, the resist film 13 is developed to form an opening 13a in the exposure light irradiation portion of the resist film 13. Then, the protective film material layer 12 is etched by etching using the resist film 13 as a mask. As a result, the pad opening 14 is formed in the protective film material layer 12.
Is formed, the peripheral edge portion of the protective film material layer 12 is removed, the peripheral edge contour of the protective film material layer 12 is adjusted to a circular shape, and the peripheral edge portion is formed on the peripheral edge portion by the pre-baking step shown in FIG. The small raised portion 12b is removed.

In the fifth step, the resist film 1 is selected by appropriately selecting the developing solution for the resist film 13.
The developing process 3 and the etching of the protective film material layer 12 may be performed in the same step. As the developer as described above, T
MAH (Tetramethyl ammonium hydroxide) can be used. Alternatively, the resist film before exposure may be used as a mask to etch the peripheral portion of the protective film material layer 12 using a rinse solution that dissolves the developer or other protective film material.

Next, in the sixth step shown in FIG. 1 (6),
After removing the resist film 13, the protective film material layer 12 is baked. As a result, the protective film 15 made of polyimide obtained by curing the protective film material layer 12 is formed.

In the above embodiment, the case where the resist film 13 is made of a positive type resist has been described. However, a negative type resist may be used as the resist film 13, and in this case, the pattern exposure is performed so that the exposure light is irradiated to a portion other than the portion forming the opening 13a.

[0017]

As described above, according to the method of forming a protective film of the present invention, the pre-baking of the protective film material layer is performed after removing the protrusions formed on the peripheral portion of the protective film material layer by spin coating. By performing the above, it is possible to prevent a large raised portion from remaining in the peripheral portion of the protective film forming material layer after the prebaking, and then to etch the protective film material layer using the resist film from which the peripheral portion has been removed as a mask. As a result, it becomes possible to form a protective film having a flat surface by removing small swells formed on the peripheral portion of the protective film material layer by the prebaking. Therefore, in the subsequent BGR process, the entire surface of the wafer on which the protective film is formed can be uniformly pressed, the in-plane uniformity of the wafer thickness can be ensured, and the chipping of the wafer can be prevented. .

[Brief description of the drawings]

FIG. 1 is a sectional process drawing showing an example of a method for forming a protective film of the present invention.

FIG. 2 is a sectional process diagram showing a conventional example.

[Explanation of symbols]

 11 Wafer 12 Protective Film Material Layer 13 Resist Film 15 Protective Film

Claims (1)

[Claims] 1. A first step of forming a protective film material layer on the entire surface of a wafer by spin coating, a second step of removing a peripheral portion of the protective film material layer, and a prebaking of the protective film material layer. A third step of removing the solvent in the protective film material layer; and a step of forming a resist film on the wafer in a state of covering the protective film material layer and exposing at least a peripheral portion of the protective film. A fourth step of removing the peripheral edge portion of the resist film above, a fifth step of etching away the peripheral edge portion of the protective film material layer by etching using the resist film as a mask, and a baking of the protective film material layer A sixth step of forming a protective film formed by curing, the method for forming a protective film.