JP3151964B2 - Window opening method for resin film for semiconductor 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 resin film used as a flattening film between a protective film or an internal wiring layer on the surface of a semiconductor device, particularly an integrated circuit device, for opening windows for external connection terminals and interlayer connection. About the method.

[0002]

2. Description of the Related Art In semiconductor devices, an inorganic material such as silicon oxide or silicon nitride, which has a very high heat resistance, is usually used for its insulating film. Insulation film that does not come into direct contact with the semiconductor surface in the semiconductor device, such as a flattening film for leveling unevenness or steps on the wiring film of the integrated circuit device, utilizing the characteristics such as excellent characteristics of the semiconductor device. It is sometimes used as a protective film to cover the surface of a semiconductor device to block intrusion. In any case, it is necessary to provide a window in the resin film for interlayer connection inside the semiconductor device and connection to the outside. In addition, the present invention relates to a window opening method for such a resin film.

[0003] When the window is opened, as is well known, a completely thermoset resin is very chemically stable, so that etching with a chemical such as an inorganic insulating film is inappropriate and easy to perform dry etching. Therefore, after applying the resin film, it is solidified by heating, but it remains in a semi-cured or partially cured state where the resin is not completely cured yet, and this semi-cured resin is dissolved in a solvent suitable for it. Usually, after the window is opened in a pattern specified by the film, complete thermal curing is performed by heating again.

For example, in the case of a resin film of a polyimide resin, a liquid resin material having a considerably high viscosity is applied to the entire surface of a wafer for a semiconductor device by a spin coating method or the like. 200 after scattering
The resin is solidified and semi-cured by heating to about ° C. Next, a photoresist film is spin-coated on the resin film, and the photoresist film is exposed to a pattern for opening a window, prebaked, and then developed to remove an etching window. Opening the window for the resin film may be performed with an appropriate solvent using this photoresist film as a mask.However, when the photoresist film is a positive type, a basic developer for development thereof is suitable as a solvent for the polyimide resin. Opening etching can be performed on the resin film simultaneously with the development of the photoresist film. After that, after removing the photoresist film from the wafer surface, the resin is completely cured at a temperature of 300 ° C. or more to obtain a resin film with a window.

[0005]

However, in the above-described conventional method for forming a window in a resin film, when the window pattern is rectangular, the size and shape of the window are likely to be inaccurate, and cracks are likely to occur in the resin film. There's a problem. FIG. 2 (a) shows this state when the window 11 for the resin film 10 shown by a thick line is opened in a rectangular pattern specified by the window 21 of the photoresist 20 shown by a thin line, and the state after the resin is completely cured. It is shown by.
As shown in the figure, the size of the window 11 of the resin film 10 is considerably larger than that specified by the window 21 of the photoresist film 20 due to the side etching SE, and the contour of the pattern is gentle but irregular. Easy to be. Further, at the four corners of the window 11, which should be rectangular, a slightly convex portion is formed so as to be slanted inward, and a crack C extending outward is formed in the resin film 11 in this portion. Likely to happen.

In order to investigate these causes, the results of observing the state during and after the etching of the resin film 10 are shown in FIG. 2 (b) and FIG. 2 (c) by an enlarged view of the upper right corner of the window 11. Show. In the state of the etching shown in FIG. 2 (b), a knob-like portion B protruding inwardly tends to remain at the corner of the window 11 as shown in the figure, and it is necessary to perform a considerable over-etching to eliminate this as much as possible. Therefore, when the etching is completed as shown in FIG. 2 (c), the shape becomes gentle as a whole, but the side etching SE proceeds, the pattern of the window 11 becomes irregular, and a small crack C is generated at the corner. Thereafter, the photoresist film 20 is removed, and the resin film is heated.
During the complete hardening of 11, it tends to grow large as shown in FIG.

The inaccurate size and shape of the window opening are, of course, a problem particularly when a small connection window for a wiring film is opened in the resin film used as the above-mentioned flattening film, and the crack C is used as a protective film. This is particularly problematic in that the protective performance of the resin film at the angle is reduced. These problems are particularly likely to occur when a resin film is opened simultaneously with the development using a developing solution for a photoresist film as described above. SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned problems of the conventional method and to provide a method for opening a window in a resin film with an accurate size and shape as specified.

[0008]

According to the method of the present invention, when a resin film coated on a wafer surface is melted with an etchant in a semi-cured state as described above to form a square window,
Specify the thickness of the resin film for the square corners of the window pattern specified by the photoresist film for the etching mask.
The above object is achieved by providing a radius of curvature of 1.5 times or more, more preferably 2 times or more.

This method of the present invention is particularly advantageous when the resin film is a polyimide resin film and a window film is etched simultaneously with the development of a photoresist film for an etching mask with a basic developer. In this case, it is preferable to use an organic alkaline developer such as a tetramethylammonium hydroxide-based developer. Further, in order to enhance the window opening accuracy as much as possible, it is very advantageous to dissolve the photoresist film with a solvent suitable for it while the wafer is rotated after etching the resin film, and to quickly remove the photoresist film.

[0010]

In the present invention, attention is paid to the point that the conventional problem is caused by the fact that etching is delayed at a corner portion of a window when a window is formed in a resin film in a rectangular pattern, as can be seen from FIG. 2 (b). In the case of isotropic etching in which the square corners of the opening pattern specified by the photoresist film for the etching mask are rounded in advance and the resin is dissolved, the amount of side etching from the pattern specified by the photoresist film Focusing on the point where the film thickness differs in the film thickness direction, the radius of curvature of the corner rounding is set to 1.5 times or more that in relation to the film thickness of the resin film, so that the etching rate for the resin film is squared. Almost uniform over the entire circumference of the pattern.

Therefore, in the method of the present invention, since the etching of the resin film always proceeds in substantially the same shape as the specified pattern by the photoresist film, it is not necessary to correct the irregularity of the window shape by over-etching as in the prior art. In addition, the dimensional accuracy of the window can be improved while preventing the occurrence of the irregular shape of the window by reducing the amount of side etching in general. In addition, since there is no inwardly protruding portion over the entire periphery of the window contour, even after the resin film is completely cured, the occurrence of cracks as in the related art can be almost completely prevented.

[0012]

An embodiment of the present invention will be described below with reference to FIG. FIG. 1A shows a window of the resin film 10 corresponding to FIG.
11 is a top view, FIG. 1B is a partially enlarged cross-sectional view, and FIG.
3 is an enlarged top view of a corner of the window 11. FIG. Resin film of this embodiment
Reference numeral 10 denotes a polyimide resin film for a protective film covering the surface of the integrated circuit device, and its window 11 is used for connection pads for connection to the outside of the integrated circuit. FIG. 1 shows a photo for opening the window. The resist film 20 is shown by a thin line over the resin film 10.

As a liquid material of the polyimide resin for the resin film 10, a material having a viscosity of, for example, about 1000 CP is used, and is spin-coated to a thickness of, for example, 3 μm on the entire surface of the integrated circuit device wafer. First, the resin is semi-cured. In order to control the degree of semi-curing accurately, the wafer is placed on a hot plate heated to 150 to 200 ° C., and the applied resin is solidified and semi-cured to a thickness of, for example, 2 μm after the solvent is scattered while directly heating from the back surface. This step is usually completed in a short time of about 5 minutes.

In this embodiment, a positive type photoresist film 20 is used as in the prior art, and a window is etched in the resin film 10 with a basic developing solution for the positive type. Figure 1 for specifying the pattern of
4A, the four corners of the rectangular window 21 of the photoresist film 20 are rounded with a radius of curvature r. As described above, the radius of curvature r is set to 1.5 times or more, more desirably, twice or more the thickness of the resin film 10. In this embodiment, the radius of curvature r is 5 μm for the 2 μm thickness of the resin film 10. Is set. Since the window 11 of the resin film 10 is for a connection pad, a photoresist film 20 is spin-coated on the resin film 10 in a semi-cured state, and then several tens to 100 μm square having a radius of curvature r of 5 μm at four corners. Is exposed to a square pattern, and then subjected to a predetermined pre-bake process.

As a developing solution commonly used for developing the window 21 exposed to the photoresist film 20 and etching the window 11 for the resin film 10, an organic alkaline solution, for example, a tetramethylammonium hydroxide-based solution manufactured by Tokyo Ohka Chemical Co., Ltd. It is preferable to use an NMD-W type developer. In order to simultaneously proceed with the development of the photoresist film 20 and the etching of the resin film 10 with this developer, the wafer may be immersed in the developer as usual, but the wafer is loaded on a stationary turntable. It is preferable that an appropriate amount of the developer is dropped thereon, and after the development and etching are advanced within a short time of about one minute, the turntable is driven to immediately shake off the developer. By performing the so-called single-wafer processing on each wafer in this way, the accuracy of the size and shape of the window 11 of the resin film 10 can be significantly improved as compared with the conventional case.

FIGS. 1 (b) and 1 (c) show a state in which the opening of the window has been completed by a partially enlarged sectional view and a top view, respectively. An aluminum film 2 for connection pads is provided on the surface of the wafer 1 shown in FIG. 1 (b), and a window 11 is opened in the resin film 10 using the photoresist film 20 as a mask so as to expose the aluminum film 2. Opening etching for this purpose is performed by dissolving the resin film 10 with the same developer following the development of the window 21 of the photoresist film 20. However, since it is isotropic etching, side etching SE always occurs. This side-etched surface is a slope 11a as shown in FIG.
Has a lateral width b shown in FIG. 1 (c) in proportion to the film thickness t.
In the present invention, this is used for etching the corners of the window 11 and the radius of curvature r of the roundness provided at the corners of the window 21 of the photoresist film 20 is determined according to the width b, that is, the thickness t of the resin film 10. Set.

That is, if the corner of the window 21 of the photoresist film 20 is not rounded as in the prior art, the width b of the slope 11a becomes narrow and the etching is delayed. For example, by giving a radius of curvature r of twice or more, the width b can be made substantially equal to a portion other than a corner, and the side etching amount SE can be made substantially uniform over the entire circumference of the window 11. Therefore, no inwardly protruding portion B as shown in FIG. 2B is formed at the corner of the window 11 as shown in FIG. 1A, and it is necessary to perform over-etching to reduce such a portion. So that the side etching amount SE is reduced overall and the window 11
Can be etched with a smooth contour.

After the window opening step, the photoresist film 20 is removed from the wafer surface, and then the wafer is heated to completely cure the resin film 10. The removal of the photoresist film 20 may be performed by immersing the wafer in a removal solution for the photoresist film, for example, a mixed solution of isopropyl alcohol and acetone, as usual.
Since the resin film 10 in the semi-cured state is slightly dissolved by the removing liquid, it is necessary to shorten the removing time as much as possible in order to improve the accuracy of opening the window. For this reason, it is desirable that the wafer is loaded on a rotary table of a spin coater and the photoresist film 20 is washed away with a strong solvent such as acetone within a very short time of about 10 seconds while the wafer is being rotated. In order to completely cure the polyimide resin of the resin film 10, it is necessary to heat the wafer to 350 to 400 ° C. In this case, too, the use of a hot plate is advantageous in shortening the curing time. According to the method of the present invention, in the resin film 10 thus opened, the occurrence of cracks C as shown in FIG. 2A can be almost completely prevented.

[0019]

As described above, according to the method of the present invention, when a resin film coated on a wafer for a semiconductor device is opened in a rectangular shape in a semi-cured state of the resin, etching is likely to be delayed at corners of the rectangular shape. Focusing on the resin film for the etching mask, the corners of the window pattern specified by the photoresist film for the etching mask are rounded with a radius of curvature that is at least 1.5 times the thickness of the resin film, thereby (a) etching the resin film. The speed is made almost uniform over the entire circumference of the rectangular pattern to prevent irregularities in the window shape, and (b) the overall amount of side etching from the specified window pattern is reduced to improve the dimensional accuracy of the window (C) The window can be formed to have a concave profile with the window facing inward over the entire circumference, so that cracks can be almost completely prevented even after the resin is completely cured.

[Brief description of the drawings]

FIGS. 1A and 1B show an embodiment of a method for forming a window in a resin film according to the present invention. FIG. 1A is a top view of the resin film and its window, and FIG. (c) is an enlarged top view of the corner of the window.

FIG. 2 shows a resin film opened by a conventional method,
FIG. 3A is a top view of the resin film and the window after the resin is completely cured, and FIG. 3B is an enlarged top view of the corner of the window during window opening etching.
FIG. 4C is an enlarged top view of the corner of the window at the end of the window etching.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Semiconductor device wafer 10 Resin film 11 Resin film window 20 Photoresist film 21 Photoresist film window r Round radius of curvature of the corner of the photoresist film window SE Side etching amount t Resin film thickness

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) H01L 21/027 G03F 7/26 H01L 21/306 H01L 21/3205 H01L 21/60

Claims (3)

(57) [Claims] 1. A method of forming a rectangular window by dissolving a resin film coated on a wafer in which a chip of a semiconductor device is formed in an semi-cured state with an etchant, comprising the steps of: forming a photoresist film for an etching mask; A method for forming a window in a resin film for a semiconductor device, wherein a rectangular corner of a pattern for specifying a window is rounded with a radius of curvature of 1.5 times or more the thickness of the resin film. 2. The method according to claim 1, wherein the resin film is a polyimide resin film, and simultaneously with the development of the photoresist film, window etching is performed on the resin film by using a basic developer for the same as an etchant. A method for opening a window in a resin film for a semiconductor device, wherein the method is performed. 3. The semiconductor device according to claim 1, wherein the photoresist film is removed by dissolving with a solvent while rotating the wafer after the window etching of the resin film. Window for resin film