JPS6142412B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for forming a buffing film on the surface of a semiconductor device.

Inorganic materials such as SiO ₂ , phosphosilicate glass, and Si ₃ N ₄ are generally used as passivation films for semiconductor devices and insulating layers for multilayer wiring. However, when a SiO ₂ film is formed on a semiconductor element using Al as a wiring material, cracks occur due to differences in thermal expansion coefficients, so the film thickness must be 1 μm or less.
On the other hand, phosphosilicate glass does not cause cracks even when the film thickness is 2 μm, but it has the drawback of high hygroscopicity. Si ₃ N ₄ has an intermediate coefficient of thermal expansion, but for any material, a high temperature of around 500°C is required to form a film, and cracks occur due to the difference in coefficient of thermal expansion with Al, so it is not thick. A passivation film cannot be formed.

In order to improve these drawbacks, heat-resistant polymer materials that can be formed into films at low temperatures and that absorb strain due to differences in thermal expansion coefficients have been used in recent years. In addition to the conventional passivation effect, that is, preventing electrical properties from becoming unstable due to alkali ions and moisture-proofing effects, this polymer material also prevents scratches that occur during bonding and is released from ceramics used for sealing. It is also expected to be effective in preventing malfunctions of semiconductors by absorbing alpha rays, and there is a demand for the formation of thick passivation films.

As a method for forming a resin film on a wafer on which semiconductor elements are formed, there are methods of applying a resin solution dissolved in a solvent by spin coating, spray coating, roller coating, dip coating, etc. In order to obtain a thick coating in one application, it is necessary to use a highly concentrated resin solution. in this case,
The surface tension of the resin solution causes bulges around the wafer to be coated, resulting in a thicker coating film.

This phenomenon will be explained below using a spin coating method as an example. As a heat-resistant polymer, Torenice for semiconductors (polyimide resin, manufactured by Toray Industries, Inc., resin content 17%)
Solvent: N・N'-dimethylacetamide, viscosity
Figure 1 shows the change in film thickness around the wafer when a wafer (1000 cps) was dropped onto the SiO ₂ surface of an 87 mm diameter wafer and spin-coated. In Figure 1, the rotation speed
In the case of 4000 rpm, the film thickness of the flat part 2 is 24 μm, and the width of the peripheral raised part 1 is 30 μm or less from the peripheral edge, but as the rotation speed is lowered to obtain a thicker film, the raised part gradually becomes larger. 400rpm
In this case, the film thickness is 10 μm, but the width of the raised portion is as large as approximately 7 mm.

Generally, after forming a passivation film,
A photoresist is applied on top of this, irradiated with light through a mask, and developed to remove the photoresist above the lead wire extraction area, and the bonding pad is exposed by etching the passivation film. A photolithography process is required. In this case, if there is a raised portion 1 of the passivation film, the adhesion of the mask will be poor, and a pattern cannot be formed on the raised portion, making it impossible to effectively remove semiconductor elements from the entire surface of the wafer.

Therefore, in order to reduce the raised portion 1 and make the film thickness uniform all the way to the wafer periphery, it is necessary to apply thin coating films over and over again at high speed rotation. For overcoating, the same process must be repeated many times, and each time the undercoat is heated to completely remove the solvent, or it is semi-cured or hardened and the solvent swells or redissolves the base coat. It is necessary to prevent this, which makes the process extremely complicated.

The present invention eliminates the above-mentioned drawbacks of the conventional method, and aims to provide a method that can form a uniform thick film with few bulges around the periphery and has simple processing steps.

This invention is a method in which a resin coating is formed on the surface of a wafer, and then a heat-resistant polymer film is laminated to form a thick film.

An embodiment of the present invention will be described below with reference to the drawings.

Example: A silicon wafer with a diameter of 87 mm on which a semiconductor element has been formed is placed on a spin coater and coated with trenise (as described above).
Approximately 1 ml of was added dropwise and rotated at 4000 rpm for 1 minute.
Then, in a nitrogen atmosphere at 100℃ for 15 minutes and
When the solvent was vaporized by stepwise heating at 200° C. for 5 minutes, a coating film having the thickness shown in FIG. 210 was formed. Next, a 12 μm film made by completely curing Trenise using a wet casting method was laminated on top of this coating at 100°C using a Hottrol laminator (HRL-24, manufactured by DuPont, USA). A film having the thickness shown in FIG. 11 was formed. Furthermore, this was heated at 200℃ in a nitrogen atmosphere.
The polyimide was completely cured by heating stepwise for 15 minutes and at 330° C. for 15 minutes to form a passivation film.

The thin coating film 10 formed by the spin coating method is
The wafer has a thick raised part 1 with a width of about 50 μm from the peripheral edge, but when a resin film is laminated on this with a hot roller, the raised part almost disappears and becomes flat, as shown at 11.

In the above embodiment, polyimide resin was spin-coated and a film made of the same polyimide resin was laminated thereon, but the resin to be applied and the film to be laminated may be of different materials.

In addition to polyimide resin, the resin to be applied includes polyamide-imide resin, epoxy resin,
Phenol resin, polycarbonate resin,
Heat-resistant polymers such as polybenzimidazole resins and polyparabanic acid resins are used, and mixtures of two or more of these may also be used.Films to be laminated include polyimide resins, polycarbonate resins, polyamideimide resins, polybenzene resins, etc. It may be a single film made of imidazole resin or polyoxadiazole resin, or a film in which a filler such as an anti-shrinkage agent or an α-ray absorber is mixed when the resin is cured.

The rotation speed varies depending on the type of resin and solvent, but in the case of the above-mentioned trenise, 2000 rpm or more is desirable.

The above-mentioned Trenice solution contains resin in the form of polyamic acid, and heating causes a dehydration reaction to form polyimide. Therefore, if the film is thick, it is difficult to volatilize and remove this water, and the residual water It has the disadvantage of causing hydrolysis and deterioration.
However, with this invention, it is possible to form a thin coating film that is easy to volatilize and remove moisture, and by laminating a film on top of it and curing it by heating at a high temperature, the moisture is completely volatilized and removed, preventing deterioration. A thin and thick film can be obtained.

In addition, Trenise shrinks by several percent when cured, but in this invention, semi-cured or fully cured films are laminated, so shrinkage is extremely small even during heating in the post-process, and distortion hardly occurs. do not.

Furthermore, when forming a coating film using the spin coating method, more than 80% of the dropped resin is blown off to the outside of the wafer and is wasted; however, in the method of this invention, most of the film thickness is occupied by the laminated film. Therefore, the amount of resin applied is small, and the amount of resin wasted during coating is extremely small, which is useful for resource saving and suitable for mass processing.

[Brief explanation of the drawing]

Fig. 1 shows the state of swelling around the wafer when a resin coating film is formed on the wafer by the conventional spin coating method, and Fig. 2 shows the coating film and film formed in an example of the present invention. This shows the state of the film when laminated. 1... Raised part, 2... Flat part, 10
...resin coating surface, 11...coating surface after lamination. Note that the same reference numerals in the figures indicate the same or corresponding parts.

Claims (1)

[Scope of Claims] 1. A method for forming a passivation film, which comprises forming a resin coating on the surface of a wafer on which semiconductor elements are formed, and laminating a resin film on the coating. 2. At least one heat-resistant polymer selected from polyimide resin, polyamideimide resin, epoxy resin, phenol resin, polycarbonate resin, polybenzimidazole resin, and polyparanic acid resin is used as the coating resin. ,
A patent for using a film made of at least one heat-resistant polymer selected from polyimide resin, polyamideimide resin, polycarbonate resin, polybenzimidazole resin, polyoxadiazole resin, and polyparabanic acid resin as the resin film. A method for forming a passivation film according to claim 1. 3. Claims 1 or 2, characterized in that a resin coating film is formed by any one of spin coating, spray coating, roller coating, or dip coating, and the resin film is compressed or thermocompressed using a roll laminator. A method for forming a passivation film as described in Section 3. 4 Apply a polyamic acid solution to the surface of the wafer, volatilize the solvent to form a coating film of polyimide resin or polyamideimide resin, and apply semi-cured or fully cured polyimide resin or polyamideimide resin on this coating film. 4. A method of forming a passivation film according to claim 1 or 3, which comprises laminating films made of resin and curing the film by heating.