JPS6154249B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for forming a surface protective film of semiconductor elements such as transistors, diodes, integrated circuit ICs, large-scale integrated circuit LSIs, etc. using polyimide resin. The present invention relates to a method for forming a surface protective film using polyimide resin on the surface of a semiconductor element in a short time, which has good adhesion to the surface material of the semiconductor element and is difficult to peel off.

2. Description of the Related Art Semiconductor devices are sometimes used with their surfaces sealed with resin for purposes such as fixing the elements, protecting the elements from external atmosphere, and dissipating heat from the elements. Resins used for this purpose are physically robust, chemically stable, have high thermal conductivity, and
Furthermore, it is necessary to have characteristics such as good adhesion to the surface material of a semiconductor element such as silicon oxide.
Polyimide resin has these properties,
In addition, it is effective against alpha rays and is suitable for filling multilayer wiring and steps, so it is often used as a surface protection film for semiconductor devices.

It is well known that polyimide resin is a material with excellent heat and stress resistance made by the reaction of pyromellitic anhydride and aromatic diamine, and when using this material to form a protective film on the surface of a semiconductor device, The above two materials are diluted with a solvent such as dimethylacetaldehyde, applied to the surface of a semiconductor device, and heated to several hundred degrees Celsius to carry out a ring-opening polyaddition reaction.

However, if semiconductor devices are exposed to high temperatures, their characteristics may deteriorate due to diffusion of donors and acceptors, so it is absolutely necessary to process them at as low a temperature as possible. Since it is necessary to form a film with good adhesion and sufficient thickness, that is, several tens of microns thick, conventionally, in the first step,
A film with a thickness of about 0.3 microns is created, and a film with a thickness of 10 microns is created in the second and third steps, resulting in a film with a total thickness of about 20 microns.The total processing time is 350 yen.
It involved a series of steps that took from 400 minutes to 400 minutes, and was heated to a maximum of about 450°C under normal pressure. That is, the number of processing steps is large, and when continuous processing is performed, the required scale of processing equipment and floor area are large, and the processing time is long.

The present invention aims to reduce the number of processing steps and shorten processing time in a method for forming a surface protective film made of polyimide resin for a semiconductor element. By performing dielectric heating using microwave power in the heated air, it is possible to achieve good adhesion to the surface material of semiconductor devices in a single process in a much shorter processing time than conventional methods. The gist is to form a surface protection film made of polyimide resin with a necessary and sufficient thickness on the surface of a semiconductor element.

Focusing on the fact that the formation mechanism of polyimide resin film is a heavy addition reaction based on heating, if dielectric heating is performed at a frequency that resonates with the material molecules before the reaction, the reaction will occur because heat is generated at the part where the endothermic reaction occurs. As a result, the reaction can proceed in the shortest time. Furthermore, once the reaction is completed and the molecular weight of the material increases, the resonance point is deviated from the material, so the heat generation efficiency decreases, and it is considered advantageous that there is no need to unnecessarily heat the semiconductor device. Next, in order to obtain good adhesion, it is considered effective to promote the dispersion of the solvent, and since the dielectric heating method described above is thought to promote the movement of solvent molecules, it is also effective in promoting the dispersion of the solvent. it is conceivable that. Furthermore, it is considered effective to reduce the ambient air pressure to promote solvent dissipation.

Therefore, we tried dielectric heating of polyimide resin using various frequencies, and found that a frequency selected from the frequency range of 1 to 100 GHz was appropriate, and that the reaction completed in about 5 minutes in the case of a thickness of 20 microns. confirmed. On the other hand, when the atmospheric pressure of the surrounding atmosphere exceeded 0.1 Torr, plasma was generated and the desired purpose could not be achieved, but it was confirmed that the desired purpose could be achieved if the pressure was reduced to 0.1 Torr or less.
In other words, the pressure inside the reaction vessel (pressure of residual gas)
When it exceeds 0.1 Torr, a plasma atmosphere containing oxygen plasma is created, and the oxygen plasma combines with carbon in the polyimide film to generate carbon dioxide, carbon monoxide, and the like. This results in a decrease in the thickness of the polyimide film. At 0.1 Torr or less, no such oxygen plasma is generated.

Next, while maintaining the above frequency and ambient air pressure conditions, we repeated trials by varying the thickness of the polyimide resin film in the range of 1 to 20 microns to see if the adhesion to silicon oxide changed. was investigated, but no particular changes were observed. Therefore, in the method according to the present invention, there was no positive need to divide the process into a plurality of steps.

By integrating the conclusions of the individual trials described above, we manufactured the following surface protective film forming apparatus for semiconductor devices. In other words, an airtight container made of quartz glass tube was made as an airtight container that can withstand temperatures of several hundred degrees Celsius required for the polymerization reaction of polyimide resin and allows microwaves to pass through with a low absorption rate.
Add a vacuum device capable of reducing the pressure below, and use it at a frequency range of 1 to
It was placed in a microwave dielectric heating furnace using a 2.45 GHz microwave selected from the 100 GHz range.
Then, a mixture of pyromellitic anhydride diluted with dimethylacetaldehyde and an aromatic diamine is applied to a thickness of about 20 microns on the silicon oxide surface of the semiconductor device, and this is placed in the airtight device, and then the container is heated. The air pressure inside was reduced to 0.1 Torr, and then dielectric heating was applied using 2.45 GHz high frequency power to form a surface protective film for the semiconductor device.

In this case, the heating time was 5 minutes, and the maximum temperature in the airtight container was 250°C.

Further, after forming a surface protective film made of polyimide resin, the portion corresponding to the terminal was etched, and after completion of wire bonding, the adhesion of the protective film was examined under a microscope and found to be satisfactory.

As explained above, according to the present invention, it is not necessary to form three layers cumulatively as in the conventional technology, and it is possible to form a protective film of about 20 microns by forming just one layer. This reduces the processing steps to 1/3, reduces the required scale of processing equipment and floor area for continuous processing to about 1/3, and significantly shortens heat treatment time to about 1/80. I can do it. The heating temperature is also reduced to 250°C, which is effective in maintaining the characteristics of semiconductor devices. Moreover, the resulting adhesion is completely equivalent to that of the prior art.

The drawings show a part of a semiconductor device coated with a polyimide resin according to the present invention.

In the figure, 11 is, for example, an N type silicon substrate, 12 is an N+ type substrate contact region selectively provided on the N type semiconductor substrate 11, 13 is a field insulating film, 14 is an electrode wiring layer, and 15 is an electrode terminal pad. , 16 is a substrate contact pad, 17 is a surface insulating protective film made of a phosphorus silicate glass layer, etc.
18 is a polyimide resin film.

[Brief explanation of the drawing]

The drawing is a sectional view showing a part of a semiconductor device coated with a polyimide resin film according to the present invention. In the figure, 18 is a polyimide resin film.

Claims (1)

[Claims] 1. A step of applying a polyimide resin forming material to the surface of a semiconductor element, a step of placing the semiconductor element in an airtight container, a step of reducing the internal pressure of the container to 0.1 Torr or less, and a step of applying a polyimide resin forming material to the surface of the semiconductor element at 1 to 100 GHz.
A method for forming a surface protective film on a semiconductor device, comprising the step of applying dielectric heating using high-frequency power having a frequency selected from the range of .