JP2748610B2 - Semiconductor device - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a semiconductor device, particularly to a resin-sealed semiconductor device.

[Prior Art] With an increase in the integration degree of LSIs, the chip size is increased and the wirings are miniaturized. Along with these, internal stress caused by curing shrinkage and thermal strain of the sealing resin has become a problem. These internal stresses cause cracks between the semiconductor chip and the sealing resin or disconnection of the aluminum wiring. Attempts to lower the thermal expansion coefficient of the sealing resin as a method to alleviate these stresses (lower stress)
And the use of polyimide resin as a protective film on a chip have been studied (Nikkei Micro Devices, May 1988
Monthly, p.42-47).

However, in the latter case, since the adhesion between the sealing resin and the polyimide resin is not sufficient, there is a problem that after the solder immersion step, the sealing resin is cracked by the influence of moisture absorbed and the reliability is reduced. Was.

[Problems to be Solved by the Invention] The present invention has been made in view of the current state of the prior art, and has as its object to provide a polyimide-based protective film having excellent adhesion to a sealing resin, and to achieve a remarkable reliability. An object of the present invention is to provide an improved semiconductor device.

[Means for Solving the Problems] An object of the present invention is to provide a resin-encapsulated semiconductor device having a protective film made of a polyimide resin on a chip, wherein the surface of the polyimide protective film has an atmosphere containing water vapor. It is achieved by a semiconductor device characterized by being subjected to a discharge treatment inside.

As the resin-encapsulated semiconductor device in the present invention, a known device can be used. For example, a semiconductor chip formed by a known method on a semiconductor material such as silicon or gallium arsenide, a die pad made of 42 alloy or a copper alloy fixed to the lower portion of the chip via a silver paste or the like, A bonding pad portion provided on the upper peripheral surface of the chip, a lead frame made of iron, copper, or an alloy thereof, and a poling wire made of gold, aluminum, or the like connecting the bonding pad portion and the lead frame are provided. A semiconductor device having a configuration in which these are sealed with an epoxy resin or the like is used.

As the epoxy resin-based sealing resin, for example, mainly composed of novolak-based epoxy resin and silica particles,
Examples of the curing agent include those which are crosslinked using amines, triphenylphosphine, or the like. Of course, it is needless to say that various epoxy curing agents and curing catalysts that open the epoxy group upon crosslinking can be used. Due to this crosslinking, the sealing resin is post-cured.

A protective film made of a polyimide resin is formed on a semiconductor chip inside such a resin-sealed semiconductor device.

As the polyimide resin used for forming the protective film in the present invention, known resins can be used, for example, a tetracarboxylic acid and a diamine are selectively combined, and these are reacted in a polar solvent to obtain a polyimide precursor. After the varnish of the poimide precursor is applied on a semiconductor chip, a heat treatment is performed at a temperature in the range of, for example, 200 to 400 ° C., and the polyimide film is formed by dehydration condensation. Specifically, pyromellitic dianhydride and 4,
4'-diaminodiphenyl ether, pyromellitic acid and paraphenylenediamine, 3,3 ', 4,4'-benzophenonetetracarboxylic dianhydride and 4,4'-diaminodiphenyl ether, 3,3', 4,4'- Benzophenone tetracarboxylic dianhydride and paraphenylenediamine, 3,3 ', 4,
4'-biphenyltetracarboxylic dianhydride and 4,4'-diaminodiphenyl ether, 3,3 ', 4,4'-biphenyltetracarboxylic dianhydride and paraphenylenediamine,
Pyromellitic dianhydride with 4,4'-diaminodiphenyl ether and bis (3-aminopropyl) tetramethyldisiloxane, pyromellitic dianhydride with 4,4'-diaminodiphenyl ether and 3-carbonamide
Polyimide synthesized from 4,4'-diaminodiphenyl ether or the like is preferably used, but is not limited thereto.

As a processing method of the polyimide, for example, a method of applying a varnish of a polyimide precursor on a silicon wafer and developing the polyimide simultaneously with the development of the positive resist using the positive resist as a mask (for example, RADine-Hart. Et al., Br. Poly.
mJ3,222 (1971), using a negative resist as a mask and etching the polyimide with an organic alkali such as hydrazine after developing the negative resist (JP-A-53-49701)
And the like, and a method of imparting photosensitivity to the polyimide precursor to directly form a pattern (JP-A-54-145794, etc.).

In the present invention, the discharge treatment in an atmosphere containing water vapor is performed by exposing the substrate to be processed to a discharge that is started and applied by applying a high DC or AC voltage between the electrodes in an atmosphere containing water vapor. Processing.

The water vapor-containing atmosphere used in the present invention is not particularly limited as long as it contains water vapor in a gas atmosphere. Preferably, the gas atmosphere has a water vapor concentration of 1% by volume or more. More preferably, the water vapor concentration is 5 to 100% by volume.
Particularly preferred is 100% by volume steam.

The gas for diluting steam is not particularly limited, but non-polymerizable gas, for example, He, Ne, Ar,
N ₂ , H ₂ , CO, CO ₂ , air and the like are preferred. Above all, Ar, CO ₂
Is more preferable from the viewpoint of discharge initiation efficiency.

The pressure of the steam-containing atmosphere is not particularly limited, but may be 10 ^-3
Glow discharge treatment, which is likely to occur in a pressure range of Torr to 10 Torr, so-called low-temperature plasma treatment, is preferable in terms of treatment uniformity and treatment efficiency. More preferably 10 ^-1 Torr
It is in the range of ~ 2 Torr.

Processing intensity is power density of 50W min / m ² or more and 30000W min / m
² or less is preferable, and more preferably 500 W
² or more and 10000 W · min / m ² or less. Here, the power density of the discharge process is a value obtained by dividing the output by the width of the discharge portion (for example, in the case of a drum electrode, the axial direction) and the moving speed of the substrate.

Note that the apparatus, electrodes, and the like for the discharge treatment are not particularly limited, and known ones can be used.

[Effects of the Invention] Since the present invention is configured as described above, the adhesiveness of the polyimide-based protective film to the sealing resin can be significantly increased, and a semiconductor device with improved reliability can be obtained.

[Measurement of Physical Properties] Adhesion Strength with Sealing Resin The adhesion strength between the polyimide protective film and the sealing resin in the present invention was measured by the following method.

(1) Polyimide is coated on a silicon wafer to a thickness of 2 μm, and heat-treated up to 350 ° C. is placed on a 170 ° C. hot plate.

(2) A silicon rubber (2 mm thick) reinforced with glass fiber with a hole of 4 mmφ was placed on the sample obtained in (1), and a sealing resin (Novolac epoxy resin manufactured by Toray Industries, Inc.) was placed in the rubber. TH-7006) was embedded.

(3) Then, a 5 kg weight was placed on top of it and left as it was for 2 minutes.

(4) After cooling, peel off the silicone rubber, 4mmφ, thickness 2
A pad of a sealing resin having a thickness of mm was obtained. This was heat-treated at 170 ° C. for 5 hours to obtain a sample.

(5) Of the samples obtained in (4), a part was 121 ° C.
168 hours pressure cooker test at 2 atm (PCT test)
And used as evaluation samples.

(6) The sample was measured by a pulling-down method (Applied Physics 56, 925, 1987) using Orientec Tensilon.

Resin crack test The resin crack test in the present invention was performed by the following method.

(1) 2 polyimide layers on a 9mm x 9mm silicon chip
It is applied in a thickness of μm and heat-treated up to 350 ° C. is fixed on a 48-pin lead frame using silver paste, and heat-treated at 100 ° C. for 1 hour.

(2) Place this in a 16 mm x 16 mm mold at a mold temperature of 17
After transfer molding was performed under the conditions of 5 ° C., a molding time of 120 seconds, and a molding pressure of 20 kg / cm ² , post-curing was performed at 175 ° C. for 5 hours. As the sealing resin, TH-80 manufactured by Toray Industries, Inc.
03 was used.

(3) The sample thus obtained was subjected to a pressure cooker test at 121 ° C. and 2 atm for 72 hours to absorb moisture, and used as an evaluation sample.

(4) This sample was immersed in a 260 ° C. solder bath for 5 seconds.
The occurrence of cracks in the resin was examined.

[Examples] Next, the present invention will be specifically described using examples, but the present invention is not limited thereto.

Example 1 Eight lines and spaces on a silicon wafer
A 5,000-Å silicon nitride film was formed by a plasma method, and a polyimide precursor varnish (“Semico Fine” SP-510 manufactured by Toray Industries, Inc.) was heat-treated. It was applied so as to have a thickness of 2 μm. Then, at 80 ° C, 200 ° C, 300 ° C and 350 ° C, 3
Heat treatment was performed every 0 minutes.

Next, using a discharge treatment apparatus of the internal electrode system having a counter electrode consisting of a drum-shaped electrode and a plurality of rod-shaped electrodes, and sets the sample to the drum electrode, was evacuated to 0.001 Torr, CO ₂ as the ambient gas 0.2 Torr, and steam was introduced up to a pressure of 0.25 Torr. Then the discharge intensity
The polyimide surface of the sample was treated under the conditions of 800 W · min / m ² .

When the adhesion between the polyimide and the sealing resin was measured, the adhesion before the PCT test was 3.0 kg / mm ² , and the adhesion after the PCT was 2.7 kg / mm ² .

Further, this sample was cut into a size of 9 mm × 9 mm, and this chip was packaged in a 16 mm × 16 mm QFP package using TH-7006 manufactured by Toray Co., Ltd. as a sealing resin. After that, resin sealing was performed under post-curing conditions at 170 ° C. for 5 hours.

The test specimen thus obtained was subjected to a thermal shock test of 300 cycles at −65 ° C. and 150 ° C. for 30 minutes each. When the peeling state of the inner chip and the sealing resin after the test was observed with an ultrasonic microscope, no peeling was observed. No cracks occurred in the resin crack test.

Example 2 1 mol of pyromellitic dianhydride, 0.96 mol of 2,2-bis (4-aminophenoxy) diphenylpropane and 1,
A sample was prepared under the same conditions as in Example 1 except that a varnish of a polyimide precursor consisting of 0.04 mol of 3-bis (3-aminopropyl) -tetramethyldisiloxane was used, and the adhesion to the sealing resin was examined. The adhesion strength before PCT was 3.3
kg / mm ² , and the adhesion strength after PCT was 3.0 kg / mm ² .

When the peeling state of the internal chip and the sealing resin after the thermal shock test was observed with an ultrasonic microscope, no peeling was observed, and no crack was observed in the resin crack test.

Example 3 1 mol of pyromellitic dianhydride, 2,2-bis (4-aminophenoxy) diphenylhexafluoropropane
A sample was prepared under the same conditions as in Example 1 except that a varnish of a polyimide precursor consisting of 96 mol and 0.04 mol of 1,3-bis (aminopropyl) dimethylsiloxane was used, and the adhesion to the sealing resin was examined. However, the adhesion strength before PCT is 3.6
kg / mm ² , and the adhesion strength after PCT was 3.3 kg / mm ² .

When the peeling state of the internal chip and the sealing resin after the thermal shock test was observed by an ultrasonic microscope, no peeling was observed, and no crack was observed in the resin crack test.

Comparative Example 1 A sample was prepared in the same manner as in Example 1 except that the polyimide surface was not subjected to a discharge treatment, and the adhesion to the sealing resin was examined. The adhesion before PCT was 1.5 kg / mm ² , The adhesion strength after PCT was 0.3 kg / mm ² .

In addition, when the peeling state of the internal chip and the sealing resin after the thermal shock test was observed in the same manner, peeling was observed, and cracks occurred in the resin crack test.

Comparative Example 2 A sample was set on the drum electrode using an internal electrode type discharge treatment apparatus having a counter electrode composed of a drum electrode and a plurality of rod electrodes, and the sample was evacuated to 0.01 Torr. Introduced to 0.2 Torr, discharge intensity 800 Wm
A sample was prepared under the same conditions as in Example 1 except that the test was performed at in / m ² , and the adhesion to the sealing resin was examined. The adhesion before PCT was 1.8 kg / mm ² , 0.6kg / mm ²
Met.

In addition, when the peeling state of the internal chip and the sealing resin after the thermal shock test was observed in the same manner, peeling was observed, and cracks occurred in the resin crack test.

Comparative Example 3 A sample was set on the drum electrode using an internal electrode type discharge treatment apparatus having a counter electrode composed of a drum electrode and a plurality of rod electrodes, and the sample was evacuated to 0.01 Torr. Introduced to 0.4 Torr, discharge intensity 800W
A sample was prepared under the same conditions as in Example 1 except that the test was performed under the conditions of min / m ² , and the adhesion to the sealing resin was examined.
Adhesion strength adhesion strength after 1.5kg / mm ^2, PCT before is 0.5 kg / mm
^{Was 2} .

In addition, as a result of observing the peeling state of the internal chip and the sealing resin after the thermal shock test in the same manner, peeling was observed, and cracks were also generated in the resin crack test.

Claims (1)

(57) [Claims] 1. A resin-encapsulated semiconductor device having a protective film made of a polyimide resin on a chip, wherein the surface of the polyimide protective film is subjected to a discharge treatment in an atmosphere containing water vapor. A semiconductor device characterized by the above-mentioned.