JPH02102567A - Manufacture of electronic device - Google Patents

Abstract

PURPOSE:To prevent the cracking and blistering by a method wherein a vacuum chamber is evacuated as an electronic device is kept in it so as to enable a vapor component contained in organic material to be evacuated, the vapor component adsorbed in a substrate or a lead frame is removed, a protective film of inorganic material is formed, and the electronic device is sealed up with organic resin. CONSTITUTION:After an electronic device has been wire-bonded 39, the whole device is kept in a vacuum chamber to enable the volatile component contained in organic material to be evacuated, and the organic material attached to the substrate or lead frames 35 and 35' due to the evaporation of the volatile organic component is removed through a plasma ashing method for instance. Protective films 27 and 27' are formed on the surface of the device cleaned and improved in adhesion, and then the device is sealed up through a plastic molding 41 treatment. By this setup, the cracking and blistering can be prevented.

Description

Detailed Description of the Invention "Industrial Application Field" This invention relates to the wire bonding of electronic devices, in which electronic components such as semiconductor devices are fixed onto a substrate or lead frame using an organic substance, and then the entire electronic component is bonded in a vacuum container. By holding the vaporized organic components in the organic material, the vaporized components in the organic matter are degassed, and by removing the organic matter attached to the substrate or the gooey of the vaporized organic component by plasma ashing, the protective film or organic matter that should originally adhere to them is removed. This is intended to improve adhesion with resin.

By improving the adhesion between the goo and the protective film that adheres to it, cracks and blisters (a phenomenon in which the molding agent on the back side of the die swells due to the vaporization of water near the goo due to temperature rise during soldering) It is intended to prevent the occurrence of cancer.

"Prior Art" Previously, the present inventor has filed a patent application (Semiconductor device manufacturing method, Patent Application No. 106452 of 1981, June 14, 1988)
(application filed in Japan) is known.

However, in the past, as shown in Fig. 5, the lead frames (35), (35') and especially the die (35') to which the IC chip is attached are made of metal such as copper or 4270I, and the surface ( On the back side) there is grudge paste (24) and the protruding part (24").

And when die attaching electronic parts (24), 10
The IC chip was fixed on the Gui (35°) by heat treatment at 0 to 200°C and pressure treatment.

However, the unnecessary organic gas (24") in the organic substance such as silver paste for die attach is degassed and adheres to the substrate or lead frame. Therefore, immediately after this, the organic resin mold (41) When the treatment is carried out, adsorbates and lower oxides li! (32), which are extremely easy to peel off, remain between the molding agent and the copper or 4270I.

``Conventional drawbacks'' For this reason, as shown in Figure 4, plastic mold packages generally have water, etc. that reduce reliability, which collects on the back side of the die of the lead frame. (dip into molten solder for 10 seconds)
At this time, the molding agent rapidly vaporizes, resulting in stress that causes the molding agent to expand. Therefore, goui (35″) and molding agent (41″)
If the adhesion between them is poor, cracks (33) (33') and voids (42) will be generated at the interface between them due to thermal strain.

Up to now, electronic components (hereinafter also referred to as chips) have been fixed on a die (35') of a metal lead frame or a substrate on which leads are formed on an insulating substrate. A fixing material (24) containing an organic substance such as an epoxy-based organic resin or a silver paste mixed with silver for this fixing material;
(24") was used. When fixing electronic components onto a board or frame using this adhesive, the organic matter that was initially in a molten state is solidified through a chemical reaction or thermochemical reaction. This is an inexpensive material. And it is extremely excellent for mass production.However, this organic matter fixing material (24), (
24") is at room temperature in the atmosphere or heated (100~
300'C), this fixed organic vaporized component remains. Since this residual material gradually vaporizes and adsorbs onto the surface of the substrate or die, it also impairs the adhesion with the protective film or molding resin that will be formed later.

``Structure of the Invention'' The present invention is directed to reducing reliability in electronic devices such as conventional DIP or flat-back molded semiconductor integrated circuits or hybrid ICs in which a plurality of electronic components are fixed on a substrate. This was done to prevent it. For electronic devices fixed with silver paste or the like, by applying a higher vacuum, the degassed organic substances will be adsorbed onto these substrates or metal lead frames. However, in the present invention, such adsorbed organic substances are removed by plasma ashing treatment using N20.0□ or a mixed gas of oxygen and argon, and more preferably, moisture-proofing is performed between the mold resin and the metal, which easily absorb moisture. It is characterized by forming a protective film of an inorganic material such as silicon nitride.

The carbon concentration at the interface between the lead frame and the protective film is 2
X 10zocm-' or less, preferably 7 XIO"cm
-3 or less is intended to remove carbon organic matter and improve adhesion.

For this reason, by holding the electronic device in a vacuum container that is evacuated with a turbo molecular pump, it is degassed and
This also prevents oil mist from flowing back from the rotary pump during exhaust processing, achieving high rotation performance.

Furthermore, if necessary, all these surfaces, including this metal surface, are then treated in the same reactor without external heating at the same time, preferably at room temperature (there is some self-heating due to the plasma), using a plasma vapor phase method. It is characterized by being coated with a protective film such as silicon nitride, and then sealed by plastic molding.

FIG. 1 shows a longitudinal sectional view of a plastic DIP (dual in-line package) or flat back package constructed according to the present invention.

In the drawing, a chip (28) is attached to a die (35') of a lead frame with a silver paste (24) containing an organic substance or the like. Unwanted organic matter to be fixed when attaching this chip protrudes around the side as (24"). Between the chip (28), the aluminum pad (38) of this chip, and the stem (35). Between,
A wire bond of gold wire (39) is made.

The present invention degasses unnecessary gas components in the organic substances (24) and (24') from the surface of the chip (28), the surface of the pad (38), the surface of the wire (39), and the back surface of the die (35'). However, by performing plasma ashing in an atmosphere containing oxide gas, they are oxidized and transformed into carbon dioxide gas and water, which are vaporized and removed. . Thereafter, remaining oxides adsorbed on this surface, such as lower oxides, carbon dioxide gas, water, etc., are degassed by plasma ashing with argon, nitrogen, or a gas obtained by adding hydrogen to these. Furthermore, protective films such as silicon nitride (27), (27°), (27°'), (2
7"").

FIG. 2 shows an overview of the device of the invention.

A plurality of substrates having a structure in which a chip is bonded to a frame and a plurality of base bodies (2) in which a plurality of such substrates are assembled (hereinafter, the substrates and the base bodies are collectively referred to as the base body) are provided. By the plasma processing method, unnecessary semi-fixed organic substances are removed by plasma ashing using oxide gas, and further by plasma cleaning using lower oxides such as argon, nitrogen, or a gas to which these and hydrogen are added. Using disilane (C3iJs) and nitrogen (N2) in the same reactor or in a connected multi-chamber system, by switching the reactive gas in the same reactor while preventing them from coming into contact with the atmosphere and adsorbing water, etc.
A silicon nitride film is coated by plasma CVD.

In Figure 2, reaction system (6), doping system (5)
have.

The reaction system includes a vacuum container (hereinafter also referred to as reaction chamber) (1), a preliminary chamber (7), and gate valves (9) and (9'). The reaction chamber (1) has a supply hood (13) inside.
, and the reactive gas from the inlet side (3) is passed through the hood (14
) is blown downward from the nozzle (13) and exhausted.

In FIG. 2, the reactive gas is supplied to the turbo molecular bong (20) in a 5×1 manner from the hood (13) to the inside of the frame-structured holder (40) and the inside surrounded by the hood (13'').
0-co~I x 10-'torr preferably l x 10-
By holding the sample at a temperature of 1.times.10@-8 torr for 5 to 30 minutes, unnecessary organic gases in the fixing agent in FIG. 1 were degassed into vacuum, and adsorption onto the substrate, frame, etc. was prevented.

The plasma ashing treatment method of the present invention uses oxygen (0□).

Nitrous oxide (NZO) is supplied from (19) and used to decompose and gasify organic matter into carbon dioxide gas and water and remove it.

The plasma cleaning treatment method of the present invention includes argon,
Inert gases such as neon, helium, krypton, etc. (1
5), hydrogen may be supplied from (18), and nitrogen or ammonia may be supplied from (16). However, argon is preferable because it has a large mass, is relatively inexpensive, and is a gas that easily turns into plasma.

Electronic equipment is placed in this vacuum, and plasma ashing processing is performed to degas unnecessary gaseous components in the organic matter, remove unnecessary organic components that have been inadvertently redeposited on the surface of the electronic equipment, and Thereafter, plasma cleaning for removing oxides and formation of a protective film of an inorganic material were performed using a plasma processing apparatus as shown in FIG. 2 without exposing the electronic device to the outside air. Further, a plastic mold (41) was formed on this upper surface.

This protective film such as a silicon nitride film is prepared by introducing disilane, a silicide gas, from (17) and further ammonia or nitrogen from (16) into the plasma reactor (1) at room temperature, and then applying electromagnetic energy thereto. It was formed by a so-called plasma vapor phase method.

After forming a protective film for preventing deterioration such as a silicon nitride film to a thickness of 300 to 5,000 layers, generally about 1,000 layers, an organic resin such as epoxy (for example, 410B) Injected and sealed by molding method. Furthermore, the frame is bent at the lead portion (37) and the tie bar is cut. Furthermore, after pickling the lead portion, the lead was solder-plated.

Using this reaction vessel, a plasma reaction was carried out to remove unnecessary organic substances, semi-organic substances, and lower oxides and to form a protective film on the substrate or substrate (2). After plasma ashing treatment, plasma cleaning treatment or plasma CVD reaction, the valve (21) is passed from the nozzle (13') of the exhaust side hood (14'') through the exhaust port (4).

The turbomolecular pump (20) further leads to a rotary vacuum pump or dry vacuum pump (23).

Respective high frequency power supplies (10-1) and (10-2)
That is, the electromagnetic energy from (10) passes through the matching box (251), (25-2), that is, (25),
A pair of mesh electrodes (11) of the same size between the upper and lower sides, (
11'), as well as the respective electrodes (11), (11°)
supplied to The phase of electromagnetic energy is 180'±30
or within 0°±30° controlled by the phase adjuster (26). Power supply (10-1), (10-2)
The other end is grounded. There is also a holder with a surrounding frame structure (
40) is a ground level (22) if it is a conductor, or it may be an insulator.

The reactive gas is excited by high frequency energy supplied by a pair of electrodes (11) and (12).

In addition, in deaeration by vacuum treatment, plasma treatment, and plasma CVD methods in the same reactor, the object to be formed (2
) (hereinafter referred to as the base (2)) is placed in a frame-structured holder (40) disposed on a supporter (40') parallel to the direction of the electric field between the pair of electrodes, and furthermore, either electrode (11). ,
It is also spaced apart from (12). The plurality of base bodies (2) are arranged at a constant interval (2 to 13 cm, for example 6 cm) or approximately at a constant interval from each other. This large number of substrates (2) is placed inside the sunlight in the plasma created by glow discharge.

The main part of this base body is shown in FIG. 3(C).

Figure 3 (8) shows the stem (35) in the base (2).

On a lead frame that integrates multiple dies (35") (
45), and a base (4) in which 5 to 25 electronic devices (29) to which semiconductor devices (28) are bonded are unitized.
5).

FIG. 3B shows one lead frame (substrate) in one lead frame (45) to which a plurality of semiconductor chips are bonded.

In the drawing, only the left side of the lead is shown for simplicity. This A-A
A vertical cross-sectional view at ' is shown in (29) of FIG. 3(C).

In FIG. 3(C), a lead frame (35), a die (35'), a semiconductor chip (2B), a metal wire (39)
Further, 5 to 300 substrates (45) made of the above are collected and integrated with a jig (44) to form the base body (2). This base body (2) corresponds to the base body (2) in FIG. Add 5 to 50 more sheets (7 sheets in the drawing)
In Figure 2, it is placed inside the positive column.

The method of degassing organic matter in the method of the present invention as shown in FIG. 2 is as follows:
Followed to hold at orr.

In the present invention, after this high vacuum degassing, the internal pressure of the reaction vessel is reduced to a medium vacuum of 5X10-'' to 5X10-' tor.
For example, oxygen plasma was generated at I x 10-' to I x 10-' torr, and plasma ashing was performed. Further, after that, plasma cleaning is performed by adding a reactive gas at the same pressure, and when forming a silicon nitride film as a protective film, a sufficiently dense insulating film can be formed without external heating.

An example of this process is shown below.

"Example 1" In the plasma processing apparatus and plasma CVD apparatus shown in FIG. 2, the doping system (5) uses disilane (SiJa), which is a silicide gas, from (17), and ammonia or nitrogen, which is a nitride gas, from (17). From (16), argon, which is a non-product gas for plasma processing, is added from (15), hydrogen from (18), oxygen or N! 0 is supplied from (19). They are controlled by a flow meter (8) and a valve (7).

For example, for mass production, the substrate temperature was set to room temperature (including self-heating by plasma) without any active external heating.

First, the reaction space (1) is I x 10-' ~ I x 10-'
torr for 5-15 minutes, then 5 x 10-8
N,0 was introduced into the torr, electromagnetic energy was applied, it turned into plasma, and the organic adsorbate on the surface of the substrate (2) was subjected to a plasma ashing process for 5 to 15 minutes. That is, for these oxide gases, the output of IK- at a frequency of 13.56 MHz is applied to a pair of electrodes (11), (11°) and a power source (10).
, and a matching box (25) to generate plasma. This removed the oil mist, unnecessary organic matter, moisture, and lower oxides adhering to the back side of the die, exposing a new metal surface and improving the adhesion of the film being formed. .

Furthermore, after this, the atmosphere was preferably replaced with argon, and then plasma treatment was performed. Hydrogen in this argon is 5~
It may be added in an amount of 30% by volume. Then, the adsorbed oxides were removed.

Next, a protective film is formed on the plasma-treated surface in the same reactor without exposing it to the atmosphere. That is, when forming a silicon nitride film, the reactive gas is, for example, 5i
zHa/Nz=115. For these reactive gases, IKW output was supplied to a pair of electrodes (11), (11') and (11') at a frequency of 13.56 MHz.

Thus, on average 200 to 2000 people (1000 ± 200
Film formation was carried out for about 10 minutes (average speed of 3 people/second).

The silicon nitride film had a dielectric strength voltage of 7×10”V/cm or more, and a specific resistance of 2×10”ΩcIll. The infrared absorption spectrum had an absorption peak of 5t-N bond at 864 cm-', and the refractive index was 2.0.

When kept in saline solution (95°C) in which 5χNaCl was dissolved, no deterioration was observed even after 20 hours. Therefore, it was possible to prove that the film can be used as a protective film for preventing deterioration of the present invention.

For electronic devices manufactured by the method of the present invention, 85°C
/85χ (relative temperature) for 1000 hours, and then soldering was performed at 260°C for 5 seconds. However, this mold did not develop any cracks or blisters.

Another 85°C/85! A reliability test was conducted under the following conditions: 300 pieces were left in the plastic mold to absorb water, and then heated at 260°C for 13 seconds.

Examples are shown in the table below.

■ Plasma ashing treatment (minutes) ■ Plasma cleaning treatment (15 minutes) Crank Defective products with internal cracks/parameter As a result, after plasma ashing treatment, plasma cleaning treatment, and protective film formation, there were 0 defective products out of 100. , all were good products (Sob 1 to 5). In addition, the number of defective products in the plasma ashing process and protective film formation process was 3/100, which was extremely low (Nα6 to 10). However, when the quality was the same as a normal commercially available product without plasma ashing treatment and without a protective film, 20 out of 20 products were defective (No. 15). Furthermore, even with the protective film, some defective products occurred without ashing treatment (Nos. 11 to 12).

Furthermore, when plasma ashing and cleaning were performed without a protective film, there was only one defect (k13).

FIG. 4 shows the following steps to confirm the cause of the experimental results of the present invention.
The relationship between the distribution in the depth direction and the ion intensity was measured and evaluated using SIMS (secondary ion mass spectrometer).

Figure 4(A) shows plasma ashing, plasma cleaning, and formation of a silicon nitride film as a protective film.
Corresponds to Nα5 in Table 1. FIG. 4(B) shows that neither plasma ashing nor plasma cleaning was performed, and a silicon nitride film was formed to reduce the Nα12 in Table 1.
corresponds to FIG. 4(C) shows an area (55
) indicates a region where silicon nitride is formed, which tends to have a thicker depth distribution. The area (57) and interface (56) of the 4270-I lead frame are also shown. This distribution in the depth direction is similar to that of the silicon nitride film (27”) in Figure 1.
This corresponds to the depth direction of the (59) direction. In FIG. 4, the vertical axis is a logarithmic scale indicating ion intensity.

Further, (50) indicates the carbon concentration, and indicates the carbon concentration in silicon nitride (50-2), the carbon concentration at the interface (50-1), and the carbon concentration in the lead frame (50-3). The silicon concentration distribution is shown by the curve (51), and the nitrogen concentration distribution is shown by the curve (51).
52), and the concentration of oxygen is shown by the curve (53).

Corresponding to the inside of the film, interface, and lead frame (53-1)
.

(53-2) and (53-3).

If plasma ashing is not performed, as shown in Figure 4 (B), carbon (50) is abundant at the interface (50-1), and its concentration varies from sample to sample, but it is 3 to 20 x 10" cm.
-3, which is extremely high density. Furthermore, as a result, the carbon concentration in silicon nitride is relatively high (50-2).

The deposited film is silicon nitride (7).

This can be seen from (52).

In addition, if plasma ashing is performed but a film is formed without plasma ashing, oxygen (53-2) remains at the interface (56) as shown in Figure 4 (C), and its concentration is 3 to 10XIO"cm. -'. Furthermore, as a result, a large amount of oxygen is mixed into the film (53-1)
. For this reason, the formed film contains a large amount of oxygen even though it is intended to be silicon nitride, and it is presumed that it is actually oxynitride.

Even in this case, carbon is present at the interface (50-1) and in the film (50-1).
2) both decrease, and the effect of plasma ashing is sufficient.

This peak value (50-1) varied depending on the sample, but was less than 2XIO"cn+-', and was a low concentration of 1 to 7X10"cn/cts3 for boat fishing. This is indirect proof that no organic matter remains or substantially does not remain at the interface.

Moreover, FIG. 4(A) shows the result of plasma ashing and plasma cleaning according to the present invention.

Then, the carbon concentration is also at the interface (50-1) and in the film (50-2).
It was sufficiently small, less than 2XIO"cm-', preferably less than 7XIO"cm-'. Similarly, the oxygen concentration was less than 2 x 1020 Ke/c-3 (53-2). Furthermore, plasma cleaning was performed to remove adsorbed oxygen, so that the silicon nitride film (53-2)
In this case, we were able to reduce the concentration sufficiently.

As a result, it was found that the deposited film was silicon nitride, which was the basis for expecting good data on other reliability properties, such as sodium resistance.

From these SIMS data, it was found that the oxide gas plasma ashing process of the present invention is extremely effective when an organic material such as epoxy is used as the die attach agent. The results are clear from Table 1.

Generally, the surface of an aluminum pad has poor adhesion to the molding material. However, when a protective film is formed on this aluminum pad (Fig. 1 (3B)) as in the present invention, the adhesion here is improved, and in addition, the silicon nitride film has a blocking effect (mask effect) against water and chlorine. big. Therefore, in electronic devices (for example, semiconductor integrated circuits) having the structure of the present invention, PCT (Pressure Cutcher Test)
Even after 20 hours at 2atoa+ and 120°C, no defects were observed, and the conventional IC chip
The defective rate used to be ~100 feet, but it has now become possible to lower that defective rate to 5 to 10 feet.

In the present invention, the material is kept under a high vacuum, and in the plasma ashing process, not only electric energy but also light energy with ultraviolet light of 300 nm or less is used in combination with a photo cleaning method for removing organic substances. That is valid.

"Effects" In the present invention, since the plasma ashing treatment using oxide gas and the subsequent plasma cleaning treatment are performed at room temperature, the organic resin used when attaching the chip to the die is not heated and deteriorated. It also requires no electricity or time for heating, and is highly productive. In addition, since adsorbed organic substances and lower oxides were removed from the back surface of the die, it was possible to improve the adhesion of the silicon nitride film or the organic resin used as the molding agent to the lead frame. Further, when a protective film is formed, there is no problem that even after a long period of time, water and chlorine in the organic resin react with the metal of the die to form lower oxides, which deteriorate reliability. This also prevents moisture from entering from the back side. Furthermore, when mounting this electronic device on a PCB using a semiconductor, it was possible to prevent the molding material from swelling due to heating, as shown in the conventional example.

The protective film in the present invention was a silicon nitride film. However, this may be a single layer or multilayer film of a DLC (diamond-like carbon) film, a silicon oxide film, or other insulating films.

Further, in the present invention, the electronic component chip is shown as a semiconductor element, but it may also be a hybrid IC in which a metal conductor is provided on an insulating substrate and a resistor and a capacitor are fixed to these, and bonding can be performed only by wire bonding. Alternatively, flip chip bonding or solder bump bonding may be used.

In the present invention, there are cases where the chip is large in size and is molded without using a die. However, even in that case, it is necessary to provide a protective film covering all of the substrate or lead frame as a base and the chip. is valid.

Although the above description describes the case where a semiconductor chip is mounted on a lead frame, the present invention is not limited to a dual-in-line type lead frame, but is applicable to a flat pack type lead frame and other lead frames. Alternatively, similar effects can be expected even if the chip has similar functions such as a surface mount chip.

[Brief explanation of the drawing]

FIG. 1 shows a main part of a plastic package semiconductor device in longitudinal section after the moisture resistance test and soldering test of the present invention. FIG. 2 shows an outline of a plasma gas phase reactor for carrying out the method of the present invention. FIG. 3 shows an enlarged view of the base portion of the device of FIG. FIG. 4 shows measurement evaluation results using SIMS (secondary ion mass spectrometer). FIG. 5 shows a main part of a conventional plastic package in a vertical sectional view after being subjected to a moisture resistance test and a soldering test. Meat! Funeral map

Claims (1)

[Scope of Claims] 1. A method for manufacturing an electronic device comprising a step of fixing an electronic component onto a substrate or a lead frame using a fixing material containing an organic substance, wherein the electronic device is held in a vacuum container, and the electronic device is vacuum evacuated. a step of degassing gaseous components in the organic matter and removing the degassed gaseous adsorbed components adsorbed or attached to the substrate or lead frame; and a step of forming an inorganic material protective film. 1. A method for manufacturing an electronic device, comprising the step of encapsulating with an organic resin. 2. In claim 1, the step of removing the degassed gas-adsorbed components on the substrate or lead frame includes a step of subjecting the surface of the substrate or lead frame to plasma ashing using oxygen or oxide gas. A method for manufacturing an electronic device, comprising: 3. A method for manufacturing an electronic device according to claim 1, which comprises the step of removing organic matter adsorbed onto a substrate or lead frame by irradiating it with ultraviolet light. 4. A method for manufacturing an electronic device according to claim 1, characterized in that the pressure within the vacuum container is 5 x 10^-^3 to 1 x 10^-^8 torr. 5. In claim 1, the vacuum vessel evacuates the interior of the reaction vessel to remove gaseous components adsorbed or adhered to the substrate or lead frame, and also removes a protective film formed on the substrate or lead frame. A method for manufacturing an electronic device, characterized in that the electronic device is formed by a gas phase reaction method in the same vacuum container or a multi-chamber vacuum container without exposing it to outside air.