JPH02144942A - Manufacture of semiconductor device - Google Patents

Abstract

PURPOSE:To enhance reliability and a yield of a sealing operation by a method wherein a cap is bonded forcibly to a base via an adhesive in such a way that a pressure at the outside of a cavity is higher than a pressure at the inside of the cavity. CONSTITUTION:A peripheral edge of a base 1 is coated with an adhesive 9; after that, a semiconductor chip 4 is bonded via a bonding layer 5; a metallized layer 3 and input/output terminals of the semiconductor chip 4 are connected by using connecting wires 6. Then, the surface of the semiconductor chip 4 is coated with a chip-coating material 7. After that, a cap 10 is bonded via the adhesive 9; this assembly is inserted into a heating chamber 11; an inside atmosphere whose dew point inside the heating chamber is higher than that in an introduction tube 14 is evacuated by reducing a pressure; a temperature of the chamber 11 is raised. Then, the high-pressure air is blown from the introduction tube 14; although a pressure inside the heating chamber 11 is not limited especially, it is set at about 2 atmospheric pressures. In this state, the adhesive 9 is melted and softened; the adhesive 9 is bonded closely to the base and the cap 10.

Description

Detailed Description of the Invention [Industrial Application Field] The present invention relates to a technique that is particularly effective when applied to a semiconductor device manufacturing technique, such as a technique that is particularly effective when applied to a semiconductor device encapsulation technique. It is related to.

[Prior Art] One of the sealing techniques for semiconductor devices is to hermetically seal a semiconductor chip using a package made of alumina ceramic. The sealing agent is applied to the joint portion of the package, melted or softened using a belt furnace, and then the semiconductor device is taken out of the belt furnace and cooled to effect sealing.

By the way, in semiconductor devices manufactured using such sealing technology, malfunctions (soft errors) of the semiconductor memory are likely to occur due to alpha rays emitted from trace amounts of uranium U and thorium Th contained in the package constituent materials. In order to suppress the occurrence of soft errors, for example, semiconductor chips are coated with resin such as polyimide, and such chip-coated semiconductor devices cannot be sealed under normal pressure. It was. Regarding the sealing method of semiconductor devices without chip coating, for example, Japanese Patent Application Laid-Open No. 1323-1983
It is described in No. 47.

In addition, recent experiments have shown that alumina ceramic has a larger coefficient of thermal expansion than semiconductor chips, and when a semiconductor chip is bonded to the base or surface of a package, relatively large thermal stress occurs and the semiconductor chip is likely to crack. Although alumina ceramics are chip-coated, it is expected that soft errors will still occur at a high rate.

Therefore, a technology is being considered to suppress the occurrence of cracks and soft errors in semiconductor chips by using silicon carbide as the base material of the package and mullite ceramic, which emits low α-rays, as the cap material6.
In addition, as low thermal expansion materials are used as package constituent materials, additives such as lead titanate and beta eucryptite are mixed into the glass sealant, which increases the heat resistance of the sealant. Efforts have also been made to lower the expansion coefficient.

[Problems to be Solved by the Invention] However, since semiconductor devices coated with a chip have conventionally been sealed under normal pressure, the following problems have arisen.

In other words, when the heating atmosphere is raised to the temperature required for sealing (300°C to 450°C), gas is generated from the chip coating material and sealant coated on the surface of the semiconductor chip, and these gases cause , during sealing, the pressure inside the cavity becomes greater than the pressure inside the belt furnace. the result,
There is a problem in that the cap is pushed up and the sealant glass or resin is not sufficiently fused to the cap, resulting in poor sealing (leakage).

Additionally, if the cap is pushed up in a heated atmosphere under normal pressure, the pressure inside the cavity will dissipate.
Although the cavity is sealed in this state, if the pressure inside the cavity is reduced due to cooling after sealing, the pressure inside the cavity becomes negative with respect to the atmosphere. As a result, water vapor existing inside the cavity tends to condense, resulting in disadvantages such as deterioration of the electrical characteristics of the semiconductor integrated circuit. Further, when the pressure inside the cavity becomes negative with respect to the atmosphere, outside air easily enters the inside of the package from a sealing failure (leakage) location, which adversely affects the reliability of the semiconductor package.

Furthermore, since the external pressure of the cavity is normal pressure, bubbles generated in the sealing agent (for example, low melting point glass) easily expand and grow in the sealing agent due to heating during the sealing operation. If thermal stress occurs in the sealant during subsequent cooling, cracks will occur in the sealant, resulting in an inconvenience that the airtightness of the package will be impaired. This trend is particularly noticeable in recent semiconductor devices, which require restrictions on package outer diameter dimensions due to increased packaging density, reduced sealing width, and fine pitch lead frame arrangement. This tendency is also noticeable in the case where silicon carbide is used as the base material and mullite ceramic is used as the cap material. In such a semiconductor device, as described above, a sealant containing additives is used, but a sealant containing additives generates a large amount of gas.

The present invention was made in view of such problems, and an object of the present invention is to provide a semiconductor device with high sealing reliability and high yield.

The above and other objects and novel features of the present invention will become apparent from the description of this specification and the accompanying drawings.

[Means for Solving the Problems] Representative inventions disclosed in this application will be summarized as follows.

That is, when sealing the cap onto the base via the sealant, the pressure outside the cavity is higher than the pressure inside the cavity, and the cap is placed on the base using the pressure difference between the inside and outside of the cavity. is forcibly sealed.

[Function] According to the above means, since the cap is sealed in a state in which the cap is pressed against the base, the heated atmosphere rises to the temperature required for sealing, and the chip coating material and the chip coating material coated on the surface of the semiconductor chip are heated. Even if moisture etc. evaporates from the sealant and the pressure inside the cavity increases, the sealant is sufficiently fused to the base and cap, improving sealing adhesion. It will be possible to achieve this goal.

In addition, since the cap is sealed in pressure contact with the base, the internal pressure of the cavity does not dissipate to the outside, and even after sealing, the internal pressure of the cavity is maintained at an elevated pressure relative to the atmosphere. This prevents dew condensation from occurring inside the cavity, and also prevents outside air from entering the package from a sealing failure (leakage) location.

Furthermore, since the pressure outside the cavity is higher than the pressure inside the cavity for sealing, the growth of air bubbles in the sealant is suppressed, thereby suppressing the occurrence of cracks in the sealing material caused by air bubbles. It turns out.

[Example] Hereinafter, a method for manufacturing a semiconductor device according to the present invention will be explained.

FIG. 3 shows an example of a semiconductor device obtained by an embodiment of the method for manufacturing a semiconductor device according to the invention.

In the figure, reference numeral 1 represents a base made of silicon carbide. A metallized layer 3 is formed on the base 1 and is connected to the solder 2. Here, the lead 2 is made of an iron-based alloy or the like, while the metallized layer 3 is made of molybdenum MO or the like. A semiconductor chip 4 is bonded onto this base 1 via a bonding layer 5 made of a resin such as silver paste. Here, the semiconductor chip 5 is a semiconductor element in which a logic circuit, a memory circuit, etc. are formed, and a specific example of the element is MO8IC.

Further, the semiconductor chip 4 and the metallized layer 3 are connected by a connector wire 6.

Further, the upper surface of the semiconductor chip 4 is coated with a chip coating material 7 made of resin such as polyimide. Furthermore, a cap 10 made of mullite ceramic is bonded to the base 1 via a sealing agent (for example, low melting point glass) 9 so that a cavity 8 is formed inside.

Next, an embodiment of a method for manufacturing a semiconductor device configured as described above, that is, a method for manufacturing a semiconductor device according to the present invention will be described with reference to FIGS. 1 and 2.

First, after applying the sealant 9 to the periphery of the base 1, the semiconductor chip 4 is bonded via the bonding layer 5, and the metallized layer 3 attached to the base 1 in advance and the input/output terminals of the semiconductor chip 4 ( (electrode) by a connector wire 6 (wire bonding).

Next, the surface of the semiconductor chip 4 is coated with a chip coating material 7. Thereafter, the semiconductor device is inserted into the heating chamber 11, and the cap 10 is sealed to the base 1.

That is, to explain the sealing process in detail, after inserting the semiconductor device into the heating chamber 11, first, the indoor atmosphere with a high dew point in the heating chamber is depressurized through the introduction pipe 14 shown in FIG. 1(B). Exhaust by. Along with that,
0 to raise the temperature of the chamber 11 to 350°C
Next, while the temperature of the chamber 11 is raised to 370° C., high pressure air with a low dew point is introduced through the introduction pipe 14 shown in FIG. 1(B) to return the inside of the furnace to normal pressure.

Next, high pressure air is blown into the heating chamber 11 through the introduction pipe 14 shown in FIG. 1(B) to bring the pressure inside the heating chamber 11 to about 2 atmospheres, although this is not particularly limited. This state is left for about 25 minutes to melt or soften the sealant 9. Although the pressure is not particularly limited, it is approximately 2.5 atm. This melting or softening of the sealant 9 causes the sealant 9 to melt into the base and cap 1.
0, which will be in close contact with the heating chamber 11.
The temperature in the heating chamber 11 is raised to 450° C., and high-pressure air is blown into the heating chamber 11 through the introduction pipe 14 to bring the pressure inside the heating chamber 11 to about 2.5 atmospheres, although this is not particularly limited. The product is left in this state for about 40 minutes to sufficiently wet the sealed portions of the base 1 and cap 10, and then the temperature of the heating chamber 11 is lowered and left to stand for about 20 minutes.

After the sealing is completed, the semiconductor device is taken out of the heating chamber 11 as shown in FIG. 1(C).

FIG. 2 shows the above flow explanatory diagram.

According to the manufacturing method of the above embodiment, the following effects can be obtained.

That is, according to the above manufacturing method, the cap 10 is attached to the base 1.
Since it is sealed in a pressure-welded state, the heated atmosphere rises to the temperature required for sealing.

Gas is generated from the chip coating material 7 and the sealing agent 9 coated on the surface of the semiconductor chip 4, and the cavity 8 is
Even if the internal pressure increases, the sealing adhesion is improved by the effect that the sealing agent 9 is sufficiently fused.

Further, according to the above manufacturing method, the cap 10 is attached to the base 1.
Since the cavity 8 is sealed in a pressurized state, the internal pressure of the cavity 8 is maintained at an elevated pressure with respect to the atmosphere after sealing, which suppresses dew condensation inside the cavity 8 and prevents the sealing. This will prevent outside air from entering the inside of the package from a leakage location.

Furthermore, since sealing is performed with the external pressure of the cavity 8 higher than the internal pressure of the cavity 8, the growth of the air bubbles 12 in the sealant 9 is suppressed, resulting in the sealing induced by the air bubbles 12. This will suppress the occurrence of cracks in the agent 9.

That is, this can be explained as follows using FIGS. 4(A) and 4(B).

Of these, FIG. 4(A) shows a cross-sectional view of the vicinity of the sealing agent 9 of a semiconductor device sealed at normal pressure.

When the semiconductor device is sealed at normal pressure in this way, the air bubbles 12 in the sealant easily expand (grow) in the sealant 9 due to heating during sealing, and when the semiconductor device is cooled. When thermal stress is generated in the sealant 9 during cooling, a crack 13 is generated in the sealant 9, and a crack 13 that penetrates from the inside of the cavity 8 to the outside of the cavity 8 is generated. As a result, the airtightness of the package will be lost.

On the other hand, FIG. 4(B) shows a cross-sectional view of the vicinity of the sealing agent 9 of the semiconductor device sealed under pressure. When pressure sealing is performed in this manner, expansion of the bubbles 12 in the sealant is suppressed. As a result, even if thermal stress occurs in the sealant 9 when the semiconductor device is cooled, the cracks 13 will be smaller than in the past, and therefore, the cracks 13 will be smaller from the inside of the cavity 8 to the outside of the cavity 8. The generation of cracks 13 is prevented.

Although the invention made by the present inventor has been specifically explained above based on Examples, it goes without saying that the present invention is not limited to the above Examples and can be modified in various ways without departing from the gist thereof. Nor.

For example, in the above embodiment, silicon carbide is used as the constituent material of the base 1, and mullite ceramic is used as the constituent material of the cap 10. Applicable.

[Effects of the Invention] The effects obtained by typical inventions disclosed in this application are briefly explained below.

That is, when sealing the cap onto the base via the sealant in a heated atmosphere so as to form a cavity inside, the pressure outside the cavity is higher than the pressure inside the cavity. Since the cap is forcibly sealed onto the base using the pressure difference between the inside and outside, the sealing adhesion and airtightness are improved, and even after sealing, the pressure inside the cavity is reduced to the atmosphere. On the other hand, since the pressure can be maintained at elevated pressure, the reliability and yield of semiconductor devices can be improved.

[Brief explanation of the drawing]

1A to 1C are process cross-sectional views of an embodiment of the method for manufacturing a semiconductor device according to the present invention, and FIG. 2 is a flow explanatory diagram showing an embodiment of the method for manufacturing a semiconductor device according to the present invention. 3 is a vertical cross-sectional view of a semiconductor device obtained by an embodiment of the method for manufacturing a semiconductor device according to the present invention; FIG. 4(A);
(B) is a comparative explanatory diagram of a semiconductor device obtained by the conventional method and a semiconductor device obtained by the method of the present example, of which FIG. FIG. 4B is a vertical cross-sectional view showing the vicinity of the sealing part in the semiconductor device obtained by the manufacturing method of the example. 1...Base, 4...Semiconductor chip, 8...
・Cavity, 9...Sealing agent, 10 cap.

Claims (1)

[Claims] 1. After coating the surface of the semiconductor chip bonded to the surface of the base with a chip coating material, the semiconductor chip is sealed on the base in a heated atmosphere so that a cavity is formed inside. When sealing the cap via the agent, the pressure outside the cavity is made higher than the pressure inside the cavity, and the cap is forcibly sealed onto the base using the pressure difference between the inside and outside of the cavity. A method for manufacturing a semiconductor device, characterized in that: 2. The method of manufacturing a semiconductor device according to claim 1, wherein the sealant is a low melting point glass.