JPH1174419A - Gas-sealed semiconductor device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a highly reliable semiconductor device even at the tempera ture rise time, by eliminating drop of a breakdown voltage in a semiconductor device, wherein a semiconductor chip is contained in a package. SOLUTION: As the sealed gas in a package, the gas including the halogen element especially fluorine having the large insulation intensity is used, and the pressure reduced state is obtained. For example, when the sealing gas in the package is made to be SF6 and the pressure in sealing is made to be in the range of 0.015-0.08 MPa, the surface dielectric strength becomes larger than the device, wherein conventional N2 is sealed. Therefore, the improvement of dielectric strength and the shortening of the insulating dimenssion as the semiconductor device can be realized. Even at the upper limit temperature, for example, at 120 deg.C at an ordinary semiconductor, the pressure in the package does not become larger than the pressure of external atmosphere, and the expansion of the package does not occur.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a gas-filled semiconductor device in which a semiconductor chip or a semiconductor pellet is sealed in a package together with a gas.

[0002]

2. Description of the Related Art In general, a semiconductor chip or a semiconductor element is sealed in a package together with a gas in order to protect the semiconductor chip or a semiconductor element from a use environment. FIG.
It is a top view and a sectional view showing a chip arrangement situation of an IGBT module in which a GBT chip 1 and a diode chip 2 are sealed in a package.

The IGBT chip 1 and the diode chip 2 are sandwiched between the upper and lower emitter-side electrodes 3 and the collector-side electrodes 5 which are air-tightly brazed on both sides of the ceramic case 6 via the collector electrode 4. An inert gas such as nitrogen is sealed in the package. In addition to the IGBT chip 1 and the diode chip 2, some members supporting them are also enclosed, but are omitted in the drawing to avoid complication.

[0004] As a gas sealed in the package,
An inert gas such as nitrogen (hereinafter referred to as N ₂ ) is usually sealed at 1 atm (0.1013 MPa), or at a pressure of 1 atm or more so as to avoid a pressure of 1 atm or less even at a low temperature. As another example, for example, Japanese Unexamined Utility Model Publication No. 59-67939 discloses that a thyristor pellet is
An example of a semiconductor element sealed with sulfur hexafluoride (hereinafter referred to as SF ₆ ) at a pressure of (1.2 kg / cm ² ) or more is disclosed.

[0005]

However, a semiconductor element sealed at a pressure of 1 atm or more causes a convex deformation of the upper and lower electrodes, called swelling of a package, due to thermal expansion of gas when the temperature rises. May occur. Therefore, there is a possibility that the displacement of the members inside the element occurs, and the stability of the structure is impaired.

[0006] In view of the above problems, an object of the present invention is to provide a semiconductor element in which upper and lower electrodes do not deform into a convex shape when a temperature rises, and do not lower reliability and dielectric breakdown voltage.

[0007]

In order to avoid deformation of the electrode, it is conceivable to lower the pressure of the gas to be sealed. However, the edge breakdown voltage decreases almost linearly as the N ₂ pressure decreases, as shown in the pressure-dependent characteristic diagram of FIG. In particular, when foreign matter is present in an insulating portion along the surface of the chip or the structural insulator, the insulating strength is further reduced. FIG. 3 is a characteristic diagram showing the effect of the size of the foreign matter on the insulation strength. The dielectric strength gradually decreases as the size of the foreign matter increases.

In order to avoid such a decrease in dielectric breakdown voltage, the insulation distance of the breakdown voltage holding portion of the semiconductor element must be increased. From the viewpoint of discharge physics, N ₂ is a gas that does not produce negative ions, and it is more difficult to detect partial discharge than a gas that produces other negative ions in the phenomenon of partial discharge due to local insulation defects. Is not an advantageous gas. Therefore, if a gas having a high insulation strength is selected as the gas to be sealed, a decrease in the edge breakdown voltage can be avoided even in a reduced pressure state.

Therefore, in order to solve the above-mentioned problems, the present invention relates to a semiconductor device in which a semiconductor chip is housed in a package, wherein the sealing gas in the package is reduced under reduced pressure of a gas containing a halogen element having a large insulation strength, particularly a gas containing fluorine. I do. The insulating gas containing a halogen element, the relative dielectric strength for N ₂ shown in Table 1. When a gas having a high insulation strength is used as described above, the pressure inside the package can be reduced without lowering the breakdown voltage.

[0010]

[Table 1] In particular the filler gas in the package is assumed to be SF _6.

SF ₆ is extremely stable and does not decompose up to about 600 ° C. Further, even if an arc discharge occurs, carbon is not released unlike other halogenated carbon.
FIG. 4 is a characteristic diagram showing electric field dependence of effective ionization coefficients of SF ₆ , N ₂ and air. At N ₂ , the effective ionization coefficient that determines the dielectric strength rises from a very low electric field,
Breakdown occurs at about 90% of air of the same molecular density. In contrast, in SF ₆ , the effective ionization coefficient does not rise to a high electric field.

Further, the sealing pressure in the package is reduced to 0.01.
It shall be in the range of 5 to 0.08 MPa. In FIG.
The pressure dependence of the breakdown voltage of SF ₆ was also shown. The ideal breakdown voltage changes according to the gas pressure, and decreases substantially in proportion to the decrease in the gas pressure. SF ₆ has about three times the insulation strength at the same gas pressure as air or N ₂ , but is relatively strong at the time of pressure reduction,
At 15 MPa, the breakdown voltage is equivalent to that of N ₂ at 0.1013 MPa (1 atm).

[0013] Thus, if the filling pressure in the package with more than 0.015 MPa, so that the N ₂ equal to or higher than the breakdown voltage of the conventional one atmosphere is maintained. In addition, if the above-mentioned sealing pressure range, the upper limit temperature of a normal semiconductor,
For example, even at 120 ° C., the pressure in the package does not exceed the pressure of the outside air, and the package does not swell. However, the internal pressure that the package can withstand mechanical force is considered to be about 0.005 MPa.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention aims at stabilizing the internal structure at high temperatures and improving the dielectric strength of a gas-filled semiconductor device by making the type and pressure of the fill gas more appropriate. It is. The SF ₆ in the package of the IGBT module shown in FIG. 2, from 0.015 to 0.08
The pressure was sealed within the range of MPa, for example, 0.05 MPa.

In the IGBT module, the package did not swell even at a high temperature, and the dielectric breakdown voltage did not lower than that of the conventional N ₂ -filled module. As described in the previous section, SF ₆ has an insulation strength of about twice or more at the same gas pressure as that of air or N ₂ , so that it is 0.1013 MPa at 0.015 MPa.
The dielectric breakdown voltage is equivalent to N _{2 at} (1 atm).
Therefore, it course breakdown voltage in the semiconductor device encapsulating SF ₆ of 0.05MPa is not reduced, the tolerance is increased with respect to foreign matter on the surface, a highly reliable semiconductor device.

Further, it is possible to improve the withstand voltage of the semiconductor element and to reduce the insulation size. Further, SF ₆ sealed at a pressure of 0.05 MPa at 25 ° C. becomes 0.066 MPa at 120 ° C., and the reduced pressure state is maintained. When only the dielectric strength equivalent to 0.113 MPa (1 atm) of N ₂ is expected, the sealing pressure is 0.015 MPa.
It can be used down to MPa. At this gas pressure, the temperature at which the pressure is equal to or higher than the atmospheric pressure is 1500 ° C., which is far higher than the heat resistant temperature of the semiconductor chip and other structures. Therefore, in practical use, the gas pressure is such that the pressure does not exceed the atmospheric pressure depending on the temperature to be used, and an increase in insulating reliability can be realized at the same time.

The upper limit temperature of a normal semiconductor is, for example, 12
If the temperature is set to 0 ° C., the upper limit of the sealing pressure is 0.075 MPa (the sealing temperature is 25 ° C.) so that the pressure becomes 1 atm at that temperature.
). Further, assuming that the internal pressure withstands by the mechanical force of the package is about 0.005 MPa, a sealing pressure of about 0.08 MPa is possible. Other fluorine-containing gases other than SF ₆ having the same insulation strength as SF ₆ can improve the insulation performance by the same use. Among the substances mentioned in the preceding paragraph, there are those having a high boiling point, but if they are mixed with a gas having a low boiling point, for example, N ₂ , the boiling point can be lowered, so that they can be used.

As mentioned earlier, Japanese Utility Model Application Laid-Open No. 59-6793.
No. 9 discloses that SF ₆ is sealed in a package of a stud type semiconductor element. However, the example is coated omitted purpose for surface protection of semiconductor pellet, and, since the improved dielectric breakdown voltage higher pressures, about the pressure of the SF ₆ 0.
The region is limited to 12 MPa (1.2 kg / cm ² ) or more, and has a different purpose from the present invention, and the pressure range does not overlap at all.

Japanese Patent Application Laid-Open No. 3-190263 discloses that SF ₆ is sealed in a flat semiconductor device. Although the publication does not describe the pressure range at all, the claim states that the semiconductor substrate is SF _6.
There is a statement to contact with
It is considered to be a purpose of omitting the coating for protecting the surface as in the case of JP-A-39, and it is considered that the coating is directed to a high pressure range.

[0020]

As described above, according to the present invention, the sealing gas in the package is a gas containing a halogen element, particularly fluorine, having a large insulating strength, or a mixed gas containing the gas, and the pressure is reduced. In addition, a highly reliable semiconductor element can be provided without lowering the dielectric breakdown voltage. In particular, if the filling gas in the package is SF ₆ and the pressure of the filling gas is in the range of 0.015 to 0.08 MPa, the surface dielectric strength becomes larger than that of the conventional N ₂ filling, so that the insulation as a semiconductor device is increased. It is possible to improve the withstand voltage and reduce the insulation size.

[Brief description of the drawings]

FIG. 1 is a diagram showing the pressure dependence of insulation strength between SF ₆ and N ₂ .

FIGS. 2A and 2B are a plan view and a sectional view showing a chip arrangement state of the IGBT module.

FIG. 3 is a graph showing a relative dielectric breakdown voltage characteristic when a foreign substance is present;

FIG. 4 is an electric field dependent characteristic diagram of the ionization coefficient of SF ₆ , N ₂ and air.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 IGBT chip 2 Diode chip 3 Emitter side electrode plate 4 Collector electrode 5 Collector side electrode plate 6 Ceramic case

Claims (4)

[Claims] In a semiconductor device in which a semiconductor chip is housed in a package, a gas sealed in the package contains a gas containing a halogen element having a large insulating strength and is in a reduced pressure state. . 2. The gas-filled semiconductor device according to claim 1, wherein the fill gas in the package contains a gas containing fluorine. 3. The gas-filled semiconductor device according to claim 2, wherein the filling gas in the package is SF ₆ . 4. The pressure of a sealed gas in a package is set to 0.01.
The gas-filled semiconductor device according to claim 1, wherein the pressure is in a range of 5 to 0.08 MPa.