JPS62239582A - Semiconductor device reinforced in its resistance to radiation - Google Patents

Abstract

PURPOSE:To reduce fixed positive charge accumulated in a gate oxide film and interfacial potential, and to improve a resistance to radiation, by forming a gate electrode in the manner such that a compression stress is applied on the boundary surface of a substrate side in the boundary region of the gate oxide film and an Si substrate. CONSTITUTION:A gate electrode is formed by adjusting its film thickness and forming temperature, etc. in the manner in which compression stress is applied both on the side of a gate oxide film and on the side of an Si substrate in a boundary region of the gate oxide film and the Si substrate. As the result of this, even if ionization radiant rays make an incidence thereon, the accumula tion of positive charge and generation of interfacial potential are suppressed, and resistance to radiation extremely increases. The range of optimum compres sion stress is estimated as 0.5-5X10<7> dyn/cm<2>.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a semiconductor device with enhanced radiation resistance;
In particular, it relates to improving the radiation resistance of semiconductor devices whose basic elements are insulated gate field effect transistors.

[Conventional technology]

In recent years, opportunities to use semiconductor integrated circuits in space, around nuclear reactors, etc. have been increasing. Semiconductor integrated circuits built in such a harsh environment are subject to constant radiation damage, which can result in damage to the circuit's operation, resulting in a decline in system functionality. Therefore, the development of semiconductor integrated circuits that are resistant to radiation is required.

The main cause of radiation damage to insulated gate field effect transistors (hereinafter referred to as MOS transistors) and bipolar transistors, which are the basic elements of highly integrated semiconductor integrated circuits, is the accumulation of positive Ti in the silicon oxide film. and an increase in the density of interface states at the interface between the silicon oxide film and the silicon substrate. In particular, in MOS transistors, damage to the gate 7 dielectric film S and the gate insulating film/silicon interface is directly reflected in fluctuations in threshold voltage and increases in leakage current, leading to deterioration in the characteristics of the integrated circuit.

The mechanism of radiation damage Z is briefly described below. When ionizing radiation is incident on a silicon oxide film, a large number of electron-hole pairs are generated. Thereafter, part of it recombines and disappears, but part of it is captured by the silicon oxide film. The mobility of electrons is high, and they diffuse out of the oxide film in a short time under positive gate voltage.

Holes have low mobility and are captured within the silicon oxide film,
A positive fixed charge is formed. It is also said that holes captured at the silicon oxide film-silicon substrate interface form an interface level.

The magnitude of the radiation damage (accumulation of fixed positive charges and generation of interface states) described above varies greatly depending on the strain applied to the silicon oxide bQ/y') substrate interface. In other words, pressure and compression stress are applied to the above interface region, rL and J:I
The damage tends to decrease and the damage increases when tensile stress is applied. This is because the atomic spacing decreases when compression stress is applied, so even if bonds are broken by holes, they are likely to recombine easily. On the other hand, when tensile stress is applied to the interface, the atomic spacing increases by 5 times, making it difficult for recombination to occur and causing damage to accumulate.

Conventional MOS transistors generally use a silicon oxide film formed on a polysilicon base as a material for the gate P3, with a material such as phosphorus introduced therein. Ta.

[Problem that the invention seeks to solve]

As mentioned above, since a polysilicon film is used for the gate electrode of the transistor (MOS) transistor, even if a polysilicon pattern is formed over the gate made of a silicon oxide film, the gate electrode will not be removed. /The stress applied to the silicon interface region hardly changes. In addition, the thermal expansion coefficient P of the silicon oxide film is smaller than that of the silicon crystal, so the second
As shown in the figure, S is present at the interface between the silicon oxide film and the silicon substrate. The tensile stress on the LS plate side and the compressive stress on the silicon oxide film periphery are bp, and after an interface state like C, the proportion of L interface units occurring is relatively large when exposed to radiation, although radiation resistance is not sufficient. There was a drawback that there was no

[Means for solving problems]

The present invention provides a semiconductor device with enhanced radiation resistance.

In the insulated gate field effect transistor, Q is placed on the silicon substrate side interface in the interface region between the gate insulating film and the silicon substrate.
5 X 10' ~ 5 X I Q' dyn k
The gate electrode is characterized in that the gate electrode is formed so that a compressive stress of IIt is applied.

〔Example〕

Next, one embodiment of the present invention will be explained with reference to the drawings.

FIG. 1 schematically shows an embodiment of the present invention, in which the gate is placed in such a way that compressive stress is applied to both the gate oxide film side and the silicon substrate side of the gate oxide film/silicon substrate interface region. It is formed by adjusting the film thickness of the electrode, the temperature at the time of electrode formation, etc. At this time, even larger compressive stress than in the case of the silicon oxide film/silicon substrate two-layer structure is generated at the interface 1g of the silicon oxide film and inside the silicon oxide film. As described above, compressive stress acts on both H and the gate insulating film/silicon substrate interface in the gate insulating film, so even if ionizing radiation is incident, the accumulation of positive charges and the generation of interface states are suppressed, and radiation resistance is reduced. Significantly improved.

Although radiation resistance improves with increasing compressive stress.

Gradually, the degree tends to reach saturation. Further, as the compression pressure increases, initial characteristics deteriorate such as a decrease in mobility, or reliability decreases such as peeling. Considering the above points, the optimal compressive stress range is 0.5~sxt
It is estimated that o' dyn/ctd.

Next, polycide (silicide/polysilicon 2)-structure) gate) MOS diode and MO are placed on the P-type silicon substrate.
S) The case where a transistor is formed will be described. Gate electrodes are not limited to polycide.

Any of silicide, aluminum 2, and high melting point metals such as tungsten may be used. 0 at the silicon substrate interface
．． It is sufficient if a compressive stress of 5 to 5 x 10' dyn/cr71 can be applied.

Figure 3 shows the amount of interface states generated ΔDit and the amount of fixed charge generated ΔQot due to ionizing radiation irradiation of the MOS diode.
showed stress dependence. Both amounts of generation decrease as the compressive stress increases, and then become saturated. Especially ΔD
The decrease in it is significant.

On the other hand, the W-period interface state X and the initially fixed 1 load suddenly increase in a region where the compressive stress is large (>5×10'dyn limit resistance). Therefore, there is an optimum region for compressive stress.

Figure WI4 shows a conventional polysilicon gate MOS transistor (tensile stress < 0.5 x 10' dyn/ff
1) and a polycide gate MOS transistor according to the present invention (compressive stress=2×10′ ayn, x=), an example of the subthreshold characteristics before and after irradiation with ionizing radiation is shown. It can be seen that although the initial characteristics are almost the same, the amount of shift in the negative direction after radiation irradiation and the variation in subthreshold swing are both smaller in the polycide gate MOS transistor of the present invention.

The above results indicate that both the accumulation of fixed positive charges and the generation of interface states are small.

〔Effect of the invention〕

As explained above, the present invention has a structure in which the gate electrode is formed so that compressive stress is applied to the interface between the gate insulating film and the silicon substrate of the insulated gate field effect transistor on the silicon side. It is possible to significantly reduce the fixed pressure load accumulated in the semiconductor device and the interface states generated at the gate insulating film/silicon substrate interface, and it is possible to significantly improve radiation resistance.

[Brief explanation of drawings]

Figure 1 is a schematic diagram showing the stress distribution of a three-layer structure of gate ionization/gate edge film/silicon substrate in one example of the present invention.
+'=:It:fSilicon oxidation, stress component of silicon substrate 2 no structure; Schematic diagram showing 15, Figure 3 shows the amount of ionizing radiation generated per interface and the fixed load accumulation due to radiation Figure 1 is a graph showing the subthreshold-ortho characteristics before and after ionizing radiation irradiation.
The solid line shows the polysilicate MOSFET transistor of one embodiment of the present invention, and the broken line shows the conventional polysiligate MOMOS transistor. Agent Patent Attorney Uchi Hara Oto Figure 1
)Figure 3

Claims (1)

[Claims] 0.5× at the silicon substrate side interface in the interface region between the gate insulating film and the silicon substrate of the insulated gate field effect transistor.
A semiconductor device with enhanced radiation resistance, characterized in that a gate electrode is formed so that a compressive stress of 10^7 to 5 x 10^7 dyn/cm^2 is applied.