JPS63276270A - Manufacture of radiation resistant semiconductor device - Google Patents

Abstract

PURPOSE:To inhibit increase of fixed positive load stored in a silicon oxide film due to radiation, by nitriding a gate insulation oxide film at a temperature lower than a thermal oxidation temperature. CONSTITUTION:Thick silicon oxide films 102 and channel stoppers 103 are formed on a silicon substrate 101, for dividing the same. Then, a gate insulation oxide film 104 is formed while the substrate is heated by a heater 106 in a reaction vessel 105. The atmosphere of ammonia is formed within the reaction vessel 105 and ultraviolet radiation 107 is applied, so that nitriding reaction occurs. A polysilicon gate electrode 108 containing phosphorus is formed and the sides of the polysilicon gate electrode 108 are oxidized to provide oxide side walls 109. Ions of arsenic or the like are implanted to form a source region 110 and a drain region 111. After a protecting insulating film is deposited all over the surface, source aud gate electrodes are formed to complete a transistor.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to improving the radiation resistance of semiconductor devices, particularly silicon MOS semiconductor devices.

[Conventional technology]

When semiconductor integrated circuits are used in outer space, around nuclear reactors, etc., they are susceptible to radiation damage, so efforts are being made to improve their radiation resistance.

MO is a basic element of semiconductor integrated circuit with high degree of integration.
S) In transistors, radiation damage appears as a change in threshold voltage and an increase in leakage current, causing characteristic deterioration. The cause of this deterioration is that a large number of electron-hole pairs generated when radiation enters the gate insulating oxide film are partially annihilated by recombination, but some are captured by the silicon oxide film, and holes in particular are It is said that this is because it is easily captured due to its low mobility, and it creates positive fixed charges within the silicon oxide film and is trapped at the silicon oxide film/silicon substrate interface to form an interface state.

The degree of radiation damage described above varies greatly depending on the method of forming the gate insulating oxide film and the subsequent heat treatment process, and it has been empirically found that devices manufactured using low-temperature manufacturing processes have good radiation resistance. There are also reports that thermal nitridation of silicon oxide films at high temperatures is sufficient.

[Problem that the invention seeks to solve]

However, the low-temperature manufacturing process for improving radiation resistance does not have a significant improvement effect, and it is necessary to further improve the resistance. In addition, in the high-temperature thermal nitriding method, a silicon oxide film is thermally nitrided in an ammonia atmosphere at a high temperature of 1000 C or more for several hours, but although the amount of interface states generated decreases, the amount of fixed positive charge accumulation is the opposite. , and the threshold voltage of the MOS transistor changes greatly.

In view of the above circumstances, an object of the present invention is to provide a manufacturing method that can achieve radiation resistance superior to conventional methods.

[Means for solving problems]

In the method of the present invention, after forming a gate insulating oxide film, the semiconductor substrate is maintained at a temperature below the thermal oxidation temperature of the gate insulating oxide film, and at least a portion of the gate insulating oxide film is nitrided. The nitriding method can be carried out by photolysis by ultraviolet irradiation in an ammonia atmosphere or by lamp heating at high temperature for a short time.

[Effect]

In the high-temperature thermal nitriding method, the amount of interface states generated decreased due to nitriding of the oxide film, but the amount of fixed positive charge accumulation increased. This is thought to be because the probability of trapping holes increases due to thermal stress caused by high temperatures, but in the present invention, since nitridation is performed at low temperatures, the latter disadvantage can be prevented. On the other hand, as an effect of nitriding, a thin nitride film layer is formed at the silicon oxide film/silicon substrate interface, reducing the amount of interface states generated, and nitrogen existing on or inside the silicon oxide film acts as a recombination center, so there is a fixed positive charge. The amount of accumulation can be reduced. Since low-temperature nitridation is used, the gold film in the gate insulating oxide film is not necessarily nitrided, but even a portion of the gate insulating oxide film is effective.

〔Example〕

An embodiment of the present invention will be described below. Examples are P
The present invention is directed to an integrated circuit in which the elements separated (by an element isolation oxide film) on a W silicon substrate are polysilicon 7-gate transistors. FIG. 1 is a cross-sectional view illustrating the steps up to the formation of a transistor structure. FIG. 1A shows a state in which a 1 oz thick silicon oxide film for isolation and a channel stopper 103 are formed on a silicon substrate 101. Next, as shown in FIG. 1(b), 1ooo
A gate insulating oxide film 104 having a thickness of 10 to 500 nm is formed at a temperature of 950 C or less, for example. Reference numeral 106 denotes a heating heater, on which the silicon substrate 101 is mounted, and keeps the temperature constant during the reaction. After completing the above oxidation process, reaction vessel 1
05 was replaced with ammonia, and a silicon substrate 10 was prepared.
The temperature of step 1 is kept below 950C, for example 900C, and UV light (λ=185nm) is applied using a low pressure mercury lamp.
is irradiated to perform a nitriding reaction. The light irradiation may be performed using a laser beam, for example, an ArF excimer laser (λ=193 nm).

The steps from FIG. 1(e) onwards are steps for forming each electrode of an N-channel MOS transistor. First, as shown in FIG. 1(C), a polysilicon gate electrode 108t containing phosphorus is formed.
- formed by known etching techniques and then oxidized 109 on the sides of the polysilicon gate electrode 108, as shown in FIG. 1(d).
After performing this, the source region 1 is implanted with ions such as arsenic.
10. A drain region 111 is formed. A protective insulating film is then deposited over the entire surface, and source and gate electrodes are formed to complete the transistor.

Figure 2 shows a MOS transistor (indicated by a broken line) manufactured by a conventional low-temperature manufacturing process and a MOS transistor manufactured by the nitriding process of the present invention.
S) An example of subthreshold characteristics before and after radiation irradiation with a transistor (indicated by a solid line) is shown. It can be seen that although the initial characteristics are almost the same, the amount of shift in the negative direction and the fluctuation of the subthreshold swing after radiation irradiation are both smaller in the MOS transistor subjected to the nitriding treatment of the present invention.

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

As a low-temperature nitriding method, instead of the ultraviolet irradiation shown in Figure 1(b), short-term high-temperature (1000-1200 C) lamp heating is performed in ammonia atmosphere for 10 seconds to 5 minutes to cause a reaction. You can do it like this. At this time, the silicon substrate is kept at a temperature below the thermal oxidation temperature. The above method,
When applied to a polysilicon gate transistor on a P-type silicon substrate similar to that shown in Fig. 1, almost the same effect was obtained.
Less radiation damage.

〔Effect of the invention〕

As explained above, the present invention nitrides the gate insulating oxide film at a low temperature below the thermal oxidation temperature, thereby eliminating the fixed positive load accumulated in the silicon oxide film caused by radiation and generated at the silicon oxide film/silicon substrate interface. The increase in interface states can be significantly reduced compared to the conventional method.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view showing an embodiment of the present invention, and FIG. 2 is a diagram showing radiation resistance characteristics of MOS transistors manufactured by the conventional method and the embodiment. 101...Silicon substrate, 102...Silicon oxide film (for element isolation), 103...
...Channel stopper, 104...Gate insulating oxide film, 105...Reaction vessel, 106...Heating heater, 107...Ultraviolet rays.

Claims (2)

[Claims] (1) In a silicon MOS semiconductor device, after forming a gate insulating oxide film, the semiconductor substrate is maintained at a temperature below the thermal oxidation temperature of the gate insulating oxide film, and at least a part of the gate insulating oxide film is nitrided. A method for manufacturing a radioactive semiconductor device. (2) The method for manufacturing a radiation-resistant semiconductor device according to claim 1, wherein the nitriding is carried out by photolysis by ultraviolet irradiation or lamp heating at high temperature and for a short time in an ammonia atmosphere.