JPS61164266A - Semiconductor device with reinforced radiation resistance - Google Patents

Abstract

PURPOSE:To form a semiconductor device with high reliability for a long time under the severe radioactive environment by a method wherein fluorine is contained in an insulating film formed on a semiconductor substrate. CONSTITUTION:Element isolating silicon oxide films 105b containing fluorine are formed on overall surface of substrate 1 by means of ion-implanting 106 the surface with silicon tetrafluoride. At this time, the ion-implanting energy is arbitrarily set up in terms of the film thickness of element isolating silicon oxide film 105b, a silicon oxide film 102 and a silicon nitride film 103 not to implant the silicon substrate 101 with needless fluorine. Moreover, the silicon nitride film 103 and silicon oxide films 4 on the element regions of silicon substrate 101 are removed removed to ion-implant the overall surface of silicon substrate 101 again with silicon tetrafluoride amounting to around 3X10<15>cm<-2>. At this time, the ion-implanting energy is restircted to around 20keV or less to reduce any damage due to ion-implantation in the element regions while it is recommanded to implant the element regions with ion obliquely.

Description

DETAILED DESCRIPTION OF THE INVENTION (Technical Field) The present invention relates to a semiconductor device, and particularly to a MIS field effect semiconductor device with enhanced radiation resistance.

With the recent development of space exploration and nuclear power generation, there is a desire to develop semiconductor devices that have high reliability over a long period of time even under harsh radiation environments.

Under the above-mentioned radiation environment, when all the ionizing radiation passes through the insulating film that makes up all parts of the semiconductor device, many electron-hole pairs are generated in the insulating film, and the holes that move slowly are insulated. This increases the total fixed positive charges in the film and causes interface states to be generated at the insulating film/semiconductor substrate interface. The positive charges and interface units generated in this manner cause deterioration of characteristics of semiconductor devices, such as generation of leakage current and parasitic transistor effect.

(Prior art) Conventionally, in order to solve such problems, optimization of oxidation conditions for silicon oxide films used as insulating films in semiconductor devices with silicon substrates, or silicon oxidation using chemical vapor deposition has been attempted. Attempts have been made to apply membranes. Attempts have also been made to mix chlorine into the oxidation atmosphere and introduce it into the silicon oxide film to reduce fixed positive charges and completely reduce the silicon dangling bonds that cause interface states. ing. However, when such conventional technology is used, a flat band voltage of a MOS diode made of a P-type silicon substrate and a silicon oxide film of 40 oha degree is a few poTorr due to an absorbed dose of ionizing radiation of about 1 megarad (Si). A negative shift of several tens of volts is fully shown, and the interface state (rl 10 ”2~10 eV-
・It is difficult to say that the effect is sufficient, as the increase is approximately 1 cm. Furthermore, regarding the method of introducing chlorine into the silicon oxide film, high-temperature oxidation of approximately 1100°C or higher is required to introduce a sufficient amount of chlorine into the silicon oxide film, and such high-temperature oxidation causes interfacial stress. There was a problem in that the effect of reducing isostatic charges and interface states due to the introduction of chlorine was offset by increasing the number of electrons and reducing electron traps.

(Object of the Invention) In order to improve the above-mentioned problems, the object of the present invention is to introduce fluorine, which is highly reactive with chlorine chloride, into an insulating film formed on a semiconductor substrate. Our aim is to provide semiconductor devices that have high reliability over a long period of time.

(Structure of the Invention) A feature of the present invention is that fluorine is introduced into an insulating film formed on a semiconductor substrate or is accumulated at the interface between the insulating film and the semiconductor substrate. , in which fluorine is injected into the surface of a semiconductor substrate or into an insulating film by ion implantation, and then low-temperature heat treatment is performed.

(Summary of the Development) The present invention allows all fluorine atoms to be contained in an insulating film on a semiconductor substrate. In this way, a semiconductor device with enhanced radiation resistance can be obtained.

Conventionally, chlorine has been introduced into an insulating film by mixing a highly purified chlorine-based gas into an oxidizing atmosphere and oxidizing a silicon semiconductor substrate at high temperatures. Through such oxidation, the fixed charges in the oxide film are reduced, and the interface states generated at the silicon oxide film/silicon substrate interface are reduced, thereby increasing the radiation resistance of semiconductor devices. It is. However, in order to introduce a sufficient amount of chlorine into the all-silicon oxide film, it is necessary to raise the oxidation temperature to a high temperature of approximately 1100'0 or higher, which is inappropriate as it may increase stress at the silicon oxide film/silicon substrate interface. It is.

In the present invention, by using highly reactive fluorine, it is introduced into the insulating film at a lower temperature than chlorine, and the radiation resistance can be effectively strengthened even when chlorine is introduced into the insulating film. In addition, all ion implantation techniques will be applied when introducing fluorine into the insulating film. This is because it is currently difficult to obtain high-purity fluorine-based gases, and mass separation during ion implantation makes it possible to introduce only fluorine-containing chemical species into the entire semiconductor substrate or insulating film. It becomes possible. Following fluorine ion implantation, if all fluorine is implanted into the semiconductor substrate, oxidation is performed at low temperature, and if all fluorine is implanted into the insulating film, annealing is performed at low temperature. Due to this low temperature oxidation or annealing, fluorine is accumulated at the insulating film/semiconductor substrate interface.

(Effects of the Invention) Here, low-temperature oxidation or annealing not only reduces stress at the insulating film/semiconductor substrate interface but also has the effect of preventing fluorine from escaping into the atmosphere.

(Action of the Invention) As described above, fluorine introduced into the upper surface of the insulating film/semiconductor substrate has the effect of reducing the total fixed charge and the interface state.

(Effects of the Invention) As described above, in a semiconductor device in which fluorine is introduced into an insulating film, an increase in electron traps in the insulating film reduces fixed positive charges caused by ionizing radiation, and Since pair recombination is promoted and the increase in interface states is suppressed, characteristic deterioration in a radiation environment is improved, and long-term reliability is achieved in 41I11.

(Embodiment) Here, an embodiment of the present invention will be explained with reference to the drawings.In the following explanation, for convenience, P-type silicon and silicon oxide films, which are currently widely used, will be taken as examples.

As shown in FIG. 1, a silicon oxide film 102 and a silicon nitride film 103 are formed on a P-type silicon substrate 101, and a desired portion is completely removed to form a P region 104 that will serve as a channel stopper for device isolation. form. Next, as shown in FIG.
04 is performed to form a silicon oxide film 105.a for element isolation. Here, as shown in FIG. 3, silicon tetrafluoride is ion-implanted 106 over the entire surface of the substrate to form the entire silicon oxide film 105.b for the molecular droplets into which fluorine is introduced. At this time, the ion implantation energy is arbitrarily set so that unnecessary fluorine is not implanted into the silicon substrate 101, taking into account the entire film thickness of the silicon oxide lN105.a1 silicon oxide film 102 and silicon nitride film 103 for element isolation. Furthermore, as shown in FIG. 4, a silicon nitride film 103 and a silicon oxide film 104 on the element region of the silicon substrate 101 are
is removed, and silicon tetrafluoride ions are again implanted into the entire surface of the silicon substrate 101 at a total concentration of about 3×10 15 crn 2. It is desirable that the ion implantation energy at this time be suppressed to about 20 KeV or less to completely reduce damage caused by ion implantation in the element region, and that the implanted ions be obliquely incident.

In order to completely reduce damage caused by ion implantation in the element region,
Instead of removing the silicon oxide film 102 in FIG. 2, ion implantation may be performed and the silicon oxide film 102 may be removed later. Subsequently, as shown in FIG. 5, oxidation is carried out in a dry oxygen atmosphere to form a gate silicon oxide film 10 into which fluorine has been introduced.
form 8. At this time, oxidation temperature If; 1950'0
The stress at the silicon oxide film/silicon substrate interface is alleviated by using the following conditions.

Gallo pressure reduction may be used to increase the growth rate of the silicon oxide film by oxidation at a relatively low temperature of 950° C. or lower. At this stage, the element isolation silicon oxide film 105.b into which fluorine has been introduced is annealed, and the fluorine atoms are incorporated into the silicon-oxygen network with chemical bonds. Subsequently, as shown in FIG. 6, a gate electrode 109 and an insulating silicon oxide film 110 are completely formed, a source or drain part 111 is provided, and later, as shown in FIG. An opening 112 is provided, wiring 113 is provided, and the cover insulating film 11 is
Cover with 4.

Through the above steps, a silicon oxide film, an element isolation silicon oxide film 105/b with fluorine introduced into the main CC silicon oxide film/silicon substrate interface, and a gate silicon oxide film 108 are formed. An effective semiconductor device is completed.

(Summary of the Invention) In the embodiment of the present invention, a case has been described in which the entire gate silicon oxide film is formed after ion implantation of fluorine into a silicon substrate. The same effect can be obtained even when ions are implanted and annealing is performed. Furthermore, in cases other than N-channel MUS field-effect semiconductor devices, similar effects can be obtained in P-channel or complementary MO8 field-effect semiconductor devices. Furthermore, the present invention is similarly effective for MI8 field effect semiconductor devices using semiconductor substrates other than silicon, insulating films other than silicon oxide films, or multilayer structure insulating films formed by combining a plurality of insulating films.

Further, as for the chemical species to be ion-implanted, the same effect can be obtained even if fluorine alone or a fluorine compound other than silicon tetrafluoride is used.

[Brief explanation of drawings]

1 to 7 are cross-sectional structural views of an embodiment of the present invention. In the figure, 101...P-type silicon substrate, 102...silicon oxide film, 103...
...Silicon nitride film, 104...Channel stopper P+ region, 105.a...Silicon oxide film for confectionery isolation, 105.b...For element isolation into which fluorine is introduced Silicon oxide film, 106...Ion implantation of silicon tetrafluoride, 107...Ion implantation of silicon tetrafluoride, 108...Fluorine gate silicon oxide Film, 109... Insulating silicon oxide film, 110... Kate electrode, 111.
...Source or drain section, 112...
...Opening, 113...Wiring, 114...
...Cover insulating film. %1 Figure 2 Figure 3 Porridge

Claims (5)

[Claims] (1) A semiconductor device characterized in that an insulating film formed on a semiconductor substrate is provided with a region into which fluorine atoms are introduced. (2) The semiconductor device according to claim 1, wherein, in an insulating film formed on a semiconductor substrate, fluorine is accumulated at an interface between the semiconductor substrate and the insulating film. (3) Claims (1) or (2) characterized in that after fluorine atoms are introduced into the surface of the semiconductor substrate by ion implantation, the surface of the semiconductor substrate is oxidized.
1. Semiconductor device described in Section 1. (4) Claims (1) or (2) characterized in that fluorine atoms are introduced into at least a portion of an insulating film formed on a semiconductor substrate by ion implantation and then annealed. 1. Semiconductor device described in Section 1. (5) Claim (1) or (2) characterized in that the oxidation or annealing is performed at a low temperature.
1. Semiconductor device described in Section 1.