JPH03280471A - Manufacture of semiconductor device - Google Patents

Abstract

PURPOSE:To obtain a gate oxide film of high quality which is excellent in dielectric breakdown strength and oxide film defect density even if a low temperature treatment is employed by a method wherein fluorine ions are implanted into the gate oxide film after or before a gate electrode film is formed on the gate oxide film through a CVD method. CONSTITUTION:A semiconductor substrate 1 is thermally oxidized at a comparatively low temperature by the use of an oxidizing agent to form a gate oxide film 2. Then, a polysilicon film 3 is deposited as a gate electrode film through a vacuum CVD method. In succession, ions of <19>F<+> are implanted into the gate oxide film 2 through the intermediary of the polysilicon film 3 so as to enable their concentration peak to be located in an SiO2 film. Then, the substrate 1 is annealed in an atmosphere of N2 for 30 minutes to combine Si of unsaturated bond with F to saturate for the formation of a gate oxide film 2a doped with fluorine. A process follows, where the polysilicon film 3 is doped with impurities to be lessened in resistance, and the impurity doped film 3 is patterned into a required shape for the formation of a gate electrode 3a.

Description

DETAILED DESCRIPTION OF THE INVENTION (a) Field of Industrial Application The present invention relates to a method for manufacturing a semiconductor device, and more particularly to a method for manufacturing a gate oxide film in a semiconductor device such as a MOS LSI.

(b) Conventional technology In the conventional technology, a gate oxide film is generally manufactured by thermally oxidizing a semiconductor substrate to form a thermal oxide film. There is a demand for thinner oxide films and higher quality. Regarding gate oxide films, it is generally known that high-temperature oxidation treatment can provide better film quality, but in order to form the thin films necessary for high integration, Since it is more suitable to form a film by oxidation treatment at a low temperature, specifically, at a temperature of 1000° C. or lower, so-called low-temperature oxidation treatment, formation of a high-quality gate oxide film by such low-temperature treatment is being considered.

(c) Problems to be Solved by the Invention However, the gate oxide film formed by conventional low-temperature oxidation treatment, for example, at a temperature of 950°C using a mixed gas of HCI gas and O gas as an oxidizing agent, cannot be processed by high-temperature oxidation treatment. It was inferior in terms of dielectric breakdown strength and oxide film defect density.

This invention has been made in consideration of the above circumstances, so it is possible to solve the above problems and form a high-quality gate oxide film with excellent dielectric breakdown strength and oxide film defect density even using low-temperature processing. The present invention provides a method.

(d) Means for Solving the Problems This invention provides a method for forming a 1f gate oxide film on a semiconductor substrate using a controlled oxidation film, and then forming a gate electrode film on the gate oxide film by CVD method before or after the gate oxide film is formed. This method of manufacturing a semiconductor device is characterized by implanting fluorine ions and ions into an oxide film.

In this invention, low-temperature oxidation refers to thermally oxidizing a semiconductor surface layer in an oxidizing atmosphere using an oxidizing agent at a relatively low temperature of 100° C. or less. For example, in the surface layer of a Si substrate, thermal oxidation A thin Stow film of 50 to 200 people is formed as a film.

A particularly preferable temperature for low-temperature oxidation is 950°C.

In addition, well-known thermal oxidation methods are used, specifically (1) dry O1 oxidation method, (2) wet method in which oxygen is passed through a container of high-purity deionized water before entering the oxidation furnace. oxidation method, (3) steam oxidation method in which high-purity deionized water stored in a container is boiled and used as an oxidizing agent without using a carrier gas, or (4) dry 0.
and several percent HCI, C1,.

IIcII oxidizes in an atmosphere containing C, HCl, etc.
Examples include method c, and method (4) in which oxygen is diluted with hydrogen, nitrogen, etc. and then oxidized.

In this invention, the ion implantation conditions for implanting fluorine ions after (a) forming the gate electrode film are as follows:
Using 11F as the ion species, the implantation energy (acceleration voltage) is preferably set to 50 to 70 keY, more preferably 60 keV, and the Fo dose is to'' to t.
o"am-", more preferably 1 to 2X 1
It is implanted into the gate oxide film with a peak until it reaches 0"cm-". The subsequent annealing process recovers crystal defects in the gate oxide film, for example, the 5ins film, and
The spread of o is determined.

That is, in order for F atoms to saturate the unsaturated bonds of Si at the interface between the Si substrate and the 5ins film as a gate oxide film formed on its surface layer, and to stabilize the above interface state, the annealing temperature must be 800°C. Preferably, the temperature is ~1000°C and the annealing time is set to 30 to 90 minutes. that time,
A carrier gas such as N, gas, or inert gas is used.

Note that the annealing temperature does not necessarily have to match the oxidation temperature.

In this invention, the ion implantation conditions for implanting fluorine ions before forming the gate electrode film (b) are as follows: 19 F° is used for ion implantation, and the implantation is at 5 to 10 keV to the extent that the Si0g film is not damaged by ion implantation. Energy is preferred, tols ~ 10110l7” Fo
A dose of . In the subsequent annealing treatment, the same annealing effect as in case (a) above can be obtained by appropriately adjusting the annealing temperature and annealing time to be sufficient to combine unsaturated Si with F and saturate it. Specifically, the annealing temperature and the annealing time are high-temperature and long-time annealing at 1000° C. or more and 60 minutes or more. Note that this annealing temperature does not necessarily have to match the oxidation temperature.

As the semiconductor substrate in this invention, a Si substrate is most preferred.

At this time, by implanting fluorine into the SiOx film as the gate oxide film, fluorine atoms can saturate the unsaturated bonds of Si at the SiO, /Si interface, stabilizing the 5iOt/St interface state, thereby stabilizing the 5rOt It is possible to reduce the density of horse mackerel sleep. This means that the binding energy of Si-0 is 369. OKJmol-' On the other hand, since the bond energy of SiF is 541.01[Jmol-' and both bond energies are almost equal, the F atom is stabilized by bonding with Si.

(e) After forming a gate oxide film on the working semiconductor substrate by low-temperature oxidation, before or after forming a gate electrode film on the gate oxide film by CVD method, fluorine ions are implanted into the gate oxide film, and then fluorine ions are implanted into the gate oxide film. As a technique for forming a gate electrode using the CVD method, patterning the gate electrode into a desired shadow shape, and further forming impurity diffusion regions as a source and drain on the semiconductor substrate, low-temperature oxidation treatment is used. However, it is possible to prevent a decrease in dielectric strength and an increase in oxide film defect density in a thin gate oxide film.

(f) Examples This invention will be described in detail based on the examples shown in the following figures.
r? Pine ``Thorn 1-) -Two-/n to n days 1 person in the middle of the day 2, it's not a thing.

In FIG. 1, a highly integrated semiconductor device is formed by the following manufacturing method. That is, the semiconductor substrate l is heated to a relatively low temperature of 950° C. and treated with an oxidizing agent HCl 10. A gate oxide film (200 layers of SiOx) 2 is formed by thermal oxidation. Next, a polysilicon film (1500 polysilicon) 3 is deposited as a gate electrode film by low pressure CVD. Next, by ion implantation into the gate oxide film 2 through this polysilicon film 3,
Ions are implanted at 11 F° with an energy of 60 key,
It is implanted at a dose of 1.78×10"1 ounce/cm" with a peak within 5 ift. Then 80
Temperature range from 0°C to 1000°C, in this example 950°C
By annealing for 30 minutes in a N gas atmosphere, the unsaturated bonds of Si are combined with F and saturated. Recovery of crystal defects in the gate oxide film and diffusion of fluorine are determined by the annealing temperature and time, as described above. 2a shown in FIG. 1 is a gate oxide film into which fluorine is implanted.

Next, impurities are doped into the polysilicon film 3 to lower the resistance, and this is patterned into a desired shape to form a gate electrode 3a (see FIG. 1C).

Although fluorine may be implanted directly onto the oxide film 2 without intervening the polysilicon film 3, there is a risk that the gate oxide film 2 will be damaged and deteriorated by the ion implantation. In this case, there is a possibility that the gate oxide film can be recovered by optimizing the implantation energy, optimizing the post-implantation annealing conditions, etc. Next, impurity diffusion regions, that is, a source and a drain are formed on the semiconductor substrate l by a known method to complete a semiconductor device.

Next, the measurement results of the dielectric breakdown strength and oxide film defect density of the gate oxide film thus obtained are shown in a histogram in FIG. Similarly, the measurement results for a gate oxide film formed by the conventional method are shown in FIG. 3 as a comparative example. In Figures 2 and 3, the horizontal axis is BREAKD
OfN FIELD (dielectric breakdown voltage) is shown, and the vertical axis is BREAKDOIN FI at each measurement point within the wafer surface.
FREQUENCY indicating how much ELD was
(percentage). Note that the measurement was performed using a 4ma+'' pattern, and the judgment current was 1 μA.

Further, the defect density was determined by the following method, with Pa5s being those with a breakdown voltage of 8 MY/cs or more.

P: Pa5s rate S: Measurement area Comparing A in Figure 2 and B in Figure 3, A has a higher FREQOENCY (higher pass rate) than B.
In addition, C and D are each I MY/c at the first measurement.
It shows the one destroyed at less than m, and C is FRE than D.
QUENCY is low (low electric field breakdown is low).

In addition, the defect density of the gate oxide film in the example was 0.5
9 cm-'', whereas that of the conventional example was 2.76 cm-''. Therefore, it can be seen that the gate oxide film of this example has better film quality than the conventional gate oxide film.

(G) Effects of the Invention According to the present invention, after forming a gate oxide film on a semiconductor substrate by low-temperature oxidation, fluorine is implanted into the gate oxide film, so that dielectric breakdown can be prevented by using low-temperature oxidation treatment. A high-quality gate oxide film with excellent pressure resistance and oxide film defect density can be obtained. Therefore, the gate oxide film can be made thinner, and the semiconductor device can be highly integrated.

[Brief explanation of drawings]

FIG. 1 is a process explanatory diagram illustrating a method for manufacturing a semiconductor device according to an embodiment of the present invention, FIG. 2 is a characteristic diagram showing the degree of dielectric breakdown voltage breakdown of the gate oxide film in the embodiment described above, and FIG. FIG. 2 is a diagram corresponding to FIG. 2 of a conventional example for comparison with the embodiment. l...Semiconductor substrate, 2...Gate oxide film, 2a-...Fluorine implantation gate oxide film, 3.
...Polysilicon film, 3a...Gate electrode. Fig. 1 a Fig. 1 Fig. 1 Fig. 3 M9Ms NJr degree = 2.76c through 2

Claims (1)

[Claims] 1. Form a gate oxide film by oxidizing the semiconductor substrate at low temperature,
A method for manufacturing a semiconductor device, which comprises implanting fluorine ions into the gate oxide film before or after forming a gate electrode film on the gate oxide film by CVD.