JPH0618173B2 - Thin film formation method - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for forming a thin film by photoexcitation.

[Prior Art] In recent years, an optical CV has been used in a semiconductor device manufacturing process.
Photo-excitation process technology such as D has been actively researched and developed as a method for lowering the process temperature and shortening the process. Photo-CVD is less prone to damage to the substrate and the device layer above it than the conventional plasma process, and is expected to be capable of forming a high-quality film at a lower temperature.

A metal material such as tungsten or molybdenum, which has already been promising as a wiring material in the future, has already been used by the photo CVD method, and a MOS
Deposition of insulators such as SiO ₂ used for the gate insulating film of IC has been realized. For example, “Appl. Phys. Lett.
0, 716-719 ", using a Boyer et al., An ArF excimer laser as a light source to produce SiH ₄ and N
It has been reported that a SiO ₂ film can be deposited using ₂ O gas as a source gas. According to this document, it is shown that the obtained deposited film has a value as excellent as the thermally oxidized SiO2 film in characteristics such as adhesion and breakdown voltage.

[Problems to be solved by the invention]

However, in the above-mentioned document, the interface state density is
_{It is} about 10 to 100 times higher than the _two films, and as an impurity,
It is described that hydrocarbons and N ₂ are considerably contained. The interface state has an adverse effect when it is used for a gate insulating film such as a MOS IC, so that it is desired that it be as low as possible. The above-mentioned document does not particularly mention the cause of the increase of the interface state, but the impurities such as N ₂ and hydrocarbons described above obviously have a bad influence.

Also, the 32nd Spring Applied Physics Society Proceedings (1985)
As shown by Sekine et al. On page 340 of 30p-K2, in some cases, the OH groups of impurities in SiO ₂ form traps for irradiation of ArF laser light, leading to an increase in interface state. is there. In order to eliminate the cause of the increase in the interface states, it is effective to reduce the content of impurities such as N ₂ , hydrocarbons and H ₂ in the CVD film as much as possible. However, the conventional photo CVD method has a problem that it is not possible to effectively reduce the mixing of these impurities.

It is an object of the present invention to provide a thin film forming method that solves such conventional problems.

[Means for solving problems]

The present invention provides a substrate in a gas containing a first gas component that causes a photochemical reaction by light having a first wavelength, irradiates the substrate with pulsed light having the first wavelength, and forms a thin film on the substrate. A method for forming a thin film, wherein a second component for etching impurity components of the thin film by irradiation with light having a second wavelength is used.
Is added to the gas to irradiate the substrate with pulsed light of the second wavelength at a cycle shorter than the time required to increase the film thickness of the thin film by one molecular layer. There is.

[Action]

In the CVD reaction using pulsed laser light, it is considered that the CVD source gas is decomposed or reacted with each irradiation of each laser pulse, and the step of depositing the generated molecules on the substrate is repeated to form a thin film. At this time, the deposition thickness per pulse is at most about 1 Å / pulse under the condition that a dense film is obtained. That is, the average thickness of the newly deposited film due to the irradiation of each pulse is
This is much thinner than one atomic layer. Therefore, after each pulse irradiation, it is considered that the atoms or molecules serving as impurities are exposed on the outermost surface of the film.

The present invention pays attention to this point, and after the irradiation of each laser pulse for CVD, the impurity atoms or molecules in the deposited thin film of atomic layer order are irradiated with light of another wavelength to perform an etching reaction. It is based on the idea that by removing this impurity component, it is possible to suppress the mixing of impurities into the CVD film.

According to this method, the CVD reaction alone produces impurities.
Even if the mixing is unavoidable, the impurities can be removed by an etching reaction before the impurities are taken into the CVD film, and as a result, a high-purity CVD film can be obtained. In addition to the effect of removing impurities by the etching reaction, the laser light that causes this etching reaction has a photodetachment effect, and this effect causes volatility of N ₂ and O ₂ adsorbed on the surface. Molecules can be removed.

〔Example〕

 The present invention will be described in detail below with reference to the drawings.

FIG. 1 is a block diagram of a thin film forming apparatus used in the first embodiment of the present invention. This example is an example in which the present invention is applied to SiO ₂ CVD. The CVD gas supply system 9 is S
A mixed gas of iH ₂ Cl ₂ , N ₂ and N ₂ O gas is supplied to the CVD cell 8. Further, the etching gas supply system 10 supplies Cl ₂ gas for etching. The first pulsed laser light source 1 composed of an ArF excimer laser is used to excite the CVD gas, and the emitted light thereof is transmitted through the second mirror 4, the third mirror 5 and the second window 7 to the CV.
It is guided into the D cell 8. The second pulsed laser light source 2 composed of a XeCl excimer-laser is used to excite Cl ₂ of the etching gas, and its emitted light is the first light.
The substrate 13 in the CVD cell 8 is irradiated through the mirror 3 and the first window 6. The heater 12 is used to raise the temperature of the substrate 13 to a temperature at which a good film can be formed. The internal pressure of the CVD cell 8 is controlled to be a predetermined value during CVD by adjusting the exhaust speed of the exhaust pump 11 and the supply amounts from the CVD gas supply system 9 and the etching gas supply system 10.

Next, experimental conditions and experimental results in this configuration will be described. The composition of the gas used in the experiment was SiH ₂ Cl ₂
1%, N ₂ 10%, N ₂ O 86%, Cl ₂ 3%, the pressure inside the CVD cell is 8 Torr, and the substrate temperature is 300.
A SiO ₂ film was formed at a temperature of ° C.

FIG. 2 is a diagram showing the irradiation timing of the irradiation laser light. The lower side is the emission timing of the ArF laser for CVD, and the upper side is the emission timing of the XeCl laser for etching. According to this emission timing, the pulsed laser light for exciting the etching gas is irradiated once for each pulsed irradiation for CVD gas excitation. According to the irradiation at this timing, even if the SiO ₂ film containing impurities is deposited by the irradiation of the ArF laser beam for CVD, Xe for the next etching
By irradiation with Cl laser light, hydrocarbons and H _{2 on the} substrate surface
Becomes a volatile chloride such as CCl ₄ or HCl and is released into the gas phase. It is considered that N ₂ is removed from the surface as N ₂ gas by the photodetachment effect. In addition, Cl
No. ₂ does not absorb at the oscillation wavelength of 193 nm of the ArF laser, and conversely, the CVD gas component does not absorb at the oscillation wavelength of 308 nm of the XeCl laser. It can be selectively caused by the wavelength of light, and unnecessary reactions other than the intended one such as a deposition reaction do not occur.

The interface state density of the photo CVD SiO ₂ film thus obtained is about 1.5 times that of the thermally oxidized SiO ₂ film, which is sufficiently lower than that of the thermal oxidation method, and is sufficient for a gate insulating film of a MOS IC. It turned out to be a usable value.
On the other hand, a normal optical CV without the above-mentioned optical etching treatment
The interface state density in the case of D is 20 with respect to that according to the present invention.
It was found that the present invention was more than doubled, and the present invention is effective in improving the interface state density which is easily affected by impurities and the like.

In the above embodiment, the number of irradiations of the pulsed laser light for exciting the etching gas was one per irradiation of the CVD gas excitation pulse. However, one irradiation of the CVD gas excitation light pulse was described. It is clear that the effect of removing the impurity component becomes more remarkable when the light pulse for exciting the etching gas is irradiated a plurality of times during the irradiation. On the contrary, when the CVD rate is extremely low, the effect of the present invention can be obtained even if the light pulse for exciting the etching gas is irradiated once for each light pulse for exciting the CVD gas.

That is, any combination may be used as long as it is a timing of irradiating the optical pulse for exciting the etching gas at a cycle shorter than the time required for increasing the thickness of the thin film by one molecular layer.

Although the first embodiment of the present invention has been described by taking the CVD of the SiO ₂ film as an example, the CVD gas, the etching gas, and these gases can be excited also in the CVD of other insulators, semiconductors, metals, and the like. If a pulsed laser light source is combined, a high-quality CVD film containing few impurities can be formed by using the method of the present invention.

FIG. 3 is a diagram showing a second embodiment of the present invention. The difference from the method of FIG. 1 is that the emitted light of the first pulse laser light source 1 is vertically incident on the substrate 13, and the dichroic mirror 14 is used to separate the second pulse laser light source 2 from the second pulse laser light source 2. Substrate that combines the light emitted from the pulsed laser light source 1
The point of irradiating 13 is different. This configuration is effective when the CVD gas molecules adsorbed on the substrate surface are entrusted to the photo CVD reaction. Examples of such a CVD gas include organic metal gas such as metal carbonyl. The third
In the figure, the same elements as those in FIG. 1 are designated by the same reference numerals.

FIG. 4 shows a third embodiment of the present invention. According to this embodiment, a mask 15 for defining an irradiation pattern and a lens 16 for transferring the pattern onto the substrate are arranged on the optical path of the thin film forming apparatus of FIG. A CVD film is formed on. In FIG. 4, the same elements as those in FIG. 1 are designated by the same reference numerals.

〔The invention's effect〕

As described above, when the conventional photo-CVD method is used, a CVD film having a high impurity concentration is deposited, so that the obtained C
VD membranes could only be used in limited applications. On the other hand, by using the photo-CVD method of the present invention, the impurity concentration can be significantly reduced as compared with the conventional method, and the photo-CVD method can be applied to a wide range of semiconductor manufacturing processes. Further, according to the conventional method, even if the combination of the CVD gas and the light source, which is difficult to be practically used because the content of impurities is too high, it is possible to form a high-purity CVD film by using the method of the present invention. C is possible and can be practically used
The range of choice of VD material can be greatly increased.

[Brief description of drawings]

FIG. 1 is a diagram showing a first embodiment of the present invention, FIG. 2 is a diagram showing emission timings of two types of pulse laser light sources having different wavelengths in the first embodiment, and FIG. 3 is a second embodiment. FIG. 4 is a diagram showing an example, and FIG. 4 is a diagram showing a third embodiment. 1 ... First pulse laser light source 2 ... Second pulse laser light source 3 ... First mirror 4 ... Second mirror 5 ... Third mirror 6 ... First window 7 ... Second Window 2 2 ... CVD cell 9 ... CVD gas supply system 10 ... Etching gas supply system 11 ... Exhaust pump 12 ... Heater 13 ... Substrate 14 ... Dichroic mirror 15 ... Mask 16 ... Lens

Claims (1)

[Claims] 1. A substrate is provided in a gas containing a first gas component which causes a photochemical reaction by light of a first wavelength, and the substrate is irradiated with pulsed light of the first wavelength to irradiate the substrate with the pulsed light of the first wavelength. In a thin film forming method for depositing a thin film, a second gas component that etches an impurity component of the thin film by irradiation with light having a second wavelength is added to the gas to increase the film thickness of the thin film by one molecular layer. A method for forming a thin film, characterized in that the substrate is irradiated with the pulsed light of the second wavelength in a cycle shorter than the time required for performing.