JPS6127623A - Light source for photochemical reactive induction - Google Patents

Abstract

PURPOSE:To enable to form an excellent optical CVD (chemical vapor deposition) film on a microscopic region by a method wherein the titled light source is composed of a continuous excitation Q switching Nd solid-state laser and an ultraviolet region higher harmonic generator. CONSTITUTION:The fundamental wave (wavelength of 1.06mum) light emitted from an Nd:YAG laser is converted into the second harmonic (SH, wavelength of 0.53mum) light by the SHG crystal 2 in position-aligned condition. The Nd:YAG laser 1 is continuously excited by a Kr arc lamp, and a Q-switch oscillation is repeated at a high repeating speed by the AOQ switch element located in a resonator. The output of the Nd:YAG laser 1 is constituted in such a manner that a high output oscillation can be performed for the purpose of facilitating the wavelength conversion to be performed in the latter stage. The obtained SH light is converted into the fourth higher harmonic (FH, wavelength of 266nm) light having the double frequency (half wavelength) by the FHG crystal 3 in a position- alighment state. An FH light only is picked out from said output by the wavelength selecting element such as prism and the like. The FH light obtained as above is condensed on the substrate 7 located in a laser CVD cell.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to a light source for inducing a chemical reaction by optical excitation, and particularly to a light source for a laser beam excitation process that is effective in manufacturing semiconductor devices.

(Prior art and its problems) In recent years, in the semiconductor device manufacturing process, optical CV
High-power ultraviolet light sources that can cause electronic excitation in materials are often used as light sources for photoexcitation processes such as D and photoetching to cause photoinduced chemical reactions such as photoCVD and photoetching. It's here. Specific light sources include excimer lasers (wavelengths of 157 nm, 193 nm,
248 nm, 308 nm, etc.), Ar laser (wavelength 5
15 nm) and the second harmonic (wavelength 257 nm) is well known. These light sources are applied to Cr(D laser CVD) on glass from Cr(CO)a vapor, and
An example of obtaining a good Cr film with a size of
It was presented by Tsukiyama et al. in 10 lectures. However, such conventional light sources have the following problems.

First of all, in the case of excimer lasers, at present, it is necessary to replenish halogen gas such as F, or HCI to maintain the oscillation output. It becomes necessary to have a processing device, an exhaust device to the outside air, a leakage detection device in case of an emergency, and various interlock mechanisms linked thereto. For this reason, the size of the light source has increased,
At present, excimer lasers cannot be called a very practical light source because of the increased cost, loss of portability, and increased burden of safety management.

On the other hand, in the case of the second harmonic of an Ar laser, the output is low, at most a few mW, so it is not possible to form a film of sufficient quality with this ultraviolet light alone, and even if high output is achieved,
Since it oscillates as a continuous wave, the shape of the deposited film becomes larger than the cross-sectional shape of the irradiated light beam due to thermal diffusion on the substrate of photo-CVD, making it almost difficult to perform microfabrication on the order of 1 μm. Therefore, although the second harmonic of the Ar laser does not have the disadvantage of using toxic gases like the excimer laser described above, it is still considered to be an ultraviolet light source that is not suitable for photoCVD.

On the other hand, in the explanation of a more practical ultraviolet light source candidate and an example of a "laser thin film forming apparatus", Cr(Go)a
It describes the case where .

However, in that case, there is no more specific description regarding the coming of light, and of course there is no mention of the results of laser CVD.

Q switch Nd: When using the fourth harmonic wave of a solid-state laser as a practical CVD light source, it is important to first increase the output of the fourth harmonic wave. In that case, it is generally considered to use a pulse-pumped Q-switched Nd:YAG laser with high peak power in order to increase the conversion efficiency to harmonics. Under this configuration, the repetition rate is approximately 5
Obtaining the fourth harmonic of 0 I'lz + peak power of about 100 ffl and pulse width of about Ions is a fairly general characteristic limit.

These characteristics are characterized in that the pulse width and repetition rate are almost the same as those of an excimer laser, and the peak power is about three orders of magnitude lower than that of an excimer laser. However, regarding the difference in peak power, if the power density per unit area is compared taking into account the difference in beam cross-sectional area, both light sources can be said to be approximately the same as #1.

Therefore, with regard to the irradiation intensity when a substance is irradiated with the same optical system, characteristics based on the excimer laser can be obtained by this fourth harmonic. Therefore, it is expected that the effect will be almost the same when used in photo-CVD, and in fact, the above-mentioned Cr(C
o) The case of CVD of Cr from s gas has been confirmed. For this reason, there is a light source that does not have the above-mentioned drawbacks of the excimer laser in its device configuration and has a photo-CVD percentage comparable to that of the excimer laser.

Conventionally, this was obtained using the fourth harmonic light of a pulse-excited Q-switched YAG laser.

However, even when this fourth harmonic light is used, the CVD characteristics for microscopic regions ranging from several microns to submicrons are insufficient, as in the case where an excimer laser is used. That is, in the case of Cr deposition from Cr(CO)e, it is difficult to form a good film quality with metallic luster unless the light induces not only photolysis but also heating of the deposited film. This was discovered in an experiment using an excimer laser (see the aforementioned 1959 Spring Conference on Applied Physics, Lecture No. 31pK10), but similar results were obtained when using the fourth harmonic of this pulse-excited YAG laser. was gotten.

Especially when depositing on a micro area of 10 μm or less.

If the energy per pulse was increased to improve the heating effect, the deposited film would be damaged by the irradiation light itself, making it impossible to obtain a good film.

(Object of the Invention) The object of the present invention is to provide a light source for photo-CVD that eliminates the drawbacks of the conventional photo-CVD light source and enables formation of a good photo-CVD film on a '4I small area. There is a particular thing.

(Structure of the Invention) The light source of the present invention is composed of a continuously pumped Q-switched Nd solid-state laser and a generator of ultraviolet harmonics.

(Principle of operation of the present invention) When forming a good film in a minute area using conventional CVD, which requires a heating action, one of the important points is to consider the cooling process of the deposited film. Cr on glass
In the case of Cr deposition from (Co)e, only the deposited Cr film itself absorbs the irradiated laser light. Cooling of a deposited film when deposited over a large area can be considered in terms of one-dimensional heat conduction in the vertical direction of the film. In contrast, when deposited on a microscopic area.

Heat diffusion in the in-plane direction of the deposited film also occurs relatively significantly. That is, three-dimensional heat conduction occurs, effectively increasing the cooling effect of the deposited film. This situation becomes more pronounced in the case of deposition in a region of several μm, where the size of the deposited film is smaller than the thermal diffusion length of the substrate. Based on the consideration of such problems with the prior art, in the present invention, instead of the fourth harmonic of the conventional pulse-pumped Q-switched YAG laser, a continuously pumped Q-switched Nd: solid-state laser and harmonics in the ultraviolet region, However, the light source is the fourth harmonic (wavelength 266 nm) of the emitted light of a continuously excited ultrasound (AO) Q-switched Nd:YAG laser. Due to this difference, the characteristics of ultraviolet light are that the pulse energy is about three orders of magnitude smaller, the pulse width is a little more than one order of magnitude wider, and the conversion efficiency to the fourth harmonic is more than one order of magnitude smaller, which is disadvantageous for general use. Becomes a characteristic. However, since the repetition rate of pulses increases by one to two orders of magnitude, it is necessary to sufficiently suppress the peak intensity of one pulse to below the threshold for optical damage to the deposited film, and to reduce the input power per pulse. The deficiency can be compensated for by a sufficient heating integral effect by increasing the recombination speed. Moreover, this heating integral effect causes CV
Since it is possible to produce a steady temperature increase effect below the D temperature, actual CVD can be limited to only the transient temperature increase caused by one individual incident pulse, and as a result, the pattern of the deposited film obtained is , a fine pattern that faithfully reflects the light irradiation area can be formed without the spreading that occurs during steady heating 8 (Example) Examples of the present invention will be described in detail below with reference to the drawings. .

FIG. 1 is a block diagram of a light source of the present invention.

Fundamental wave from Nd:YAG laser 1 (wavelength 1.06 μm
IrL) The light is transferred to the second phase by the SHG crystal 2 in one phase matching state.
It is converted into harmonic (SH, wavelength 0.53 μm) light. N
d: The YAG laser 1 is continuously excited by a Kr arc lamp and by an AOQ switch element in the resonator.

Q-switch oscillation is repeated at a high repetition rate of around 1 ktlz. The Q switch and trigger circuit that controls the Q switch oscillation has an external trigger terminal that can be externally controlled by various automatic control signals. Nd:YAG
The output of laser 1 is TE to facilitate wavelength conversion in the subsequent stage.
It has a configuration that allows high output oscillation on the order of IOW in Moo mode. As the SHG crystal, it is effective to use ODA and KTP, which are capable of highly efficient wavelength conversion.The conversion efficiency to SH light is 10% or more, and the average power of SH light has a maximum characteristic of about IW. realizable. The obtained SH tip is further divided into two parts by the phase-matched FHG crystal 3.
The fourth harmonic (FH, wavelength 2) of double the frequency (half the wavelength)
66 nm) is converted into light. As FHG crystal, KD
It is desirable to use P. In that case, from SH light to FH-
The conversion efficiency to X depends on the state of focusing on the FHG crystal,
Although it varies depending on the uniformity of the crystal, the deuterium substitution rate, etc., about 5 to 10% can be achieved, so an FH element of a pulse train with a maximum average output of 50 to 1 oomW can be obtained. From the output, only PHff is extracted by a wavelength selection element 4 such as a prism.

The FH source thus obtained was focused on a substrate in a laser CVD cell and used to form a good CVD film. FIG. 2 is a conceptual diagram of the loading structure when this light source is used for optical CVD.

The FH source is transferred to the substrate 70 in the CVD cell 6 using the condensing lens 5.
Irradiate the surface. This is because the inside of the cell is filled with Cr(Co)e vapor diluted with Ar buffer gas.

Due to the above-mentioned photolysis effect and heating effect due to FH element)
A Cr metal film is deposited. With this configuration, the fourth
It has been confirmed that the formation of a good Cr film in a micro area with a diameter of several μm, which could not be obtained when using harmonic light, was achieved on the quartz substrate 7, and that it is possible to achieve a minimum diameter of 1 μm. . The adhesion of the obtained Cr film to the substrate is very high.
It was confirmed that the film quality was sufficiently dense and had light-shielding properties and conductivity.

Due to these characteristics, there has been no sufficiently practical method in the past.
It is believed that this configuration can have a significant effect on the technology for correcting pinhole defects in photomasks, which has been pending.

In the above embodiments, an A-OQ switched Nd:YAG laser was used as the continuously pumped Q-switched Nd solid-state laser, but other materials capable of continuous oscillation, such as Nd:YLF and Nd:YAG, were used as the laser material. It goes without saying that alternative materials such as GGG can be used for scales. In addition, as a generator of ultraviolet harmonics, the case of the fourth harmonic was explained here, but in relation to the absorption wavelength of CVD gas, the third harmonic light (354 nm) and the fifth harmonic light (213 nm) are also used. Needless to say, the scales are used. In the former case, sum frequency generation of the second harmonic light (532 nm) and fundamental wave light (1,064 μm), in the latter case, sum frequency generation of the fourth sieve harmonic source and fundamental wave light 9 or second harmonic light Phase-matched nonlinear optical crystals may be used to generate the sum frequency of the third harmonic light and the third harmonic light, respectively.

Further, as a description of the specific application series of the present invention, optical CV
Although the deposition of Cr in D has been described, the light source according to the present invention can be used for CVD of not only metals but also other insulators and semiconductors.
, is also effective as an ultraviolet light source for inducing photochemical reactions such as photoetching of these materials.

(Effects of the present invention) As described above, the continuous excitation Q switch Nd of the present invention:
4th harmonic light of YAG laser's high-speed repetition
By using this method, it is possible to enhance the photochemical effect and photoheating effect on microscopic areas while avoiding optical damage, which cannot be achieved with conventional low-speed repetitive pulse light sources or continuous wave light sources. For this reason, when this light source is applied to optical CVD or optical etching, it is possible to perform excellent processing on a minute area unlike before.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an embodiment of the present invention, and FIG. 2 is a diagram showing an example in which the light source of the present invention is used in a CVD apparatus. In the figure, 1 is a Q-switched Nd solid-state laser, 2 and 3 are harmonic generators, and 4 is a wavelength selection element.

Claims (1)

[Claims] A light source for inducing a photochemical reaction, comprising a continuously pumped Q-switched Nd solid-state laser and an ultraviolet harmonic generator.