JPS63113A - Device for forming thin film - Google Patents

Abstract

PURPOSE:To contrive the reduction of an impurity concentration by controlling the emission time of a second pulse laser beam source so as to make its phase different from a phase of a first pulse laser beam source. CONSTITUTION:A delay circuit 22 gives a delay to a first trigger signal tr.S1 of a first pulse laser beam source 1 and an output signal of a clock generating circuit 23 which starts the generation of repetitive pulses is outputted as a second trigger signal tr.S2 for controlling a second pulse laser beam source 2 through a gate circuit 19 which is switched by an output of a counter circuit 18. The counter circuit 18 operates so as to open the gate circuit 19 only during the time from an output of the delay circuit 22 is accepted till a predetermined number of clock signals are counted. At this time, a delay time, a clock period, and a counted number of the counter are so predetermined that a series of time from a repetitive period control unit 14 accepts the first trigger signal till the output of the second trigger signal finishes becomes shorter than a repetitive period of the first pulse laser beam source 1. Thus, the overlapping of the emission time of the pulse laser beam sources 1 and 2 can be avoided.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a thin film forming apparatus that forms a thin film by optical excitation.

[Conventional technology and its problems]

In recent years, in the semiconductor device manufacturing process, optical CV
D-nato photoexcitation process technology is being actively researched and developed as a technology that can lower process temperatures and shorten process steps. Compared to conventional plasma processes, photo-CVD causes less damage to substrates and device layers thereon, and has high expectations as a method that enables the formation of acceptable films at lower temperatures. We have already used photo-CVD techniques to develop metal materials such as tungsten and molybdenum, which are promising as future wiring materials.
Deposition of insulators such as 5i02 used for gate insulating films of MOS ICs has been realized. For example, Applied Physics Letters (,~pplied
Physics 1etters, Volume 40, No. 7
On pages 16 to 719, Boyer et al. used an ArF excimer laser as a light source to
It has been reported that a SiO□ film can be deposited using N20 and N20 gases as raw material gases. According to this document, it is shown that the obtained deposited film has properties such as adhesion and breakdown voltage that are comparable to those of the thermally oxidized SiO□ film. However, the interface state density is about 10 to 100 times higher than that of the thermally oxidized 5i02 film, and as impurities,
It has been described that it contains considerable amounts of hydrocarbons and nitrogen. The interface level is desired to be as low as possible because it has an adverse effect when used in a gate insulating film of a MOS IC or the like. Although this paper does not specifically address the cause of this increase in interface states, it is clear that the impurities mentioned above, such as nitrogen and hydrocarbons, have a negative effect. Also, the third
As shown in the 2nd Spring Proceedings of the Japan Society of Applied Physics (1985), lecture number 30p-2, page 340, the OH groups of impurities in SiO In some cases, traps are formed at the interface, leading to an increase in interface states. In order to eliminate the causes of these increases in interface levels, it is effective to reduce the content of impurities such as nitrogen, hydrocarbons, and hydrogen in the CVD film as much as possible. However, conventional photo-CVD equipment has a problem in that it is not possible to effectively reduce the incorporation of these impurities.

[Means for solving problems]

The thin film forming apparatus of the present invention includes a first pulsed laser light source that generates light of a first wavelength, a CVD cell provided with a window, and a CVD cell that directs the emitted light of the first pulsed laser light source to a substrate within the CVD cell. a first optical system that guides a gas containing a first gas component that causes a deposition reaction by irradiation with light of the first wavelength.
A CVD raw material gas supply system that supplies a VD cell, and the CVD
In a thin film forming apparatus equipped with a mechanism for holding the substrate in a D cell, a second gas component that etches the main impurity component of the thin film produced by the deposition reaction by irradiation with light of a second wavelength is applied. an etching gas supply system that supplies the CVD cell; a second pulsed laser light source that generates light of the second wavelength; and guides the emitted light of the second pulsed laser light source to the substrate within the CVD cell. a second optical system; and a repetition process that controls the emission timing of the second pulsed laser light source at a predetermined repetition period shorter than the time required to grow a monolayer of the thin film and out of phase with the first pulsed laser light source. It is equipped with a periodic control unit.

[Principle and operation of the present invention] In the C'V D reaction using pulsed laser light, the CVD raw material gas decomposes and reacts with each irradiation of each laser pulse, and the generated molecules are deposited on the substrate. It is thought that a thin film is formed by repeating the steps. At this time 1
The deposition thickness per pulse is at most about one person/pulse under conditions where a dense film can be obtained. In other words, the average thickness of the newly deposited film due to each pulse irradiation is
Each layer is sufficiently thinner than one atomic layer. Therefore, after each pulse irradiation, atoms or molecules serving as impurities are considered to be exposed at the outermost surface of the film. The present invention focuses on this point, and etches the impurity atoms or molecules in the deposited atomic layer-order thin film by irradiating light of a different wavelength immediately after irradiation with each laser pulse for CVD. By causing a reaction and removing this impurity component, C
This is based on the idea that it is possible to suppress the incorporation of impurities into the VD film. According to this method, even if the generation and contamination of impurities cannot be avoided with CVD reaction alone, CVD
Impurities can be removed by an etching reaction before they are incorporated into the D film, resulting in highly pure C.
A VD film can be obtained. In addition to the effect of removing impurities due to the etching reaction, the laser light that causes this etching reaction has a photodesorption effect, which causes volatile molecules such as nitrogen and oxygen adsorbed on the surface to be removed. can be removed.

〔Example〕

Next, embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is a block diagram of the main parts of a first embodiment of the present invention.

This example is an example in which the present invention is applied to CVD of 5i02. The CVD raw material gas supply system 9 is 5iH2C2□N
2. Supply a mixed gas of N20 gas to the CVD cell 8.

In addition, the etching gas supply system 10 is a gas supply system 10 for etching.
1!2 Supply gas. A first pulsed laser light source 1 composed of an ArF excimer laser is used to excite CVD raw material gas, and its emitted light is sent to a second mirror 4.
, third mirror 5, and second window 7 into the CVD cell 8. The second pulsed laser light source 2, which is composed of a Xel' excimer laser, uses etching gas CI! The emitted light is used to excite the CVD cell 2, and the emitted light is irradiated onto the substrate in the CVD cell through the first 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 a predetermined value during CVD by adjusting the exhaust speed of the exhaust pump 11 and the supply amount from the CVD raw material gas supply system 9 and the etching gas supply system 10. . The repetition period control unit 14 receives the emission signal of the first pulsed laser light source 1 and generates a trigger with a predetermined delay shorter than the repetition period of the first pulsed laser light source 1 from this emission signal through a delay circuit. The configuration is such that the signal is given to the second pulsed laser light source 2.

FIG. 2 is a block diagram of a first specific example of the repetition period control unit.

A delay circuit 22 gives a delay to the first trigger signal of the first pulsed laser light source 1, and the output signal of the clock generation circuit 23, which starts generating repetitive pulses in response to this delayed signal, is generated by the output of the counter circuit 18. It is output as a second trigger signal to control the second pulsed laser light source 2 through a gate circuit 19 that is opened and closed. At this time, the counter circuit 18 is operated by the gate circuit 1 only during the period from receiving the output of the delay circuit 22 until counting the clock signal by a predetermined number.
It operates to open 9. In this case, the delay time, clock period, and count number of the counter are such that the series of times from when the repetition period control unit 14 receives the first trigger signal to when the output of the second trigger signal ends is the same as that of the first trigger signal. It is set to be shorter than the repetition period of the pulsed laser light source 1. By doing so, it is possible to avoid overlapping the emission timings of the first pulsed laser light source 1 and the second pulsed laser light source 2. In this way, for each irradiation from the first pulsed laser light source 1, irradiation can be performed multiple times from the pulsed laser light source 2 of the sibling 2.

FIG. 3 is a block diagram of a second specific example of the repetition period control unit.

The counter circuit 20 counts the first trigger signal from the first pulse laser light source 1, outputs a pulse signal when a predetermined number is counted, and outputs a second trigger signal through a delay circuit 21 for shifting the emission timing. The structure is such that a pulse signal is output when the paper is closed. In this case, irradiation can be performed from the second pulse laser light source 2 once for every plurality of irradiations from the first pulse laser light source.

In either case, the emission timings of the first pulsed laser light source and the second pulsed laser light source do not overlap, and the light pulses for excitation of the etching gas are irradiated at appropriate intervals according to the deposition rate. Can be done.

Next, a thin film forming method using this example will be explained. The composition of the gas used was 5iH2Cff21%, N2
10%, N2086%, and 6223%, the pressure inside the CVD cell 8 was 1066 f'a, and the substrate temperature was 300° C. to form a SiO□ film.

FIG. 4 is a trigger signal waveform diagram for controlling the irradiation laser.

The solid line shows the first trigger signal for controlling the F laser for CVD, and the dashed line shows the second trigger signal for controlling the XeCJ7 laser for etching.According to the timing irradiation this evening, the ^ "Even if a 5i02 film containing impurities is deposited by irradiation with the F laser beam, the hydrocarbons and N2 on the substrate surface will be converted to volatile materials such as cCe4 and FrC47 by the next irradiation with the XeCj' laser beam for etching. It becomes a chloride and separates into the gas phase.

It is believed that N2 is removed from the surface as N2 gas due to photodesorption effects. Note that C22 does not absorb at the oscillation wavelength of 193 nm of the ArF laser, and conversely, the raw material gas component for CVD does not absorb at the oscillation wavelength of 308 nm of the XeCe laser, so each reaction of CVD and etching is different from each other. The optical CVD method obtained in this way can be selectively caused by the wavelength of the irradiated laser light, and unnecessary reactions other than the intended one, such as deposition reactions, do not occur.
The interface state density of the 5i02 film is 1.
It was found that the value can be reduced to about 5 times, which is almost comparable to that of the thermal oxidation method, and is a value that can be used as a gate insulating film of MOS IC. - On the other hand, the interface state density in the case of normal photo-CVD without the above-mentioned photo-etching process is more than 20 times higher than that according to the present invention,
It has been found that the present invention is effective in improving the interface state density, which is susceptible to the effects of impurities and the like.

In the above example, the number of irradiations with the pulsed laser beam to excite the etching gas is once for each pulse irradiation for excitation of the raw material gas for CVD.
It is obvious that the effect of removing impurity components will be more significant if the light pulse for excitation of the etching gas is irradiated multiple times for every light pulse for excitation of the CVD source gas. Conversely, if the CVD rate is extremely low, one light pulse for excitation of the etching gas may be irradiated for every plurality of light pulses for excitation of the CVD source gas.

In the above example, CVD of 5i02 film was explained as an example, but in CVD of other insulators, semiconductors, metals, etc., it is possible to combine CVD source gas, etching gas, and a pulsed laser light source that can excite these gases. If so, the thin film forming apparatus of the present invention can be used to produce high-quality carbon with few impurities.
A VD film can be formed.

FIG. 5 is a block diagram showing a second embodiment of the present invention.

The difference from the first embodiment is that the first pulsed laser light source 1
The emitted light of They are different in that they are irradiated. This configuration is
The raw material gas molecules for CVD adsorbed on the substrate surface are photo-CVD.
It is effective when it participates in a reaction. Examples of such raw material gas include organometallic compounds such as metal carbonyl.

FIG. 6 is a block diagram showing a third embodiment of the present invention,
Mask 1 that defines the irradiation pattern on the optical path in the second embodiment
6 and a lens 17 for transferring the pattern onto the substrate. This configuration has the advantage that the CVD film can be selectively formed only at required positions on the substrate.

〔Effect of the invention〕

As described above, since the thin film forming apparatus of the present invention is equipped with a second pulsed laser light source that excites the gas that etches impurities, it is possible to form thin films with significantly reduced impurity concentration compared to conventional apparatuses. Therefore, it becomes possible to apply the photoCVD method to a wide range of semiconductor manufacturing processes. In addition, the device of the present invention can be used for combinations of CVD raw material gas and light source that are difficult to use practically because the content of impurities in the film becomes too high with conventional devices.
It becomes possible to form a high-purity CVD film, and the range of choices of practically usable CVD materials can be greatly increased.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of the main parts of the first embodiment of the present invention,
Figures 2 and 3 show the first cycle of the repetition cycle control unit. A block diagram of the second specific example, FIG. 4 is a trigger signal waveform diagram,
Figures 5 and 6 are the second figures of the present invention. FIG. 7 is a block diagram of the main parts of the third embodiment. DESCRIPTION OF SYMBOLS 1... 1st pulse laser light source, 2... 2nd pulse laser light source, 3... 1st mirror, 4... 2nd mirror, 5... 3rd mirror, 6 ...first window, 7
...Second window, 8...CVD cell, 9...CVD
raw material gas supply system, 10... etching gas supply system, 11... exhaust pump, 12... heater, 13...
- Substrate, 14... Repetitive cycle control unit, 15...
・Dichroic mirror, 16...Mask, 17...
- Lens, 18... Counter circuit, 19... Gate circuit, 20... Counter circuit, 21.22... Delay circuit, 23... Clock generation circuit.阜 l 口；゛に

Claims (1)

[Claims] a first pulsed laser light source that generates light of a first wavelength;
a CVD cell equipped with a window; a first optical system that guides emitted light from the first pulsed laser light source to a substrate within the CVD cell;
A first component that causes a deposition reaction by irradiation with light of the first wavelength.
CVD supplying a gas containing a gas component to the CVD cell.
In a thin film forming apparatus equipped with a raw material gas supply system and a mechanism for holding the substrate in the CVD cell, impurity components of the thin film generated by the deposition reaction are etched by irradiation with light of a second wavelength. an etching gas supply system that supplies a second gas component to the CVD cell; a second pulsed laser light source that generates light of the second wavelength; and an etching gas supply system that supplies the second gas component to the CVD cell; a second optical system that guides the substrate to the substrate within the cell; and a second pulsed laser light source that is out of phase with the first pulsed laser light source and that has a predetermined repetition period shorter than the time required to grow one monolayer of the thin film. 1. A thin film forming apparatus comprising: a repetition cycle control unit that controls emission timing of the .