JPH0520504B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an apparatus for forming a thin film by photoexcitation.

[Prior art and its problems]

In recent years, in the semiconductor device manufacturing process, process technologies such as optical CVD have been actively researched and developed to lower process temperatures and shorten process steps. Ultraviolet light sources, which can cause electronic excitation in substances, have often been used as light sources to cause photoinduced reactions in photoCVD. Among these, pulsed ultraviolet light sources can heat the light irradiated area while suppressing the spread of heat from the irradiated area by appropriately selecting the characteristics of the irradiated light, so they can form fine patterns directly on the substrate. It has the advantage of being able to As this type of light source, excimer lasers and fourth harmonic systems of Nd:YAG lasers are known. Quartz substrate, Cr CVD gas
In 1984, experiments using a KrF excimer laser as a (CO) ₆ laser light source showed that the optical heating effect during the high CVD reaction process had a significant effect on improving film quality.
2019 Conference on Laser and Electro Optics [CLEO (Conference
This was clarified by Yokoyama et al. in a paper published on page 222 of Technical Digest FD-6 (on Lasers and Electro Optics). In addition, similar experiments using the fourth harmonic of an Nd:YAG laser as a light source and simulation calculations of thermal spread revealed that if pulsed laser light is used, the spread of the deposited film from the light irradiated area can be reduced to less than 1 μm. The 27th Semiconductor Integrated Circuit Symposium (1984)
(December 4, 2013), as shown by Morishige et al. on page 6 of the collection of lecture papers. These results demonstrate that repeatedly pulsed UV light sources are useful as optical CVD light sources.

However, in conventional laser-based CVD equipment, including these examples, the light intensity of the irradiated laser light is kept constant during the CVD time, and the optimal irradiation conditions are found simply by selecting the magnitude of that constant value. Therefore, this conventional optical CVD apparatus had the following serious drawbacks.

In the following, we will explain how to apply an ultraviolet pulsed light source onto a quartz substrate.
Using chromium film formation from Cr(CO) ₆ as an example, we will explain the shortcomings of conventional equipment and their causes. The quartz substrate is transparent to ultraviolet light, and the heating effect due to absorption by the substrate can be ignored. Let us consider the temperature rise of the CVD film in this case. The intensity of the irradiated laser light is constant during the CVD time. Immediately after the start of CVD, the absorption of laser light was absorbed by the substrate surface.
This occurs due to CVD gas and vapor phase CVD gas. At this stage, the temperature rise on the substrate surface is slight;
Decomposition products mainly due to photochemical reactions are deposited on the substrate. As time passes, as the thickness of the deposited layer on the substrate surface increases, the proportion of laser light absorbed by the deposited layer increases, and as a result, the peak surface temperature of the CVD film increases. Increasing the film temperature improves the quality of the film, but an excessive rise in temperature causes evaporation of the film, so there is an upper limit to the temperature that can be raised. The increase in film temperature is maximum when the CVD film thickness is about the absorption length of the irradiated laser beam, and when the thickness increases beyond that,
The increase in heat capacity of the CVD film suppresses the temperature rise of the film. Therefore, in a region where the CVD film thickness is equal to or greater than the absorption length of the irradiated laser beam, the film quality deteriorates again. As a result, large compositional non-uniformity occurs in the depth direction of the CVD film. Another drawback was that the film quality was poor immediately after the start of deposition, and the adhesion to the substrate was low. Also
When growing a relatively thick film of 1 μm or more, significant surface roughness occurs, which is thought to be caused by a drop in surface temperature, making it difficult to form a film with a smooth surface.

[Purpose of the invention]

The purpose of the present invention is to eliminate the drawbacks of conventional equipment that forms thin films while keeping the irradiation light intensity constant during CVD time, and to make it possible to form CVD films with high adhesion and excellent uniformity in the depth direction. An object of the present invention is to provide a thin film forming apparatus for forming a thin film.

[Structure of the invention]

The present invention provides a repetitive pulse light source, an optical system that guides the emitted light of the repetitive pulse light source to a substrate, a gas supply system that guides a gas that causes a photochemical reaction onto the substrate by irradiation with the emitted light, and a gas supply system that guides the substrate to the substrate. In a thin film forming apparatus comprising a reaction cell having a mechanism for holding in an atmosphere and a window for introducing the emitted light, the optical system is provided with an optical modulator, and the temperature of the light irradiation part on the substrate is adjusted. A temperature monitor unit is provided to detect the temperature, and a control unit is provided which includes a circuit for obtaining a peak signal of the output of the temperature monitor unit and a circuit for obtaining a difference signal between the peak signal and a predetermined reference signal. The optical modulator is driven by an output signal of a circuit for obtaining the difference signal.

[Working principle of the invention]

In order to solve the problems such as adhesion of CVD films and non-uniformity in the thickness direction, which were clarified in the description in the section of the prior art and its problems, it is necessary to adjust the peak temperature of the film during light pulse irradiation during CVD time. It is effective to maintain the temperature at a substantially constant level at which good film quality can be obtained. To this end, the temperature of the CVD film is increased in the time region immediately after the start of deposition and in the time region when the film thickness becomes thicker than the light absorption length, and the peak surface temperature of the CVD film during the deposition time is reduced. Keep the temperature slightly below the transpiration temperature. Furthermore, since there is almost no absorption of irradiation light at the start of deposition, the required irradiation intensity required to sufficiently heat the deposit becomes extremely high, which may cause damage to the substrate. Keep the irradiation intensity below the threshold for board damage. In addition, it is known that the cleanliness of the substrate surface before deposition is greatly related to adhesion strength, so it is important to apply strong light irradiation to sufficiently heat the film immediately after the start of deposition. Surface cleaning by desorption is also performed at the same time, and the adhesion to the substrate can be improved. For these reasons, if thin films are formed using the apparatus of the present invention, non-uniformity in the film thickness direction can be eliminated, and as a result, it is possible to deposit films as thick as 1 μm or more. Moreover, high adhesion force can be obtained between the substrate and the thin film.

〔Example〕

Embodiments of the present invention will be described in detail below with reference to the drawings. FIG. 1 is a block diagram of a specific embodiment of the present invention. This thin film forming device uses a Q switch.
A repetitive pulse light source 1 consisting of a fourth harmonic system of an Nd:YAG laser, an optical attenuator 2 that attenuates the intensity of the emitted laser beam, an optical modulator 3 that modulates the optical intensity, a mirror 4, and a slit 5. , a beam splitter 6, and a lens 7, and includes an optical system that guides the laser beam emitted from the repetitive pulse light source 1 to the substrate. The optical attenuator 2 is used to avoid damage to the substrate at the start of deposition as described in the section on the principle of operation of the present invention, and the optical attenuator 2 is used to prevent damage to the substrate when the transmittance of the optical modulator 3 is at its maximum. The irradiation light intensity is set to be maximum within a range that does not cause damage to the substrate. A beam splitter 6 placed between the slit 5 and the lens 7 is coated with a coating that transmits the light from the pulsed light source 1 and reflects the infrared light from the substrate.

The thin film forming apparatus further includes a reaction cell 11 installed on the stage 10 and a gas supply system 12 that supplies a gas that causes a photochemical reaction by irradiating the reaction cell with emitted light.
has a mechanism for holding the substrate 9 in the gas atmosphere and a window 8 for introducing the emitted light. Note that the stage 10 is used to irradiate light onto a desired position on the substrate 9.

The thin film forming apparatus includes a temperature monitor unit 14 having an infrared detection type temperature detector that detects temperature from infrared light reflected from the beam splitter 6, as described later, and a temperature monitor unit 14 that detects the temperature based on the signal from this unit. It further includes a control unit 13 for driving the modulator 3. The control unit 13 includes a peak hold circuit 16 that determines the peak temperature during light irradiation from the output of the temperature monitor unit 14, and a reference signal generator 17 that generates a signal corresponding to the reference temperature.
and a differential amplifier 15 that amplifies the difference signal between the output of the reference signal generator 17 and the peak hold circuit 16, and the output of the differential amplifier 15 is input to the modulation terminal of the optical modulator 3. There is. The temperature monitor unit 14, the control unit 13, and the optical modulator 3 perform feedback control of the irradiation light intensity so that the surface temperature of the thin film deposited on the substrate is within the optimum growth temperature range of the thin film. In other words, if the peak temperature measured by the temperature monitor unit 14 is higher than the reference temperature, the transmittance of the optical modulator 3 is lowered to lower the intensity of the irradiated light, and conversely, if the peak temperature is lower, the intensity of the irradiated light is increased. Take control. In the thin film forming apparatus configured as described above, the operation of forming a chromium film from Cr(CO) ₆ on the substrate 9 will be described below.

First, the gas supply unit 12 supplies Cr(CO) ₆ vapor to the reaction cell 11 using Ar gas as a carrier gas. Next, the stage 10 is used to move the substrate 9 to a desired position. Repeated pulse light source 1
When driven, pulsed light is emitted repeatedly,
After passing through the optical attenuator 2, the optical modulator 3, the mirror 4, the slit 5, and the lens 7, the light is transmitted to the substrate 9 in the reaction cell 11.
The chromium film starts to be deposited on the substrate 9. At the start of deposition, the optical modulator 3 is set to maximize transmittance by the feedback loop, and the pulsed light from the light source 1 is controlled by the optical attenuator 2 to reduce the intensity of the light irradiated onto the substrate 9. It is set to the maximum value within a range that does not cause damage. Therefore, the intensity of the irradiated light is high immediately after the start of deposition, and surface cleaning is performed by photodesorption. When the chromium film begins to accumulate, the absorption of the irradiated light increases and the temperature of the light irradiated area on the substrate rises. The infrared light from the substrate passes through the lens 7, is reflected by the beam splitter 6, and enters the temperature detector of the temperature monitor unit 14. The temperature detector detects the temperature of the light irradiation part on the substrate based on the incident infrared light. The detected temperature is input to the peak hold circuit 16 of the control unit 13. When the peak hold circuit holds the peak value of the input temperature, it inputs it to one input terminal of the differential amplifier 15. On the other hand, the reference signal generator 17 generates a signal corresponding to the reference temperature and inputs it to the other input terminal of the differential amplifier 15. The differential amplifier 15 amplifies the difference signal between the output of the reference signal generator 17 and the output of the peak hold circuit 16, and inputs the amplified difference signal to the modulation terminal of the optical modulator 3. The optical modulator 3 changes its transmittance based on the output of the differential amplifier 15. By the feedback loop as described above, the peak temperature of the light irradiation portion of the substrate 19 is controlled so as to always be within the optimum temperature range.

In the case of a substrate that absorbs little irradiated light, even if the transmittance of the modulator 3 reaches its maximum due to the operation of the feedback loop at the start of deposition, the substrate surface temperature will remain low.
It may happen that the temperature does not reach the optimum temperature range of the CVD film, but even in that case, after a very small amount of the CVD film has been deposited on the substrate, the peak temperature of the light irradiated area on the substrate will become a feedback loop. The temperature is always controlled to be within the optimum temperature range. The optimum temperature range is approximately 800°C to 1200°C for Cr(CO) ₆
At this time, a good film with a metallic luster and a smooth surface is deposited, and when the temperature is lower than 800°C, a transparent film with a severely rough surface is deposited;
When the temperature was higher than ℃, holes were observed in some parts of the film due to transpiration. The light irradiation intensity is set at the start of deposition.
10MW/cm ² , 5 seconds after starting 2MW/cm ² , after starting
At 2.5MW/ ^cm2 after 10 seconds, the thickness is 0.3μm,
There is no deposited layer with poor quality immediately after the start of deposition, and
The uniformity of the film in the thickness direction has also been greatly improved.
A deposit of Cr film was obtained. It was also found that the adhesion force between the substrate and the thin film at this time was so strong that it did not come off in a pull test using tweezers even when the substrate 9 was not cleaned.

In the above example description, the CVD gas is Cr(CO)
₆ , but good CVD can be achieved with other metals, semiconductors, or insulators.
It is obvious that the present invention is effective for materials in which the optical heating effect plays an important role in obtaining a film.
Furthermore, even in CVD that does not require a photoheating effect, the present invention can greatly improve adhesion as long as the substrate has a photocleaning effect that is effective in improving adhesion. In addition, in the above embodiment, Nd:YAG was used as the repetitive pulse light source.
Although the case where the fourth harmonic of a laser is used has been described, the present invention can also be applied to other visible light pulsed laser light sources or a light source made by dividing a continuous wave light source into pulses with a chopper, in that the heating effect of the pulsed light is affected. Since these effects can be expected, it goes without saying that the apparatus according to the present invention can be realized using these light sources.

〔Effect of the invention〕

As described above, the deposition time of the present invention can be applied to materials and substrates for which it is difficult to deposit a film with good adhesion to the substrate and uniformity in the thickness direction when forming thin films using conventional equipment. Using a device that temporally controls the intensity of the irradiated light so that the peak temperature of the CVD film inside is always within the optimum range, it is possible to obtain a good CVD film with high adhesion and excellent film uniformity. Become.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram of an embodiment of the present invention. 1... Repeated pulse light source, 2... Optical attenuator,
3... Optical modulator, 4... Mirror, 5... Slit, 6... Beam splitter, 7... Lens, 8
... window, 9 ... board, 10 ... stage, 11 ...
...Reaction cell, 12... Gas supply unit, 13
... Control unit, 14 ... Temperature monitor unit, 15 ... Differential amplifier, 16 ... Peak hold circuit, 17 ... Reference signal generator.

Claims (1)

[Claims] 1 A repetitive pulse light source, an optical system that guides the emitted light of the repetitive pulse light source to the substrate, a gas supply system that guides a gas that causes a photochemical reaction onto the substrate by irradiation with the emitted light, and a substrate that is placed in an atmosphere of the gas. In a thin film forming apparatus comprising a holding mechanism and a reaction cell having a window for introducing the emitted light, the optical system is provided with a light modulator and detects the temperature of the light irradiation part on the substrate. A temperature monitor unit is provided, and a control unit is provided which includes a circuit for obtaining a peak signal of the output of the temperature monitor unit and a circuit for obtaining a difference signal between the peak signal and a predetermined reference signal, A thin film forming apparatus characterized in that the optical modulator is driven by an output signal of a circuit for obtaining the signal.