JPH0775224B2 - Thin film forming equipment - Google Patents

Description

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

[Conventional technology]

As a conventional technique, there has been a thin film forming apparatus using synchrotron radiation as an excitation source as shown in FIG. this is,
For example, it is described in Japanese Patent Application No. 61-193088. In FIG. 6, 1 is an electron storage ring, 2 is a mirror chamber, 3 is a toroidal mirror for focusing light, 4 is a beam line (light propagation path), 5 is a reaction chamber, 6 is a substrate, 7 is a heating motor, Reference numeral 8 is an exhaust port, 9 is a source gas nozzle, 10 is a counter electrode, and 11 is a bias power supply.

The apparatus shown in FIG. 6 configured as described above guides the emitted light from the electron storage ring 1 into the reaction chamber 5 as an excitation source, installs the substrate 6 perpendicularly to the emitted light, and It is characterized in that a raw material gas is caused to flow to deposit a thin film on the substrate 6. In this type of device, in order to increase the light intensity per unit area in order to increase the deposition rate, for example, the toroidal mirror 3 provided upstream of the beam line 4 collects the emitted light, and the irradiation light In order to prevent absorption and attenuation by gas molecules in the gas phase before reaching the substrate 6, the irradiation light is spatially narrowed between the reaction chamber 5 and the beam line 4 to reduce the exhaust conductance (operation). The exhaust part) was provided. However, in this case, there is a drawback that the thin film formation region becomes narrow. Therefore, in order to expand the thin film formation region, for example, a mechanism for reciprocating the substrate 6 in the direction perpendicular to the irradiation light during deposition was newly required. However, the reciprocating motion causes a decrease in the deposition rate by that amount.

As another conventional technique, there is a thin film forming apparatus using an excimer laser 13 as an excitation source as shown in FIG. For example, this is described in the document “Yoshikawa and Yamaya, Japanese Applied Physics, 23
Volume (1984) Issue L91 (A. Yoshikawa and S. Yamaga, Jpn. J. Ap
pl. Phys., 23 (1984) L91) ". In this type of device, a window material (such as quartz or synthetic glass) 14 that allows the excitation light to pass therethrough and insulates the raw material gas in a vacuum can be used. Therefore, as shown in FIG.
Unlike the case where a line or vacuum ultraviolet light is used as the excitation light, it is not necessary to consider differential pumping.

[Problems to be solved by the invention]

However, the cross-sectional area of the laser beam is not so large as about 15 × 7 mm ^2, and if the substrate is installed tilted with respect to the laser beam in order to form a thin film on a large area, the light intensity per unit area will drop and therefore the deposition It had the drawback of slowing down.

The present invention has been made in view of the above circumstances, and an object of the present invention is to use soft X-rays or vacuum ultraviolet light as an excitation source when the product of the deposition rate and the thin film formation area is in the conventional technique. To provide a larger device.

[Means for solving problems]

In order to achieve such an object, the present invention provides a reaction chamber in which a substrate for depositing a thin film is installed, a gas introduction means for introducing a source gas into the reaction chamber, and a soft X-ray or vacuum ultraviolet ray in the reaction chamber. An irradiating means for irradiating light as irradiating light, an inclining means for inclining the substrate at an arbitrary angle with respect to the irradiating light, and a steep pressure difference between the reaction chamber and a beam line for guiding the irradiating light. For this purpose, the beam passage part of the connection part of the beam line to the reaction chamber is narrowed down and the differential exhaust part with a small exhaust conductance is provided, and the light collecting means for collecting the irradiation light is installed in the middle of the beam line. It is a thing.

[Action]

In the thin film forming apparatus according to the present invention, the substrate is installed so as to be inclined with respect to the irradiation light, the incident angle of the irradiation light on the substrate is reduced, the number of photoelectrons and the amount of reflected light from the substrate are increased, and these are gas phase gas. Excites the molecule, increasing the overall deposition rate.

〔Example〕

The present invention focuses on the fact that the deposition rate increases by increasing the contribution of the gas phase reaction among the components that govern the reaction mechanism, and is characterized by forming a thin film by inclining the substrate with respect to irradiation light. To do.

An embodiment of the thin film forming apparatus according to the present invention will be described below with reference to FIGS.

FIG. 1 is a configuration diagram showing the basic configuration of the present apparatus.
In FIG. 1, 1 is an electron storage ring as an irradiation means which is a soft X-ray or vacuum ultraviolet light generation source, 1a is an electron, 2 is a mirror chamber, 3 is a toroidal mirror as a condensing means, 4
Is a light propagation path (beam line) consisting of a vacuum pipe, 5 is a reaction chamber, 6 is a substrate to be processed, 7 is a heater for heating,
8, 15 are exhaust ports, 9 is a source gas nozzle as a gas introducing means, 12 is a substrate holder as an inclining means, 16 is a light propagation path 4
This is a radiant light introduction port with a reduced exhaust conductance in order to apply differential exhaust between the reaction chamber 5 and the reaction chamber 5.

In this apparatus configured as described above, a differential exhaust unit including the radiant light introducing port 16 and the exhaust port 15 is incorporated in order to provide a steep pressure distribution between the light propagation path 4 and the reaction chamber 5. There is. The opening area of the synchrotron radiation inlet port 16 is 7 × 13m
m ^2, the length 18cm, the pumping speed of the vacuum exhaust pump attached to the exhaust port 15 is 330 / sec. With this configuration, when the pressure in the reaction chamber 5 is 13 Pa, the pressure directly above the exhaust port 15 in the light propagation path 4 is 0.36 Pa, which is about 37 times the pressure difference between the two points.

Next, the operating principle, features, and main effects of this device will be described with reference to FIG. FIG. 2 shows the dose amount of the deposited film thickness (electron storage ring) using the device shown in FIG. 1 and the angle θ between the emitted light and the substrate 6 (hereinafter referred to as “oblique incidence angle”) as a parameter. 1) shows the dependence defined by the product of current and time. The experimental conditions are that the pressure of silane (SiH ₄ ) is 2.7 Pa, the pressure of nitrogen (N ₂ ) is 60 Pa, and the temperature of the substrate 6 is about 200 ° C. The current value of the electron storage ring 1 during the experiment was 1
It was about 00 to 200 mA. In FIG. 2, S1 is a characteristic curve with an oblique incident angle θ = 90 degrees, S2 is a characteristic curve with an oblique incident angle θ = 45 degrees, and S3 is a characteristic curve with an oblique incident angle θ = 30 degrees. As is clear from FIG. 2, the smaller the oblique entry angle θ, the higher the deposition rate.

FIG. 3 shows the 1 / sin θ dependence of the deposition rate ratio (deposit rate, the ratio of a certain oblique incident angle and the deposition rate / the deposition rate at an oblique incident angle of 90 degrees) using the gas pressure condition during the experiment as a parameter.
Although the 1 / sin θ dependency differs depending on the gas pressure condition, the deposition rate also increases as the oblique incident angle θ decreases. In FIG. 3, S4 is the pressure of the silane (SiH ₄₎ 2.7P
a, Characteristic curve when nitrogen (N ₂ ) pressure is 13Pa, S5 is silane (SiH ₄ ) pressure 2.7Pa, nitrogen (N ₂ ) pressure 60Pa
It is a characteristic curve in the case of. As can be seen from FIG. 3, the characteristic curve S5 begins to saturate near θ = 50 degrees, and the deposition rate ratio does not change significantly at θ = 50 degrees, 45 degrees, and 30 degrees.

As the oblique incident angle θ decreases, the irradiation area on the substrate 6 increases and the light intensity per unit irradiation area decreases. Therefore, if the deposition rate is proportional to the light intensity, as described in the section of the prior art, as the oblique entry angle θ decreases,
The deposition rate should decrease. Therefore, Figs. 2 and 3
Another mechanism must be considered to explain the results in the figure.

FIG. 4 is a diagram for explaining the mechanism of emission of photoelectrons from the substrate 6 in order to consider this point. When the radiated light 17 having the beam cross-sectional area S is incident on the substrate 6 at an oblique incident angle θ, the light is absorbed up to a certain penetration distance l in the substrate 6 determined by the absorption coefficient, and in the process, atoms forming the substrate 6 are excited. And generate photoelectrons. The generated photoelectrons collide with another atom to be excited, or excite a lattice system to lose energy, while some photoelectrons completely lose energy in the substrate 6. It jumps out from outside with constant kinetic energy. The escape depth dε is a measure of how much the photoelectrons jump out from the surface of the substrate 6. The escape depth dε varies depending on the kinetic energy of photoelectrons, but is about 5 to 50Å. This is described in, for example, the document “Electron spectroscopy, edited by The Chemical Society of Japan, Academic Publishing Center, Tokyo, 1977, p. 97”.

On the other hand, for the penetration distance l of the radiated light, for example, when the wavelength is 100Å and the substrate is Si, the linear absorption coefficient is about 100 μm ⁻¹ , so
It becomes 100Å, and l> dε. Therefore, in such a case, when obtaining the number of photoelectrons generated from the substrate 6, as a first approximation, as shown in FIG. 4, the substrate structure within the depth dε under the area irradiated by the radiated light is used. Consider the number of atoms N1. N1 is given by the following equation, where the atomic density of the substrate is n [pieces / cm ³ ].

N1 = S.d.epsilon.n / sin θ [pieces] (1) The number of photoelectrons N2 generated is I [photons /
(Sec · cm ² )], and the photoionization cross section is σ [cm ² ],
It is given by the following formula.

N2 = I · N1 · σ [pieces / second] (2) That is, from equations (1) and (2), when the oblique incident angle θ becomes small, the photoelectrons generated are proportional to 1 / sinθ. You can see that it increases. Detailed analysis considering the reflection of synchrotron radiation on the substrate surface and the angle dependence of the photoelectron generation direction
For example, reference “Kobayashi, Record of 5th Lecture on Accelerator Science and Technology, 1984, p. 250 (M. Kobayashi, Proceedings o
f the 5th Symposium on Accelerator Science and Tec
hnology, (1984) p.250) ”.

Further, in the light of the soft X-rays and the vacuum ultraviolet region used as the excitation source in this device, the real part n of the complex refractive index of the substrate is a value slightly smaller than 1, so the vertical reflectance is extremely low. As the angle of oblique incidence θ is decreased, total reflection occurs at a certain critical angle. On the other hand, in the case of visible light or ultraviolet light, n is generally larger than 1 and the vertical reflectance is to some extent, but total reflection does not occur even if the oblique incident angle θ is reduced. Therefore, in this device, if the oblique inclination angle θ is made small, the number of photoelectrons from the substrate increases and the reflected light from the substrate increases, and they excite gas phase gas molecules to Therefore, it is considered that the deposition rate is increasing.

In FIG. 3, the dotted line S6 is a straight line proportional to 1 / sin θ. When the gas pressure in the reaction chamber 5 is high, that is, the characteristic curve S5, the deposition rate closely matches the straight line of 1 / sin θ when the oblique inclination angle θ is about 45 degrees or less, and the reaction is caused by the photoelectrons generated from the substrate. It suggests that we are making progress. On the other hand, when the gas pressure is low, that is, when the characteristic curve is S4, the deposition rate does not increase much even if the oblique incident angle θ becomes small. By the way, under the condition of the characteristic curve S4, it is proved from the analysis of the inclination of the edge of the deposited silicon nitride film pattern that the reaction mechanism is dominated by the substrate surface excitation reaction rather than the gas phase reaction. This can be seen, for example, in the reference "Kuraki and Urisu, 18th SDS DM (19
86) A-7-6LN, p. 727 (H. Kyuragi and T. Urisu, 18th
SSDM (1986) A-7-6LN.p.727) ".

Considering the results of both S4 and S5, when the gas pressure is high, the gas-phase excited reaction becomes dominant, and therefore, it is easily affected by photoelectrons from the substrate and reflected light from the substrate. on the other hand,
It can be interpreted that when the gas pressure is low, the substrate surface excitation reaction is the main and is not significantly affected by photoelectrons and reflected light.

From the above results, in the method of depositing a thin film by irradiating the substrate 6 placed in the reaction chamber 5 filled with the reaction gas with soft X-rays or vacuum ultraviolet light, when the pressure of the reaction gas is high, it is particularly remarkable. By reducing the oblique incident angle θ which is the angle formed by the irradiation light and the substrate 6, it is possible to increase the deposition rate and the thin film deposition area. Also,
Even if the pressure of the reaction gas is low, the product of the deposition rate and the thin film deposition area can be increased by decreasing the oblique incident angle θ.

Considering this effect under the condition that the thin film deposition area is constant, it means that the cross-sectional area S of the irradiation light can be narrowed. Therefore, even if the emitted light from the electron storage ring 1 is collected by the toroidal mirror provided in the upstream part of the beam line 4 in order to increase the light intensity per unit area and increase the deposition rate, the thin film deposition area is reduced. It can be constant. In addition, as shown in FIG. 1, the irradiation light is spatially narrowed between the reaction chamber 5 and the beam line 4 to increase the pressure in the reaction chamber 5 and between the reaction chamber 5 and the beam line 4. It is possible to provide a steep pressure distribution. If the pressure in the reaction chamber 5 increases,
Naturally, the deposition rate will increase.

FIG. 5 illustrates another effect utilizing the incident angle dependence of the deposition rate. In FIG. 5, θ1 is irradiation light
The incident angle of 17 with respect to the substrate and 18 is the deposited film. When the substrate has minute irregularities, for example, when there is a line-and-space pattern, the irradiation light 17 is vertically incident on the substrate at the tops of lines and the valleys of spaces.
However, the incident light enters the side wall of the line portion at an incident angle θ1. Therefore, even if there is such a step and the aspect ratio is as high as possible, since the deposition rate at the side wall portion is high, it is possible to deposit a thin film with good coverage. Normal decompression CV
In the D method and the plasma CVD method, although the coating property is good, in principle, a certain amount of deposited film thickness is required to cover the step with a high aspect ratio as long as the deposition is from a gas phase reaction. However, in the case of the present apparatus, the substrate surface excitation reaction is the main and the deposition rate on the side wall can be increased, so that the step can be covered even with an extremely thin film thickness.

However, in this case, it is necessary to irradiate the surface of the substrate with soft X-rays or vacuum ultraviolet light, and if the incident angle θ1 is too small, total reflection occurs on the surface of the substrate and photons penetrating into the substrate are reduced. It must be taken into consideration that the number of photoelectrons generated will decrease. For example,
When light of wavelength 93.4Å is incident on the Si substrate, θ1 <5.1
Since total reflection occurs at a degree, the inclination α (= 90 ° -θ1) of the convex portion formed on the substrate must be 84.9 degrees or less. Of course, this value depends on the substrate material and the irradiation wavelength. An effective wavelength can be selected by providing a spectroscopic element on the optical axis in FIG. This spectroscopic element may be provided on the optical axis between the electron storage ring 1 and the toroidal mirror 3 or between the toroidal mirror 3 and the reaction chamber 5. Also, the toroidal mirror 3 may be replaced with a spectroscopic element that also serves as a light collector.

〔The invention's effect〕

INDUSTRIAL APPLICABILITY As described above, the present invention irradiates soft X-rays or vacuum ultraviolet light onto a substrate to be processed installed in a reaction chamber into which a source gas is introduced, and deposits a thin film on the substrate. By adjusting the angle formed by the tilting means,
Since the product of the thin film deposition area and the deposition rate can be increased, the thin film can be uniformly deposited with high throughput.

Further, since the irradiation light can be converged at a constant thin film forming region and the pressure inside the reaction chamber can be increased by providing a differential exhaust unit between the reaction chamber and the beam line, further increase in deposition rate can be expected. effective.

Further, when applied to the case of depositing a thin film on a substrate having irregularities, there is an effect that it is possible to form a thin film with excellent coverage even with a step having a high aspect ratio, with an extremely thin film.

[Brief description of drawings]

FIG. 1 is a configuration diagram showing an embodiment of a thin film forming apparatus according to the present invention, FIG. 2 is a graph showing a dose amount dependency of a deposited film thickness, and FIG. 3 is a graph showing an incident angle dependency of a deposition rate. FIG. 4 is an explanatory view for explaining a photoelectron emission mechanism from the substrate, FIG. 5 is an explanatory view showing a case where the present invention is applied to a substrate having unevenness, and FIGS. 6 and 7 are conventional drawings. It is a block diagram which shows a thin film forming apparatus. 1 ... Electron storage ring, 2 ... Mirror room, 3 ... Toroidal mirror, 4 ... Light propagation path (beam line), 5 ...
Reaction chamber, 6 ... Substrate, 7 is heater for heating, 8,15 ... Exhaust port, 9 ... Raw material gas nozzle, 12 ... Substrate holder, 16 ...
Synchrotron radiation introduction port.

Claims (4)

[Claims] 1. A reaction chamber in which a substrate for depositing a thin film is installed, gas introducing means for introducing a raw material gas into the reaction chamber, and the reaction chamber is irradiated with soft X-rays or vacuum ultraviolet light as irradiation light. In order to provide a sharp pressure difference between the irradiation means, the tilting means for installing the substrate at an arbitrary angle with respect to the irradiation light, and the reaction chamber and the beam line for guiding the irradiation light, A differential pumping section in which the beam passing section of the connecting section of the beam line to the reaction chamber is narrowed down to reduce the pumping conductance, and a focusing means for focusing the irradiation light is installed in the middle of the beam line. A thin film forming apparatus characterized by the above. 2. The thin film forming apparatus according to claim 1, wherein the irradiation means is an electron storage device. 3. The thin film forming apparatus according to claim 1, wherein the tilting means has an oblique incident angle between the irradiation light and the substrate of 50 degrees or less. 4. The thin film forming apparatus according to claim 1, wherein the beam line is provided with a spectroscopic element for selecting the wavelength of irradiation light in the middle of the beam line.