JPS63145777A - Production of hexagonal boron nitride film - Google Patents

Abstract

PURPOSE:To deposit a satisfactorily crystallized hexagonal boron nitride film in the form of a thin film on a substrate, by bringing a nitrogen compd. and boron compd. into reaction at a specific temp. by a chemical vapor deposition method. CONSTITUTION:The substrate is disposed in a reaction tube of a CVD device. The nitrogen compd. (NH3, etc.) and the boron compd. [B(C2H5)3, etc.] are introduced with gaseous hydrogen as a carrier into the reaction tube and are brought into reaction in a 700-1,700 deg.C range to form the hexagonal boron nitride film on the substrate. The inflow rates of the respective compds. at this time are regulated to, for example, about >=25NH3/B(C2H5)3 molar ratio. A quartz glass plate or the like having about 0.3-2.0mm thickness is used for the substrate and the preferable thickness of the hexagonal boron nitride film is about 0.5-50mu. The intrusion of impurities into the film is preventable if consideration is paid for the conditions for production. Application of adequate tensile stress to the film is possible by the control and determination of the material quality, thickness and crystal direction of the substrate. The hexagonal boron nitride film used for the mask substrate, etc., in X-ray lithography is thereby produced.

Description

DETAILED DESCRIPTION OF THE INVENTION "Field of Industrial Application" The present invention relates to a method of manufacturing a hexagonal boron nitride film used as a mask substrate in X-ray lithography.

"Conventional Technology" In recent years, microfabrication technology in the so-called submicron region has been in the spotlight as one of the trends toward miniaturization of semiconductor manufacturing technology. Microfabrication technology can be roughly divided into those using electron beams, those using ion beams, and those using X-rays, but in particular, microfabrication technology using xe;t (
X-ray lithography (hereinafter referred to as X-ray lithography) is capable of forming patterns as fine as 0.1 μ7 on a substrate because the wavelength of the X-rays it irradiates is short (about a few to several tens of meters). It has advantages and is attracting attention.

The mask substrate used in area X-ray lithography, on which the original pattern for transfer is formed, must be sufficiently transparent to the curved X-rays, so the materials it is made from are limited to light elements. reactor. Further, other conditions required for the X-ray mask substrate include the following.

(Eye) Be transparent to the X-ray source in the most sensitive area of the resist.

(2) It must have appropriate strength both in terms of handling and in forming patterns.

(3) It must be thermally and chemically stable, considering the process of creating patterns etc. on the substrate.

(4) Be stable against X-ray irradiation.

(5) Be optically transparent to enable overlapping of masks in the visible light range.

(6) The surface should be flat within an allowable range for forming a mask pattern.

In addition to silicon (Si) substrates conventionally used in semiconductor manufacturing, boron nitride (
BN), boron carbide (B, c), boron silicide* (I3.Si)
Mask substrates for X19 lithography using borides have been proposed in recent years (for example, Japanese Patent Publication No. 56-37G92).

Among these borides, boron nitride is particularly used in (2) and (6) above.
), which almost satisfies the other conditions except for the condition L,
It can be said that it is a suitable material as a mask substrate for line lithography f.

As a manufacturing method for this boron nitride film for X-ray lithography, boron halide (BCl, [3Fz,
Chemical vapor deposition (CV) using diborane (B, Hll) and ammonia (Nll++)
A common method is to deposit a thin film on a substrate using method D). At this time, the reaction temperature was set at 400°C so as not to give excessive stress to the boron nitride film after formation.
The temperature was usually around 700°C.

``Problems that the invention cannot solve'' By the way, there were problems that remained when the aforementioned boron nitride film was used as a substrate for X-ray lithography. In order to maintain the flatness of the resulting film, it was necessary to apply an appropriate tensile stress to the film.

However, pure boron nitride (I3N) belongs to a hexagonal system with a crystal structure similar to graphite etc., and although it is a colorless and transparent crystal, conventionally provided boron nitride thin films have a yellow color and are amorphous. Most of them were membranes. This is because, according to research by the present inventors, the conventional boron nitride thin film contains less nitrogen than boron and 20-30% hydrogen.
This is an amorphous film in which about 30% of hydrogen is mixed in. Due to the mixing of hydrogen, it is difficult to obtain the strength that mononitride crystal should originally have in the thin film state, and it is also difficult to use it as a mask substrate for X-ray lithography. In this case, the heat resistance against the generation of heat accompanying X-ray irradiation or the X-ray resistance due to changes in composition are not good, which is a cause for improvement.

The application of stress to the formed film has traditionally been controlled by the film formation temperature, gas pressure, RF power, etc., but the factors that apply stress to the boron nitride film are still not fully understood. Therefore, as mentioned above, it has been difficult to provide a boron nitride film with a level of flatness suitable for use in X-ray lithography.

This invention was made in view of the above-mentioned problems, and its purpose is to provide a method for manufacturing a hexagonal boron nitride film that can satisfy the requirements for a mask substrate for X-ray lithography. be.

“A means to solve problems.

In order to solve the above-mentioned problems, the present invention provides a method for depositing a nitrogen compound and a boron compound by a chemical vapor deposition (CVD) method.
The present invention constitutes a method for manufacturing a hexagonal boron nitride film in which the reaction is carried out within the range of 0°C to 1700°C.

Hereinafter, the method for manufacturing a hexagonal boron nitride film of the present invention will be described in detail step by step with reference to FIGS. 1 to 5.

FIG. 1 is a diagram showing a hexagonal boron nitride film manufactured according to the present invention. In the figure, reference numeral 1 indicates a hexagonal boron nitride film, and the peripheral edge of this hexagonal boron nitride film 1 is supported by a substrate 2 made of quartz glass or the like formed on a frame to maintain its flatness. There is.

Hexagonal boron nitride film according to this invention! The nitrogen compounds used in the production include ammonia (NH3), hydrazine (NtH,), trialkylamine (N (Cn
Hzn+t)3), etc., but ammonia is preferred from the viewpoint of handling.

Further, as the boron compound, boron halide (
BCl, BF2, BBrs, etc.), diborane (nt■
−t a ), triedylborane < s (c tr+
5) 3) or trimethoxyborine (13(C
Among them, trimethoxyborine is most preferable from the viewpoint of ease of handling, and in this case, hydrogen or nitrogen may be used as the carrier gas.

Using these nitrogen compounds and boron compounds, a hexagonal boron nitride film l as shown in FIG. 1 is produced by chemical vapor deposition (hereinafter referred to as CVD).
The CVD equipment for realizing method D is a normal pressure CVD equipment,
A well-known device such as a low-pressure CVD device may be used, and special means may be required.
No equipment required. Furthermore, when an organic metal such as triethylborane or l-rimethoxyborine is used as the boron compound, so-called metal-organic pyrolysis chemical vapor deposition (MOC) can be used.
A hexagonal boron nitride film is formed by the reaction of a nitrogen compound and a boron compound (organic gold) using a method called VD) method.
In this case as well, a conventionally used ~10CVD apparatus may be used. In addition,
The thickness of the hexagonal boron nitride film l deposited on the base@2 may be determined as appropriate depending on its intended use, and may be from 0.5 to 5.
Approximately 0 μm is preferable.

A feature of the method for producing hexagonal boron nitride 1121 according to the present invention is its reaction temperature, that is, the nitrogen compound and boron compound are heated at 700°C to 1700°C, preferably at 9°C.
The hexagonal boron nitride film 1 is deposited on the substrate 2 by reacting at a temperature within the range of 00°C to 1100°C.

In the reaction at a temperature lower than 700°C, as described above, the substrate 2
If the boron nitride deposited on top is not sufficiently crystallized (
, hydrogen I used as a carrier gas for the boron compound
I.

Furthermore, the rate of deposition is slow, which is uneconomical. Further, in a reaction at a temperature higher than 1700° C., the raw material compound is decomposed on the surface of the reaction tube of the CVD apparatus, and the rate of deposition onto the substrate 2 is reduced, which is uneconomical.

The inflow rate of the nitrogen compound and boron compound to be avoided into the reaction tube of the CVD apparatus is - For example, when ammonia is used as the nitrogen compound and triethylborane is used as the boron compound, the molar ratio of NH3/B (CtH5)3 ≧ 25, the boron nitride film 1 having a substantially chemical composition is deposited on the substrate 2. Conversely, when the molar ratio is less than 25, the nitrogen/boron component ratio N/ in the boron nitride deposited on the dam plate 2 is
B! It will drop even more. Moreover, within the above temperature range, a boron nitride film whose component ratio N/n is approximately close to 1 can be produced. As shown in FIG. 2, the substrate 2 placed in the reaction tube of the CVD apparatus and on which the boron nitride film is deposited is a quartz glass plate having a thickness of about 0.3 to 2.0 ffiI11; Examples include an aluminum oxide (sapphire) plate or a silicon substrate, but in order to apply an appropriate tensile stress to the boron nitride film when the temperature is returned to room temperature after the reaction at the high temperature, the thermal expansion coefficient of boron nitride ( IxlO-') has a lower thermal expansion coefficient than silica glass (thermal expansion coefficient 5XIO-
') Substrate is preferred. Furthermore, if the thickness of the substrate 2 is adjusted appropriately according to the difference in the thermal expansion coefficients, the stress applied to the boron nitride film due to shrinkage due to a decrease in temperature can be adjusted. It is possible to apply appropriate tension to the That is, substrate 2
When a substrate with a low coefficient of thermal expansion, such as a quartz glass substrate, is used, if the thickness of substrate 2 is thin, this substrate will curve significantly when returned to room temperature. This is because the thicker the layer, the smaller the degree of curvature.

Further, since the quartz glass substrate also has a large difference in coefficient of thermal expansion from boron nitride, it is preferable to form a buffer layer on the substrate 2 in advance, which is made of a material whose coefficient of thermal expansion is relatively similar to that of boron nitride. This buffer layer may be a buffer layer formed of silicon dioxide (SiO2), which is the same material as the silica glass, to a thickness of 0.2 to 1 μm on the upper surface of the substrate 2 by vapor deposition or sputtering. Can you name it?

In this case, the rate of vapor deposition or sputtering is
A buffer layer having a desired coefficient of thermal expansion can be obtained by increasing the speed to 100 persons/second, which is higher than usual.

Furthermore, hexagonal boron nitride is thought to be a two-dimensional series of boron and nitrogen atoms bonded alternately to form borano rings similar to benzene, which are stacked together by van der Waals forces. Therefore, the thermal expansion coefficient (IXIO-M) in the direction parallel to the borazine ring (a-axis direction) and the thermal expansion coefficient (4×1O-6) in the direction perpendicular to the borazine ring (c-axis direction) are significantly different. According to the research results of the present inventor, the crystal direction of the hexagonal boron nitride film l manufactured by the method for manufacturing a hexagonal boron nitride film l according to the present invention is as follows. It has been revealed that boron nitride crystals grow in the direction of the so-called "bonding hands" on the substrate 2 side, depending on the structure of the substrate and the surface on which the boron nitride film is deposited, such as quartz glass. By appropriately controlling the structural state of this substrate 2, it is possible to control the crystalline state of the hexagonal boron nitride film 2, and its thermal expansion coefficient approaches that of the quartz glass. , it becomes possible to control the thermal expansion coefficient to a desired value.

By the method described above, it is possible to produce a crystallized hexagonal boron nitride film l on the substrate 2 as shown in FIG. Thereafter, in order to use the substrate 2 as a mask substrate for X-ray lithography as described above, it is necessary to remove part or all of the substrate 2 made of quartz glass or the like to form a single film. At this time, since the hexagonal boron nitride film 1 is a type of so-called heat-resistant ceramics, it has good resistance to etching solutions, and there is no need to pay close attention to changes in its characteristics. Below, I will explain this procedure step by step.

First, the hexagonal boron nitride film l deposited on the substrate 2 as shown in FIG. Apply wax 3 without touching the etching solution. This wax 3 may be a wax that has been conventionally used in semiconductor manufacturing processes, and does not need to have similar special properties. Next, an etching solution (
For example, when quartz glass is used for the substrate 2, hydrofluoric acid (I
As shown in FIG. 5, the substrate 2 is removed using an etching solution (IF'), leaving only its peripheral portion. Thereafter, by removing the wax 3, a hexagonal boron nitride film l as shown in FIG. 1 can be obtained.

The method for manufacturing the hexagonal boron nitride film l described above is characterized by reacting a nitrogen compound and a boron compound at a temperature of 7006C to 1700C by chemical vapor deposition (CVD). According to this manufacturing method, it is possible to obtain a sufficiently crystallized hexagonal boron nitride film l deposited on the substrate 2 in the form of a thin film. , it becomes possible to obtain a boron nitride film in which almost no impurities are mixed. In addition, if the material and thickness of the substrate 2, the thickness of the buffer layer, and the crystal direction of the hexagonal boron nitride film 1 are controlled and determined according to the method described above, the chamber can be... Appropriate tensile stress can be applied to the crystalline boron nitride film l.

Therefore, according to this manufacturing method, it is possible to realize a method for manufacturing a hexagonal boron nitride film that can satisfy the requirements for a mask dam for X-ray lithography.

The hexagonal boron nitride film 1 produced by the hexagonal boron nitride film production method according to the second invention can be used not only as a mask substrate for X-ray lithography as described above, but also as a thin film for electronic circuits, acoustic elements, etc. It is suitably used as a substrate.

EXAMPLE 2 Hereinafter, the method for producing a hexagonal boron nitride film of the present invention will be explained in more detail with reference to Examples, but the method for producing a hexagonal boron nitride film of the present invention is not limited to the Examples shown below.

(Experiment example) Total 3600m1. In a quartz glass reactor with an inner diameter of 25zxφ, triedylborane (hereinafter abbreviated as TEB, purity 98%), ammonia (purity 999%), hydrogen (purity 99.999%), and argon (purity 99.99)
5%), and a hexagonal boron nitride film was manufactured by the MOCVD method. The substrate on which the boron nitride film is deposited is an aluminum oxide plate (sapphire, dimensions 12XI2X
0.6zff3) and silicon substrate (dimensions +2x12
xO,25■3) was used. These substrates are placed on a sintered boron nitride film substrate holder from a horizontal direction.
It was mounted and fixed at an angle, and heated to a predetermined temperature in an external furnace. The temperature around the substrate was measured using a thermoelectric chamber inserted into the reactor.

TE[3 was transported by bubbling hydrogen gas into this TEIl. Also, the temperature of this TEB saturator is
The temperature was selected between 0°C and 25°C and kept constant. T E B
The flow rate was calculated from the 'rEB loss amount from this TE[3 saturator. Other experimental conditions for this experimental example are as shown in Table 1.

Table 1 When the thin film deposited on the substrate by the method described above was analyzed by X-ray diffraction, a strong peak was detected only in the (002) direction. This indicates that the crystal was deposited with the C-axis of the crystal axis oriented perpendicular to the substrate surface, and thus the thin film deposited on the substrate had a hexagonal crystal structure. There was found.

Next, the lattice constant C8 (in) is calculated from the X-ray diffraction data, and the vertical axis is the lattice constant C8, and the deposition temperature (°C) is
FIG. 6 shows the relationship between the lattice constant C6 and the deposition temperature when C6 is plotted on the horizontal axis. As the temperature increases, the lattice constant C
8 becomes smaller and approaches asymptotically to the lattice constant of 6.66, which is the lattice constant of the boron nitride crystal obtained in the bulk state. That is, as the deposition temperature increases, the crystallization of the boron nitride film deposited on the substrate becomes more complete. Also, this is
This was also supported by the experimental results that the half width of the peak in the X-ray diffraction narrows as the temperature rises.

In addition, the experimental results were obtained by calculating the thin film deposition rate on the substrate from the peak intensity of the X-ray diffraction, and graphing the logarithm of this deposition rate on the vertical axis and the reciprocal of the absolute reaction temperature on the horizontal axis. It is shown in FIG. In addition, at this time, the molar ratio of TEB and ammonia N H3 / B (Cttt, ), = 30
was constant. As shown in the figure, the deposition rate was 0.025μm (2,5xlO") for 7 seconds at a temperature of 750°C, and 0.96μx (9,a) at 1000°C.
xto') increases to 7 seconds.

Furthermore, fluorescent X-rays from the boron nitride film deposited on the substrate are measured using a micropoint X-ray analyzer, and the composition of the boron nitride film is determined from the shift product of α and vA due to the nitrogen component in boron nitride. was measured. The component ratio N/B of nitrogen and boron obtained from this measurement result is plotted on the vertical axis, and 'r E B
and ammonia molar ratio NH3/B (CtH5)
FIG. 8 shows the experimental results graphed with 3 on the horizontal axis. Note that the temperature at this time was 1000°C, and the TEB flow rate was 0.
．． 8 shoulders Q/min, the total flow rate is l 30 y (1/min), and the amounts of each nitrogen and boron component were corrected using a standard boron nitride sample.As shown in FIG. If the ratio is 25 or more, it is possible to deposit a stoichiometrically perfect boron nitride film on the substrate, i.e., the TEB and ammonia can be injected such that the molar ratio is 25 or more. It can be understood from the above experimental results that a substantially pure boron nitride film can be obtained if this is done.

Further, FIG. 9 shows the experimental results, which are graphed with the nitrogen and boron component ratios plotted on the vertical axis and the deposition temperature plotted on the horizontal axis. In addition, at this time, the molar ratio of TE [(and ammonia) N II
3/ B (C!II S) 3 is 2 of 10 and 30
Set to type. As seen in FIG. 9, the component ratios shown in the figure (@) reach a peak at a deposition temperature of about too° C., similarly to FIG. 7 above. In other words, from the results shown in Figures 7 and 9, the temperature is around 1000℃, that is, 900℃ to 1100℃.
It can be seen that fabricating a boron nitride film within the range of is most efficient.

Finally, a boron nitride film deposited on the aluminum oxide plate with a wavelength of 2.5 μl to 50 μl (wave number 1000 C [1 to
The infrared reflection (dashed line in the figure) and transmission (solid line in the figure) spectra at 200 cm-' are shown in Figure 1O. Here, as a reference for reflectance and transmittance, an aluminum vapor-deposited film and a silicon substrate with no surface processing were used. In the figure, the absorption band corresponding to the wave number 1,600C [1 to 1,300cm-'] indicates the in-plane vibration of boron nitride.
From this, it can be understood that a pure boron nitride film is formed on the substrate.

"Effects of the Invention" As explained in detail above, the present invention is capable of depositing a nitrogen compound and a boron compound by a chemical vapor deposition (CVD) method.
According to the present invention, a sufficiently crystallized hexagonal boron nitride film is deposited in the form of a thin film on a substrate. It is possible to obtain a boron nitride film in which almost no impurities are mixed, provided that the manufacturing conditions are maintained. In addition, by controlling and determining the material and thickness of the substrate on which the hexagonal boron nitride film is deposited, the formation of the buffer layer, and the crystal orientation of the hexagonal boron nitride film, the hexagonal boron nitride film can be deposited at room temperature. Appropriate tensile stress can be applied to the boron nitride film.

Therefore, according to this manufacturing method, it is possible to realize a method for manufacturing a hexagonal boron nitride film that satisfies the requirements for a mask substrate for X-ray lithography.

[Brief explanation of the drawing]

FIG. 1 shows a hexagonal boron nitride film manufactured by the hexagonal boron nitride film manufacturing method according to the present invention. Figure 6 is a diagram showing the relationship between lattice constant and deposition temperature, Figure 7 is a diagram showing the relationship between deposition rate and absolute reaction temperature, and Figure 8 is a diagram showing the relationship between nitrogen and Figure 9 shows the relationship between the boron component ratio and the molar ratio of ammonia and triethyl boron, Figure 9 shows the relationship between the nitrogen and boron component ratio and deposition temperature, and Figure 1θ shows the relationship between the infrared reflection and the boron nitride film. It is a figure showing a transmission spectrum. 1... Hexagonal boron nitride film, 2... Substrate. Applicant Masaru Nakamura Nippon Sanso Co., Ltd. Figure 1 Figure 2 Figure 3 Figure 4 and Figure 5 Semi-semiconductor temperature ('C) l Plate temperature ('C)

Claims (1)

[Claims] A method for producing a hexagonal boron nitride film, comprising reacting a nitrogen compound and a boron compound at a temperature of 700°C to 1700°C by chemical vapor deposition (CVD).