JPH03280698A - Manufacture of diamond diaphragm - Google Patents

Abstract

PURPOSE:To prevent production of internal distortion in a diamond by forming an uppermost layer of a base to be a W (tungsten) layer. CONSTITUTION:A diamond is vapor-deposited from the gas phase onto a W base whose at least uppermost phase is a W (tungsten) layer, then the W base the surface of which a diamond is deposited is rinsed by an acid to remove the W base. Then no thermal stress is caused between the diamond and the base at cooling after chemical gas phase vapordeposition by using the W whose linear expansion rate is close to that of the diamond for the base in this way. Thus, the diaphragm with excellent acoustic characteristic without causing internal distortion to the diamond is realized.

Description

Detailed Description of the Invention [Industrial Application Field] The present invention relates to a method for manufacturing a diamond acoustic diaphragm, and a method for producing a diamond diaphragm with a desired shape at a high and low temperature by using W as a substrate on which diamond is deposited. It is manufactured by dripping.

[Prior art] In general, an acoustic diaphragm needs to have high efficiency and good transient characteristics, and in order to extend the high frequency range, it must have a small mass, a high Young's modulus, and a high strength. etc. are required. A diamond diaphragm is known as a device that satisfies these requirements.

This diamond diaphragm is manufactured by patent application No. 59-143498.
As described in Japanese Patent Publication No. 55-33237, chemical vapor deposition method (hereinafter referred to as
It is abbreviated as CVD method. ) After depositing diamond, the Si substrate is removed.

[Problem to be solved by the invention] However, in the above manufacturing method, a silicon substrate having a coefficient of linear expansion of 2.4xlO-6 in the range of 20 to 50°C has a thermal expansion coefficient of 0 to 75
Since diamond is precipitated with a coefficient of linear expansion of 4.5×10 −6 in the range of 0° C., thermal stress is likely to occur between the substrate and the diamond during cooling after CVD. This causes internal strain in the diamond, which not only deteriorates the characteristics of the diaphragm but also causes problems such as cracking and peeling.

This invention has been made to solve the above problems, and provides a method for obtaining a diaphragm with excellent acoustic characteristics using a small drop of water by reducing the occurrence of thermal stress during cooling after diamond precipitation. is intended to provide.

[Means for Solving the Problems] The manufacturing method of the present invention includes depositing diamond in a vapor phase on the surface of a substrate processed into the shape of a speaker diaphragm, and then
In a method of manufacturing a diamond diaphragm by removing a base, at least the uppermost layer of the base is made of W (tungsten).

[Function] Since W, which has a coefficient of thermal expansion close to that of diamond, is used as the base material, it is possible to reduce the occurrence of thermal stress during cooling after CVD.

The present invention will be explained in detail below. In this specification, unless otherwise specified, % indicates volume %.

The manufacturing method of the present invention consists of (1) a substrate manufacturing process, (2) a CVD process, and (2) a substrate removal process.

(2) Substrate manufacturing process This process is a process for manufacturing a W substrate that will be the deposition substrate for the diamond acoustic diaphragm. This W substrate is not particularly limited as long as at least the top layer is made of W. In addition to those made by processing a W plate material into the shape of a diaphragm, the W substrate has a coefficient of linear expansion close to that of W, and is not particularly limited. An alloy plate or a ceramic plate whose surface is easily coated with W can be used. Here, W or an alloy or ceramic coated with W is used as the base because the coefficient of linear expansion of W is 4.
3X10-', which is very close to that of diamond.

When such a substrate is used, it is possible to prevent thermal stress from occurring between the diamond and the W substrate during cooling after CVD, so that internal strain is not generated in the diamond. Therefore, it is possible to prevent the diamond from peeling off or cracking from the base, and to obtain a diaphragm with excellent acoustic properties.

Furthermore, since W is a metal that is easier to work with than S, it also has the advantage that the base body can be easily worked into a desired shape.

Furthermore, the use of W as a substrate has the advantage of widening the range of optimal conditions for diamond precipitation during CVD.

■CVD process Next, diamond is deposited on the W substrate.

For diamond precipitation, thermal CVD method, plasma CVD method
Any known CVD method such as a method or an ion beam evaporation method can be used.

As the raw material gas, hydrocarbons such as CH, gas, etc. are used at 0.2~
It can be used in a carrier gas at a concentration of 2.0%. This carrier gas contains Ht (hydrogen)
Alternatively, a mixed gas of H2 and an inert gas, or a mixed gas containing a trace amount of oxygen, Ht2O, etc., can be used. Here, the CH4 gas concentration in the raw material gas is 0.
If it is less than 2%, the diamond precipitation rate will be slow;
Moreover, if it is more than 20%, an amorphous carbon film will grow and the internal strain in the diamond will increase, which is not preferable.

The W substrate is heated to 650-1100°C. If the W substrate temperature is below 800°C, there is a high probability that diamond will peel off during cooling after CVD, and if it is above 1000°C, the precipitated diamond crystal grains will become too large.
This is because internal distortion increases.

(2) Substrate Removal Step Next, diamond is deposited on the surface and the W substrate is pickled to remove the W substrate. As this cleaning solvent, various acids such as a mixed solution of nitric acid and hydrofluoric acid can be used.

In the manufacturing method of the present invention, W, which has a coefficient of linear expansion close to that of diamond, is used as the base, so no thermal stress is generated between the diamond and the base during cooling after CVD.

Therefore, since no internal strain occurs in the diamond, a diaphragm with excellent acoustic characteristics can be obtained. Furthermore, it is possible to prevent the diamond from peeling off or cracking, and it is also possible to improve the product droplet production during the manufacture of the diaphragm.

Furthermore, in the method of the present invention, since diamond is deposited on the W substrate, which is easier to process than Si, a diamond diaphragm having a desired shape can be easily obtained.

[Example 2 (Example 1) A W plate was prepared and processed into a desired diaphragm shape to obtain a W substrate. Microwave plasma CVD was applied to the surface of this W substrate.
Diamond was precipitated by the method. At this time, the W substrate temperature was 850°C, and the CH and gas concentration in the source gas was 0.5
%. Next, this W with diamond precipitated on the surface
The base was pickled and the W base was removed to obtain a diamond diaphragm. A mixed solution of nitric acid and hydrofluoric acid was used for this cleaning.

(Comparative Example 1) When an attempt was made to manufacture a diamond diaphragm by the same operation as in Example 1 above, except that a Si substrate was used instead of the W substrate, during cooling after diamond precipitation,
Cracks occurred in the Si substrate, and a diaphragm could not be obtained.

(Test Example) A W plate and a Si plate were each cut into 20 mm square pieces to prepare test pieces. Using these test pieces as a base, the heating temperature was set to 80°C.
Diamond was deposited on the surface of each test piece in exactly the same manner as in Example 1 above, except that the temperature was 0°C. Next, each test piece was pickled and removed in the same manner as in Example 1 to obtain a diamond plate.

The deformation of these diamond plates was then investigated. The results are shown in Table 1.

From the results in Table 1, it can be seen that when a Si substrate is used, a large internal stress is generated in the diamond, and as a result, the radius of curvature of the diamond plate becomes smaller (the degree of deformation becomes larger). It could be confirmed.

It was confirmed that the degree of deformation of the diamond plate when the W substrate was used was suppressed to about 75% of that when the Si substrate was used.

[Effects of the Invention] As explained above, since the manufacturing method of the present invention uses W, which has a coefficient of linear expansion close to that of diamond, as the base material, there is a gap between the diamond and the base material during cooling after CVD. Since no thermal stress is generated, it is possible to prevent internal strain from occurring in the diamond.

Therefore, a diamond diaphragm with excellent acoustic properties can be obtained with a high droplet size.

Further, since W is a metal that is easier to process than Si, a diamond diaphragm having a desired shape can be obtained.

Claims (1)

[Claims] A method for manufacturing a diamond diaphragm by vapor-depositing diamond on the surface of a substrate processed into the shape of a speaker diaphragm and then removing the substrate, wherein at least the uppermost layer of the substrate is made of W ( Method for manufacturing a diamond diaphragm characterized by being made of (tungsten)