GB2366804A

GB2366804A - Cast diamond tools and their formation by chemical vapor deposition; diamond hoses

Info

Publication number: GB2366804A
Application number: GB0022947A
Authority: GB
Inventors: Shin-Cheng Lin; Yang-Liang Pai; Chien-Min Sung; Chiu-Hsiang Guan
Original assignee: Kinik Co
Current assignee: Kinik Co
Priority date: 2000-09-19
Filing date: 2000-09-19
Publication date: 2002-03-20
Anticipated expiration: 2020-09-19
Also published as: GB2366804B; DE10046973A1; GB0022947D0; DE10046973B4; FR2815045B1; FR2815045A1

Abstract

A method and design of cast diamond tools includes a mold that contains a negative body shape and surface finish of an intended diamond tool. Diamond deposited by a vapor phase, such as by chemical vapor deposition, is applied to the mold. After depositing diamond to a certain thickness, the mold is dissolved in acid or another suitable solvent, leaving behind the diamond cast that duplicates the intended body shape and surface finish. The diamond cast is then used to fabricate suitable tools, such as a cutting insert, or a wire-drawing die. In addition pad conditioners for polishing silicon wafers may be manufactured using this process, where the soluble mold is formed of silicon. In a variation a diamond hose is formed by overcoating a twisted wire with diamond after which the central metal core is dissolved leaving a hollow diamond hose which is then cast in an epoxy resin.

Description

<Desc/Clms Page number 1> CAST DIAMOND TOOLS AND THEIR FORMATION BY CHEMICAL VAPOR DEPOSITION 1. Field of the Invention The present invention relates to a manufacturing method and design of cast diamond tools.

2. Description of Related Art As a material, diamond has many extreme properties, such as high wear resistance, high thermal conductivity, rapid transmission of sound waves, and corrosion inertness. These superior properties have made diamond the ideal material for many advanced applications. For example, diamonds have been used widely as superabrasives, heat spreaders, acoustic devices, and chemical barriers. Conventionally, diamonds are synthesized under high pressure (more than fifty times atmospheric pressure), but such diamonds are typically in grit form. Although they are ideal for superabrasives (e.g., for diamond saws), they are not suitable for non-mechanical applications (e.g., heat spreaders).

In recent years, diamond films up to lmm in thickness have also been deposited commercially. These films are deposited by CVD methods using gas reactants. The gases included typically a small amount ( < 5%) carbonaceous material, e.g., methane (CH4), that is diluted in an ample amount of

hydrogen (H2). During the process, the gases are heated to a high temperature so the carbonaceous gas will decompose to free up carbon atoms. At the same time, hydrogen molecules will dissociate to form atoms. Normally, carbon atoms will deposit as either amorphous carbon or graphite, but with the surrounding of hydrogen atoms, they will maintain the diamond structure (spa bond), as in the case of methane, and precipitate out as diamond. Even with the formation of non-diamond carbon, the ready presence of hydrogen will convert the carbon back to methane. Hence, hydrogen atoms play a key role in catalyzing the formation of diamond. Hence, the higher the concentration of hydrogen atoms, the better the quality of diamond that is formedThere are various ways to heat the gas mixture, among them hot filament (e.g., using tungsten), microwave agitation, oxyacetylene flame, and direst current (DC) arc are commonly used. Although the temperature for diamond deposition is typically in the range of 800 C to 900 C , the reaction temperature for the gases is much higher. In fact, the higher the reaction temperature is, the more complete the decomposition of the gases to form carbon and hydrogen atoms, and the faster the deposition rate of the diamond. Thus, the hot filament method can only reach 2000 C or slightly over, so its

deposition is the slowest (about 1 micron per hour). The microwave agitation can heat the gases to a higher temperature, so the deposition rate is intermediate (about 10 microns per hour). The oxyacetylene can attain an even higher plasma temperature, so its deposition rate is quite high (e.g., 30 microns per hour). The DC arc method can surpass the gases to the highest temperature (about 6000 C) and hence it can deposit diamond at the highest rate (e.g., 50 microns per hour) of the above methods. However, the higher the deposition rate, the smaller the area of the deposition, and the less uniform the diamond film produced. Hence, there is a tradeoff between deposition rate and deposition area.

CVD diamond films contain polycrystalline diamond grains. Diamond nuclei are first formed on the surface of the substrate, and these nuclei will grow with ever increasing coarseness, as shown in Figs. la to ld. Hence, the film on the nucleation side tends to show the same surface finish as the substrate material, but the growing side becomes ever- increasingly rough with the coarsening of the grain. For most applications (e.g., heat spreader), the rough surface must be ground and polished. However, as diamond is the hardest material known, the machining of the-coarse diamond is extremely difficult and tedious. As a result, the cost associated with the finishing of a

diamond film is often higher than that for its deposition.Fig. 1 shows the nucleation and growth of a diamond film. Note the nucleation surface is a negative of the substrate surface, and the growing surface is becoming more and more rough with the deposition time.

Moreover, certain machining procedures, such as to cut a curved groove on the diamond surface, or to drill a square hole through diamond are almost impossible to achieve. Such limitations have severely constrained diamond films' potential applications.

For example, CVD diamond films have been used as a premium cutting insert. When it is used to cut ductile material (e.g., copper alloy), the long cutting thread must be interrupted from time to time. This is conveniently done by providing a trough near the cutting edge, as commonly done with other cutting tools, to bend and break the material being removed during the thread cutting operation. However, it is not possible to make such a trough on the flat diamond film. Hence, CVD diamond cutters, although extremely durable, are not suitable to cut ductile materials.

As another example, many advanced applications, e.g., circuitry in the electronics industry, would require using triangular, square, or irregularly-shaped shaped metal wires.

These wires cannot be drawn with conventional diamond wiredrawing dies that contain only circular holes. Hence, there is no suitable product to serve this significant demand from the market.

Furthermore, most applications use the surface (e.g., an extruding die) of diamond films, hence the property of the bulk body may not be critical. However, the conventional CVD method must produce the diamond film from the bottom up. Hence, if the top surface is required, the entire film must be grown slowly to reach the top portion. Such a tedious growth process can be very costly.

Example 1- Cutting Inserts Made of Diamond Conventional diamond cutting inserts include two main types. The first type is to coat a WC insert with thin diamond film (e.g., 30 microns). The problem of this design is that the deposited diamond surface is rough, so the cutting surface does not have a fine finish. Alternatively, a thick diamond film (e.g., 300 microns) can be grown. The diamond film can then be ground and polished by a laser to form a triangular cutting tip. This tip is then brazed onto a WC insert. This method is tedious and expensive. In addition to the above described drawbacks, these diamond film cutting inserts suffer another deficiency which is that their top faces are always flat. Hence,

they do not possess chip breakers for efficiently cutting ductile materials.

Fig. 2 shows a conventional WC insert (10) with a depressed chip breaker (12) near each cutting corner. Fig. 3 shows a diamond coated WC insert (14) without a chip breaker. Fig. 4 illustrates a thick diamond brazed onto a WC insert (16), again without a chip breaker.

Example 2 - Wire Drawing Dies Made of Diamond Many metal wires are drawn by using polycrystalline diamond (PCD) tools. The PCD (30) is enclosed by WC (32) (Fig. 8), and a hole (34) is drilled through the PCD (30) (Fig. 9), typically by a laser. The hole (34) is then enlarged to form a flare (340), as shown in Fig. 10, and the surface is polished by using fine diamond paste. Although there is much laborious finishing work involved, such PCD dies are still the best tools used for drawing metal wires. Even so, PCD dies contain only round holes, hence, it is not possible to draw polygonal wires, such as those with square cross-sections.

All PCDs contain more than 10% cobalt. As cobalt can reconvert diamond to amorphous carbon or graphite, so the PCD must be kept below a temperature of about 700 'C. Hence, the lubrication and cooling by water or other liquid is critical.

However, during the drawing process, the metal wire tends to press against the PCD and it may weld with cobalt embedded in the PCD. As a result, excessive heating is inevitable and the PCD may deteriorate rapidly due to the reconversion to amorphopus carbon or graphite. Moreover, the dragging may damage the surface of the metal wire by causing weld spots and burn marks.

Example 3 - Pad Conditioners Made of Diamond Chemical Mechanical Polishing (CMP) is an essential step for manufacture silicon chips with sophisticated architecture. During the CMP process, silicon wafers are pressed against a rotating pad typically made of polyurethane. The table is fed with a stream of slurry that contains ultrafine (less than 0.2 microns) abrasive (e.g., silica or alumina). The wafers are therefore polished by the abrasive to reach a certain flatness and smoothness. However, the polished debris can coat the pad and make the latter unusable, so a diamond conditioner is required to scrape off the deposited debris from time to time.

The pad conditioner contains a plurality of diamond grits that are attached to a metal substrate (e.g., stainless steel). These grits are used to rake the pad to prevent its top from glazing. The effectiveness in cleaning the pad, and the durability of the conditioner are dependent on two critical

factors: the separation of diamond grits, and the leveling of their tops. These two factors are notoriously difficult to control. Hence, almost all diamond conditioners used commercially contain randomly distributed diamond grits with a high variability of the top height.

The object of this invention to make diamond film products that either eliminate or minimize the expensive post- synthesis operations.

It is another object of this invention to produce diamond film products with irregular and novel body shapes and surface finishes.

It is yet another object of this invention to simplify the diamond manufacture process by casting only the critical part of the diamond film, and then filling in the non-critical part with fast grown diamond or other material.

In the drawings Figs. I shows stages of diamond nuclei formed on a surface of a substrate; Fig. 2 shows a conventional tungsten carbide tool insert; Fig. 3 shows a conventional diamond coated tungssten carbide tool insert without a chip breaker; Fig. 4 shows conventional tungsten carbide with a thick diamond film but without a chip breaker;

Fig. 5 shows a thin metal mold for use in the present invention; Fig. 6 shows the mold of Fig. 5 filled with diamond film deposition, in accordance with the present invention; Fig.7 shows the mold of Fig. 5 dissolved away; Fig. 8 shows a prior art polycrystalline diamond (PCD) enclosed by tungsten carbide; Fig. 9 shows the PCD of Fig. 8 with a hole drilled therethrough; Fig. 10 shows the PCD of Fig. 9 with the hole enlarged; Fig. 11 shows a mold for use with the present invention; Fig. 12 shows the mold of Fig. llwith diamond deposition ; Fig. 13 shows the diamond deposition of Fig. 12 formed as a die, with the mold dissolved away; Fig. 14 shows the diamond of Fig. 13 with the diamond die encased by a metal; Fig. 15 shows a silicon wafer in accordance with the present invention; Fig. 16 shows the silicon wafer of Fig. 15 cast with chemical vapor deposition (CVD) diamond; Fig. 17 shows the silicon wafer of Fig. 16 with an epoxy resin layer; Fig. 18 shows a disk with diamond pyramids after the the

silicon has been.dissolved away; Fig. 19 shows a wire having been twisted, in accordance with the present invention; Fig. 20 shows the wire of Fig. 19 coated with chemical vapor deposition diamond; Fig. 21 shows the wire of Fig. 19 dissolved away, leaving a diamond hose; and Fig. 22 shows the diamond hose of Fig. 21 encased in resin. This invention reverses the common practice of growing diamond film to form a body and then machining it to a required shape. Instead, a diamond film is cast in a mold to form the body shape and surface finish it in a single process. A remaining portion can then be filled in at a later stage using a much less expensive material or method. This novel concept can produce the cast that duplicates the body shape and surface finish of the mold, hence, expensive post-synthesis machining works are eliminated. Moreover, the complicated body shape or delicate surface finish can both be achieved from the mold. As a result, diamond film products with novel and unique geometries can now be produced for the first time.

A key ingredient of this invention is the ability to reproduce a surface finish of the mold to the deposited diamond cast and experiments have been performed to test this

feasibility. Many materials with different surface finishes have been used as the substrate for depositing CVD diamond. The CVD reactor used is a large production system manufactured by spa, Inc. of California. The reactor is a hot filament system with a deposition area of 30 cm x 40 cm. It has been discovered that if the substrate material is suitable (e.g., copper, tungsten carbide), and the surface treatment is proper (i.e., thoroughly cleaned), diamond films so deposited can faithfully reproduce the surface feature of the substrate. Hence, the concept of reverse deposition was proven.

Conventional diamond films have their growing sides used as appropriate tool surfaces. This invention relies on using a nucleation side for the application. The nucleation side contains diamond microcrystals that have been formed on the substrate. These newly formed nuclei may not be chemically pure, nor structurally sound. Moreover, amorphous carbon or pyrolitic graphite may be co-deposited there. As the nucleation side will be used as the tool surface, it is critical to make this side contain as much diamond as possible.

Several techniques have been applied to improve the diamond quality of the nucleation side. For example, during the early phase of diamond deposition, the methane flow rate is reduced and the gas pressure is increased. In this way, the

decomposition rate of carbon will decrease, but the concentration of hydrogen atoms will increase. The slow deposition rate coupled with the increased amount of catalyst can assure that diamond nuclei formed are of high quality.

Moreover, the nucleation rate must be increased to fill up the minute crevices of the substrate. The nucleation rate can be effectively boosted (up to one million times) by applying a negative bias (e.a., 100 V) on the substrate. Alternatively, the substrate can be polished by using a fine diamond paste. After polishing, the embedded diamond micron powders can serve as effective seeds for diamond nucleation. If the nucleation rate can be raised, the diamond quality on the nucleation side will increase, and the substrate finish can be faithfully translated onto the nucleated surface.

Certain metals. e.g., iron, cobalt, nickel and their alloys, can catalyze at a high temperature (>700 degrees Celsius) diamond back to amorphous carbon or graphite. It is important that the substrate material contains as little as possible of such metals. For example. a good substrate material for diamond deposition is cob < < lt cemented tungsten carbide (WC). If WC is used for diamond deposition, the mount of cobalt should be limited to 4% or less. In recent years, binder free WC materials have been available. These materials are suitable to

make molds (e.g.. the hole for a wire-drawing die). If the WC grain is ultrafine (submicron), the diamond nucleation will further increase. The result is a very smooth surface of high diamond content, which is ideal for many applications.

Fig. 5 shows a thin metal mold (20) that has the negative geometry of a conventional cutting insert with chip breakers. The metal can be W. Mo, Ta, Zr, Ti, Cr, V, Cu, Si or other suitable material. Fig. 6 shows that this metal mold (20) is filled up by the deposition of diamond film. Fig. 7 shows that the metal mold (20) is dissolved away, e.g., by soaking in acid. A bottom part (22) of the remaining diamond film contains the same geometrical form of the metal mold (20). A top part is then packed with WC particles or other refractory grains (e.g., SiC) and infiltrated with an alloy (e.g., copper-manganese alloy). The solidi Pied alloy can then serve as the substrate of the cutting insert as shown in Fig. 7. This diamond insert contains the original surface of the metal mold (20), including the chip breaker. This diamond cutting tool does not require expensive mechanical finishing work.

This invention can solve all the above mentioned problems of the prior art.

Referring to Fig. 11, a center column (40) made of a binderless WC (or W metal) is first fabricated with the

appropriate geometry and surface finish. As shown in Fig. 12, this center column (-10) is then coated with CVD diamond (42) to a thickness of 50 to 100 microns. The center column (40) is subsequently dissolved in acid, leaving a diamond tube cast in the same geometrN of the center column (40), as seen in Fig. 13. This diamond tube is placed at the center of a stainless steel ring (46), and a space between them is packed with WC particles or SiC grains. A pile of copper-manganese-nickel alloy is placed on top of these particles. The set up is next placed in a vacuum I@urnace and heated to cause the melting of the copper alloy. The copper alloy will then infiltrate into the powder and consolidated the assembly. This rigid assembly contains a stainless steel outer ring and a diamond inner tube (44). Moreover, the diamond tube is compressed by the shrinking copper alloy that reduces the volume significantly during the solidification process. This compression is highly desirable as it will protect the tube from expansion due to the outward pushing force exerted by the drawing wire. Furthermore, this compressional force is adjustable in that may be varied to suit the type of wire to be drawn (e.g., low for drawing copper and high for drawing tungsten). The compressional force can be varied simply by adjusting the powder/metal ration. the more metal used, the higher the

cornpression force is.

The above described novel technology not only eliminates the expensive finishing operation, and hence greatly reduces the production cost. but also it improves the quality of the wire drawing die i n many aspects. For example. unlike PCD that contains less th < < n 90% in volume of diamond, CVDD is made entirely of diamond, hence, its wear life can be much higher than I'CD (the service life is not linearly proportional to the diamond content, but is an exponential function).

CVDD is much more slippery than PCD that contains metal adhering cobalt. hence the heat generated during wire drawing would be significantlv less. Moreover, CVDD can stand a temperature of 1200 3C that is much higher than 700 C for PCD. Hence, the use of liquid lubrication may not be necessary. The elimination ol@ liquid lubricant not only pays for the cost of the wire drawing clie itself, but also it avoids environmental contamination associated with the lubricant. Concern about protecting the environment is forcing the machining industry to operate "dry". so this invention anticipates such a world trend.

Furthermore. the elimination of cobalt in the contact surface can improve greatly the surface finish of the wire, e.g., to make it have a reflective finish. Such a high quality wire is

highly welcomed by the electronics industry (e.g., contamination-free copper wires) and the jewelry business (e.g., shinning gold wires).

An even more sianificant breakthrough based on this invention is that wire drawing with non-circular holes can be performed as easily as circular holes. Hence, wires with triangular or square cross sections can be produced readily. The introduction of non-circular wires currently unavailable can allow new designs of products for certain fields (e.g., in the electronics industry), hence it may spur the creation of a new industry.

Using the cast diamond concept as taught by this invention, an extremely high quality diamond conditioner can be fabricated with strict control of diamond separation and top height. Firstly, a silicon wafer (50) is machined with impressions of identical pyramids that are placed in specific locations (e.g., with a fixed distance from the neighbor) as shown in Fig. 15. Secondly, the engraved silicon wafer is cast with CVD diamond (52), as shown in Fig. 16. Thirdly, an epoxy resin (54) is then attached on the top, as shown in Fig. 17. The entire assembly is then dipped in hydrofluoric acid to dissolve the silicon substrate. The remaining disk, when inverted, will show identical diamond pyramids protruding to the same height,

as shown in Fig. 18. Such a diamond layout is ideal for making a CMP pad conditioner. This method can also allow new designs of pad conditioners. For example, the distribution of the pyramids may be such that they follow a spiral pattern. In this way, the slurry may be guided to follow the pattern so as to improve the distribution of the abrasive. The result can be an increased polishing rate of the wafer and a reduced consumption of the expensive slurry. Moreover, the uniformity and flatness of the wafer may also be improved.

Diamond Hose This invention can allow the manufacture of novel and unique diamond devices, such as a diamond hose that can be used to transmit corrosive fluid. The manufacturing steps follow the same procedures as described above. Firstly, the hose is fabricated using a metal (e.g., by twisting a W wire (60)), as shown in Fig. 19. Secondly, the twisted wire (60) is overcoated by CVDD (62), as shown in Fig. 20, to form a center metal core. Thirdly, the center metal core is dissolved, leaving a hollow diamond hose, as shown in Fig. 21. Finally, this diamond hose is cast in an epoxy resin (64) to form an easily handled tool, as shown in Fig 22.

The same idea may be applied to manufacture of other novel objects, such a5 a diamond flask or a diamond gear.

There is no limitation of the type of shape that may be produced by CVD diamond.

The above fe\@- examples are merely used to illustrate the flexibility of applying this invention.

It is to be understood, however, that even though numerous characteristics Lend advantages of the present invention have been set forth i the foregoing description, together with details of the structure and function of the invention, the disclosure is illustrative only, and changes may be made in detail, especially in natters of shape, size, and arrangement of parts within the principles of the invention to the full extent indicated by the broad general meaning of the terms in which the appended claims are expressed.

Claims

CLAIMS: 1. A CVD diamond product cast by a mold with the surface features determined by contact interface of the mold.
2. The product as described in Claim 1, wherein the mold is made of metal.
3. The product as described in Claim 2, wherein the metal is essentiallv an,,,- metal selected from the group of W, Mo, Ta, Ti, Zr, V, Cr, or any of its carbides, and Cu.
4. The product as described in Claim 1, wherein the mold has a concave shape.
5. The product as described in Claim 4, wherein the concave shape is a CLIP.
6. The product as described in Claim 1, wherein the mold has a convex shape.
7. The product a5 described in Claim 6, wherein the convex shape is cylindrical.
8. The product as described in Claim 1, wherein the CVD diamond has a thickness of 30 to 200 microns.
9. The product as described in Claim 1, wherein the product is one of a cutting tool made of diamond, a wire drawing die made of diamond, a pad conditioner made of diamond, a diamond diaphragm, or a diamond pipe.
10. The procllIct ,is described in Claim 9, wherein the

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cutting tool contains chip breakers.
11. The product as described in claim 9, wherein the wire drawing die has a noilspherical hole.
12. The product as described in Claim 9, wherein the wire drawing die is produced by infiltrating molten alloy around a CVD diamond tube.
13. A method to make a CVD diamond product, comprising the following steps: a. making a negative mold that contains a shape and a surface of an inteilded product; b. depositing a CVD diamond to a desired thickness at an interface of the mold: c. dissolvinL@ the mold by acid or another solvent; and d. mounting a remaining diamond object in a suitable holder.
14. The method according to Claim 12, wherein the CVD diamond is deposited by a method using hot filament, microwave plasma. oxyacetylene flame, or DC arc to heat gas used therein.
15. The method according to Claim 13, wherein the gas contains methane and hydrogen.