AU758885B2 - Method of electroplating a substrate, and products made thereby - Google Patents

Description

AUSTRALIA

Patents Act 1990 COMPLETE SPECIFICATION STANDARD PATENT Applicant(s): THE BOARD OF TRUSTEES OF THE UNIVERSITY OF ARKANSAS Invention Title: METHOD OF ELECTROPLATING A SUBSTRATE, AND PRODUCTS MADE THEREBY The following statement is a full description of this invention, including the best method of performing it known to me/us: WO 96/33298 PCTIUS96104754 la TITLE METHOD OF ELECTROPLATING A SUBSTRATE, AND PRODUCTS MADE THEREBY BACKGROUND OF THE INVENTION I. Field of the Invention The present invention relates to methods of electroplating and to products made thereby. In another aspect, the present invention relates to methods of electroplating a conductive metal onto a substrate, and to products made thereby. In even another aspect, the present invention relates to methods of electroplating conductors onto a seed layer supported by a substrate, and to products made thereby. In still another aspect, the present invention relates to methods of electroplating conductors onto a seed layer supported by a diamond substrate, and to products made thereby.

2. Description of the Related Art It is the physical and chemical properties of natural diamonds which render ::::*diamonds suitable for use in a wide range of applications. For example, natural diamonds are the hardest substance known and exhibit lowv friction and wear properties.

Specifically, a natural diamond's thermal conductivity, thermal diffu~sivity properties, electrical resistivity and microhardness invite its substitution in various applications.- Specifically with respect to electronic applications, diamond, with a thermal conductivity four times that of copper and a dielectric constant less than alumiuna or aluminum nitride, has long been recognized as a desirable material for electronic substrates.

It is likewise believed that diamond films would find utility in a broad range of

I

WO 96/33298 pCTIUS96104754 2 electronic uses.

Unfortunately, diamond films are not naturally occurring, but rather must be manufactured using any of a host of techniques.

Fortunately, however, the physical and chemical properties of synthetic diamond films have been found to be comparable to those of bulk diamond.

For example, it has been reported that electron assisted chemical vapor deposition films have electrical resistivities greater than 101 3 Q-cm, microhardness of about 10,000 HV, thermal conductivity of about I 100 W m' and thermal diffusivity of 200 to 300 mm2/s. These compare favorably to those properties of natural diamond, i.e, resistivities in the range of 10' to 1020 Q-cm, microhardness in the range of 8,000 to 10,400 HV, thermal conductivity in the range of 900 to 2100 W and thermal diffusivity of 490 to 1150 mrn 2 Thermal gavimetric analysis demonstrates the oxidation rates of diamond films in air are lower than those of natural diamond. Additionally, it is reported that the starting temperature of oxidation for microwave-assisted chemical vapor deposition diamond film is about 800°C, as evidenced by weight loss, while the morphology shows visible oxidation etching pits at temperatures as low as 600°C.

Thus, diamond films also show promise for finding utility in a multitude of applications, including electrical applications.

Currently, chemical vapor deposition diamond film has experienced limited market entry primarily as heat sinks for laser diodes. However, there are many other industrial uses planned for diamond film, virtually all of which require metallization.

For example, diamond film substrates have been hailed as the only solution to many of the thermal management problems currently encountered in the electronie and optoelectronics packaging area. As the packing density of electronic systems increases, this thermal management problem is only going to exacerbate. Metallization of diamond film substrates with highly conducting metals such as gold and copper is essential for these applications. Some of the applications which are in dire need of the development of a tenaciously adhering conducting metal film on a diamond substrate include laser diodes and diode arrays for telecommunications, power modules for on-board satellites, high powered microwave modules, MCMs, and especially 3-D MCMs.

WO 9 33298PCT1US96104754 3 However, while the industry is in dire need of a tenaciously adhering (>IlKpsi on peel test) electroplated conducting metal film on a diamond substrate, the chemrical inertness of diamond resists the formation of adherent coatings on it. This is especially true for large area (>1mm x 1mm) diamond film substrates and thick metal films (>2 microns).

Presently, mnetallization is accomplished through some form of physical vapor deposition. While this produces a high quality flmn it also produces high material cost due to its extreme waste of metal. Electroplating is preferable because is allows metal to be deposited selectively, which would cut waste by over 90% from what is consumned in a physical vapor deposition process.

Physical vapor deposition processes are currently the industry standard because films deposited by such processes tend not to blister or peel at high temperatures. In a physical vapor deposition process, the substrate is mounted inside a high vacuum chamber. The chamber is evacuated, and metal is either evaporated or sputtered to form a coating on the substrate. The inefficiency of the technique is due to the metal coating that is deposited onto the rest of the vacuum chamber at the same time. Only a small percentage of the metal that is consumed by the process lands on the substrate,'with the rest being lost.

Electroplating would seem to be the proper candidate for metallizing diamond film with gold. With electroplating, the plated metal is applied directly to the target, resulting in much less waste as compared to physical vapor deposition. However, even though electroplating has establishe d itself as a workhorse technology for cost effective thin film and foil fabrication in the electronics industry, only sputtering and evaporation of gold and copper have so far been commercially successfully utilized in metallizing diamond film 25 substrates (and onl~y on small substrates and only to small thicknesses).- "Metallizing CVD Diamond For Electronic Applications", Iacovangelo et at.

International Journal of Microelectronics And Electronics Packaging, Vol. 17, No. 3, at 252-258 (1994), discloses a physical vapor deposition technique for depositing a gold layer onto a diamond film. As disclosed by Iacovangelo ef aL, thin gold films are applied to metal seed layers on diamond films by either a sputtering process or a chemical vapor WO 96/33298 PCTIUS96/04754 4 deposition process.

As shown for coat numbers 11-13, the gold layers applied by the teachings of lacovangelo et al. exhibit adhesion to the diamond substrate on the order of 4 to 10 Kpsi.

Unfortunately, the gold layers produced by lacovangelo et al were on the order of microns thin, too thin for use in most applications.

lacovangelo et al., further disclose the electroplating of a triple layer of copper, nickel and then gold onto a patterned thin film. However, as shown in Figure 4 of lacovangelo et al., this electroplated layer is on the order of 200,pm wide, far too narrow for many applications. Electroplating onto diamond film substrates on the order of 1 cm x Icm or larger requires that the problems induced by thermal stress be solved.

lacovangelo et al. do not disclose or teach how to electroplate onto larger diamond film substrates in a manner sufficient to overcome the problems induced by thermal stress. Biaxial stresses increase with increasing diamond film size.

Additional problems with applying metal layers to diamond films include blistering, peeling and delamination.

Therefore, there is a need in the art for a process for metallizing diamond and other types of substrates which does not suffer from one or more of the prior art limitations.

There is another need in the art for an electroplating process for metallizing 20 diamond and other types of substrates which does not suffer from one or more of the prior art limitations.

There is even another need in the art for an electroplating process for metallizing diamond and other types of substrates which provides a product with suitable-adhesion between the gold layer and the diamond film.

25 There is still another need in the art for an electroplating process for metallizing diamond and other types of substrates which provides a product with suitable surface roughness.

There is yet another a need in the art for metallized diamond and other types of substrates which do not suffer from the prior art limitations.

There is even still another need in the art for a metallized diamond and other types WO 96133298 pCTIUS96JO4754 of substrates with suitable adhesion between the gold layer and the diamond film.

There is even yet another need in the art for a metallized diamond and other types of substrates with suitable surface roughness.

These and other needs in the art will become apparent to those of skill in the art upon review of this specification.

SUMMARY OF THE INVENTION It is one object of the present invention to provide a process for metallizing diamond and other types of substrates which does not suffer from one or more of the prior art limitations.

It is another object to provide for an electroplating process for metallizing diamond and other types of substrates which does not suffer from one or more of the prior art limitations.

It is even another object to provide for an electroplating process for metallizing diamond and other types of substrates which provides a product with suitable adhesion between the gold layer and the diamond film.

It is still another object to provide for an electroplating process for metallizing diamond and other types of substrates which provides a product with suitable surface roughness.

It is yet another object to provide for metallized diamond and other types of substrates which do not suffer from the prior art limitations.

It is even still another object to provide for a metallized diamond and other types of substrates with suitable adhesion between the gold layer and the diamond film.- It is even yet another object to provide for a metallized diamond and other types of substrates with suitable surface roughness.

These and other objects of the present invention will become apparent to those of skill in the art upon review of this specification.

According to one embodiment of the present invention there is provided a method of electroplating an article having a surface with peaks and valleys, and articles made therefrom. The method generally includes electroplating a conductive metal onto the WO 96/33298 pCTJUS96/047S4 6 peaks to cover the peaks with the conductive metal, and into the valleys to substantially fill the valleys with the conductive metal.

According to another embodiment of the present invention there is provided a method of electroplating an article having a surface with a surface roughness, and articles made therefrom. The method generally includes electroplating a conductive metal onto the surface utilizing a current density less than or equal to to form a conductive metal layer having a surface roughness no greater than the article surface roughness.

According to even another embodiment of the present invention there is provided a method of electroplating an article comprising a supporting member and a seed layer supported by the supporting member, with the seed layer having a surface with peaks and valleys, and articles made therefrom. The method generally includes electroplating a conductive metal onto the peaks to cover the peaks with the conductive metal, and into the valleys to substantially fill the valleys with the conductive metal.

According to still another embodiment of the present invention there is provided a method of electroplating an article comprising a supporting member and a seed layer supported by the diamond member, with the seed layer having a surface with a surface roughness, and articles made therefrom. The method generally includes electroplating a conductive metal onto the seed layer surface utilizing a current density less than or equal to J, to form a conductive metal layer having a surface roughness no greater than the seed layer surface roughness.- According to yet another embodiment of the present invention there is provided a method of metallizing a diamond film, and articles made therefrom. The method generally includes a first step of applying a seed metal onto the diamond film to form a seed layer having a surface roughness, with the seed layer having a surface with peaks and *25 valleys. The method further includes electroplating a conductive metal onto the peaks to cover the peaks with the conductive metal, and into the valleys to'substantially fill the valleys with the conductive metal.

According to even still another embodiment of the present invention these is provided a method of metallizing a diamond film, and articles made therefrom. The method generally includes applying a seed metal onto the diamond film to form a seed WO 96/1.33298 pCT[US96/0473-4 7 layer, with the seed layer having a surface with a surface roughness. The method further includes electroplating a conductive metal onto the seed layer surface utilizing a current density less than or equal to to form a conductive metal layer having a surface roughness no greater than the seed layer surface roughness.

According to even yet another embodiment of the present invention there is provided a method of electroplating an article to form an electroplated layer having a desired surface roughness, and articles made therefrom. The method generally includes electroplating at a current density, a conductive metal onto the article to form an electroplated layer. The method further includes determining the surface roughness of the electroplated layer. The method still further includes increasing the current density of step if the surface roughness determined in step is less than the desired surface roughness, and decreasing the current density of step if the surface roughness determined in step is greater than the desired surface roughness. This method may be operated interactively until the desired surface roughness is obtained for the thickness required.

BREF DESCRIPTION OF THE DRAW2NG FIGs. IA-C, show respectively, substrate 10 with irregularity 20'without an electroplated metal, substrate 10 with irregularity 20 electroplated over by electroplated metal 30, and substrate 10 with irregularity 20 electroplated substantially filled by electroplated metal DETAILED DE-SCRIPTION OF THE NV TION- The present invention provides a method for electroplating a conductive metal onto a target conductive metal layer surface, such that the formed electroplated metal layer will have a resulting surface roughness less than the initial surface roughness of the target layer.

C The present invention also provides a method for electroplating a conductive metal onto a target conductive metal layer surface, such that the formed electroplated metal layer will have reduced likelihood of blistering away from the target layer at elevated PCT/US96/04754 WO 96/33298 8 temperatures, and will have good adhesion to the target layer.

The present invention generally includes a first step of metallizing a supporting substrate to form a seed layer, followed by electroplating a conductive layer onto the seed layer. Alternatively, the present invention may also be utilized to electroplate a conductive metal directly onto a conductive substrate even without a seed layer.

In the practice of the present invention, the substrate may comprise any material that will be suitable for the desired application. Non-limiting examples of supporting substrate materials include metals, diamond, semiconductors, ceramics, thermoplastics or thermosets.

Although much of the following description for the present invention makes reference to diamond film as the substrate, it is to be understood that this invention finds applicability to any type of substrate.

The diamond films utilized in the practice of the present invention are well known to those of skill in the art. The diamond films utilized in the present invention may be made by any suitable process. Generally, such suitable methods of making diamond films are generally characterized as chemical vapor deposition techniques such as hot filament, DC arcjet, RF arcjet, microwave plasma, and microwave plasma jet methods.

Initial treatment of the supporting substrate In the practice of the present invention, the supporting substrate must generally be cleaned to provide a proper surface for metallizing. For example, with diamonds and 0. many metals, such cleaning generally includes degreasing, removal of residual carbon, and the removal of the cleaning solutions.

For example, methods of cleaning a diamond film are well known to those of skill in the art, and any suitable method may be utilized. Degreasing is generally accomplished by boiling the diamond film in suitable chemical solvents, non limiting examples of which include trichloroethylene, acetone and alcohols. The removal of residual carbon is generally accomplished at slightly elevated temperatures utilizing an acid wash followed S :by a base wash. As a non limiting example, residual carbon may be removed using sulfuric 30 acid/chromium trioxide at 160 0 C followed by ammonium hydroxide/hydrogen peroxide

I

WO 96/33298 pCTJUS96/04754 9 at 70 0 C. Residuals of these cleaning solutions are then removed by subjecting the diamond film to ultrasonic cleaning in deionized water.

In some applications, it will be necessary that the surface roughness of the final electroplated conductive layer be quite low. For example, many electrical applications will require the final electroplated conductive layer have a surface roughness less than about 350 rim, preferably less than about 300 rim, and more preferably less than about 250 nm, and most preferably less than about 200 rim. Of course, it is to be understood that the present invention can be utilized to form a final electroplated conductive layer having almost any desired surface roughness.

The surface roughness of the underlying substrate will tend to influence the surface roughness of the final electroplated conductive layer. It is generally preferred to start with a substrate having a surface roughness near that desired in the final electroplated conductive layer. Likewise, the surface roughness of the seed layer on the substrate will.

also tend to influence the surface roughness of the final electroplated conductive layer.

Thus, if a seed layer is utilized it is generally preferred to utilize one having a surface roughness near that desired in the final electroplated conductive layer.

Application of seed layer Once the substrate is degreased and cleaned, the optional seed layer may be *20 applied. Methods of applying a seed layer to a substrate, especially a diamond film are well known to those of skill in the art. In the practice of the present invention, the'seed layer may be applied using any suitable technique. In general, physical vapor deposition methods are utilized to create the seed layers. Such techniques include sputtering techniques, thermal evaporation, and electron-beam evaporation, and are well known to those of skill in the art.

Apparatus for accomplishing physical vapor deposition are well known, and any suitable apparatus may be utilized in the practice of the present invention. Suitable equipment includes a standard thermal evaporator such as the Edwards E306A (Edwards Company, Great Britain) coating system.

According to the present invention, the seed layer may include one or more WO 96/33298 PCTUS96/04754 subsurface layers. Optionally, the seed layer may further include a top surface layer of the same metal as the metal to be electroplated onto the seed layer. Of course, any metal or material that will adhere to the supporting substrate, and provide a suitable surface for the electroplated metal may be utilized. Non-limiting examples of materials suitable for use as the seed layer(s) include aluminum, copper, chromium, gold, nickel, niobium, palladium, platinum, silicon, tantalum, titanium, tungsten, and combinations of any of the foregoing.

Titanium will tend to diffuse into gold. Therefore, if titanium is utilized as a subsurface seed layer, a layer of platinum or tungsten is generally utilized between the titanium and gold layers.

With some metals, the seed layer will tend to be susceptible to delamination unless the substrate is heated prior to and during the physical vapor deposition process. The temperature is generally great enough to discourage delamination of the final seed layer but less than the degradation temperature of the diamond film or the metal melting point, whichever is less. For example, generally during the physical vapor deposition process of depositing a chromium seed layer onto diamond film, the diamond film is heated to a temperature in the range of about 150C to about 400°C. Preferably, the physical vapor deposition process is carried out at a temperature in the range of about 175*C to about 300°C, and most preferably at a temperature in the range of about 185°C to about 225°C.

While various operating pressures may be utilized, it is preferred that the physical vapor deposition process for applying the seed layer is generally carried out at near S* vacuum, on the order of about 6X10' millibar or less, preferably on the order of about 1X10' millibar or less. It is important that the vaporized chemical be thermally driven-to the target in a relatively unimpeded manner. Thus, it is necessary to create proper conditions so that the vaporized chemical will have a high mean free path, on the order :of a magnitude greater than the distance between the chemical target and the supporting substrate.

Generally, the vacuum chamber is purged with nitrogen prior to obtaining the 3* vacuum, to remove substantially all oxidants.

30 In the practice of the present invention, the seed layer must have a relatively.

*i W0 96133298 pCT[US96/04754 perfect crystal structure, which structure can be influenced by the application rate. Low seed layer application rates are utilized to provide a seed layer with the proper crystal structure. Suitable application rates are on the order of 5-i 1QA/sec or lower.

Electroplating a conductive layer Once the seed layer is in place, the conductive layer is applied onto the seed layers utilizing an electroplating technique.

The inventors have determined that electroplating at low electroplating rates, RD, utilizing low electroplating current densities, JL, will result in an electroplated layer having a surface roughness less than that of the underlying layer upon which it is electroplated, with roughness decreasing with decreasing R. and Jji The inventors have also determined that electroplating at high electroplating rates, RH, utilizing high electroplating current densities, 1 H, will result in an electroplated layer having a surface roughness greater than that of the underlying layer upon which it is electroplated, with roughness increasing with increasing RI, and Jtj. An intermediate electroplating rate P, utilizing an intermediate cur-rent density such that RL<RO<RH, and JL<Jo<JH, will result in an electroplated layer having a surface roughness equal to that of the underlying layer upon which it is electroplated.

The present invention thus provides a method of forming an electroplated layer having a surface roughness less than or equal to the surface roughness of the target layer, 20 by utilizing an electroplating rate less than or equal to 3 at intermediate current density less than or equal to J,* The present invention also provides a method of forming an electroplated layer having a target surface roughness by monitoring the roughness of the forming electroplated layer, and increasing the electroplating rate and cur-rent density above and Jo, if the monitored roughness is less than the target roughness, and by decreasing the electroplating rate and current density below 0 and ;3 if the monitored roughness is greater than the target roughness.

*The particular deposition rate or current density which will result in an electroplated layer having a roughness greater than, less than or equal to that of the layer upon which it is electroplated, will vary according to the type of metal being electroplated, WO096/33298 pCT/US961047S4 12 the type of electroplating solution utilized, pH, solution density, bath temperature, anodeto-cathode ratio, type of agitation, as well as other factors. It is generally necessary to conduct a simple test over a range of deposition rates or current densities to determineR.

and Jo, and the ranges for RL, 3 L, RH and J,, For example, when utilizing a certain commercially available gold plating solution, it is generally necessary to provide a current density at the anode of less than 1 m.A/cm 2 to provide an electroplated layer having a surface roughness less than the roughness of thle underlying layer. Preferably, the current density at the anode will be in the range of about 0.001 to about 0.95 mA/cm', more preferably in the range of about 0.01 to about 0.7 mA/cm, even more preferably in the range of about 0. 1 to about 0.5 mA/cm 2 and most preferably in the range of about 0. 1ito about 0.2 mA/cm 2 to provide an electroplated layer having a surface roughness less than the roughness of the underlying layer.

The surface of a substrate is not regular and may contain many irregularities, which may be naturally occurring, an unwanted result of processing or handling, or may intentionally manufactured into the substrate (such as vias). As used herein, the irregularity will be characterized as having a valley or low region, and peaks or high regions.

An alternative electroplating embodiment of the present invention includes electroplating a surface having surface irregularities such as crevices, cracks, grooves, exposed rnicrocavities, scratches, slits, slots, openings, hollow portions, cavities, chambers, notches, pits, holes, vias, and/or voids. According to this alternative embodiment, the electroplating is conducted such that the surface irregularity is *substantially filled by the electroplating process.

Reference is now made to FIGs. IlA-C, which show respectively, substrate 10 with irregularity 20 without an electroplated metal, substrate 10 with irregularity *electroplated over by electroplated metal 30, and substrate 10 with irregularity substantially filled by electroplated metal Whiile not wishing to be limited by theory the inventors believe that electroplating over irregularities, as shown in FIG. lB will result in lower adhesion, and will provide trapped electroplating solvents which will boil at elevated temperatures and blister the WO 96/33298 PTU914S 13 article. The inventors also believe that the prior art electroplating methods generally would electroplate over any surface irregularities, because at higher current densities, the electroplating charge: would accumulate at the surface of the substrate, at peaks, and be depleted at the bottom, or valley, of the irregularity. The inventors further believe that lower current densities allow for the metal to substantially fill the irregularity, resulting in better adhesion Thus, the present invention includes electroplating a surface having surface .irregularities such as crevices, cracks, grooves, exposed ricrocavities, scratches, slits, slots, openings, hollow portions, cavities, chambers, notches, pits, holes, vias, and/or voids, to substantially 61 substantially all of the irregularities with the electroplated metal.

Preferably the volume of an irregularity is at least 50 percent, more preferably at least 80 percent, even more preferably at least 90 percent and even more preferably at least 95 percent, still more preferably at least 98 percent, and most preferably at least 99 percent filled. Preferably at least 50 percent, more preferably at least 80 percent, even more preferably at least 90 percent and even more preferably at least 95 percent, still more preferably at least 98 percent, and most preferably at least 99 percent of the irregularities on the surface will be filled.

The proper electroplating rate can be easily determined by varying the electroplating rate over -a range and analyzing the filling of the irregularities.

in the practice of the present invention, the electroplating is. generally carried out as follows. The supporting member with seed layer is connected to a cathode and a platinum plate connected to the anode. With the supporting member and platinum plate submerged in an electroplating solution, a. current is applied to drive the electroplating process.

The process of the present invention finds utility in providing useful products for use in electronic applications. The products of the present invention have utility in a broad range of electronic applications, including specifically as diodes, flat panel displays, power amplifiers, and as multichip modules in general.

0:S 14 I CLAIM: 1I 1 A ball and valve seat assembly comprising: 2 a hollow tubular member having an internal crass-sectional area; 3 a valve seat mounted within the tubular member, having a seating passage 4 with a seating crass-sectional area; a ball positioned within the tubular member above the valve seat;, 6 a piston movably mounted within the tubular member below the valve seat, 7 comprising an actuator for engaging the ball through the passage while the ball is seated 8 on the seat, and comrnpising a first sealing member with a first sealing area for sealing the 9 tubular member below the valve seat across the entire-iinternal cross-sectional area of the tubular member, wherein the sealing area is greater than the seating cross-sectional areat 1I I hri h aladvlesa scoe ytebl en etdo h av et 12 and opened by an increase in fluid pressure below the piston acting upon the sealing area 13 causing the piston to rise and engage the ball with the actuator and thereby unseat the ball.

1 2. The assembly of claim I fizther comprising channels in the hollow tubular 2 member for diverting liquid around the piston when the piston is engaging the ball.

1 3. The assembly of claim 1 wherein the engaging means engages the ball 2 asymmnetrically with respect to a vertical axis through the center of the ball.

1 4. The assembly of claim 3 wherein the engaging means comprises an end for~ *2 engaging the ball that is angled to urge the ball toward a wail of the tubular 3 member, *1 5. Trhe assembly of claim 3 ftirther comprising channels in the hollow tubular 2 member for diverting liquid around the piston when the piston is engaging the ball.

1 6. The assembly of claim 5 wherein the ratio of the sealing area to the seating 2 cross-sectional area is at least 2.

WO 96/33298 PCTIU S96i04754 sulfuinc acid in a 600 ml Pyrex beaker. Next, the beaker is placed on a standard hot plate inside a fume hood. By means of the hot plate, the mixture of sulfuric acid/chromium trioxide powder is heated to 160*C. The diamond film is placed in the mixture for minutes and then removed.

A similar procedure is repeated with a mixture of 200 ml of semiconductor grade amnmonium hydroxide and 200 ml of hydrogen peroxide in a 600 ml Pyrex beaker. This beaker is placed on a standard hot plate inside a fume hood. By means of the hot plate, the mixture is heated to 70'C. The diamond film is placed in the mixture for 30 minutes and then removed.

Removal of residual cleaning solution The diamond sample is placed in 600 ml of deionized water in a 600 mrl Pyrex beaker. The beaker is then placed inside a standard ultrasonic cleaner, with the diamond sample subjected to ultrasonic cleaning for at least three hours.

Preparation of the seed laye A seed layer was applied to the cleaned diamond film samples of Procedure 1 utilizing an Edwards E306A coating system. The Edwards E306A is a standard thermal evaporator, the operation of which is known to those of skill in the art, and which was operated generally as follows.

Mounting of the diamond film samples A~fter venting the vacuum chamber with nitrogen gas, the bell jar is removed.

Removal of the bell jar provides access to and permits subsequent removal of the sample holder, i.e. the metal plate at the top of the apparatus under the jar. Next, one of the screws in the sample holder metal plate is loosened, and a corner of the diamond film sample is placed under the screw. The diamond sample is oriented such that the substrate side of the sample is against the plate, with the growth side of the sample facing out. The screw is then tightened until the washer is snug against the holder, sufficiently tight- to WO 96/33298 PCT1US96104754 16 secure the sample when the plate is held upside down. The sample holder is then placed in the evaporator. The piezoelectric holder is then placed in its standard position.

Mounting the chromium and gold targets First, the center target holder, and two of' the peripheral target holders on the target holding apparatus are loosened. Next, a standard thermal evaporation chromium stick, commercially available from R.D. Mathis Company, is positioned with one end in the center target holder, and the other end in one of the peripheral target holders. A standard thermal evaporation molybdenum boat, also commnercially available from R.D.

M~athis Company, is positioned with one end in the center target holder, and the other end in the other peripheral target holder. To encourage good electrical connections, a small metal shim is inserted between the molybdenum boat and washer of the center target holder, and the chromium holder is rotated until the chromium target is in electrical contact with the side electrode. 'Next, all the target holders are tightened to secure the chromium stick and the molybdenum boat. Finally, a small 2mm x 2mm x 2mrn nugget of gold of at least 99.99% purity is placed in the molybdenum boat.

HetAdsment For proper operation, it is necessary that the radiant heater is pointed at the diamond film samples, that the thermocouple is close to the diamond film samples, but not shadowing any of them from the evaporating metal, and that the window on the radiant heater is clear and not covered 'with metal.

The rotary pump is engaged to pump down the vacuum chamber until the Pirannu 000gauge reads 0.06 mnbar. Next, the diffusion pump is engaged and filled with liquid ~0*nitrogen. To protect the operator from exposure to the radiant heater, a cover is placed over the bell jar. The radiant heater is set to 200*C and engaged. Over the next few hours, the diffusion pump is operated to take the pressure in the vacuum chamber down to 6E-6 mbar.

WO 96/33298 pCTfUS96/047S4 17 Thermal evaporation of the seed layer The thermal evaporator is first operated to form a chromium layer directly on the diamond film, and then operated to form a gold layer on the chromium layer.

First utilizing the chromium stick as the target, the current is increased until a chromium deposition rate of 0.5 to 1.0 nm/sec is achieved, to form a chromium layer from 17.5 nm to 22.5 nm thick. Subsequently, the target holding apparatus is rotated so that the gold nugget in the molybdenum boat is now the target. The current is increased until a gold deposition rate of 0.5 to 1.0 nm/sec is achieved, to form a gold layer from 275 nm to 325 nm thick.

Once the chromium and gold layers are formed, the current is stopped, the substrate heater is turned off, the diffusion pump is disengaged, and the chamber is vented once. The chamber is pumped down again, but with the roughing pump instead of with the diffusion pump. The apparatus is then allowed to cool at room temperature for about an hour, at which time the chamber is again vented, and the seed layer coated diamond film removed.

Procedure IH Preparation of gold layer Diamond film samples from Procedure II having a chromium and gold seed layer are utilized in this Example.

800 ml of a sulfite-based, non-toxic gold electroplating solution, available from Englehard is utilized in a 1500 ml Pyrex beaker. The solution must be tested to make sure its operational parameters are within tolerances. The pH, which must be and 11, is increased with KOH and decreased with DI water. The density, which must be between 12' Baume and 16°Be, is increased with gold concentrate from S..Englehard, and decreased with DI water.

During the electroplating operation, the solution is agitated by means of a magnetic stir bar, and the solution temperature is maintained between 55*C and 60°C by means of an electrical hot plate.

30 The diamond sample is attached to the cathode alligator clip, and a platinum plate 0004 WNO 96/33298 pCTIUS96/047:54 x is attached to the anode alligator clip. Only about 5 cm2 of the anode is placed into the solution. A standard BP power supply which provides current measurable to a tenth of a milliamp is utilized.

The electroplating is conducted at a current of O.5mA, which sets the current density at the cathode to 0.5 mA/cm', to provide a deposition rate of about 0.4 microns g :old/hr. The electroplating is continued until the desired thickness of gold is obtained.

Peel Test Procedure The plated diamond films from Procedure III are tested using the "Peel Test" procedure of ASTM B-57 1 except that an aluminum test strip is substituted for the steel or brass strip. The equipment utilized was a Sebastian III tester.

The non-electroplated (back) side of the diamond film is secured to an aluminum backplate using J.B. Weld epoxy. An aluminum pull strip is secured to the electroplated (front) side of the diamond film using J.B. Veld Epoxy. A metal clip is utilized to press the pull strip against the sample. The sample is then allowed to cure at 1 50'C for 3 hours, and at room temperature for 21 hours. The Sebastian III tester is then utilized to provide a pulling force at a pulling angle 900 to the surface of the film, to pull the aluminum pull strip off of the diamond film. The digital display will indicate the force with which the ::20 machine was pulling when the pull strip was removed. By dividing this force value by the area of the pull strip, it can be reported in pounds per square inch.

Control At igh Deposit Rate A I cm x 1cm diamrond sample was coated with a seed layer of 200A chrom-ium and 3000A gold by Procedures I and II as shown above. Seven gold layers were then applied at various current densities utilizing Procedure III above at the parameters as shown in Table I below.

WO 96/33298 PCTfUS961(04754 Total Thickness Deposit Layer No. Current Density (nAcm') Electroplating time (min) Layer Thickness (Pr) Total Thickness Deposit Rate (pm/hr) 4 1. 0.3 36 0..3 36 2 5 1 0.4 0.7 24 3 4 10 2 0.8 1.5 24 10 2 0.5 2.0 10 4 1.0 3.0 Is S6 6 I i i I 3.5 4.0 is I I Peel Test of Procedure IV was conducted on the above 7 layer sample: sample peeled at 20 pounds (350psi).

Control At High Deposit Rate A 1 cm x I cm diamond sample was coated with a seed layer of 200A chromium and 3000A gold by Procedures I and I as shown above. A 4.5 g.Im gold layer was applied at a deposition rate of 18 hrm/hr utilizing Procedure III. Peel Test results utilizing Procedure IV was as follows: peeled at 251bs (440 psi)..

Euampir,_ Roughness vs. Deposit Rate Two I1cm x 1cm diamond samples an were each coated with a seed layer of 200A chromium and 3000A gold by Procedures I and II as shown above. Eight layers of gold were then deposited on each seed layer by Procedure III above, with surface roughness measured initially and after deposition of each gold layer. Results are presented in Table 2.

WO 96133298 PCTIUS96/04754 Table 2 X pL4 Ann ealine f eed layr 3 1 cm x I1cm diamond samples were each coated with a seed layer of 200A chromium and 3000A gold by Procedures I and f1 as shown above- 3 1 cm x 1 cm. diamond samples were each coated with a seed layer of 200A chromium and 1000oA gold by 30 Procedures I and 11 as shown above, and an additional 2000A gold by Procedures I and WO 96133298 pCTIU S96104754 11 as shown above, except that an deposition temperature of 50'C was utilized.

For samples C- I and D-l1, the seed layer was not annealed, for sample C-2 and D- 2, the seed layer was annealed at 300'C, and for samples C-3 and D-3, the seed layer was annealed at 400 0 C. All samples were then electroplated with a 5A thick gold layer at 0.8 mAICM 2 by Procedure III above.

These six electroplated samples were all subjected to annealing at 3 50 0 C. Finally, all samples were subjected to the Peel Test of Procedure IV. Results are shown in the following Tables 3-6.

Ta0e Surface Roughness Of Seed Layer Before Electroplating (nm) SAMPLES C SAMPLES

D

I (SEED LAYER NOT 250 250 ANNEALED)__ 2 (SEED LAYER 254 269 ANNEALED AT 300 0 C) 3 (SEED LAYER ANNEALED AT 400-C) 262 1.00 Table- Surface Roughnes Of Electroplated Gold Layer (nm) SAMPLES C [1(SEED LAYER NOT 181 ANNEALED) 207 2 (SEED LAYER ANNEALED AT 300"C) 3 (SEED LAYER ANNEALED AT 400 0

C)

150IS PCT1US96/047!54 WO 96/33298 22 Tabe Surface Rou~ns f Electroplatd Gold Layer After Anneafin At. 350 0 C (nm) Samples in the bottom row blistered, accounting for the high surface roughness.

Table 6 Peel Test Results (PST) 6* 0 *t 30 Thermal Stress ad Thra Cyin Of Larme Samle1(0 m x21mm 2 1mm x 2 1 mm samples were each coated with a seed layer of 200A chromium and 3000A gold by Procedures I and. II as shown above. Seed layers were subjected to no annealing, annealin g at 350*C, or annealing at 400TC. A. gold layer of 5A was then deposited on the seed layer of each sample by Procedure III above. One set of samples was then subjected to thermnal stress (annealing) at 350*C or 400 0 C for 30 minutes.

WO 96/33298 PCTIUS96/04754 23 Another set of samples was then subjected to thermal cycling from 150 0 C to -65°C, in close agreement with military standards. The samples were subjected to 16 cycles, with a cycle as follows: climbing to 150°C in 15 minutes, dwell for 15 minutes, down to in 15 minutes, dwell for 15 minutes. This procedure varied from standard military specifications in that 15 minute temperature increments were utilized instead of 10 minute increments.

Table 7 Peel Testina After Thermal Cycling (PSI SAMPLES For Thermal SAMPLES For Thermal Stress Cycling 1 (SEED LAYER NOT 350 0 C: 3600 3600 ANNEALED) 400 0 C: 2000 2 (SEED LAYER ANNEALED 350°C: 3600 3600 AT 300 0 C) 400°C: 1800 (SEED LAYER ANNEALED 350 0 C: 0 0 •AT 400 0 C) Example 6 20 21mm x 21 mm samples of diamond were degreased and cleaned according to Procedure I above. The teachings of Procedure II were followed to deposit the seed layer, except that the thickness of chromium was always 300 angstroms, and copper was deposited instead of gold. The copper was deposited to a thickness of 2000 angstroms, but at varying substrate temperatures. Also, the base pressure in the thermal evaporator 25 chamber was varied. Also, the temperature of the seed layer anneal step was varied. All "of the samples were then electroplated with cooper to a thickness of 8-10 microns. All *I of the samples were then annealed at 350 0 C. All of the samples were then observed for blisters.

0 0 1 0 0a 00.

.0.0 o o.

SAMPLE

2 3 4 6 7 8 9.

Tables EVAPORATION

EVAPORATION

SUBSTRATE BASE PRESSURE TEMPERATURE

(MBAR)

200 1.3E-6 200 1.3E-6 200 1.3E-6 Cr: 200 1.3E-6 Cu: 50 1.SE-7 Cr: 200 1.3E-6 Cu: 50 1.5E-7 Cr: 200 1.3E-6 Cu: 50 1.5E-7 Cr: 200 1.3E-6 Cu: 50 1.5E-7 Cr: 200 1.3E-6 Cu: 50 1.SE-7 Cr: 200 1.3E-6 Cu: 50 1.5E-7 SEED LAYER

ANNEAL

TEMPERATURE

AMBIENT

300 400

AMBIENT

300 400

AMBIENT

300 400

BLISTER

RATING

MEDIUM

MEDIUM

MEDTUM

LOW

LOW

VERY LOW

HIGH

HIGH

N/A (etched off) While the illustrative embodiments of the invention have been described with particularity, it will be understood that various other modifications will be apparent to and can be readily made by those skilled in the art without departing from the spirit and scope of the invention. Accordingly, it is not intended that the scope of the claims appended hereto be limited to the examples and descriptions set forth herein but rather that the claims be construed as encompassing all the features of patentable novelty which reside in the present invention, including all features which would be treated as equivalents thereof by.those skilled the art to which this invention pertains.

In this specification, except wherq the context requires otherwise, the words "comprise", "comprises", and "comprising" mean "include", "includes", and "including", respectively. That is, when the invention is described or defined as comprising specified features, various embodiments of the same invention may also include additional features.

Claims (23)

1. 2. The method of claim 1 wherein the article comprises metals, diamond, semiconductors, ceramics, thermoplastics or thermosets.
2. 3. The method of claim 1 wherein the article comprises a supporting member and a seed layer forming the conductive surface. 25 4. The method of claim 3 wherein the seed layer comprises aluminum, copper, chromium, gold, nickel, niobium, palladium, platinum, silicon, tantalum, titanium, tungsten, or combinations of any of the foregoing.
3. 5. The method of claim 3 wherein the supporting member comprises diamond, and the seed layer comprises chromium and gold, and the conducting metal comprises gold, wherein the chromium is adhered to the diamond.
4. 6. A method of electroplating an article having a conductive surface with a surface roughness Ro, the method H:\Pcabral\Keep\speci\40896.0o.doc 16/01/03 26 comprising: cleaning the conductive surface; and electroplating a conductive metal onto the surface utilizing a current density less than or equal to Jo, to form a conductive metal later having a surface roughness RE no greater than the article surface roughness Ro; wherein Jo is a current density which will result in the conductive metal layer having a surface roughness RE equal to Ro.
5. 7. The method of claim 6 wherein the article comprises metals, diamond, semiconductors, ceramics, thermoplastics or thermosets.
6. 8. The method of claim 6 wherein the article comprises a supporting member and a seed layer.
7. 9. The method of claim 8 wherein the seed layer comprises aluminum, copper, chromium, gold, nickel, niobium, palladium, platinum, silicon, tantalum, titanium, tungsten, or combinations of any of the foregoing.
8. 10. The method of claim 8 wherein the supporting member comprises diamond, and the seed layer comprises chromium and gold, and the conducting metal comprises gold, wherein the chromium is adhered to the diamond.
9. 11. A method of electroplating an article comprising 30 a supporting member and a seed layer supported by the supporting member, with the seed layer having a conductive surface with peaks and valleys, the method comprising: cleaning the conductive surface; and electroplating a conductive metal onto the peaks to cover the peaks with the conductive metal, and into the valleys to substantially fill the valleys with the conductive metal wherein the electroplating is carried out \\melbjiles\homeS\L)Coles\Keeppeci\408960-00 claims.doc 20/09/0020/09/00 27 at a current density less than or equal to Jo; wherein Jo is a current density which will result in the conductive metal layer having a surface roughness RE equal to Ro.
10. 12. The method of claim 11 wherein the article comprises metals, diamond, semiconductors, ceramics, thermoplastics or thermosets.
11. 13. The method of claim 11 wherein the seed layer comprises aluminum, copper, chromium, gold, nickel, niobium, palladium, platinum, silicon, tantalum, titanium, tungsten, or combinations of any of the foregoing.
12. 14. The method of claim 11 wherein the supporting member comprises diamond, and the seed layer comprises chromium and gold, and the conducting metal comprises gold, wherein the chromium is adhered to the diamond.
13. 15. A method of electroplating an article comprising a diamond member and a seed layer supported by the diamond member, with the seed layer having a conductive surface 0 with a surface roughness, the method comprising: cleaning the conductive surface; and 25 electroplating a conductive metal onto the seed layer surface utilizing a current density less than or equal to Jo, to form a conductive metal layer having a surface roughness no greater than the seed layer surface roughness. m. 16. The method of claim 15 wherein the seed layer comprises aluminum, copper, chromium, gold, nickel, niobium, palladium, platinum, silicon, tantalum, titanium, tungsten, or combinations of any of the foregoing.
14. 17. The method of claim 15 wherein the supporting member comprises diamond, and the seed layer comprises \\melb-jiles\home\LJColes\Keep\Speci\408960-00 claims.doc 20/09/0020/09/00 28 chromium and gold, and the conducting metal comprises gold, wherein the chromium is adhered to the diamond.
15. 18. A method of metallizing a diamond film comprising: applying a seed metal onto the diamond film to form a seed layer having a surface roughness Ro, with the seed layer having a conductive surface with peaks and valleys; cleaning the conductive surface; and electroplating a conductive metal onto the peaks to cover the peaks with the conductive metal, and into the valleys to substantially fill the valleys with the conductive metal, to form an electroplated article having a surface roughness RE, wherein the electroplating is carried out at a current density less than or equal to Jo; wherein Jo is a current density which will result in the electroplated article having a surface roughness Ra equal to Ro.
16. 19. The method of claim 18 wherein in step the diamond film is heated prior to applying the seed metal. :20. The method of claim 18 wherein the seed metal comprises chromium, and the substrate is heated to a temperature in the range of about 150 0 C to about 400 0 C prior to applying the chromium. "21. The method of claim 20 wherein the seed metal further comprises gold.
17. 22. The method of claim 21 wherein the conductive metal comprises gold.
18. 23. The method of claim 22 wherein the electroplating \\melbfiles\homeS\.jColes\Keep\peci\408960-00 claims.doc 20/09/0020/09/00 29 is conducted at a current density in the range of about 0.001 to about 0.95 mA/cm 2
19. 24. A method of metallizing a diamond film comprising: applying a seed metal onto the diamond film to form a seed layer, with the seed layer having a conductive surface with a surface roughness Ro; electroplating a conductive metal onto the seed layer surface utilizing a current density less than or equal to Jo, to form a conductive metal layer having a surface roughness RE no greater than the seed layer surface roughness Ro; wherein Jo is a current density which will result in the electroplated article having a surface roughness RE equal to Ro.
20. 25. The method of claim 24 wherein in step the diamond film is heated prior to applying the seed metal. o. 26. The method of claim 24 wherein the seed metal comprises chromium, and the diamond film is heated to a 25 temperature in the range of about 150 0 C to about 400 0 C prior to applying the chromium.
21. 27. The method of claim 26 wherein the seed metal further comprises gold.
22. 28. The method of claim 27 wherein the conductive metal comprises gold.
23. 29. The method of claim 28 wherein the electroplating is conducted at a current density in the range of about 0.001 to about 0.95 mA/cm 2 \\melb-files\homeS\uJCooes\Keep\Speci\40896a-o claims.doc 20/09/0020/09/00 30 A method of electroplating onto a conductive surface of an article to form an electroplated layer having a desired surface roughness RD, the method comprising: electroplating at a current density, a conductive metal onto the conductive surface of the article to form an electroplated layer of surface roughness RE; determining the surface roughness RE of the electroplated layer; increasing the current density of step (a) if the surface roughness RE determined in step is less than the desired surface roughness RD, and decreasing the current density of step if the surface roughness RH determined in step is greater than the desired surface roughness RD. Dated this 20 th day of September 2000 THE BOARD OF TRUSTEES OF THE UNIVERSITY OF ARKANSAS By their Patent Attorneys GRIFFITH HACK Fellows Institute of Patent and Trade Mark Attorneys of Australia *o*o eoee \\melb-Eile\homeS\.JColes\Keep\Speci\408960-00 claims.doc 20/09/0020/09/00