CA2506690A1 - Apparatus and process for metal carbonyl vapour deposition - Google Patents

Abstract

An improved process and apparatus for the production of metal or a metal-coated object by a metal carbonyl vapour deposition process, comprising a) placing an object having a surface to be treated with metal carbonyl gas by the metal vapour deposition process into a deposition chamber having an IR
transparent window;
b) feeding the gaseous metal carbonyl gas to the deposition chamber;
c) passing 1R radiation from an infrared source through the window for radiant heating of the surface of the object to a temperature at which decomposition of the metal carbonyl gas occurs or the surface of the object, the improvement wherein (a) the window is formed of a material having an effective transparency to radiation of wavelengths in the range 0.2 µm-2.5 µm; and (b) the infrared source provides said IR radiation to the window at a power level intensity insufficient to heat the window material to a temperature of at least 100°C under steady state conditions, but is sufficient to heat the object surface at a temperature sufficient to effect decomposition of the metal carbonyl on the object surface. The process and apparatus does not produce fogging of the chamber window with deposited metal, for example, nickel.

Description

MEAL CARBON~1L VAPOUR .~E,~ffSITiON
,APPARATUS AND PROCESS
This invention relates to metal carbonyl vapour decomposition and metal deposition processes for use in the manufacture of metal or metal coated objects, particularly nickel deposition, and more particularly to infrared heating in said processes; and to apparatus of use in said processes.
Chemical vapour deposition is a well-known method for depositing films or coatings on substrates. One known chemical vapour used for depositing a nickel film or coating on a substrate is nickel carbonyl in the so-called Nickel Vapour Deposition proccss (NVD). Typically, the substrates to be'nickel coated are heated within a reaction or deposition chamber to a predetermined suitable reaction temperature, typically 1.75°C-180°C in an atmosphere of nickel carbonyl, Ni(CO)4. The nickel carbonyl decomposes at the surface of the heated substrate to deposit the Ni film or coating thereon.
Nickel carbonyl from a liquid supply tank flows through a vapourizer where it is converted into a gas stream to which gaseous stream may be added a small amount of carrier gas, such as carbon monoxide.
Typically, nickel carbonyl vapour is continuously introduced to the deposition chamber, wherein it reacts to produce elemental nickel and carbon monoxide by-product. The spent gas is continuously purged from the chamber in order td maintain proper circulation of reactive nickel carbonyl across the surfaces of the substrates.
The substrates may be heated according to well-known methods, such as heat conduction, infrared radiation, inductance and the like.

Infrared heating (IR) is required or otherwise desirable when the substrate to be heated is not electrically conductive wherein the IR radiation is directed into the deposition chamber through infrared transparent windows to heat the substrate.
Preferably, the IR radiation selectively heats the substrate within the chamber, not the metal carbonyl gas or the 1R transparent window. If the metal carbonyl gas is heated above its decomposition temperature, it spontaneously decomposes. Similarly, if the IR transparent window is heated above the decomposition temperature of the metal carbonyl gas, the gaseous compound, undesirably, decomposes on the 1R
transparent window, which essentially results in a stoppage of the carbonyl plating on the substrate because the 1R radiation cannot effectively penetrate the fogged windows.
To remove this problem, the windows must be removed, periodically, to be cleaned or replaced. The metal deposited on the window is also not infrared transparent, which causes increased infi~ared heating of the window.
One source of this problem is that infrared transparent windows constructed of materials such as borosilicate glass, clear fused quartz, polyethylene, terephthalate, polytetrafluoroethylene, poly-tetrafluoroethylenepropylene and other materials are not perfectly transparent to inirrared radiation and,vin consequence, the window becomes hot enough to cause metal deposition thereon.
U.S. Patent No. 3,213,827 - Jerkin describes an air-cooled cooling duct for cooling an infrared transparent chamber wall. However, due to the inefficiencies of air-cooling, it is believed that the design of Jerkin is insufficient to effectively prevent fogging.
European Patent Application No. 0424183A1 - Paserin and U.S. Patent No.
5,145,716 - Paserin, to prevent fogging of infrared windows in carbonyl decomposition chambers, uses liquid coolant, which substantially infrared transparent for allowing infrared radiation through the infrared transparent window and cooling passage into the chamber. The laboratory test setup.utilized windows having two infrared transparent glass sheets sold under the trademark PYREX~spaced 6 mm apart. The space between the PYREX~ sheets was filled with various fluids. The tests utilized PYREX~ sheets 4 and 5 mm in thickness. Spaced adjacent on one side of the PYREX~ sheets and test fluid was a 140 volt, 440 watt infrared lamp. The filament of the infrared lamp was heated to a temperature of 1980 ° C, having a peak wavelength of 1.46 microns. Different coolants were used: water, ethylene glycol, ethylene glycol diacetate, tetrachlorethane and tetrachloroethylene.
However, there is still a need to provide an improved process of significantly reducing or completely preventing deposition of metal on the window.
It is an object of this invention to effectively prevent fogging of the windows in carbonyl decomposition chambers without using any cooling systems for windows.
Another object of this invention is to reduce power losses of the metal carbonyl decomposition process.
The present invention provides an improved process and apparatus wherein the deposition chamber window does not require cooling during the deposition of metal on a substrate.
Accordingly, in one aspect, the invention provides an improved process for the production of metal or a metal-coated object by a metal carbonyl vapow deposition process, comprising a) placing an object having a surface to be treated with metal carbonyl gas by said metal vapour deposition process into a deposition chamber having a partial IR
radiation transparent window;
b) feeding said gaseous metal carbonyl gas to said deposition chamber;
c) passing 1R radiation from an infrared source through said window for radiant heating of said surface of said object to a temperature at which decomposition of said metal carbonyl gas occurs on said surface of said object, the improvement wherein (a) said window is formed of a material having an effective transparency to radiation of wavelengths in the range 0.2 Eun-2.SEun; and (b) said infrared source provides said IR radiation to said window at a power level intensity insufficient to heat said window material to a temperatiue to effect metal deposition thereon under steady state conditions, but 'is sufficient to heat said object surface at a temperature sufficient to effect decomposition of said metal carbonyl on said object surface.
Preferably, the applied power level intensity should be insufficient to heat the window material to a temperatiue of at least 100°C.
The window material is preferably 90%, and more preferably 95% transparent to the wavelength in the range 0.25Eun - 2.SEun.
The invention is most valuable in Ni(CO~ vapour decomposition to nickel and carbon monoxide.
In a further aspect the invention provides an improved apparatus for the production of metal or a metal-coated objet by a metal carbonyl vapour deposition process, comprising (i) a metal carbonyl decomposition chamber for receiving said object I S having a surface; said chamber having a partial IR radiation transparent window and adapted to receive metal carbonyl vapour;
(ii) an IR radiation source adjacent said chamber for operably projecting IR radiation through said window into said chamber to heat said surface of said object; the improvement wherein ~ a) said window is formed of a material having an effective transparency to radiation of wavelengths in the range of 0.2 dun-2.5 um; and b) said 1R radiation source operably provides said IR radiation to said window at a power level intensity insufficient to heat said window material to a temperature to effect metal deposition thereon under steady state conditions, but sufficient to heat said object surface at a temperature to effect decomposition of said metal carbonyl on said object surface.
The window is preferably transparent to at least 90%, and more preferably at.
least 95% to wavelength in the range 0.25 - 2.SEun.

In order that the invention may be better understood, a prefen;ed embodiment will now be described, by way of example only, with reference to the accompanying drawings, wherein Fig. 1 is a diagrammatic layout of a process and apparatus according to the invention;
Fig. 2 is a spectral radiation distribution of halogen lamp with filament temperature 2400 K;
Fig. 3A and Fig. 3B are transmission curves for VICOR Glass (quartz type);
and Fig. 4 is a transmission curve for BOROFLORAT'~ borosilicate.
DETAILED DESC$~"101~1 (,~ PREFERRED E~ODnVIENTS
With reference to Fig 1 this shows generally as 10 a metal deposition chamber 12 with associated 1R source 14, filter 16 and conveyance assembly 18 for IR
emitter 16.
In more detail, chamber 12 has a feed nickel carbonyl vapour inlet 20 and spent carbon monoxide-containing exhaust gas outlet 22. Chamber 12 has an 1R
radiation transparent window 24.
Adjacent window 24 at an effective distance and parallel thereto is the 1R
radiation source 14, which in this embodiment has means 18 for transversely conveying IR emitter 14 parallel to window 24 to provide uniform radiation across and through the full length of window 24.
In this preferred embodiment, filter 16 is located intermittent between 1R
source 14 and window 24.
Suitably disposed at a central location within chamber 12 is an object 26 having a surface 28 upon which the nickel carbonyl is decomposed and nickel deposited.

Window 24 (1.8 cm thick) is made preferably of fused quartz and more preferably 7913 VYCORT"' glass (Coming) having very good transparency within the wavelength range 0.2-2.5 mICm.
A heat absorbing filter can be installed between the radiation source and the window. The filter most preferably absorbs in the range between 2.0 lun to at least, 5.0 lrm wavelength to decrease heat absorption by the window.
Filter 16 is preferably formed of a borosilicate glass which is visible to near IR
radiation (0.35-2.SmKm) but which is able to absorb radiation of than 2.Spm, preferably when made of BOROFLORATT"~ borosilicate glass (Edmund Industrial Optics, Barrington, New Jersey, U.S.A.). A typical filter has a diameter of about 20cm and a thickness of about 0.65cm.
The maximum radiation spectrum of the source is most preferably in the range between W and Medium Infrared wavelengths, i.e. in the visible part of the spectrum to provide maximum transmission through the window and minimum absorption so as I S to keep the window temperature below which decomposition of the metal carbonyl gas occurs. Preferably, the window temperature does not reach 100°C in the practice of the invention. Preferred IR emitters are halogen lamps having a favourable radiation emission wavelength range of 0.2-2.~pm with a maximum of about 1.1 to 1.4 mKm.
The 1R radiation emitter preferably is attaches to a traveling means to move it across transverse the,window evenly to provide uniform heating of the substrate surface. An ambient air ventilator can be installed between window and 1R
source to prevent convection heat transfer, if the distance between the window and IR
source cannot be optimized. It might be needed if the high density of the heat flow is requiral to heat a thick high thermal conductive object, an object with low emissivity.
Selective halogen 1R radiation emitters can be supplied (Heraeus, Germany).
The most appropriate, is Short Wave IR emitter (1800°C -2000°C filament temperature; peak kWlm2). Halogen lamp short wave emitters are preferred because of their rigid canstrucdon and durability for the voltage variation requirement.
It should be noted that the filter and window can be made of the same material. In preferred embodiments thermal heat transfer from the filter to the window may be reduced by means of ventilation or vacuum of the intervening space between them. Filament temperature of standard Halogen lamp of use in the practice of the invention is about 2100°C which provides a maximum wavelength~at about l.3wm.
An alternative preferred IR radiation emitter is of the double carbon filament type provided with a gold reflector.
The purpose of the filter is to cut oil any long wavelength tail of the 1R
radiation, since quartz and VICORTM glass type start to absorb above about 2 iriKm.
EXAMPLES
It was found in several.test experiments that it was possible to use radiation according to the invention to induce deposition of Ni on a substrate or object surface through the quartz window without metal deposition on the glass surface. A 1.5 kW
halogen lamp and a traveling system, to provide the uniformity of the growing film thickness by scanning the surface was used. It was found that the uniformity of the deposited Ni on an object having a 20 cm diameter silicon wafer surface was 0.025-0.25mm, at a deposition rate in the various runs of from 0.1 to 0.4 mmlh.
The results showed that most favourably control of parameters, such as surface and thickness of the substrate, flow of carbonyl and carrier gases and radiation can be achieved. The window is made of a material which is substantially transparent in the wavelength range between UV and Near Infrared wavelengths and is, thus, not heated so as to prevent the decomposition reaction of the metal carbonyl vapour on the window occurring.
Most satisfactory results were achieved with uniform deposition on flat thin substrates made even from materials with very low thermal conductivity.
Expected problems of uniform radiant heating, masking and separation of the metal, i.e.
in this embodiment, nickel replica from the substrate after deposition were readily addressed.
The preferred optimum distance between the IR lamp and the window is chosen as to prevent heating of the glass by providing ambient air convection or by use of an air-moving ventilator. The surface of the window inside the chamber is cooled by the incoming mixture of precursor nickel carbonyl and carbon monoxide carrier gases. The temperature of the incoming gases, clearly, has to be higher than the condensation temperature of the Ni(CO)4 precursor and significantly lower than its decomposition temperature. I have surprisingly found that this cooling effect is enough to keep the temperature of the window below about 100°C and, thus, any deposition temperature.
The nickel deposition on various substrates from different materials was successfully done inside this chamber without fogging of the window. It was found out the certain advantages of the IR heating of the substrates:
As the deposited surface of the substrate is heated directly, the thermal conductive properties of the substrate material do not have a significant role and, in principle, any material can be used for the substrate. The only demand is that the material withstand the deposition temperature.
Although this disclosure has described and illustrated certain preferred embodiments of the invention, it is to be understood that the invention is not restricted to those particular embodiments. Rather, the invention includes all embodiments which are functional or mechanical equivalence of the specific embodiments and features that have been described and illustrated.

Claims (13)

1. An improved process for the production of metal or a metal-coated object by a metal carbonyl vapour deposition process, comprising a) placing an object having a surface to be treated with metal carbonyl gas by said metal vapour deposition process into a deposition chamber having a partial IR
radiation transparent window;
b) feeding said gaseous metal carbonyl gas to said deposition chamber;
c) passing IR radiation from an infrared source through said window for radiant heating of said surface of said object to a temperature at which decomposition of said metal carbonyl gas occurs on said surface of said object, the improvement wherein (a) said window is formed of a material having an effective transparency to radiation of wavelengths in the range 0.2 µm-2.5 µm; and (b) said infrared source provides said IR radiation to said window at a power level intensity insufficient to heat said window material to a temperature to effect metal deposition thereon under steady state conditions, but is sufficient to heat said object surface at a temperature sufficient to effect decomposition of said metal carbonyl on said object surface.

2. A process as defined in claim 1 wherein said material is at least 90%
transparent to radiation of wavelength in said range of 0.2µm - 2.5 µm.

3. A process as defined in claim 1 or claim 2 wherein said power level intensity is insufficient to heat said window to at least 100°C.

4. A process as defined in anyone of claims 1 to 3 further comprising passing said IR radiation through a filter to absorb IR radiation having a wavelength greater than 2.5 µm located between said 1R source and said window.

5. A process as defined in any one of claims 1 to 4 further comprising traversing said IR source in a plane parallel to and adjacent said window.

6. A process as defined in any one of claims 1 to 5 wherein said window is formed of a borosilicate glass essentially transparent to Near IR radiation.

7. A process as defined in claim 1 or claim 2 wherein said metal is nickel.

8. An improved apparatus for the production of metal or a metal-coated object by a metal carbonyl vapour deposition process, comprising (i) a metal carbonyl decomposition chamber for receiving said object having a surface; said chamber having an IR radiation transparent window and adapted to receive metal carbonyl vapour (ii) an IR radiation source adjacent said chamber for operably projecting IR radiation through said window into said chamber to heat said surface of said object; the improvement wherein a) said window is formed of a material having an effective transparency to radiation of wavelengths in the range of 0.2 µm-2.5 µm; and b) said IR radiation source operably provides said IR radiation to said window at a power level intensity insufficient to heat said window material to a temperature to effect metal deposition thereon under steady state conditions, but sufficient to heat said object surface at a temperature to effect decomposition of said metal carbonyl on said object surface.

9. Apparatus as defined in claim 8 wherein said window material is at least 90%
transparent to radiation of wavelength in said range of 0.2µm - 2.5 µm.

10. Apparatus as defined in claim 8 or claim 9 wherein said IR radiation operably heats said object surface to a temperature of about 150-175°C.

11. Apparatus as defined in any one of claims 8 to 10 further comprising conveying means adapted to conveyer said IR radiation source parallel to said window to effect uniform heating of said object surface to provide uniform metal deposition.

12. Apparatus as defined in any one of claims 8 to 11 further comprising filter means to operably absorb IR radiation having a wavelength greater than 2-5µm located between said IR radiation source and said window.

13. Apparatus as defined in any one of claims 8 to 12 wherein said window is formed of aborosilicate glass essentially visible to near IR radiation.