CA1292965C - Metal adhesion by low energy irradiation of an organic substrate - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE

A technique is described for improving metal-organic substrate adhesion and for reducing stress between the metal film and the substrate. Beams of low energy reactive ions, electrons, or photons are incident upon the substrate to alter the surface chemistry of the substrate to a depth of from about 10 angstroms to a few hundred angstroms. The energy of the incident reactive ions and electrons is about 50-2000eV, while the energy of the incident photons is about 0.2 - 500eV. Irradiation of the substrate can occur prior to or during metal deposition. For simultaneous metal deposition/particle irradiation, the arrival rates of the metal atoms and the substrate treatment particles are within a few order of magnitude of one another. Room temperature or elevated temperatures are suitable.

Description

~292965 IMP~O~D METAL-POLYMER .~D~ESi~ BY LOW E~ERGY

DESCRIPTION

Field of the Invention This invention relates to a technique for improving metal-polymer adhesion and reducing stress ir. a de?os-ited metal film, wherein low energy bombardment of the polymer is used to enhance adhesior, and more partic-ularly to such a technique in which low energy reactive ~ns, electrons, or photo~s are used to alter ~he sur-face chemistry o the polywer to a shallow depth in order to enhance adhesion.

Background Art The metailization of organic substrales, such as plastic materials, is becoming 1ncreasingly important, espe-cially in the electronics field. Most packaging ap-proaches require metallization to be applied to organic Y0985-014 -l-:
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1292~65 ~?oly~e ) substrates such as, for example, copper on poly~m-de. In th_ prio_ art, copper has been deposited by a number or techniques, including pla~ing, vacuum e.7aporation, and sputtering. Often~ chemical condi-tioning of the substrate surface is utilized prior to deposition in order to have better adherence of the metal film to the substrate. However, the problem of poor adhesion between the metal and the organic substrate is still the major problem to overcome.

Many approaches have been tried in the art to enhance adhesion between metal films and o-ganic substrates, with varying degrees of su~cess. In some situations, metals are matched with particular resi~ous subs~ra~es where it has been determined that adherence therebetween i5 ~ superior to other metal-substrate combinations.
Still other situations use extensive pre-cleAning of the substrates prior to metal deposition i~ order to remove con~aminants and roughen the substrate surface. In many of these methods, expensive and/or toxic chemical ele-ments are employed, which is a further disadvan~age.

Other techniques utilize glow discharges or ~lasma dis-charges to affect the polymer surface prior to metal ~: deposition. Examples of the use of a glow discharge to ~

enhance adhesion are found in U. S. Patents 4,165,394 and 4,250,225. This type of technique is also described by L. R. Yetter in I~M Technical Disclosure Bulletin, Vol. 16, No. 7, page 2(:45, December 1973. In glow dis-charge teci~sliques, a brush or glow discharge is created by introducing residual gasses into a vacuum chamber and applying a high voltage in order to creata ions which activate the polymer substrate surface. Examples of the gasses which can be introduced into the vacuum chamber include air, oxygen, nitrogen, helium, neon, argon, krypton, xenon, and radon. After the glow discharge activation, the metal film is deposited by techniques such as electroless plating, evaporation, and sputter-lng.

lS Another technique for enhancing sdhesion between metal films and organlc substrates ls plasma treatment of the ';
substrates. Thl8 technique is very similar to the aforementionet glow discharge technique and is described ln, for example, U. S. Patents 4,337,279 and 4,382,101.
, In this technique, the organic substrate is placed ,.~. .
in a plasma reactor, where the plasma is produced ¦ by the introduction of a gas such as helium, argon, ~ CF4, C3F8, C4F8, CHF3, carbon fluoride, nitrogen, : l oxygen Y09~85-014 - 3 -YO9-85-014 4 ~Z9Z965 etc.. Plasma treatment of the substrate occurs for varying periods of time measured from minutes to several hours.

Another treatment process for enhancing metal-organic substrate deposition is the use of high energy ion beams.
Examples of this technique are described by J.E. Griffith et al, Nuc. Instr. and Methods, 198, 608 (1982) and in papers presented by J. Baglin et al at the Materials Research Society Meeting, Boston, Mass., November 14-17, 1983. In ion beam enhanced adhesion, a high energy beam of ions is incident upon the organic substrate prior to deposition of a metal layer. For example, copper can be deposited on polymer substrates by electron beam deposition, after high energy ion irrAdiatlon of the substrAtes. In this procedure, both reactive and inactive ions can be used, and the ion beam energy ranges upwàrd from about 200 keV.

While some degree of success has been recorded for these techniques to enhance adhesion, none of such techniques is without difficulties. For example, plasma and glow discharge tochniques offer very poor control of ion energy and current, ambient gas pressure, substrate temperature, etc. Also, it is very difficult to obtain good .~ .

12~; :965 control ~f the en~rgy be2m flux in plasma anà glow dis-charge syslems. These systems require high pressures, of the order of 1 Torr. which corresponds to 1 x 1021 gas atoms/cm -sec., in order to maintain the discharge.
S These rates dominale all other rates in the system.
Thes~ rates also cannot be readily matched with me~al eva~ora~ion rat~s, and evaporation cannot be carried out at such high pressures. This in tuTn means that metal deposition has to be by plasma sputtering, rather th2n any other technique. Further, in plasma and glow dis-charge systems, there is very poor control over the in-cident ion beam direction as the ions strike the substrate surface. It ls also the situation that the purity of residual gas control in such systems is not well controlled and is often suficiently high that contamination can ea~ily occur.

High energy ion beam enhancement o adhesion is also not without problems. Such systems are costly and require complicated apparatus to produce the high energy, fo-cussed ion beam. The nature of the ion beam makes it impossible to be able to process large substrate areas : ~ .
simultaneously, and therefore is not readily suitable for high throughput in commercial systems. Further, ~ high energy ion beams can cause damage to the organic l5 ~ Y0985-014 ~;-,, :

Y09-85-014 6 lZ92965 substrate and require large amounts of power. It is also extremely difficult to make large, high energy ion beams with the proper flux and power over a large area.

Wet processing steps, such as chemical steps, are also difficult to control and often require toxic or otherwise offensive solutions. When chemical cleaning is used, there is always a later exposure of the substrates to the environment, and therefore possible contamination can occur.
In general, it is preferable to have a completely dry processing system for both surface preparation and metal deposition.

Accordingly, it is a primary object of this invention to provide a simple technique for improving metal-organic substrate adhesion, which is suitable for use in commercial manufacturing processes.

It is another object of this invention to provide improved metal-organic substrate adhesion at low cost and high reliability.

: ~
It is another object of the present invention to provide an improved technique for enhancing the peel strength of metals on organic substrates.

Il is ar.~her object of this invention to provide a dry p.ocessing technique for simply and rapidly enhancing the adhesion between metals and organic substrates.

It is a further object OL this invention tO provide an improved ~echnique for enhancing metal-organic substrate ~dhesion, where ~he method can be used to process large areas of the substrate.

It is a still further object of this invention to provide an improved technique for enhancing metal-substrate ad-hesion, which technique will also reduce stress between the metal and the organic substrate.

It is another object o this i~vention to provide an improved technique for enhancing metal-organic substrate adhesion, where the technique is suitable for use with many types of metals and organic substrates, including the most commonly used metals and substrates.

It is another object of this invention to provide a simplified technique for enhancing metal-organic substrate adhesicn, where the technique is readily con-trollable and can be used to optimize adhesion.

Y0~85-014 -7-:
-It is ano~her object of Ihis invention to provide a technique for improving metal-organic substra~e adhe-sion, wherein dry processing with lOh' energy particles is utilized, and wherein the apparatus for providing the particles is si~ple and of low cost.

It is another object of the present invention to provide a simplified technique for enhancing metal-organic substrate adhesion, where the possibility of contam-ination by other substances is minimized.

Disclosure of Inven~ion This technique for enhancing metal-organic substrate adhesion uses low energy reactive ion, electron, or photon irradiation of thé organic substrate in order to alter the surace chemistry of the substrate ~o a tepth from about 10 2~gstroms to a few hundred angstroms, so that enhanced adnesion between the ~etal and the substrate will occur. The energy of the irradiated particles is about 50-2000eV and preferrably about 2QO-;OOeV. In this technique, the dominant mechanism for ; ~20 adb2sion is an alteration of the surface chemistry of the substrate, rather than a rearr~ngement of the sur-, :

face aroms and molecules. For this reason, i~ is dis-tir;guish-~d from the high energy ion beam techniques described hereinabove, which physically alter Ihe atomic zrrangement in the surface of the substrate. Il- further distinc~ion with the high ion beam energy t~ ~niques oE
the prior art, the present invention requires reactive ions and will not work with inert ions. Such inert ions do not chemically alter the surface of the substrate, and are inappropriate for use in the present invention.
iO Still further, the present invention can use electrons and photons as iLcident particles. Since these parti-cles have negligible mass, momentum transfer is not the dominant mechanism for the changes which occur; insteac these particles are used to alter the surface chemistry, This ur~her distinguishes the present technlque from the prior art high energy ion bombardment techniques wherein momentum transfer is a dominant ~echanism.

n the practice of this invention, ~he low energy par-~icle irradiation can occur prior to metal deposition, or simultaneously with metal deposition. If par~icle irradiation occurs simultaneously with metal depositio~, the arrival rates of the metal atoms and the par~icles . ",,~ .
are adjusted to be comparable, at least within about 2 orders of magnitude of each other. Only by controlled YOg85-014 -9-, A' . V . i . i . .

- ` 12~2965 en2` gy beam irraalalion can the relA~ive impingement a'te of the energy bea~l and the metal atoms be provided with sigr.ificant ~ynamic rar.ge ~o achieve optimum adhe-sion. This feature further dis_inguishes the aforemen-tloned prior art glow discharge and plasma techniques for enhancing adhesion.

~any types of metals can be deposited on the organic substrates including, for example, ~i, Cu, Ti, Cr, Al, ~o, W, Rh, Pt, Pd, etc.. The substrates are organic malerials including plastics, polyimide, polyesters, Teflon ~a trademar'~ of E.I. duPont deNemours), Mylar (also a trademark of E.I. duPont deNemours), epoxies, etc.. Typically, the substrates are organic polymers.
The reactive ion species which can be used include many 1~ different ions, such as F, Cl, S, 0, N, C~4, CC14, C0, H, etc Substrate irradiation and metal deposition can occur over a range of temperatures, including room temperature and elevated temperatures. Commercially available ion sources can be used to provide low energy ion beams, and ~he metal deposition step is also a dry processing step, such as sputtering or evaporation.

Y0~85-014 -10-~2~2965 These and o~her objecls, .efitures, and advanlages will be a?par4nl from the following more par~icular de-scription of the preferred embodiments.

Brief Description of the ~rawings FIG. 1 schematically illustrates an apparatus for car-rying out the present invention.

FIG. 2 is a spectrum of a polyimide surface produced by ultraviolet photoemission spectroscopy, which indicates the change in surface chemistry of the polyimide after ~0 irradiation by low energy reactive ions in accordance wich the present invention.

Best Mode For Carrying Out The Invetnion In this invention, low energy beams are used to alter the surface chemistry of a thin layer at the surface of ~5 the organic substrate onto which metal is to be depos-ited. The particles which can be used to irradiate the organic substrate are reactive ions, electrons, and photons, having energies in the appropriate range. For Y0~85-014 lZ~Z965 example, the reactive ions and electrons can have energies in the range 50-2000eV, with preferred particle energies being in the range 200-500eV. The energy range suitable for photons is about 0.2eV to 500eV, with the preferred range being 0.5 to lOeV. Infrared radiation will provide photons having energies of about 0.2eV and greater, while ultraviolet radiation will provide photons having energies of about 2-lOeV. In the practice of this invention, the surface chemistry of the organic substrate is modified to a depth up to a few hundred angstroms, and in particular about 10-3000 angstroms. Low energy particle irradiation of the substrate can occur prior to or during metal deposition.

During the low energy particle bombardment, chemical bonds in the organic substrate are broken and altered and/or the surface of the substrate is heated. Parameters important for adhesion, such as the rate of metal deposition, are closely correlated to the rate of arrival of the low energy particles in order to provide the relative impingement rates to achieve optimum adhesion. The dominant mechanism for enhancing adhesion is a chemical one in which the chemical activity of the surface layer of the substrate is altered by the low energy particle irradiation. Any physical rearrangement of ~, A, ~ ~ I ' ''`

lZ92965 atoms and molecules in the substrate occurs only to a very small degree, and is not a significant mechanism in producing enhanced adhesion.

It is the initial deposition of the metal onto the substrate which is important for adhesion. Once approximately 300 angstroms of continuous metal film are formed on the surface of the substrate, the metal deposition rates can be increased without affecting metal-substrate adhesion. Typically, the metal is initially deposited at rates of from 1-100 angstroms/sec., corresponding to lol5 lol7 particles/cm -sec.. The particle flux of the incident reactive ions, electrons, or photons, in the radiation beam are o this order to provide enhanced metal-substrate adhesion.

Particle irradiation can occur at room temperature, or at elevated substrate temperatures. For significantly enhanced metal-substrate adhesion, the teachings of copending Canadian Application No. 498,399, filed December 20, 1985 and assigned to the present assignee, can be referenced to indicate optimum substrate temperatures. Further, the angle of incidence of the low energy particles is not critical, except that very shallow grazing angles (less than about 10-20~
will not have a significant . ~"~~

~292965 e-fect ~n the chem_s~ry of Ihe sl-rface layer of the s~bstrate within reasonable periods of lime. For angles with incidence greater than grazing angles, and espe-cially with the common practice o~ using ne~lr rormal S incidence, substrate irradiatioa with low energy reac-tive ions, electrons, or photons can occur over time periods ranging from minutes to slveral hours in order ~o chemically activate the substrate.

At least wo modes of operation can be undertaken. In iO the first, the subslrate surface is irradiated with re-active ions, electrons, or photons to alter the surface chemistry in the substrate. After irradiation with these low energy particles for a sufficient period of time to provide surface chemistry alteration to a depth LS in the substrate of about 300 angstroms or less, the irradiation is stopped. After this, the metal film is deposited using a dry process such as evaporation or sputtering. Deposition of the metal can occur in the same vacuum chamber as that in which the low energy ZO particle irradiation occurs, in order to minlmize con-tamination and to achieve the total in-situ processing.

-~ ~ In a second mode of operation, low en~rgy particle irradiation occurs slightly prior to (optional) and YOg85-014 -14-::

..

Y09-85-01~ 15 lZ9Z965 during metal deposition. In this process, the incident reactive ions, electrons, or photons have the same effect as in the first mode of operation, that is, they modify the surface chemistry of the organic substrate. In order to optimize adhesion in this second mode of operation, the energy beam must combine properly with the metallization beam and for this reason the arrival rates of the low energy particles are comparable (i.e., within one or two orders of magnitude) to the arrival rates of the metal atoms. This is easily accomplished with a controlled ion beam source, an electron beam source, or a photon source. For example, for initial metal deposition rates of 1-100 angstroms/sec, 1015 -1017 pArticles/cm2 -sec. are corresponding p~rticle fluxes.

Accurate control of the low energy particle fluxes in relation to the metal deposition rate for the initial phases of metal deposition is extremely important, as emphasized in the previous paragraph. As a follow-on to an earlier discussion, such control of fluxes cannot be obtained using plasma or glow discharge systems for energy beam impingement of a substrate. Those systems require high pressures of the order of 1 torr., which corresponds to about 1021 gas atoms/cm2 -sec., in order to maintain the discharge. These rates will dominate lZ9Z965 all othe-- rates in the system. Fur,hermore, these ra.es cannot be ~atched with metal evapora~ion rates wnich must be fairly slow during the initial formation or the metal layer on the substrate. ~lso, metal evaporation cannot be carried out at such high pressures.

Any type of metal can be deposited by sputtering or evaporation in-situ after or during low energy impingement of the organic substrate. In the practice of this invention, the low energy particles are either reactive ions, electrons or photons. The organic substrates include all ~ypes of polymer materials, in-cluding 'assic, epoxies, polyimide, polyesters, Terlon, Mylar, e_c.. Th,se organic materials can be layered onto glasses, semiconductors, ceramlcs, insulators, lS etc., Further, the substrate can be made up of lami-nations of polymer-type materials.

The low energy particles suitable for altering the sur-face chemistry of the organic substrate in accordance with the present invention include all types of reactive ~20~ ions, as well as electrons and photons. Suitable exam-: ples of reactive ions include 0, N, Cl, CF4, CC14, C0, H, F, S, etc. In general, the low energy particles are those which will react with the material of tne , ~
~ Y0985-014 -16-~ ': :
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1292~65 substra~e to produce ~hemical changes in the firs~ few hundred angstroms o~ the substrate.

The adheslon of any metal to the organic substrate is enhanced by the practice of this invention. HoweverJ
the enhancement o adhesion will vary in aegree with he m~tal and substrate combination that is chosen. For example, the adhesion of Cu on polyimide is signif-icantly enhanced by reactive oxygen or nitrogen treat-ment of the polyimide, improving adhesion by a fac~or of 10 or more. In another example, reactive ion treat-ment of polyimide improves the adhesion of Cr thereto, and also minimizes stress between the Cr and the polyimide. This also aids a & esion and yields a Cr-polyimide structure having 2 significantly greater peel lS ~trength.

It appears that the chemistry of the organic substrate is =odified sufficiently that metastable compounds can be formed in the surface of the substrate wher, the metal atoms impinge on the substrate. These metastable com-~0 pounds are not those which can be formed by simple heating, as by annealing the substr~te. This change in the chemistry of the metal-substrate interface improves adhesion and lessens stress between the deposited meta ..

129Z9~5 rilm and he substrate, perhaps by controiling the microstructure o, ~he ~e~al-substrate interface.

FI~. 1 schemalically illustrates a structure which is suitable to practice the present invention. The struc-ture includes a vacuum chamber 10 in which is located an ion source 12 and an evaporant source 14, placed in a holder 16. A substrate holder 18 supports a substrate 20. Output port 22 can be connected to a vacuum pump (not shown) in order to adjust the pressure within chamber 10. Although it is not shownin detail, the ion s~urce would include an input port for providing gasses, such as oxygen and nitrogen, to the ion source. Ion bea~
sources are well '~nown in the a-t and a suitable one is a Kaufman-type ion source such as those described in U.S. Patent 4,259,145 and by H.R. Kaufman et al, J. Vac, Sci. T~ch. 21 (3~, p, 92;, Sept/Oc~. 1982. This type or source provides a u~iform flux of ions over a large area, and can be easily controlled to provide low energy -ions having energies in the range of about ;0-2000eV.

:
In FIG~ 1, the dashed lines 24 indicate ~he ions whlch ~; are directed to the substrate 20, while the dashed lines ~; ~ 26 indicate the evaporated metal which deposits upon substrate 20.

Y~985-014 -18-lZ92965 In practic~, the required gasses are introduced through a typicai .~etering syste~ inlo the ion source 12 at the required flow rate for sustaining a discharge in the ion source Or.ce the discharge is established, the ion beam is enèrgized at a low energy, ;0-2000eV. These ions are accelera~ed to the substrate in order to modify its surface chemistry. Either simultaneously with the ion bea3 or af er ion trea~ent of the substrate, ~etal can be deposited.

The apparatus of FIG. 1 can be modified slightly if electrons or photons are used to change the surface chemistry of the suostrate. Any type of pho~on source with the proper energy range, such as a laser or a flash 7amp~ car~ be used although lasers are preferred. The electron source can be a commercially available source where the electron source is located in the vacuum chamber. Thus, the source 12, in its broadest sense, represents a reactive ion source, a photon source, or an electron source ~IG. 2 illustrates the effect of the low energy particle irradiation on the organic substrate. In this figure, photoemission spectroscopy is used to show the spec~rum of photoemitted electrons N~E) as pIotted against ~he Y0~85-014 -19-elec_ro~ binding energy (eV). Th-ee dirferen~ curves A, B, and C ere shown. C~lrve .4 illustrates the spectrum cbtained from a polyimide film whicn has been annealed, but untreated by reactive ions. Curve B illus,ra~.~s the S change in surface chemistry of the polyimide film when it has been irradiated by reactive oxygen ions. Curve C indicates the effect of post-annealing on ~he oxygen ion lrradiated polyimide, and indicates that the post-annealing step shifts the energy spectrum so that it is more similar to the original spectrum ~A).

FIG, 2 indicates the number of electrons N(E) emitted from the polyimide due to the incidence of photons hav-ing an energy of 40.8eV and shows a significantly dif-ferent spectrum in curve B. This spectrum indicates the ~5 chang2 in surface chemistry of a shallow surface layer of the polyimide, indicating tha~ reactive oxygen ion bombardDent has altered the surface chemistry of the polymide, It is this alteration of the surface cneDis-try which leads to increased adhesion and reducet stress in metals deposited on the po}yimide.

:~ The following examples will demonslrate the use of low energy reactive ions, electrons or photons to improve metal-substrate adhesion, .

EXA~IPT F.

The adhesion between copper films and polyimide was in-crea~ed by bombarding a polyimide surface ~ith a low energy oxygen or nitrogen ion beam prior to deposition of copper. Adhesion improved by a ractor of 10 or more.
The deposition and ion treatment were pe~formed in an electron beam evaporator having a Xaufman-type ion beam source installed inside the processing chamber. This allowed in-situ bombardment followed by copper deposi-iO tion onto the rreated polyimide surface, where the substrate always remained within the processing cham~er.
Nitrogen and oxygen were introduced through a metering system into the ion source at the re~Iuired flow rate for sustaining a glow discharge. Once the discharge is es lS tablished the beam is energized at a low energy, in this examplè a~ 50 - 500eV. The ions were accelerated to the substrate coated with polyimide for a sufficient amount of time to allow thorough treat=ent of the polyimide.
This can range from minutes to a couple of hours. Once the surface was modified, the copper was deposited.

~- Conventional peel testing was undertaken on a tensile strength ~ester, yielding the following minimum values:

YO'~85-014 -21-Adhesion of Cu to ?olyimide (untr~ated) - 3gm/~m.
Adhesion of Cu tO poiyimide (2 ion treated) >35Om/mm.
Adhesion of Cu tO polyimide (N2 ion treated) >30gm/mm.

Copper was again deposited on polyimide. The polyimide was spun on~o an aluminum-covered silicon wafer. Reac-tive nitrogen and oxygen ion bombardment was carried OUt in-situ prior to the copper deposition using a standard sputter ion gun at 250eV in an oxygen or nitrogen partial LO pressure of 2-3 x 10 4 torr....... The ion beam current density was of the order of a microamp/cm2 for one hour.
After this treatmer.t, a copper layer 8 microns thic'~ was deposit~d onto the treated pol~Jimide surface.

Surface analysis prior to copper deposition showed that the reactive ion bombardment changed the compositior. of the polyimide surace. X-ray photoemission spectroscopy revealed that nitrogen or oxygen incorporated into the polyimide by ion bombardment was in a different chemical state than the corresponding atomic species already present in Ihe untreated polyimide. Ultraviolet photoemission spectroscopy also showed valence state chemical bonding cha~ges. These observations, as well Y0!38;-014 -22-as the absence of adhesion improvement for inert gas ion (Ar) bombardment, der..onst-ated that ~he ennanced adhe-sion is a _esult o_ chemical activation of the polyimids surface.

; EXl~MPLE 3 The following table shows the results of various pre-treatment steps in the preparation of ~he polyimide or KaptonTM substrates. All pretreatment steps occurred at room temperature. At higher temperatures, the adhe-lOsion increased. From the table, it is apparent that oxygen ion and nitrogen ion pretreatments of polyimide significantly improve the adhcsion, while other pre treatment steps, such as argon ion bombardment and KOH
etching, do not significantly improve adhesion.

TABLE

Sample Pretrea~ment Composition Adhesion Strength ; C : N : O g~s/mm 1 ~s preparèd 8.2:1.0:1.7 .~one ~ Argon-spul~ering19.2:i.0:0~3 ~one 3 KOH-Etcn~ng 23.2:1.0:6.6 0.211 0.2~8 4 0 -Sputtering 9.3:1.0:1.2 1.27 1.41 N -Sputtering 5.3:1.0:0.6 1.63 1.03 6 Evap. on Kapton9.3:1.0:4.4 4.57 2.88 In the practice of this invention, lcw energy reactive ions, electrons, and photonc are used to alter ~he surface chemistry of a thin layer of an organic substrate in order tc promote increased adhesion between the substrate and a metal layer deposited thereon. It is important that the energy of the incident particles ~reactive ions, electrons, and photons) be less than about 2000eV, and that the incident particles are those which will alter thç
surface chemistry of a thin surface region of the substrate.
lS This chemistry is altered to a depth of approximately 300 angstroms or less. Still further, if the particle treatme~t occurs simultaneously with the metal deposition, the arrival rates of the metal ato~s and the reactive ions, electrons, or photons must be within about on~ Jr -wo orc~r~ o: --Jnit_de Ot each ,;~
.

12~2965 other sc ~hat maYimu.~ chemistry alte-ation and mixing can occu_ al the ~etal-subs rale in erface. ~lntil a continuous film of metal is established on the surface of the substrate, metal a_om ar_ival rates are chosen to be less than about 100 angstroms/sec..

S While the invention has been described with respect to particular embodiments thereof, it will be apparent to those of skill in the art that variations exist without departing from tne spirit and scope of the present invention.

Y0985-014 -2;-

Claims (15)

1. A method for improving metal adhesion to an organic substrate, including the steps of:

irradiating a surface of said substrate with low energy particles, said particles being selected from the group consisting of reactive ions, electrons and photons, wherein said reactive ions and electrons have energies in the range of about 50-2000eV and said photons have energies in the range of about 0.2-500eV, said particles being incident on #aid surface with a particle flux of about 1015-1017 particles/cm2-sec.;

depositing a metal film onto said substrate simultaneously with said irradiation by low energy particles, said metal film being deposited from the vapor phase at an initial rate of deposition of approximately 1-100 angstroms per second, and continuing said metal deposition until the desired thickness of metal is obtained on said substrate.

2. The method of claim 1, where said metal is deposited by evaporating or sputtering.

3. The method of claim 1, where said metal is deposited at a temperature greater than room temperature but less than the curing temperature of said substrate.

4. The method of claim 1, where said metal is deposited at room temperature.

5. The method of claim 1, where said substrate is a polymer.

6. The method of claim 5, where said substrate is selected from the group of plastics consisting of polyimide, polyesters, polytetrafluorethylene and epoxies.

7. The method of claim 5, where said substrate is polyimide.

8. The method of claim 1, where the rates of arrival at said substrate surface of said low energy particles and atoms of said metal are within approximately two orders of magnitude.

9. The method of claim 1, where said metal is selected from the group consisting of Ni, Cu, Ti, Al, Cr, Mo, W, Rh, Pt, and Pd.

10. A method for enhancing the adhesion of copper to polymers comprising the steps of:

irradiating a polymer with a beam of low energy particles having a particle flux less than about 1017 particles/cm2sec. selected from the group consisting of reactive ions, electrons and photons, said reactive ions and electrons having energies in the range of about 50-2000eV, said photons having energies in the range of about 0.2-500eV, depositing copper from the vapor phase onto said irradiated surface of said polymer at a rate which is sufficiently slow to enhance adhesion of copper atoms to said polymer to a depth of up to approximately a few hundred angstroms into said polymer, said rate of deposition of copper initially being approximately 1-100 angstroms per second, said copper depositing step and said irradiating step occurring simultaneously at least until a continuous copper film is formed on said polymer.

11. The method of claim 10, where the rates of arrival at said substrate of said copper and said particles are within approximately two orders of magnitude.

12. The method of claim 11, where the temperature of said polymer surface is less than about 360°C.

13. The method of claim 11. where said reactive ions are selected from the group consisting of oxygen and nitrogen.

14. The method of claim 10, where the temperature of said polymer is less than about 60% of its glass transition temperature during said simultaneous copper deposition and particle irradiation.

15. The method of claim 10, where said polymer is polyimide.