KR100532515B1 - Method for electroless deposition and patterning of a metal on a substrate - Google Patents

Abstract

In accordance with the present invention, a method of making a patterned metal layer on a substrate is provided, comprising electrolessly depositing a blanket metal film of a predetermined metal on a substrate, followed by patterning the metal layer by microcontact printing. The laminated metal may be overplated with another metal that may be microcontact printed to act as an etching mask.

Description

METHOD FOR ELECTROLESS DEPOSITION AND PATTERNING OF A METAL ON A SUBSTRATE}

The present invention relates to a method for electroless precipitation and patterning of metal on a substrate. Specifically, the present invention relates to a method in which the microcontact printing process step and the electroless precipitation process step are combined.

Patterning metal on a substrate is an important process that is often required in modern technology. In other words, this technique applies, for example, to the manufacture of microelectronics and displays. Such patterning usually requires vacuum depositing the metal over the substrate surface and selectively removing it using photolithography and etching techniques. Vacuum deposition of metals and consumption of photoresists constitute a significant cost factor in the fabrication of metal structures and limit the size of substrates that can be patterned by this approach.

Techniques for electroless precipitation (hereinafter ELD) of metals on (insulated) surfaces may provide an alternative method for vacuum lamination of metals to substrates (eg, "Electroless Plating: Foundations and Applications", GO Mallory , JB Hadju, Eds .; American Electroplaters and Surface Finishers Society, Orlando, Fl. 1990).

Electroless precipitation of metals such as copper, silver, gold, nickel, rhodium and cobalt is a widely used process for making fine metal patterns in printed circuits. Electroless precipitation occurs by an autocatalytic redox process, where the metal cations to be deposited are reduced by soluble reducing agents on the surface of the metal features to be formed or on the surface of the catalyst used to initiate the electroless precipitation. do. This redox process generally occurs only at the surface that can be catalyzed. The noncatalytic surface must first be activated with a metal catalyst such as palladium before metallization takes place. Selective deposition can be achieved by selective deactivation of the catalyst substrate or by selective activation of the non-reactive surface by the catalyst. Several methods of making patterned catalysts are known, most of which are based on photolithographic techniques. The size of the metal features made by electroless precipitation of the metal can be as small as 0.1 μm.

Microcontact printing may also provide an alternative method for metal patterning using photolithography.

Microcontact printing (hereinafter, μCP) is a technique for forming a pattern of organic monolayers with lateral dimensions of micrometers and submicrons. This technique provides experimental simplicity and flexibility in printing any form of pattern by printing molecules from the stamp onto the substrate. To date, most of the prior art has relied on the excellent ability of long chain alkanethiolates to form self-assembled monolayers, for example on gold or other metals. These patterns protect the support metal from corrosion by suitably formulated etchants, thereby acting as a thin nanometer resist, or allowing the fluid to be selectively placed in the hydrophilic region of the printed pattern. The pattern of self-assembled monolayers, which can have a lateral dimension of less than 1 micron, is a metal substrate using an alkanthiol solution dissolved in ethanol as an "ink", which uses an elastomer "stamp". It can be formed by printing on. The stamp is made by molding a silicone elastomer using a master (or mold) prepared using other techniques such as photolithography or electron-beam lithography. Patterning of such stamp surfaces is disclosed, for example, in EP-B-0 784 543.

Hidber et al., "Microcontact Printing of Palladium Colloids: Micron-sized Patterning by Electroless Precipitation of Copper" (Langmuir, vol. 12, 1996, p1375-1380), provides micron and submicron sized copper patterns on the surface. A method is disclosed. This method uses μCP to print colloids that act as catalysts for selective electroless precipitation of copper. A patterned elastomeric stamp made from poly- (dimethylsiloxane) (hereinafter PDMS) is used to transfer the catalyst (palladium colloid stabilized with tertaalkylammonium bromide and dissolved in toloene) to the surface of the substrate. Electroless precipitation of copper on the substrate occurred only where palladium colloids were printed and transferred to the substrate. Electroless precipitation catalyzed by colloids formed metal structures with features of submicron dimensions.

WO 00/79023 A1 discloses a method of electrolessly depositing a conductive material on a substrate using a stamp with a patterned surface, the stamp being pressed onto the surface of the substrate to print the substrate and the printed substrate. Immersion in a plating bath provides a catalyst pattern on a substrate where metal deposition occurs during electroless precipitation.

As such, these two references show how to combine μCP and ELD. In summary, these approaches include (i) directing the substrate to a chemical functional group that has affinity for the catalyst for electroless precipitation, (ii) ink treating the micropatterned PDMS with the catalyst solution, and (iii) Printing a catalyst on a substrate and (iv) electrolessly depositing a metal over the printed catalyst pattern. In summary, this strategy may be referred to as "print & electroless precipitation". This strategy can be modified depending on exactly what is printed on the substrate. Apart from printing the catalyst on a substrate, molecules can be printed on the substrate to increase the affinity of the catalyst for that substrate. In this variant, the printed substrate must be submerged in the catalyst bath to add the catalyst to the printed area of the substrate. Another variant involves homogeneously coating the substrate with a catalyst layer for electroless precipitation, printing the molecules to deactivate the catalyst already present on the surface of the substrate. Another variant may be to homogeneously coat the substrate with a pre-catalyst layer and to print the molecules onto the pre-coated substrate to activate the precatalyst molecules.

However, the "print & electroless precipitation" strategy and its possible variations have some serious drawbacks. First, chemicals that provide adhesion between the catalyst for the electroless precipitation and the glass substrate tend to become self-reactive and cannot easily be inked over the "classic" PDMS stamp, or the substrate is homogeneous. Can't transition up. PMDS is a hydrophobic elastomer, in which case surface treatment of the PDMS may be necessary to make the PDMS hydrophilic.

Next, typical electroless precipitation catalysts, such as Pd / Sn colloids, are used in solutions of high acidity (usually concentrated hydrochloric acid) because these colloids are usually unstable in other types of solutions. These colloids are catalysts for the electroless precipitation of many metals and are very active. These colloids are particularly well optimized for electroless precipitation, but the compatibility of printing tools and high acid inks can be a problem. That is, hydrochloric acid gas from the ink corrodes the metal backing of the printing tool and stamp, and these vapors cause safety problems.

In addition to these disadvantages, no compatibility with the stamp as an activator (or deactivator) of the electroless precipitation catalyst that can be printed has been identified. This precludes using another approach to "print & electroless precipitation" described above to combine electroless precipitation and μCP.

In addition, in the case of using ink for "print & electroless precipitation", the following problems have not been solved yet. In other words, how do you ink the stamp? How to dry it How can you use a stamp repeatedly with just one ink treatment? How should ink be removed from the stamp? How can I control and prevent ink diffusion over the substrate during printing? How can the ink be homogeneously stamped and ink delivered without changing the activity of the catalyst over large substrates? And importantly, how can reasonable process throughput be achieved to make “print & electroless deposition” economically attractive in solving the problem of reducing the cost of forming metal structures on substrates?

Achieving good adhesion between the electrolessly deposited metal and its substrate is the most important challenge in radioactive precipitation. The electroless precipitated metal is subjected to post-processing or subsequent device-fabrication during precipitation, during removal of the plated substrate from the electroless precipitation bath, during or after rinsing or drying the newly plated metal. It may lose its adherence to the substrate in the plating bath during the step. As a result, good adhesion between the stack and the substrate is always required, which is often radioless, starting with treating the substrate received from the supplier and then post-treating the laminated metal to remove stress in the material. The result of optimizing all the details of the solution extraction process.

1A is a light image by light upon reflection, showing a high quality line pattern of NiB alloy on glass patterned according to the present invention.

FIG. 1B is a light image by light transmitted through the glass substrate, corresponding to the image of FIG. 1A.

FIG. 1C is an atomic force microscope image of the pattern according to FIGS. 1A and 1B.

2A and 2B show X-ray photoelectron emission spectra obtained in the macroscopic region of NiB and glass resulting from patterning NiB according to the present invention.

It is therefore an object of the present invention to provide a method for electroless precipitation and patterning of metals on a substrate, which combines a microcontact printing process and an electroless precipitation process step.

It is a further object of the present invention to provide such a method which allows for good adhesion between the electroless precipitated metal and its substrate when one step comprises microcontact printing.

These and other objects and advantages of the present invention are achieved by a method as defined in claim 1.

Preferred embodiments of the invention are described in the dependent claims.

EMBODIMENT OF THE INVENTION Below, this invention is demonstrated in detail with drawing.

As mentioned above, the strategy proposed by Hewber et al. And WO 00/79023 A1 may be referred to as “Print & ELD”.

Another strategy according to the present invention is to use electroless precipitation to prepare a metal blanket film, which film can subsequently be patterned by microcontact printing. This strategy is called "ELD & Print." It should be noted that the two strategies are not symmetric, that is, the two strategies do not simply involve performing the same steps in different, ie reversed order.

The present invention proposes a new combination of μCP process steps and ELD process steps.

Changing the process of performing the printing step and the electroless precipitation step solves many of the problems described above, and instead requires a fairly new process flow. Changing the process like this yields localized electroless precipitation of the metal, but the stacked metal can be overplated with another metal, which can be microcontact printed to act as an etching mask.

In general, the new process flow is as follows.

1. Prepare an electrically insulating surface by catalyst lamination,

2. electrolessly depositing the first metal from the solution,

3. Prepare the first metal surface for printing, ie annealing, reduction of surface oxides using forming gas, oxidation in air, cleaning or deposition of additional metal films via electrolytic or electroless precipitation, and microcontact Prepare the surface of the second metal for printing.

4. Pattern the surface using μCP of the appropriate ink to serve as an etching barrier in the subsequent etching step.

5. Etching the metal or metal film in a suitable solution.

The simplest possible approach includes electroless precipitation of gold, microcontact printing a self-assembled alkaneol monolayer on the gold, and subsequently selectively etching the gold.

Microcontact printing of alkanethiol on gold substrates down to a resolution of 1 micrometer is the only application of the well established microcontact printing (see, Delamarche et al., J. Phys. Chem. B, Vol. 102, 1998, p3324-3334). Next, it may seem best to develop a strategy based on electroless precipitation of gold, printing the deposited gold with a seed, and etching it for patterning.

This approach is not good due to problems such as cost, poor adhesion of gold to the substrate, and depending on the application, semiconductor contamination (by the formation of recombination centers (traps) in silicon due to diffusion of gold atoms into adjacent silicon layers). . Silver may also be used for this application, but electroless precipitation of silver is difficult to control and usually results in a film with poor adhesion to a smooth insulating substrate. Ag also poses the problem of semiconductor contamination, and Ag is easy to electromigrate and easily corroded. Copper may also be printed with alkanethiol and may optionally be etched, given the high sensitivity to oxides and certain etchants present on the surface of this metal. As with gold and silver, the adhesion of plated copper films on smooth insulating surfaces is limited.

Thus, another approach is provided for electroless precipitation of a first metal, followed by stacking and printing a second metal.

Since a single electroless precipitation metal (eg, gold, silver, copper) may not provide the desired properties such as good adhesion and compatibility with microcontact printing, a multilayer metallization and printing process may be desirable. For example, an electroless precipitated Ni, Co or Pd (or alloys thereof) film is used as the first layer, and a second metal layer such as Cu, Ag or Au (electroless precipitated or electroplated) is printed. And as an etching barrier. In particular, Ni and Ni alloys (NiB, NiP, NiWP, NiReP, etc.) are excellent candidate groups for electroless deposition on smooth insulating substrates. There are several Ni baths that produce highly conductive plated Ni and are commercially available. In the present invention, glass treatments and processes have been developed that generally improve the adhesion of electrolessly precipitated Ni to glass. Cu is convenient for electroplating, inexpensive, compatible with Ni when electroplated, and may be a good substrate for microcontact printing of alkanesol. The high conductivity of NiB and Cu helps to maintain current density uniformly on large samples during the electroplating step, which is important for obtaining an electroplated mask of uniform thickness. The printed Cu can be selectively etched to act as a mask for the underlying Ni. The Cu mask can be easily removed at the end of the process if desired.

A typical flow of the "electroless precipitation & print" process according to the invention is as follows.

1. An organic layer having affinity for the electroless precipitation catalyst is grafted from the solution onto the glass substrate.

2. A uniform layer of catalyst particles is deposited from the solution onto the treated glass substrate, and the catalyst is "activated".

3. The substrate is immersed in an electroless precipitation bath to deposit the desired metal.

4. The substrate is mounted on a cathode frame and immersed in an electrochemical cell where the sacrificial mask is electroplated. The frame contacts the metal layer at all its periphery to distribute a uniform current to the layer and prevents the metal layer from being damaged (scratched) on the inside of the substrate from which the device is made.

5. The mask is selectively protected by microcontact printing of resist (self-assembled monolayer, SAM).

6. Next, the mask and the electroless precipitated metal are selectively etched.

7. Finally remove the mask completely.

In the following description, one example of the method according to the invention is given. This is merely illustrative, as will be readily apparent to one skilled in the art, and it should be noted that the present invention is not limited to the substrates, metallurgical, etching baths, chemicals, etc. mentioned in the examples, but may be used with other substrates and materials. do.

Corning a glass substrate in a solution of N- (2-aminoethyl) -3-aminopropyltrimethoxysilane (hereafter 0.250 mL of EDA-Si (Gelest # SIA0591.0) in 120 mL of ethanol and 20 mL of water) # 1737) soak for 3 minutes at room temperature. During this step, the EDA is bound to the glass. The glass is then separated from the grafting bath, rinsed with water and dried. The glass substrate is baked on a hot plate at 150 ° C. or in an oven for 10 minutes. This results in a homogeneous and thin grafted layer on the glass substrate having affinity for some Pd / Sn colloids. The treated glass substrate can be stored or used immediately after cooling.

Next, the glass substrate was immersed in an acidic Pd / Sn solution (Fidelity, product # 1018, 50% concentration diluted with hydrochloric acid) for 30 seconds to uniform Pd / S for electroless precipitation on the grafted glass substrate. A Sn catalyst particle layer is formed.

Subsequently, the Pd / Sn glass substrate is rinsed in abundance with deionized water and soaked in "accelerator" solution (Fidelity, product # 1019, 10% in deionized water) for 30 seconds, followed by deionized water. Rinse and dry. The glass substrate thus activated is placed on a hot plate at 80 ° C. It should be noted that this activation or heating step is optional, ie in some cases, the electroless precipitation may well consist of inactivated catalysts.

Now, the preheated glass substrate was immersed in NiB (Shipley, Niposit ^R 468, prepared as recommended, adjusted to pH 7.2 with ammonia) operated at 60 ° C. without stirring in an electroless plating bath, without stirring, about 20-30 nm Laminate NiB at a rate of / min. The thickness of the electroless precipitated NiB film can be controlled by the lamination rate and the immersion time.

Subsequently, a glass substrate with a thin (about 50-400 nm) NiB film is placed on a hot plate at 150 ° C. for 10 minutes to improve adhesion between the Ni laminate and the glass substrate.

Following this step, a pyrophosphate Cu bath is used to electroplate a thin (50 nm) Cu layer onto the NiB stack. 1.1 g of CuSO ₄ .5H ₂ O, 3.0 g of Na ₄ P ₂ O ₇ and 20.0 mg of NaH ₂ PO ₄ are dissolved in 120 mL of deionized water. The bath has a pH of about 9 and is used at 30 ° C. The original Ni oxides normally present on the electrolessly precipitated NiB are etched prior to electroplating by dipping the NiB covered sample in 0.3 M HCl solution and rinsing it with deionized water. NiO _x removal is not strictly necessary, but provides better adhesion between Ni and Cu.

Electroplating of Cu is -0.7 to -1.0 V (relative to Ag / AgCl reference electrode), with a titanium grid plated as a counter electrode (30 cm ² , larger area samples require larger electrodes) It is done with a potentiostat, model 263A (sold by EG & G), which operates at a fixed potential between. Current monitoring during plating indicates the deposition rate of Cu and its thickness (0.15 Ccm ⁻² for 50 nm Cu).

The Cu covered substrate is immersed in 0.1 M HCl solution for 10 seconds to remove copper oxide from its surface, rinsed with deionized water and dried before printing to ensure a homogeneous and dense protective monolayer is formed during the printing step.

Now, micropatterned stamps made with PDMS (Sylgard ^R 184 from Dow Corning) were first subjected to a 0.2 mM solution with eicosanethiol (ECT, product # SV109 / 4 from Robinson Brothers Limited) in ethanol. Inked, dried, and used to print the electroplated Cu for 20 seconds, resulting in a monolayer in the contact area.

Unprinted Cu is etched at room temperature in a 0.025 M KCN solution (buffered at pH 12 in deionized water) with proper agitation (Cu etch rate of about 50 nm per minute). The NiB laminate was not etched at all during this step.

Subsequently, the NiB is etched in 1 MH ₂ SO ₄ for 20 minutes with adequate agitation at room temperature (NiB etching rate of about 5-10 nm per minute, which etching rate also depends on the geometry of the pattern). The selectivity of the etching is very high if a Cu mask is still protected by the thiol monolayer. The thiol monolayer on the Cu is only removed later for this reason.

The sample is now immersed in an aqueous solution containing KOH and 10% H ₂ O ₂ (pH 14) for 20 minutes to remove all organic layers (ECT monolayer on copper and EDA grafted layer on the glass substrate). do. Pd / Sn catalysts present on NiB etched glass substrates can also be removed during this step by underetching Sn, EDA grafts and small amounts of glass. The electroplated Cu starts to etch equally during this step, although at a very slow rate. This step may be important if the areas remaining between NiBs should be light transmissive or electrically insulating because some Pd / Sn remaining in these areas may block some light, This is because it can conduct a degree of current.

All remaining Cu is then etched in 2 minutes in a 0.025 M solution (buffered with pH 12) containing KCN in water.

The Ni pattern on the resulting glass substrate is again immersed in a solution containing KOH / 10% H ₂ O ₂ for a short time (less than 5 minutes) and washed with 0.3 M HCl solution for 2 minutes. This process is completed by rinsing with water and drying.

The last two steps are optional steps. Maintaining the sacrificial mask may not be a problem depending on the application, and removing the organic layer and the catalyst likewise may not be necessary depending on the chosen application.

The light image upon reflection (FIG. 1A) shows a high quality NiB line pattern on the patterned glass as provided in the example. The corresponding image upon transmission (FIG. 1B) highlights the possibility of patterning the light absorbing structure on glass by the method according to the invention. Finally, atomic level micrographs (FIG. 1C) obtained on the edge of one line show good resolution and contrast of this pattern.

The X-ray photoelectron emission spectrum shown in FIG. 2 is obtained in the macroscopic region of NiB and glass obtained by patterning NiB as provided in the example. High levels of control on the etching chemistry in this example lead to glass surfaces free of metals (Cu, Ni, Pd / Sn), while the Ni portion of the sample is covered with a thin nickel oxide layer without Cu.

Electroless deposition of metal onto the substrate is a way for all the details to be determined in each case. Beyond the above examples, the present invention

Several types of substrates (different forms of glass, ceramics, oxidized surfaces, Si / SiO ₂ , indium-tin-oxides, indium-zirconium-oxides, tantalum oxide, aluminum oxide, etc.)

Several kinds of electrolessly deposited first metal layers (eg Ni, NiB, NiP, NiWP, Co, CoWP, CoP, Pd, etc.)

Several types of electroplated masks (eg Au, Cu, Ag)

-Alkanthiol, which selectively protects the mask and is compatible with PDMS micropatterned stamps

Can be extended to

Claims (27)

A method of making a patterned metal layer on a substrate, a) grafting an organic layer onto the substrate, subjecting the substrate to a precondition; b) depositing a catalyst layer on the preconditioned substrate; c) depositing a metal layer on the catalyst layer using an electroless precipitation technique; d) depositing a sacrificial mask on the metal layer; e) depositing a patterned etch-protective layer on the sacrificial mask using microcontact printing; f) etching the sacrificial mask in the free region of the patterned etching-protective layer; g) etching the electroless precipitated metal layer in the region without the sacrificial layer How to include. The method of claim 1, further comprising activating the catalyst layer for electroless precipitation after step b). The method of claim 1 or 2, further comprising etching the remainder of the sacrificial layer. The method of claim 1 or 2, further comprising etching the grafted organic layer and the catalyst layer. The method according to claim 1 or 2, wherein the organic layer is N- (2-aminoethyl) -3-aminopropyltri-methoxysilane (EDA). The method of claim 1 or 2, wherein the stacking of the catalyst layer is performed by immersing the substrate in a solution containing catalyst particles. The method of claim 6, wherein the catalyst particles comprise Pd / Sn. The method of claim 2, wherein the activating step is by immersing the substrate in a promoter solution. The method of claim 8, wherein the accelerator solution comprises HBF ₄ . The method of claim 1 or 2, wherein the sacrificial mask comprises copper. The method of claim 10, wherein the sacrificial mask is laminated by electroplating. The method of claim 1 or 2, wherein the etch protective layer is applied by printing a self-assembled monolayer (SAM) of icosane seedol by a micropatterned stamp. The method of claim 12, wherein the micropatterned stamp is a poly (dimethylsiloxane) (PDMS) stamp. The method of claim 1, wherein etching the sacrificial mask is performed with a KCN / oxygen etching bath. The method of claim 1 or 2, wherein etching the metal layer is performed with an aqueous H ₂ SO ₄ solution. The method of claim 3, wherein etching the remainder of the sacrificial layer is performed with KCN. The method of claim 4, wherein etching the organic layer and the catalyst layer is performed with an aqueous mixture of KOH and H ₂ O ₂ . The method of claim 1 or 2, wherein the substrate is selected from the group consisting of glass, ceramics, oxidized surfaces, Si / SiO ₂ , and the like. The method of claim 1 or 2, wherein the electrolessly deposited metal layer is selected from the group consisting of Ni, NiB, NiP, NiWP, Co, CoWP, CoP, Pd and the like. The method of claim 19, wherein the metal layer deposited on the catalyst layer comprises an alloy of Ni and B. 20. The method of claim 1 or 2, wherein the sacrificial mask is selected from the group consisting of Au, Cu, and Ag. The method of claim 12, wherein the micropatterned stamp is ink treated with alkanethiol. The method of claim 22, wherein the alkanethiol is an icosanoic thiol. The method of claim 1 or 2, wherein etching of the sacrificial mask is performed by an etching agent that is selective to the mask. The method of claim 1 or 2, wherein the metal layer is etched using any etching chemistry selective to the sacrificial mask. The method of claim 1 or 2, wherein a cathode frame is used to electroplate the sacrificial mask. 27. The method of claim 26, wherein the frame contacts the metal layer at all its perimeters.