WO2016022147A1

WO2016022147A1 - Method of controlling oxygen levels for electroless plating of catalytic fine lines or features

Info

Publication number: WO2016022147A1
Application number: PCT/US2014/050331
Authority: WO
Inventors: Danliang Jin; John-Paul O'NEIL; Yieu Chyan
Original assignee: Uni-Pixel Displays, Inc.
Priority date: 2014-08-08
Filing date: 2014-08-08
Publication date: 2016-02-11

Abstract

A method of controlling oxygen levels for electroless plating of catalytic fine lines or features includes selecting a substrate that includes a plurality of catalytic lines or features that are part of or are disposed on the substrate. The plurality of catalytic lines or features include at least one catalytic fine line or feature and at least one catalytic standard line or feature. A dissolved oxygen concentration of an electroless plating solution is regulated to a candidate controlled oxygen level. The candidate controlled oxygen level is set to a smallest value in a regulated range in a first pass of the method. The substrate is submerged in the solution for a period of time sufficient to initiate plating of the at least one catalytic standard line or feature. The substrate is evaluated and candidate controlled oxygen level is incremented or the previous value is selected as the regulated oxygen level.

Description

METHOD OF CONTROLLING OXYGEN LEVELS FOR ELECTROLESS PLATING OF CATALYTIC FINE LINES OR FEATURES

BACKGROUND OF THE INVENTION

[0001] Electroless plating is an autocatalytic reaction that may be used to deposit a metal on the surface of catalytic portions that are part of or are disposed on a substrate. Electroless plating may be described as a redox reaction with both partial reactions, anodic and cathodic, occurring at the same electrode. The anodic partial reaction includes the oxidation of a reducing agent contained within the electroless plating solution to yield one or more electrons that are transferred to the metal and/or by-products. The cathodic partial reaction includes the reduction of free metal ions or metal complexes to a metal lattice. The overall reaction results in metal plating onto the surface of the catalytic portions that are part of or are disposed on the substrate and then onto the deposited metal itself in a continuous process.

BRIEF SUMMARY OF THE INVENTION

[0002] According to one aspect of one or more embodiments of the present invention, a method of controlling oxygen levels for electroless plating of catalytic fine lines or features includes selecting a substrate that includes a plurality of catalytic lines or features that are part of or are disposed on the substrate. The plurality of catalytic lines or features include at least one catalytic fine line or feature and at least one catalytic standard line or feature. A dissolved oxygen concentration of an electroless plating solution is regulated to a candidate controlled oxygen level. The candidate controlled oxygen level is set to a smallest value in a regulated range in a first pass of the method. The substrate is submerged in the electroless plating solution for a period of time sufficient to initiate plating of the at least one catalytic standard line or feature and then removed from the electroless plating solution. The substrate is evaluated to determine whether the at least one catalytic fine line or feature initiated at approximately the same time as the at least one catalytic standard line or feature and is evaluated to determine whether the at least one catalytic fine line or feature exhibits one or more failure modes. If the at least one catalytic fine line or feature initiated at approximately the same time as the at least one catalytic standard line or feature and did not exhibit one or more failure modes, the candidate controlled oxygen level is incremented by an increment. If the at least one catalytic fine line or feature exhibits one or more failure modes, the previous value of the candidate controlled oxygen level is selected as a regulated oxygen level.

[0003] Other aspects of the present invention will be apparent from the following description and claims.

BRIEF DESCRIPTION OF THE DRAWINGS

[0004] Figure 1 shows an electroless plating system in accordance with one or more embodiments of the present invention.

[0005] Figure 2 shows catalytic lines or features having different feature sizes in accordance with one or more embodiments of the present invention.

[0006] Figure 3 shows electroless plated fine lines on substrate that exhibit issues because of prolonged exposure to electroless plating solution prior to initiation of electroless plating.

[0007] Figure 4 shows a catalytic fine line or feature disposed on substrate that exhibits etching because of prolonged exposure to electroless plating solution prior to initiation of electroless plating.

[0008] Figure 5 shows a method of controlling oxygen levels for electroless plating of catalytic fine lines or features in accordance with one or more embodiments of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

[0009] One or more embodiments of the present invention are described in detail with reference to the accompanying figures. For consistency, like elements in the various figures are denoted by like reference numerals. In the following detailed description of the present invention, specific details are set forth in order to provide a thorough understanding of the present invention. In other instances, well-known features to one of ordinary skill in the art are not described to avoid obscuring the description of the present invention.

[0010] Figure 1 shows an electroless plating system 100 in accordance with one or more embodiments of the present invention. Electroless plating system 100 may include an electroless plating bath 110 and a liquid electroless plating solution 120 disposed in the bath 110. One or more control systems 130 may optionally be used to control one or more operational characteristics of the system 100. The electroless plating system 100 may include, for example, a temperature control system (not independently illustrated), a pump control system (not independently illustrated), a turbulence control system (not independently illustrated), a dosing control system (not independently illustrated), a sparging control system (not independently illustrated), and/or other control system (not independently illustrated). The one or more control systems 130 may be discrete or one or more control systems 130, or the function or functions that they implement, may be integrated together. One of ordinary skill in the art will recognize that electroless plating system 100 may include other control systems 130 in accordance with one or more embodiments of the present invention.

[0011] As previously discussed, the one or more control systems 130 may optionally be used to control one or more operational characteristics of electroless plating system 100. For example, a temperature control system may be used to control a temperature of electroless plating solution 120. A pump control system may be used to control a recirculation speed of electroless plating solution 120 within electroless plating bath 110. A turbulence control system may be used to control the agitation and/or the mixing of electroless plating solution 120 within electroless plating bath 110. A dosing control system may be used to control the pH or a component concentration level of electroless plating solution 120 by timed, manual, or sensor-activated dosing of the appropriate chemicals at the appropriate time. A sparging control system may be used to control a flow rate of air, oxygen, or inert gas that may be bubbled into electroless plating solution 120. Other aspects of electroless plating system 100 may be controlled by the combination of one or more of the above-noted control systems 130. For example, in one or more embodiments of the present invention, a dissolved oxygen concentration of electroless plating solution 120 may be controlled by a sparging control system and one or both of a pump control system and a turbulence control system. One of ordinary skill in the art will recognize that one or more control systems 130 may be used to control other operational characteristics of electroless plating system 100 in accordance with one or more embodiments of the present invention.

[0012] One or more maintenance systems 140 may optionally be used to maintain operation of electroless plating system 100. Electroless plating system 100 may include, for example, a cleaning maintenance system (not independently illustrated), a fluid transfer maintenance system (not independently illustrated), a filtration maintenance system (not independently illustrated), and/or other maintenance system (not independently illustrated). The one or more maintenance systems 140 may be discrete or one or more maintenance systems 140, or the function or functions that they implement, may be integrated together. One of ordinary skill in the art will recognize that electroless plating system 100 may include other maintenance systems 140 in accordance with one or more embodiments of the present invention.

[0013] As previously discussed, the one or more maintenance systems 140 may optionally be used to maintain operation of electroless plating system 100. For example, a cleaning maintenance system may be used to clean some aspect of electroless plating system 100. A fluid transfer maintenance system may be used to remove one or more fluids (not shown) from, add one or more fluids to, and/or transfer one or more fluids within electroless plating system 100. A filtration maintenance system may be used to maintain electroless plating system 100 by filtering or removing extraneous plating and/or particulate matter from electroless plating solution 120. One of ordinary skill in the art will recognize that one or more maintenance systems 140 may be used to maintain other operational aspects of electroless plating system 100 in accordance with one or more embodiments of the present invention.

[0014] One or more conveyor systems 150 may optionally be used to move one or more substrates 160 in and out of the electroless plating bath 110 as part of a production line. One of ordinary skill in the art will recognize that the types of control, maintenance, and/or conveyor systems used in electroless plating system 100 may vary based on an application or design in accordance with one or more embodiments of the present invention. One of ordinary skill in the art will also recognize that the configuration of electroless plating system 100 may vary based on an application or design in accordance with one or more embodiments of the present invention.

[0015] When a substrate 160 is submerged in the electroless plating solution 120, an autocatalytic reaction occurs that results in the deposition of metal (not shown) on the catalytic portions (not shown) that are part of or are disposed on the substrate 160 and then on the deposited metal itself in a continuous process. Substrate 160 may be composed of one or more of a semiconductor, glass, films, thermoplastic resins, thermosetting resins, other polymers, ceramics, composites, fabric, paper, and/or other material suitable for use as a substrate. The catalytic portions comprise a material or substance that increases the rate of reaction without being consumed by the reaction. The deposition process continues until the catalytic portions are no longer in contact with electroless plating solution 120, any one or more of the reactants of the electroless plating solution 120 are depleted, there is excessive buildup of by-products (not shown) within the electroless plating solution 120, or the electroless plating bath 1 10 crashes or plates out. One of ordinary skill in the art will recognize that electroless plating system 100 may be used to electroless plate metals including, for example, copper, nickel, palladium, other platinum group metals, bismuth, gold, silver, cobalt, chromium, some composites, or alloys thereof in accordance with one or more embodiments of the present invention.

[0016] For the purposes of illustration only, the chemical mechanism of a copper- based electroless plating process using formaldehyde as the reductant is discussed in more detail below. One of ordinary skill in the art will recognize that the chemical mechanism of a copper-based electroless plating process may vary based on the chemistry, such as, for example, the composition of the electroless plating solution used and the application, such as, for example, the operational characteristics of the bath. One of ordinary skill in the art will also recognize that other chemical mechanisms may occur in other metal-based electroless plating processes, such as, for example, a nickel-based electroless plating process or a palladium-based electroless plating process. While the chemical mechanisms may vary, the method of controlling oxygen levels for electroless plating of catalytic fine lines or features may be used to control dissolved oxygen concentration, or another aspect of the bath that is applicable in a similar manner, for other metal-based electroless plating processes in accordance with one or more embodiments of the present invention.

[0017] Returning to the copper-based electroless plating example, the chemical mechanism of an electroless plating bath can be described as a redox reaction with both partial reactions, anodic and cathodic, occurring at the same electrode. In certain embodiments, the anodic partial reaction may include the hydrolysis of HCHO to methylene glycol as set out in equation (1). The methylene glycol may dissociate as set out in equation (2). The intermediate may adsorb on the metal surface as set out in equation (3). The intermediate may dissociate and desorb as set out in equation (4). The adsorbed hydrogen may desorb as set out in equation (5).

HCHO + H₂0→ H₂C(OH)₂ ( 1 ) H₂C(OH)₂ + OH-→ H₂C(OH)0^~ + H₂0

H₂C(OH)0-→ [HC(OH)0-]_ads + H_ads

[HC(OH)0^"]ads + OH^"→ HCOO^" + H₂0 +

H_ads→ 0.5 H₂ or H_ads→ W + e^"

[0018] There are two cathodic partial reactions that may take place. The first possible cathodic partial reaction occurs when free copper ions in the electroless plating solution react directly with the electron from the anodic half reaction as set out in equations (6) and (7).

RDS

Cu²⁺ + e^" → Cu^T (6) Cu⁺ + e^"→ Cu (7) The second possible cathodic partial reaction occurs when complexed copper adsorbs onto the metal surface (the catalytic portions that are part of or are disposed on the substrate) and charge is transferred to ligands which then dissociate as set out in equations (8) and (9), where the remaining Cu²⁺ may be further reduced.

[CuL _x]^2+xp→ Cu ⁺ + xL ^p (8)

CU²⁺ + 2e^_→ Curtice (9)

[0019] The chemistry of the electroless plating bath is in a constant state of change.

As part of the autocatalytic reaction, a portion of the reducing agent and a portion of the metal source in the electroless plating solution are consumed such that the concentration of the reducing agent and the concentration of the metal source in the solution decrease over time, hi certain circumstances, the reduction of reactants may lead to undesirable plating characteristics prior to depletion of any given reactant. Undesirable plating characteristics may include, for example, poor adhesion of the deposited metal to the catalytic portions that are part of or are disposed on the substrate, non-uniform morphology, high amounts of undesired extraneous plating on non-target surfaces, undesired plating rate changes, skip plating, changes in reflectivity, changes in brittleness, and/or any other characteristic that may render an end product unusable for its intended purpose. If the reducing agent is depleted, the anodic partial reaction ceases and there is no electron source for the cathodic reaction. If the metal source is depleted, adsorption of the metal ceases. During operation, a dosing control system may replenish one or more consumed reactants in the electroless plating solution when their concentrations fall outside specified ranges to avoid depletion. Alternatively, when the buildup of imdesired by-products has reached a threshold that produces undesirable plating characteristics for a given process, the electroless plating bath may be taken offline to purge and replace the electroless plating solution.

[0020] The autocatalytic reaction produces by-products in the electroless plating solution that may accumulate and affect the plating characteristics of the bath. The concentration of by-products in the solution typically increases over time and may negatively impact or inhibit the deposition of metal. Because they are not consumed by the reaction, concentrations of some ionic species and complexants may also increase as bath components are dosed to maintain metal source concentrations, reducing agent concentration, and/or the pH of the bath. If a dosing control system is used to maintain reactants at near constant concentrations, the specific gravity of the bath may be used as an approximate indicator of the buildup of by-products in the bath. To minimize accumulation of solid by-products suspended within the bath, a maintenance system, such as, for example, a filtration maintenance system may be used to filter portions of electroless plating solution 120. Otherwise, if the concentration of by-products exceeds a certain threshold, the electroless plating bath may be taken offline and a maintenance control system, such as, for example, a cleaning maintenance system and/or a fluid transfer maintenance system, may be used to purge and replace some or all of the electroless plating solution in the bath. The autocatalytic reaction may also produce insoluble byproducts such as, for example, metal particles, in the electroless plating solution. These particles may increase in size as they plate in the bath. At a certain threshold, the bath may crash, or plate out, resulting in the uncontrolled plating of these metal particles or other areas of extraneous metal plating causing most or all of the remaining metal source in the electroless plating solution to quickly plate out of the bath. If the bath crashes, the crashed electroless plating solution may be purged, the bath may be cleaned, and new solution may be disposed in the bath prior to bringing the bath back online.

[0021] An electroless plating bath may be characterized by the electroless plating solution used and the operating conditions of the electroless plating bath. The operating conditions of the electroless plating bath may be dictated, in part, by the composition of the electroless plating solution used and the commercial vendor's recommended operating conditions for their electroless plating solution. The composition of the electroless plating solution may vary based on the composition of the catalyst being used to dispose, for example, the catalytic portions on substrate. The composition of the electroless plating solution may vary based on the type of metal source, such as, for example, copper, nickel, or palladium, to be deposited. The composition of the electroless plating solution may also vary in accordance with a commercial vendor's proprietary formulation of solution.

[0022] Electroless plating solutions are inherently unstable and the electroless plating bath chemistry tends to deteriorate over time. While commercial vendors of electroless plating solutions do not disclose the composition of their solutions, they typically specify normal operating conditions for an electroless plating bath that uses their solution. One or more control systems and/or one or more maintenance systems may be used to sense and/or regulate the operating conditions of the electroless plating bath to operate within the normal operating conditions. The normal operating conditions may include, for example, an acceptable pH range and an acceptable temperature range for the electroless plating solution. If the electroless plating bath is operated outside of the normal operating conditions, the bath may become unstable and ultimately crash. If the electroless plating bath crashes, or plates out, the bath may be taken offline, the crashed electroless plating solution may be purged, the bath may be cleaned, and new solution may be disposed in the bath prior to bringing the bath back online.

[0023] While it is desirable to operate the electroless plating bath within its normal operating conditions to avoid crashing the bath, the bath chemistry tends to deteriorate over time from normal usage. One measure of efficiency of an electroless plating bath is the up-time of the bath, sometimes referred to as the bath life. The bath life is the amount of time that a bath is online and capable of effectively plating without undesirable plating characteristics. The bath life may be negatively impacted by control events that take the bath outside normal operating conditions, maintenance events that are required because of depletion of reactants or by-product accumulation, or other failure modes including changes in bath chemistry such as, for example, crashes, or plate outs.

[0024] Figure 2 shows catalytic lines or features on substrate 160 having different feature sizes in accordance with one or more embodiments of the present invention. In certain embodiments, the catalytic portions 210, 230 that are part of or are disposed on substrate 160 may have different feature sizes such as, for example, a different width and/or a different thickness. For example, substrate 160 may include one or more catalytic fine lines or features 210 disposed on substrate 160 that have a feature size, such as, for example, a width 220, which is on the order of magnitude of nanometers or micrometers. In certain embodiments, the catalytic fine lines or features 210 may have a width 220 less than approximately 5 micrometers. In other embodiments, the catalytic fine lines or features 210 may have a width 220 in a range between approximately 5 micrometers and approximately 10 micrometers. In still other embodiments, the catalytic fine lines or features 210 may have a width in a range between approximately 10 micrometers and approximately 20 micrometers. In certain embodiments, substrate 160 may also include one or more catalytic standard lines or features 230 disposed on substrate 160 that have a feature size, such as, for example, a width 240, of at least 20 micrometers or larger. In other embodiments, substrate 160 may also include one or more catalytic standard lines or features 230 disposed on substrate 160 that have a feature size, such as, for example, a width 240, which is on the order of magnitude of millimeters or larger. In still other embodiments, substrate 160 may also include one or more catalytic standard lines or features 230 disposed on substrate 160 that have a feature size, such as, for example, a width 240, which is on the order of magnitude of centimeters or larger. In still other embodiments, substrate 160 may also include one or more catalytic standard lines or features 230 disposed on substrate 160 that have a feature size, such as, for example, a width 240, which is on the order of magnitude of decimeters or larger.

In the electroless plating bath (e.g., electroless plating bath 110 of Figure 1), the plating process includes two stages: an initiation stage (also referred to as the induction stage) and a buildup stage (also referred to as the bulk plating stage). In the initiation stage, the catalytic portions 210, 230 that are part of or are disposed on the substrate 160 initiate the autocatalytic reaction. The catalytic portions 210, 230 may be comprised of a catalytic metal, catalytic metal alloy, catalytic metal compound, or materials containing catalytic metals, alloys, or compounds that may be the same as, or different from, the metal being plated by the bath. The exposed surfaces of the catalytic portions 210, 230 may form the active surface for plating during initiation. Once the electroless plating process is initiated, the autocatalytic reaction continues to deposit metal (not shown) during the buildup stage. The exposed surface of the metal plated during the initiation stage may form the active surface for plating during buildup. The amount of time substrate 160 is submerged in the electro less plating bath may be controlled to achieve a desired thickness of deposited metal. For example, if an application or design requires a thin layer of deposited metal, the substrate may be submerged in the electroless plating bath for a shorter amount of time than an application or design that requires a thicker layer of deposited metal. However, the bath is caustic and if the substrate is submerged in solution for too long, without uniform initiation of plating that can form a protective metal surface, the catalytic portions 210, 230 that are part of or are disposed on the substrate 160, as well as the substrate 160 itself, may be damaged.

[0026] The plating rate is a measure of the plating thickness achieved per unit of time in a particular application or design. Generally, the plating rate is a function of the time required to initiate the autocatalytic reaction and the application-specific time required to achieve a buildup of a desired thickness of metal. For catalytic standard lines or features 230, the initiation time may be on the order of magnitude of seconds to minutes, depending on the bath conditions. In certain embodiments, the initiation time of catalytic standard lines or features 230 may be in a range between approximately 10 seconds and approximately 40 seconds. As previously noted, once initiated, bulk plating begins and deposition continues until the substrate is removed from the electroless plating bath or the bath chemistry fails. However, for catalytic fine lines or features 210, the initiation time is substantially longer than that of catalytic standard lines or features 230 in a conventional electroless plating bath that uses commercially available electroless plating solution operated at normal operating conditions. The initiation time for catalytic fine lines or features 210 may be at least twice, and potentially substantially longer, than that of catalytic standard lines or features 230. As such, catalytic fine lines or features 210 do not initiate, if they initiate at all, until after their catalytic standard line or features 230 counterpart. Consequently, in a conventional electroless plating bath, a substrate 160 that includes catalytic lines or features with diverse feature sizes, but include at least one catalytic fine line or feature 210, plates in a non-uniform maimer because the catalytic fine lines or features 210 take substantially longer to initiate, if they initiate at all, and then buildup.

[0027] Because the catalytic fine lines or features 210 take longer to initiate and plate to a desired thickness, the catalytic standard lines or features 230 spend more time in the bulk plating stage and the buildup of deposited metals on the catalytic standard lines or features is substantially thicker than that of the catalytic fine lines or features 210. The non-uniform deposition of metal may affect the electrical performance of the deposited metal. For example, thin layers of deposited metal may have a higher electrical resistance and lower conductivity than thick layers of deposited metal. As a consequence, the electrical performance of the deposited metal and, by extension, the end product that incorporates it, may be negatively impacted. Similarly, the non-uniformity may negatively impact reliability. The thicker deposits of metal on the catalytic standard lines or features 230 may cause adhesion issues that cause the deposited metal to peel off of the substrate 160. As a consequence, the reliability of the deposited metal and, by extension, the end product that incorporates it, may be reduced.

[0028] Because the catalytic fine lines or features 210 take longer to initiate and plate to a desired thickness, the overall plating rate of a substrate 160 with catalytic lines or features of different sizes may be dominated by the plating rate of the catalytic fine lines or features 210 and it may be difficult to achieve high- volume in a production environment. To increase the number of substrates 160 that may be plated in a certain amount of time, such as, for example, a production run, one or more additional electroless plating baths may be required. Each additional electroless plating bath requires significant physical space, increases capital costs, increases material costs, and increases operational costs.

[0029] Another issue with non-uniform plating is potential damage to the catalytic portions that are part of or are disposed on substrate, as well as the substrate itself, when the substrate is submerged in the electroless plating solution for an extended period of time required to initiate and plate the catalytic fine lines or features. Figure 3 shows electroless plated fine lines 310 on substrate 160 that exhibit issues because of prolonged exposure to electroless plating solution prior to initiation of electroless plating. In certain applications, such as, for example, touch sensor applications, flexographic printing may be used to print a catalytic ink image (not shown) of a conductive pattern on substrate 160 for subsequent electroless plating. In this example, the catalytic ink serves as the catalytic portions that are disposed on the substrate 160 and are metallized by the electroless plating process. When the catalytic ink image includes a mix of catalytic standard lines or features (not shown) and catalytic fine lines or features, such as, for example, micrometer-fine catalytic lines 310, the substrate 160 may be submerged in the electroless plating solution longer than would otherwise be required for the catalytic standard lines or features alone. If the substrate is submerged too long, the solution may etch away portions of the catalytic ink image on substrate, especially the portions of the catalytic ink image that correspond to the catalytic fine lines or features 310, prior to initiation, if it initiates at all. As such, portions of the catalytic ink image printed on substrate may be etched away and, as a consequence, the electroless plating process may plate on top of the altered catalytic ink image, if it plates at all. Plated fine lines or features 310 may be altered such that the deposited metal may include unintended narrow portions 320, breaks or discontinuities 330, or wide portions 340 that negatively impact the electrical performance, functionality, reliability, optical properties, and/or yield of the end product (not independently illustrated).

[0030] In one or more embodiments of the present invention, a method of controlling oxygen levels for electroless plating of catalytic fine lines or features regulates the dissolved oxygen concentration of the electroless plating solution to ensure consistent plating of catalytic lines or features with diverse feature sizes that include at least one catalytic fine line or feature. The method increases the plating rate, provides substantially uniform plating for diverse feature sizes, improves production efficiency, reduces production costs, improves reliability, and improves yield.

[0031] In a production environment, there are a number of interrelated goals for the electroless plating process. From an end product perspective, the electroless plating bath should not significantly alter the catalytic portions that are part of or are disposed on the substrate prior to the deposition of metal, provide substantially uniform plating for diverse feature sizes on substrate that include at least one catalytic fine line or feature, provide appropriate connectivity, resistivity, and conductivity of the deposited metal, and the deposited metal should adhere to the substrate. From an electroless plating bath perspective, the electroless plating bath should provide the highest possible plating rate, substantially uniform plating for diverse feature sizes, and the highest possible up-time or bath life.

[0032] In an electroless plating bath, dissolved oxygen in the electroless plating solution serves as a stabilizer. If the dissolved oxygen concentration in the electroless plating solution is too low, the bath life, or time in which the bath may be operated, is reduced. When the dissolved oxygen concentration is too low, the bath may crash or plate out and spontaneously precipitate metal throughout the solution instead of depositing metal on the catalytic portions that are part of or are disposed on the substrate. If the dissolved oxygen concentration in the electroless plating solution is too high, exceeding the amount a given solution was designed for, any plating in process will cease and no further plating will take place. When the dissolved oxygen concentration is too high, the oxygen renders the catalyst less effective in catalyzing the reaction such that metal deposition does not take place.

[0033] Conventional commercially available electroless plating solutions typically include a high dissolved oxygen concentration. Conventional commercially available electroless plating solutions typically include at least 5.0 parts -per-million ("PPM") dissolved oxygen concentration or more. Because the concentration of commercially available electroless plating solutions is sufficient to plate catalytic standard lines or features, such as, for example, copper clad circuit board blanks, the dissolved oxygen concentration is typically not monitored or regulated, nor do the manufacturers of commercial electroless plating solution recommend doing so.

[0034] To the extent some commercial vendors do consider dissolved oxygen concentration, some manufacturers of commercially available electroless plating solutions recommend bubbling air into the electroless plating solution to maintain the high dissolved oxygen concentration or potentially increase it without monitoring the actual concentration. This high dissolved oxygen concentration is necessary to achieve stable plating for the high bath loading factor that is typically used in a conventional electroless plating bath application. The bath loading factor is the ratio of the surface area to be plated per volume of electroless plating solution in the bath. Commercially available electroless plating solutions for high bath loading factor baths typically require a great deal of air to be bubbled through the solution because oxygen is the principle stabilizer for the bath. Adding this oxygen partially inhibits imdesired extraneous plating, but still allows plating on the desired catalytic lines or features because the surface area of the catalyst is so high that consumption of the reactants and the plating rate is high enough to overcome the inhibition of plating due to dissolved oxygen. In these conventional applications with a high bath loading factor, the rate of consumption of reactants is so high that high dosing rates, high agitation levels, and high levels of air bubbling are required to prevent the bath from crashing. As the bath ages and shows signs of instability, the bath loading factor may be reduced to prolong the bath life. Some manufacturers of commercially available electroless plating solutions recommend increasing the dissolved oxygen concentration to prevent plating in one or more control systems and/or one or more maintenance systems that come into contact with the electroless plating solution, but are not involved in the substantive deposition of metal.

[0035] However, when a substrate that includes one or more catalytic fine lines or features and one or more catalytic standard lines or features is electroless plated in a conventional electroless plating bath using commercially available electroless plating solution, the high dissolved oxygen content of the solution prolongs or inhibits the initiation stage of the electroless plating process for the one or more catalytic fine lines or features. As a consequence, the one or more catalytic fine lines or features are exposed to the electroless plating solution for a longer period of time and are prone to etching prior to metal deposition. Figure 4 shows a scanning electron microscope image of a catalytic ink pattern 410 printed on substrate 160 that is etched prior to electroless plating. When a catalytic ink pattern 410 is exposed to electroless plating solution for an extended period of time prior to initiation (if it initiates at all), such as, for example, in a case where a high dissolved oxygen concentration poisons catalytic sites, portions of the catalytic ink pattern 410 may be damaged by etching. This etching phenomenon may alter the catalytic ink pattern 410, resulting in, for example, unintended narrow portions, breaks or discontinuities, wide portions, or removal of one or more surface layers. In this instance, the damage due to etching has removed one or more surface layers of the catalytic ink pattern 410, exposing one or more metal catalyst nanoparticles 420 of the catalytic ink pattern 410. If this catalytic ink pattern 410 initiates and plates, poor adhesion will result because one or more metal catalyst nanoparticles 420 are no longer embedded in the ink 410, but sit loose on the surface of the ink itself.

[0036] During the up-time of an electroless plating bath, the dissolved oxygen concentration may decrease over time because of one or more of the aging of the bath chemistry, increased side reactions, buildup of by-products, which can reduce the solubility of oxygen in the solution or eventually precipitate out and provide nucleation sites for further electroless plating to occur, or other causes. As the dissolved oxygen concentration decreases, the bath activity, such as, for example, the plating rate, increases resulting in further reduction of dissolved oxygen and the bath life decreases. If the dissolved oxygen concentration decreases to a certain threshold, the bath life may be significantly reduced. The threshold may vary based on a particular commercial vendor's formulation of electroless plating solution or the amount of chemical stabilizer added to the bath. [0037] In a conventional electro less plating bath, the amount of time required to initiate may vary based on the feature sizes of the catalytic lines or features. In certain embodiments, such as, for example, embodiments where flexographic printing is used to print a catalytic ink pattern on substrate for subsequent electroless plating, the catalytic ink may include catalyst nanoparticles with a loading percentage by weight that is typically less than that of the polymer content of the ink. As such, the catalytic ink may be considered a polymer network containing embedded catalytic sites. Initiation is an inherently probabilistic process in which the relevant reactants need to diffuse within close proximity of the catalytic sites. Dissolved oxygen may act as a catalytic poison and render some of these catalytic sites inactive while adsorbed to the surface of the catalytic component of the ink. While one would expect the same percentage of larger versus fine catalytic sites to be affected by the adsorption of oxygen, there may be a feature size dependence. For example, once initiated, catalytic activity tends to increase such that it is no longer impacted by oxygen adsorption. Once the initial nucleation occurs and the size of the catalytic site increases, the impact of oxygen becomes smaller as oxygen adsorption is less likely to impact the entire catalytic line or feature. This may be assisted by the actual change in catalytic effectiveness as the metal composition changes. This effect is in competition with an etching effect in which catalytic sites may be etched by the etchant. As such, catalytic standard lines or features tend to initiate faster than catalytic fine lines or features in a conventional electroless plating bath as more catalytic sites are available for local diffusion, even when they have the same ratio of oxygen deactivated sites to active catalytic sites.

[0038] In a conventional electroless plating bath, the amount of time required to initiate may vary based on the feature sizes of the catalytic lines or features. In certain embodiments, such as, for example, embodiments where flexographic printing is used to print a catalytic ink pattern on substrate for subsequent electroless plating, catalytic fine lines or features tend to have a thickness that is less than that of catalytic standard lines or features as an artifact of the flexographic printing process, hi certain embodiments, catalytic ink is largely comprised of a polymeric material. The diffusion rate of oxygen, which is contained within a polar media such as, for example, water, may vary from the diffusion rate of the reducing agent, which is typically a small organic molecule. Thus, the surface of catalytic sites tend to be passivated first, leaving the interior of the catalytic line or feature still catalytically active. As the thickness of catalytic lines or features increases, larger (thicker) catalytic lines or features tend to have more active sites available. As such, catalytic standard lines or features tend to initiate faster than catalytic fine lines or features in a conventional electroless plating bath.

[0039] In one or more embodiments of the present invention, the dissolved oxygen concentration is regulated to a regulated oxygen level, catalytic fine lines or features initiate quickly and at approximately the same time as larger, or standard, catalytic lines or features. When the dissolved oxygen concentration is within a certain regulated range, the time to initiate is independent of the feature size such that catalytic lines or features with diverse feature sizes initiate at approximately the same time. In certain embodiments, the initiation time may be in a range between approximately 10 seconds and approximately 40 seconds, regardless of feature size. The regulated dissolved oxygen concentration range may vary based on the shape, size, and configuration of the catalytic lines or features on substrate. If no historical data from using the method exists to indicate witich regulated range may be appropriate for a given application or design, the largest regulated range may be used to focus in on the appropriate controlled oxygen level. In certain embodiments, the regulated dissolved oxygen concentration may be in a range between approximately 0.6 PPM and approximately 1.6 PPM. In other embodiments, the regulated dissolved oxygen concentration may be in a range between approximately 1.0 PPM and approximately 1.2 PPM. In still other embodiments, the regulated dissolved oxygen concentration may be in a range between approximately 0.9 PPM and approximately 1.3 PPM. In still other embodiments, the regulated dissolved oxygen concentration may be in a range between approximately 0.8 PPM and approximately 1.4 PPM. In still other embodiments, the regulated dissolved oxygen concentration may be in a range between approximately 0.7 PPM and approximately 1.5 PPM.

[0040] In certain embodiments, the dissolved oxygen concentration may be controlled by one or more of controlling a depth at which a substrate is submerged in electroless plating solution, controlling the exposed surface area of the electroless plating solution to air, controlling the bubbling of one or more of air, oxygen, a gas that contains oxygen, or an inert gas into the electroless plating solution, and controlling the recirculation and/or agitation of the electroless plating solution to affect diffusion. In certain embodiments, where the electroless plating solution has a non-volatile reducing agent, a pressure/vacuum control system may be used alone, or in combination with one or more of the above, to control the dissolved oxygen concentration.

A depth at which a substrate is submerged in electroless plating solution may be controlled by a system (not shown) configured to submerge the substrate at a desired depth of electroless plating solution. In certain embodiments, where the agitation level of the electroless plating solution in the bath is relatively low, a gradient of localized dissolved oxygen concentrations may occur. Typically, the highest localized dissolved oxygen concentration may be observed nearest the surface of the electroless plating solution and decreases with depth. Certain bath chemistries, including, for example, formaldehyde-based electroless plating solutions, exhibit this effect because the reaction of the electroless plating chemistry reduces the dissolved oxygen concentration. The reduction of dissolved oxygen concentration is more pronounced near the active surface of the substrate where plating occurs. In the absence of significant agitation, oxygen must diffuse through the electroless plating solution to replace the oxygen reduced by the reaction. If the substrate is located near the surface of the electroless plating solution, diffusion of oxygen from the air-solution interface may exceed the rate at which oxygen is depleted by the reaction. However, if the substrate is submerged at a certain depth, diffusion of oxygen from the air-solution interface may be less than the rate at which oxygen is depleted by the reaction. As such, an electroless plating bath with a given electroless plating solution may be characterized such that the localized dissolved oxygen concentration levels within the gradient are identified by depth. Thus, a depth at which a substrate is submerged in electroless plating solution may be controlled to ensure that the substrate and the reaction take place at a desired localized dissolved oxygen concentration. For example, a roller system (not shown) may be used to submerge a substrate at a depth of, for example, two to three inches, below the surface of the electroless plating solution. One or more of the rollers of the roller system configured to submerge the substrate at depth may have a diameter suitable to depress the substrate at a desired depth. The diameter of the roller may have a bend radius that does not exceed a maximum bend radius allowed by the flexibility of the substrate material being used or the plated material. In certain embodiments, such as, for example, a production electroless plating line configured for electroless plating of roll-to-roll substrate material, a first depth setting roller may be disposed near an entry point of the substrate material to the electroless plating solution and a second depth setting roller may be disposed near an exit point of the substrate material from the electroless plating solution.

[0042] The exposed surface area of the electroless plating solution to air may be controlled with a cover (not shown). The cover may be placed over the electroless plating bath (110 of Figure 1) to control the exposure of the electroless plating solution to air. If a conveyor system (150 of Figure 1) is used, the conveyor may cause an input and/or output gap, however, the cover should be capable of substantially covering the bath. In certain embodiments, the cover may allow for variable amounts of coverage such that the exposed surface area may be increased or decreased as needed. The exposed surface area of the electroless plating solution to air may be reduced to promote reduction in the dissolved oxygen concentration or to regulate a dissolved oxygen concentration when a nitrogen, or another inert gas, blanket is employed. The exposed surface area of the electroless plating solution to air may be increased to promote an increase in the dissolved oxygen concentration from the solution/air interface when recirculation or agitation is employed. Recirculation or agitation may be employed to move electroless plating solution from the bottom to the top of the bath, thereby exposing other portions of the electroless plating solution to air.

[0043] The bubbling of one or more of air, oxygen, a gas that contains oxygen, or an inert gas, such as nitrogen, may be controlled with a sparging control system. Air, oxygen, or a gas that contains oxygen may be bubbled into the electroless plating solution to increase the dissolved oxygen concentration. Nitrogen, or another inert gas, may be bubbled into the electroless plating solution to decrease the dissolved oxygen concentration. At any given temperature, pressure, and total solute concentration, there is a maximum amount of gas that will be soluble in a solution. Typically, the relative concentrations of the gasses will closely reflect the partial pressures of the gas with which the liquid is in contact with. By bubbling nitrogen the effective partial pressures of nitrogen that the solution is exposed to will be higher. The nitrogen, or inert gas, may also form a blanket over the exposed surface area of the electroless plating solution reducing the introduction of oxygen into the electroless plating solution from the solution/air interface. Blanketing works in a similar manner by reducing the partial pressure of oxygen in the gas above the plating solution. For this reason, the higher the surface area of the bubbles, the more effective sparging may be in reducing the dissolved oxygen concentration.

[0044] The recirculation and/or agitation of the electroless plating solution may be controlled with a pump control system and/or a turbulence control system. A pump control system may control a recirculation speed that may be used to control the mixing and/or diffusion of oxygen within the electroless plating solution. A turbulence control system may control agitators that may be used to control the mixing and/or diffusion of oxygen within the electroless plating solution. A sparging control system may also be a source of agitation as a gas is bubbled through the electroless plating solution.

[0045] In certain embodiments, if an operator of the electroless plating system wishes to reduce the dissolved oxygen concentration, nitrogen, or another inert gas, may be bubbled into the electroless plating solution. The nitrogen, or inert gas, forms a blanket over the electroless plating solution that reduces or eliminates the introduction of oxygen into the electroless plating solution from the air that would otherwise be disposed above the electroless plating solution. In other embodiments, if the operator wishes to reduce the dissolved oxygen concentration, a vacuum may be pulled. In still other embodiments, the electroless plating system may include a roller system configured to submerge the substrate at a depth where the localized dissolved oxygen concentration is lower. One of ordinary skill in the art will recognize that one or more of the above-noted techniques for reducing the dissolved oxygen concentration may be used in combination in accordance with one or more embodiments of the present invention. One of ordinary skill in the art will also recognize that the one or more of the above-noted techniques used may vary based on an application or design in accordance with one or more embodiments of the present invention.

[0046] In certain embodiments, if the operator of the electroless plating system wishes to increase the dissolved oxygen concentration, air, oxygen, or a gas that contains oxygen may be bubbled into the electroless plating solution by a sparging control system or other control system. A pump control system may be used to increase the recirculation of the electroless plating solution within the bath and promote mixing and/or diffusion of oxygen throughout the solution. A turbulence control system may be used to agitate the electroless plating solution within the bath and promote mixing and/or diffusion of oxygen throughout the solution. The pump control system and the turbulence control system may be used independently or at the same time to achieve the desired mixing and/or diffusion. In other embodiments, if the operator wishes to increase the dissolved oxygen concentration, a spray or cascade system may be used to increase the exposed surface area and promote the introduction of oxygen into the electroless plating solution. The spray or cascade system may be used with or in place of a sparging control system that may be used to bubble oxygen, or a gas mixture that contains oxygen, into the electroless plating solution. In still other embodiments, if the operator wishes to increase the dissolved oxygen concentration, the exposed surface area of the electroless plating solution to air may be increased using any suitable means for increasing the exposed surface area. A pump control system and/or a turbulence control system may be used to promote the diffusion of oxygen throughout the solution. One of ordinary skill in the art will recognize that one or more of the above-noted techniques for increasing the dissolved oxygen concentration may be used in combination in accordance with one or more embodiments of the present invention. One of ordinary skill in the art will also recognize that the one or more of the above-noted techniques used may vary based on an application or design in accordance with one or more embodiments of the present invention.

[0047] One of ordinary skill in the art will recognize that any other means of controlling the exposed surface area of the electroless plating solution, controlling the bubbling of air, oxygen, a gas that contains oxygen, or an inert gas into the electroless plating solution, controlling the recirculation and/or agitation of the electroless plating solution, or other means of controlling the dissolved oxygen concentration level may be used in accordance with one or more embodiments of the present invention. One of ordinary skill in the art will also recognize that any combination or permutation of any of the above methods of control may be used in accordance with one or more embodiments of the present invention.

[0048] Figure 5 shows a method of controlling oxygen levels for electroless plating of catalytic fine lines or features in accordance with one or more embodiments of the present invention. One of ordinary skill in the art will recognize that the method may be performed at laboratory scale, e.g., in a beaker, or in a production scale, e.g., production electroless plating bath in accordance with one or more embodiments of the present invention. If the method is performed at laboratory scale, one of ordinary skill in the art will recognize that the results may be used in production scale in accordance with one or more embodiments of the present invention.

[0049] In step 510, a substrate may be selected that includes a plurality of catalytic lines or features that are part of or are disposed on the substrate. The plurality of catalytic lines or features include at least one catalytic fine line or feature and at least one catalytic standard line or feature. In certain embodiments, the at least one catalytic fine line or feature may have a width less than approximately 5 micrometers. Li other embodiments, the at least one catalytic line or feature may have a width in a range between approximately 5 micrometers and approximately 10 micrometers. In still other embodiments, the at least one catalytic line or feature may have a width greater than 10 micrometers, but on the order of magnitude of micrometers. In certain embodiments, the at least one catalytic standard line or feature may have a width on the order of magnitude of at least a millimeter or more. In other embodiments, the at least one catalytic standard line or feature may have a width on the order of magnitude of at least a centimeter or more. In still other embodiments, the at least one catalytic standard line or feature may have a width on the order of magnitude of at least a decimeter or more.

[0050] For purposes of testing the diversity of feature sizes, the at least one catalytic fine line or feature may represent the smallest width among the plurality of catalytic lines or features that are part of or are disposed on the substrate. If the substrate is a test substrate used to determine a dissolved oxygen concentration range that works well for a production substrate, the at least one catalytic fine line or feature may represent the smallest width among a plurality of catalytic lines or features that are part of or are disposed on the production substrate. Similarly, the at least one catalytic standard line or feature may represent the largest width among the plurality of catalytic lines or features that are part of or are disposed on the substrate. If the substrate is a test substrate used to determine a dissolved oxygen concentration for a production substrate, the at least one catalytic standard line or feature may represent the largest width among a plurality of catalytic lines or features that are part of or are disposed on the production substrate.

[0051] In step 520, the dissolved oxygen concentration of the electroless plating solution may be regulated to a candidate controlled oxygen level. Generally, the highest dissolved oxygen concentration level that initiates the at least one catalytic fine line or feature as fast as the at least one catalytic standard line or feature, but does not exhibit one or more failure modes, is desirable from a plating performance/bath life tradeoff perspective. However, a lower dissolved oxygen concentration level may be used at the expense of reduced bath life. The candidate controlled oxygen level may be determined by incrementing the previous candidate controlled oxygen level by an increment or setting the candidate controlled oxygen level to the smallest value in a regulated range of dissolved oxygen concentration.

[0052] In a first pass of the method, the candidate controlled oxygen level may be set to the smallest value in the regulated range of dissolved oxygen concentration. The regulated range may vary based on the shape, size, and configuration of the catalytic lines or features on substrate. If no historical data from using the method exists to indicate which regulated range may be appropriate for a given application or design, the largest regulated range disclosed herein may be used to focus in on an appropriate controlled oxygen level. In certain embodiments, the regulated dissolved oxygen concentration may be in a range between approximately 0.6 PPM and approximately 1.6 PPM. In other embodiments, the regulated dissolved oxygen concentration may be in a range between approximately 1.0 PPM and approximately 1.2 PPM. In still other embodiments, the regulated dissolved oxygen concentration may be in a range between approximately 0.9 PPM and approximately 1.3 PPM. In still other embodiments, the regulated dissolved oxygen concentration may be in a range between approximately 0.8 PPM and approximately 1.4 PPM. In still other embodiments, the regulated dissolved oxygen concentration may be in a range between approximately 0.7 PPM and approximately 1.5 PPM.

[0053] In a subsequent pass of the method, the candidate controlled oxygen level may^¬ be increased by an increment that may vary based on an application or design. For example, the regulated dissolved oxygen concentration range may be divided into a number of equal increment values that are used to increment the candidate controlled oxygen level. The number of equal increment values may vary based on an application or design.

[0054] The dissolved oxygen concentration of the electroless plating solution may be regulated by one or more of controlling the surface area of the electroless plating solution exposed to air, controlling a flow rate of inert gas introduced into the electroless plating solution, controlling a flow rate of oxygen or a gas that contains oxygen into the electroless plating solution, controlling a recirculation speed of the electroless plating solution, and/or controlling an agitation of the elecUoless plating solution. The candidate controlled oxygen level may be achieved by increasing or reducing the dissolved oxygen concentration of the electroless plating solution.

[0055] In certain embodiments, the dissolved oxygen concentration of the electroless plating solution may be increased by introducing oxygen or a gas that contains oxygen into the electroless plating solution and diffusing the introduced oxygen or gas containing oxygen in the electroless plating solution. In certain embodiments, the oxygen or gas that contains oxygen may be introduced into the electroless plating solution with a sparging control system that bubbles oxygen or gas that contains oxygen into the electroless plating solution. In other embodiments, a spray or cascade system may be used in place of, or in addition to, the sparging control system to increase the surface area of electroless plating solution that is exposed to air. In still other embodiments, the surface area of electroless plating solution exposed to air may be increased to promote the introduction of oxygen into the electroless plating solution from the solution/air interface by, for example, removing a cover and/or removing an inert gas blanket that may be disposed over the electroless plating solution. The increase in exposed surface area may be used in place of or in addition to the sparging control system and the spray or cascade system. The electroless plating solution may be recirculated by a pump control system and/or agitated by a turbulence control system to promote mixing and diffusion of the introduced oxygen throughout the electroless plating solution.

[0056] In certain embodiments, the dissolved oxygen concentration of the electroless plating solution may be reduced by bubbling nitrogen, or another inert gas, into the electroless plating solution that forms an inert gas blanket over the electroless plating solution. The nitrogen, or inert gas, blanket reduces or eliminates the introduction of oxygen into the electroless plating solution from the solution air interface. In other embodiments, using electroless plating solution with non-volatile components, a vacuum may be pulled either directly upon the plating vessel or on a suitable porous membrane to reduce the dissolved oxygen concentration.

[0057] In step 530, the substrate may be submerged in the electroless plating solution for a period of time sufficient to initiate plating of the at least one catalytic standard line or feature. The time may vary based on the feature size of the at least one catalytic standard line or feature. This time may be determined from historical data, empirical data, or trial and error. In step 540, the substrate may be removed from the electroless plating solution for evaluation. In step 550, the substrate may be evaluated to determine whether the at least one catalytic fine line or feature initiated at approximately the same time as the at least one catalytic standard line or feature. The at least one catalytic standard line or feature and the at least one catalytic fine line or feature may be examined with an optical microscope, scanning electron microscope, atomic force microscope, laser profilometry, or other characterization tool. A surface of the least one catalytic standard line or feature may be examined for evidence of initiation on the surface. A surface of the least one catalytic fine line or feature may be examined for evidence of initiation, or lack thereof, on the surface. The evidence of initiation for the at least one catalytic standard line or feature may be compared to the evidence of initiation, or lack thereof, of initiation for the least one catalytic fine line or feature. The at least one catalytic line or feature may be determined to have initiated at approximately the same time as the least one catalytic standard line or feature if the at least one catalytic fine line or feature exhibits approximately the same evidence of initiation on its surface as that of the least one catalytic standard line or feature. If the at least one catalytic fine line or feature did not initiate at approximately the same time as the at least one catalytic standard line or feature, the candidate controlled oxygen level may be incremented and the method may iterate as shown in step 560. If the at least one catalytic fine line or feature initiated at approximately the same time as the at least one catalytic standard line or feature, the next determination may be made.

In step 570, the substrate may be evaluated to determine whether the at least one catalytic fine line or feature exhibits one or more failure modes. The substrate may be examined with an optical microscope, scanning electron microscope, atomic force microscope, laser proftlometer, or other characterization tool and tested for electrical functionality and various stress tests that simulate long term reliability. The one or more failure modes may include etching from prolonged exposure to electroless plating solution prior to initiation, narrow portions, wide portions, breaks or discontinuities, brittleness, grain size issues, adhesion issues, porosity issues, color issues, or any other indicator of plating issues. A shape of the at least one catalytic fine line or feature may be examined. A shape of the at least one catalytic fine line or feature may be compared to a shape of a corresponding line of feature in a source design, such as, for example, a design file that w^ras used to generate the at least one catalytic fine line or feature. The at least one catalytic fine line or feature may be determined to have etched prior to initiation if the at least one catalytic line or feature exhibits narrow portions, breaks, or discontinuities that do not exist in the corresponding line or feature in the source design. If the at least one catalytic fine line or feature did not exhibit one or more failure modes, the candidate controlled oxygen level may be incremented and the method may iterate as shown in step 560. If the at least one catalytic fine line or feature exhibits one or more failure modes, the previous value of the candidate controlled oxygen level may be selected as the regulated oxygen level that may be used for the substrate in production as shown in step 580. If there is no previous value of the candidate controlled oxygen level, the method may be repeated using one of the larger regulated ranges.

[0059] In this way, a regulated dissolved oxygen concentration range, that is substantially lower than the dissolved oxygen concentration of commercially available electroless plating solutions may be explored to identify the highest dissolved oxygen concentration within the regulated range that initiates the at least one catalytic fine line or feature at approximately the same time as the at least one catalytic standard line or feature and does not exhibit one or more failure modes. The candidate controlled oxygen level may be incremented and the method may repeat using the newly incremented candidate controlled oxygen level until one or more failure modes are exhibited. When one or more failure modes are exhibited, the previous value of the candidate controlled oxygen level may be selected as the regulated oxygen level for production. The dissolved oxygen concentration may be regulated to the regulated oxygen level for production.

[0060] If the at least one catalytic fine line or feature initiated at approximately the same time as the at least one catalytic standard line or feature and did not exhibit one or more failure modes, the candidate controlled oxygen level may be incremented by an increment and the method may be repeated using the newly incremented candidate controlled oxygen level. In this way, the process may explore the highest possible candidate controlled oxygen level that may be used so as to extend the bath life while still providing the benefit of fast initiation of catalytic fine lines or features.

[0061] In certain embodiments, further optimization may be achieved by repeating the method starting with the selected regulated oxygen level, a narrower regulated range, and a smaller increment size to focus in on the highest possible dissolved oxygen concentration that may be used. The bath life may be extended by using the highest dissolved oxygen concentration within the regulated range that does not exhibit one or more failure modes.

[0062] Advantages of one or more embodiments of the present invention may include one or more of the following:

[0063] In one or more embodiments of the present invention, a method of controlling oxygen levels for electroless plating of catalytic fine lines or features monitors and regulates the dissolved oxygen concentration of the electroless plating solution during electroless plating operations.

[0064] In one or more embodiments of the present invention, a method of controlling oxygen levels for electroless plating of catalytic fine lines or features regulates the dissolved oxygen concentration of the electroless plating solution to a certain range such that the time required to initiate is feature size independent and is not sensitive to variations in feature size, width, and/or thickness of the catalytic portions that are part of or are disposed on the substrate.

[0065] In one or more embodiments of the present invention, a method of controlling oxygen levels for electroless plating of catalytic fine lines or features regulates the dissolved oxygen concentration of the electroless plating solution to a certain range that ensures consistent plating of lines or features with diverse feature sizes that include at least one fine line or feature.

[0066] In one or more embodiments of the present invention, a method of controlling oxygen levels for electroless plating of catalytic fine lines or features regulates the dissolved oxygen concentration of the electroless plating solution to a certain range that ensures uniform plating of lines or features with diverse feature sizes that include at least one fine line or feature.

[0067] In one or more embodiments of the present invention, a method of controlling oxygen levels for electroless plating of catalytic fine lines or features reduces or eliminates etching of the catalytic portions that are part of or are disposed on the substrate that are submerged in electroless plating solution. Because all lines or features initiate at approximately the same time, the fine lines or features are not exposed to electroless plating solution for a prolonged period of time prior to initiation.

[0068] In one or more embodiments of the present invention, a method of controlling oxygen levels for electroless plating of catalytic fine lines or features reduces or eliminates peeling caused by poor adhesion between the plated metal and the catalytic portion that is part of or is disposed on the substrate or by poor adhesion between the catalytic portion that is part of or is disposed on the substrate.

[0069] In one or more embodiments of the present invention, a method of controlling oxygen levels for electroless plating of catalytic fine lines or features provides substantially uniform plating for lines or features with diverse feature sizes.

[0070] In one or more embodiments of the present invention, a method of controlling oxygen levels for electroless plating of catalytic fine lines or features provides substantially uniform plating for lines or features on substrate that have diverse feature sizes and include at least one fine line or feature.

[0071] In one or more embodiments of the present invention, a method of controlling oxygen levels for electroless plating of catalytic fine lines or features provides substantially uniform plating for lines or features with diverse feature sizes that are disposed on one or more sides of a substrate, including opposing sides of the substrate.

[0072] In one or more embodiments of the present invention, a method of controlling oxygen levels for electroless plating of catalytic fine lines or features reduces or eliminates peeling caused by non-uniform plating that results in some lines or features that have a substantially thicker buildup of metal than other lines or features on substrate.

[0073] In one or more embodiments of the present invention, a method of controlling oxygen levels for electroless plating of catalytic fine lines or features increases the up-time or bath life by tuning the oxygen content for the specific application.

[0074] In one or more embodiments of the present invention, a method of controlling oxygen levels for electroless plating of catalytic fine lines or features increases the range of temperature in which the electroless plating may be operated.

[0075] In one or more embodiments of the present invention, a method of controlling oxygen levels for electroless plating of catalytic fine lines or features is not sensitive to a type of substrate material, a type of catalytic portions that are part of or are disposed on the substrate including precursor, or catalytic, ink, an age of a precursor, or catalytic, ink, a feature size such as width or height of the catalytic portions that are part of or are disposed on the substrate.

[0076] In one or more embodiments of the present invention, a method of controlling oxygen levels for electroless plating of catalytic fine lines or features provides a consistent and a uniform plating of lines or features with diverse feature sizes and include at least one fine line or feature.

[0077] In one or more embodiments of the present invention, a method of controlling oxygen levels for electroless plating of catalytic fine lines or features improves the plating rate.

[007S] In one or more embodiments of the present invention, a method of controlling oxygen levels for electroless plating of catalytic fine lines or features improves production efficiency.

[0079] In one or more embodiments of the present invention, a method of controlling oxygen levels for electroless plating of catalytic fine lines or features reduces material cost.

[0080] In one or more embodiments of the present invention, a method of controlling oxygen levels for electroless plating of catalytic fine lines or features improves yield.

[0081] In one or more embodiments of the present invention, a method of controlling oxygen levels for electroless plating of catalytic fine lines or features improves reliability.

[0082] While the present invention has been described with respect to the above- noted embodiments, those skilled in the art, having the benefit of this disclosure, will recognize that other embodiments may be devised that are within the scope of the invention as disclosed herein. Accordingly, the scope of the invention should be limited only by the appended claims.

Claims

CLAIMS What is claimed is:

1. A method of controlling oxygen levels for electroless plating of catalytic fine lines or features comprising:

selecting a substrate that includes a plurality of catalytic lines or features that are part of or are disposed on the substrate, wherein the plurality of catalytic lines or features include at least one catalytic fine line or feature and at least one catalytic standard line or feature;

regulating a dissolved oxygen concentration of an electroless plating solution to a candidate controlled oxygen level, wherein the candidate controlled oxygen level is set to a smallest value in a regulated range in a first pass of the method;

submerging the substrate in the electroless plating solution for a period of time

sufficient to initiate plating of the at least one catalytic standard line or feature; removing the substrate from the electroless plating solution;

evaluating the substrate to determine whether the at least one catalytic fine line or feature initiated at approximately the same time as the at least one catalytic standard line or feature;

evaluating the substrate to determine whether the at least one catalytic fine line or feature exhibits one or more failure modes;

if the at least one catalytic fine line or feature initiated at approximately the same time as the at least one catalytic standard line or feature and did not exhibit one or more failure modes, incrementing the candidate controlled oxygen level by an increment and iterate the method; and

if the at least one catalytic fine line or feature exhibits one or more failure modes, selecting the previous value of the candidate controlled oxygen level as a regulated oxygen level.

2. The method of claim 1,

wherein the at least one catalytic fine line or feature has the smallest width among the plurality of catalytic lines or features that are part of or are disposed on the substrate; and

wherein the at least one catalytic standard line or feature includes the largest width among the plurality of catalytic lines or features that are part of or are disposed on the substrate.

3. The method of claim 1 , wherein the at least one catalytic fine line or feature has a width less than approximately 5 micrometers.

4. The method of claim 1 , wherein the at least one catalytic fine line or feature has a width in a range between approximately 5 micrometers and approximately 10 micrometers.

5. The method of claim 1 , wherein the at least one catalytic fine line or feature has a width in a range between approximately 10 micrometers and approximately 20 micrometers.

6. The method of claim 1, wherein the at least one catalytic standard line or feature has a width on the order of magnitude of at least 20 micrometers.

7. The method of claim 1, wherein the at least one catalytic standard line or feature has a width on the order of magnitude of at least a millimeter.

8. The method of claim 1, wherein the at least one catalytic standard line or feature has a width on the order of magnitude of at least a centimeter.

9. The method of claim 1, wherein the at least one catalytic standard line or feature has a width on the order of magnitude of at least a decimeter.

10. The method of claim 1, wherein regulating the dissolved oxygen concentration comprises controlling a surface area of the electroless plating solution exposed to air.

1 1. The method of claim 1 , wherein regulating the dissolved oxygen concentration comprises controlling a flow rate of inert gas that is introduced into the electroless plating solution .

12. The method of claim 1, wherein regulating the dissolved oxygen concentration comprises controlling a flow rate of oxygen or gas containing oxygen that is introduced into the electroless plating solution.

13. The method of claim 1 , wherein regulating the dissolved oxygen concentration comprises controlling a recirculation speed of the electroless plating solution.

14. The method of claim 1, wherein regulating the dissolved oxygen concentration comprises controlling an agitation level of the electroless plating solution.

15. The method of claim 1, witerein regulating the dissolved oxygen concentration comprises increasing the dissolved oxygen concentration.

16. The method of claim 15, wherein the dissolved oxygen concentration may be increased by: introducing oxygen or a gas containing oxygen into the electroless plating solution and diffusing the introduced oxygen or gas containing oxygen in the electroless plating solution.

17. The method of claim 15, wherein the dissolved oxygen concentration may be increased by increasing a surface area of the electroless plating solution exposed to air.

18. The method of claim 1, wherein regulating the dissolved oxygen concentration comprises reducing the dissolved oxygen concentration.

19. The method of claim 18, wherein the dissolved oxygen concentration may be reduced by introducing an inert gas into the electroless plating solution.

20. The method of claim IS, wherein the dissolved oxygen concentration may be reduced by pulling a vacuum.

21. The method of claim 1, wherein the regulated range is in a range between approximately 0.6 PPM and approximately 1.6 PPM.

22. The method of claim 1 , wherein the regulated range is in a range between approximately 0.7 PPM and approximately 1.5 PPM.

23. The method of claim 1, wherein the regulated range is in a range between approximately 0.8 PPM and approximately 1.4 PPM.

24. The method of claim 1, wherein the regulated range is in a range between approximately 0.9 PPM and approximately 1.3 PPM.

25. The method of claim 1 , wherein the regulated range is in a range between approximately 1.0 PPM and approximately 1.2 PPM.

26. The method of claim 1, wherein the determination of witether the at least one catalytic fine line or feature initiated at approximately the same time as the at least one catalytic standard line or feature comprises:

examining a surface of the at least one catalytic standard line or feature for evidence of initiation;

examining a surface of the at least one catalytic fine line or feature for evidence, or lack thereof, of initiation; and

comparing the evidence of initiation for the at least one catalytic standard line or feature to the evidence, or lack thereof, of initiation for the at least one catalytic fine line or feature;

wherein the at least one catalytic fine line or feature is determined to have initiated at approximately the same time as the least one catalytic standard line or feature if the at least one catalytic fine line or feature exhibits approximately the same evidence of initiation as that of the at least one catalytic standard line or feature.

27. The method of claim 1 , wherein the determination of whether the at least one catalytic fine line or feature etched prior to initiation comprises:

examining a shape of the at least one catalytic fine line or feature; and

comparing the shape of the at least one catalytic fine line or feature to a shape of a corresponding line or feature in a source design; wherein the at least one catalytic fine line or feature is determined to have etched prior to initiation if the at least one catalytic line or feature exhibits narrow portions, breaks, or discontinuities that do not exist in the corresponding line or feature in the source design.

28. The method of claim 1, wherein the dissolved oxygen concentration is monitored by dipping a dissolved oxygen meter into the electroless plating solution.