Cleaning and liquid contact with solids – Processes – For metallic – siliceous – or calcareous basework – including...
Reexamination Certificate
1999-03-23
2004-12-14
Markoff, Alexander (Department: 1746)
Cleaning and liquid contact with solids
Processes
For metallic, siliceous, or calcareous basework, including...
C134S002000, C134S041000
Reexamination Certificate
active
06830627
ABSTRACT:
FIELD OF THE INVENTION
This invention pertains generally to compositions and processes for cleaning copper or copper alloy (hereinafter collectively referred to as copper) surfaces during the fabrication of microelectronic packages and, more particularly, to selective copper microetching at the interface or in the vicinity of noble metals and their alloys typically found at plated edge connectors, contact pads, plated through holes (PTH), and embedded resistors.
As is known in the art, there is a trend to reduce the size of microelectronic packages. This results in “dense” microelectronic packages having finer and thinner printed circuit lines, smaller diameter plated through holes, and more multilayering. One problem with making dense printed circuit boards is that the yield from the manufacture of these boards is relatively low due to such problems as poor adhesion of layers in packages, shorting or bridging caused by contaminants, and open circuits due to breaking of the microcircuit lines typically caused by harsh cleaning or galvanic etching. It has therefore become a more difficult problem since cleaning of the microelectronic packages must be performed during their manufacture, yet precise conditions must be maintained otherwise the fragile microcircuits will be irrevocably damaged during such cleaning processes.
BACKGROUND OF THE INVENTION
At the present time, cleaning of copper on microelectronic substrates is performed either by chemical means, mechanical means or a combination of both. Contaminants present during printed wiring board (PWB) manufacture include photoresist materials, residual organic and residual metallic contaminants such as alkali metals and native/metallic oxides. Metallic films comprising metal oxides and metal halides are also inadvertently deposited onto electronic packages during immersion into etchant or resist stripper baths. If mechanical means have been used for cleaning, there is the possibility that residues of abrasive particles, such as pumice, will be adsorbed on the surface of the copper.
This cleaning process also called “microetching or soft etching” is ideally designed to exclusively clean the surface of the copper without diminishing or changing the dimensions of the copper itself or attacking adjacent materials (i.e., there is complete selectivity for eliminating surface contaminants on the copper and no bulk erosion or attack of the electrical microcomponents). The benefit of such idealized cleaning is to provide microelectronic packages with reduced rates of malfunction or failure due to delamination, shorting or open circuits.
For example, it is known that corrosive chlorides can be deposited on microelectronic packages causing weakening or embrittlement of electrical connectors as well as delaminate the layers of the package resulting in current leakages or physical failure. As miniaturization of microelectronic packaging is an important target, the problem of obtaining high levels of selectivity has been exacerbated due to the fragility of microcomponents such as fine-line copper circuits. Compounding the problem of finding an ideal microetching process is the desire to provide a manufacturing process that is fast and efficient. However, typically the faster the cleaning process the lower the selectivity which can ultimately be achieved. This is well known in the art of copper polishing where it is preferred that mild chemical polishing agents are used at longer processing times in order to minimize the loss of bulk copper. It is also recognized that although numerous chemical copper-etchant compositions are known in the art of microelectronic package manufacture they cannot indescriminantly be used in this application since they, by definition, will erode the bulk of the copper. Such etchants include copper or ferric chlorides, chromium salts, alkaline-ammonia, hydrogen peroxide-sulfuric acid or nitric acid compositions, and persulfate salts. Each of these compositions has certain limitations and disadvantages as described hereinbelow.
The metal etchants, in particular the chromium salts, create a deleterious environmental impact. It is also known that chromium salts are human carcinogens; therefore, their use and disposal are especially problematic.
Nitric acid, either alone or in combination with sulfuric acid or copper nitrate, has been reported by Brittey (U.S. Pat. No. 4,695,348) to be useful for etching copper in wiring boards. However, nitrogous oxide gas is a byproduct of this process.
The alkaline-ammonia compositions are used commercially because they are relatively fast, have substantial copper-carrying capacity and are reasonably tolerant of some metal resists and some dry film resists. However, these same compositions have poor selectivity for copper versus other metals and alloys. Significant process control is required to achieve acceptable selectivity. It is also known that these compositions may not work well with fine line copper geometries. Furthermore, the dissolved copper is difficult to recover. Also, fumes from the ammonia composition present worker exposure concerns.
The hydrogen peroxide-sulfuric acid compositions, generating permonosulfuric acid, used in copper etching processes are very clean to operate and can be recycled. However, these same compositions have relatively slow etching rates and require substantial cooling for stability control due to the autodecomposition reaction of the hydrogen peroxide. Additionally, both the performance of the process and the decomposition of the peroxide are very sensitive to trace impurities via homo- or heterocatalysis. Stabilizers are necessary for peak performance but these are metal specific. Brasch (U.S. Pat. No. 4,378,270) teaches phenol-sulfonic acid for copper containing solutions. It is also known from Alderuccio, et al (U.S. Pat. No. 3,269,881) that these compositions are adversely affected by chloride or bromide ion at levels of 2 mg/liter, causing reduced etch rates. Elias (U.S. Pat. No. 4,130,455) teaches that the addition of sodium or potassium thiosulfate can counteract this effect.
But use of these additives does not address the basic problem of the catalytic decomposition of the peroxide discussed hereinabove. This decomposition has two important implications: firstly, the depletion of the peroxide in the etchant solution reduces the etchant rate; and secondly, there is potential for uncontrolled decomposition of large volumes of high temperature solutions, generating high concentrations of oxygen and increasing the safety risks therefrom. Because decomposition of the peroxide is accelerated at elevated temperatures, processing temperatures must be kept low. This adversely affects the rate of the etching process and exacerbates the already low copper-carrying capacity of the peroxide-sulfuric acid composition.
Another problem associated with using aqueous acidic solutions of hydrogen peroxide for microetching is that it typically requires a two step process. After the treatment step, a further step with diluted sulfuric acid or diluted hydrochloric acid is required due to formation of oxide films on the copper surface.
Tytgat and Magnus report in U.S. Pat. No. 4,981,553 that a combination of hydrogen peroxide, chloride ions, phosphoric acid, and phosphate and hydrogenphosphate ions, in quantities to impart a pH of 1.25 to 3, may be used as a copper polishing formulation not requiring excess working temperatures or intense mechanical agitation, however; the process under these conditions is designed to take one or more hours to obtain adequate results. Tytgat et al report that the chloride ion is added for the purpose of protecting the metal against uncontrolled local corrosion and the phosphate ions are added to maintain the desired pH range (i.e., it is added as a buffer). There is no mention or indication that the phosphate ions can function to inhibit etching of other metals in the vicinity of the copper, nor is there teaching that other oxidants can be used in this invention.
Heretofore salts of persulfate have been utilized for microet
Covert Kathleen L.
Hawley Kelly
Lauffer John M.
Moschak Peter A.
Fraley Lawrence R.
Hawley Kelly
International Business Machines - Corporation
Mark Levy & Associates
Markoff Alexander
LandOfFree
Copper cleaning compositions, processes and products derived... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Copper cleaning compositions, processes and products derived..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Copper cleaning compositions, processes and products derived... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3298481