Etching process, metal adhesion

A process has been developed using Semitool s patent-pending ECD seed layer deposition. This process is capable of depositing a copper film on very thin PVD copper flash layers that are used to provide adhesion for the ECD seed. The proprietary chemistry was developed so as not to etch the copper adhesion layer, and it is able to convert copper oxide to copper metal. Submicron trenches and vias have been successfully filled after the ECD seed process. 

Applications that are relevant to the topic of adhesion include the determination of the growth kinetics and densification of polymer films at surfaces, quahty control of anodization and other surface-modification pre-treatments, measurement of adsorption and determination of molecular orientation and compaction of adsorbed layers and Lang-muir-Blodgett films, detection of surface damage in plasma-etching processes and measurements of thinning of lubricant films. Metallization from the solution or vapour phase can be studied up to the stage at which the metal becomes opaque (around 40-nm thick for most metals). 

Before electroless plating plastic parts, the surfaces have to be treated to ensure good adhesion. The etching process usually involves the use of a chromic acid solution to provide a microscopically roughened surface to the plastic part. The catalytic process is sometimes referred to as seeding. Here very small particles of an inactive noble metal catalyst, normally palladium, are deposited into the micro-cracks created during the etching process. The palladium will act as active catalyst sites for chemical reduction of the electroless... 

Because sputtering deposition covers the sloped wall of vias, this technique is also suitable for the metallization of vias patterned in a photosensitive dielectric, vias formed through laser ablation, and wet-etched vias in poly-imide. However, it is difficult to sputter a thick metal film, because stress in the deposited film leads to poor adhesion. The typical metal thickness is around 2 pm. Therefore, the vias are partially filled and a staircase or staggered via layout is normally used, which limits interconnect density. In addition, the interconnect lines have sloped sidewalls because both vertical and lateral etching occur in the wet-etching process. 

Incoming Copper. The quality of the surface of the copper is very important for achieving good solder mask adhesion. All traces of the etch resist metallization, t icaUy tin or solder, must be removed prior to the solder mask surface preparation process. Solder mask does not adhere well to tin or solder residues or tin-copper intermetallic surfaces. 

A very good alternative to abrasive or chemical cleaning is to impart an oxide to the copper surface. If the copper has not been cleaned or if there are residual etch resist metals on the surface, the copper will not oxidize. The oxide provides a fine stmcture and microronghness for very good adhesion. When using this techniqne, the fabricator shonld use a reduced oxide so that cleaning chemistries in subsequent processes will not attack the oxide layer and cause adhesion loss at the mask-copper interface. 

Fluoroplastic films such as FEP can be metallized by vacuum deposition. Metal adhesion is enhanced if the surface has been treated for adhesion by sodium etching or other procedures. Untreated general purpose FEP film may be vacuum-metallized for some applications depending upon the specific metal and deposition process. Copper, aluminum, silver, gold, and some metallic oxides have been applied to FEP film by vacuum metallization.f ]... 

There are a number of other screen process formulations, including the use of sublimation dyes, printable resists, and printable liquid adhesives, which can also benefit from substrate pretreatment. When heat and pressure convert sublimation dyes into a gas phase decoration that is typically transferred from a paper carrier to the sublimate (material to be decorated), the hydrophilicity of the receiving sublimate is key. The same can be said about the need to remove low molecular weight organics to heighted the hydrophilicity of metal surfaces which must accept screen-printable resists prior to the final acid etching process. And, if adhesive patterns are required for bonding two similar or dissimilar materials, the need for... 

The important beneficial effects that substrate roughness can bring were firmly established in the late sixties and early seventies, principally as a result of work in two areas. The first was associated with the electroless deposition of metals onto plastics such as ABS and polypropylene. In the process the plastics must be etched in a way which produces pits on a micrometre scale. Such a topography had been shown to be a necessary, but not sufficient condition for adequate adhesion [40]. 

Many applications of novolacs are found in the electronics industry. Examples include microchip module packaging, circuit board adhesives, and photoresists for microchip etching. These applications are very sensitive to trace metal contamination. Therefore the applicable novolacs have stringent metal-content specifications, often in the low ppb range. Low level restrictions may also be applied to free phenol, acid, moisture, and other monomers. There is often a strong interaction between the monomers and catalysts chosen and attainment of low metals levels. These requirements, in combination with the high temperature requirements mentioned above, often dictate special materials be used for reactor vessel construction. Whereas many resoles can be processed in mild steel reactors, novolacs require special alloys (e.g. Inconel ), titanium, or glass for contact surfaces. These materials are very expensive and most have associated maintenance problems as well. 

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