In the electroless plating of dielectric substrates, sensitization and activation pretreatments are used to provide catalytic sites. The presence of the catalytic sites provides a path for the initiation of the electroless plating process. Based upon findings in this laboratory, a new sensitizing composition containing tin(II) and tin(IV) compounds was developed. This sensitizer was found to be particularly useful in the case of hydrophobic surfaces, and has resulted in good uniformity of metallic coverage on hydrophobic surfaces. In preparing the final sensitizer composition, the use of aged stannic chloride solution was responsible for the improved performance. The present investigation reveals the various chemical changes taking place during the aging of stannic chloride solution. Based upon the current findings, it is believed that during the aging process, a slow formation of a fl-stannic acid takes place. This material is a polymeric form, which causes a light scattering effect to take place. It is the presence of ~-stannic acid and its interaction with tin (II) that accounts for the improvement in sensitizer performance.It has been demonstrated (1-3) that contact angle measurements can be an effective technique by which sensitizer solutions may be evaluated. It was also demonstrated (1, 2) that the addition of stannic compounds to tin-type sensitizers can have a major influence on the effectiveness of such solutions, especially when hydrophobic substrates are employed. The results obtained (1, 2) employed sensitizers prepared by aging the stannic chloride stock solution prior to mixing with SnCl~ solution. Specially prepared and aged (4-6) stannic chloride solutions are most effective when added in low concentrations to solutions for the sensitization of dielectric substrates. By contrast, the startnic chloride normally present in typical stannous chloride does not result in improved wetting in spite of the fact that it is present in the same approximate concentration range as the added aged stannic chloride concentrations.However, according to Cohen et al. (7,8) the presence of stannic ions in conventional sensitizers (SnC12/ HC1) constitutes the basis for a proposed mechanism of sensitization. Employing the Mossbauer spectroscopy of tin, a model based upon colloidal stannic hydroxide (hydrated oxide) with bound stannous ions on the colloid surface was proposed. This colloid is present in bulk solution as well as on the sensitized surface. Sard (9), using electron diffraction had shown that sensitized films derived from conventional SnC12 sensitizers are adsorbed clumps of material several hundred angstroms in diameter. Luce et al. (10) and Drotar et al. (11) also described sensitizers in which excess stannic chloride was added to conventional sensitizer media (SnC1JHC1). However, in all cases, no attempt was made to precondition the stannic solution while in the present work, the stannic halide solutions are first prepared, allowed to age, and then mixed with the stannous chloride solution. Bernhardt (12...

Passivation coatings are widely used to improve the performance and reliability of silicon devices of various types, ranging from discrete mesa‐type diodes and transistors to complex planar silicon integrated circuits, and including both hermetic and plastic‐encapsulated devices. This paper reviews the materials and techniques used to apply passivation coatings to completed silicon devices. Principal production techniques used in passivation of silicon devices include thermal oxidation, high‐temperature diffusion, high‐temperature chemical vapor deposition of Si3N4 or Al2O3 , low‐temperature chemical vapor deposition of glasslike SiO2 or phosphosilicate layers (deposited at approximately 400°C), rf sputtering of SiO2 , mechanical deposition of glass frit layers which are subsequently fused, and application of organic polymer films.The effects of passivation layers on silicon device reliability are discussed, and the interrelationships among the silicon device, the passivation layer or layers used and the final encapsulation are indicated. Pertinent references on passivation and on related topics are cited in the text.

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Film deposition and etching techniques for producing multilevel metallized structures on complex devices are reviewed. Emphasis is placed on process procedures for controlled contouring of topographic features induced during pattern etching, techniques for ensuring coverage by deposited films of topography introduced into the substrate, and dielectric deposition procedures that enhance breakdown strength and minimize pinholes. Broadly, the classes of processes discussed are the following: (i) metallization techniques that reduce susceptibility to electromigration and hillock formation and that ensure step coverage; (ii) dielectric deposition techniques that result in good step coverage, low stress, and low pinhole density; (iii) photolithographic and etching techniques that can taper steps generated in the films and that do not form pinholes.

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