Substrate cleanliness

As the width and thickness of IC layers and patterns continue to shrink into the submicrometer range, Si02 layers need to be fabricated of 5—20 nm thickness. These thin oxides have properties that are very sensitive to the substrate cleanliness and uniformity, gas purity, and temperature control. 

Adhesion values are also influenced by the method of coating. Aqueous, extruded melt, and solvent coatings all wet substrate surfaces differently. The condition of the substrate (cleanliness, degree of oxidation, etc.) also has a marked influence on the adhesion values attained. ... 

As with all adhesives, substrate cleanliness is the key to strong, durable bonds. It is essential that all mold releases, oils, residual acids, etc., be removed initially. This can best be accomplished by wiping the surface with a cloth wetted with acetone or naphtha. If the surface itself is acidic, a wash in a mildly alkaline solution or treatment with a cleaning-activator solution is recommended. For metal bonding, the surface should be solvent cleaned, abraded with sandpaper, followed again by a solvent wash. 

Metallization layers are generally deposited either by CVD or by physical vapor deposition methods such as evaporation (qv) or sputtering. In recent years sputter deposition has become the predominant technique for aluminum metallization. Energetic ions are used to bombard a target such as soHd aluminum to release atoms that subsequentiy condense on the desired substrate surface. The quaUty of the deposited layers depends on the cleanliness and efficiency of the vacuum systems used in the process. The mass deposited per unit area can be calculated using the cosine law of deposition ... 

Surface cleanliness of the substrate is important for all thermal spray processes. Degreasing, which formerly often reHed on freons or chlorinated... 

The tltanla-based thin film catalyst models were constructed by first oxidizing the titanium surface In 5 x 10 torr of O2 for approximately 30 minutes at 775 K. This produced an AES llneshape consistent with fully oxidized TIO2. The metal was then vapor deposited onto the oxide support with the latter held at 130 K. The thickness of the metal overlayer and Its cleanliness were verified by AES. After various annealing and adsorption procedures, these thin films were further characterized using SSIMS, AES and TDS. For comparison, some work was done with Pt on Al20s. In this case a Mo foil covered with AI2O3 replaced the Tl(OOOl) substrate. 

Sulfiir-anchored SAMs and thin films, mostly from organosulfiir precursors, have been discussed at length by a number of authors [10, 181]. SAMs of organosulfiir compounds (thiols, disulfides, sulfides) form on gold substrates by spontaneous adsorption from either the liquid or the vapor phase. A number of experimental factors can affect the formation and structure of SAMs such as choice of solvent, temperature, concentration, immersion time, purity of adsorbate, oxygen concentration in solution, cleanliness, and structure of the adsorbate. Interestingly, the... 

For the present purpose, we take the term ultrathin to refer to an evaporated metal film where the concentration of metal on the substrate is low enough for the film to consist of small isolated metal crystals. If the average concentration of metal atoms on the substrate is of the order of a monolayer or less, the metal crystals are small enough for ultrathin films to serve as models for highly dispersed metal catalysts, but where surface cleanliness and catalyst structure can be better controlled. 

Recently, ultrathin evaporated films have been used as models for dispersed supported metal catalysts, the main object being the preparation of a catalyst where surface cleanliness and crystallite size and structure could be better controlled than in conventional supported catalysts. In ultrathin films of this type, an average metal density on the substrate equivalent to >0.02 monolayers has been used. The apparatus for this technique is shown schematically in Fig. 8 (27). It was designed to permit use under UHV conditions, and to avoid depositing the working film on top of an outgassing film. ... 

As in all processing steps, cleanliness of the exposure hardware is of paramount importance. Any particle that lands on the resist prior to exposure, will shield the film underneath the particle from the exposing radiation and give rise to opaque spots in the case of positive resist, or pinholes in the case of negative resists. Particulate contamination is especially troublesome with electron beam and ion beam systems where the probability of a particle landing on a substrate is increased relative to other techniques because of the much longer exposure times involved. 

ISO 8501 (all parts). Preparation of steel substrates before application of paints and related products - Visual assessment of surface cleanliness. 

Preparation of an extremely clean substrate is an absolutely essential step in successful preparation of film electrodes. Neglecting this step is an excellent means of assuring poor quality or even unusable films. For complex devices produced by photolithography with very small feature size, even the most minute dust or particulate contamination can ruin a device. Thus, care for cleanliness and particle removal becomes an increasingly heroic enterprise as the feature size decreases. 

Deposition of metals by vacuum evaporation is normally carried out in a high-vacuum system (10"5-10 8 torr). The high vacuum is necessary to insure that the mean free path of evaporated particles is long enough to reach the substrate, but perhaps more importantly, to maintain cleanliness of the substrate. 

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