Fig. 5. Model of anisotropic etching in evacuated wet system. Effective diffusion barrier was formed by small hydrogen bubbles on aluminum side wall surface. Here, open and filled circles indicated hydrogen and phosphoric acid, respectively, and arrows show the flux of each molecule.shown in Fig. 4 as a function of pressure. This shows that lateral etching uniformity was improved remarkedly with decreasing pressure. That is, the deviation of 0.2 ~m at atmospheric pressure decreased to 0.03 ~m (5%) at 30-100 torr and increased again at still lower pressures. This indicates clearly that evacuated wet etching system offers excellent lateral etching uniformity. Thus, one is able to achieve fine pattern electrode etching with 1.0-1.2 ~m linewidth, by the evacuated etching, if the end point detection technique employing electrochemical potential is used.In wet aluminum etching, hydrogen bubbles are generated on the aluminum film by the chemical reaction with phosphoric acid. Therefore, control of hydrogen bubble removal is important to the improvement of etching uniformity and reproducibility. The fact that the etch rate of aluminum films normal to the wafer surface was constant with time while the lateral (undercutting) etching rate decreased with decreasing pressure suggests the model shown in Fig. 5, which shows the flux of hydrogen bubbles (open circles) and ions of phosphoric acid (filled circles) during the etching. It is clear from pressure and time variations of the etch rate that the removal rate of hydrogen bubbles through the very narrow channel region (1 ~m thick) beneath the photoresist can apparently be restrained with decreasing pressure. Detailed features of this model are reported elsewhere (3). ConclusionsThe consideration of the evacuated wet etching of A1/Si (2%) electrodes resulted in the following conclusions.1. The etch rate of aluminum films normal to the wafer surface was nearly constant at a value of approximately 0.18 ~m/min over the pressure range studied.2. The amount of lateral etching in the grooves decreased with decreasing pressure, resulting in increased linewidth. Typical undercutting of the conventional (isotropic) wet etching was 0.8 ~m. This was reduced to 0.42 ~m at 9 torr. Thus, the etching has changed from isotropic to quasi-anisotropic.3. Uniformity of lateral etching within a wafer was also improved with decreasing pressure. The standard deviation for side etching within a wafer reaches a minimum value of 0.03 ~m (5%) at 30-100 torr. This is greater uniformity than conventional wet and dry etchings.4. Overetching for fine pattern aluminum electrodes can be reduced markedly by precisely monitoring the end point. This leads to 1.0-1.2 ~m linewidth etching including the deviation. ABSTRACTThe reaction of silane and nitrous oxide at high temperatures and low pressures was investigated for a large range of mole ratio of the reactants. For a nitrous oxide/silane mole ratio of approximately 100, silicon dioxide having the stoichiometric refractive index of 1.45 is obtained for growth...

The growth of silicon‐rich and stoichiometric oxide from silane and nitrous oxide by low pressure chemical vapor deposition in a vertical‐flow reactor has been examined.