Drying and gas or vapor contact with solids – Process – With nondrying treating of material
Patent
1993-03-02
1994-11-08
Bennet, Henry A.
Drying and gas or vapor contact with solids
Process
With nondrying treating of material
34413, 34 62, F26B 700
Patent
active
053615158
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The invention relates to a field of microelectronics, electrical engineering, and more particularly--to a method of production of a protective polymer coating applied onto a surface of an article from a solution, and a device for effecting thereof.
BACKGROUND ART
In the planar technology of semiconductor devices and microcircuits widely known is a method of drying a protective polymer coating applied onto a surface of an article from a solution, including a stage of holding the coating at temperatures of the process room, a stage of subsequent holding at an elevated temperature under an excessive pressure, and a stage of cooling. The method is intended to tackle the problems of producing high-quality defect-free polymer films and maintaining their protective properties during a certain period of time. The protective properties of coatings are greatly affected by microcracks, blisters, which are formed and propagated depending on physico-chemical processes, occurring during drying (as used herein drying is a process of escape of a solvent from the polymer coating).
Drying-out of the coating material (drying) includes the processes of transfer of the solvent in the polymer itself (liquid diffusion), in gaseous atmosphere (gas diffusion) and a transition of the solvent from the liquid state into vapor (a phase transformation of the first kind). Kinetic characteristics of the above-indicated processes determine the mechanism of escape of the solvent from the coating.
The initial stage of drying, which is carried out at temperatures of the process room (20.degree.-24.degree. C.), is characterized by a high content of the solvent in the polymer coating and high rates of its liquid diffusion. As the coating becomes dry, the solvent diffusion in the polymer material is retarded, which leads to lowering the drying rate.
It is known that by holding the polymer coating only at temperatures of the process room, it is impossible to obtain high values of protective properties (adhesion, defect-free condition).
Therefore, the temperature is held at the second stage at an elevated temperature. The temperature is selected for reasons of necessity to obtain a high flow of the polymer for increasing the rate of diffusion and relieving internal stresses of the coating, but with reference to thermostability of the polymer material, since a high temperature and its long action result in undesirable reactions of thermodestruction or thermopolymerization.
At the initial stage of holding of the polymer coating at an elevated temperature there registers a sharp increase of the rate of escape of the solvent. Having then reached its maximum value, this rate drops to zero.
It is thought that in parallel with evaporation of the solvent, on the external surface of the coating there occurs a phase transition (evaporation) also on the surface of gas microcracks, present in the coating (internal vapor formation).
Experiments confirm a connection between internal vapor formation and protective properties of, for example, a photoresistive coating. Kinetic characteristics of the process of evaporation of the solvent inside a microcrack are determined by a great number of factors: content of the solvent in the coating, pressure of the solvent vapor, initial forms and sizes of microcavities, density of distribution of microcracks in the coating volume, coefficient of liquid diffusion of the solvent, toughness and surface tension of the polymer coating, and by temperature of the coating.
The increase of the rate of internal vapor formation is accompanied by increase of unsoundness and decrease of adhesion of the coating to an article. The phenomena occur as a result of propagation of microcracks, saturated with vapors of the solvent, and subsequent opening of them on the coating external surface.
The location of closed microcracks relative to the coating external surface and the coating-to-article boundaries exert a great effect on the process of defects formation. Thus, microcracks located close to the external surface of th
REFERENCES:
patent: 4621439 (1986-11-01), Maw-Chyi
patent: 4908231 (1990-03-01), Nelson
V. P. Lavreschev, et al. "The Investigation of the Mechanism for Removing . . . photoresist Film", Microlectronics Tech, Series 3, 1975, pp. 58-65.
V. V. Anufrienko, et al., Unit AII-2 for Shaping Fluoro-Resistive Coatings, Registration Date of Article, Jun. 1, 1978.
Bennet Henry A.
Nauchno-Prorvodstvennaya Firma Aktsionernoe Obschestov Zaknytogo
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