General description

Where glass substrates are to be held on the processing stage by vacuum chucking, there can occur an incident of failure to ensure consistently stable holding of any glass substrates due to their warping.This session explains the production techniques to ensure steady and stable vacuum chucking of those glass substrates which have any warp.

Explanation

(1)Warped glass substrates and their vacuum holding

・Where glass substrates are loaded into the chemical process, position alignment, and other automated lines, some trouble in transfer and/or processing can result without adoption of appropriate methods for the profile and/or extent of any warp of glass substrates.
・As explained in #291, the effectiveness of vacuum-chuck holding of glass substrates greatly depends on the warp profile of glass substrates.
・Glass substrates vary in warp according to the manufacturing lot.This is due to the difference in residual stress produced on the front and back sides in the manufacturing process of glass substrates. The warp profile may be grouped into concave warp, convex warp, and combined warp (Fig.1).
・These glass substrates having a variety of warp profiles must be consistently held properly by vacuum chucking.

(2)Explanation about possible factors for failure in vacuum holding on the processing stage

・Depending on the profile and/or size of any warp of glass substrates, vacuum holding may fail.
・Regarding the glass substrates having concave warp, the central region can be vacuum-chucked but the outer region may fail to be vacuum-chucked because the vacuum chucking force is hard to act. (See #291).
・Regarding the glass substrate having combined warp, the glass substrates may be dislocated during the vacuum chucking.This is attributable to the vacuum chucking force acting unevenly because of uneven and deviated gap between the glass substrate and the processing stage (Fig.2).

(3)Solutions for failure in chucking in the vacuum holding

・To succeed in effective vacuum chucking of the central region of a glass substrate first then vacuum-chucking of the outer region after some time delay, thereby ensuring stable chucking of the glass substrate.
・Control of position and timing of the vacuum chucking may be attained as follows: For the former or control of vacuum chucking position, design the paths of hole independently for the central region and the outer region (Fig.3). For the latter or control of the timing of chucking, control the timing of the solenoid valve in the vacuum chucking control circuit.