Browse Prior Art Database

SINGLE POINT ANODIC BONDING PROCESS FOR X-RAY MASKS

IP.com Disclosure Number: IPCOM000006823D
Original Publication Date: 1993-Mar-01
Included in the Prior Art Database: 2002-Feb-05
Document File: 4 page(s) / 147K

Publishing Venue

Motorola

Related People

William A. Johnson: AUTHOR [+3]

Abstract

The image placement distortion of an x-ray mask can be a significant component of the overlay error budget. For the largest process latitude in manufactur- ing, it is important to minimize mask distortions. One of the most important sources of distortion in x-ray masks comes from mask tiring when the mask is clamped in the stepper for alignment and exposure. The purpose of this note is to document a mask fabrication, method that minimizes this error component.

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MOTOROLA INC. Technical Developments Volume 18 March 1993

SINGLE POINT ANODIC BONDING PROCESS FOti X-RAY MASKS

by William A. Johnson, Whitson G. Waldo and Kuniaki Yamazaki

  T'he image placement distortion of an x-ray mask can be a significant component of the overlay error budget. For the largest process latitude in manufactur- ing, it is important to minimize mask distortions. One of the most important sources of distortion in x-ray masks comes from mask tiring when the mask is clamped in the stepper for alignment and exposure. The purpose of this note is to document a mask fabrication, method that minimizes this error component.

  The standard x-ray mask structure is outliied in Fig- ure 1. It consists of a thin membrane that supports the patterned x-ray absorber features, a thick silicon supporting wafer snmhs, and a Pyrex glass holding frame that is clamped in the x-ray alignment tools when the mask is exposed. In one of the typical x-ray mask fabri- cation processes, tint the absorber features are patterned on a thick silicon wafer overcoated with the membrane material. This structure is bonded to the Pyrex holding frame and the membrane is formed by etching the sili- con wafer away from the membrane in the defined expo- sure field area. Anodic bonding of the silicon wafer to the ring is one of the preferred ways of attaching the silicon wafer to the Pyrex holding frame due to the very strong chemical bond obtained between the silicon wafer and the Pyrex interfaces. Typically, the whole wafer is anodically bonded.

  To date the standard piactice used to minimize tix- turing induced pattern placement errors is to hold x-ray masks "kinematically" in the critical steps during fabri- cation (ebeam exposure tool during patterning) and in the stepper exposure tool for x-ray patterning. This approach is costly (a Suss x-ray al&e, kinematic mask holder costs -3OOK$) and is still subject to inducing distortions of the order of 5-10 mn (maximum vector) if not properly implemented (see Figure 2).

  An akemz&ve mask fabrication technique that uses a single point "glue" bond b&vtxn the wafer and the glass holding frame (1) has been reported (see Fire 3). It has been found that the mounting forces !?om the step- per will not be transmitted through this single bonding point into the membrane tiea, thereby essentially elimi- nating (52 nm-maximum vector) any fixturing induced pattern distortion error...