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Overlay and Process Bias Monitor Measured by Voltage Contrast Scanning Electron Microscopy

IP.com Disclosure Number: IPCOM000036779D
Original Publication Date: 1989-Oct-01
Included in the Prior Art Database: 2005-Jan-29
Document File: 2 page(s) / 32K

Publishing Venue

IBM

Related People

Bentson, LR: AUTHOR [+2]

Abstract

Patterns in two levels of materials, at least one of which is a conductor, are measured for overlay and process bias with a special monitor observed by scanning electron beam microscope (SEM) voltage contrast due to beam charging. Measurement of alignment of a conductor pattern to a via hole pattern in an insulating layer over a doped substrate is described to illustrate the method. More detail may be found in the paper "An Overlay Vernier and Process Bias Monitor Measured by Voltage Contrast SEM" by Edmund J. Sprogis, published in the Proceedingsof the 1989 IEEE International Conference on Microelectronic Test Struc- tures, March 15, 1989, Edinburgh, Scotland.

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Overlay and Process Bias Monitor Measured by Voltage Contrast Scanning Electron Microscopy

Patterns in two levels of materials, at least one of which is a conductor, are measured for overlay and process bias with a special monitor observed by scanning electron beam microscope (SEM) voltage contrast due to beam charging. Measurement of alignment of a conductor pattern to a via hole pattern in an insulating layer over a doped substrate is described to illustrate the method. More detail may be found in the paper "An Overlay Vernier and Process Bias Monitor Measured by Voltage Contrast SEM" by Edmund J. Sprogis, published in the Proceedingsof the 1989 IEEE International Conference on Microelectronic Test Struc- tures, March 15, 1989, Edinburgh, Scotland.

Referring to the figure, a series of small via holes 2 in an insulating layer is the monitor pattern for the insulating layer mask level. Doped substrate is exposed through the etched holes 2. Larger squares 4 of metal form the metal level monitor pattern. Metal squares 4 are larger and on a smaller pitch than via holes 2.

Contact of substrate to metal squares 4 is determined by observing the monitor pattern in a SEM. Metal squares 4 in electrical contact with the substrate lose the beam charge quickly, thus providing a bright secondary electron image. Metal squares 4 insulated from the substrate become charged by the beam and have a dark SEM image. Thus, there is sharp brightness contrast between metal squares 4, ma...