US 5,103,367 AGranted

Electrostatic chuck using A.C. field excitation

AssigneeUnisearch Limited

InventorsChristopher M. Horwitz, Stephen Boronkay

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Abstract

An electrostatic chuck for semiconductor wafers (10) uses at least three electrodes (12, 13, 14). Two electrodes (13, 14) defining a substantially planar surface and embedded in a thin dielectric film (11), are respectively excited by a low-frequency A.C. supply (15, 16, 17, 18, 23) to produce sinewave fields of controlled amplitude and phase, provided a low resultant voltage on the wafer surface. A third electrode (12) acts as a shield electrode or as a reference point for the other two electrodes (13, 14). In addition, by controlled rates of voltage application and removal, low voltage gradients are obtained on the wafer (10); and no retentive forces exist in the dielectric medium (11). A low A.C. amplitude excitation of the chuck enables capacitive current sensing of the relative positions of the wafer (10) and the dielectric film (11), enabling simple control of voltage application to the two electrodes (13, 14).

Claims17

Dependent claims

An electrostatic chuck for semiconductor wafers comprising:

a first electrode having a planar upper surface,
a second electrode having a planar upper surface said upper surfaces of said first and second electrodes being substantially in the same plane,
and a third electrode,
a first thin insulating layer disposed over said upper surfaces of said first and second electrodes for supporting a wafer substrate thereby defining a first substrate supporting surface;
a first excitation circuit for exciting said first electrode with a sinusoidal a.c. potential,
said first excitation circuit having a first a.c. signal output connected to said first electrode and a reference signal output connected to said third electrode;
a second excitation circuit for exciting said second electrode with a sinusoidal a.c. potential,
said second excitation circuit having a second a.c. signal output connected to said second electrode and a second reference signal output connected to said third electrode;
said third electrode being a reference electrode to said first and second electrodes;
said sinusoidal a.c. potentials of said first and said second electrodes being substantially balanced thereby minimizing a voltage gradient across the substrate wafer held by said chuck.

7 more elements

Dependencies are inferred from the claim text.