Semiconductor device manufacturing: process – Making device or circuit responsive to nonelectrical signal
Reexamination Certificate
2001-05-30
2002-07-30
Mulpuri, Savitri (Department: 2812)
Semiconductor device manufacturing: process
Making device or circuit responsive to nonelectrical signal
C438S692000
Reexamination Certificate
active
06426237
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to micro-electromechanical devices, and more particularly to the optical planarity of micro-electromechanical device gratings.
BACKGROUND OF THE INVENTION
Micro-electromechanical spatial light modulators with a variety of designs have been used in applications such as display optical processing, printing, optical data storage and spectroscopy. These modulators produce spatial variations in the phase and/or amplitude of an incident light beam using arrays of individually addressable devices.
Chemical mechanical planarization (CMP) has become a key technology as currently practiced in the semiconductor art, for the planarization of metals and dielectrics. In micromachining, the same technique can be used on a fill layer to obtain flat surfaces. However, many of the micromachined structures typically fall into the regime of wide (>10 &mgr;m wide) recesses and sparsely populated structures. One of the difficulties encountered with CMP planarization is the “dishing” effect which occurs in the planarization of wide recesses. The “dishing” effect during planarization results in thinning of a fill layer in wide recesses and a non-planar surface. The polish rate is affected by the topology of the surrounding areas with dishing becoming worse in sparsely populated regions. Therefore, dishing problems present a severe manufacturing constraint in micromachining.
Non-uniform removal of a fill material across the wafer is also an important consideration in micromachining. When a fill layer is a sacrificial layer, it must be removed outside of the active regions in order to assure adhesion of the release layers. Any residual sacrificial material outside of the active region will be attacked during release. Conventional polishing that ensures complete removal of a sacrificial layer outside of the active region will cause over-polishing and excess removal of the sacrificial material in the active regions.
The dishing phenomenon is illustrated by reference to the schematic cross-sectional diagrams of
FIG. 1
a
and
FIG. 1
b
. Shown in
FIG. 1
a
, is a substrate
100
onto which a first layer
150
is deposited. A narrow recess
110
and the wide recess
120
are shown formed in the first layer
150
. The surface of the first layer
150
will contain small areas
130
between recesses and large areas
140
between recesses
110
and
120
. Deposited over the first layer
150
and into both the narrow recess
110
and the wide recess
120
is a blanket conformal fill layer
160
. Shown in
FIG. 1
b
are the results of planarizing through a conventional chemical mechanical planarization(CMP) method and the blanket conformal fill layer
160
as illustrated in
FIG. 1
a
. As shown in
FIG. 1
b
, the surface of the planarized filled wide recess
170
is severely dished in comparison with the surface of planarized filled narrow recess
180
. This marked contrast most resembles the large differences in the problems addressed by the semi-conductor industry versus those skilled in micro-electromechanical systems. Planarized filled narrow recess
180
has the narrow dishing experience in the semi-conductor industry, while planarized wide recess
170
has the complications experienced by the MEMS skilled artisans. A self-aligned mask formed by CMP and used within the severely dished planarized wide recess
170
would be completely polished away in any attempt to address the dishing phenomenon.
There is also shown in
FIG. 1
b
the presence of a fill residue layer
190
, formed simultaneously over the small areas
130
and large areas
140
on the surface of the first layer
150
when the blanket conformal fill layer
160
is planarized through the chemical mechanical planarization (CMP) method to form the planarized filled recesses
180
and
170
. As is understood by a person skilled in the art, when planarizing large areas of the blanket conformal fill layer
160
, generally of dimensions greater than about 1000 microns, the blanket conformal fill layer
160
will in addition to planarizing more rapidly over the wide recess
120
and forming a dish within the planarized filled wide recess
170
, simultaneously also polish more slowly over the large area
140
on the surface of the first layer
150
and leave the fill residue layer
190
formed over the large area
140
on the first layer
150
. Attempts to remove the fill residue layer
190
by further planarization will cause increased dishing of the planarized filled recesses
180
and
170
. Fill residue layers such as the fill residue layer
190
are undesirable since they impede further device processing on the planarized surface. Fill residue layers also impede ribbon attachment to end supports in electromechanical grating structures.
What is needed is a method to create an optically planar surface on the fill layer while eliminating any fill residue layers.
SUMMARY OF THE INVENTION
The need is met according to the present invention by providing a method for producing optically planar surfaces for micro-electromechanical system devices (MEMS), comprising the steps of: depositing a first layer over a substrate; forming a channel in the first layer wherein the channel has a depth defined by a thickness of the first layer and a width greater than 10 microns; depositing a second layer over the first layer wherein the second layer has a thickness greater than the depth of the channel and is composed of a different material than the first layer; removing the second layer from outside the channel leaving an overlap at the edge of the channel; and polishing the second layer that fills the channel to obtain an optically planar surface for the MEMS device.
The present invention achieves technical advantages by intentionally removing the second layer outside of the active regions prior to chemical mechanical polishing.
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Brazas, Jr. John C.
Jech, Jr. Joseph
Kowarz Marek W.
Lebens John A.
Eastman Kodak Company
Mulpuri Savitri
Shaw Stephen H.
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