U.S. patent application number 11/642049 was filed with the patent office on 2007-05-03 for selective reactive ion etching of wafers.
This patent application is currently assigned to Systems On Silicon Manufacturing Co. PTE. Ltd.. Invention is credited to Tan Kok Tong, Sim Kwang Ye.
Application Number | 20070095786 11/642049 |
Document ID | / |
Family ID | 36610175 |
Filed Date | 2007-05-03 |
United States Patent
Application |
20070095786 |
Kind Code |
A1 |
Ye; Sim Kwang ; et
al. |
May 3, 2007 |
Selective reactive ion etching of wafers
Abstract
The invention comprises a device for assisting in the selective
reactive ion etching of wafers comprising, a graphite base plate
including an opening for housing a wafer, and a plurality of
graphite strips that can be arranged over the graphite base plate
to select a site of a wafer housed in the base plate for
etching.
Inventors: |
Ye; Sim Kwang; (Jalan
Membina, SG) ; Tong; Tan Kok; (Dover Close East,
SG) |
Correspondence
Address: |
HARNESS, DICKEY, & PIERCE, P.L.C
7700 BONHOMME, STE 400
ST. LOUIS
MO
63105
US
|
Assignee: |
Systems On Silicon Manufacturing
Co. PTE. Ltd.
|
Family ID: |
36610175 |
Appl. No.: |
11/642049 |
Filed: |
December 19, 2006 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
11022014 |
Dec 23, 2004 |
|
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11642049 |
Dec 19, 2006 |
|
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Current U.S.
Class: |
216/41 ;
156/345.3; 257/E21.218; 257/E21.219; 257/E21.252 |
Current CPC
Class: |
H01L 21/67069 20130101;
H01L 21/3065 20130101; H01L 21/30604 20130101; H01J 37/32431
20130101; H01L 21/31116 20130101 |
Class at
Publication: |
216/041 ;
156/345.3 |
International
Class: |
C23F 1/00 20060101
C23F001/00 |
Claims
1.-11. (canceled)
12. A method of selectively reactive ion etching a portion of a
wafer comprising the steps of, placing the wafer in a base plate,
identifying the portion of the wafer to be etched, arranging a
plurality of strips over the wafer and base plate to cover all
portions of the wafer that are not to be etched and leave exposed
the portion of the wafer to be etched, and performing a reactive
ion etch on the wafer.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to selective reactive ion
etching of wafers and in particular to selective reactive ion
etching of wafers where the etching site can be any site on the
wafer.
[0003] 2. Description of the Prior Art
[0004] Reactive ion etchers can be used for dry isotropic etching
of dielectrics (for example, polyimides, oxides, SiO.sub.2, and
nitrides Si.sub.3N.sub.4). Reactive ion etchers can also be used
for employing reactive ion etching for the de-processing of silicon
chips.
[0005] If selective etching of a particular site on a wafer is
required there are two approaches that are currently used. In the
first approach the wafer is diced by wafer cleaving or wafer
sawing. The die to be etched is then extracted from the diced wafer
and etched. This approach has the disadvantage of destroying the
wafer and all the good dies on the wafer near the die to be
etched.
[0006] In the second approach a graphite shield with an opening the
size of the die is used to cover the wafer as shown in FIG. 1. As
can be seen in this Figure the target wafer 1 is sandwiched between
a chuck platen 2 and a graphite shield 3. The graphite shield 3
includes an opening through which etching will take place. Plasma
is then formed in the reactive ion etcher and isotropic reactive
ion etching begins. Only the portion of the wafer directly under
the opening of the graphite shield will be etched and the graphite
shield prevents etching of the rest of the wafer.
[0007] There are problems with the second approach including that
only the centre die can be etched using the graphite shield. The
shape and size of the hole in the graphite shield determines the
size and shape of wafer that will be etched using the shield. If
another shape and size wafer is to be etched another shield is
needed. Further if the wafer to be etched is not in the centre of
the die another shield will be needed. These expensive and heavy
graphite shields require fabrication with the vendor. Using this
second approach a number of different shields may be required which
is costly and inefficient.
BRIEF SUMMARY OF THE INVENTION
[0008] Accordingly in the present invention there is provided a
device for assisting in the selective reactive ion etching of
wafers comprising a base plate including an opening for housing a
wafer and a plurality of strips that can be arranged over the base
plate to select a site of a wafer housed in the base plate for
etching.
[0009] Preferably the strips and base plate are formed from
graphite. Alternatively the strips and base plate may be formed
from aluminium.
[0010] Preferably the strips are all the same length.
[0011] Preferably the strips can have different widths. If the
strips have different widths, preferably the widths are multiples
of a unit dimension.
[0012] Preferably the opening in the base plate is circular.
[0013] Preferably the site selected for reactive ion etching is
opened to reactive ion etching by arranging the strips in two
dimensions.
[0014] In another embodiment there is provided a method of
selectively reactive ion etching a portion of a wafer including the
step of placing the wafer in a base plate, identifying the portion
of the wafer to be etched, arranging a plurality of strips over the
wafer and base plate to cover all portions of the wafer that are
not to be etched and leave exposed the portion of the wafer to be
etched and performing a reactive ion etch on the wafer.
BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS
[0015] The invention will be further described by way of example
only and without intending to be limiting with reference to the
following drawings, wherein:
[0016] FIG. 1 is a view of a reactive ion etching process using a
currently used graphite shield;
[0017] FIG. 2 is a view of one embodiment of the invention showing
the layering of graphite strips over a graphite base plate and
wafer, and
[0018] FIG. 3 is a view of a second embodiment of the invention
showing the layering of graphite strips over a graphite base plate
and wafer.
DETAILED DESCRIPTION OF THE INVENTION
[0019] It should be noted the throughout the detailed description
the strips are referred to as graphite strips. This is by way of
example only and is not intended to limit the invention to graphite
strips. The strips may be any suitable material as described below.
In some embodiments the strips may be aluminium
[0020] Referring now to FIG. 2 there is shown therein an assembly
of a wafer 11, graphite base plate 12, and plurality of graphite
strips 13. For clarity some portions of the strips are shaded and
others are not to show the wafer and graphite base plate beneath
the strips.
[0021] The graphite base plate provides a base on which the wafer
sits. In preferred embodiment the graphite base plate includes a
central aperture in which the wafer is positioned. This aperture
can a circular opening be of any suitable diameter. For example the
opening can be 6 inches in diameter, 8 inches in diameter, or 12
inches in diameter. In alternative embodiments the graphite base
plate may include a base portion onto which the wafer is set and
side portions that extend from the base portion.
[0022] The surrounds of the graphite base plate around the central
aperture or ides of the base plate extend to at least the height of
the wafer and preferably beyond the height of the wafer to provide
surfaces on which the graphite strips rest.
[0023] In preferred embodiments the graphite base plate is formed
from graphite and is about half an inch think between the wafer and
one quarter of an inch thick around the central aperture.
[0024] In preferred embodiments the base plate and strips are
formed from graphite. In alternative embodiments the base plate and
strips may be formed from aluminium. The base plate must be formed
from a highly conductive material so as not to interfere with the
reactive ion etching The base plate material must not be reactive
to the gas species used in the reactive ion etching. These gases
are mainly CHF.sub.3, C.sub.2F.sub.6, CF.sub.4, and O.sub.2. The
temperature within the reactive ion etch chamber can be as high as
100.degree. C. so the melting point of the base plate material must
be a few hundred degrees Celsius. One material that meets all of
these requirements is graphite. Another suitable base plate
material is aluminium. Either of these materials may be used for
the base plate and strips.
[0025] Graphite strips 13 are positioned on the graphite base plate
after a wafer is placed on the graphite base plate. In the
preferred embodiment graphite strips 13 are all the same length. In
this embodiment the graphite strips are laid out parallel to the x
axis and y axis as shown in FIG. 2. The graphite strips may have
different widths. In this embodiment it is preferred that the
widths of the graphite strips are multiples of a unit dimension.
For example the unit dimension may be the typical width of a die
within the wafer. In FIG. 2 strips 13a and 13b are twice the width
of the remaining graphite strips. In other embodiments some
graphite strips may be 3 or more times as wide as the least wide
graphite strip.
[0026] In one embodiment in a cross-sectional or side view the
strips form a straightened Z shape with parallel upper and lower
members and a connecting member between the upper and lower
members. In preferred embodiments the connecting member is an
overlap between the upper and lower members. In alternative
embodiments the connecting member may be a separate member and is
preferably at right angles to the upper and lower members. This
arrangement of the strips allows the strips to overlap when
arranged around a target site. The overlapping arrangement assists
in protecting the wafer under the strips from the etching
process.
[0027] In use when a wafer is to be selectively etched the wafer is
first placed on the graphite base plate. If the graphite base plate
includes a circular aperture the wafer should be placed in the
aperture. After this the portion of the wafer to be etched is
identified. If the wafer if circular and placed in a circular
aperture in the graphite base plate preferably the wafer is aligned
within the base plate so that the sides of the portion of the wafer
to be etched are parallel to the sides of the base plate (as shown
in FIG. 2). The graphite strips are then placed over the wafer and
base plate to cover all areas of the wafer that are not to be
etched and leave exposed the portion of the wafer to be etched. In
FIG. 2 this is shown by the different shading on the strips. The
shaded areas show the intersection every second x-axis strip with
every second y-axis strip. The clear areas are covered by strips by
have been left clear to show the wafer and graphite base plate
below the graphite strips. Only portion 14 is left exposed. A
reactive ion etch is then performed. This etch will only affect the
exposed portion of the wafer.
[0028] The graphite strips are preferably laid in one direction and
then the other. For example, the wafer strips may be laid parallel
to the x-axis and then a second layer may be laid parallel to the
y-axis.
[0029] In alternative embodiments the axes chosen for laying the
graphite strips may be different. In these alternative embodiments
the lengths of the graphite strips may be different. It should also
be noted that the axes along which the strips are laid are
orthogonal in the preferred embodiment but need not be so long as
the wafer is covered leaving only the selected portion to be
etched.
[0030] FIG. 3 shows another embodiment of the invention. In this
embodiment there are five strips 16a-16e that run parallel to the
x-axis and eight strips 17a-17h that run parallel to the y-axis to
expose target site 15.
[0031] As can be seen in FIG. 3, the width of the strips parallel
to the y-axis range from unit dimension width, strip 17a, to three
times the unit dimension width, strips 17e, f, and h. The width of
the strips parallel to the x-axis range from twice the unit
dimension width, 16a, to seven times the unit dimension width, 16e.
The strips along one axis are laid first omitting a strip that win
cover the target site. Then the strips along the other axis are
laid, again omitting a strip that will cover the target site. This
means that all areas of the wafer are covered by two strips except
the areas in line with the target site on the x and y axes and the
target site. It should be noted that in this embodiment the size of
the target site is not the same as the minimum width of the
graphite strips.
[0032] The advantages of the present invention include that it
provides the flexibility to perform a reactive ion etch on any
selected site or location on the target wafer. The present
invention also allows target sites of differing sizes, in fact the
target site can be any size required. The invention also protects
the unexposed areas of the wafer from the reactive ion etch to
allow further testing. Another advantage is that the invention is
simple to implement and is highly effective.
[0033] During reactive ion etching chemical etching and physical
ion sputtering occurs. Some of the etch species or compounds can be
redeposited back onto the surface of the wafer. Use of the strips
of the invention prevents re-deposition of etched species or
compounds onto the non-selected areas.
[0034] The foregoing describes the invention including preferred
forms thereof Alterations and modifications as will be obvious to
those skilled in the art are intended to be incorporated in the
scope hereof as defined by the accompanying claims.
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