Combined CMP and plasma etching wafer flattening system

Details Combined CMP and plasma etching wafer flattening system Combined CMP and plasma etching wafer flattening system

1999-03-01

2001-07-03

Mills, Gregory (Department: 1763)

Adhesive bonding and miscellaneous chemical manufacture

Differential fluid etching apparatus

With microwave gas energizing means

C118S504000

Reexamination Certificate

active

06254718

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a wafer flattening process for flattening the surface of a wafer polished to a mirror surface in a previous process to a further high precision by a plasma etching apparatus, a wafer flattening system, and a wafer.
2. Description of the Related Art
FIG. 15
is a process diagram showing an example of a wafer flattening process of the related art.
In
FIG. 15
, reference numeral
100
is a chemical mechanical polishing (CMP) apparatus, while reference numeral
200
is a plasma etching apparatus.
In this wafer flattening process, first, in the CMP apparatus
100
, a wafer W held and pressed by a carrier
101
is made to rotate in an opposite direction to a rotating platen
102
to chemically mechanically polish the surface Wa of the wafer W to a mirror surface by a polishing pad
102
a
of the platen
102
. Suitably thereafter, the wafer W is conveyed to the plasma etching apparatus
200
where the surface Wa is turned upward and the wafer W held by a holder
201
. Next, ion or radical or other activated species gas G produced in a plasma generator
202
is sprayed from a nozzle
203
to the surface Wa of the wafer W to locally etch a portion of the surface Wa thicker than the reference thickness value (hereinafter referred to as a “relatively thick portion”).
Specifically, as shown in
FIG. 16
, the holder
201
is made to move to position where the nozzle
203
directly above a relatively thick portion of the wafer W and locally etch the relatively thick portion by the activated species gas G from the nozzle
203
to further flatten the surface Wa.
The wafer flattening process of the above related art, however, suffered from the following problems.
The activated species gas G sprayed from the nozzle
203
is a fluid and etches a substance by a chemical reaction with that substance. Accordingly, if the conditions of the region of spraying of the activated species gas G differ, the amount of etching of the substance also changes.
That is, as shown in
FIG. 16
, when the nozzle
203
is positioned at the inside portion of the wafer W, since the activated species gas G is sprayed under evacuated environment existing only wafer, the activated species gas G is sprayed almost symmetrically toward the center of the nozzle, thereby reacting silicon and the like of the surface Wa and etching relatively thick portion thereof at predetermined amount.
In contrast, shown in
FIG. 17
, when the nozzle
203
is positioned over the outer peripheral portion of the wafer W, the activated species gas G is sprayed across the outer peripheral portion of the wafer W and the holder
201
and activated species gas G causes a chemical reaction with the holder
201
formed by aluminum etc. As a result, the product A of the chemical reaction between the holder
201
and the activated species gas G deposits on the surface etc. of the outer peripheral portion and inhibits the etching of the outer peripheral portion and the amount of etching of the outer peripheral portion ends up drastically falling.
Further, as shown in
FIG. 18
, when there is a level difference between the surface Wa of the wafer W and the surface of the holder
201
, the flow of the activated species gas G becomes disturbed at the level difference portion, more activated species gas G ends up flowing to the outside of the wafer W, and the amount of etching of the outer peripheral portion drastically falls.
In this way, in the wafer flattening process of the related art, due to the difference in the conditions between the inside portion and the outer peripheral portion of the wafer W, the outer peripheral portion of the wafer W remains as shown in FIG.
19
and the fall in the total thickness value (TTV) of the wafer W becomes a problem.
SUMMARY OF THE INVENTION
The present invention was made to solve the above problems and has as its object to provide a wafer flattening process designed to flatten the entire surface of the wafer to a higher precision by projecting the fall in the etching rate at the outer peripheral portion of the wafer and forming the outer peripheral portion of the wafer thinner in advance before plasma etching the entire surface of the wafer, a wafer flattening system, and a wafer flattened by the same.
To achieve the above object, according to an aspect of the present invention, there is provided a wafer flattening process comprising: an outer peripheral portion processing step for processing the outer peripheral portion of the wafer so that a maximum thickness at a predetermined width of the outer peripheral portion of the wafer surface becomes not more than a minimum thickness at a portion inside from the outer peripheral portion; and a plasma etching step for locally etching a relatively thick portion by spraying plasma activated species gas from a nozzle of a predetermined diameter of opening toward the corresponding relatively thick portion of the wafer surface after the outer peripheral portion processing step.
In this configuration, it is possible to process the outer peripheral portion of the wafer in the outer peripheral portion processing step, then etch the entire surface of the wafer in the plasma etching step. At this time, the etching rate of the outer peripheral portion becomes lower than the etching rate of the portion inside from the outer peripheral portion, but since the outer peripheral portion is processed so that its maximum thickness becomes not more than the minimum thickness of the portion inside from the outer peripheral portion, the situation where the fall in the etching rate causes the outer peripheral portion to remain thickly does not arise.
The outer peripheral portion processed in the outer peripheral portion processing step may be any width, but as an optimum example, the width of the outer peripheral portion is substantially the same as the diameter of the opening of the nozzle.
Further, the outer peripheral portion processing step need only process the outer peripheral portion of the wafer to a predetermined thickness. This may be achieved by various processing methods such as polishing and plasma etching.
Therefore, according to the aspect of the invention, the outer peripheral portion processing step is a polishing step which brings the surface of the wafer held by the carrier into contact with a polishing pad of a rotating platen and makes the pressing force on the outer peripheral portion of the wafer higher than the pressing force on the inside portion so as to polish the outer peripheral portion to a mirror surface. Further, as a prime example of the polishing, according to the aspect of the invention, the outer peripheral portion processing step is chemical mechanical polishing.
Further, as a prime example of application of plasma etching to this outer peripheral portion processing step, according to the aspect of the invention, the outer peripheral portion processing step comprises etching only the outer peripheral portion by spraying an activated species gas from above an etching protection plate toward the entire surface of the wafer.
In this configuration, only the outer peripheral portion not covered by the etching projection plate is etched by the activated species gas and is etched to a predetermined thickness.
Further, according to the aspect of the invention, the outer peripheral portion processing step etches the outer peripheral portion by arranging a hollow ring member of a shape corresponding to the outer peripheral portion of the wafer facing the outer peripheral portion, supplying the activated species gas into the hollow ring member, and spraying it from a plurality of holes formed at predetermined intervals in the hollow ring member.
In this configuration, the outer peripheral portion is etched by the activated species gas from a nozzle moving relative to the outer peripheral portion.
Further, the wafer flattening process of the above aspect of the invention may stand as an invention of a system by using specific apparatuses for executing the different steps.
Therefore,

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