Partial photoresist etching

Details Partial photoresist etching Partial photoresist etching

2001-10-11

2004-02-03

Duda, Kathleen (Department: 1756)

Radiation imagery chemistry: process, composition, or product th

Imaging affecting physical property of radiation sensitive...

Making electrical device

C216S041000

Reexamination Certificate

active

06686129

ABSTRACT:

FIELD OF THE INVENTION
This invention relates generally to the etching process used in semiconductor manufacture, and more particularly to an inventive partial photoresist etching process.
BACKGROUND OF THE INVENTION
Patterning is one of the basic steps performed in semiconductor processing. Patterning is also referred to as photolithography, masking, oxide or metal removal, and microlithography. Patterning enables the selective removal of material deposited on a semiconductor substrate, or wafer, as a result of deposition. The process of depositing layers and removing selective parts of them, in conjunction with other processes, permits the fabrication of semiconductor devices.
Patterning can be a dry etching or a wet etching process. Wet etching refers to the use of wet chemical processing to selectively remove the material from the wafer. The chemicals are placed on the surface of the wafer, or the wafer itself is submerged in the chemicals. Dry etching refers to the use of plasma stripping, using a gas such as oxygen (O
2
), C
2
F
6
and O
2
, or another gas. Whereas wet etching is a low-temperature process, dry etching is typically a high-temperature process.
One common type of dry etching uses photoresist, which is described in conjunction with
FIGS. 1A-1E
. In
FIG. 1A
, a stop layer
102
is initially deposited. The stop layer
102
may be a type of oxide, and prevents the etchant from removing material beyond the stop layer
102
. Next, there is a layer of polysilicon
104
, which is specifically not doped, and of which an −type region
106
and a P+ type region
108
have been specifically doped. There is also a hard mask
110
. The hard mask
110
may be silicon dioxide, silicon nitride, an inorganic anti-reflective coating, or another type of mask. Finally, there is a layer of photoresist
112
.
In
FIG. 1B
, a mask
114
is placed over the photoresist
112
. The mask
114
includes dark regions
116
and
118
. Ultraviolet rays
120
are then applied, which develops, or exposes, those parts of the photoresist
112
not directly underneath the dark regions
116
and
118
, which are indicated as the photoresist
112
′. The unexposed photoresist
112
is unpolymerized, whereas the exposed photoresist
112
′ is polymerized.
In
FIG. 1C
, the photoresist
112
′ that was polymerized as a result of exposure to the ultraviolet rays
120
is developed, or removed. The only remaining photoresist is the unpolymerized photoresist
112
beneath the dark regions
116
and
118
. Thus, the remaining photoresist
112
has a pattern corresponding to the dark regions
116
and
118
of the mask
114
.
In
FIG. 1D
, the mask
114
, the −type region
106
, the P+ type region
108
, and the polysilicon
104
are etched. The only parts of the mask
114
, the regions
106
and
108
, and the polysilicon
104
that remain are those underneath the remaining photoresist
112
. Finally, in
FIG. 1E
, the remaining, unpolymerized photoresist
112
is stripped, resulting in an −type stack
122
, and a P+ type stack
124
.
Another type of dry etching does not use photoresist. This photoresist-free etching instead uses the hard mask itself for the patterning of the underlying polysilicon. This type of etching is described in conjunction with
FIGS. 2A-2D
. In
FIG. 2A
, a stop layer
102
is initially deposited. Next, there is a layer of polysilicon
104
, which is specifically not doped, and of which an −type region
106
and a P+ region
108
have been specifically doped. Finally, there is a hard mask
110
. In
FIG. 2B
, a mask
114
is placed over the hard mask
110
. The mask
114
includes dark regions
116
and
118
. Ultraviolet rays
120
are then applied, which develops, or exposes, those parts of the hard mask
110
that are not directly underneath the dark regions
116
and
118
, and that are indicated as the hard mask
110
′.
In
FIG. 2C
, the hard mask
110
′ that was exposed to the ultraviolet rays
120
is removed. The only remaining hard mask
110
is that which was beneath the dark regions
116
and
118
. Therefore, the remaining hard mask
110
has a pattern corresponding to the dark regions
116
and
118
of the mask
114
. In
FIG. 2D
, the N-type region
106
, the P+ region
108
, and the polysilicon
104
are etched. The only parts of the regions
106
and
108
and the polysilicon
104
that remain are those underneath the remaining hard mask
114
. Thus, there is an −type stack
122
and a P+ type stack
124
.
The result of the photoresist-free dry etching process shown in
FIG. 2D
is therefore theoretically identical to the result of the photoresist dry etching process shown in FIG.
1
E. However, each of these processes has advantages and disadvantages. The photoresist of the photoresist process acts as a passivation surface, which helps to ensure the proper shaping of the profiles of the stacks
122
and
124
. That is, the passivation functionality of the photoresist ensures that the vertical surfaces of the stacks
122
and
124
are substantially perpendicular to the horizontal surface of the stop layer
102
.
Disadvantageously, however, the photoresist process poorly controls the critical dimensions of the semiconductor device being fabricated. The critical dimensions of the device are the widths of the lines and the spaces of critical circuit patterns of the device. In particular, the photoresist process frequently exhibits a proximity effect that can narrow the desired widths of the stacks
122
and
124
.
The proximity effect is shown in FIG.
3
. The mask
312
positioned over the photoresist
310
has a dark region
314
of a given width, such that ideally the width of the unpolymerized photoresist
310
′ is identical after exposure to the ultraviolet rays
316
. However, because of the proximity effect, the width of the unpolymerized photoresist
310
′ is in fact less than the width of the polymerized photoresist
310
. The stack of polysilicon
304
, doped polysilicon
306
, and hard mask
308
on top of the stop layer
302
that will result, as indicated by the arrow
318
between the dotted lines
320
and
322
, will not identically correspond to the dark region
314
. That is, the width of the stack will be less than the width of the dark region
314
. Where the stack is a critical pattern of the device, this means that the photoresist dry etching process poorly controls the critical dimensions of the device.
By comparison, the photoresist-free dry etching process provides for good control of the critical dimensions of the device being fabricated. However, the lack of photoresist in the photoresist-free process disadvantageously means that no passivation surface is present to help ensure the proper shaping of the profiles of the stacks
122
and
124
. Necking of the doped regions
106
and/or
108
may result. Necking is shown in FIG.
4
. On top of the stop layer
402
are polysilicon
404
, an −type region
406
, and a hard mask
408
forming a stack
410
. The N-type region
406
of the stack
410
has an hourglass shape, resulting from the etching of this region
406
and the polysilicon
404
underneath the hard mask
408
. The hourglass shape results during etching because there is no passivation surface to ensure the proper shaping of the profile of the stack
410
.
Therefore, there is a need for a dry etching process that avoids the disadvantages of the photoresist process and the photoresist-free process, while maintaining the advantages of both processes. There is a need for a new etching process that provides for good critical dimension control, desirably by limiting the proximity effect. There is a need for a new etching process that also provides for proper profile shaping, such as that which results resulting from using a passivation surface. For these and other reasons, there is a need for the present invention.
SUMMARY OF THE INVENTION
The invention relates to partial photoresist etching. A film on a semiconductor wafer in

Affiliated with

Also associated with

Rating

Partial photoresist etching does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with Partial photoresist etching, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Partial photoresist etching will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-3333578