Radiation imagery chemistry: process – composition – or product th – Imaging affecting physical property of radiation sensitive... – Removal of imaged layers
Reexamination Certificate
2002-08-30
2004-08-17
Schilling, Richard L. (Department: 1752)
Radiation imagery chemistry: process, composition, or product th
Imaging affecting physical property of radiation sensitive...
Removal of imaged layers
C134S001100, C134S001200, C134S001300, C216S067000
Reexamination Certificate
active
06777173
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to semiconductor fabrication, and more particularly, to methods and apparatuses for using H
2
O vapor as a processing gas for stripping photoresist material from a substrate having a patterned photoresist layer previously used as an ion implantation mask.
2. Description of the Related Art
During semiconductor fabrication, integrated circuits are created on a semiconductor wafer (“wafer”) composed of a material such as silicon. To create the integrated circuits on the wafer, it is necessary to fabricate a large number (e.g., millions) of electronic devices such as resistors, diodes, capacitors, and transistors of various types. Fabrication of the electronic devices involves depositing, removing, and implanting materials at precise locations on the wafer. A process called photolithography is commonly used to facilitate deposition, removal, and implantation of materials at precise locations on the wafer.
In the photolithography process, a photoresist material is first deposited onto the wafer. The photoresist material is then exposed to light filtered by a reticle. The reticle is generally a glass plate that is patterned with exemplary feature geometries that block light from passing through the reticle. After passing through the reticle, the light contacts the surface of the photoresist material. The light changes the chemical composition of the exposed photoresist material. With a positive photoresist material, exposure to the light renders the exposed photoresist material insoluble in a developing solution. Conversely, with a negative photoresist material, exposure to the light renders the exposed photoresist material soluble in the developing solution. After the exposure to the light, the soluble portions of the photoresist material are removed, leaving a patterned photoresist layer.
The wafer is then processed to either deposit, remove, or implant materials in the wafer regions not covered by the patterned photoresist layer. After the wafer processing, the patterned photoresist layer is removed from the wafer in a process called photoresist stripping. It is important to completely remove the photoresist material during the photoresist stripping process because photoresist material remaining on the wafer surface may cause defects in the integrated circuits. Also, the photoresist stripping process should be performed carefully to avoid damaging the electronic devices present on the wafer.
As with many other wafer fabrication processes, an ion implantation process utilizes photolithography to protect specific areas of the wafer where ion implantation is not desirable. The ion implantation process, however, introduces difficulty in removing the photoresist material during the subsequent photoresist stripping process. Specifically, during the ion implantation process, ions penetrate into the outer regions of the photoresist material causing chemical bonds in the photoresist material outer regions to become cross-linked. Thus, the cross-linked outer regions of the photoresist material form a photoresist crust which is difficult to remove during the photoresist stripping process.
FIG. 1A
is an illustration showing a cross-section of a patterned photoresist layer previously used as an ion implantation mask, in accordance with the prior art. During the ion implantation process, ions
131
are implanted into target regions
129
of a substrate material
121
, where the target regions
129
are not protected by the photoresist material. Ions
131
entering the photoresist material cause the chemical bonds in the photoresist material to become cross-linked. Since the ions
131
only penetrate a limited distance through the photoresist material, the cross-linked photoresist is found near the outer portions of the photoresist material. The cross-linked photoresist is commonly called photoresist crust. The photoresist crust is typically characterized by a top photoresist crust
125
and a side photoresist crust
127
. The thickness of the photoresist crust is generally dependent on the dosage of implant species and the ion implant energy in the photoresist material. Since the ions generally bombard the photoresist material in a downward direction, the top photoresist crust
125
is generally thicker than the side photoresist crust
127
. The unaffected photoresist material underneath the photoresist crust is referred to as a bulk photoresist material
123
.
Generally, the stripping process for photoresist materials used in wafer fabrication processes other than ion implantation involves heating the photoresist material to a sufficiently high temperature to cause the photoresist material to be removed through volatilization. This high temperature photoresist stripping process is commonly called ashing. Ashing, however, is not appropriate for stripping photoresist material that has been used as an ion implantation mask. Specifically, the photoresist crust is resistant to the ashing process. As the temperature increases, the pressure of the volatile bulk photoresist portion underneath the photoresist crust increases. Eventually, at high enough temperature, the bulk photoresist portion will “pop” through the photoresist crust. Such “popping” causes fragments of the photoresist crust to be spread over the wafer and the chamber. The photoresist crust fragments adhere tenaciously to the wafer. Thus, removal of the photoresist crust fragments from the wafer can be difficult if not impossible. Furthermore, the ion implantation process often uses elements such as arsenic which can present a serious hazard when contained in photoresist crust fragments being cleaned from the chamber. Therefore, removal of the photoresist crust is generally performed at a low enough temperature to prevent popping.
FIG. 1B
is an illustration showing the problem wherein the bulk photoresist portion pops through the top photoresist crust, in accordance with the prior art. The bulk photoresist portion
123
is shown popping through the top photoresist crust
125
at a location
141
. The resulting top photoresist fragments
143
are shown adhering to the substrate material
121
.
Stripping of the photoresist crust at low temperature is typically performed by exposing the photoresist crust to radicals formed from various processing gases such as O
2
:N
2
H
2
, O
2
:N
2
:CF
4
, NH
3
, O
2
, O
2
:CF
4
, and O
2
:Cl
2
, where “:” denotes a gas mixture. The radicals serve to break the cross-linked chemical bonds of the photoresist crust, thus allowing the photoresist crust to be removed. Photoresist stripping using these processing gases at low temperature typically requires an extended amount of time, thus reducing wafer throughput. Also, handling some of these processing gases such as N
2
H
2
, NH
3
, and Cl
2
generally involves special requirements and safety features which can increase the capital cost of the wafer processing equipment. Furthermore, photoresist stripping using these processing gases commonly results in a problem wherein the side photoresist crust is removed before the top photoresist crust, thus allowing the bulk photoresist portion to be removed from underneath the top photoresist crust. This problem is commonly called “bulk photoresist undercut”.
FIG. 1C
is an illustration showing the undercut problem wherein the side photoresist crust is removed allowing the bulk photoresist to be undercut, in accordance with the prior art. The side photoresist crust (not shown) is removed prior to the top photoresist crust
127
. Removal of the side photoresist crust causes the bulk photoresist portion
123
to be exposed to the radicals. Exposure of the bulk photoresist portion
123
to the radicals along with the volatile nature of the bulk photoresist portion
123
causes an undercut
151
region to be created. The undercut region
151
leaves the top photoresist crust
127
susceptible to breaking off or falling onto the substrate material
121
. If allowed to contact the substrate material
121
, the top photoresist c
Chen Anthony
Lo Gladys So-Wan
LAM Research Corporation
Martine & Penilla LLP
Schilling Richard L.
LandOfFree
H2O vapor as a processing gas for crust, resist, and residue... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with H2O vapor as a processing gas for crust, resist, and residue..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and H2O vapor as a processing gas for crust, resist, and residue... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3299577