Semiconductor wafer clamp retainer

Details Semiconductor wafer clamp retainer Semiconductor wafer clamp retainer

1997-09-04

2004-02-10

Ryan, Patrick (Department: 1745)

Chemistry: electrical and wave energy

Apparatus

Coating, forming or etching by sputtering

C156S345510, C118S500000, C118S503000, C118S728000

Reexamination Certificate

active

06689264

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to fabricating a semiconductor wafer and, more particularly, to a retainer used for biasing a wafer clamp against a wafer during processing upon the wafer and for raising the clamp from the wafer after processing.
2. Description of the Related Art
A semiconductor wafer is classified as a monolithic substrate containing both conductive and non-conductive materials. Materials upon the wafer are selectively fashioned across the semiconductor wafer to form an integrated circuit. Each layer of material is patterned according to a technique generally known in the art, and henceforth described as “lithography”.
A typical lithography process involves a sequence of steps beginning with a layer of material deposited entirely across the semiconductor wafer. Next, a photoresist (or resist) layer is spin-coated upon the deposited layer. The resist layer may be selectively radiated with, for example, ultraviolet light, electrons, or x-rays. An exposure tool, such as a mask, data tape (in electron beam lithography), etc., is used to selectively expose the resist. Patterns in the resist are formed when the wafer, and specifically the resist, undergoes a subsequent development step. Areas of resist remaining after development protect portions of the deposited layer. The resist which has been removed therefore exposes the underlying material to a variety of additive (e.g., lift-off) or subtractive (e.g., etching) processes that transfer a pattern from the exposure tool onto the conductive or non-conductive material.
There are numerous critical steps involved in accurately and reproducibly placing a pattern upon a semiconductor wafer. Certainly an important step in the expose-develop-etch sequence is the etch step. Accurate etching is of benefit to ensure materials are removed only where they are exposed. While offering high selectivity to only the material being removed, wet etching processing are typically isotropic. That is, wet etching generally attacks the material being removed with the same vigor in all directions. An unfortunate aspect of isotropic etching is undercutting. As film thicknesses decrease, and patterns being transferred become less than, e.g., 2.0 &mgr;m, it becomes difficult if not impossible to reliably use isotropic etching. Alternative pattern transfer processes are therefore needed to fabricate integrated circuits with such dimensions.
An alternative pattern transfer mechanism known as dry etching offers the capability of non-isotropic (“anisotropic”) removal. Dry etching can involve either pure physical removal or a combination of both chemical and physical removal. A popular dry etch process involving both chemical and physical removal is the reactive ion etching (“RIE”) or reactive ion beam etching (“RIBE”) technique.
Dry etching utilizes a glow discharge of chemically reactive species (atoms, radicals and ions) from a relatively inert molecular gas. The glow discharge region occurs by biasing a pair of electrodes separated from one another. Typically, one electrode is coupled either to a DC or RF source, while the electrode is typically grounded. The chemically reactive species within the glow discharge react with the material to be etched, leaving a reaction byproduct which is volatile and thereby readily evacuated from between the parallel spaced electrodes. In addition, energetic ions occur within the glow discharge. The ions are directed by the DC or RF field toward a wafer placed upon one of the electrodes arranged between the electrode pair. The energetic ions strike the wafer surface and ablate or sputter remove exposed material from that surface, wherein the exposed material is material residing beneath a space between patterned resist.
As the chemically reactive species adsorb onto the wafer surface, and as ions strike that surface, the surface is somewhat heated. Mechanisms have evolved to allow backside cooling of the wafer as the wafer is being etched on its frontside. Cooling can involve, for example, forwarding a cooling gas, such as helium, across the gap which exists between the wafer backside surface and a wafer pedestal to which the wafer is clamped. Flow of the cooling gas helps maintain a nearly constant temperature gradient across the semiconductor wafer surface during processing. Temperature uniformity is critical to assuring process reproducibility and achieving consistent processing results.
Typical wafer clamps extend across the wafer frontside surface around the edge or periphery of the wafer to seal between the edge to the wafer pedestal. Proper amounts of downward force on the wafer clamp toward the pedestal minimizes or prevents leakage of cooling gas from the wafer backside, through the edge/pedestal gap and into the wafer processing environment. This helps eliminate or significantly mitigate cooling gas interference with critical glow discharge parameters and chemistry.
FIG. 1
illustrates one example of a typical processing tool
10
which can initiate and sustain dry etching and, preferably, ion-assisted etching such as RIE and RIBE. Tool
10
includes a reaction chamber
12
adapted to receive incoming gas
14
through an inlet port. Gas
14
is used to bring about glow discharge during times when parallel-placed electrodes
16
a
and
16
b
are powered. Volatile byproducts
18
can be evacuated from the glow discharge area by an outlet port, as shown.
Lower electrode
16
b
is considered a wafer pedestal in that it accommodates a wafer
20
placed thereon. Various apertures may exist within electrode
16
b
to allow cooling gas flow across the backside surface of wafer
20
. To ensure wafer
20
is sealed against electrode
16
b
, a wafer clamp, configured similar to a ring, is designed to abut against the upper surface of wafer
20
about the wafer perimeter. Clamp
22
is retained in a movable, biased position relative to upper electrode
16
a
so that when upper electrode
16
a
moves, so will clamp
22
to some extent.
FIG. 1
illustrates wafer clamp
22
retained upward away from wafer
20
to allow ingress to wafer
20
during loading and unloading of the wafer into chamber
12
. During processing, the gap between electrodes
16
a
and
16
b
diminishes, and clamp
22
is forced downward upon the perimeter of wafer
20
. Clamp
22
is retained using clamp retainers
24
.
FIG. 2
illustrates one example of portions of a dry etch mechanism, a suitable mechanism being that obtainable from LAM Research Corp., model no. 4720, 4600, 9600, etc. The portions shown in
FIG. 2
comprise a ring
28
configurable within an upper electrode
16
a
(shown in FIG.
1
). Ring
28
is secured using various attaching devices, or screws
30
. Coupled to the underside surface of ring
28
may be a non-reactive plate
32
. Plate
32
serves to cover ring
28
and various reactive materials within ring
28
as well as upper electrode
16
a
. Plate
32
preferably comprises a material which does not react to the glow discharge material between the electrodes, or the gas species
14
introduced into the chamber. According to a metal etch example, plate
32
may comprise a quartz or ceramic material which is substantially inert to metal etchants delivered into the chamber.
Coupled a biased distanced below plate
32
and ring
28
is wafer clamp
22
. Wafer clamp
22
appears somewhat like a ring or flat washer having a downward extending flange or lip
34
. Lip
34
abuts with the upper surface at the perimeter of a wafer
20
. Regions radially outside lip
34
accommodate various apertures
36
circumferentially placed about clamp
22
.
Apertures
36
within clamp
22
, along with apertures
38
within plate
32
, accommodate passage of a retainer
24
. A sleeve
40
may be inserted into aperture
36
between the inward facing wall of aperture
36
and retainer
24
to prevent friction between the rigid plate
32
and the rigid material of retainer
24
. Preferably, sleeve
40
is made of a Teflon® substance.
Once sleeve
40
is in place, retainer
24
extends through apert

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