Alignment mark shielding ring and method of using

Details Alignment mark shielding ring and method of using Alignment mark shielding ring and method of using

1998-12-02

2001-01-09

McDonald, Rodney (Department: 1753)

Chemistry: electrical and wave energy

Processes and products

Coating, forming or etching by sputtering

C204S192150, C204S192170, C204S192250, C204S298110, C204S298150, C118S503000, C118S720000, C118S721000, C118S728000

Reexamination Certificate

active

06171453

ABSTRACT:

FIELD OF THE INVENTION
The present invention generally relates to an alignment mark shielding ring and a method of using such ring in a sputter chamber and more particularly, relates to an alignment mark shielding ring for shielding a wafer during a physical vapor deposition process which can be mechanically joined to a wafer pedestal such that any pedestal movement does not alter the position of the shielding ring on the wafer and a method for using such ring.
BACKGROUND OF THE INVENTION
Physical vapor deposition (PVD) is a frequently used processing technique in the manufacture of integrated circuit chips that involves the deposition of a metallic layer on the surface of a silicon wafer. The technique is also known as a sputtering process. In more recently developed advanced semiconductor manufacturing technology, the PVD technique is frequently used to deposit metallic layers such as TiN as anti-reflective coating or barrier layers.
In a typical PVD process, an inert gas such as argon is first ionized in an electrical field producing a plasma of charged gas particles. The particles are then attracted toward a negatively charged source (or target). The energy of these gas particles physically dislodges, or sputters of atoms of the metallic target material. PVD is a versatile technique in that many different materials can be deposited by using an RF or a DC power source.
In a typical PVD process chamber
10
, as shown in
FIG. 1
, major components of the chamber include a stainless steel chamber body
12
that is vacuum tight and is equipped with a pump
16
capable of reducing the chamber pressure to at least 10
−6
m Torr, a pressure gauge
18
, a sputter source or target
20
, a power supply (not shown), a wafer holder
14
and a clamp ring
22
. The sputter source
20
and the wafer holder
14
are positioned facing each other. The target may be a titanium disc when sputtering of TiN is desired. One of such PVD process chamber is commercially available as Endura® 5500 from Applied Materials, Inc. of Santa Clara, Calif.
The wafer holder
14
is normally a pedestal of a disc shape. In a top surface of the pedestal, metal screws
24
are used as pedestal pins for supporting a wafer
26
at the tips of the screws
24
. The pedestal pins allow a gap of approximately 1 mm to be maintained between the wafer
26
and the top surface
28
of the pedestal body
14
. The distance is necessary such that a subsequently deposited film, for instance, a TiN layer does not glue the wafer to the pedestal surface
28
. A thin TiN layer is frequently used on top of an aluminum-copper film layer as an anti-reflective coating for a subsequent lithography process. In a typical PVD deposition process, a plasma cloud
30
is generated by a cascading ionization reaction in which electrons and ion pairs are formed. For instance, when an electron bumps into an argon atom, it forms an argon ion and another electron. The newly formed electron then collides with another argon atom such that a chain reaction or ionization reaction is started. When the electrons bombard the wafer surface, the surface may be charged to a negative voltage higher than 30 volts.
One of the more important components in a sputter chamber is the clamp ring
22
which serves several functions during a sputter process. For instance, one of the functions is to clamp a wafer to a pedestal heater. The clamp ring holds the wafer in place on the pedestal when a positive gas pressure is applied between the heater and the pedestal such that heat can be efficiently conducted from the heater to the wafer. Another function served by the clamp ring is to allow a predetermined flow of argon to leak from under the wafer into the sputter chamber. A clamp ring is constructed in a circular shape with an oriented cut-out to match a wafer's flat side. A hood portion
32
is built into the clamp ring
22
for shadowing purpose to protect the lip of the clamp ring from being coated by the sputtered metal particles. A plane view of the clamp ring
22
and the hood portion
32
of the clamp ring are shown in FIG.
2
.
One other function served by the clamp ring
22
, and specifically by the hood portion
32
is the shielding of specific area along the edge of a wafer that should not be covered by sputtered metal particles. A typical area is the alignment marks which are scribed onto a top surface of a wafer for alignment in various process machines and onto various wafer platforms. An alignment mark would not be recognizable in a subsequent lithography process if covered by sputtered metals. The protection of an alignment mark from sputtered metal particles is therefore an important step in a sputtering process.
FIGS. 3A and 3B
show a conventional physical vapor deposition chamber with a wafer pedestal in a release and in a process position, respectively. The PVD chamber
40
is constructed of a wafer pedestal
42
, a clamp ring
44
, an upper chamber shield
46
and a lower chamber shield
48
which are enclosed in chamber wall
50
. A clamp shield
52
and an adapter plate
54
for mounting the upper shield
46
and the lower shield
48
thereto are further shown in
FIGS. 3A and 3B
.
A perspective view of the major components in the PVD chamber
40
is shown in FIG.
4
. It should be noted that in this conventional construction of a PVD chamber, the clamp ring
44
is not equipped with an extended hood portion for shielding an edge portion of the wafer or for shielding an alignment mark formed on the wafer.
In a modified conventional PVD chamber
60
, as shown in
FIGS. 5A and 5B
, attempts have been made to shield an edge portion of a wafer by an improved clamp ring
64
and to fix the position of the clamp ring in relation to the wafer
26
by alignment pins
66
. In this conventional construction, a modified clamp ring
64
which is equipped with an extended hood portion
70
is used to shield an edge portion
72
of the wafer
26
. The modified clamp ring
64
is further equipped with alignment pins
66
which are fixed to an edge
74
of the clamp ring
64
. Correspondingly located apertures
62
are provided for positioning the alignment pins
66
. The alignment pins
66
and the locating apertures
62
are provided such that the locating pins
66
may enter or exit the locating apertures
62
freely when the clamp ring
64
is lifted up by the wafer pedestal
42
away from the apertures or lowered into the apertures. This is shown in
FIGS. 5A and 5B
in an release and a process position, respectively.
While the alignment pins
66
utilized in the modified conventional PVD chamber
60
assist in the locating of the clamp ring
64
positioned on top of the wafer pedestal
42
, the modified clamp ring
64
does not always function properly to shield alignment marks provided on the wafer surface. For instance, during an upward movement of the wafer pedestal
42
by the upward movement of the elevator
76
, the clamp ring
64
and its associated alignment pins
66
are no longer held in place by the locating apertures
62
in the lower chamber shield
68
, as shown in FIG.
5
B. The movement of the wafer pedestal
42
may cause a shift in position of the clamp ring
64
in relation to the wafer pedestal
42
and the wafer
26
placed on top. As a result, the extended hood portions
70
may no longer shield the alignment marks that were placed directly under the hood portions
70
. The subsequent metal sputtering process therefore covers up the alignment marks and cause problems in the subsequent processing step.
It is therefore an object of the present invention to provide an alignment mark shielding ring for use in a sputter chamber that does not have the drawbacks or shortcomings of the conventional clamp rings.
It is another object of the present invention to provide an alignment mark shielding ring for use in a sputter chamber that is effective in shielding alignment marks placed on a top surface of a wafer positioned on a wafer pedestal.
It is a further object of the present invention to provide an alignment mark shielding ring

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