Methods for cleaning substrate surfaces after etch operations

Details Methods for cleaning substrate surfaces after etch operations Methods for cleaning substrate surfaces after etch operations

1999-12-09

2001-02-13

Smith, Matthew (Department: 2825)

Semiconductor device manufacturing: process

Chemical etching

Having liquid and vapor etching steps

C438S745000

Reexamination Certificate

active

06187684

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates generally to substrate fabrication, and more particularly to semiconductor wafer cleaning after etch operations.
2. Description of the Related Art
As is well known, semiconductor devices are fabricated from semiconductor wafers, which are subjected to numerous processing operations. These operations include, for example, impurity implants, gate oxide generation, inter-metal oxide depositions, metallization depositions, photolithography pattering, etching operations, chemical mechanical polishing (CMP), etc.
To facilitate discussion,
FIG. 1
illustrates a cross-section view of a layer stack, representing the layers formed during the fabrication of a typical semiconductor integrated circuit (IC) device. It should be noted that additional layers above, below, or between the layers shown may be present. Further, not all of the illustrated layers need necessarily be present and some or all may be substituted by a variety of different layers.
At the bottom of the layer stack, there is shown a substrate
10
. An oxide layer
11
which is typically a silicon dioxide (SiO
2
) is shown formed over the surface of the substrate
10
. A barrier layer
12
, typically formed of Ti, TiW, TiN or other suitable barrier materials, may be disposed between oxide layer
11
and a subsequently deposited metallization layer
13
. Barrier layer
12
, when provided, functions to substantially prevent diffusion of silicon atoms from oxide layer
11
and into the metallization layer
13
.
Metallization layer
13
typically includes aluminum, copper or one or more of a variety of known aluminum alloys such as Al—Cu, Al—Si, and Al—Cu—Si. Also shown is an anti-reflective coating (ARC) layer
14
that is formed over metallization layer
13
. As is well known in the art, ARC layer
14
is typically composed of Ti, TiN or TiW. Generally speaking, ARC layer
14
is useful in preventing light used in photolithography processes from reflecting and scattering off of the metallization layer
13
surface. Another oxide layer
16
is then formed over the ARC layer
14
. In this simplified example, a photoresist layer
18
is then spin coated over the oxide layer
16
and patterned to define windows where etching is desired. As is well known, photoresist layer
18
represents a layer of conventional photo-sensitive resist material that may be patterned using patterned reticles and a stepper that passes selective light waves onto the surface of photoresist layer
18
. The layers of the layer stack are readily recognizable to those skilled in the art and may be formed using any number of known deposition processes, including chemical vapor deposition (CVD), plasma-enhanced chemical vapor deposition (PECVD), physical vapor deposition (PVD) such as sputtering, spin coating, etc.
At this point, an etch operation
20
is performed in order to selectively remove portions of the oxide
16
. In this example, a feature
17
is etched into the oxide
16
, and the feature
17
may be a trench, a via hole, or any other geometric pattern. Preferably, the etch
20
is chosen to have good selectivity to enable efficient etching of the oxide
16
. During the etching operation, however, polymer formation
22
is known to occur on the sidewalls of features
17
being etched. This polymer formation
22
, as shown, typically takes on the shape of a crown or a veil. This shape therefore is observed to extend along the sidewalls and up onto the photoresist layer
18
.
The actual composition of the polymer formation
22
depends upon the material being etched, the chemistry used for the etching, and the underlying material (e.g., the ARC layer
14
). Although there are many types of chemistries used to plasma etch through an oxide layer
16
, typical chemistries may include CF
4
and O
2
, NF
3
, and C
4
F
8
among others. Thus, the material representing the polymer formation
22
will generally be an oxide material containing some of the etch chemistry components, carbon from the photoresist, and metallization material (e.g., Ti, TiN, Al, Si, and Cu) from the ARC layer
14
and the metal layer
13
.
After the plasma etching is performed, the conventional process is to perform what is referred to as an ashing operation to remove the photoresist layer
18
. This ashing operation may remove some of the polymer formation
22
, however, most may still remain on the sidewalls of the etched oxide layer
16
. To remove this remaining polymer formation
22
, it is conventional practice to move the wafer into a chemical bath containing liquids that are designed to remove the polymer formation
22
. An example chemical bath may include a chemical referred to as EKC-265, which is available from EKC, Inc. of Hayward, Calif.
Although chemical bath rinsing has worked in the past, the demand for smaller device features has increased the need to have a very clean environment at every step of a fabrication process. Unfortunately, bath rinsing is inherently an unclean environment. Polymer material being rinsed in the bath may therefore contaminate the bath, and the removed material may be deposited or can attach to other parts of a wafer or to other wafers being processed through the bath. In some cases, the polymer formation
22
material may become lodged at the base of an etched feature, and due to its oxide composition, the material may prevent electrical contact through that feature (e.g., once a next metal formation step is performed to fill the oxide etched feature). Accordingly, surface particles and contaminants can detrimentally impact the performance of an integrated circuit device.
In view of the foregoing, there is a need for improved methods that will enable efficient removal of post plasma etch polymer materials from etched features. The removal should be efficient enough to remove the polymer material and prevent further contamination of other surface areas of a wafer being processed.
SUMMARY OF THE INVENTION
Broadly speaking, the present invention fills these needs by providing methods for efficiently cleaning etched features of given layers of a semiconductor wafer. Preferably, the cleaning is designed to efficiently remove post plasma etch polymers from etched features. It should be appreciated that the present invention can be implemented in numerous ways, including as a process, an apparatus, a system, a device, or a method. Several inventive embodiments of the present invention are described below.
In one embodiment, a method for cleaning a semiconductor wafer after process operations is disclosed. The method includes plasma etching a feature in an oxide layer having a photoresist mask. Then, the semiconductor wafer is processed through an ashing operation to remove the photoresist mask. The semiconductor wafer is then scrubbed implementing chemicals that are configured to remove polymer residues deposited in and around the feature during the plasma etching. In a preferred embodiment, the chemicals are selected from one of: (a) a combination of NH
4
OH and DI water, (b) a combination of H
2
O
2
, HF, and DI water, (c) a combination of O
2
, NH
4
OH, and DI water, and (d) a combination of HF and DI water.
In another embodiment, a method for post plasma etch cleaning a semiconductor wafer is disclosed. The semiconductor wafer has a plurality of layers formed thereon, and one of the plurality of layers is an oxide layer that has a photoresist mask. The method includes plasma etching a feature in the oxide layer. The plasma etching is configured to generate a polymer film on sidewalls of the plasma etched feature. An ashing operation is then performed to remove the photoresist mask. The oxide layer and the plasma etched feature are then brush scrubbed with chemicals followed by a DI water rinse. The chemicals are defined to be a combination of H
2
O
2
, NH
4
OH, and DI water, and the brush scrubbing is configured to remove the polymer film from the sidewalls of the plasma etched feature. Still further, the chemicals can also be dilute HF.
In yet a further embodime

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