Brushing – scrubbing – and general cleaning – Machines – Brushing
Reexamination Certificate
1999-06-25
2002-06-18
Stinson, Frankie L. (Department: 1746)
Brushing, scrubbing, and general cleaning
Machines
Brushing
C015S077000, C015S088300, C134S06400P, C134S12200P, C134S172000, C134S902000
Reexamination Certificate
active
06405399
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to semiconductor wafer cleaning and, more particularly, to techniques for more safely applying a rinsing liquid to the surface of a semiconductor wafer after a fabrication operation.
2. Description of the Related Art
In the semiconductor chip fabrication process, it is well-known that there is a need to clean the surface of the wafer after fabrication operations that leave unwanted residues or organic contaminants on the surface of the wafer. Examples of such fabrication operations include plasma etching (e.g., tungsten etch back (WEB)) and chemical mechanical polishing (CMP).
If left on the surface of the wafer for subsequent fabrication operations, unwanted residual material and organic contaminants may cause inappropriate interactions between metallization features. In some cases, such defects may cause devices on the wafer to become inoperable. In order to avoid the undue costs of discarding wafers having inoperable devices, it is necessary to clean the wafer adequately yet efficiently after fabrication operations that leave unwanted residue and contaminants on the surface of the wafer.
FIG. 1
shows a high-level schematic diagram of a wafer cleaning system
50
. The cleaning system
50
typically includes a load station
10
where a plurality of wafers in a cassette
14
may be inserted for cleaning through the system. Once the wafers are inserted into the load station
10
, a wafer
12
may be taken from the cassette
14
and moved into a brush box one
16
a
, where the wafer
12
is scrubbed with selected chemicals and water (e.g., DI water). The wafer
12
is then moved to a brush box two
16
b
. After the wafer has been scrubbed in the brush boxes
16
, the wafer is moved into a spin, rinse, and dry (SRD) station
20
where de-ionized water is sprayed onto the surface of the wafer while the wafer is spun at a speed of between about 100 and 400 revolutions per minute, and then is spun to dry. After the wafer has been placed through the SRD station
20
, the wafer is moved to an unload station
22
.
By way of example, when the wafer
12
enters the cleaning system
50
, the wafer
12
enters the cassette
14
and may be sprayed with water while in the cassette in order to wet the surface. Alternatively, the wafer can be sprayed with water as the wafer
12
enters brush box one
16
a
or brush box two
16
b
. Unfortunately, in such water spraying operations, the application of water tends to be non-uniform in that portions of the wafer may receive the application of water before other portions. The portions of the wafer that are sprayed initially will likely undergo unwanted reactions with the chemicals that were on the wafer
12
after the WEB operation. Although the spraying operation may saturate the entire surface of wafer
12
, the initial droplets that are applied to the wafer surface will necessarily cause the wafer to have portions of stained surface and portions of non-stained surface. Furthermore, in addition to stains, the technique of spraying water may cause micro-scratches on the surface of the wafer.
Unwanted stains or micro-scratches on the wafer surface may cause, among other things, inappropriate reactions between metallization features. These reactions may destroy the operability of devices on the wafer. A wafer with stains or micro-scratches typically must be discarded, which will ultimately add substantial cost to the overall fabrication process. Unfortunately, the stains or micro-scratches on the surface generally cannot be removed in subsequent cleaning or fabrication operations.
In order to avoid formation of unwanted stains and micro-scratches or introduce other unwanted chemicals onto the wafer surface, some manufacturers will use an additional step by processing the wafer through an SRD station before sending the wafer to the scrubber of brush box one
16
a
. However, this SRD station will have to be an application specific unit, which will necessarily add significant costs to the construction of a cleaning system
50
. Not only does this add significant costs to the station, standard SRD stations are not well configured to perform the pre-cleaning of the wafer surface. The reason standard SRD stations are not well configured is because an SRD station applies a non-controlled spray of water or chemicals over the wafer surface while the wafer is rotated at high speeds. Thus, the incorporation of this additional application specific SRD station will, in most cases, still cause micro-scratching and stains. In view of the foregoing, there is a need for a cleaning process that avoids the problems of the prior art by implementing wafer rinsing techniques for efficiently avoiding the formation of unwanted stains and micro-scratches.
SUMMARY OF THE INVENTION
Broadly speaking, the present invention fills these needs by providing a method and system for more safely applying liquid to a surface of a semiconductor wafer. 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 system is provided for cleaning a surface of a wafer following a fabrication operation. The system comprises a brush box, which includes a fluid manifold and at least one nozzle. The nozzle is connected to the fluid manifold by a flexible conduit. The nozzle is configured to spray a liquid onto the surface of the wafer at an application angle and at a fan angle. The application angle is defined between a plane of the surface of the wafer and a spraying plane of the liquid. The fan angle and the application angle are configured such that the spraying liquid covers the surface of the wafer in a quiescent manner.
In another embodiment, a method is provided for cleaning a surface of a wafer following a fabrication operation. The method comprises transferring the wafer into a cleaning unit and spraying a fan of liquid onto the surface of the wafer as the wafer is being transferred into the cleaning unit. The fan of liquid is applied at an application angle. The application angle is defined between a plane of the surface of the wafer and a plane of the fan of liquid. The fan of liquid is adjusted to be sprayed onto the surface of the wafer at a fan angle. The fan angle and the application are configured such that the spraying liquid covers the surface of the wafer in a quiescent manner.
In yet another embodiment, a wafer spraying apparatus is provided. The wafer spraying apparatus comprises a manifold for delivering a flow of liquid, a flexible conduit connected to the manifold, and a nozzle. The nozzle is connected to a distal end of the flexible conduit. The flexible conduit is configured to transport the flow of liquid from the manifold to the nozzle. The nozzle is configured to spray a fan of the flow of liquid onto the surface of the wafer. The fan of the flow of liquid is applied at an application angle defined between a plane of the fan of the flow of liquid and a surface of the wafer that is configured to receive the flow of liquid from the nozzle. The nozzle is positioned above the surface of the wafer at a nozzle height. The nozzle height and the application angle are adjustable by way of the flexible conduit.
Advantageously, the present invention provides methods and systems for applying liquid to the surface of a wafer by using a quiescent and symmetrical application technique. As a result, where a wafer has undergone a fabrication operation, the applied liquid will not undergo unwanted reactions with residual chemicals on the wafer surface. In addition to substantially eliminating stains, the techniques of the present invention substantially reduce the number of micro-scratches that may be formed on the wafer surface during cleaning operations. The methods of the present invention are particularly beneficial in post-plasma etching and post-CMP cleaning operations, whereby the wafers are sprayed usi
Farber Jeffrey J.
Svirchevski Julia S.
Lam Research Corporation
Martine & Penilla LLP
Stinson Frankie L.
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