Method for chemical mechanical polishing of semiconductor wafer

Details Method for chemical mechanical polishing of semiconductor wafer Method for chemical mechanical polishing of semiconductor wafer

2000-11-21

2001-10-09

Nelms, David (Department: 2818)

Semiconductor device manufacturing: process

Chemical etching

Combined with the removal of material by nonchemical means

C438S692000

Reexamination Certificate

active

06300246

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to semiconductor fabrication processes, and a more particularly, to a method for cleaning the slurry remnants left on a polishing pad and wafer after the completion of a chemical-mechanical polish (CMP) process conducted for global polarization of a semiconductor wafer.
2. Description of Related Art
In the fabrication of semiconductor products, such as CPU's and various memory devices, the (MP technique is a global planaization process which can provide a flat and polished surface for a semiconductor wafer. It is currently the only semiconductor technology that can provide a global planaization of semiconductor wafers.
In a CMP process, the Surface of the wafer that is to be polished (hereinafter referred to as the process surface of the wafer) is placed upside down on a polishing pad on a CMP machine. The polishing pad can be rotated so as to rub against the process surface of the wafer. During the CMP process, a chemical agent, which is customarily referred to as a slurry, is applied on the wafer to assist the polishing pad in polishing the process surface of the wafer.
The Slurry can be a mixture of colloidal silica, dispersed alumina, and an alkaline solution, Such as KOH or NH
4
OH or CeO
2
base slurry. Tlie colloidal silica and dispersed alumina particles, which are highly abrasive in nature can help to polish the process surface of the wafer on the polishing pad.
After the completion of each CMP process, the slurry remnants left on the polishing pad should be cleaned away prior to processing a subsequent CMP process on another wafer. One conventional method of cleaning the slurry remnants on the polishing pad after the completion of a CMP process is depicted in detail in the following with reference to
FIGS. 1A and 1B
.
Referring to
FIG. 1A
, there is shown a polishing pad
10
after the completion of a CMP process. This polishing pad
10
has been treated by a pad dresser (not shown). After the CMP process, a large amount of slurry remnants
12
are left on the polishing pad
10
, which should be cleaned away before another wafer can be placed and polished on the polishing pad
10
. To remove the slurry remnants
12
, a stream of deionized water
14
is jetted on the polishing pad
10
so as to clean away the slurry remnants
12
left on the polishing pad
10
.
One drawback to the foregoing method, however, is that it is not effective at thoroughly cleaning away all of the slurry remnants
12
left on the polishing pad
10
. As shown in
FIG. 1B
, a small amount of the slurry remnants
12
may still remain on the polishing lopad
10
. When these uncleaned slurry remnants
12
dry out, they could cause scratches to the subsequent wafers that are placed on the polishing pad
10
to undergo a CMP process. This will significantly affect the wafer yield rate.
SUMMARY OF THE INVENTION
It is therefore a primary objective of the present invention to provide a method for cleaning the slurry remnants left on a polishing pad after the completion of a CMP process in which two slurry materials are used for a primary and secondary polish.
It is another objective of the present invention to provide a method for aggressively rinsing the first slurry remnants left on a polishing pad and wafer after the completion of the primary polish step which starts the first slurry remnants left on the polishing pad and wafer to be more easily cleaned away and to minimize the cross contamination of slurry materials.
In accordance with the foregoing and other objectives of the present invention, a new method for cleaning the first and second slurry remnants left on a polishing pad after the completion of a CMP process is provided.
In the method of the invention, the first polish is conducted using a first slurry and a second polish is conducted using a second slurry of different chemical composition. The polishing pad, of the first polish, and the wafer are cleaned between the first and second polish to avoid cross-contamination.
Prior to second polish a water cleaning spray is directed onto the wafer to remove contaminants prior to the second polish step. A cleaning agent such as DI H
2
O is used to rinse the polishing pad. The wafer is then forced against the pad with a second slurry material being applied for the appropriate polish, and subsequently followed by a low pressure rinse step on the same pad, known as, the buffing and cleaning step.
It is a distinctive feature of the invention that when using two different slurries, the problem of cleaning the pad and wafer is aggravated by several factors. The greatest problem results from the chemical interaction when the slurries come into contact with each other. This contact results in precipitates which, due to resulting nature of the new precipitates Ihave a great affinity to the processed surface of the wafer.


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