Data processing: generic control systems or specific application – Specific application – apparatus or process – Nonreactive mixing process
Reexamination Certificate
2002-02-15
2004-05-04
Gandhi, Jayprakash N. (Department: 2125)
Data processing: generic control systems or specific application
Specific application, apparatus or process
Nonreactive mixing process
C700S266000, C700S285000
Reexamination Certificate
active
06732017
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to semiconductor wafer planarizing, and more particularly, to methods and systems for controlling and mixing chemicals for a chemical mechanical planarizing process.
2. Description of the Related Art
In the fabrication of semiconductor devices, there is a need to perform a variety of substrate preparation and fabrication operations including chemical mechanical planarization (CMP) operations, substrate cleaning, substrate polishing and buffing, substrate rinsing and drying, and other similar operations. Planarization, polishing, and cleaning operations are routinely performed on semiconductor wafers at various stages in the fabrication process. Typically, such operations are efficiently combined within process systems that are configured, for example, to receive batches of wafers at a time to be processed through CMP, polishing, buffing, cleaning, rinsing, and/or drying, followed by wafer processing through subsequent wafer fabrication operations.
Typically the chemicals required for such a CMP processes are prepared in a batch process system
100
such as shown in FIG.
1
.
FIG. 1
is a schematic diagram of a prior art system for mixing chemicals for a CMP process. A first chemical
101
is stored in a first supply tank
102
and a second chemical
103
is stored in a second supply tank
104
. When a batch of the first and second chemicals
101
,
103
, is mixed, the respective supply valves
106
,
108
are opened and a selected amount of the first and second chemicals
101
,
103
are transferred to the batch mixing tank
110
. The first and second chemicals
101
,
103
are then mixed in the batch-mixing tank
110
. Typically the mixed batch is tested through manual processes such as weighing the respective quantities of the first and second chemicals
101
,
103
that are added to the batch mixing tank
110
. Once the mixed batch of the chemicals is fully prepared and ready to be used, the batch supply valve
120
is opened and the batch-mixing tank
110
is pressurized to cause the mixture
123
to flow to a delivery tank
122
. The delivery tank
122
can then be pressurized to deliver the mixture
123
to a mixture distribution manifold
124
. The manifold
124
distributes the mixture to multiple points of use
130
,
132
,
134
, through point of use supply valves
136
,
138
,
140
respectively. Each of the points of use
130
,
132
,
134
can represent a different CMP process tool or different locations within a single CMP process tool.
One of the problems with the batch process system
100
described above is that often the mixture
123
can only be used for a limited time period. For example, often, optimum CMP results require the mixture be used within the first sixty minutes after the mixture
123
is formed in the batch-mixing tank
110
. The time limits may be due to reactivity of the mixture
123
or due to coagulation effects common to the slurry-type chemical used in the CMP process.
Another problem with the batch process system
100
is that the mixture
123
must be transferred to each point of use
130
,
132
,
134
via a distribution system (e.g., the manifold
124
, the respective point of use supply valves
136
,
138
,
140
and interconnecting piping). When each batch of the mixture
123
expires or is no longer needed, the entire distribution system must be fully flushed and cleaned so that impurities of the previously expired batch do not contaminate successive batch mixtures. Further, the remaining mixture
123
contained in the distribution system becomes a waste product that must be disposed of which is both inefficient and typically expensive.
Yet another problem with the batch process system
100
is that often the mixture
123
is hazardous (e.g., caustic, acidic, flammable, poisonous, etc.). Because the mixture
123
is hazardous, the pressurized batch mixing tank
100
and delivery tank
122
must be very closely monitored and controlled. Further the batch-mixing tank
100
and delivery tank
122
are typically double walled to provide added safety containment of the hazardous mixture
123
. The safety requirements of storing and pressurizing quantities of the hazardous mixture
123
increase the complexities of the batch process system
100
and the cost. Therefore the batch process system
100
is more expensive and less reliable than required.
Typically the batch process system
100
yields inconsistent batches because one batch is not exactly the same as another batch. Inconsistent batches often cause inconsistent CMP process results. The batches may be inconsistent because the measurements, such as the respective amounts of the first and second chemicals
101
,
103
, are different from one batch to another or because one batch has aged longer before use than another batch.
Similarly, the batch process system
100
does not produce a continuous and consistent mixture. This is because typical mixture control is in the batch mixing process in the batch-mixing tank
110
. Once the mixture
123
is combined in the batch mixing tank
100
there typically is no further monitoring or testing to determine if the mixture is correct or becomes too aged or contaminated. As a result, if the mixture
123
becomes incorrect, then the CMP results could also become incorrect.
Another problem with most batch-type mixing systems is that a quantity of the mixture
123
is prepared in advance of the actual need of the mixture
123
. If for any reason the mixture
123
is not needed (e.g., the CMP process is delayed until after the mixture
123
is too aged), then the entire mixture
123
must be discarded as a waste product. This results in excessive waste, which is both inefficient and typically expensive.
In view of the foregoing, there is a need for a more efficient, accurate delivery system of the CMP chemicals.
SUMMARY OF THE INVENTION
Broadly speaking, the present invention fills these needs by providing a point of use chemical mixing system in a chemical mechanical planarization system. It should be appreciated that the present invention can be implemented in numerous ways, including as a process, an apparatus, a system, computer readable media, or a device. Several inventive embodiments of the present invention are described below.
A chemical mechanical planarization system includes a point of use chemical mixing system. The point of use chemical mixing system includes a first and a second pump, a first and a second flow sensor, a mixer and a controller. The first pump has an input coupled to a first chemical supply and the first flow sensor coupled to the output of the first pump. The second pump has an input coupled to a second chemical supply and the second flow sensor coupled to the output of the second pump. The mixer has inputs coupled to the output of the first and second flow sensors. The controller is configured to receive signals from the first and second flow sensors and to produce control signals for the first and second pumps and the mixer. The controller is further configured to cause a mixture of the first and second chemicals upon a demand from the CMP process.
A method of mixing two or more chemicals for a CMP system includes pumping a first and a second chemical to a point of use. Monitoring a flow rate of the first chemical from a first pump and monitoring a flow rate of the second chemical from a second pump. Controlling the flow of the first and second chemicals into a mixer upon demand for a mixture of the first and second chemicals. Outputting the mixture to the CMP process.
In one embodiment, the flow of the first and the second chemicals into the mixer is controlled according to an aspect of the mixture such as a pH level of the mixture or a density of the mixture.
In one embodiment, the first and second pumps include a tubephram-type pump.
Mixing the CMP chemicals, upon demand, at the point of use reduces waste and provides more accurate and consistent chemical mixtures. A point of use mixing system also allows constant fe
Nguyen Tuan
Pham Xuyen
Quach Vien
Zhou Ren
Gandhi Jayprakash N.
Lam Research Corp.
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