Measuring and testing – Sampler – sample handling – etc. – Plural parallel systems
Reexamination Certificate
2000-08-15
2003-09-09
Noland, Thomas P. (Department: 2856)
Measuring and testing
Sampler, sample handling, etc.
Plural parallel systems
C073S028010, C073S061710, C073S863030, C073S864340, C438S014000
Reexamination Certificate
active
06615679
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The field of the invention relates to apparati and methods for monitoring particles in clean environments of the integrated circuit, electronic, pharmaceutical and other industries.
2. Statement of the Problem
The semiconductor and data storage industries are moving away from ballroom cleanrooms with exposed process environments toward enclosed process tools with autonomous air handling systems. Each process tool may be viewed as comprising a mini-environment, in which one or several process functions are performed. A mini-environment-based process tool may contain one or more than one clean-zone, each clean-zone incorporating separate filtration services and product handling systems. Thus, a modern integrated circuit manufacturing plant, commonly known as a fab, typically contains hundreds of smaller, miniaturized mini-environments. Mini-environments exist in a wide range of sizes, a typical size having a volume of 3 m×3 m×3 m. Because the air handling systems of a mini environment are close to the product, extremely isolated contamination events occur. Contamination is often not constant rather it may be a result of a process event. Thus, contamination events may be spatially or chronologically isolated. One of the serious problems of the integrated circuit manufacturing industry, as well as other industries requiring very clean environments, is the detection of these isolated events.
In typical fabrication sequences, front-opening-unified pods (FOUPs) carry wafers to the many mini-environments, robotics transfer wafers from the FOUPs to a manufacturing process zone, and after processing, the wafers return to the FOUPs. Data from mini-environments show that they are not as clean as initially imagined. Consequently, a mini-environment requires particle monitoring, and indirect air handling and compartmentalized nature of the mini-environment necessitates a particle counter with small dimensions and high probability of detecting an isolated particle event.
There are several basic methods known in the art for monitoring a mini-environments. The first is to use a dedicated sensor for each mini-environment to do continuous monitoring. A second technique is to use a multiplexed system, including a stepping manifold system and a single particle detector. With this technique, samples are drawn continuously from numerous mini-environments or from multiple points in a single mini-environment and are measured sequentially in steps a single sample at a time. A third, non-automated method uses a mobile sensor that is moved from one mini-environment to another. The sensor is attached to a “particle port” on the mini-environment.
FIG. 1
shows a diagrammatic sketch of a dedicated sensor system
100
as known in the art. A process tool
102
includes an enclosed gaseous mini-environment
104
, which is being monitored for use of a sampling probe
106
which is connected by sampling to
108
to particle detector
110
. A dedicated sensor, provides the obvious advantage that it continuously monitors the sampling zone of the sample probe, capturing brief intermittent events. A serious disadvantage, however, is that the sampling zone of a dedicated sensor is relatively small, typically having a footprint less than one square foot. A dedicated sensor, therefore, provides limited spatial coverage, detecting particles only in the sampling zone, and not in the other locations of the mini-environment. For example, a diagram of a process tool
202
is depicted in
FIG. 2
containing a mini-environment
204
and four process functions
206
,
208
,
210
,
212
. The movement of a semiconductor wafer
214
through process tool
202
includes travel through zones designated by dashed area
220
, including the liquid environments of process functions
206
,
208
,
210
. Movement through the process tool
202
also includes travel through a gaseous clean zones along the path designated by arrows
230
. A 12-inch wafer has a surface area of 0.8 sq. ft. If the exposed path through the gaseous mini-environment of the process tool is 24 feet, then the effective exposed area for the wafer is 19 sq. ft. A particle contamination event is generally localized to an area corresponding to 1 square foot or less. Thus, a dedicated sensor located at a single point along the 24-foot exposed process path
230
would detect a contamination event only if the event occurred within several inches of the location of the sampling probe. It is, however, economically and sometimes physically impractical to provides a large number of dedicated sampling probes and corresponding expensive particle counters to monitor continuously the entire process path of a process tool.
In a multiplexed monitoring system, a number of sampling probes are connected to a multiplexed stepping manifold. A diagrammatic sketch of the multiplexed monitoring system
300
is depicted in FIG.
3
. Typically, fluid is drawn from each sample point
302
continuously through the multiplexing stepping manifold
310
by pump
350
. In sequence, the manifold controller
312
selects a single sample
320
that is tested by the particle detector
330
, while all other fluid flow from the unselected samples is discarded in the exhaust system
340
. A multiplexed, stepping manifold system
300
allows monitoring of many locations using a single particle detector. A multiplexed system has a disadvantage, however, that a contamination event may go undetected for a relatively long time until the sample from the probe location reaches its turn in the multiplexing sequence. Indeed, a brief or intermittent contamination event may go completely undetected if its occurrence does not coincide with the timing of the multiplexing sequence. In a variation, referred to as a mixed-fluid manifold technique, two particle detectors are connected to each stepping manifold. A single sample is selected by the manifold and sent to one particle detector, as in a basic system, while the samples from all the other sample probes are combined and sent as a mixture to the second particle detector. In this manner, each sample probe location is monitored individually in sequence, while a combined mixed-fluid stream of all of the remaining samples is monitored continuously. This technique is expensive, however, because it requires two particle detectors and an expensive multiplexed stepping manifold with extra controls.
Conventional monitoring systems using stepping manifolds to monitor a mini-environment at a number of sample points typically draw a large volume of the air, sometimes greater than 1 cubic foot, from each sample point. This may adversely affect the whole fluid environment. The tubing leading to the probes takes up limited space in the process tool. When there are many sampling points to be monitored, it may be impossible to provide access for tubing to all of the sampling probes. Particles in the tubing, especially aerosol particles, may settle in the tubing, leading to false negative or low measurements and to clogging of the tubing. The stepping manifolds used in conventional techniques typically way on the order of 20 pounds, and occupy a large volume of space, having a diameter of a foot or more.
The mobile system has the advantage of having the lowest capital cost. But, it has the disadvantage of increased manpower costs and has a very low duty cycle.
The problems described above with respect to monitoring clean gaseous environments are also encountered in regard to maintaining clean liquid environments.
The integrated circuit manufacturing industry, as well as other industries requiring clean environments, needs a particle monitoring system that monitors and detects contamination events in a clean environment, providing good spatial coverage without significant gaps in time, in a manner that is economically and physically feasible.
Solution
The invention described in this specification provides an ensemble manifold, a system and a method that alleviate the problems described above.
An ensemble manifold in ac
Bast Bryan
Brandon Glenn W.
Knollenberg Brian A.
Noland Thomas P.
Particle Measuring Systems, Inc.
Patton & Boggs LLP
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