Drying and gas or vapor contact with solids – Process – Gas or vapor contact with treated material
Reexamination Certificate
1999-01-04
2001-01-23
Ferensic, Denise L. (Department: 3749)
Drying and gas or vapor contact with solids
Process
Gas or vapor contact with treated material
C034S467000, C034S508000, C034S559000, C034S565000, C034S092000, C034S087000, C034S107000, C034S202000, C034S210000
Reexamination Certificate
active
06176023
ABSTRACT:
TECHNICAL FIELD
The invention relates to a device for transporting flat objects, called cassettes or, and a process for transferring these objects between said device and a processing machine thereby guaranteeing a specific environment around the object, without any interruption of the specifications of the environment even when the object is transferred to the process machine.
STATE OF PRIOR ART
The invention relates to the production of flat objects in an ultraclean medium. Production of this kind conventionally uses clean room technology consisting of the global treatment of the atmosphere in which these objects are produced, handled and stored. In food processing, pharmaceutical and microelectronic industries, in particular, many objects are thus produced in a clean room atmosphere in order to avoid risks of contamination.
In the microelectronic industry, contamination is particularly dreaded during the production of components that require very fine etchings and very thin layers, for example flat screens (LCD), and especially during the production of semiconductor devices such as microprocessors or static or dynamic memories, etc. where the integration density is very high.
To simplify this description, the example that will be used throughout this document will be the microelectronic industry, and more particularly, the case of the processing of semiconductor, for example silicon. Indeed, the production of electronic circuits on semiconductor wafers, circular ones for example, requires that said wafers be processed, handled and stored in an ultraclean atmosphere, i.e. surrounded by an ultraclean and/or ultrapure gas such as very clean air or nitrogen.
There are two major types of contamination. They are contamination of particulate origin and contamination of physico-chemical origin or molecular contamination.
Contamination of particulate origin is due to a physical deposit of particles on the manufactured product, which is likely to generate physical phenomena. In the field of microelectronics, such particles on semiconductor wafers can lead to short circuits or electric power-cuts which can lead to falls in output.
Contamination of physico-chemical or molecular origin comes mainly from the air in the clean room, which is particularly rich in volatile carbon components.
These contaminants pass through the filtering system. They are also often generated in the clean room by filters, filter seals, plastic surfaces and also in the vicinity of silicon wafers (baskets and plastic transportation boxes).
Even though the relation between the presence of molecular contaminants and the loss of output is still difficult to establish, it is known that these species can be chemically absorbed at the surface of the silicon wafer. New chemical bonds are revealed by thermal processing and become real defects which affect output. These contaminants may result from the processes themselves and are conveyed by the silicon wafer itself, which will contaminate all the surfaces near the wafer.
Currently, several solutions can be used to avoid particulate contamination.
A first solution consists in subjecting the premises where the semiconductor wafers are handled to an ultraclean atmosphere, i.e. a controlled atmosphere.
The monitoring of the object's environment consists, therefore, in protecting it from all the sources of contamination originating mainly from operators and production machines. This protection is carried out by creating as laminar a flow of air as possible, in the room to create veins of protection around objects and to carry away all particles towards renewal openings that are generally placed in the intermediate ceiling.
This solution is the most frequent one. It enables class 1 dust levels to be obtained meaning that there is no more than one particle larger than 0.5 &mgr;m in a cubic foot (1 foot=0.3048 m, standard 209 Federal Standard, Airborne Particulate Cleanliness Classes in Clean Rooms and Clean Zones). With this mode of protection, it is expected that classes lower than 1 will be attained. Since all possible limits have almost been reached where filters are concerned, the only way to achieve greater cleanliness is to increase the number of air renewals in the room.
It is clear that the limits of “clean room” technology have been reached, and that if there are any improvements to made, they can only be achieved by a significant increase in operating costs resulting from the quantity of energy needed to ensure the recycling of air.
In this solution, silicon wafers
10
are arranged in baskets
11
containing twenty-five wafers. As
FIG. 1
shows, these baskets
11
are manually loaded onto the input-output ports of the production equipment, this operation being a particularly contaminating one.
For transportation within the production or storage unit, baskets are arranged and protected by a transportation box
12
.
FIG. 1A
shows the work and equipment areas and the input ports of cross-wall equipment. This figure represents one reactor
1
, a robot
2
, an elevator
3
, operations
4
being manual operations.
FIG. 1B
represents the circulation and storage areas. A second solution consists in limiting the “ultraclean” volumes to only those places where silicon wafers are handled. Therefore, these mainly concern work stations. Mini-environments are created around these sensitive areas (Enclosure on Canopy) in which a very sensitive filtering system (
5
) is installed as shown in FIG.
2
. As in
FIGS. 1A and 1B
,
FIG. 2A
corresponds to work areas and
FIG. 2B
to transfer and storage.
In this case, baskets
11
of wafers
10
are placed in to boxes
12
(or “Pod”) that are “practically” airtight. These boxes are automatically opened (
6
) in the ultraclean environment of the mini-environment to enable basket
11
or wafers
10
to be transferred under excellent conditions of cleanliness. This technology, used mainly in the field of microelectronics, is called the Standard Mechanical Interface (SMIF) and results in significant reductions in operating costs. This approach doubtless enables a slight improvement in the dust class, however it is faced by the same limits as those of the conventional clean room.
Furthermore, these improvements are obtained to the detriment of an interfacing with more complex machines that often require costly robot elements.
To obtain classes of cleanliness that are lower than 1, the so-called WAFEC technology, depicted in
FIG. 3
, proposes the local creation of a mobile miniclean room around basket
11
. This technology is designed so that the baskets of wafers can be placed on the machine inlets without any additional devices. Conditions of cleanliness are ensured by a permanent flow of ultraclean air around the wafers. Furthermore, a localized flow of air accompanies the wafer in an ultraclean air stream up to the machine reactor inlets.
FIG. 3A
corresponds to work areas and
FIG. 3B
to transfer-storage areas. In this technology, there is a dynamic protection of the enclosure, a close protection of wafers
13
and the automatic transfer of cassette
14
.
As a result of this technology, classes lower than 0.01 have been attained. Although it is promising, the technology has not met with the expected industrial success. This is because the permanent generation of ultraclean air requires mobile air generators to accompany containers. These devices are however not accepted in a production environment.
These three solutions can doubtless solve the problem of particulate contamination, but none of them can guarantee an environment that is free from molecular contaminants that are always present in clean rooms and generated by all plastic components, filters, filter seals, baskets and transport boxes materials.
Moreover, these three solutions handle conventional baskets that often contain 25 wafers. None of these solutions provides the flexibility that the microelectronic industry needs to optimize the waiting time on machines in order to reduce cycle time.
To consider a solution to the problem of purity (an environment fr
Anderson Kill & Olick P.C.
Commissariat A l'Energie Atomique
Ferensic Denise L.
Joyce Andrea M
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