Storage box for an object to be protected against...

Details Storage box for an object to be protected against... Storage box for an object to be protected against...

1997-09-29

2001-04-10

Robinson, Ellis (Department: 1772)

Stock material or miscellaneous articles

Hollow or container type article

Polymer or resin containing

C206S710000, C216S037000, C216S067000, C427S534000, C427S539000, C427S574000, C427S579000, C427S585000, C428S036600, C428S036700, C428S336000

Reexamination Certificate

active

06214425

ABSTRACT:

The invention relates to a storage box for an object to be protected against physicochemical contamination.
More specifically, the invention relates to the field of the manufacture of products in an ultra-clean environment. This production uses clean room technology consisting of treating the atmosphere in which the product is produced. In the agroalimentary or pharmaceutical, as well as the microelectronics industries, numerous products are consequently produced in a clean room atmosphere in order to avoid contamination risks. In the microelectronics field, contamination is more particularly feared in the production of parts having very fine geometries and using thin films such as LCD's or sensors and in the manufacture of semiconductor devices, such as microprocessors, static or dynamic memories, etc.
There are essentially two types of contamination, namely particulate contamination and physicochemical contamination.
Particulate contamination is due to a physical deposit on the product produced and which is liable to give rise to physical phenomena. Thus, in the microelectronics field, e.g. on silicon wafers, such deposits can lead to short circuits or to interruptions or disconnections to electrical connections. In this field, the size of the active geometries decreases every year and has passed from a few microns in the 1970's to submicron dimensions at the start of the 1990's. Industrialists now have technical equipment enabling them to manufacture electronic components with geometries of 0.2 to 0.5 &mgr;m. A particulate contamination of such components cannot be avoided by simply using conventional clean room procedures.
Physicochemical contamination can be due to the actual production processes, i.e. cleaning or annealing at high temperatures under a chemically active atmosphere. It can also be due to contact of the produced product with its direct environment by mechanical friction on the product support or by interacting with the surrounding atmosphere, e.g. oxidation during storage between two stages of the process.
In order to avoid contamination, at present two different procedures are used, namely the control of the environment in the manufacturing workshop or the selective control of the environment of the product.
The control of the environment in the manufacturing workshop consists of dealing with all the environmental conditions concerning the production equipment, the products produced and the human operators. This is the most widely used solution. However, due to the presence of the human operator, a source of significant chemical and particulate contamination, this procedure is limited to a cleanness equivalent to class 0.5 to 1. (Class 1 corresponds to the presence of less than one particle, whose diameter exceeds 0.5 &mgr;m per cubic foot: Federal standard 209c, “Airborne Particulate Cleanliness Classes in Clean Rooms and Clean Zones”). The quality of such an environment is difficultly compatible with the manufacture of films having geometries lower than 0.20 &mgr;m.
Moreover, in such a manufacturing workshop where all the atmosphere is controlled, the manufactured product is generally transported in a box or container ensuring a good protection against particulate contamination, but a mediocre seal with respect to the surrounding atmosphere. Therefore the gas of the workshop atmosphere, polluted by the human operator, tends to diffuse through the wall of the container or box and leads to a high chemical contamination.
The selective control of the environment of the product consists of solely optimizing the conditions around the manufactured product. In this case, the product is placed within a container, whose internal atmosphere is free from particulate contamination. The advantage of this solution is that it is theoretically possible to arrive at a system complying with the best possible specifications as regards chemical contamination, because the manufactured product is no longer in contact with the surrounding air and the human operator is then no longer a particulate and chemical contamination source. The control of the environment of the product during the transportation and storage phases taking place during its manufacturing process is consequently made much easier and the chemical contamination is then mainly dependent on the impermeability performance characteristics of the container.
In the microelectronics field and in the manufacture of silicon wafers, this solution is known as standard mechanical interface or SMIF.
FR 2 697 000 also envisages producing a flat, active confine box controlling the environment of the product during the open and storage phases of said box. More specifically, said box is equipped with an aeraulic unit having a diffuser issuing into the interior of the box and which can be connected to an inert gas, e.g. nitrogen supply means.
In the microelectronics field, the storage box for a product such as a silicon wafer must comply with the following specifications:
low unit production cost,
impossibility of using polluting materials, such as e.g. aluminium, iron or stainless steel,
good electrical conduction to obviate problems associated with static electricity discharges through the transported product,
low degassing rate in time,
easy cleaning,
good mechanical strength and
low weight permitting human handling.
In order to comply with these requirements, virtually all storage boxes are manufactured from plastics, e.g. polycarbonate or polypropylene. Although these materials comply with the above requirements, it has been found that they do not meet the future requirements as regards the permeability of contaminating agents, whose diffusion through plastics material is fast, even at ambient temperature.
The object of the invention is to develop a storage box meeting the aforementioned specifications and solving the problems of the prior art. It therefore relates to a storage box for an object to be protected against physicochemical contamination. The walls of said box are made from a plastics material.
According to the characterizing part of the invention, the inner surface and/or outer surface of the walls of said box is coated with at least one protective layer of a material having the general formula:
SiO
x
N
y
H
t
,
where t is lower than x and/or y and x and y are preferably in the following ranges:
0<x<2
0≦y<0.4
Preferably, x is in the range 0.3 to 1.8.
The contribution of hydrogen to the composition SiO
x
N
y
H
t
will usually be very low, essentially coming from the gaseous precursor of the silicon used for performing the deposit, which is in general a molecule containing hydrogen. Therefore, in all cases t is less than at least one of the parameters x, y and x only in the case where y is zero (no nitrogen contribution to the material).
As a result of the characteristics of the invention, a storage box is obtained in which the chemical contamination resulting from the diffusion of gases through the plastic material wall is very significantly reduced.
In the case where deposition takes place on the inner wall of the box, the organic chemical contamination due to the degassing of the plastics material walls towards the inside of the box kept under a vacuum is reduced. There is also an improvement to the surface state of the interior of the box and its cleaning is facilitated. There is also an improvement to the mechanical strength of the inner surface of the thus treated box and a reduction of the particulate contamination mechanically produced by impacts or scratches.
Preferably, the protective layer is deposited on said surface or surfaces of the box by plasma enhanced chemical vapour deposition (PECVD). This procedure makes it possible to make homogeneous deposits of limited thickness on a plastics material. The thickness of the protective layer is advantageously at least 0.1 &mgr;m. The minimum thickness of the layer is imposed on the one hand by specifications linked with permeation and on the other by the need for a mechanical strength.
According to an advantageous embodiment of the

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