Abstrict A method for protecting substrates used in the manufacture of semiconductors,
memory products, and other electronic devices from the effects of
moisture during transport and storage is disclosed. This method
involves the use of a cassette or box made from polycarbonate or
another material having similar hydroscopic properties, treating
the cassette or box to reduce its moisture content, and surrounding
the cassette or box, and the substrates held therein, with a moisture
barrier. This results in a package which will keep the substrates
dry and eliminates the need for a separate desiccant within the
package.
Claims I claim:
1. A package for substrates used in the manufacture of semiconductors
and other electronic devices comprising:
(a) a cassette for holding at least one substrate, said cassette
made of a hydrophilic plastic material which has been dried to reduce
the moisture content of said material;
(b) a sealed, moisture-proof barrier surrounding said cassette
and its contents so that moisture inside the barrier is absorbed
by the hydrophilic plastic material of the cassette and moisture
outside the barrier does not penetrate the barrier.
2. The package of claim 1 wherein said hydrophilic plastic material
is polycarbonate.
3. The package of claim 1 wherein said sealed moisture-proof barrier
is a bag made of plastic laminate.
4. The package of claim 1 wherein said plastic laminate is comprised
of a layer of polyethylene, a layer of polyester, a carbon conductive
layer, an acrylic resin layer, and a vinylidene layer.
5. A system for protecting in a single package one or more substrates
of the type used in the manufacture of semiconductors and other
electronic devices, said system including:
(a) cassette means made of a hydrophilic plastic material for holding
at least one substrate;
(b) means for drying said cassette means to reduce the moisture
content of said hydrophilic plastic material; and
(c) means for forming a moisture-proof barrier around said cassette
means and any substrate held in said cassette means.
6. The system of claim 5 wherein said hydrophilic plastic material
is polycarbonate.
7. The system of claim 5 wherein said means for drying said cassette
means is a nitrogen source.
8. The system of claim 5 wherein said means for drying said cassette
means is a source of hot air.
9. The system of claim 5 wherein said means for drying said cassette
means is a vacuum chamber.
10. The system of claim 5 wherein said moisture-proof barrier is
made of a plastic laminate.
11. The system of claim 5 wherein said moisture-proof barrier is
a sealed bag.
12. A method for packaging at least one substrate of the type used
in the manufacture of semiconductors and other electronic devices
comprising the steps of:
(a) placing the substrates to be packaged into a cassette, said
cassette made at least in part from a hydrophilic plastic material;
(b) exposing said cassette to a drying environment to reduce the
moisture content of the hydrophilic plastic material;
(c) providing a sealed, moisture-proof barrier around the cassette
and the substrates contained therein so that moisture inside the
barrier is absorbed by the hydrophilic plastic material from which
the cassette is made and moisture outside the barrier does not penetrate
the barrier.
13. A method for packaging at least one substrate of the type used
in the manufacture of semiconductors and other electronic devices
comprising the steps of:
(a) providing a cassette capable of holding at least one substrate,
said cassette being made at least in part of a hydrophilic plastic
material;
(b) exposing the cassette to a drying environment to reduce the
moisture content of said hydrophilic plastic material;
(c) inserting at least one substrate into said cassette after the
moisture content of the hydrophilic plastic material has been reduced;
(d) providing a sealed, moisture-proof barrier around the cassette
and any substrates contained therein so that moisture inside said
barrier is absorbed by the hydrophilic plastic material from which
the cassette is made and moisture outside the barrier does not penetrate
the barrier.
14. The method of claim 12 or claim 13 wherein said hydrophilic
material is polycarbonate.
15. The method of claim 12 or claim 13 wherein said drying environment
consists of heated air.
16. The method of claim 12 or claim 13 wherein said drying environment
consists of nitrogen.
17. The method of claim 12 or claim 13 wherein said drying environment
is a vacuum.
18. The method of claim 12 or claim 13 wherein said drying environment
has an atmospheric pressure less than normal atmospheric pressure.
19. The method of claims 12 or 13 wherein said sealed, moisture-proof
barrier is made of a plastic laminate.
20. The method of claim 19 wherein said plastic laminate includes
a layer of polyethylene, a layer of polyester, a carbon conductive
layer, an acrylic resin layer, and a vinylidene layer.
Description BACKGROUND OF THE INVENTION
I. Field of the Invention
The present invention relates to packaging for storing and shipping
substrates used in the manufacture of semiconductors, memory products
and other electronic devices. More specifically, the present invention
relates to packaging which protects such substrates and electronic
devices from the harmful effects of moisture during transport and
storage.
II. Description of the Prior Art
Substrates used in the manufacture of semiconductors, memory products,
and electronic devices tend to be very fragile and sensitive. Manufacturing
of such devices is generally done in clean room environments. Much
research and development has gone into the design of substrate handling
equipment as well as transport carriers and packages for such substrates.
Much of this research and development revolves around steps which
can be taken to protect the substrate and prevent physical damage.
See, for example, U.S. Pat. No. 5398481 granted on Mar. 21 1995
to Takeuchi et al.
Substrates used in the manufacture of semiconductor and memory
products can be damaged in a variety of ways. They are easily scratched,
cracked or chipped. Very significant problems can arise from chemical
reactions which can occur when such items are stored in the presence
of moisture.
Various packaging techniques have been used to prevent the problems
associated with moisture. For example, U.S. Pat. No. 4553020 issued
on Nov. 12 1985 to Val describes a hermetically sealed, encapsulation
package for electronic components and integrated circuits. This
packaging includes a base and cover. The base includes a separate
moisture retention element which retains any water molecules remaining
within the package after sealing or which may enter the package
through a leak. This retention element is made of an absorbent and
porous glass type material in the zeolite group capable of retaining
water molecules. Alternatively, the retention element can be formed
by a material which reacts chemically with water. Examples cited
in the Val patent include silicon, titanium, zirconium, tantalum,
vanadium, aluminum and tin. In each case, supplying power to the
moisture retaining element is used to improve its performance. In
the case of zeolite, applying power constitutes a degassing treatment
which reduces the water molecules in the moisture retaining element
to a minimum. In the case of the other materials listed above, using
power to heat the moisture retaining element at predetermined intervals
after closure of the package ensures that the atoms of the reactive
metal diffuse toward the surface and through any oxide layer which
has already been formed to renew the moisture retaining capacity
of the moisture retaining element.
Another example of a technique developed to protect substrates
and related electronics devices from moisture is described in U.S.
Pat. No. 5274914 which issued on Jan. 4 1994 to Kitamura et al.
In this patent, the item to be packaged, along with a silica gel
desiccant, is place inside a moisture-proofing bag which is heat-sealed.
The bag can be made of a laminate film having a polyethylene layer,
a polyester layer, a carbon conductive layer, an acrylic resin layer,
and a vinylidene chloride layer. The bag is, of course, sealed before
intrusion of moisture occurs.
U.S. Pat. No. 5287962 which issued to Nomi et al on Feb. 22
1994 also represents an effort to deal with the susceptibility
of semiconductors to moisture because of the permeability of the
molding compounds. The Nomi patent describes a packaging medium
which consists of a shipping means for carrying a semiconductor
device, a flexible dry-pack bag for containing the shipping means,
and a vacuum seal indicator. The devices to be packaged are baked
until dry just prior to packaging. The dry-pack bag is vacuum-sealed
around the device to be packaged. No desiccant is provided. This
system relies on the assumption that the device is dry before it
is placed in the package and will remain dry as long as the vacuum
seal is not broken.
Each of the systems recognize the need for substrates and associated
electronic devices to be kept dry. The Val and Kitamura patents
utilize separate desiccants which can serve to increase processing
and packaging costs or serve as a contaminant. A real need exists
for a substrate packaging system which is economical and does not
introduce any potential contaminants which could damage the substrate.
SUMMARY OF THE INVENTION
One object of the present invention is to provide an economical
substrate packaging system which is capable of reducing the adverse
effects of moisture.
A further object of the present invention is to provide such a
packaging system which controls moisture levels without the use
of a separate desiccant.
Another object of the present invention is to provide a packaging
system which can contain a plurality of substrates in a protected
fashion in a moisture-controlled environment.
These and other objects are achieved by providing a packaging system
consisting of a cassette and a sealable bag. The cassette is preferably
made of polycarbonate or some other durable material having similar
hydrophilic characteristics. The sealed bag provides a moisture-proof
barrier. The system also requires some suitable means for drying
the cassette prior to use so that the material of the cassette acts
as a desiccant during transport and storage of substrates in the
package. Such means could include a source of warm air, a source
of nitrogen, a vacuum chamber, or the like.
One packaging method contemplated by the invention would be to
dry the cassette to reduce the moisture content of the material
from which the cassette is made. When sufficiently dried, the substrates
are loaded into the cassette and the cassette and substrates are
sealed inside the bag. Another method contemplated by the invention
involves loading the substrates into the cassette, drying the cassette,
and then sealing the cassette inside the bag. Still another method
might involve the use of a cassette consisting of a wafer carrier
and a separate box, either or both of which can be dried and thus
prepared to serve as a desiccant before being sealed in the bag
with the substrates.
BRIEF DESCRIPTION OF THE DRAWINGS
The features and advantages of the present invention will become
better understood from the following detailed description read in
conjunction with the accompanying drawings. In the drawings:
FIG. 1 is an exploded view showing a substrate carrier and a box;
FIG. 2 is a perspective view showing a substrate carrier inside
a gas flow desiccating chamber;
FIG. 3 is a perspective view showing a substrate carrier inside
a vacuum chamber;
FIG. 4 is a perspective view showing a substrate carrier inside
a heating oven;
FIG. 5 is a perspective view showing the substrate carrier within
a moisture-proof barrier;
FIG. 6 is a perspective view showing a transport box within a moisture-proof
barrier.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
FIG. 1 illustrates a typical prior art packaging system used to
store and transport substrates. This packaging system includes a
substrate carrier 2 and a box 3 having a bottom 4 and a top 6. The
box 3 is designed to hold the substrate carrier 2 and any substrates
held therein. Further information related to the packaging system
shown in FIG. 1 can be found in U.S. Pat. No. 4966284 which issued
on Oct. 30 1990 in the name of Gregerson et al.
Those skilled in the art will recognize that the prior art also
includes the use of substrate carriers, like carrier 2 shown in
FIG. 1 without a separate box. Likewise, the prior art includes
boxes designed to hold substrates without the need for a separate
carrier. Throughout this application, the term "cassette"
is used generically to cover substrate carriers used separately
or with a box and boxes used separately or with a carrier. As used
herein, the word "cassette" is intended to cover any portable
device designed to hold and protect one or more substrates during
transport or storage.
The purpose of the present invention is to protect substrates from
the harmful effects of moisture during transport and storage. This
is achieved by making the cassette, or at least a part thereof,
out of a hydrophilic plastic material. One suitable plastic material
is polycarbonate.
Cassettes made out of hydrophilic materials such as polycarbonate
can be treated in a number of ways to reduce the moisture content
of the material. FIG. 2 shows, by way of example, a substrate carrier
2 in combination with a gas source 10. The gas source 10 can be
used to create a flow of gas around the carrier 2 to dry out the
hydrophilic material from which the carrier 2 is made. The gas could,
for example, be nitrogen or even heated air. Bathing the carrier
2 in such a gas serves to reduce moisture content of the hydrophilic
material.
FIGS. 3 and 4 show alternative techniques for reducing the moisture
content of the hydrophilic material from which the carrier 2 is
made. The carrier 2 for example, can be placed inside a vacuum
chamber 16 as shown in FIG. 3. Evacuation of the chamber 16 using
a pump 14 will serve to draw moisture from the hydrophilic material
to reduce the total moisture content. The carrier 2 could also be
placed in an oven 17 as shown in FIG. 4. Using heating elements
18 to warm the oven 17 to a temperature between 100.degree. F. and
150.degree. F. will serve to reduce the moisture content of the
carrier 2. This temperature range, while high enough to draw the
moisture out of the hydrophilic plastic material, is not high enough
to melt the plastic or otherwise undermine the structural integrity
of the carrier 2.
FIGS. 2-4 show the cassette being dried without the substrates
in place. This may be preferred to prevent the substrates from being
damaged by the drying process. However, the substrates can be present
in the cassette during the drying operation as long as the particular
drying process used will not adversely affect the substrates. Many
substrates can easily withstand temperatures in the 100.degree.
F. to 150.degree. F. range and are not adversely affected by nitrogen,
warm air or vacuum treatment.
FIGS. 5 and 6 each show cassettes surrounded by a moisture-proof
barrier 20. This moisture-proof barrier 20 is added after the cassettes
have been dried to encapsulate the cassette and its contents. Given
this arrangement, the dried cassette acts as a desiccant absorbing
any water molecules within the moisture-proof barrier 20. The moisture-proof
barrier 20 prevents water molecules from passing through the barrier
or at least limits the number of molecules passing through to a
level where such molecules will also be absorbed by the cassette.
The moisture-proof barrier 20 can be made of any one of a number
of suitable materials. Definite advantages are achieved by using
a laminated plastic film which can be heat sealed. One such laminate
includes a layer of polyethylene, a layer of polyester, a carbon
conductive layer, an acrylic resin layer, and a vinylidene layer.
When the packaging system of the present invention is used, a cassette
comprising a substrate carrier 2 or a box 3 or both, is provided.
At least a portion of the cassette is made of a hydrophilic plastic
material. The material is treated as described above and then is
sealed, along with the substrates, in a moisture-proof barrier 20.
The substrates may be inserted into the cassette before the cassette
is treated or between the treatment of the cassette and encapsulation
of the cassette in a moisture-proof barrier 20. When this procedure
is used, the cassette acts as a desiccant and works in combination
with the moisture-proof barrier 20 to protect the substrates from
moisture. |