Ready-for-dispatch package for semiconductor wafers, and method for the ready-for-dispatch packaging of semiconductor wafers

Abstract

The invention relates to a ready-for-dispatch package for semiconductor wafers, comprising a) a closeable plastic container which is loaded with the semiconductor wafers and has a lid and a body, a seal between the lid and the body and a particle filter which is integrated with the container and allows exchange of gas between the interior space of the container and the external environment of the container; b) a first sheath made from plastic, which surrounds the container and rests closely against the container with the aid of reduced pressure; c) a means for binding moisture; d) a second sheath made from coated plastic, with a coating which blocks the passage of moisture and rests closely against the first sheath and against the container with the aid of reduced pressure; e) a shock-absorbing structure which embeds the sheathed container in a positive-fitting manner; and f) an outer packaging which surrounds the double-sheathed and embedded container in a positive-fitting manner. The invention also relates to a method for the ready-for-dispatch packaging of semiconductor wafers in a packaging of this type.

Description

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to a ready-for-dispatch package for semiconductor wafers and to a method for the ready-for-dispatch packaging of semiconductor wafers in the package.

2. Background Art

Semiconductor wafers are generally dispatched from the manufacturer to the purchaser's premises. During transportation, long distances often have to be covered and the means of transport frequently have to be changed. Therefore, there is a considerable risk that the sensitive semiconductor wafers may be damaged. Even without any visible damage caused by scratches or fracturing, impurities may have a considerable adverse effect on the semiconductor wafers or even make them unusable for the desired purpose, namely the fabrication of electronic components.

U.S. Pat. No. 6,131,739 discloses a shock-absorbing package for a plurality of containers holding semiconductor wafers, consisting of two half-shells of foamed plastic configured with recesses into which the containers are placed in a positive-fitting manner. In this sector of the industry, commercially available containers are known as FOSBs, which stands for “Front Opening Shipping Box”. A container of this type is described, for example, in U.S. Pat. No. 6,581,264. A shock-absorbing package of this type is suitable for reducing the risk of mechanical damage to the semiconductor wafers during transport.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a ready-for-dispatch package for semiconductor wafers which further reduces the risk of damage and makes it possible to ensure that semiconductor wafers transported therein can be removed from the containers in a state which corresponds substantially to the state of the semiconductor wafers when the containers were loaded. This and other objects are met by a ready-for-dispatch package for semiconductor wafers, comprising

• a) a closeable plastic container which is loaded with the semiconductor wafers and has a lid and a body, a seal between the lid and the body and a particle filter which is integrated in the container and allows the exchange of gas between the interior space of the container and the external environment of the container;
• b) a first sheath made from plastic, which surrounds the container and rests closely against the container with the aid of reduced pressure;
• c) a moisture absorber;
• d) a second sheath made from coated plastic, with a coating which blocks the passage of moisture and rests closely against the first sheath and against the container with the aid of reduced pressure;
• e) shock-absorbing elements which embed the sheathed container in a positive-fitting manner; and
• f) an outer package which surrounds the double-sheathed and embedded container in a positive-fitting manner.

The invention is also directed to a method for the ready-for-dispatch packaging of semiconductor wafers in the package, which includes the steps of

• a) cleaning and drying a plurality of the containers, the containers forming a batch;
• b) analyzing one container of the batch for the presence of impurities caused by particles, metals and organic substances;
• c) loading the other containers of the batch with semiconductor wafers and closing the containers with lids, provided that the analyses have shown that the respective impurities are below defined limit values;
• d) sheathing the individual containers with a first sheath and creating a reduced pressure inside the first sheath until the first sheath rests closely against the containers;
• e) sheathing the individual sheathed containers with a second sheath, and creating a reduced pressure inside the second sheath, until the second sheath rests closely against the sheathed containers;
• f) introducing a means for binding moisture at least either between the containers and the first sheath (during step d)) or between the sheathed containers and the second sheath (during step e));
• g) embedding the double-sheathed containers in shock-absorbing elements; and
• h) packing the double-sheathed and embedded container(s) into the outer packaging and closing the outer packaging; or, if the analyses performed in step b) have shown that the respective impurities are not completely below defined limit values, continuing with step a), with the other containers of the batch forming a new batch.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates one embodiment of a package of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT(S)

The package according to the invention is particularly suitable for the dispatch of semiconductor wafers, in particular for the dispatch of semiconductor wafers made from silicon with a diameter of at least 300 mm. It is distinguished in particular by the fact that the semiconductor wafers inside it are effectively protected from damage caused by vibrations and from contamination by foreign substances of any type. Furthermore, the structure of the package enables the semiconductor wafers to be taken out of the container without any risk of causing contamination of the semiconductor wafers during removal thereof. The invention is explained in more detail below with reference to FIG. 1, which diagrammatically depicts all the features of the packaging.

The semiconductor wafers 1 are in a commercially available container 2 made from plastic, which comprises a body 3 and a lid 4. Suitable plastics are in particular polycarbonate (PC), polybutylene terephthalate (PBT), polyolefin elastomers (POE) and polyethylethylene (PEE). A seal, preferably a sealing ring 5 made from plastic, is provided between the body 3 and the lid 4, preventing particles from being produced through friction when the lid 4 is being opened and closed and also forming a barrier against the penetration of particles from the outside. The container 2 provides space for holding a plurality of semiconductor wafers 1, a number of 25 being typical. The semiconductor wafers stand, for example, in regularly spaced slots which have lateral guide strips, and are generally held in position standing upright by spring tongues which are integrated in the lid, after the lid has been closed. Furthermore, the container 2 has at least one gas-permeable opening which is closed off by a particle-retaining filter 6. The opening may be provided in the lid 4 or the body 3 of the container.

The container 2 is sheathed by at least two sheaths. The first sheath 7, which rests directly against the container, is preferably a transparent plastic film, polyethylene (PE) being preferred. The film is preferably reinforced by a coating which increases the resistance to tearing and puncturing. A coating comprising a layer of polyamide (PA) or polyethylene terephthalate (PET) or a combination of the two layers is particularly preferred. The second sheath 8 consists of a coated plastic, which is once again preferably PE, the coating increasing the mechanical strength, in particular the resistance to tearing and puncturing, and forming a barrier against external moisture. An aluminum-coated plastic film is preferred, most preferably a film of this type which is additionally reinforced with an outer layer to increase the resistance to tearing and puncturing. The outer layer preferably consists of polyamide (PA) or polyethylene terephthalate (PET) or a combination of these two layers. To protect against moisture from the inside, there is a moisture absorber 9 which binds moisture, preferably one or more paper or material pouches filled with a substance which extracts water, i.e. a dessicant. The moisture absorber 9 is preferably positioned between the first sheath and the second sheath and takes up moisture which diffuses through the first sheath 7. It does not matter if the moisture absorber releases particles, since the semiconductor wafers 1 continue to be protected by the container 2 and the first sheath 7. However, it is also possible for the moisture absorber 9 additionally or alternatively to be arranged between the container 2 and the first sheath 7. Each of the two sheaths and the container may be provided with labels.

There is a pressure difference between the interior of the container, on the one hand, and the space between the container 2 and the first sheath 7 and the space between the first sheath 7 and the second sheath 8, on the other hand, so that the sheaths rest closely against the container or one another. This is important because the sheaths consequently do not form any bubbles which alter the shape of shock-absorbing elements 10 or form resilient spaces between the elements and the sheathed container 2. This also prevents the elements from being damaged by such alterations of their shape, as well as the possibility of relative movements between the sheathed container and the elements, which would in each case generate particles. The pressure difference is preferably up to 50 mbar. There are preferably two elements 10 which engage on two opposite sides of the sheathed container. The shock-absorbing elements 10 preferably consist of a foamed plastic or a material with similar properties. Shock-absorbing elements made from polypropylene (PP), polystyrene (PS) or polyurethane (PU) are particularly preferred. The elements have recesses in which the sheathed container is embedded in a positive-fitting manner, and their external dimensions correspond to the internal dimensions of an outer packaging 11. The outer packaging 11 surrounds the elements 10 and the sheathed container 2 embedded therein, likewise in a positive-fitting manner. There is therefore no possibility of the container 2 or the elements 10 moving in the outer packaging 11 during transportation of the semiconductor wafers 1. The outer packaging preferably consists of a cardboard material or of light metal. Its external dimensions are preferably such that it is ready for dispatch as such and can, if desired, be stacked on pallets.

The semiconductor wafers are protected against the action of moisture in two ways in the ready-for-dispatch package described, namely from the inside by the moisture absorber 9, and from the outside by the second sheath 8, which forms a barrier against the penetration of moisture. Particular protection against the penetration of particles is provided by the sealing ring 5 between the lid 4 and the body 3 of the container 2, and by the filter, which is impermeable to particles 6, in the container wall. Particular protection against contamination of the semiconductor wafers by organic substances, metal traces and particles is provided by the use of materials for the container and sheaths which do not cause any such contamination. Contamination is strictly tested in the case of the container. The test method is part of the overall method according to the invention, which is explained in more detail below.

Before the container is loaded with semiconductor wafers, it is cleaned and dried. The cleaning is preferably carried out in an immersion bath filled with cleaning agent or in an installation in which the cleaning agent is sprayed onto the container. The cleaning agent is preferably water, optionally containing surfactant. The cleaning is preferably carried out over a defined period of time and under controlled external conditions, most preferably in a clean room of class 10 or below in which a defined temperature and atmospheric humidity have been established. A container is only loaded with semiconductor wafers once it has passed quality control. Quality control comprises analyses for particles, metal traces, traces of ions, and traces of organic impurities, as well as, if desired, a visual inspection for damage and defects, and is only passed if the analyses and inspection have shown that defined limit values have not been exceeded in any case and there is no damage or defect. The quality control analysis is carried out on one container which represents a batch of identical containers. If this quality control is concluded without objection, the other containers of the batch are released for loading with semiconductor wafers. Otherwise, the other containers of the batch are cleaned and dried again or if appropriate excluded from further use.

The following limit values should not be exceeded:

• a) in the LPC test, in which the container is filled with particle-free ultra-pure water and pivoted and then a sample with a volume of 50 ml is removed and checked for the presence of particles (LPC, liquid particle count) using a commercially available laser scattered light measuring appliance:
• when determining particles with a diameter of >1 μm, fewer than 50 particles, preferably fewer than 10 particles;
• when determining particles with a diameter of >0.3 μm, fewer than 1,000 particles, preferably fewer than 100 particles;
• when determining particles with a diameter of >0.2 μm, fewer than 2,000 particles, preferably fewer than 200 particles;
• b) in the metal and metal ion test, in which the container is filled with 50 ml of ultra-pure water without any impurities and is pivoted, and the sample is analyzed by means of ICP-MS (inductively coupled plasma—mass spectroscopy) or by means of CE (capillary electrophoresis):
• in the determination by ICP-MS, a total weight of metals of at most 100 ng, preferably at most 10 ng;
• in the determination by CE, a total weight of ions of at most 200 ng, preferably at most 100 ng;
• c) in the organic impurity test, in which container material is heated to an elevated temperature and the escape of gaseous organic impurities (e.g. e-amino-caprolactam, tetrahydrofuran) is analyzed by gas chromatography:
• in the determination by gas chromatography, a total concentration of organic impurities of <50 ppm, preferably <5 ppm, based on the weight of the container material tested.

A container which has been released for loading is loaded with the semiconductor wafers and closed. This is preferably done with the aid of a robot. The container is then sheathed with the first sheath; if desired, a moisture-extracting pouch is placed between the container and the sheath, the pressure in the interior of the sheath is reduced, and the sheath is welded. The gas atmosphere which is present in the container preferably consists of air, nitrogen, a noble gas or any desired mixture of the abovementioned gases. Then, the container which has been sheathed once is sheathed with the second sheath, if desired, a moisture-extracting pouch is placed between the first and second sheath, the pressure inside the second sheath is reduced, and the second sheath is welded. The gas atmosphere which is present in the second sheath preferably consists of air, nitrogen, a noble gas or any desired mixture of the said gases. The container which has been sheathed twice in the manner outlined above is placed into the shock-absorbing elements, the package formed in this way is packed into the outer packaging and the latter is closed. Additional sheaths, while not ordinarily necessary, may also be provided if desired.

The quality control and the structure of the ready-for-dispatch package ensure that the recipient is able to remove from the package semiconductor wafers whose properties correspond to the properties when the container was loaded. Furthermore, the recipient still has considerable flexibility with regard to unpacking of the semiconductor wafers. For example, the outer packaging, the shock-absorbing elements and the second sheath can be removed while still outside clean room conditions. However, the first sheath and in particular the lid of the container should be removed in a clean room at the recipient's premises.

The invention prevents volatile organic impurities from condensing on the semiconductor wafers during shipping of the semiconductor wafers in amounts which would subsequently have an adverse effect on the fabrication of electronic components, in particular components with line widths of less than 0.1 μm. Residual moisture is also prevented from condensing, which would likewise lead to problems in the fabrication of electronic components. The semiconductor wafers are also prevented from being contaminated by particles originating from the packaging during transportation, which would likewise lead to problems in the fabrication of electronic components. Furthermore, in particular, the use of a reduced pressure during packaging prevents the container from being able to move relative to the outer packaging as a result of inclusions of air, which in the event of transport-induced vibrations could lead to semiconductor wafers jumping out of the spring tongue holders and being weakened, in particular in the edge region, in such a manner that there would be an increased risk of fracturing for example during heat treatments involved in component fabrication. The packaging without any play also prevents damage to the sheaths during shipping, which would lead to contamination of the semiconductor wafers when they are unpacked.

The invention ensures that contamination of the semiconductor wafers caused by foreign substances in the form of localized light scatterers (LPD, light point defects) with a diameter of more than 0.05 μm, of which there were fewer than 10 defects per side face before the semiconductor wafers were packaged, does not exceed this level even after the semiconductor wafers have been shipped and unpacked.

While embodiments of the invention have been illustrated and described, it is not intended that these embodiments illustrate and describe all possible forms of the invention. Rather, the words used in the specification are words of description rather than limitation, and it is understood that various changes may be made without departing from the spirit and scope of the invention.

Claims

1. A ready-for-dispatch package for semiconductor wafers, comprising

a) a closeable plastic container which is loaded with semiconductor wafers and has a lid and a body, a seal between the lid and the body and a particle filter which is integrated with the container and allows the exchange of gas between the interior space of the container and the external environment of the container;

b) a first sheath of plastic, which surrounds the container and rests closely against the container through the aid of reduced pressure;

c) a moisture absorber;

d) at least a second sheath made from coated plastic, which rests closely against the first sheath and against the container with the aid of reduced pressure, at least one coating being a coating which blocks the passage of moisture;

e) a shock-absorbing structure which embeds the sheathed container in a positive-fitting manner; and

f) an outer package which surrounds the double-sheathed and embedded container in a positive-fitting manner.

2. The package of claim 1, wherein the first sheath is transparent.

3. The package of claim 1, wherein the second sheath has a tear-resistant outer coating.

4. The package of claim 1, wherein the reduced pressure between the first sheath and the second sheath and the outside environment of the second sheath is up to 50 mbar.

5. A method for the ready-for-dispatch packaging of semiconductor wafers in the package of claim 1, comprising:

a) cleaning and drying a plurality of containers, the plurality of containers constituting a batch;

b) analyzing one container of the batch for the presence of impurities caused by particles, metals and organic substances and defining a limit value for each;

c) loading the other containers of the batch with semiconductor wafers and closing the container lids, provided that the analyses have shown that the respective impurities are below the defined limit values;

d) sheathing individual containers with a first sheath and creating a reduced pressure inside the first sheath until the first sheath rests closely against the container;

e) sheathing the individual sheathed containers with a second sheath, and creating a reduced pressure inside the second sheath, until the second sheath rests closely against the sheathed container;

f) introducing a moisture absorber between the container and the first sheath during step d) or between the sheathed containers and the second sheath during step e), or between both the containers and the first sheath and the first sheath and the second sheath;

g) embedding double-sheathed container(s) in a shock-absorbing structure; and

h) packing the at least double-sheathed and embedded container(s) into the outer package and closing the outer package.

6. The method as claimed in claim 5, wherein the following limit values are defined for the analyses carried out in step b):

a) in a liquid particle count test:

particles with a diameter of >1 μm, fewer than 50 particles;

for particles with a diameter of >0.3 μm, fewer than 1,000 particles;

for particles with a diameter of >0.2 μm, fewer than 2,000 particles;

b) for traces of metals and metal ions by

ICP-MS, a total weight of metals of at most 100 ng;

by CE, a total weight of ions of at most 200 ng;

c) for organic impurities

by gas chromatography, a total concentration of organic impurities of <50 ppm, based on the weight of the container material tested.

7. The method of claim 5, further comprising i) selecting containers which constitute a batch which has failed the analyses of step b), and repeating steps a) through h) and optionally i).