US20060032784A1

US20060032784A1 - Foam laminate system for semiconductor wafers

Info

Publication number: US20060032784A1
Application number: US10/917,048
Authority: US
Inventors: Valoris Forsyth
Original assignee: Illinois Tool Works Inc
Current assignee: Illinois Tool Works Inc
Priority date: 2004-08-12
Filing date: 2004-08-12
Publication date: 2006-02-16

Abstract

A cushion-like device is provided for the transportation of semiconductor wafers. The device includes an interior formed from polyethylene closed cell foam that utilizes a foaming agent that imparts minimal alkanes and cations into the polyethylene foam material. An electrostatic discharge dissipative polyethylene film surrounds the foam interior and is joined thereto by hot melt EVA material. An array of apertures of approximately 0.010 inch diameter and less than 0.25 inch spacing is formed in the film to allow the foam to compress upon impact.

Description

BACKGROUND OF THE INVENTION

1. Field of the Invention
The present invention relates to a foam laminate system for use in semiconductor wafer portion, particularly from the front-end to an assembly location.
2. Description of the Prior Art
The transportation of semiconductor wafers, particularly transportation from the front-end to an assembly location, which typically may involve a trans-oceanic voyage, presents a set of challenges. Mechanical and electrostatic protection must be provided. Contamination levels must be kept low to prevent the introduction of ions that, in combination with moisture vapor, generate corrosion, pitting and/or transistor inversion. Extreme cleanliness required during the shipping of the semiconductor wafers. Similarly, mechanical protection of the semiconductor wafers during transportation can be problematic if the wafer container is not completely full.

OBJECTS AND SUMMARY OF THE INVENTION

It is therefore an object of the present invention to provide a cushion-like element for the transportation of semiconductor wafers which maintains the low contamination levels required for such transportation.
It is therefore a further object of the present invention to provide a cushion-like element which provides mechanical and electrostatic protection to semiconductor wafers during transportation.
These and other objects are attained by providing a cushion with a cylindrical interior formed of closed cell polyethylene foam, typically one quarter to three eighths of an inch thick, with a diameter approximately equal to the diameter of the semiconductor wafers to be transported. A thin outer surface of electrostatic discharge (ESD) dissipative polyethylene is laminated to the polyethylene foam interior by hot melt EVA adhesive. The exterior surface is perforated with small apertures, typically less than 0.010 inches in diameter, to allow for compression upon impact. The ESD dissipative polyethylene is heat wire cut to seal the ends about the periphery of the cushion.

BRIEF DESCRIPTION OF THE DRAWINGS

Further objects and advantages will become apparent from the following description and from the accompanying drawing, wherein:
FIG. 1 is a top plan view of the cushion-like device of the present invention.
FIG. 2 is a cross-sectional view along plane 2-2 of FIG. 1.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring now to the drawings in detail wherein like numerals indicate like elements throughout the several views, one sees that FIG. 1 is a top plan view of the cushion-like device 10 of the present invention. The cushion-like device 10 is symmetric so that FIG. 1 could likewise be a bottom view. Device 10 is cylindrically shaped with a diameter approximately equal to the diameter (typical diameters include, but are not limited to, eight or twelve inches) of the semiconductor wafers to be transported. As shown in FIG. 2 the interior of device 10 is formed by a shallow cylindrically shaped portion 12 of polyethylene closed cell foam which is typically neither treated nor dyed. The closed cell foam of portion 12 uses a foaming agent that imparts minimal alkanes and cations into the polyethylene foam material. Portion 12 of polyethylene close cell foam is typically one quarter to three eighths of an inch thick, but those skilled in the art, after review of this disclosure, will recognize that different thicknesses may be appropriate for various applications. The exterior of device 10 is covered with antistatic film (or laminate) 14. Antistatic film 14 is typically Richmond/Valeron® material, such as 1207 LLDPE Laminate Grade Film (86-R0438) which is sold by assignee Illinois Tool Works Inc., using the specification number 86-R0438 which details the formulation and property requirements for this antistatic film. Antistatic film 14 is typically 0.003 inches thick and includes perforations 16 which typically are spaced less than one fourth of an inch apart and have a diameter of 10 mils (0.010 inches). This allows compression of portion 12 of polyethylene closed cell foam while maintaining the required clean environment around device 10. Antistatic film 14 is secured to portion 12 of polyethylene closed cell foam by a laminating glue which is a hot melt EVA material that is likewise substantially free of cations and alkenes and is highly compatible to polyethylene materials. As shown in FIG. 2, the antistatic film 14 is cut and heat sealed around the edges to form circular peripheral seam 18 thereby minimizing particulation of the foam upon aging. The antistatic film 14 typically provides electrostatic dissipative characteristics to both sides of portion 12 of polyethylene closed cell foam at low voltages, such as ten volts.
The cushion-like device 10 is designed to generate contamination levels below 50 ppm (leachable alkanes, anions, halogens, ammonias or cations) as detected through leach testing at 60°0 and 90° Centigrade testing at one hour soak durations, as well as organic and inorganic analysis. The low organic/inorganic and acid compound material contamination reduces ion contamination, pitting and corrosion on tight geometry 90 nanometer (and below) semiconductor wafers during shipping.
In order to use cushion-like device 10, the user typically places separations (not shown) between successive semiconductor wafers (not shown). A separator which is particularly well adapted for this application is disclosed in U.S. provisional application Ser. No. ______, filed on Jul. 13, 2004, entitled “Scribed Interleaf Separator Wafer Packaging”. The cushion-like device 10 is placed at one or both ends of the stack of semiconductor wafers and separators and the resulting stack is placed into a container adapted for semiconductor wafer transportation. A container which is partially well adapted for this application is disclosed in PCT/US04/14659, filed on May 10, 2004, entitled “Wafer Box with Radially Pivoting Latch Elements”. The appropriate number and thickness of cushion-like devices 10 are chosen so that the semiconductor wafers are mechanically constrained within the container.
Thus the several aforementioned objects and advantages are most effectively attained. Although a single preferred embodiment of the invention has been disclosed and described in detail herein, it should be understood that this invention is in no sense limited thereby and its scope is to be determined by that of the appended claims.

Claims

1. A device for cushioning semiconductor wafer, comprising:

a foam interior; and

a film surrounding said foam interior, said film having antistatic characteristics and apertures to allow for compression of said foam interior upon impact.

2. The device of claim 1 wherein said foam interior comprises closed cell polyethylene foam.

3. The device of claim 2 wherein said closed cell polyethylene foam utilizes a foaming agent which imparts minimal alkanes and cations to said closed cell polyethylene foam.

4. The device of claim 1 wherein said foam interior is cylindrical with a thickness substantially in the range of one quarter to three eighths of an inch thick.

5. The device of claim 1 wherein said film is secured to said foam interior by hot melt material which is substantially free of cations and alkanes.

6. The device of claim 1 wherein said film is an electrostatic dissipative polyethylene.

7. The device of claim 6 wherein said film is approximately 0.003 inches thick.

8. The device of claim 7 wherein said apertures are approximately 0.010 inches in diameter and are spaced less than 0.25 inches apart.

9. The device of claim 1 wherein said film includes a plurality of pieces which are joined together by a seam formed by heat sealing.