Semiconductor device manufacturing: process – Semiconductor substrate dicing – Having specified scribe region structure
Reexamination Certificate
1999-01-20
2002-10-15
Whitehead, Jr., Carl (Department: 2822)
Semiconductor device manufacturing: process
Semiconductor substrate dicing
Having specified scribe region structure
C438S460000, C438S465000, C438S928000, C438S113000, C438S114000, C438S033000
Reexamination Certificate
active
06465329
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to microcircuit packaging in general, and in particular, to a method and apparatus for protecting hypersensitive microcircuits on a semiconductor wafer from contamination and mechanical damage during die sawing and subsequent die-handling operations.
2. Description of the Related Art
Microcircuits are typically fabricated on the surface of a wafer of a semiconductor material, e.g., silicon, in a rectangular array of identical devices. The typical manufacturing process involves numerous manufacturing steps, such as cleaning, printing, etching, doping, coating, plating, and ion implantation. Upon completion of these steps, and prior to the packaging of the individual microcircuits for use in electronic devices, the microcircuits, together with an underlying portion of the wafer, are separated from wafer into individual dies, or “chips.” This separation is typically accomplished by a mechanical sawing operation, or by breaking the wafer along scribe lines created in the wafer by a laser or a diamond-tipped scribe.
In conventional microcircuit die sawing practice, a layer of a sticky tape, such as that sold by the Nitto Denko Corporation of Osaka, Japan under the name “Nitto tape,” or that sold by the Lintec Company of Shiga, Japan, is attached to the backside of the wafer, which is then placed face up on the saw table, and sawn through down to, but not including, the tape backing. The individual dies are then removed from the tape by automated “pick-and-place” die-handling equipment that includes a needle that pierces the sticky tape from the underside to contact the bottom surface of the die and separate it from the tape, and an arm that grasps the upper, circuit-containing surface of the die with, e.g., a vacuum collect, and transports it to another location for subsequent processing
Typical microcircuits manufactured in the above manner are substantially flat, i.e., the circuit components and elements are closely integrated with each other, are substantially planar in form, and are typically on the order of a few angstroms to a few microns thick. As such, they are moderately resistant to contamination by dust particles and vapors generated during the die-sawing operation, as well as to mechanical damage occasioned by handling of the dies during die sawing and subsequent manufacturing operations. In some instances, this resistance to contamination and/or mechanical damage can be enhanced by the vapor deposition of a protective layer of silicon dioxide or silicon nitride on the face of the microcircuits prior to die separation.
However, there are at least two classes of microcircuit devices that are highly sensitive to contamination by die-sawing byproducts and/or to mechanical damage occasioned by handling during manufacturing, namely, the so-called “optical sensor” and “micro-machine” devices. An example of the former would include the “micro-mechanical display logic and array” of A. M. Hartstein, et al., (U.S. Pat. No. 4,229,732), while examples of the latter would include the “electrostatic motor” described by R.T. Howe, et al. (U.S. Pat. No. 4,943,750), or the “machine structures” made by the method of Sparks et al. (U.S. Pat. No. 5,427,975).
These latter types of devices have in common that both types include highly fragile micro-structures and/or specialized reflective surfaces that either extend, or face, upward from the face of the die, and they may also include microscopic openings into the underlying semiconductor substrate, such as might be found in an integrated circuit pressure transducer. For obvious reasons, these structures are highly susceptible to both contamination by the dust, cooling liquids, and/or vaporous by-products generated by die-sawing, as well as to the mechanical damage that could result from, e.g., a slight, unintended gust of air or drop of water incident on the face of the wafer. Such contamination or damage could result in an entire wafer of relatively expensive devices being ruined and scrapped.
Accordingly, special manufacturing procedures and equipment are needed to handle these hypersensitive types of devices. This is particularly so at the stage of their manufacture at which the micro-features are fully defined on the face of the wafer or on the separated dies, such as during the die-sawing operation, or during subsequent die-mounting procedures. The prior art methods and apparatus for dealing with these special types of microcircuits described below, while workable, have some associated drawbacks that adversely effect their efficiency.
The prior art method for die-sawing these hypersensitive types of microcircuits is described in some detail in U.S. Pat. No. 5,362,681 to C. M. Roberts, Jr., et al. The method includes inverting the wafer face down on the saw table and sawing it from the back face of the wafer. To protect the microcircuit devices on the front face of the wafer, the wafer is attached to a spacer film, typically a Mylar tape, carried on a stretcher frame. The film has a pattern of openings in it corresponding to the array of dies on the face of the wafer, and is adhered to the front face of the wafer, rather than to its backside, as is done with conventional microcircuits. The spacer film is sized such that its periphery overhangs the margin of the wafer. Four sets of alignment holes, oriented with respect to the “streets” between the dies, are punched into the tape on opposite sides of the wafer outside of its margin. A second film is then adhered to the backside of the spacer film to seal the component openings in the spacer film.
The wafer is then placed upside-down on the saw table, and aligned with respect to the saw blade by means of an alignment system that aligns the wafer with respect to the above-described four sets of alignment holes in the spacer film. The wafer is sawed through its back side down to, but not through, the spacer film to singularize the dies from the wafer. The dies are then individually pushed and lifted from the spacer film by means of specially designed pick-and-place equipment that includes a special, hollow “needle cluster” that pushes upwardly through the spacer film to contact the edges of the die to separate it from the film, and an arm that grasps the die from the back side with a vacuum collet. The arm then inverts the die 180 degrees such that its front face faces upward, then hands the die off to a second arm also equipped with a special hollow vacuum collet that enables the arm to grasp the sensitive front side of the die without damaging the microcircuit thereon.
While the above prior art method is workable, it has several drawbacks associated with it: First, since the wafer is sawn upside down, the underside of the dies, rather than their top surfaces, are presented for removal of the dies from the spacer film. This prevents the use of conventional automated pick-and-place equipment, and necessitates the use of the specially adapted pick-and-place apparatus described above to accommodate the sensitive micro-structures located on the top side of the die. It would be desirable if conventional pick-and-place die handling equipment could be used with these hypersensitive types of chips.
Also, because removing the dies from the spacer film destroys the sealed enclosure that protects the microcircuits during the sawing operation, once the dies are removed from the spacer film, they must thereafter be maintained in a clean room environment and are at increased risk of mechanical damage and/or contamination until they have been individually packaged in a protective enclosure. It would therefore be desirable if the protection afforded the delicate microstructures during the sawing operation could be retained with the individual dies after sawing so that they could be safely handled and stored in a less critical environment.
Further, because the wafer is sawn face down on the table, the scribe lines on its face, and indeed, the microcircuits themselves, are not directly accessible for saw alignment purposes. Instead
Amkor Technology Inc.
Duong Khanh B.
Jr. Carl Whitehead
LandOfFree
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