Metal working – Method of mechanical manufacture – Electrical device making
Reexamination Certificate
2002-01-28
2004-08-10
Vo, Peter (Department: 3729)
Metal working
Method of mechanical manufacture
Electrical device making
C029S564600, C029S743000, C029S832000, C257S678000, C257S618000, C264S571000
Reexamination Certificate
active
06772509
ABSTRACT:
FIELD OF THE INVENTION
This invention in general relates to the making and handling of a very thin semiconductor die and, more particularly, to an improved procedure for separating and handling very thin dice for better throughput and yield.
BACKGROUND OF THE INVENTION
As technology progresses, integrated circuits are being formed on smaller and thinner semiconductor dice for a variety of applications. Relatively thin integrated circuits (ICs) or semiconductor dice, also known as “ultra-thin” or “super-thin” ICs or dice, are used in applications such as smart cards, smart labels, sensors, and actuators. A thin die for sensors is described in U.S. Pat. No. 6,427,539, incorporated herein by reference in its entirety. There, a relatively thin semiconductor die with piezo-resistors act to measure the pressure of fluids in vehicles. The thin semiconductor die is bonded to a stainless steel port in order to measure diaphragm deformation.
For smart card applications, the thickness of the die may be as low as 100 micrometers (&mgr;m). In the future, it is anticipated that an even smaller thickness will be necessary. For sensors, a thin die may have a thickness of between 5 and 50 &mgr;m as described in U.S. Pat. No. 6,427,539.
When making and handling a very thin semiconductor die, care must be taken not to fracture or otherwise damage the die. Currently, a need exists for improved methods and procedures to fabricate, separate, and transport a thin die for high volume applications where automated techniques are required to produce high throughput and acceptable yields.
It is known to separate and handle integrated circuits on thin semiconductor die by mechanical grinding, chemical etching and dry etching with the assistance of adhesive or UV related release tapes and carrier wafers. Some of the approaches taken in the electronics industry to separate thin wafers into dice and handle thin dice include dicing by cutting and dicing by thinning. In dicing by cutting, a dicing tape is mounted on frames. The wafers are mounted to the dicing tape, backside down. Dicing is carried out by sawing, laser cutting, dry etch, etc. After cutting, the dice are separated on the dicing tape and sent to the assembly line on a wafer frame for pick and place. The thin die is then ejected from the backside of the tape with the help of an ejector pin and picked by a vacuum tip. An example of this process flow is described in Muller et al., “Smart Card Assembly Requires Advanced Pre-Assembly Methods,” SEMICONDUCTOR INTERNATIONAL (July 2000) 191.
In dicing by thinning, trenches are etched or sawed on the topside of a device wafer. Laminating tapes are then placed on a carrier wafer for mounting the carrier wafer to the topside of the device wafer. The bottom side of the device wafer is then thinned until the topside trenches are opened from the bottom side. A second carrier wafer is then mounted to the bottom side of the device wafer by a high-temperature release tape. The first carrier wafer is removed and then the thin dice can be removed by locally heating a vacuum-picking tool. An example of this process flow requiring multiple carrier wafers and tape transfers is described in C. Landesberger et al., “New Process Scheme for Wafer Thinning and Stress-Free Separation of Ultra Thin ICs,” published at MICROSYSTEMS TECHNOLOGIES, MESAGO, Dusseldorf, Germany (2001).
Alternatively, it has been known to saw or cut a carrier wafer into carrier chips, each of them carrying a thin die. In this case, the carrier chip is removed after die bonding by thermal release of the adhesive tape. An example of this process flow is described in Pinel et al., “Mechanical Lapping, Handling and Transfer of Ultra-Thin Wafers,” JOURNAL OF MICROMECHANICS AND MICROENGINEERING, Vol. 8, No. 4 (1998) 338.
Conventional procedures have been met with a varying degree of success. The combination of carrier transfers and tape transfers necessitate multiple steps with long cycle times and yield loss. Moreover, the use of heat release and other tapes may exhibit unacceptable residual adhesion. Further, when used in combination with an ejector pin, the edges may not delaminate from the tape due to the lack of flexural rigidity of the thin die and due to the die's small size in the in-plane directions. The small size of the die may also limit the net suction force that could be exerted by the vacuum tip to overcome residual tape adhesion. With regard to conventional dicing and wafer sawing methods, these steps often result in damage to the thin die that causes device failure or performance degradation. Conventional ejector pins may exert excessive stress that damages the thin die, also causing cracking and device failure. Carrier transfer or tape transfer may lead to die contamination on both sides of the die. Multiple transfers by wafer carriers typically lead to lower yield due to increased handling and contamination. In the case of a very thin die for sensor applications, organic adhesive may leave residue on the die surface, causing poor bonding with the surface being measured.
It is, therefore, desirable to provide an improved device and method of fabricating, separating and handling very thin dice to overcome most, if not all, of the preceding problems.
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Chen Shiuh-Hui Steven
Field Cheryl
Lefebvre Didier R.
Wang Joe Pin
Mancini Brian M
Miller Thomas V
Motorola Inc.
Nguyen Donghai D.
Vo Peter
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