Patent Application
20070004174
The invention relates to the manufacture of semiconductor devices. More particularly, the invention relates to methods and systems for saw singulation in the manufacture of semiconductor devices.
It is known to fabricate numerous semiconductor devices on a wafer and subsequently singulate the devices for final testing and packaging. Singulation may be accomplished by sawing, or by partial sawing combined with controlled breaking along the saw kerfs, also known as scribing and breaking. Generally, the wafer singulation process includes steps for aligning the wafer in a position for cutting, and then sawing through, or partially through, the wafer along prepared singulation or saw streets according to predetermined die dimensions. The sawing is performed using a metallized or resin-bonded diamond disc saw blade rotating at a high speed. After singulation, the devices undergo further processing such as cleaning, testing, and packaging.
Because semiconductor wafers upon which individual semiconductor devices are fabricated are generally disc-shaped, a saw blade coming into contact with the edge of the wafer upon entry or exit may be deflected horizontally. The degree of deflection is largely dependent upon the angle of the saw blade entry relative to the edge of the wafer. Sawing in a line nearly perpendicular to the edge of the wafer may result in little or no deflection. Sawing in an angle oblique to the edge of the wafer may induce more pronounced deflection. The deflection of the saw blade can result in damage to devices, for example by causing the saw blade to stray from the saw street and cut into the wrong location, or induce increased chipping caused by deviation from a straight saw path. Also, the saw blade itself may be damaged by deflection-induced stresses or may experience uneven wear. It is known in the arts to use a slow table rate, the rate at which the wafer is presented to the cutting edge of the saw blade, in order to reduce the effects of deflection. This solution is somewhat effective at reducing the above problems at the expense of throughput rate. Another approach is to provide wider saw streets between the devices on the wafer. Wider saw streets provide a greater margin of protection by allowing for some deviation in the cut, and for chipping. Using wider saw streets also permits the use of thicker saw blades, which may be more resistant to deflection. A major problem with this approach, however, is the loss of useable space on the wafer due to the increase in sacrificial material between devices.
Due to these and other problems related to wafer sawing and device singulation, it would be beneficial to implement improved methods and systems for sawing with reduced potential for damage to singulated devices. Such improvements would be particularly advantageous if they could be accomplished without reducing device density, and without reducing throughput rate. Further advantages could potentially be realized in the form of improved saw control, resulting in reduced waste and longer blade life.
In carrying out the principles of the present invention, in accordance with preferred embodiments thereof, the invention provides methods and systems for sawing and singulating individual devices from a semiconductor wafer.
According to an aspect of the invention, in a preferred embodiment, a method is provided in which a wafer is secured for sawing and is then presented to a saw blade. At least one parameter associated with sawing the wafer is continuously monitored and the rate of presentation of the wafer to the saw blade is dynamically controlled responsive to the one or more monitored parameters.
According to another aspect of the invention, a step of monitoring the saw blade spindle current is included.
According to yet another aspect of the invention, a step of monitoring the saw blade motor voltage is included.
According to still another aspect of the invention, a semiconductor wafer sawing system provides means for securing a wafer for sawing and for monitoring at least one parameter associated with sawing the wafer. Means are also included for presenting the wafer to a saw blade for sawing at a rate dynamically responsive to the monitored parameter.
According to further aspects of the invention, wafer sawing systems according to preferred embodiments of the invention further include means for monitoring the sawing parameters and means for using the monitored data for controlling the sawing process.
The invention has advantages including but not limited to potential for higher quality cuts, improved throughput, higher density of devices per wafer, higher yield, reduced waste, longer saw blade life, and decreased costs. These and other features, advantages, and benefits of the present invention can be understood by one reasonably skilled in the arts upon careful consideration of the detailed description of representative embodiments of the invention in connection with the accompanying drawings.
The present invention will be more clearly understood from consideration of the following detailed description and drawings in which:
References in the detailed description correspond to like references in the various drawings unless otherwise noted. Descriptive and directional terms used in the written description such as first, second, top, bottom, side, etc., refer to the drawings themselves as laid out on the paper and not to physical limitations of the invention unless specifically noted. The drawings are not to scale, and some features of embodiments shown and discussed are simplified or amplified for illustrating the principles, features, and advantages of the invention.
Referring primarily to
Now also referring to
Referring now to
The methods and systems of the present inventions provide decreased saw blade deflection and increased efficiency by dynamically monitoring and adapting sawing parameters including those associated with the entry and exit angles. Referring once more to the simplified overview of systems and methods for the implementation of the invention shown in
Thus, as the saw blade 24 encounters increased resistance at the wafer 10, the table rate may be slowed, and as the resistance decreases the table rate may be increased. The dynamic control of the rate at which the wafer 10 is presented to the saw blade 24 facilitates spinning the saw blade 24 at a constant rate. In this way, since the table rate may be adjusted from cut-to-cut, and also from wafer edge-to-edge within each cut, high quality saw cuts and efficient throughput rates may be obtained.
Exemplary blade deflection and spindle current monitoring results are depicted in
Additionally, the monitored parameters are preferably also used in conjunction with inspection of the sawing process output in order to establish control limits for the sawing process. Thus, the real-time monitored parameters may be compared during sawing with parameters predetermined to be within acceptable limits. Departure from acceptable limits may be used to make automatic adjustments to selected parameters, to trigger a warning signal, or to shut down the sawing process to allow a human operator to intervene. The increased level of dynamic control may provide additional advantages in preventing defective devices that might otherwise remain undetected during the completion of the sawing process, ultimately increasing overall yield and throughput and reducing costs.
The methods and systems of the invention provide advantages including but not limited to providing sawing methods with improved saw blade control and increased longevity. While the invention has been described with reference to certain illustrative embodiments, those described herein are not intended to be construed in a limiting sense. Various modifications and combinations of the illustrative embodiments as well as other advantages and embodiments of the invention will be apparent to persons skilled in the arts upon reference to the drawings, description, and claims.
