Semiconductor device manufacturing: process – Packaging or treatment of packaged semiconductor – Making plural separate devices
Reexamination Certificate
2000-11-03
2003-10-21
Coleman, William David (Department: 2823)
Semiconductor device manufacturing: process
Packaging or treatment of packaged semiconductor
Making plural separate devices
C451S015000
Reexamination Certificate
active
06635512
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method of producing a semiconductor device by cutting out separate pieces of semiconductor chips from a semiconductor wafer, and a grinding machine for use in the method of producing the semiconductor device.
2. Description of Related Art
Production processes of a thin semiconductor device such as a semiconductor device for IC chips include a grinding process for grinding an inactive surface (back surface) of a semiconductor wafer with a grinder. This grinding process is carried out prior to a dicing process for dicing a semiconductor wafer to divide it into semiconductor chips. This is because if the grinding process is carried out after the dicing process, the back surface of each semiconductor chip has to be separately ground, which causes the grinding process to take labor.
However, cutting such a thin semiconductor wafer with a dicing saw causes cracking of the semiconductor wafer and chipping of semiconductor chips. For this reason, a semiconductor wafer cannot be made thinner than a limit thickness, which is about 50 &mgr;m, by grinding prior to the dicing process.
Accordingly, carrying out the dicing process prior to the process of grinding the back surface of the semiconductor wafer has been recently proposed. That is, after an active surface of a semiconductor wafer is cut with a dicing saw so as to form grooves, a tape for protecting the surface is stuck to the surface of the semiconductor wafer. In this condition, the back surface of the semiconductor wafer is ground by a grinder. This back surface grinding is continued until the surface of the semiconductor wafer subject to grinding (back surface) by the grinder reaches the grooves, when thinned separate pieces of semiconductor chips can be obtained.
The arrival of the surface subject to grinding at the grooves may be detectable based on, for example, a change in a torque current flowing in a motor for driving the grinder. That is, when the surface subject to grinding reaches the grooves, the contact area between the back surface of the semiconductor wafer and the grinder decreases, causing the torque applied from the back surface of the semiconductor to the grinder to decrease. As a result, the quantity of the torque current flowing in the motor for driving the grinder lessens, according to which the arrival of the surface subject to grinding at the grooves maybe detected. Additionally, when grinding by using a chemical is performed as in the case of the CMP (Chemical-Mechanical Polishing) process, the arrival of the surface subject to grinding at the grooves may be detected based on a change in the pH level of the chemical.
However, since the change in the torque current or that in the pH level due to the arrival of the surface subject to grinding at the grooves is so little that it is impossible for both of the above-mentioned methods to precisely detect that the surface subject to grinding has reached the grooves. Accordingly, terminating the back surface grinding in response to the detection of the arrival of the surface subject to grinding at the grooves by such methods tends to lead to insufficient or excessive grinding, causing the produced semiconductor chips to scatter in the thickness.
In addition, as another method for detecting the arrival of the surface subject to grinding at the grooves, the method as shown in
FIG. 10
is also possible. In this method, a gaugel G is pressed against the surface of a semiconductor wafer W subject to grinding to measure (monitor) the thickness between a wafer stage
91
on which the semiconductor wafer W is mounted and the surface of the semiconductor wafer W subject to grinding so as to determine that the surface subject to grinding has reached the grooves when the thickness of the semiconductor wafer W has become a predetermined value. However, due to unevenness in thickness of a surface protection tape
92
stuck to the surface of the semiconductor wafer W, the results of the measurement by the gauge G include a significant margin of error. Accordingly, it is impossible to obtain a desired thickness e.g. 50 &mgr;m of the semiconductor chips with high accuracy.
SUMMARY OF THE INVENTION
It is an object of this invention to provide a method of producing a semiconductor device capable of preventing occurrence of cracking or chipping in semiconductor chips as well as suppressing variation in the thickness of the semiconductor chips, and a grinding machine for use in the production method of this semiconductor device.
The method of producing a semiconductor device according to this invention comprises: a groove forming process for forming a groove with a pattern according to an outer contour of a desired semiconductor chip in a front surface of a semiconductor wafer; a wafer holding process following the groove forming process for holding, with a wafer holding mechanism, the front surface of the semiconductor wafer, for instance, by sticking a wafer holding mechanism to the front surface of the semiconductor wafer; a back surface grinding process for grinding a back surface of the semiconductor wafer being held by the wafer holding mechanism by a grinder; and a finish timing determining process for detecting opening of a bottom face of the groove during the back surface grinding process and determining the timing for finishing the back surface grinding process based on the detection.
The opening of the bottom face of the groove (penetration) may be detected by an electromagnetic wave sensor for detecting electromagnetic waves including light or microwaves that pass through the groove. In addition, the method may include a back surface grinding process for grinding the back surface of a semiconductor wafer being held by the wafer holding mechanism, an air sucking process for sucking air inside the groove during the back surface grinding process, and an air pressure monitoring process for detecting and monitoring air pressure inside the groove during the air sucking process, thereby detecting the penetration of the groove based on a change in the air pressure detected during the air pressure monitoring process.
The grinding machine for carrying out the production method of this invention may be one which comprises a wafer holding mechanism for holding the front surface of the semiconductor wafer, for example, by adhering to the front surface of the semiconductor wafer, a grinder for grinding the back surface of the semiconductor wafer being held by the wafer holding mechanism, a penetration detecting mechanism for detecting opening of a bottom face of the groove formed in the semiconductor wafer being held by the wafer holding mechanism, and a control section for determining the timing for finishing the process of grinding the back surface of the semiconductor wafer by the grinder, which determination being made based on-an output from the penetration detecting mechanism.
The penetration detection mechanism may include an electromagnetic wave sensor for detecting an electromagnetic wave such as light or microwave that passes through the groove.
According to this invention, by grinding the back surface of a semiconductor wafer after forming grooves in the semiconductor wafer by dicing, the semiconductor wafer is divided into individual semiconductor chips. Accordingly, cracking or chipping of the semiconductor chips does not occur during the dicing, and extremely thin semiconductor chips being 50 &mgr;m or less in thickness can be produced in good order.
Meanwhile, the timing for finishing the back grinding of the semiconductor wafer is determined, for example, based on an output of an electromagnetic wave sensor such as a light sensor.
A light sensor may be disposed in the wafer holding mechanism or in the grinder so as to detect light, which is directed from a light source disposed in the grinder or the wafer holding mechanism and passes through the groove. In this case, when the surface of the semiconductor wafer subject to the grinding by the grinder reaches the groove and the groo
Hikita Junichi
Ino Kazuhide
Yoshida Ikuo
Coleman William David
Rabin & Berdo P.C.
Rohm & Co., Ltd.
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