Metal working – Means to assemble or disassemble – Means to assemble electrical device
Reexamination Certificate
2002-05-07
2004-04-20
Hong, John C. (Department: 3726)
Metal working
Means to assemble or disassemble
Means to assemble electrical device
C029S705000, C029S729000, C029S737000, C029S603090, C029S603040
Reexamination Certificate
active
06722022
ABSTRACT:
FIELD OF THE INVENTION
The present invention generally relates to ion implanters and more particularly, relates to an apparatus and a method for calibrating the zero-angle position of a wafer platform in an ion implanter.
BACKGROUND OF THE INVENTION
Ion beam implanters are used to implant or “dope” silicon wafers with impurities to produce n or p type doped regions on the wafers. The n and p type material regions are utilized in the production of semiconductor integrated circuits. Implanting ions generated from source materials such as antimony, arsenic or phosphorus results in n type material. If p type material is desired, ions generated with source materials such as boron, gallium or indium are typically used.
The ion beam implanter includes an ion source for generating positively charged ions from ionizable source materials. The generated ions are formed into a beam and accelerated along a predetermined beam path to an implantation station. The beam is formed and shaped by apparatus located along the beam path en route to the implantation station. When operating the implanter, the interior region must be evacuated to reduce the probability of ions being deflected from the predetermined beam path as a result of collisions with air molecules.
During ion implantation a surface is uniformly irradiated by a beam of ions or molecules, of a specific species and prescribed energy. The size of the wafer or substrate (e.g. 8 inches or greater) is typically much larger than the cross-section of the irradiating beam which deposits on the wafer as a spot or “ribbon” of about 1 inch. Commonly, in high current machines, the required uniform irradiance is achieved by moving the wafer through the beam.
Operation of an ion implanter results in the production of certain contaminant materials. These contaminant materials adhere to surfaces of the implanter beam forming and shaping structure adjacent the ion beam path and also on the surface of the wafer support facing the ion beam. Contaminant materials also include undesirable species of ions generated in the ion source, that is, ions having the either the wrong atomic mass or undesired ions of the same atomic mass.
In a conventional ion implanter
10
such as that shown in
FIG. 1
, an ion beam
12
is emitted from an ion source
14
and passed through a pre-analyzing magnet
16
to remove undesired types of ions. Ions having identical energies but different masses experience a different magnetic force as they pass through the magnetic field due to their differing masses thereby altering their pathways. As a result, only those desired ions of a particular atomic mass unit (AMU) are allowed to pass through a pre-positioned orifice in the pre-analyzing magnet.
After passing through the pre-analyzing magnet the ion beam is accelerated to a desired energy by an accelerator
18
. Negative ions are changed into positive ions by a charge exchange process involving collisions with a chemically inert gas such as argon. The positive ions then pass through a post-analyzing magnet (not shown), and a pair of vertical and horizontal scanners
20
,
22
finally reach a wafer
24
where they impact the wafer
24
and are implanted.
Ion implantation has the ability to precisely control the number of implanted dopant atoms into substrates to within
3
%. For dopant control in the 10
14
-10
18
atoms/cm
3
range, ion implantation is superior to chemical diffusion techniques. Heavy doping with an ion implanter, for example, can be used to alter the etch characteristics of materials for patterning. The implantation may be performed through materials that may already be in place while other materials may be used as masks to create specific doping profiles. Furthermore, more than one type of dopant may be implanted at the same time and at the same position on the wafer. Other advantages include the fact that ion implantation may be performed at low temperature which does not harm photoresist and in high vacuum which provides a clean environment.
A sample mounting stage
30
for the ion implanter
10
is shown in FIG.
2
. The sample mounting stage
30
is constructed with a wafer platform
32
for positioning a wafer thereon. The wafer platform
32
may be equipped with electrostatic chucking (ESC) device or be provided with a mechanical clamping device. The wafer platform
32
is controlled by the mechanical motion of the rotating head
34
. During the normal operation of an ion implanter, the sample mounting stage
30
must be frequently calibrated. Particularly, the wafer platform
32
for mounting of a wafer thereon must be accurately calibrated such that when a wafer (not shown) is positioned on the wafer platform
32
, it is parallel with the ion beam from the ion planter. Prior to the implantation process, the wafer must first be clamped, or otherwise affixed to the wafer platform
32
and then rotated by the rotating head
34
to 90°. After the rotation or tilt of 90°, the ion beam from the ion implanter and the normal line of the wafer are parallel, and thus the commonly known term of “zero-angle”. After repeated usage of the ion implanter, and the repeated rotation of the wafer platform
32
, the angle of the wafer platform may be displaced with an error and therefore, the position of the wafer platform must be calibrated and corrected.
A commonly used implantation angle between the ion beam and the wafer surface is about 7° such that a channel effect can be avoided to eliminate errors caused by inaccurate depth of implantation. Under other operating conditions, for instance, at large angle implantation for the sidewalls or under a gate, the ion implanter may need constant calibration in order to carry out an accurate implantation process. A most frequently used base point for calibration is the zero-angle formed between the ion beam and the normal line of the wafer. The calibration can be advantageously carried out as long as the zero-angle between the ion beam and the normal line of the wafer is achieved.
During an attempt to calibrate the wafer platform
32
to a zero-angle position, it was discovered that the machine supplier for a medium density ion implanter does not supply a calibration tool which can be used to accurately calibrate the positioning of the wafer platform. For instance, a crude method for determining the calibration of the wafer platform is to measure the distance between the wafer edge and the support wall of the implanter. When an unequal distance is measured, the screws that fixed the position of the wafer platform are removed and then, the distances are adjusted until a ruler measures equal distance to the support wall from the wafer edge. The method is crude and difficult to execute. Its reproducibility is poor between different machine operators.
It is therefore an object of the present invention to provide a calibration method for a medium current ion implanter that does not have the drawbacks or the shortcomings of the conventional method.
It is another object of the present invention to provide an apparatus for calibrating the zero-angle of a wafer platform in a medium density ion implanter which can be used to produce reproducible result.
It is a further object of the present invention to provide an apparatus for calibrating the position of a wafer platform in a medium current ion implanter that is constructed of a curvilinear piece supported by two linear rods.
SUMMARY OF THE INVENTION
In accordance with the present invention, an apparatus and a method for calibrating the position of a wafer platform in a medium current ion implanter are provided.
In a preferred embodiment, an apparatus for calibrating the position of a wafer platform in an ion implanter is provided which includes a curvilinear piece formed of a first rigid material, the curvilinear piece has a half-circular shape, a predetermined thickness, a predetermined depth, an inside diameter, an inside peripheral surface, a first open end and a second open end, the inside diameter is substantially equal to an outside diameter of the wafer platform such that the i
Chen Lu-Chang
Peng Yu-Chun
Tang Yi-Yao
Hong John C.
Taiwan Semiconductor Manufacturing Co. Ltd
Tung & Associates
LandOfFree
Apparatus for calibrating the position of a wafer platform... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Apparatus for calibrating the position of a wafer platform..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Apparatus for calibrating the position of a wafer platform... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3241560