Radiant energy – Irradiation of objects or material – Irradiation of semiconductor devices
Reexamination Certificate
1999-03-29
2001-12-11
Arroyo, Teresa M. (Department: 2881)
Radiant energy
Irradiation of objects or material
Irradiation of semiconductor devices
C250S442110, C250S492200, C250S492300
Reexamination Certificate
active
06329664
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to an apparatus for ion implantation, and particularly relates to a structure of a wafer disc for holding wafers provided in the apparatus for executing ion implantation on wafers using a batch type production system for producing semiconductor devices.
2. Background Art
In a batch type ion implantation treatment apparatus, ion implantation is carried out for a plurality of wafers supported by a wafer disc with a large diameter. In general, the wafer disc comprises a plurality of wafer holders arranged around its periphery, and each wafer is supported and fixed in each wafer holder by a fixing means such as a clamp. In a practical ion implantation operation, the wafer disc is driven to rotate and to move in reciprocating motions about an ion beam incident perpendicularly on wafer surfaces such that a plurality of wafers on the wafer disc are subjected to homogeneous ion implantation.
However, the following problems are encountered in conventional batch-type ion implantation apparatuses.
This batch-type ion implantation apparatus comprises a fixed number of wafer holders, that is, the number of wafers which can be treated as one batch is fixed. However, in practical ion implantation operations, the number of wafers to be treated is not always the same as the number of wafer holders, and sometimes the number of wafers is less than the number of fixed wafer holders. In this case, since the ion beam scans the whole surface area of the wafer disc, it is necessary to cover vacant wafer holders by, for example, dummy wafers. The use of dummy wafers raises the cost per wafer, and causes inflation of the manufacturing cost of the wafers.
In addition, even though the number of wafers is less than the number of wafer holders, ion irradiates the whole peripheral surface area of the wafer disc including wafer holders, so that a problem arises that the ratio of the area of the product wafers to the total area of ion irradiation is low, which results in causing a low through-put.
Furthermore, even if it is desired to change the ion dose for wafers in one batch, the only way to do this in conventional ion implantation apparatuses is to provide wafers with different ion doses in different batches.
It is therefore an object of the present invention to solve the above described problems and to provide an apparatus for ion implantation which is capable of executing ion implantation without using dummy wafers even when the number of untreated wafers is less than the number of one full batch such that the manufacturing cost can be reduced and the through-put is improved, and also to provide an ion implantation apparatus which is capable of producing wafers with different ion doses in the same batch.
SUMMARY OF THE INVENTION
In order to attain the above object, an ion implantation apparatus is provided which has a wafer disc having a plurality of wafer holders to support a plurality of wafers, and which carries out ion implantation for each wafer, while said wafer disc is rotating and while said wafer disc is shifting back and forth by a reciprocating motion perpendicular to the ion beam such that the wafers on the wafer holders are irradiated by the ion beam, wherein said plurality of wafer holders are designed such that they can move in the radial direction of the wafer disc by holder arms of the wafer holders, and wherein said apparatus comprises a control means for controlling the center of the shifting position of the reciprocating motion in the radial direction of the wafer disc such that said plurality of wafers supported on said wafer holders are irradiated by the ion beam.
According to another aspect of the present invention, the ion implantation apparatus of the above aspect further comprises holder arms connected to said plurality of wafer holders and the holder arms are designed so as to be extendable and contractable in the radial direction of the disc, and a driving means for driving so as to extend or to contract those holder arms automatically.
In the ion implantation apparatus of the present invention, a plurality of wafer holders can be moved in the radial direction of the wafer disc. Thus, it is possible to separate wafer holders into a group supporting the wafers and another group of vacant wafer holders at different positions. The control unit then controls the center position of the reciprocating motions of the wafer disc such that the region where the wafer holders supporting untreated wafers are irradiated by the ion beam. Accordingly, since the filled holders and vacant holders are separated geometrically, and the regions of vacant holders are not subjected to the ion beam, it is not necessary for this ion implantation apparatus to use dummy wafers which were required in conventional apparatuses.
Furthermore, when the number of wafers of a batch is small in comparison with the number of wafer holders, there was a problem in the conventional apparatus that the throughput was decreased due to the small area ratio of the product to the ion irradiation. In contrast, since it is necessary in the present ion implantation apparatus to carry out ion implantation in the restricted area in which holders supporting untreated wafers are positioned, the area ratio becomes larger than that of the conventional apparatus and the throughput is further improved.
According to another aspect of the present invention, the ion implantation apparatus according to the first aspect further comprises a center of gravity adjusting means for adjusting the center of gravity of the disc so as to coincide with the position of the disc center.
In the ion implantation apparatus according to the first aspect of the present invention, when said control means recognizes that a plurality of ion doses are required for untreated wafers in a batch, and the number of untreated wafers is less than the number of wafer holders, said control means forms a plurality of concentric circular regions corresponding to the number of ion doses by shifting the positions of the wafer holders, and ion implantation is executed by changing the speed of the reciprocating motions of the wafer disc using the intermediate range as the transition region of the speed change.
According to this constitution, wafers to be treated with the same ion dose are arranged in the same circular region on the wafer disc, and wafers in a batch are separate in separated concentric circular regions. By setting the optimum scanning speed for each region, and if it is possible to change the scanning speed for each region smoothly, untreated wafers in the same batch can be treated with different ion doses, which results in improving the working efficiency of the ion implantation.
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Arroyo Teresa M.
NEC Corporation
Payne Sharon
LandOfFree
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