Data processing: generic control systems or specific application – Specific application – apparatus or process – Product assembly or manufacturing
Reexamination Certificate
2000-09-07
2004-09-07
Picard, Leo (Department: 2125)
Data processing: generic control systems or specific application
Specific application, apparatus or process
Product assembly or manufacturing
C700S099000, C700S103000
Reexamination Certificate
active
06788990
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a process control device and a process control method for control of process steps in which high precision processing is applied to a lot. More particularly, the present invention relates to a process control device and a process control method for control of at least two process steps that are applied to the same lot, before the lot is completed, at the same processing part having a plurality of processing devices placed in parallel therein.
2. Description of the Background Art
In manufacture of various kinds of semiconductor devices such as DRAMs, it is often the case that one process step is performed by a plurality of processing devices placed in parallel with one another to increase production efficiency. In such a process step, each processing object (hereinafter, referred to as “workpiece” or “lot”) for which a preceding process step has been completed is successively allocated to one of the plurality of processing devices that is currently available. If this process step is of the kind that requires extremely high precision processing, like a photolithographic step, processing results often vary even if the same mask is used under the same processing conditions. This is due to subtle differences in lens property or spectral distribution from a light source of respective processing devices, which are integrated to produce variation in the processing result. For the semiconductor devices such as DRAMs, miniaturization of products have been drastically advanced, and processing devices have reached their limit in capability. Such variation in the processing results according to the processing devices would cause considerable variation in product characteristics, and it would further increase a proportion of the products for which the processing should be done again (hereinafter, a “redo rate”). This hinders the improvement in productivity.
A proposal has been made to suppress such variation uncontrollable by processing conditions. It states that, if a workpiece is of the kind that is subjected to identical processing more than once at a processing part having a plurality of processing devices provided in parallel therein, the workpiece should be processed by the same processing device in such process steps (Japanese Patent Laying-Open No. 6-168865). Respective processing devices exhibit subtle deviating inclinations specific thereto, which may appear in different directions. For example, assume that a stepper _A tends to deviate a resulting pattern to the right as a whole, whereas a stepper _B will deviate it to the left at large. Applying the steppers _A and _B to the same workpiece will lead to a serious problem. Specifically, if an interconnection and a contact hole are formed using different steppers of which one exhibits an inclination to the right and the other to the left, the interconnection and the contact hole that should overlap will be separated from each other, hindering implementation of a circuit. There may also be a case where two interconnections that should be separated will overlap with each other. On the contrary, if the same workpiece is processed using the same processing device in the identical processing at different steps, such subtle deviating inclination unique to the processing device is always in the same direction, and thus, it is possible to limit the variation in a fixed range. The method as proposed is effective when it is applied to a photolithographic process step during manufacture of a semiconductor device. If each workpiece is processed by one and the same photolithographic device, variation will be suppressed, and good product characteristics will be readily obtained.
The manufacturing steps, however, of the semiconductor device are complicated. The above-described photolithographic process steps, for example, are repeated twenty to thirty times through the entire processing. Therefore, when two or more lots arrive at a particular processing device at the same timing, the lot(s) may have to wait before being processed even if there is another processing device not in use. Thus, the good product characteristics had to be set off by low production efficiency.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a process control device and a process control method for control of processing steps of workpieces in which at least two process steps are applied to the same workpiece at a processing part having a plurality of processing devices placed in parallel therein, that ensure good product characteristics while maintaining high production efficiency.
The process control device according to an aspect of the present invention is a process control device for control of a first process step for processing workpieces sorted into a lot and a second process step for further processing the lot processed in the first process step performed at the same processing part having a plurality of processing devices placed in parallel therein. The processing control device includes: a device group information storing unit for storing information about grouping of the processing devices into a plurality of device groups; and a device group selecting unit for selecting the device group such that the lot is processed in the second process step by a processing device included in the same device group as a processing device used in the first process step.
With such grouping of processing devices, it is unlikely that lots waiting to be processed cluster around a single, specific processing device. This prevents degradation of production efficiency. A lot is processed in identical processing at different steps by any of the processing devices belonging to the same device group. Thus, variations attributable to deviating inclinations of processing devices are prevented from appearing in a wide range extending to the right and to the left. As a consequence, it is possible to obtain good product characteristics and also to maintain high production efficiency since the same process steps need not be done again. Note that “a processing device included in the same device group as a processing device used in the first process step” in the above description includes the very processing device used for the first process step.
In the process control device according to the one aspect described above, the device group selecting unit may include a corresponding-device-group-name storing unit that stores the name of the device group corresponding to a lot.
By storing the name of the device group corresponding to the lot, the second process step is reliably performed by a device group the same as that for the first process step. Note that the action to store the name of the device group corresponding to a lot may also be expressed as “to hold the device group name” in the description below.
In the process control device according to the one aspect described above, the device group information storing unit may store the grouping of the device groups that is predetermined such that the processing devices having identical deviating characteristics are grouped into the same group.
The expression reading “the processing devices having identical deviating characteristics” means that the processing results of the processing devices appearing on the lots exhibit identical deviating characteristics; for example, the patterns formed tend to deviate to the right, not to the left, as a whole. As the processing devices that are likely to produce the similarly deviating processing results belong to the same device group, variation attributable to the deviating inclinations of the devices can be restricted. If the processing device is a stepper, steppers that tend to make the patterns deviate to the right as a whole are put into one group, and steppers that are likely to make the patterns deviate to the left as a whole are put into another group. In other words, the steppers exhibiting deviating inclinations to the right and those exhibiting deviating inclinations to the left are n
Ohtsuka Hirofumi
Okabe Masataka
Yanaru Taichi
Frank Elliot
McDermott Will & Emery LLP
Picard Leo
Renesas Technology Corp.
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