Radiant energy – Irradiation of objects or material – Irradiation of semiconductor devices
Reexamination Certificate
1999-03-08
2001-04-10
Bowers, Charles (Department: 2813)
Radiant energy
Irradiation of objects or material
Irradiation of semiconductor devices
C250S492220, C250S398000, C250S310000
Reexamination Certificate
active
06215127
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to techniques which are used during the fabrication of semiconductor devices. More specifically, the invention relates to a technique which uses multiple mappings of critical dimensions of selected features formed on a wafer during the process of forming integrated circuits, to enable tool set calibration/qualification in an efficient manner and with particular regard to mitigating effects which are encountered during the various steps which are carried during the constructive processes.
2. Description of the Related Art
When a new tool set, which should be understood throughout the disclosure to mean at least the combination of a stepper, a wafer track an associated apparatus for moving the wafers to and from the various production stages and locating the wafer in each of the same, is introduced into an IC production line, a great deal of set-up and adjustment is necessary before the arrangement is ready for regular production. For example, calibration or qualifying of the stepper is necessary before production can begin. It is also necessary to calibrate the operation of the wafer track and associated robotics in order to determine that the wafer is being moved between and disposed in, the stepper and processing chambers (e.g. etching chambers) in an optimally correct manner, and thus assure that the wafer is reproducibly set on the table of the stepper in a correctly oriented and located position.
That is to say, during the fabrication of an IC it is necessary to imprint images on resist coating and to etch, deposit, implant or the like, any number of times before the devices on the wafer are completed. It is therefore necessary to ensure that hardware which is used to move the wafer(s) back and forth, manipulate and to photolithograph, is operating in a manner wherein each and every wafer undergoes the same manipulations/operations during each and every stage of production. For example, accurate reproducible location of the wafer in the stepper is necessary. U.S. Pat. No. 5,392,361 issued on Feb. 21, 1998 in the name of Imaizumi et al., discloses the use of a mark on the wafer and a mark position detecting method and apparatus which uses fuzzy logic to improve alignment accuracy.
For further examples of the type of arrangements which are associated with the tool set reference can be had to U.S. Pat. No. 4,641,071 issued in February 1987 in the name of Tazawa et al, and U.S. Pat. No. 4,719,357 issued in January 1998 in the name of Ayata et al.
However, no matter what measures are taken, in the final analysis, the only way of determining if all of the necessary adjustments have been made in an optimal manner, is to make a test run and to examine the end product (viz., conduct empirical testing). However, this technique tends to leave it to chance as to which adjustment or setting needs to be fine tuned in order to bring this highly complex arrangement into truly optimal operational status. That is to say, the setting and arrangement of the reticle which is set in the optics of the stepper must be carefully examined in order to determine if adjustments to this vital piece of apparatus is necessary to correct some less than desirable outcome of the IC production.
This is a kind of feedback type of approach. An adjustment to the stepper operation the robotics which move the wafers from the wafer track to the stepper table, the position to which the wafer track moves the wafers prior to transfer, in combination with a possible change in the reticle or even in a resist or etching recipe, may, even though it would appear contrary to what might be conventionally considered to be correct and/or appropriate, enable the end result to be improved and, hence, would be highly beneficial.
Nevertheless, without some form of sophisticated analysis which can be carried out in a reliable and reproducible manner, the above types of adjustment and changes in technique amount to nothing more than guess work. Accordingly, there remains a need for a reliable technique via which a new tool set can be introduced and qualified in a manner which identifies the problems which need to be addressed in order to achieve set-up quickly and relatively inexpensively.
SUMMARY OF THE INVENTION
The present invention provides a technique for implementing a type of feedback control in a manner that enables the calibration or qualification of a new tool set. The underlying technique is based on sequential mappings which are carried out at each of a select number of production stages, and wherein critical dimension (CD) data, accumulated during each of the mappings, is examined, compared and used to determine what adjustments should be made to ensure that the closest possible adherence to the design requirements is achieved.
In other words, the present invention enables a kind of feedback control data base. For example, mapping of results of the etching are examined. If it is found that a line width or corner is too great or too small, or the configurations of given features are not as good as is required to assure the best performance of the device (e.g., features necessary to optimize the speed and performance of a microprocessor for example), it is possible to determine what adjustments can be made to the various pieces of apparatus which go to make up the tool set so as to influence the processes at each of the stages which are involved in the process, and to instigate changes/adjustments which will enable improvements to be made and for a better product to be realized.
In particular, the inventive technique enables the qualifying or calibrating a new tool set be to checked/modified so as to achieve the best possible results prior to actually beginning production. Once the operation of the stepper and associated apparatus, such as a wafer track, are modified/adjusted and performance assured, the amount of mapping which is used during actual production runs can be reduced to conventional levels or more preferably that which is necessary to determine that the process is running properly and that the new reticle is functioning optimally.
More specifically, a first aspect of the present innovation resides in a method of improving IC fabrication comprising the steps of: mapping the critical dimensions of a predetermined plurality of features at each of a predetermined number of stages of production of an IC; comparing the data collected at each of the mappings; and determining, from the comparison, what changes are required in the operation(s) of a tool set which is used in the production stages, to bring the critical dimension of the predetermined features into agreement with a predetermined set of design critical dimension. These predetermined features comprise ring oscillators, turning forks, test transistors, and wafer electrical testing-purpose (WET) transistors.
Another aspect of the invention resides in a method of qualifying an apparatus used in the production of integrated circuits, the method comprising the steps of: disposing a reticle in a stepper and using the stepper to move a wafer, which has been set on a table of the stepper using robotic apparatus, in a predetermined manner with respect to the reticle and to sequentially expose a predetermined number of exposure fields on the wafer; mapping the critical dimension of all features that impact integrated circuit speed performance, including ring oscillators. turning forks, test transistors, and wafer electrical testing-purpose (WET) transistors, which are located in the exposure field, which are contained in a selected group of the predetermined number of exposure fields; comparing the mapped critical dimension with a set of corresponding prerequisite critical dimension values; and adjusting the operation of at least one of the stepper and the robotic apparatus in order to bring the critical dimension which are derived using the mapping into accordance with a difference between the mapped critical dimension and the prerequisite critical dimension values.
A fu
Advanced Micro Devices , Inc.
Bowers Charles
Schillinger Laura
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