Computer-aided design and analysis of circuits and semiconductor – Nanotechnology related integrated circuit design
Reexamination Certificate
1999-03-12
2001-09-25
Nelms, David (Department: 2818)
Computer-aided design and analysis of circuits and semiconductor
Nanotechnology related integrated circuit design
C430S005000
Reexamination Certificate
active
06295629
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method for correcting focus in an aligner (stepper) and a method for manufacturing semiconductor devices by using an aligner in which focus is corrected by the focus correcting method.
2. Description of the Background Art
Conventionally, the management of focusing of aligners includes the focus calibration performed several times a day (the management in which the distance between the stage and reticle is measured and the variation is fed back to focusing in exposure), the best focus check performed several times a month by forming resist pattern by using a test reticle (the management in which resist pattern is formed and the deviation of the present focusing value from the best focus is calculated by viewing, or by measuring dimensions of the test pattern and is fed back to the aligner), and the leveling function check (the management in which the inclination of the wafer plane and the image plane of the shots in the aligner is measured and adjusted). These management processes are too time consuming to perform frequently, and therefore periodical variation of focus of the aligner having several-hour or shorter cycle cannot be followed, which leads to increased variation of the resist pattern due to defocusing.
As conventional aligners, for example, Japanese Patent Laying-Open Gazette No.9-92606 discloses a device which adjusts focus on the basis of correction data obtained from level marks formed on the wafer, Japanese Patent Laying-Open Gazette No.5-190419 discloses a device which adjusts focus by using test pattern formed on a test substrate, and Japanese Patent Laying-Open Gazette No.7-86135 discloses a device which adjusts focus with weighted focus information to compensate for phase lag of focusing signal.
In the conventional focus correcting methods performed as stated above, it is difficult to measure the focus deviation, and therefore the focus deviation cannot be measured for each lot manufactured in short cycle so that the measured deviation can be utilized for the next lot, which raises the problem of difficulty in improving the focus correcting accuracy.
SUMMARY OF THE INVENTION
According to a first aspect of the present invention, a focus correcting method for use in an aligner capable of adjustment of focus position by setting a focusing value comprises the steps of: (a) forming a resist pattern with at least one focus measuring mark by exposing a resist by the aligner; (b) measuring length of the at least one focus measuring mark in elongate direction; (c) measuring length of a tapered part of the at least one focus measuring mark in which the resist becomes thinner toward an end of the at least one focus measuring mark; and (d) determining a magnitude of deviation from a best focus on the basis of a measurement in the step (b) and also determining direction of the deviation from the best focus on the basis of a measurement in the step (c) to obtain a deviation amount from the best focus, and then setting the focusing value on the basis of the deviation amount from the best focus.
Preferably, according to a second aspect, the focus correcting method further comprises the step of (e) storing data about the deviation amount from the best focus every time the step (d) is repeated for each of a plurality of sets of products of a same type, and the step (d) comprises the step of statistically processing the data to calculate a predicted focusing value which enables the best focus in exposure, and setting the focusing value on the basis of the predicted focusing value.
Preferably, according to a third aspect, in the focus correcting method, the step (e) comprises the step of defining a sum of the focusing value and the deviation amount from the best focus as a true deviation, and storing the true deviations about the plurality of sets of products as the data, and in the step (d), the true deviations about a predetermined number of sets of products are extracted from the data stored in the step (e) and an average value of the true deviations about the predetermined number of sets of products is used as the predicted focusing value.
Preferably, according to a fourth aspect, in the focus correcting method, in the step (d), true deviations about a predetermined number of sets of products are calculated from the data stored, a value proportional to a difference between the true deviations about successively manufactured at least two sets of products in the plurality of sets of products is added to an average value of the true deviations about the predetermined number of sets of products, and a sum of the average value and the difference is used as the predicted focusing value.
Preferably, according to a fifth aspect, in the focus correcting method, the at least one focus measuring mark is including a plurality of focus measuring marks, and with the plurality of focus measuring marks arranged in one shot, inclination of the shot is calculated on the basis of the true deviations of the resist pattern from the best focus in individual positions of the plurality of focus measuring marks, and the predicted focusing value is obtained by considering the inclination.
Preferably, according to a sixth aspect, in the focus correcting method, the at least one focus measuring mark is including a plurality of focus measuring marks, and with the plurality of focus measuring marks arranged in peripheral part and center part of one shot, the predicted focusing value is calculated on the basis of a value between the true deviation from the best focus in the peripheral part of the shot and the true deviation from the best focus in the center part of the shot.
Preferably, according to a seventh aspect, in the focus correcting method, the at least one focus measuring mark is including a plurality of focus measuring marks, and with the plurality of focus measuring marks arranged in a plurality of positions in one shot, the true deviations from the best focus measured at the plurality of positions are weighted in accordance with pattern layout and arrangement in the shot and averaged so as to calculate the predicted focusing value.
Preferably, according to an eighth aspect, in the focus correcting method, the at least one focus measuring mark is including a plurality of focus measuring marks, and with one of the plurality of focus measuring marks arranged in one position in one shot, an amount of remaining warp of the wafer is calculated on the basis of the deviation amounts of the plurality of focus measuring marks formed in several positions on the wafer in a plurality of exposures and the predicted focusing value is obtained by considering the amount of remaining warp.
Preferably, according to a ninth aspect, in the focus correcting method, the at least one focus measuring mark is a polygon having at least one corner having an angle of 90° or smaller.
A tenth aspect of the present invention is directed to a method of manufacturing a semiconductor device using an aligner in which focus is corrected by using a given focus correcting method and focus position can be adjusted by setting a focusing value. According to the tenth aspect, the semiconductor device manufacturing method comprises the steps of: (a) setting the focusing value; and (b) manufacturing semiconductor devices by using the aligner in which the focus position is adjusted by setting the focusing value. The step (a) comprises the steps of: (c) forming a resist pattern with at least one focus measuring mark by exposing a resist by the aligner; (d) measuring length of the at least one focus measuring mark in elongate direction; (e) measuring length of a tapered part of the at least one focus measuring mark in which the resist becomes thinner toward an end of the at least one focus measuring mark; and (f) determining a magnitude of deviation from a best focus on the basis of a measurement in the step (d) and also determining direction of the deviation from the best focus on the basis of a measurement in the step (e) to obtain a deviation amoun
Le Thong
Mitsubishi Denki & Kabushiki Kaisha
Nelms David
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
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