Radiant energy – Photocells; circuits and apparatus – Photocell controls its own optical systems
Reexamination Certificate
2003-05-16
2004-10-12
Luu, Thanh X. (Department: 2878)
Radiant energy
Photocells; circuits and apparatus
Photocell controls its own optical systems
C356S401000
Reexamination Certificate
active
06803592
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a position detection method and position detector, an exposure method and exposure apparatus, and a device and device manufacturing method and, more particularly, to a position detection method and position detector for obtaining arrangement information of divided areas on an object, an exposure method and exposure apparatus using the position detection method, and a device manufactured using the exposure method and a manufacturing method thereof.
2. Description of the Related Art
In a lithography process for making semiconductor devices, liquid crystal display devices, and the like, an exposure apparatus which transfers a pattern formed on a mask or reticle (to be generally referred to as a “reticle” hereinafter) onto a substrate (to be referred to as a “sensitive substrate or wafer” as needed hereinafter) such as a wafer, glass plate, or the like coated with a resist or the like via a projection optical system is used. As such an exposure apparatus, stationary exposure type projection exposure apparatus such as a so-called stepper, or a scanning exposure type projection exposure apparatus such as a so-called scanning stepper is mainly used.
In these exposure apparatuses, position adjustment (alignment) between a reticle and wafer must be accurately performed prior to exposure. To achieve this alignment, position detection marks (alignment marks) are formed (transferred by exposure) in the previous lithography process on the wafer in each of shot regions, and the position of the wafer (or a circuit pattern on the wafer) can be detected by detecting the positions of the alignment marks. Alignment is performed on the basis of the detection results of the positions of the wafer (or a circuit pattern on the wafer).
Such alignment schemes include a die-by-die scheme for performing alignment by detecting alignment marks in each shot, and an enhanced global alignment (to be abbreviated as “EGA” hereinafter) scheme for, after measuring alignment marks (position adjustment marks transferred together with a circuit pattern) at several positions in a wafer, computing arrangement coordinate positions of each shot area by a statistical scheme such as a least square approximation and, upon exposure, stepping a wafer using the accuracy of a wafer stage and the computation result. This EGA scheme is disclosed in, e.g., Japanese Patent Laid-Open No. 61-44429 and corresponding U.S. Pat. No. 4,780,617. Of these schemes, the EGA scheme is prevalently used nowadays in terms of the throughput of the apparatus.
In this EGA scheme, in order to determine a plurality of parameters that uniquely specifies the actual arrangement coordinate positions of shot areas relative to ideal arrangement coordinate positions in terms of design, more positions of alignment marks than the minimum number of those required to obtain the plurality of parameters are measured. Then, statistically valid parameter values are determined using a statistical scheme such as a least square approximation.
Upon applying such statistical scheme, error analysis is performed under the premise that “all position measurement results of alignment marks have the same reliability” (hereafter, this case is referred to as “prior art 1”).
Also, as disclosed in Japanese Patent Publication No. 7-120621, a technique for determining the predetermined parameters by executing a fuzzy process based on fuzzy inference using statistical values such as the average value and variance of the measured positions of the alignment marks and obtaining the arrangement coordinate positions of the shot areas has also been proposed (hereafter, this case is referred to as “prior art 2”).
When all alignment marks are equally formed, the premise of prior art 1 that “all position measurement results of alignment marks have the same reliability” is true, but not true when the shapes of alignment marks differ depending on their positions on a substrate. Therefore, when the shapes of alignment marks differ depending on their positions on a substrate, all position measurement results, whether their reliabilities are high or low, equally contribute to determination of the arrangement coordinate positions of shot areas their different reliabilities.
The accuracy of the arrangement coordinate position determination of shot areas determined under the above premise suffices to achieve conventionally required exposure accuracy, but does not suffice for the increase of integration degree in recent years.
Prior art 2 is free from any problem of the accuracy of the arrangement coordinate position determination of shot areas unlike in prior art 1. However, since prior art 2 requires a huge computation volume for fuzzy inference, a long period of time is required to determine the arrangement coordinate positions of shot regions, and this makes it difficult to improve the throughput of exposure. In order to prevent such low throughput, a large-scale computation resource is needed. However, the use thereof causes the whole exposure apparatus to be large and complicated.
Upon applying the conventional statistical scheme, the positions of alignment marks to be measured on a wafer are determined empirically or on a trial-and-error basis that after transferring a pattern onto a wafer while aligning the wafer using a temporarily selected sample set, the same patterns on the wafer are measured, and that if desired results are not obtained, another sample set is selected.
As described above, in the conventional method, a sample set of alignment marks as a subset of a set of all alignment marks is determined by an aleatory method, and the validity of determination of that sample set is not quantitatively evaluated. Therefore, it is not guaranteed that the error distribution of the positions of a plurality of alignment marks as elements of a sample set determined by the conventional method appropriately reflects the error distribution of positions of all alignment marks.
For trying to solve this problem, there is the following method: the position control using a plurality of parameters which are obtained using a provisional sample set determined empirically or arbitrarily and uniquely specify the arrangement coordinate positions of shot regions, when the sample set includes shot areas (so-called “isolated shots”) having much larger alignment errors than those of other shot regions, alignment marks contained in such isolated shots are excluded from the sample set. This method presupposes that only few isolated shots exist, and that those alignment marks cause the decrease of alignment accuracy for all shot regions.
However, if alignment marks of two isolated shot regions, of which pattern shift directions are almost opposite to each other (i.e., the two shot areas having negative correlation), are selected, high-accuracy alignment is possible. Therefore, exclusion of the measured position information of alignment marks contained in an isolated shot area may result in an alignment accuracy decrease.
In the case where a wafer is aligned on the basis of the position measurement results of alignment marks included in a subset (sample set) selected from a large number of alignment marks, upon examining the validity of a method for selecting the desired sample set, evaluating separately individual alignment marks in the sample set does not have much sense. This is because it is ideal that the sample set broadly reflects the entire set and because it is preferable that alignment marks in the sample set preferably have a position distribution that corresponds to that of alignment marks in the entire set. For example, in the case where one of five alignment marks in a sample set is an alignment mark contained in an isolated shot region, if one fifth of all the alignment marks are contained in isolated shot regions, the sample set is more valid than a sample set excluding alignment marks of isolated shot regions. That is, position errors of measured alignment marks reflect the position distribution of all the align
Luu Thanh X.
Nikon Corporation
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