Radiant energy – Irradiation of objects or material – Irradiation of semiconductor devices
Reexamination Certificate
2001-04-27
2003-12-23
Wells, Nikita (Department: 2881)
Radiant energy
Irradiation of objects or material
Irradiation of semiconductor devices
C250S492300, C250S492220, C250S310000, C250S398000, C250S3960ML
Reexamination Certificate
active
06667483
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to an apparatus using charged particle beam with a sample stage drive device on which a sample to be measured including observation thereof is mounted, and, in particular, relates to an apparatus using charged particle beam such as a scanning type electron microscope which is suitable for automatic observation of a sample with such as a scanning type electron microscope and an optical type microscope, of which configuration, internal structure or location is known in advance.
CONVENTIONAL ART
It is already known a few methods in which when observing with a scanning type electron microscope a sample of which configuration, internal structure or location is known in advance, drawings or photographs showing the same and coordinate used for designating position of observation portion in the sample are related with displacement of a sample stage with some proper measure and a portion on the sample desired to be observed is quickly and automatically displaced in a simple manner into a visual field. Among these methods a method, for example, disclosed in U.S. Pat. No. 4,814,682 is one of effective ones. The disclosed method is intended to reduce workload for observation by manually designating position of a portion desired of observation, however, in a current scanning type electron microscope the disclosed method is further advanced and an automatic designation through a computer is performed. Currently, the method is used for the purpose of observing a microscopic pattern desired to be observed existing in a chip which can not discriminate and recognize on a chip design sheet while assuming respective chips, which are formed in a plurality of pieces on a common supporting body called as a wafer with a same design pattern and with a geometrical location relationship with a predetermined accuracy, as respective samples.
After once mounting actually a wafer on a sample stage, the position where the wafer is fixed temporarily on the sample stage at this instance is assumed as a reference position for observation position designating coordinate on the wafer. A control device for the scanning type electron microscope virtually registers the plurality of chips in a grid shape on the wafer according to the coordinate at this instance while framing such as the chip size, location and rotation direction in the wafer plane in a square chip outer configuration in a relationship based on the chip design data. By making use of the grid coordinate values of observation pattern, portions within a chip are thereafter determined.
Under a condition where a sample is actually mounted on a sample stage, the sample stage is displaced manually while observing the sample with the scanning type electron microscope and the position of a portion designed to be observed is manually designated in advance on the actual sample. The control device for the scanning type electron microscope determines the position of the portion desired to be observed after converting the same into a coordinate value within the chip from the coordinate value of the sample stage at the moment and the chip alignment, and stores the same together with the scanning type electron microscope image of the observed portion while relating thereto. Thereby, for the subsequent observation the control device for the scanning type electron microscope determines a coordinate value of a position to which the sample stage is to be automatically displaced from the coordinate value within the chip of the position for the observation portion and the chip alignment position registered in advance, and further performs an automatic identification of the observation portion through a picture image collation with the image of the observation portion which is stored while relating to the observation portion.
In the above U.S. Pat. No. 4,841,682, before performing an observation with respect to two portions on the actual sample among any portions showing characteristic sample structures the positions based on the design data on the drawing sheet and the position on the actual sample are related, thereby coordinate calibration is performed between the sample stage coordinate and the coordinate on the sample drawing sheet, in that the coordinate used by a coordinate designation means. As a result, when a position of a observation portion is designated by the coordinate designation means thereafter, the observation position can be brought into a visual field with a predetermined accuracy. In particular, when samples which permit designation of an observation position on a same design sheet are mounted on the same supporting body (for example, IC patterns arranged on a sample stage for a pattern comparison), through a provision of a switching function by a sample selection switch, the designation of observation positions of plural samples can be enabled by the same drawing sheet.
In the above U.S. Pat. No. 4,814,682, a sample (IC pattern) arranged on a common supporting body (sample stage) was an object for observation, however, in a recent scanning type electron microscope used for semiconductor manufacturing processes the object for observation is being replaced to a combination of IC patterns arranged on a wafer. Herein, the designation of two characteristic points is not limited on the same sample (the same chip), but is permitted over a plurality of samples (a plurality of chips). Therefore, coordinate on the coordinate designation means which can cover the entire samples located is set and then coordinate calibration between the coordinate on the coordinate designation means and the sample stage coordinate is performed. In such instance, since the plurality of samples (the plurality of chips) are located geometrically on a common supporting body (a wafer) with a predetermined accuracy, an observation position (x, y) can be determined from chip alignment pitch (px, py), chip location (nx, ny) and in-chip position (xd, yd) according to the following equation (1);
x
=
px
×
nx
+
xd
y
=
py
×
ny
+
y
d
}
(
1
)
In this method, as a preparation before observation, registration of two portions having characteristic structures is performed. Namely, with reference to the mounted position of the wafer on the sample stage at this moment a two dimensional coordinate designed by two characteristic portions on the mounted wafer is prepared as designated coordinate on the coordinate designation means. On this coordinate a drawing used in the coordinate designation means is prepared from an arrangement of a grid representing such as a chip size and chip location which are defined according to the design data. When observing in subsequent observations another wafer locating totally identical samples (chips) and being mounted on the sample stage, the position for the observation portion on the sample stage is designated based on the above designation coordination. However, the mounting position of a wafer on the sample stage is determined by mechanical contact between the sample stage and the wafer, therefore, a small amount of deviation is caused from the instance when registering the two characteristic portions previously, and the deviation amount varies every observation. In order to correct such deviation, the positions of the two same characteristic points located at the same positions as those registered previously are compared with the positions registered first to thereby perform coordinate calibration. Thus, coordinate calibration between the coordination at the time of registration giving the coordination of the coordinate designation means and the sample stage coordination at the time of observation is performed. Further, the coordination calibration performed by correspondence between two points within the sample in U.S. Pat. No. 4,814,682 was applied to the coordinate representing a geometric location of a plurality of samples (chips) on a common supporting body (wafer) as well as to the coordinate representing the positions of observation portions within a sample (chip) as i
Kobaru Atsushi
Otaka Tadashi
Dickstein , Shapiro, Morin & Oshinsky, LLP
Hitachi , Ltd.
Wells Nikita
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