Radiant energy – Photocells; circuits and apparatus – With circuit for evaluating a web – strand – strip – or sheet
Reexamination Certificate
2000-05-12
2003-02-04
Kim, Robert H. (Department: 2882)
Radiant energy
Photocells; circuits and apparatus
With circuit for evaluating a web, strand, strip, or sheet
C250S311000
Reexamination Certificate
active
06515296
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to a pattern dimension measuring system and a pattern dimension measuring method. More specifically, the invention relates to a system and method for measuring the dimensions of a pattern formed on the surface of a sample, while moving a stage, on which the sample is mounted.
2. Description of the Prior Art
In recent years, pattern dimension measuring systems are widely utilized for measuring the dimensions of a pattern formed on the surface of a semiconductor device, such as a very large scale integration (VLSI).
Referring to the accompanying drawings, a conventional pattern dimension measuring system will be described below. Furthermore, in the following drawings, the same reference numbers are assigned to the same portions, and the descriptions thereof are suitably omitted.
FIG. 1
is a schematic block diagram showing an example of a conventional pattern dimension measuring system. In this figure, a pattern dimension measuring system
110
comprises an electron beam lens-column
111
, a vacuum sample chamber
2
and a host computer
104
.
The electron beam lens-column
111
includes an electron gun part
11
and an electron lens system, and has a resolving power of about 5 nm corresponding to the scale down of semiconductor devices. The electron gun part
11
is designed to irradiate a sample
5
with electron beam
96
. The electron lens system has a condenser lens
21
, a deflecting lens
102
and an objective lens
103
. The electron lens system is designed to control the trajectory and focal length of the electron beam
96
so that the electron beam
96
focuses on the sample
5
.
The vacuum sample chamber
2
houses an X-Y stage
3
, a sample conveyance system
12
and a secondary electron detector
31
in vacuum atmosphere. The sample conveyance system
12
is designed to convey a sample
5
, such as a semiconductor wafer, to the X-Y stage
3
. The X-Y stage
3
is designed to support the conveyed wafer
5
(sample) on the upper surface thereof, and to move in an optional direction on the X-Y plane with a high stopping accuracy of about 1 &mgr;m on the basis of a control signal supplied from a stage control part
113
. The secondary electron detector
31
is designed to detect secondary electrons, reflected electrons and back scattered electrons (which will be hereinafter referred to as “secondary electrons and so forth”), which are emitted from the surface of the sample
5
irradiated with the electron beam
96
, to supply the detected results to an image data processing part
132
. The image data processing part
132
is designed to receive the detected results of the secondary electron detector
31
to supply image data, which form a SEM image by a predetermined data processing, to the host computer
104
. The host computer
104
has a pattern dimension calculating part
16
for calculating the dimensions of a target pattern on the basis of the image data, which are fed from the image data processing part
132
, to suitably store the calculated results in a memory
14
.
Referring to
FIG. 2
, an example of a sequence for measuring the dimensions of a pattern, which is formed on the surface of the wafer
5
using the pattern dimension measuring system
110
shown in
FIG. 1
, will be described below.
FIG. 2
is a schematic diagram showing the moving direction of the X-Y stage
3
. In this example, the stage
3
is designed to move from a measurement start position Ps to a measurement end position Pe while drawing a locus shown by the dotted line in FIG.
2
.
First, by the sample conveyance system
12
, the wafer
5
is conveyed into the vacuum sample chamber
2
to be mounted on the upper surface of the X-Y stage
3
.
Then, global alignment marks {circle around (
1
)} and {circle around (
2
)}, which are formed on the surface of the wafer
5
at substantially center and peripheral portion thereof, respectively, are used to carry out the global alignment to calculate a correlation between a pattern layout coordinate system and a stage coordinate system on the wafer
5
.
Then, the stage
3
is moved so that the position of a target pattern to be measured, e.g., the vicinity of pattern {circle around (
3
)} shown in
FIG. 2
, is a position irradiated with the electron beam
96
, and stopped at this position. Then, the exciting current of the objective lens
103
is controlled so that the edges of the target pattern are within a beam focal depth by the automatic focus. Then, while the stage
3
is moved again in the direction of the dotted line arrow in
FIG. 2
, the electron beam
96
is scanned on the pattern {circle around (
3
)} to detect secondary electrons and so forth, which are emitted from the surface of the wafer
5
, by unit of the secondary electron detector
31
. The detected signal is data-processed by the image data processing part
132
to be inputted to the host computer
104
as an image signal constituting a SEM image. The host computer
104
detects the target pattern {circle around (
3
)} existing in the SEM image by the pattern recognition processing. The pattern dimension calculating part
16
in the host computer
104
detects the bottom edges of the detected target pattern {circle around (
3
)} on the basis of the optimum measuring algorithm to measure the dimensions of the pattern. Moreover, if the next target pattern ({circle around (
4
)}-{circle around (
7
)}) exists, the X-Y stage
3
is moved again toward the next target pattern to be stopped again in the vicinity thereof, and then, the above described operations are repeated. Such a series of operations are controlled by the host computer
104
in accordance with a sequence which is set by a recipe file stored in the memory
14
of the pattern dimension measuring system or the like.
However, in the above described sequence, the measurement of the dimensions is carried out by repeating the movement and stopping of the X-Y stage
3
any number of times, so that it takes a lot of processing time in the case of a multipoint measurement for measuring the dimensions of patterns at a large number of measuring places.
FIGS. 3A and 3B
are graphs for explaining the throughput, of the pattern dimension measuring system shown in
FIG. 1
, and show the variation in stage traveling speed. It can be also understood from
FIGS. 3A and 3B
that the stage
3
is stopped in front of the global alignment mark and the pattern to be measured for focusing (AF) and pattern recognition (PM).
Particularly in recent years, the need for multipoint measurement is enhanced (a) at the initial stage of the development of process devices, (b) in the evaluation of the lens aberration of an aligner and in the evaluation of a wafer for making exposure conditions, and (c) due to the increase of the number of measured points as the increase of the diameter of the wafer. However hand, the throughput in the above described sequence is 30 wafers/hour to 40 wafers/hour, so that there is a problem in that it takes several hours to carry out a multipoint measurement even with a full automatic measurement in the present circumstances.
SUMMARY OF THE INVENTION
It is a first object of the present invention to provide a pattern dimension measuring system with a high throughput.
It is a second object of the present invention to provide a pattern dimension measuring method with a high throughput.
According to the first aspect of the present invention, there is provided; a pattern dimension measuring system comprising: a movable stage for mounting a sample on the upper surface thereof, the sample having a pattern to be measured formed thereon; a first control unit for moving the stage; an electron beam irradiation unit for irradiating the sample with an electron beam; an electron beam deflecting/scanning unit for deflecting and scanning the electron beam in a region on the sample, the region including a first portion normally scanned with the electron beam along and around an outgoing beam axis, and a second portion outside the first portion,
Komatsu Fumio
Miyoshi Motosuke
Okumura Katsuya
Kim Robert H.
Song Hoon K.
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