JP2695797B2 - Small size measurement method - Google Patents

Description

Description: BACKGROUND OF THE INVENTION The present invention relates to a method for measuring the line width of a fine pattern such as a semiconductor surface pattern, and more particularly to a method for measuring a fine dimension which is highly accurate and resistant to noise and the like. [Prior Art] In recent years, the miniaturization of semiconductors has progressed, and the resolution of conventional optical measurement has become insufficient for line width measurement used for control of the manufacturing process, and a scanning electron microscope (Scanning microscope) using high resolution has been used. Electron Microscope (hereinafter abbreviated as SEM) has come to be used. A manual (manual) length measurement, in which two cursors are superimposed on the image of the semiconductor surface by SEM and the cursor is moved to both ends of the semiconductor surface pattern and the interval is divided by the magnification, and the line width is obtained. Although mainly performed, various automatic length measurement methods are being studied in order to speed up the measurement and eliminate personality. In the automatic length measurement, an electron beam is scanned perpendicularly to the pattern on the semiconductor surface, and the line width is measured from the scanning waveform. Specifically, in FIG. 6 (a), the surface of the sample 1 is scanned, and the position of the pattern end point 2 in FIG. 6 (a) is obtained from the scanning waveform 3 shown in FIG. 6 (b). Ask for. Various methods have been considered to determine the pattern end point 2 from the scanning waveform 3. For example, Japan Society for the Promotion of Science 132
There is a scheme discussed in the 89th meeting of the committee, pp5-8. This method is referred to as a straight line approximation method, in which the scanning waveform 3 in FIG. 2 is approximated by a bottom approximation line 4 and a slope approximation line 5, and the position of the intersection is set as a measurement edge position 6. Another typical method is a method called a threshold method. (For example, "micro line width measuring device",
In this threshold method, the threshold value 7 is set for the scanning waveform 3 in FIG. 3, and the scanning waveform 3 takes the threshold value 7 in this threshold method. Is the measurement edge position 9. This threshold value can be determined according to the material shape. If the threshold value 8 is set, the measurement edge position 10 can be obtained. Others related to the present method are disclosed in, for example, JP-A-58-117404 and JP-A-55-6370.
No. 4 and No. 57-96206. [Problems to be Solved by the Invention] Among the above-described prior arts, in the linear approximation method described first, the relationship between the measurement edge position 6 in FIG. 2A and the pattern end point 2 in FIG. Not to do
No consideration is given to the fact that it changes depending on the material and cross-sectional shape. Further, in the threshold method described later, inaccuracy may be caused by the influence of noise. Specifically, in FIG. 4, with respect to the scanning waveform 11 with noise applied,
When the threshold value 12 is determined, there is a problem that three points of the measurement edge position 13, the measurement edge position 14, and the measurement edge position 15 correspond to each other, and uncertainty remains. The object of the present invention is to be able to cope with differences in materials and cross-sectional shapes,
Another object of the present invention is to provide a micro-size measuring method which is less affected by noise. [Means for Solving the Problems] The above object is achieved by, in the straight-line approximation method, raising and lowering the horizontal approximation line according to the material and shape, and setting the intersection with the inclined portion approximation line as the measurement edge position. Is done. [Operation] By moving the horizontal approximate straight line up and down by a predetermined amount according to the material and shape, a measurement edge position that is not affected by changes in the material and shape is obtained. Also, unlike the threshold method, the slope is approximated by a straight line, so that the influence of noise is small. Embodiment FIG. 1 is a hardware configuration diagram of an embodiment of a length measuring SEM system according to the present invention. An electron beam 19 emitted from an electron gun 18 in an SEM mirror 17 is deflected by an electron lens system 20 and enters a sample 22 on a sample stage 21. Secondary electrons 23 are emitted from the sample 22 in response to the incidence of the electron beam 19 and are captured by the detector 24 to become a signal, thereby forming an image on the display 25. This signal is processed by the computer 26 according to an instruction input from the keyboard 27. FIG. 7 is a flow chart showing the length measurement processing procedure in the computer 26. At block 71, a scanning waveform is read.
In this block 72, a threshold value is set. There are various methods for setting the threshold, one example of which will be described with reference to FIG. The scanning waveform 3 is a typical scanning waveform for the sample surface 1 shown in FIG. 6 (a), and includes a maximum peak 81, a minimum dark area 82, and an upper flat area 9
3, consisting of a bottom portion 84 and an inclined portion 85. The maximum peak 81 height,
It is known that the depth of the minimum dark part 82 and the inclination of the inclined part 85 mainly reflect the shape, and the relative relationship between the upper flat part 83 and the bottom part 84 mainly reflects the material. The signal values of the characteristic points of these waveforms, that is, the maximum value 86, the minimum value 87, and the signal value of the upper flat portion
Threshold value 7 is determined from 88, the signal value 89 at the bottom. Maximum value 8
6 is I _max , the minimum value 87 is I _min , the signal value 88 of the upper flat portion is I _t , the signal value 89 of the bottom portion is I _b , and the threshold value 7 is I _th . Can be decided as follows. This determination method includes a method in which a measurement experiment is performed on a sample having a true edge position and a method in which the scanning waveform is theoretically calculated. Next, in a block 73, the scanning waveform 3 in FIG. For this purpose, the waveform of the inclined portion may be approximated by the least square method or the like. Next, at block 74, the threshold value 7 obtained at block 72 is obtained.
The edge is determined by setting the intersection of the slope approximated curve 5 obtained by the block 73 as the measured edge position 16. At block 75, the measurement result is displayed on the display 25 of FIG. [Effects of the Invention] According to the present invention, the line width of a fine shape such as a semiconductor surface pattern can be measured by a SEM in response to a change in shape or material and without being affected by noise. There is an effect that measurement can be performed.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a hardware configuration diagram of one embodiment of the present invention, FIG. 2 is an explanatory diagram of a linear approximation method, FIG. 4 is a diagram in which the threshold value method is applied to a noise-applied scanning waveform, FIG. 5 is a diagram illustrating the principle of the present invention, FIG. 6 is a cross-sectional view of a measurement sample and a typical scanning waveform diagram, and FIG. FIG. 8 is a flowchart of the software according to an embodiment of the present invention. FIG. 8 is an explanatory diagram of a threshold value determining method.

   ────────────────────────────────────────────────── ─── Continuation of front page    (72) Inventor Toshihiro Furuya               882 Ma, Katsuta-shi, Ibaraki Pref.               Inside the Naka Factory                (56) References JP-A-61-99809 (JP, A)                 JP-A-60-161514 (JP, A)                 JP-A-58-117405 (JP, A)                 JP-A-58-117404 (JP, A)                 JP-A-57-96207 (JP, A)

Claims (1)

(57) [Claims] The fine pattern is scanned with an electron beam, and a characteristic waveform of an edge portion of the pattern of an electric signal obtained by the scanning is represented by an oblique straight line on a side wall, a bottom level, a top level, and a maximum value of the waveform. , Approximation with a horizontal straight line determined by a set of parameters such as waveform characteristics, minimum value, etc., and an externally given parameter.
2. The micro-dimension measuring method, wherein the operation 2 is performed on both side walls, and a pattern width is determined by an interval between two pattern ends.