JPH01101407A - Line width measuring method - Google Patents

Abstract

PURPOSE:To measure line width easily and speedily by discriminating the kind of an edge of an image signal positively and detecting a target edge matching with the kind of an edge of a measurement profile whose kind is specified. CONSTITUTION:The profile of a fine pattern formed on a substrate made of a silicon wafer, etc., having a uniform reflection factor is classified into four kinds, and there are four kinds of a large leading edge, a small leading edge, a large trailing edge, and a small trailing edge having a regularity in array order. When a measurement is taken, an operator specifies which profile of four kind profiles A1-D1 is applied to the fine pattern on the sample and a target edge. Then which of the kinds A1-D1 the edge corresponds to is discriminated according to the irregularity of the array order of edges obtained from an optical image of the fine pattern and when a coincidence is obtained, it is decided that the edge is the edge specified by the operator.

Description

[Detailed Description of the Invention] <Industrial Application Field> The present invention is applicable to minute patterns formed on a substrate with uniform light reflectance within a measurement area, such as a thin film pattern formed on a silicon wafer or a semiconductor process. The present invention relates to a line width measuring method for measuring the width or pitch of a chromium (Cr) pattern, etc. on a glass mask used in.

<Prior Art> This type of conventional line width measuring method will be explained with reference to FIG.

In the figure, 1 is a microscope, 2 is a sample such as a silicon wafer or a glass mask set in the microscope 1, 3 is a binocular eyepiece for visually confirming the sample 2, and 4 and 5 are light sources. The light source 4 is used when measuring a reflective sample such as a silicon wafer, and the light source 5 is used when measuring a transmissive sample such as a glass mask. The optical image of the fine pattern formed on the surface of sample 2 is captured by CCD6.
The image is formed on a photoelectric conversion element such as , and converted into an image signal. The image signal output from the CCD 6 is given to the signal processing device main body 7, where it is appropriately processed, and then given to the CRT 8. In addition, numeral 9 is a keyboard for specifying a measurement profile and moving a cursor, which will be described later;
0 is a glinter that prints the measurement results.

FIG. 6 shows a fine pattern (hatched area) on the sample surface projected on the CRT 8.

Two cursors L+ and Lx are displayed on the CRT 8 along with the fine pattern on the surface of the sample. The operator moves these two cursors L, , L by operating the keyboard 9, and selects the pattern to be measured using the cursors L5, . Specify by sandwiching it between Lx.

After positioning the sample as described above, a measurement profile corresponding to the sample is specified by operating the measurement profile key provided on the keyboard 9. Here, the measurement profile is a waveform symbolically showing the light intensity of an optical image of a fine pattern. In the case of a fine pattern with uniform reflectance formed on a substrate with uniform reflectance such as a silicon wafer or a glass mask, Fig. 7 (AI)
, (Bl).

There are four types of measurement profiles as shown in (C1) or (Dl). In addition, FIG. 7 (A2) to (B2) are
FIG. 3 is a cross-sectional view of a sample from which each measurement profile is obtained.

Figures 7 (A1) and (B1) are measurement profiles of a fine pattern made of a metal coating such as chromium formed on a transparent substrate such as a glass mask;
01) is a measurement profile of a resist film pattern formed on a reflective substrate such as a silicon wafer. Since the stepped portion of a metal coating such as a chrome pattern formed on a glass mask is steep,
The measurement profile is represented by two values: H level and L level.

On the other hand, the step part of the resist film pattern formed on the silicon wafer is inclined, and the inclined part causes diffuse reflection.
The level of the measurement profile is shown in Figure 7 (C1) and ([11
), there are three stages.

As mentioned above, there are four types of measurement profiles, but in order to specify which part of the fine pattern is to be measured, the measurement profile keys shown in Figure 8 (1) to 0ω are used when measuring line width. There are 10 types of keys as shown. In the figure, the distance between the target edges indicated by broken lines is the line width to be measured.

Furthermore, the keyboard 9 is equipped with 12 types of measurement profile keys as shown in FIG. 9(1) to 021 for measuring the pitch of the pattern. The O mark shown in each measurement profile is the target edge that is the target of pitch measurement.

After the operator aligns the sample 2 and specifies the measurement profile as described above, the specified line width (or pitch) is measured as follows.
.

For example, assume that the sample is a silicon wafer and the CCD 6 detects a light intensity distribution as shown in FIG. First, the operator uses cursor operations to select the pattern whose line width is to be measured using the two cursors L,...
Suppose that the operator then operates the measurement profile key to specify, for example, the measurement profile shown in FIG. 8(5). In this case, edge 1 and edge 3 shown in FIG. 10 are detected, and the dimension between these two edges is measured. Specifically, Figure 8 (5)
When the measurement profile shown in FIG. 5 is specified, in the signal processing device main body 7 shown in FIG. The edge (edge 3) is considered to be the right edge.

When the positions of the left and right edges are detected, the dimension between the two edges is calculated based on the pixel pitch of the CCD 6.

<Problems to be Solved by the Invention> As described above, in the conventional line width measurement method, when detecting a target edge corresponding to a specified measurement profile, the line width measurement method uses a cursor operated and positioned by an operator as a reference. The target edge is detected using an extremely simple method, such as setting the numbered edge as the left edge or the right edge according to the specified measurement profile. Therefore, due to an operator's operation error, for example, two patterns are moved with the cursor Ll as shown in FIG.

If it is sandwiched by L%, there is a problem that the dimension W' between edges 1 and 3' is measured even though it is actually desired to measure the dimension W between edges 1.3.

Furthermore, according to conventional measurement methods, cursor operations by the operator are essential, so when trying to measure the line widths of a large number of patterns, cursor operations must be performed for each pattern, which takes a long time. There is also the problem that it is necessary.

The present invention has been made in view of the above circumstances, and is capable of correctly detecting a target edge according to a specified measurement profile and quickly measuring the width or pitch of a large number of patterns. The purpose of this paper is to provide a method for measuring line width that is possible.

Means for Solving the Problems> In order to achieve the above object, the present invention has the following configuration.

That is, the present invention converts an optical image obtained by enlarging and projecting a fine pattern on a sample into an image signal, and uses this image signal to perform at least two purposes corresponding to a measurement profile specified in advance depending on the sample. In a line width measuring method that measures the convergence or pinch of a fine pattern by detecting an edge and calculating the dimension between the two edges, the process of detecting the target edge includes detecting the rising or falling edge of the edge and The type of edge of the image signal is identified based on the magnitude relationship of , and if this edge type matches the edge type of the specified measurement profile, that edge is detected as a target edge.

Effect> As explained in FIG.
In the case of a fine pattern with uniform reflectance, the profile is 4.
Can be classified into types. There are four types of edges that appear in this profile: (1) large rising edge (2) small rising edge (3) large falling edge (4) small falling edge. Moreover, the order in which these edges are lined up is: ・(1)→(3)→(1)→(3)→・Old...
(1) → (3) → (2) → (4) → (1) → (3) → (
2) → (4) →... In either case, there is a regularity in the order in which they are lined up, and the present invention creates an optical image of a fine pattern based on that regularity. To automatically determine which edge among edges in an image signal obtained by conversion is a target edge.

First, the operator selects (Al) and (Bl) in Fig. 7.
.

Among the profiles (C1) and (DI), which profile matches the fine pattern on the sample, and which edge in that profile is the target edge is specified. next,
Based on the rising or falling and magnitude relationship of the edge in the image signal with the adjacent edge, the edge can be determined based on the regularity of the order in which the edges are lined up as described in (1) above. - (4) to which type it corresponds is identified. Therefore, it is examined and considered whether the type of the edge that it consists of matches the target edge in the profile specified by the operator, and if it does not match, the same process is followed for adjacent edges in turn until they match. The edges are examined, and if they match, it is determined that the edge corresponds to the edge specified by the operator.

As described above, according to the present invention, in the process of detecting a target edge, the edge of the image signal is detected as a specified edge in the specified profile based on the rising or falling edge of the edge and the size relationship of the thickness edge. Since the target edge is automatically detected, there is no need for cursor operation, and the target edge corresponding to the measurement profile can be easily and quickly detected. be done.

<Example> Hereinafter, an example of the present invention will be described in detail based on the drawings.

FIG. 1 is a schematic block diagram of an apparatus using a measuring method according to an embodiment of the present invention.

In this figure, the parts indicated by the same reference numerals as those in FIG. 5 are the same constituent parts, so the description thereof will be omitted here.

The optical image of the fine pattern on the sample surface magnified by the microscope 1 is projected onto the CCD 6. The CCD 6 outputs image signals corresponding to the light intensity of the optical image in parallel.

This image signal is converted into a serial image signal by a parallel-to-serial converter 11, then converted into a digital signal by an A/D converter 12, and provided to the RAM 13.

The timing pulse generator 14 is a parallel-to-serial converter 11
．． The operation timing is given to the A/D converter I2 and the address designator 15. The address designator 15 counts these timing pulses and provides the counted value to the RAM 13 as an address signal. RA specified by this address signal
Each pixel signal of the CCD 6 is stored in the storage area of M13.

The CPU 16 executes signal processing to be described later on the image signal stored in the RAM 13, processing for detecting target edges corresponding to a measurement profile, calculation of dimensions between target edges, etc., according to a processing program stored in the ROM 17. In addition, the code 18 is a CRT8, a keyboard 9
, and an input/output interface for connecting the printer 10 to the CPU 16. Keyboard 9 has the 8th
The measurement profile keys and the like described in FIG. 9 and FIG. 9 are provided.

Next, the measurement method according to this embodiment will be explained through an explanation of the operation of the above-mentioned apparatus.

For example, when measuring the line width of a resist pattern on a semiconductor wafer, an operator places the pattern at a point within the field of view of a microscope or within the display range of a CRT (e.g., the center of the field of view).
Align to. Next, use the measurement profile key to select (AI), (B1), (CI),
Among the profiles of (DI), specify the profile of (C1) that matches the target edge to be measured,
When the measurement start key on the keyboard 9 is pressed after (or before) 0 or more operations specifying that the target edges in the profile are the edges on both the left and right ends, the capture of image signals from the CCD 6 starts. , after performing appropriate preprocessing such as sensitivity correction between each pixel of the CCD 6 and averaging processing. The image signal for each pixel of the CCD 6 is
For example, edges are detected by performing differential processing.

Then, for each of these detected edges, the starting and ending positions of each edge, the edge size calculated from the difference therefrom, and the positive/negative sign corresponding to the rising or falling edge are stored in the RAM 13. are stored respectively. An edge number (for example, 1 to No.) is assigned to each detected edge in order from, for example, the left end within the measurement area. Figure 2(a) shows the preprocessed image signal;
Figure (b) shows image signals that have been subjected to arithmetic processing such as differential processing to detect edges and determining the edge size and positive/negative sign. Note that such arithmetic processing does not necessarily need to be performed at the preprocessing stage, and may be performed during the process of target edge detection processing, which will be described later.

After the above processing is performed, processing for detecting the left and right target edges corresponding to the edges of the designated measurement profile and processing for calculating the dimensions between the target edges are performed. below,
This processing procedure will be explained according to the flowchart shown in FIG.

Step Sl: Set edge selection number rN1 to rlJ. In this way, for example, the leftmost edge in the image signal within the measurement area (the edge with edge number "1" shown in FIG. 2) is selected, and whether or not this edge is the target edge is determined in the following steps.

- Step S2: Set a flag F in rQJ to determine whether to identify the left edge or the right edge of the specified measurement profile.

When the flag F is rol, processing is performed to search for the left edge, and when flag F is rll, processing is performed to search for the right edge.

Step Sl The size of edge rN1 (edge r11 at the start of measurement), that is, the size of edge r13, is RA
Read from M13 and set this value in the same area 'N+J in RAM13.

Below, the edge set in area 'N+J is
It is called tJ.

Step S4: Read the size of edge rN+11 (edge r2'') and store this value in area 'N' in RAM 13.
Set to zJ. Hereinafter, the edge set in the area 'NiJ will be referred to as edge 'NzJ.

S+7”S 5: zfushirN, J, 'N
g J Determine whether the no side is a rising edge and the other is a falling edge. If there is dust or the like on the sample surface, profile a where two adjacent edges both rise or profile b where two adjacent edges both fall may appear, as noted in step S5 in Figure 3. For,
Edges caused by such causes are excluded from identification targets. If such an abnormal edge is detected, the process advances to step S6.

Step S6: To select the next edge, set the edge selection number rN1 to rN+IJ (ie, N-2), and return to step S4. As a result, step S3
Edge 'IJ (rN, set to J) read in step S4 and edge '3 newly read in step S4 for the second time.
The type of edge rlJ is identified by the combination with J ('Nz set to J). As a result, the edge r23 caused by adhesion of dust or the like is skipped, and the type of edge v11 is identified based on the combination with edge r33.

Step S7: In step S5, edge 'rL+
If it is determined that one of the edges J, rN, 4 is a rising edge and the other is a falling edge, it is determined whether the edge rN, 1 is a rising edge. Such a judgment is made by checking the sign of the edge size (differential value) set to 'N+J.

Step S8: The case where the edge rN, , is determined to be a rising edge includes the profile c-f added to step s7. However, since profiles e and f do not exist in the profiles shown in FIG. 7, it is necessary to eliminate edges that form such profiles e and f. Therefore, in step S8, it is determined whether the sizes of edge 'N+J and edge rN,'' are approximately equal, and in the next step S9, abnormal edges are excluded from the identification target. Note that the above-mentioned profiles e and f are often generated by Fresnel diffraction at the pattern periphery on the substrate (and their occurrence frequency is quite high, and it is extremely beneficial to exclude them from the identification target.

If the sizes of the step Sl edge 'Nt'J and the edge 'NtJ are not equal, the edge selection number rNJ is set to rN+IJ in order to select the next edge, and the process returns to step S4.

Step S10: It is determined that the sizes of edge 'NIJ and edge rNyoj are equal in profile c,
d, that is, (large rising edge)→(large falling edge) or (small rising edge)→(small falling edge). Therefore, in order to judge whether edge 'N+J has a large rise or a small rise, the value of edge rH+21 is read and this value is stored in RAM1.
Area 'N' in 3 is set to 1. Hereinafter, area 'Ns
The edge set to J is called edge 'N3J.

Step S11: It is determined whether the sizes of edges rN, J and edge 'Nsx are approximately equal.

Step 77S12: :L 7'; rNi J To1
When the magnitude of edge 'NsJ is equal to that of edge 'NsJ, the edge 'Nt1 is a large fall, and the edge 'NsJ is a large rise, since the profile j is as added to step Sll.

Step 313: Therefore, it is determined that edge 'NIJ is a large rising edge.

In step S14, the edge 'N
The magnitudes of xJ and edge 'NsJ are judged to be unequal when edge 'NtJ has a small rise, as in the profile added to step Sll, and when edge 'NtJ has a large rise, as in profile l. be. In order not to judge which type of Etsuji'N+J it is, Etsuji'N! Compare the sizes of J and edge 'Nsr.

Step S15: Since the edge rNt is smaller in the case of the profile, in this case it is determined that the edge rN2J is a small fall and the edge rN,4 is a large rise.

Step S16: Therefore, it is determined that edge 'N+J is a small rising edge.

Step S17: In step S14, edge rN
, 1 is not smaller than edge 'NsJ (that is, edge 'N3J is smaller) in the case of profile l. It is determined that N3J has a small rise.

Step 318: Therefore, the edge 'N'tJ is '
It is judged that this is a large rise.

Step S19 In step S7, edge 'N+
It is in the case of profiles g, h, and i that it is determined that J is not a rising edge, that is, edge 'N+J is a falling edge. Therefore, it is determined whether or not the size of this stainless steel 7'S19 TEHA, ERA';'N+J TOZY')'NxJ is approximately equal.

Step 320: both x, difNI J, 'N!
J is equal only in the case of profile g, so in this case it is determined that the edge 'N+J is a large falling edge, and the edge rpJ,1 is a large rising edge.

In step S21 and step S19, both edges'
It is in the case of profiles h and i that N+ J and 'Nt J are determined not to be equal. The profile h is (small fall) → (large rise), and the profile i is (large fall) → (small rise). Therefore, in this step S21, the edge rN
, 4 and edge 'NzJ to identify the type of edge.

Step S22: If edge 'N+J is smaller,
Since the profile is h, it is determined that the edge 'N+J is a small falling edge, and the edge 'NzJ is a large rising edge.

Sft”fS23::LyjirN+ J 4!Etsujir
If it is not smaller than Nz J (that is, edge 'NJ is smaller), it is profile i, so it is determined that edge 'N+J is a large fall and edge 'NzJ is a small rise.

Step S24 2 Step S13. 516. S1
8. Edge rN in S20, S22 and S23
When the type of IJ is identified, the process advances to step S24, where it is checked whether the flag F is rQJ, and the edge 'Nt
It is determined whether the type of J is to be compared with the left or right edge of the specified measurement profile.

Step S25: When the flag F is rQj, the type of the left edge of the profile specified in advance by the operator's operation of the measurement profile key and the edge 'N
Check whether the IJ type matches the IJ type.

Step S26: If they do not match, the edge selection number rN
Jt-rN+IJ) and returns to step S3 to identify the type of the next edge (for example, edge r21 if edge rlJ does not match the desired left edge).

Step S27: If the type of edge 'N+J matches the type of the left edge of the measurement profile, edge'!
'Memorize the LJ position as the left edge.

Step 328 After completing step S27, flag F is set to .rll.

Step S29: Next, set the edge selection number rN4 to rN+
Set it to IJ, return to step S3, and press the next edge (
For example, the type of edge “21) is identified.

The type of the next edge (edge r2'') is identified through each process from step S30 to step S23, and when step 324 is reached, the flag F is r
Since it is ll, the process advances to step S30. In this step 330, it is checked whether the edge 'NIJ (edge r21) matches the type of right edge of the specified measurement profile.

Spyp s31:xyjirN+J (eng7jir21
) does not match the type of the swallowed edge, □ sets the edge selection number rN1 to rN+IJ, returns to step S3, and identifies the type of the next edge (for example, edge r3'').

Step S32: If the type of edge 'N+J matches the type of the right edge, the position of that edge is stored as the right edge.

Step S33: When two edges matching the types of left and right edges of the designated measurement profile are identified, it is determined whether the pattern having these edges is the closest to the center of the visual field.

The field of view center corresponds to the center position of CCD6, so
Its location is known. Therefore, by comparing the distances from the positions of the identified edges to the center of the visual field, the pattern closest to the center of the visual field is determined.

Step S34: If the pattern is not the closest to the center of the visual field, set the edge selection number rN1 to rN+IJ, return to step S2, identify the next edge, and repeat the above process until the pattern closest to the center of the visual field is found. Execute repeatedly.

Step S35: When the pattern closest to the center of the visual field is found, the dimension between the left and right edges of that pattern is calculated from the positions of the left and right edges.

Step S36: Output the calculated line width to the printer,
Finish the process.

Next, a process for measuring the line widths of all patterns within a measurement area corresponding to a designated measurement profile will be described based on FIG. 4.

Since steps 81 to 332 are the same as the flow shown in FIG. 3, they are omitted in FIG.

Step 5378 When measuring all patterns,
Following step S32, it is checked whether all edges within the measurement area have been identified.

This means that the edge selection number rN4 is the maximum value (i.e., No.
) by checking whether it is equal to or not.

Step 338: If all edges have not been identified, set the edge selection number -rNJ to QJ+IJ, return to step S2 shown in FIG. 3, and perform the identification process for the next edge. .

Step S39: When all edges have been identified, the stored dimensions between the left and right edges are calculated.

Step S40: Output the calculated line width of each pattern to the printer, and end the process.

In addition, although the above-mentioned Example demonstrated the case where the line width of a pattern was measured, the same process is performed also when measuring the pitch of a pattern. However, in the case of pitch measurement, a desired profile is designated from among the measurement profiles shown in FIG. 9, and in this case there is only one type of target edge.

In addition, in the above-mentioned embodiment, edge identification processing was performed in order from the edge of the visual field, but it is also possible to perform edge identification processing in order from the center of the visual field. The contents can be modified in various ways. A further modification is possible by identifying the edge type of the image signal based on the rising or falling edges and the size relationship of the edges, which is a feature of the present invention, and identifying the edge type of the image signal based on the edge type of the specified measurement profile. As long as the edge is detected as a target edge when the type matches, it is included in the present invention.

<Effects of the Invention> As described above, according to the present invention, in the target edge detection process in line width measurement for measuring the width and pitch of a pattern on a substrate, the type of edge of an image signal is actively identified,
Since the edge whose type matches the edge type of the specified measurement profile is detected as the target edge, the measurement pattern can be sandwiched between two cursors as in the conventional method, and the edge can be simply measured using these cursors as a reference. Line width measurement can be performed easily and quickly compared to those that select . Furthermore, misidentification caused by unnecessary edges caused by Fresnel diffraction or dust adhesion can also be eliminated.

Also, when measuring the width or pitch of many patterns within the measurement area, there is no need to operate the cursor for each pattern, which is convenient when measuring the width of many patterns continuously. In this sense, the present invention is a measuring method suitable for automatic line width measurement.

[Brief explanation of the drawing]

FIG. 1 is a schematic block diagram of an apparatus using the measuring method according to the present invention, FIG. 2 is a waveform diagram of an image signal and its differential signal detected in an embodiment of the present invention, and FIG. A flowchart showing the processing procedure for measuring the line width of the pattern closest to the center of the visual field, which is an embodiment of the present invention. FIG. 5 is a schematic block diagram of an apparatus using the conventional measurement method, FIG. 6 is an explanatory diagram of cursor operation in the conventional method, and FIG. 7 is a diagram showing a part of the processing procedure according to the present invention. FIG. 8 shows a waveform diagram of a measurement profile common to an embodiment of the present invention and a conventional example, and a cross-sectional view of a sample corresponding to each. FIG. 9 shows an example of a measurement profile specified when pitch measurement is common to the present invention and the conventional example, and FIG.
The figure is an explanatory diagram of a conventional edge detection method. ■...Microscope 2...Specimen 3...Binocular eyepiece 4.5...Light source 6...C0D 8...CRT 9...Keyboard 10...Printer 11...Parallel-Series Converter 12...A/D converter 13...RAM 14...Timing pulse generator 15...Address designator 16...CPU 17...ROM 18...I/O interface Applicant Dainippon Screen Mfg. Co., Ltd. Representative Patent Attorney Tsutomu Sugitani Figure 1 Figure 2 Figure 4 Figure 5 Figure 6 Figure 7 Figure 10/8 <1) (2) (3)

Claims (1)

[Claims] An optical image obtained by enlarging and projecting a fine pattern on a sample is converted into an image signal, and from this image signal, at least two purposes corresponding to a measurement profile specified in advance depending on the sample are obtained. In a line width measurement method that measures the width or pitch of a fine pattern by detecting an edge and calculating the dimension between both edges, the process of detecting the target edge includes measuring the rising or falling edge and the size of the edge. A line width characterized in that an edge type of an image signal is identified based on a relationship, and if this edge type matches an edge type of the specified measurement profile, that edge is detected as a target edge. Measuring method.