JPH0763542A - Method and device for measuring length of electron beam - Google Patents

Abstract

PURPOSE:To eliminate the dimensional error in length measurement by an adhered contamination when the length of a pattern on a sample is measured by an electron beam length measuring device. CONSTITUTION:In the length measurement of an electron beam, the measurement is carried out in a position to be length-measured a designated number of times, and measurement results L1...Ln are stored in a memory means 25 every measurement. After the measurement is finished, the measurement results L1...Ln are represented by Lm=a.n+L0 in an arithmetic means 26, when a true dimension is L0 and a proportional constant is (a), to calculate the true dimension L0 from the measurement results L1...Ln.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus for measuring a pattern width with an electron beam and a method for measuring the pattern width.

[0002]

2. Description of the Related Art FIG. 4 is a schematic view showing a conventional electron beam length measuring apparatus. In the figure, 1 is an electron beam, 2 is a sample to be length-measured, 3 is a secondary electron detector tube for detecting secondary electrons 6 emitted from the sample by irradiating the sample 2 with an electron beam during length-measurement, 4 Is a display means for receiving a signal output from the secondary electron detection tube 3 and measuring the width of a pattern to be measured from the signal, and a length measuring system 5 for displaying an output result from the length measuring device 4.

Next, the operation will be described. When the electron beam 1 is focused, scanned on the sample, and the length is measured, secondary electrons 6 are ejected from the sample 2 and detected by the secondary electron detection tube 3, and a secondary electron signal corresponding to the unevenness on the sample is generated. The distance between the edges of the pattern is read from the signal sent to the length measuring means 4, and the width of the pattern is measured by the length measuring means 4.

However, when the observation is continued, as a result of the contamination 9 adhering to the sample 2, for example, as shown in FIG.
The width 7a includes the amount of contamination attached.
The value of the width 7a is displayed on the output result display means 5 as it is.

[0005]

According to the conventional electron beam length measuring apparatus and length measuring method, as shown in FIG.
Due to the contamination 9 due to irradiation, a difference occurs between the length measurement value 7a and the true dimension 7b. In this contamination 9, carbohydrates in a vacuum atmosphere are altered by electron beam irradiation and adhere to the surface. The sources of the carbohydrates are the pump, the wall of the vacuum vessel, and the sample itself, and nothing can be ruled out. As a result, for example, in the dimensional standard inspection of LSI, there is a standard that the standard dimension is within ± 10% of the design dimension. However, in the standard inspection, the nonstandard one is the standard or the standard one is the nonstandard. This causes the problem of affecting yield.

The present invention has been made to solve the above problems, and provides an apparatus capable of knowing the true dimension of a pattern width to be measured and a method for determining the true dimension. Is intended.

[0007]

In the electron beam length measuring method according to the present invention, the same point is measured a plurality of times to obtain measured values L ₁ ... L _n.
Is the true dimension L ₀ and L _m = a · m +
Here to represented by L _0, and calculates the true dimension L ₀ from the measured value L ₁ ... L _n. Further, the electron beam length measuring apparatus of the present invention comprises a length measuring means, a control means for issuing a command to the length measuring means to measure the same portion a designated number of times, and a storage means for storing the length measuring value. And a calculation means for calculating the true dimension L ₀ from the length measurement value and a result display means for displaying the calculation result.

[0008]

In the electron beam length measuring method according to the present invention, the same position is measured a plurality of times, and the measurement value L _{m of} each measurement is such that the contamination adhesion rate is a, the number of measurements is m, and the true dimension is L _0. Then, L _m = a · m + L ₀ is represented, and the true dimension L ₀ is obtained from the measured values L ₁ ... L _n for each time.
Further, in the electron beam length measuring apparatus of the present invention, the control means issues a command to the measuring means to measure the same location a specified number of times, and the length measurement values L ₁ ... L _n are stored in the storage means, The true dimension L _{0 is} calculated by the calculation means using the length measurement values L ₁ ... L _n.
By calculating and displaying the calculation result on the result display means,
You can know the true dimensions.

[0009]

【Example】

Example 1. When measuring with a constant electron beam irradiation amount for each length measurement, the contamination increases at a constant rate for each length measurement of the electron beam.
ORNAL OF APPLIED PHYSICS
VOL. 26, No. 3, MARCH, 1987, PP
512. On the other hand, the contamination adhesion phenomenon is that carbohydrates in a vacuum atmosphere are deteriorated by electron beam irradiation and fixed on the surface as described above. It is regarded as the sealing material and the sample itself. The growth rate of contamination that accompanies each measurement is almost constant, but it varies depending on the conditions inside the device and the sample. The conditions in the device differ from time to time, and the influence of contamination on each measurement cannot be expected.
Therefore, it was decided to irradiate the same area with the same amount of electrons at the time of length measurement and determine the most probable value of the true dimension from the measurement result. However, the location to be measured is a test pattern or the like in a wafer among LSI devices.

FIG. 1 is a block diagram of the apparatus of the present invention. 1 is an electron microscope, 3 is a secondary electron detector tube, 4 is a length measuring system, 25 is a storage means for storing the measurement result, and 23
Is a determination means for determining whether or not the length has been measured a set number of times, 26 is a calculation means for performing calculation based on the measurement result stored in the storage means 25, and 5 is a result calculated by the calculation means 26. It is an output result display means for displaying.

Next, the operation will be described. The length measurement is performed according to the flowchart shown in FIG. First step 4
At 1, the number of measurements is set in the judging means 23. Next, the measurement point is selected. Next, in step 43, the length measurement system 4 starts length measurement. The length measuring system 4 sends a signal to start measuring the length to the electron microscope 1, and then, in step 44, receives the signal of the secondary electrons emitted at the time of electron beam irradiation from the secondary electron detecting tube 3 to measure the length. To do. The measurement result is stored in the storage means 25 in step 45, and the determination means 23 determines in step 46 whether or not the number of times of length measurement has reached the initially set number of times, n. In step 47, the count of the number of times of measurement is incremented by 1,
Then, the length measurement system 4 measures again. Step 4
When it is determined by the determination means 23 that the length has been measured n times in 6, the true dimension L ₀ is obtained by the calculation means 26 in step 48.

Next, the calculation means will be described. It is considered that it is represented by the _n - _th length measurement value L _n = a · n + L ₀ (1). Here, a is a rate at which contamination adheres, and L ₀ is a true dimension. Here, assuming that the measured values for each of the n times are L ₁ , L ₂ , L ₃ ... L _n , the observation equation is as follows. The normal equation is (4) with the most probable value of a · L ₀ as X ₁ X _2.
It is represented by a formula. When X ₁ and X ₂ are calculated from this normal equation (4), (5)
It becomes an expression. From (5), the true dimension L ₀ is The value L ₀ derived from the measured values L ₁ , L ₂ , ... L _{n by the} equation (6) is determined as the true dimension.

The values L ₁ , L ₂ , stored in the storage means 25,
The calculation means 26 performs the calculation of the equation (6) using L _n , and the measured result output display means 5 outputs the calculated value of L ₀ . However, it is assumed that the amount of electron beam irradiation is constant for one measurement.

[0014]

As described above, according to the present invention, in the electron beam length measurement, the error due to the thickness of the contamination included in the length measurement dimension can be eliminated and the true dimension can be known. In the dimensional inspection of LSI devices,
Prevents erroneous inspection and prevents yield reduction.

[Brief description of drawings]

FIG. 1 is a block diagram of an electron beam length measuring device according to the present invention.

FIG. 2 is a flowchart of electron beam length measurement according to the present invention.

FIG. 3 is a cross-sectional view of a pattern at a measuring position on a conventional electron beam measuring sample.

FIG. 4 is a block diagram showing a conventional electron beam length measuring apparatus.

[Explanation of symbols]

 1 Electron Microscope 2 Sample 3 Secondary Electron Detector Tube 4 Length Measuring System 5 Result Display Means 6 Secondary Electron 7a First Measured Value 7b True Dimension 9 Contamination 25 Storage Means 26 Computing Means

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Yukinori Hirose 4-1-1 Mizuhara, Itami-shi, Hyogo Mitsubishi Electric Corporation ULS Development Research Center

Claims (2)

[Claims] 1. A method of focusing an electron beam and scanning the sample to measure the pattern dimension of the sample, wherein a plurality of same points are measured, and the obtained measured values L ₁ ... L _n are true. The dimension L ₀ is represented by L _m = a · m + L ₀ , where L is the proportionality constant, and the true dimension L ₀ is determined from the measured values L ₁ ... L _n. . 2. A length measuring device for focusing an electron beam and scanning the sample to measure the pattern dimension of the sample, wherein the length measuring means and the length measuring means measure the same position a specified number of times. A control means for issuing a command to increase the length, a storage means for storing the length measurement value, a calculation means for calculating the true dimension L ₀ from the length measurement value, and a result display means for displaying the calculation result. An electron beam length measuring device characterized by being provided.