JPH0745674A - Measuring method for voltage waveform of electron beam tester - Google Patents

Abstract

PURPOSE:To provide a method by which the slice level of an electronic beam tester can be appropriately set and corrected and the convergence factors of S-curves can be pertinently set and evaluated. CONSTITUTION:In a method for measuring the voltage waveform of an electron beam tester, the correcting amount dSL of the slice level SL of the tester is found during the measurement of the voltage waveform based on the convergence factors of S-curves (inverse numbers C1 and C2 of the inclinations of the S-curves) at the intersections of the S-curves with the slice level SL and the slice level SL is corrected based on the correcting amount dSL. In addition, the transition areas (transition points) where the S-curves shift to saturation areas are detected and the initializing value of the slice level is set so that the value cannot exceed the transition areas (transition points). Moreover, weighted convergence factors are found based on the convergence factors at a specific low- and high-phase levels. Furthermore, the convergence factors are evaluated based on the S/N of the convergence factors.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a voltage waveform measuring method by an electron beam tester used for diagnosing a semiconductor integrated circuit, and more particularly to a slice level correcting method and a setting method in the voltage waveform measuring method.

[0002]

2. Description of the Related Art In an electron beam tester, a measurement point of a sample is irradiated with an electron beam, secondary electrons emitted from the irradiation point are detected, and a secondary electron signal amount is converted into a voltage value to measure the sample. The voltage waveform at the measurement point of is measured.

[0003]

When a sample is irradiated with an electron beam, contamination adheres to the irradiation point,
The problem of being charged arises. Due to these factors, the change curve of the detected secondary electron signal quantity at each phase point of the voltage waveform at the measurement point obtained by changing the voltage applied to the secondary electron energy analyzer during voltage waveform measurement (hereinafter ,
A change in the shape of the S curve) occurs.

Voltage waveform measurement by an electron beam tester
Since it is performed by obtaining the analysis voltage that gives the intersection between the S curve and the slice level that has been obtained in advance, if the shape of the S curve changes during measurement in this way, the accuracy of the measurement waveform decreases and the measurement is performed. It becomes unstable.

Therefore, when the shape of the S curve changes, it is necessary to correct the slice level according to the change to maintain the measurement accuracy and stability. However, a change in the shape of the S curve may occur due to a combination of a decrease in amplitude, drift, and shift, and it has been difficult to appropriately correct the slice level.

Next, referring to FIGS. 12 and 13,
The above problems will be further described. It is generally known that irradiation of a sample with an electron beam causes problems such as adhesion of contamination and charging at the irradiation point. Due to this, the S-curve shape changes during the measurement, which often affects the measurement.

FIG. 12 shows the change of the S curve due to the above problems during the voltage waveform measurement.
(B) and (C) show amplitude reduction, shift, and drift of the S curve, respectively. FIG. 13 shows the position of the corrected slice level according to the conventional method. In the cases of FIGS. 13B and 13C, the setting of the correction S _L has an error.

Here, when the amplitude of the S-curve decreases, or when the S-curve drifts, the fixed-slice level exceeds the saturation level of the S-curve, excessive feedback occurs, and the voltage waveform is measured. Have a great effect on. Therefore, the slice level S _L needs to be corrected when the amplitude decreases.

On the other hand, when the S curve shift occurs,
It is not necessary to correct the slice level S _L. But,
In many cases, the amplitude reduction and the shift occur at the same time, and there is no method for detecting them separately. Therefore, the slice level correction is necessary in this case as well.

Next, FIG. 14 shows a slice level setting method according to the conventional method. An ideal S curve has a shape as shown in FIG. The part of the S curve in FIG. 14A is the base level of the S curve, the part of the S curve is the rising region,
If the portion of is defined as the saturated state of the S-curve, the portion of is a transition region (transition point) that transitions to the saturated state. In general, the rising region of the S curve moves in parallel if the measurement voltage changes, and thus the voltage is measured by obtaining this amount of movement. However, in the transition region, the translation amount may be larger or smaller than that in the rising region, and it is difficult to perform accurate measurement in this region.

Further, when there is a local electric field effect, FIG.
As shown in 4 (B), the saturation level of the S curve is separated between the LOW level phase and the HIGH level phase. Moreover, since the wiring around the measurement wiring is also operating, the electric field created by the peripheral wiring causes a change in the shape of the S curve, and in particular, the saturation level is not constant and the shape becomes as shown in FIG. 14C. Not a few things. Therefore, in the voltage waveform measurement, which level to set the slice level is
It greatly affects the measurement accuracy.

Here, in the slice level setting method according to the conventional method, the base level S _min and the maximum value S _max of the S curve are detected for an ideal S curve shape, and the S
_The slice level is set between _min and S _max .

For example, if the slice level is set to 50% of the S curve amplitude, the slice level S _L is set as shown in FIG. 14A for an ideal S curve. In addition, when there is a local electrolysis effect, FIG.
Even when the saturation level is separated as shown in FIG. 14, if the smaller one of the maximum values of the S curve is S _max ,
The slice level S _L is set as shown in FIG.

However, when the shape is as shown in FIG. 14C, the slice level is set as shown in FIG. 14C even if S _max is the smaller of the maximum values of the S curve, and the voltage waveform is changed. It becomes impossible to measure correctly. That is, the slice level is set beyond the transition point (saturation point) of the S curve to the saturation level. FIG. 7B described later is a measurement waveform when the slice level is set in the transition region in the case of the S curve of FIG. 14C. As shown in FIG. 7B, HI
The waveform shape on the GH phase side changes.

Another object of the present invention is to provide a setting method capable of appropriately setting a slice level in an electron beam tester. Therefore, another object of the present invention is to provide a correction method capable of appropriately correcting the slice level in an electron beam tester.

Still another object of the present invention is to provide a setting method capable of appropriately setting the convergence coefficient in an electron beam tester and an evaluation method of the convergence coefficient.

[0017]

A voltage waveform measuring method for an electron beam tester according to a first aspect of the present invention irradiates a measurement point of a sample with an electron beam and detects secondary electrons emitted from the irradiation point,
In the electron beam tester that measures the voltage waveform at the measurement point of the sample by converting the secondary electron signal amount into a voltage value, the measurement point of the measurement point obtained by changing the voltage applied to the secondary electron energy analyzer is measured. Change curve of detected secondary electron signal quantity at each phase point of voltage waveform and slice level S
_In the voltage waveform measuring method in which the secondary electron signal amount is converted into a voltage value by obtaining the analyzer applied voltage that gives the intersection with _L , the change curve shifts to the saturation region It is characterized in that a transition area (transition point) is detected and an initial setting level of the slice level is set so as not to exceed the transition area (transition point).

Further, the voltage waveform measuring method of the electron beam tester of the second invention irradiates the measuring point of the sample with the electron beam, detects the secondary electrons emitted from the irradiating point, and detects the secondary electron signal amount. In an electron beam tester that measures the voltage waveform at the measurement point of the sample by converting it to a voltage value, each phase point of the voltage waveform at the measurement point obtained by changing the voltage applied to the energy analyzer for secondary electrons The secondary electron signal amount is converted into a voltage value by obtaining the analyzer applied voltage that gives the intersection of the change curve (S curve) of the detected secondary electron signal amount in S and the slice level S _L, and in the voltage waveform measuring method of an electron beam tester that the voltage waveform, (inverse of the slope of the variation curve, C _1, C ₂₎ convergence factor at the point of intersection S curve in the voltage waveform measuring auxiliary slice level on the basis of Determine the amount DSL, the correction amount dS
It is characterized in that the slice level S _L is corrected based on L.

The voltage waveform measuring method of the electron beam tester according to the third aspect of the invention irradiates the measurement point of the sample with the electron beam, detects secondary electrons emitted from the irradiation point, and detects the secondary electron signal amount. At each phase point of the voltage waveform of the measurement point obtained by changing the voltage applied to the energy analyzer of the secondary electron in the electron beam tester that measures the voltage waveform of the measurement point of the sample by converting to the voltage value The secondary electron signal amount is converted into a voltage value by obtaining the analyzer applied voltage that gives the intersection of the change curve (S curve) of the detected secondary electron signal amount and the slice level, and the voltage waveform at the measurement point In the method of setting the convergence coefficient in the voltage waveform measuring method of the electron beam tester,
Let CC (LOW) be the convergence coefficient at the W phase level, and CC (HIG) be the convergence coefficient at the HIGH phase level, which is the specific phase.
H) and the coefficient Pr = (HIGH phase level score / total phase score), the desired convergence coefficient CC (with weight)
CC = CC (LOW) + (CC (HIGH) -CC (LOW))
It is characterized by being obtained as × Pr.

Further, the electron beam tester of the fourth invention has an electric power source.
The pressure waveform measuring method calculates the analysis voltage difference in the specific phase.
ΔV_rAnd two suns having the analysis voltage difference ΔVr.
Secondary power with multiple samplings at pulling points
Let σ be the variance of the difference ΔS in the child signal amount _dsAnd the convergence coefficient
S / N of S / N〓ΔS_MEAN/ 3σ_ds And evaluate the convergence coefficient based on this S / N.
Characterize.

[0021]

In the voltage waveform measuring method for the electron beam tester according to the first aspect of the present invention, attention is paid to the fact that the slope of the change curve (convergence coefficient C ₁ , C ₂ ) changes due to the occurrence of the amplitude decrease, and The slice-level correction amount dSL is calculated from the change in the convergence coefficient (C ₁ , C ₂ ) (FIG. 1).

Further, the voltage waveform measuring method of the electron beam tester of the second invention will be explained. It is a necessary condition that the slice level is set between the base level and the saturation level. However, the conventional method cannot detect where the saturation level is, which affects the voltage waveform measurement. Therefore, in the present invention, the transition point of the change curve to the saturation level is detected, and the initial setting level of the slice level is set so as not to exceed the transition point. Here, the saturation point detection method is to obtain two differential curves of the change curve (differential change curve) of LOW and HIGH phases, and use the intersections of the differential curve and the 0 level as respective transition points (FIG. 4).
(A), (B)) or setting the slice level based on the maximum value of the differential curve (FIG. 5 (A),
(B)), the shift amount of the S curve at the LOW and HIGH levels is obtained, and the point at which the shift amount greatly changes is the transition point (FIGS. 6A and 6B).

In the voltage waveform measuring method of the electron beam tester of the third invention, the convergence coefficient at the LOW phase level which is the specific phase is CC (LOW), and the convergence coefficient at the HIGH phase level which is the specific phase is CC (LOW). HIGH) and the coefficient Pr =
When (HIGH phase level score / total phase score),
The convergence coefficient CC (weighted) to be calculated is CC = CC (LOW) + (CC (HIGH) -CC (LOW))
Since it is obtained as × Pr, the convergence coefficient weighted according to the phase level ratio can be obtained, and correct feedback control is performed.

Further, in the voltage waveform measuring method for the electron beam tester of the fourth invention, the convergence coefficient S / N can be obtained as S / N = ΔS _MEAN / 3σ _ds , and the convergence coefficient S / N can be obtained. Since it can be evaluated, the convergence coefficient can be obtained with desired accuracy.

[0025]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT A preferred embodiment of the present invention will be described below with reference to the drawings. Configuration of Electron Beam Tester First, FIG. 2 shows a block diagram of the configuration of the electron beam tester.

In FIG. 2, a sample 12 is placed on a stage 14 in an electron beam cylinder 10, and an electron beam EB from an electron gun 16 is a magnetic field lens 18, a pulsing polarization plate 20, and a pulsing. The sample 12 on the stage 14 is irradiated through the aperture 22, the magnetic lens 24, the deflector 26, the analysis grid 28, the buffer grid 30, the extraction grid 32, and the objective lens 34, and the sample 1
The secondary electrons SE from 2 are detected by the detector 36.
In this detector 36, the secondary electron signal amount is converted into a voltage value, the voltage value is amplified by an amplifier 38, converted into a digital signal by an A / D converter 40, and then the computer 4
2 is supplied. A keyboard 44 and a display device 46 are connected to the computer 42.

The computer 42 controls a driver 48.
Control the electron beam cylinder 10. In addition,
The data 42 controls the clock generator 50 to control the clock φ.₁
And φ₂Is output. Clock φ₁To the counter 52
The count value is supplied to the delay unit 54.
It is also supplied to the computer 42. Well
Clock φ₂Is supplied to the test signal generation circuit 56.
The test signal generating circuit 56 outputs the clock φ.₂Based on
The test signal to the sample 12 is controlled at a precise timing. Ku
Lock φ₂Is further supplied to the delay unit 54,
The delay unit 54 is a clock φ.₂Based on Taimi
A / A according to the count value from the counter 52
The electron beam cylinder 10 is controlled while controlling the D converter 40.
Control. Slice level correction method FIG. 1 shows a method of correcting a slice level according to an embodiment of the present invention.
A graph is shown to illustrate the method.

In FIG. 1, the amplitude reduction + shift + drive is added to the S curve.
We are considering the case where there is a lift, and in this case the secondary e-mail
Slice level S in terms of volume_L， Base level
S_b1, S _b2Is expressed by the following equation (1).

[0029]

[Equation 3] Here, C ₁ and C ₂ are convergence coefficients, and V ₃ and V ₄ are S
_The analysis voltage that gives the intersection of the _L and S curves, V ₂ −V
₁ indicates the shift amount of the S curve. In addition, b and c show the intersection of the extension line of the slope part of the S curve and the vertical axis as shown in FIG.

[0030] Transforming the equation _{(1), C 2 × (S L -S} b2) -C 1 × (S L -S b1) = (V 4 -V 3) - (V 2 -V 1) ... (1) '

[0031] Here, V ₂ -V ₁ is from represents the shift amount (1) 'equation can be modified as follows.

[0032]

[Equation 4] Then, the slice level correction amount dSL can be obtained from the above equation (2).

By the way, in reality, the S-curve drift rarely occurs in a short time when the voltage waveform is measured, and even if it occurs, it is almost negligible.
Therefore, by obtaining the base level in advance before the measurement, S _b1 = S _b2 = S _b can be obtained, and the above equation (2) is transformed as follows.

[0034]

[Equation 5] Therefore, the slice level correction amount dSL can be obtained only from the convergence coefficient change (C ₂ −C ₁ ) based on the equation (3).

Here, as described above, S _L is the slice level, C ₁ and C ₂ are the convergence coefficients V ₁ and V ₂ at the first and second feedbacks, and the base level S of the S curve.
_b and analysis voltage applied to the intersection of the S-curve, V _3, V ₄ analysis voltage applied an intersection point between the slice levels S _L and S curve, DSL is a correction amount of the slice level.

FIG. 3 shows the measured waveform when the S curve is shifted. In the case of the conventional method of FIG. 3A, the falling (rising) portion of the waveform becomes dull, and the correct waveform cannot be measured. On the other hand, in the case of the embodiment of the present invention shown in FIG. 3B, a correct voltage waveform can be measured. Setting method of slice level When setting the slice level, the transition point to the saturation level of the S curve is detected, and the initial setting level of the slice level is set so as not to exceed the transition point. Here, there are a differential S-curve method and an S-curve shift method as methods for detecting the saturation point, and both methods will be described below. Differential S-Curve Method In this method, as shown in FIGS. 4 and 5, first, two S-curves (LOW phase level and HIGH phase level) are acquired. In this case, the S of the acquisition S curve
In order to improve / N, the S curve can be added multiple times. Here, the acquisition S-curve is 4 which is the conventional acquisition score.
The data is acquired at a double data interval (the number of data points is ¼), and the differential S curve is obtained by the smoothing differential method with respect to this discrete S curve. This has the effect of reducing the acquisition time of the S-curve and removing the noise contained in the data, and it is possible to acquire a smooth differential S-curve.

In FIGS. 4A and 4B, the transition points are
Intersection points V _LOW and V _High between the obtained differential S curve and 0 level
Becomes Obtained LOW / HIGH 2 one transition point V _LOW at phase level, compares the S _max L and S _max H corresponding to V _High, smaller as S _max, the slice level between S _min and S _max To set.

Alternatively, as shown in FIGS. 5A and 5B, the maximum values DL and DH of the differential S curve are detected, and the S curve level corresponding to the maximum values DL and DH is changed to S.
There is also a method of setting the slice level to the smaller one of _max L and S _max H. The reason for this is that the maximum values DL and DH of the differential S-curve are places where the slope of the S-curve becomes the largest, so if the convergence coefficient is defined as the reciprocal of the slope of the S-curve, there is an effect that the feedback becomes faster. Is. The maximum value DL, DH of the differential S curve at this time
As a detection method of S, first, the maximum value of the differential S curve is obtained, and 1/2 of the maximum value is set as the slice level sl, and sl is set.
Peak detection is performed in the range exceeding. According to this detection method, it is possible to prevent a minute peak due to a noise component near the base level from being erroneously detected as the maximum value. S-curve shift method FIGS. 6A and 6B show the transition point of the S-curve as LOW / H.
This shows a method of obtaining the shift amount of the S curve of the IGH phase level, and this method uses that the shift amount changes abruptly at the transition point. A slice level is set between the transition point of the shift amount and the transition points S _min and S _max .

Next, FIGS. 7A and 7B show measurement examples of voltage waveforms. Compared with the case where the slice level in FIG. 7B is set beyond the transition point (conventional example), the case in which the slice level in FIG. 7A is set below the transition point (implementation of the present invention In the example), the correct voltage waveform can be measured. Convergence Coefficient Evaluation Method Next, a convergence coefficient evaluation method used for voltage waveform measurement by an electron beam tester used for determination of a semiconductor integrated circuit will be described.

When the measurement point is irradiated with an electron beam and the analysis voltage V _r applied to the analysis grid is swept from the minimum value to the maximum value, the amount of secondary electrons passing through the analysis grid and captured by the analyzer is , With the above-mentioned sweep operation, it changes to almost S-shape. That is, after obtaining a step of rapidly increasing while drawing a function curve from a step of stable transition at a predetermined minimum value, an S value that stabilizes at a predetermined maximum value is obtained.
Draw a curved curve.

FIG. 8A is a diagram showing an ideal S curve, where the horizontal axis represents the magnitude of the analysis voltage V _r and the vertical axis represents the secondary electron signal amount. S _L is a slice level (hereinafter, target voltage), and the analysis voltage is fed back so that the target voltage and the output of the analyzer match.

For example, when a secondary electron signal quantity S0 is obtained when the analysis voltage is V _ro , the value of α
(S0−S _L ) ”is shifted to the right by a new analysis voltage V _R1 . Further, S1 obtained for this V _R1 is used to shift to the right by“ α (S1−S _L ) ”. The new analysis voltage V _R2 is obtained. That is, in this example, in the region where the slope of the S curve is small, the analysis voltage is increased (however,
S0 <When S _L, S0> whereas when the S _L is varied greatly decreasing side), in the region the inclination of the S-curve is greater analytical boosting side (however, S1 <When S _L, S1> S _L In this case, the target voltage S _L is gradually converged by gradually changing to the decreasing side).

Here, the above α is a feedback gain (so-called convergence coefficient), and as shown in FIG. 8B, it is the reciprocal of the slope β of the straight line tangent to the intersection of the S curve and the slice level S _L (however, Sign inversion). That is, α = δV / δS.

In the conventional voltage waveform measuring method, the convergence coefficient used is fixed and required as a pretreatment for the measurement. Moreover, there is a problem that the evaluation accuracy of the convergence coefficient obtained in the specific phase constantly fluctuates under the condition of the fixed number of additions.

Further, the contamination due to the irradiation of the electron beam during the measurement causes a decrease in the secondary electron signal amount, which may cause a measurement error or a voltage decomposition evaluation error with the fixed convergence coefficient.

In the conventional convergence coefficient evaluation method in the voltage measurement method, the number of averaging for increasing the S / N is fixed. Therefore, when the S / N of the secondary electron signal amount at the measurement point is good, it is excessive. However, when the S / N is bad, sufficient addition and averaging is not performed, resulting in excess and deficiency of accuracy.

As a result, the proportion or increase of the preprocessing time with respect to the measurement time, the problem of feedback due to lack of accuracy, the lengthening of the measurement time, and the deterioration of the accuracy of voltage decomposition evaluation will be brought about.

Further, when the amplitude of the S curve is reduced due to the adhesion of contamination during the measurement, the fixed convergence coefficient causes an error in the convergence coefficient that actually needs to be used,
The voltage measurement error may increase or become unstable.

Further, the amplitude (slope) of the S curve in each phase changes due to the local electrolytic effect. Therefore, if the fixed convergence coefficient obtained at the specific phase is used for the measurement of all phases, there arises a problem.

Incidentally, FIG. 9B shows an example of the voltage waveform when the measurement is performed with the convergence coefficient of which accuracy is insufficient. This Figure 9
In the example of (B), it can be seen that the measured waveform has divergence as compared with the voltage waveform of FIG. 9A (when the measurement is performed with the correct convergence coefficient).

As described above, conventionally, the convergence coefficient is obtained before the measurement, and during the measurement, the convergence coefficient is a fixed convergence coefficient using only the convergence coefficient. Moreover, since the convergence coefficient evaluation is performed with a fixed number of additions, the accuracy of the obtained convergence coefficient may not be good. In addition, the measurement is performed with the convergence coefficient obtained at the specific phase (LOW phase level). When all phases are measured with the convergence coefficient of a specific phase, the actual slope of each phase may differ. In particular, when the ratio of the phase level for which the convergence coefficient is desired to be occupied is small, feedback is performed under disadvantageous conditions, which may impair the stability and reliability of measurement. Further, the convergence coefficient may be obtained in advance for all the phases and feedback may be performed using the convergence coefficient for each phase, but in reality, the processing time for obtaining the convergence coefficient in advance becomes long. Further, if a dynamic convergence coefficient correction method that evaluates and corrects the convergence coefficient during measurement is used and measurement is always performed with an optimum convergence coefficient, improvement in measurement accuracy is expected. However, the convergence coefficient evaluated by this dynamic convergence coefficient correction method is the average value of the convergence coefficients of all phases, that is, the weighted convergence coefficient, so the convergence coefficient at a specific phase is the convergence coefficient obtained at the start of measurement. If it is used, a large error will be included in the first feedback, which causes inconvenience.

Therefore, it is necessary to perform feedback from the beginning with the convergence coefficient weighted according to the phase level ratio, and it is difficult to obtain the weighted convergence coefficient with a good S / N in the conventional method. is there.

Therefore, by the following method, as an initial value, two phases of a specific phase LOW and HIGH phase level are obtained.
Obtain the convergence coefficient for each. Where LOW / HIGH
Assuming that the phase level ratio is known, the weighted convergence coefficient C
C becomes as follows.

[0054]

[Equation 6] Further, in order to obtain the convergence coefficient at each level with high accuracy, the convergence coefficient is obtained by the following method.

First, the convergence coefficient of a specific phase is set to a desired S / N.
In order to obtain with, it becomes as follows. The function of the secondary electron signal and the convergence coefficient is as follows. Letting ΔS be the secondary electron signal difference sampled under two conditions with the analysis voltage difference ΔV _r , its average value be ΔS _MEAN , and its noise component be ε, the convergence coefficient C is defined by the following equation.

[0056]

[Equation 7] Here, when the SE signal noise ε is sufficiently small (ε / ΔS
_{MEAN <<} 1 _} is as follows.

[0057]

[Equation 8] However, C _MEAN is the average value of the convergence coefficient. Here, assuming that the separation of the secondary electron signal difference ΔS is σ _ds , the noise 3σ of the convergence coefficient and its S / N are as follows.

[0058]

[Equation 9] From this result, it is possible to evaluate the S / N of the convergence coefficient based on the secondary electron signal difference ΔS sampled between the two points and its variance σ _ds , and therefore the convergence coefficient can be obtained with desired accuracy. It will be possible.

By using the convergence coefficient obtained in the LOW / HIGH phase by the above method, by knowing the LOW / HIGH level ratio of the measured voltage waveform,
It is possible to obtain the weighted convergence coefficient.

FIG. 10 shows a flowchart of the above-described convergence coefficient evaluation method, and the weighted convergence coefficient CC is obtained based on the processing of steps 100 to 114. As another example for obtaining the weighted convergence coefficient, the LOW / HIGH level convergence coefficient can be obtained as follows.

Since the convergence coefficient is defined by the reciprocal of the slope of the S curve, a differential curve (differential S curve) of the S curve at the LOW / HIGH phase level is obtained, and a slice level setting method using the differential S curve method. It is possible to obtain the convergence coefficient corresponding to the slice level.

That is, if the slice level is set,
The slope of the S curve at the intersection of the slice level and the S curve can be obtained from the differential S curve. By using the thus obtained convergence coefficient, it is possible to calculate the weighted convergence coefficient in the same manner as described above.

FIG. 11 shows the fluctuation of the dynamic slice level correction result and the measurement result of the voltage waveform. FIG. 11A shows a case where the measurement is performed with the optimum convergence coefficient (in the case of this method). FIG. 11B shows the case of measurement with a convergence coefficient with a large error (case of the conventional method),
It can be seen that according to this method, the fluctuation of the dynamic slice level is small (the graph on the left side of FIG. 11A) and an appropriate voltage waveform is obtained (the graph on the right side of FIG. 11A).

As described above, according to this method, the convergence coefficient can be evaluated with a desired S / N. Further, it becomes possible to stabilize the measurement. Next, an embodiment of the present method will be described below.

Irradiating the measurement point on the sample with the electron beam,
The secondary electrons emitted from the irradiation point pass through the analyzer to which the voltage _Vr is applied, and the detected secondary electron signal amount is changed according to the applied voltage _Vr. In an electron beam tester that feeds back to the analysis voltage and measures the voltage waveform at the measurement point so that the difference between the quantity slice levels becomes 0, the convergence coefficient used to obtain the feedback voltage of the analysis voltage is measured voltage waveform. L
It is characterized in that it is obtained by the OW / HIGH phase level and is converted into a weighted convergence coefficient CC according to the LOW / HIGH phase level score ratio using the obtained two convergence coefficients, and is used as the initial value of the convergence coefficient for voltage waveform measurement. Convergence coefficient evaluation method.

In the above-mentioned convergence coefficient evaluation method, the convergence coefficient evaluation and the S / N evaluation of the convergence coefficient are performed simultaneously, and the convergence coefficient initial value is obtained with a desired accuracy regardless of the S / N of the secondary electron signal amount at the measurement point. A convergence coefficient evaluation method characterized by obtaining a value.

In the above convergence coefficient evaluation method, S
The secondary electron signal amount difference ΔS sampled between two points of V _r ± dV _r near the analysis voltage V _r that gives the intersection of the curve and the slice level is obtained a plurality of times, and the average values ΔS _MEAN and ΔS
From the variance σ _ds of S, the S / N of the convergence coefficient is obtained by S / N = ΔS _MEAN / 3σ _ds , the convergence coefficient evaluation and the convergence coefficient accuracy are evaluated simultaneously, and the S of the secondary electron signal amount at the measurement point is calculated. A convergence coefficient evaluation method, characterized in that the convergence coefficient is obtained with a desired accuracy regardless of / N.

In the above convergence coefficient evaluation method, L
Set the convergence coefficient of the OW / HIGH phase level to LOW / HIG.
Obtained from the differential S curve obtained by differentiating the S curve of the H phase level, and using the obtained two convergence coefficients, it is converted into a weighted convergence coefficient CC according to the LOW / HIGH phase level score ratio,
A convergence coefficient evaluation method, characterized in that an initial value of the convergence coefficient of voltage waveform measurement is used. Etc.

[0069]

As described above, according to the first invention, the slice level can be appropriately set in the electron beam tester, and the voltage waveform measurement can be performed safely and accurately. Produce an effect.

According to the second invention, the slice level can be properly corrected in the electron beam tester, and the voltage waveform can be measured safely and accurately.

According to the third aspect of the invention, the convergence coefficient weighted according to the phase level ratio can be obtained, and correct feedback control is performed, so that there is no dynamic slice level fluctuation. Appropriate voltage waveform measurement can be performed.

According to the fourth invention, the convergence coefficient S
Since / N can be evaluated, the convergence coefficient can be obtained with desired accuracy, and the measurement can be stabilized.

[Brief description of drawings]

FIG. 1 is a graph illustrating a method of correcting a slice level according to an exemplary embodiment of the present invention.

FIG. 2 is a block diagram showing a configuration of an electron beam tester.

3A and 3B are graphs showing determination waveforms when the S curve is shifted, where FIG. 3A shows the case of the conventional method and FIG. 3B shows the case of the embodiment of the present invention.

4A and 4B are graphs for explaining a slice level correction method according to an embodiment of the present invention (differential S-curve method is shown, and the obtained differential S-curve and the zero-level crossing point are shown). Find the transition point).

5 (A) and 5 (B) are graphs for explaining a slice level correction method according to an embodiment of the present invention (differential S curve method is shown, and based on the obtained maximum value of the differential S curve. Set the slice level).

6A and 6B are graphs (showing a curve shift method) for explaining a slice level correction method according to an embodiment of the present invention.

FIG. 7 is a graph showing a determination waveform of a voltage waveform,
(A) shows the case where the slice level is set below the transition point (embodiment of the present invention), and (B) shows the case where the slice level is set beyond the transition point (conventional example).

FIG. 8 is a graph diagram for explaining an S curve,
(A) shows an ideal S curve, and (B) shows a convergence coefficient α.
Shows the concept of.

FIG. 9 is a graph showing a determination waveform of a voltage waveform,
(A) shows the case where the determination is made with the correct convergence coefficient,
(B) shows a case where measurement is performed with an incorrect convergence coefficient.

FIG. 10 is a flowchart of a convergence coefficient evaluation method.

11A and 11B are graphs showing the fluctuation of the determination result of the dynamic slice level and the measurement result of the voltage waveform, in which FIG. 11A shows the case where the determination is made by the optimum convergence coefficient, and FIG. The measurement results are shown in.

FIG. 12 is a graph showing a change in shape of the S curve,
(A), (B), and (C) show the amplitude decrease, shift, and drift of the S curve, respectively.

FIG. 13 is a graph showing a corrected slice level according to a conventional method, in which (A), (B), and (C) are S respectively.
In the case of the amplitude decrease of the curve, the case of the amplitude decrease of the S curve + shift, and the case of the amplitude decrease of the S curve + shift + drift are shown.

FIG. 14 is a graph showing a slice level setting method according to a conventional method, and (A), (B), and (C) show the conventional method when an ideal S-curve is used and when there is a local electric field effect. An example of erroneous slice level setting is shown.

[Explanation of symbols]

S _L ... Slice level dSL ... Slice level correction amount C ₁ , C ₂ ... Convergence coefficient (C ₁ : before change, C ₂ : After change) S _b1 , S _b2 ... Base level (S _b1 : before change, S _b2 : After change)

Claims (14)

[Claims] 1. A voltage waveform at a measurement point of a sample by irradiating the measurement point of the sample with an electron beam, detecting secondary electrons emitted from the irradiation point, and converting the secondary electron signal amount into a voltage value. Change curve (S curve) of the detected secondary electron signal quantity at each phase point of the voltage waveform at the measurement point obtained by changing the voltage applied to the secondary electron energy analyzer in the electron beam tester for measuring And slice level (S
_In the voltage waveform measuring method of the electron beam tester, the secondary electron signal amount is converted into a voltage value by obtaining the analyzer applied voltage that gives the intersection with _L ), and the change curve is Transition region (transition point) that transitions to the saturation region
Is detected, and the initial setting level of the slice level is set so as not to exceed the transition region (transition point). 2. The voltage waveform measuring method for an electron beam tester according to claim 1, wherein the transition region (transition point) of the change curve is LOW of the waveform to be measured.
/ A voltage waveform measuring method for an electron beam tester, characterized in that it is obtained from the waveform of a differential change curve obtained by differentiating the change curve obtained in the HIGH phase. 3. The voltage waveform measuring method for an electron beam tester according to claim 2, wherein the secondary electron signal amount S corresponding to a transition region (transition point) from the differential change curve corresponding to the LOW / HIGH phase.
_max L and S _max H are obtained, and the smaller one of S _max L and S _max H is taken as S _max, and the base level of the change curve is S
_{When min} , the desired slice level X [%] is (S
_max + S _min ) A voltage waveform measuring method for an electron beam tester, characterized in that the level is set to X / 100. 4. The electron beam tester voltage waveform measuring method according to claim 1, wherein LOW / HI is obtained without detecting a transition region (transition point).
A method for measuring a voltage waveform of an electron beam tester, characterized in that the slice level is set to the smaller one of the secondary electron signal levels corresponding to the maximum value of the differentiated change curve obtained by the GH phase. 5. Any one of claims 1 to 4
In the voltage waveform measuring method for an electron beam tester described in the paragraph 3, the electron beam tester is characterized in that a discrete change curve is acquired and obtained as a discrete differential change curve to shorten the acquisition time and improve the S / N. Voltage waveform measurement method. 6. The voltage waveform measuring method for an electron beam tester according to claim 1, wherein the transition region (transition point) of the change curve is obtained from the shift amount of the change curve obtained by the LOW / HIGH phase of the waveform to be measured. A method for measuring a voltage waveform of an electron beam tester, comprising: 7. A voltage waveform at the measurement point of the sample by irradiating the measurement point of the sample with an electron beam, detecting secondary electrons emitted from the irradiation point, and converting the secondary electron signal amount into a voltage value. Change curve (S curve) of the detected secondary electron signal quantity at each phase point of the voltage waveform at the measurement point obtained by changing the voltage applied to the secondary electron energy analyzer in the electron beam tester for measuring And slice level (S
_The voltage applied to the analyzer is converted to a voltage value by finding the voltage applied to the analyzer that gives the intersection with _L ), and the voltage waveform is measured at the electron beam tester. Then, the slice level correction amount (dSL) is obtained based on the convergence coefficient change (the reciprocal of the slope of the change curve, C ₁ , C ₂ ) at the intersection of the change curve, and the slice level (dSL) based on the correction amount (dSL). A method for measuring a voltage waveform of an electron beam tester, characterized in that S _L ) is corrected. 8. The voltage waveform measuring method for an electron beam tester according to claim 7, wherein the correction amount (dSL) is obtained when an amplitude change of the change curve is detected, and the change curve A voltage waveform measuring method for an electron beam tester, which is characterized in that a correction amount is not generated for left and right shifts. 9. The method for measuring a voltage waveform of an electron beam tester according to claim 7, wherein the correction amount (dSL) is obtained when an amplitude change of the change curve and a vertical drift of the change curve occur. And the change in the convergence coefficient at the intersection of the slice level and the change curve at that time (the reciprocal of the slope of the S curve, C ₁ ,
C ₂₎ by measuring the amount of correction slice level (DSL)
A method for measuring a voltage waveform of an electron beam tester, which is characterized by: 10. A voltage waveform measuring method of an electron-beam tester of claim 9, wherein the convergence coefficient (C _1, C ₂₎ when calculating a correction amount of the slice level (DSL) is a slice level S _L And the convergence coefficient at the intersection of the slice level S _L and the change curve is C _1, and the base level of the change curve is S 1.
_{If b1} and the convergence coefficient at the slice level S _L after the change of the change curve are C ₂ and the base level of the change curve at that time is S _b2 , the slice level correction amount dS
Let L be A method for measuring a voltage waveform of an electron beam tester, characterized by: 11. The electron beam tester voltage waveform measuring method according to claim 9, wherein the variation of the base levels (S _b1 , S _b2 ) of the change curve is ignored and S _b2 = S _b1 is set to correct the slice level. Amount dSL
Is calculated by the following formula, Further, the correction level (dSL) of the slice level during the measurement is obtained by measuring the convergence coefficient change C ₂ -C ₁ by measuring the change curve base level before the measurement of the base level S _b1. A method for measuring a voltage waveform of an electron beam tester, comprising: 12. A measurement point of a sample is irradiated with an electron beam,
It is applied to the secondary electron energy analyzer in the electron beam tester that measures the voltage waveform at the measurement point of the sample by detecting the secondary electrons emitted from the irradiation point and converting the secondary electron signal amount into a voltage value. The secondary electron signal is obtained by determining the analyzer applied voltage that gives the intersection of the change curve of the detected secondary electron signal amount at each phase point of the voltage waveform at the measurement point obtained by changing the voltage In the voltage waveform measurement method of the electron beam tester, which converts the amount into a voltage value and uses it as the voltage waveform at the measurement point, the convergence coefficient at the LOW phase level, which is the specific phase, is CC
When (LOW) and the convergence coefficient at the HIGH phase level that is the specific phase is CC (HIGH) and the coefficient Pr = (HIGH phase level score / total phase score), the desired convergence coefficient CC (with weight) is CC = CC (LOW) + (CC (HIGH) -CC (LOW))
A method for measuring a voltage waveform of an electron beam tester, characterized in that x Pr is obtained. 13. The method for measuring a voltage waveform of an electron beam tester according to claim 12, wherein the analysis voltage difference in the specific phase is ΔV _r, and two sampling points having the analysis voltage difference ΔVr are sampled a plurality of times. When the average value of the difference ΔS of the secondary electron signal amount is ΔS _MEAN , its noise component is ε, and ε / ΔS _MEAN << 1, the convergence coefficient C at the specific phase to be obtained is obtained.
C = (ΔV _r / ΔS _MEAN ) + (ΔV _r / S _MEAN ) × (ε
/ ΔS _MEAN ) = C _MEAN + C _MEAN × (ε / ΔS _MEAN ) (where C _MEAN is the average value of the convergence coefficient obtained by sampling a plurality of times). 14. The method of measuring a voltage waveform of an electron beam tester according to claim 13, wherein when the dispersion of the difference ΔS in the secondary electron signal amount due to a plurality of samplings is σ _ds , the convergence coefficient S / A voltage waveform measuring method for an electron beam tester, wherein N is S / N〓ΔS _MEAN / 3σ _ds and the convergence coefficient is evaluated based on this S / N.