JP2986974B2 - Electron beam tester - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electron beam tester used for diagnosis of a semiconductor integrated circuit.

[0002]

2. Description of the Related Art A conventional voltage waveform measuring method using an electron beam tester will be described with reference to FIGS. Hereinafter, numerical values in parentheses are step identification numbers in the figure.

(50) The applied voltage at the measurement point on the sample is 0 V
Then, as shown in FIG. 8A, a so-called S curve of the secondary electron detection amount S with respect to the analysis voltage V is obtained. The average value of the maximum value S _MAX and the minimum value S _MIN of the secondary electron detection amount S and the slice level S _L. Then, the analysis voltage V where S = S _L
0 and a convergence coefficient α = −1 / β are obtained. Where β is S
This is the slope of the S curve at the intersection of the curve and the straight line S = S _L.

(51) An initial value 0 is substituted for a counter i representing the number of scans.

(52) An initial value 0 is substituted for a phase identification variable j.

(53) Set the analysis voltage V to V _ij . The initial value V _0j is the same value for all values 0 to m of the phase j and is set in advance.

(54) In the phase j, the measurement point of the sample is irradiated with the pulsed electron beam EB, and the secondary electron detection amount S
_{Get ij} .

(55) V _{i + 1j} = V _ij + α (S _ij −S _L )
Is calculated. The analysis voltage V _ij is, as shown in FIG.
With increasing phase j converges to analyze the voltage V = V _ej of intersection of the S curve and the slice level S _L.

(56) The phase j is compared with the phase maximum value m.

(57) If j ≠ m, the phase j is incremented, and the process returns to step 53.

(58) When j = m, the analysis voltage V _{i + 1j}
Is determined to have converged to the analysis voltage _Vej . That is, it is determined whether | V _{i + 1j} −V _ij | ≦ ε holds for all values of j from 0 to m.

(59) If it is determined that the analysis voltage V has not converged to V _ej , the counter i is incremented and the process returns to step 52.

When the analysis voltages V _ij (j = 0 to m) converge to the voltage V _ej by repeating the processing of steps 52 to 59, the processing shifts to the voltage waveform measurement processing shown in FIG.

(60) An initial value 0 is substituted for a counter k representing the number of repetitions. _Further , the value V _{i + 1j} is substituted for the new initial value V _0j of the analysis voltage in the phase _j, and the initial value V _0j is substituted for the cumulative addition value VT _j of the analysis voltage in the phase j. The processing in the following steps 61 to 66 is substantially the same as the processing in steps 52 to 57 shown in FIG.

(61) An initial value 0 is substituted for a phase identification variable j.

(62) Set the analysis voltage V to V _kj .

(63) At the phase j, the measurement point of the sample is irradiated with the pulsed electron beam EB, and the secondary electron detection amount S
_{Read j} .

(64) Calculate V _{k + 1j} = V _kj + α (S _j −S _L ).

(65) The phase j is compared with the phase maximum value m.

(66) If j ≠ m, the phase j is incremented and the process returns to step 62.

(67) k is equal to a preset maximum value N
It is determined whether it is acceptable. N is usually 2 ^Four~ 2⁸In the value of the degree
Yes, it is set in advance.

(68) If k ≠ N, the counter k is incremented, and the process returns to step 61.

(69) If k = N, the average value of the analysis voltage VM _j = VT _j / (k + 1) at the phase j is calculated from j = 0 to m
Is calculated for each of. As described above, an averaged voltage waveform VM _j −V ₀ (j = _{0 to} m) is obtained.

[0024]

However, since a single measurement point is irradiated with a pulsed electron beam many times, the measurement point is charged, contamination is attached to the measurement point, and the secondary electron detection amount S Decreases, and as shown in FIG.
The curve changes. Therefore, the convergence coefficient α changes in the course of the iterative processing shown in FIG. 7, and an error occurs in the measured voltage obtained assuming that the convergence coefficient α is constant.

An object of the present invention is to provide an electron beam tester capable of more accurately measuring a voltage waveform by updating the convergence coefficient α during voltage waveform measurement in view of such problems. It is in.

[0026]

FIG. 1 shows the principle configuration of an electron beam tester according to the present invention.

In the present invention, the electron beam 2 is irradiated on the measurement point on the sample 3 by the electron beam irradiation apparatus 1 and the secondary electrons 4 emitted from the irradiation point are converted into an energy analyzer 5 to which an analysis voltage V is applied. detected by the secondary electron detector 6 through, when the secondary electron detection amount S of the analysis voltage for incremental δS secondary electron detection amount at the point at which the slice level S _L increment of .DELTA.V, the convergence factor alpha alpha = - [Delta] V / delta] S and, in each phase j, the secondary electron detecting amount S is converged to the slice level S _L and the secondary electron detection amount in the k times of the phase scan after convergence and analysis voltages S respectively _{kj, Assuming} that V _kj , V _{k + 1j} = V _kj + α (S _kj −S _L ) (1) The analysis voltage V _{k + 1j} is obtained, and a value VM _{j obtained} by adding and averaging V _kj to k is used as a reference. in the electron-beam tester of a difference between the value V ₀ and measured voltage in the phase j according to an increase of k, the analysis voltage V near the increment δV of _kj and secondary electron detection amount S
Convergence coefficient updating means 7 and 8 for updating the convergence coefficient α based on the increment δS near _kj are provided.

According to the present invention, during the voltage waveform measurement, the convergence coefficient α is determined based on the increment δV near the analysis voltage V _kj and the increment δS near the secondary electron detection amount S _kj in accordance with the increase in the number of phase scans. Because it is updated, the electron beam 2
Is irradiated many times, the measurement point is charged, contamination is attached to the measurement point, the secondary electron detection amount S decreases, and even if the S curve changes as shown in FIG. The waveform can be measured.

In the first embodiment of the present invention, the convergence coefficient updating means 7 and 8 convert the analysis voltage into V _kj + δV /
The secondary electron detection amount SH _{j at 2} and the analysis voltage V
give the secondary electron detection amount SL _j when the _{kj -δV} / 2,
Value SH of the secondary electron detection amount SH _j were averaged for j
And secondary electron detection amount SL _j calculates the value SL obtained by averaging the j, α + κ (-δV / δS-α) and a new convergence factor alpha. Here, δS = SH−SL, κ is 0 <
κ ≦ 1. S _kj = (SH _j + SL _j )
/ 2, the analysis voltage V _{k + 1j} is _obtained based on the above equation (1).

In the case of 0 <κ <1, even if the convergence coefficient α suddenly changes suddenly, the convergence coefficient α is gradually updated to an accurate value without being affected so much. If it is almost impossible for the convergence coefficient α to suddenly change suddenly, it is preferable to set κ = 1. Further, since the average values SH and SL are used for δS, the accuracy of updating the convergence coefficient α increases. Furthermore, since S _kj = (SH _j + SL _j ) / 2, there is no need to detect secondary electrons with the analysis voltage V _kj .

In the second embodiment of the present invention, for each k, V
It calculates the variance Va _k of _{F kj = V k + 1j -V} kj, the dispersion Va _k
And the value of k is determined (9).

The smaller the variance Va _k and the larger the k, the higher the resolution of the measured voltage. Therefore, in this configuration, it is possible to prevent k from becoming unnecessarily large and the processing time from being lengthened. be able to.

[0033] In a third aspect of the present invention calculates the voltage resolution V _re in _{V re = 3 [(Va 0} + Va 1 + ··· + Va k) / {2 (k + 1) 2}] 1/2, wherein The time when the voltage resolution _Vre falls below the set value is determined as the final value of k (9).

In the case of this configuration, the average of the variance (Va ₀ + V
because of the use of _{a 1 + ··· + Va k)} / (k + 1), it is possible to evaluate the voltage resolution V _re more accurately, it is possible to more properly determine the final value of k.

[0035]

An embodiment of the present invention will be described below with reference to the drawings.

FIG. 2 shows a hardware configuration of a main part of the electron beam tester.

The electron beam irradiator 10 converts the electron beam EB emitted from the electron gun 11 into a condenser magnetic lens 12A, a pulsating deflecting plate 13, a pulsating aperture 14, a condenser magnetic lens 12B, a deflector 15 and an objective. The measurement point on the sample 18 fixed on the stage 17 is converged and irradiated through the magnetic lens 16. The secondary electrons SE emitted from the irradiation point are supplied to an extraction grid 191 and a control grid 192 disposed inside the objective magnetic field lens 16.
And detected by the secondary electron detector 20 through the energy analysis grid 193. The output current of the secondary electron detector 20 is converted into a voltage by the amplifier 21 and amplified,
The data is digitized by the / D converter 22 and supplied to the computer 30.

On the other hand, the clock generator 23 outputs the clock φ
₁ was fed to the clock input terminal of the counter 24, and supplies the test signal generation circuit 25 and the delay unit 26 the clock phi ₂ with the clock phi ₁ to the circumferential example 1/512 minutes as a trigger signal. Test signal generation circuit 25, in synchronism with the clock phi _2, and supplies a periodic test signal to the sample 18. The output gate of the clock generator 23 is controlled by a start / stop signal from the computer 30. The counter 24 counts the clock φ1, supplies the counted value to the computer 30, and supplies the lower 9 bits of the counted value to the delay unit 26 as the phase i, for example. After receiving the clock φ ₂ , the delay unit 26 applies the electron beam EB to the pulse deflecting plate 13 so that the electron beam EB passes through the pulse aperture 14 when the phase i from the counter 24 becomes j. Control the voltage. This phase j is incremented by the clock φ2.

The computer 30 is connected to a keyboard 31 for inputting set values and a display device 32 for displaying set values, voltage measurement waveforms and the like.

Next, referring to FIG. 5, the procedure of the voltage waveform measurement processing by the computer 30 will be described with reference to FIGS.

(70) The analysis voltage V _{i + 1j} when the analysis voltage V converges to the voltage V _ej (FIG. 8) by performing the processing shown in FIG.
For the phases j = 0 to m.

(71) An initial value 0 is substituted for a counter k indicating the number of repetitions. _Further , the value V _{i + 1j} is substituted for the new initial value V _0j of the analysis voltage in the phase _j, and the initial value V _0j is substituted for the cumulative addition value VT _j of the analysis voltage in the phase j.

(72) The initial value 0 is substituted for the phase identification variable j, and the initial value 0 is substituted for the cumulative addition value SHT of the secondary electron detection amount S.

(73) Set the analysis voltage V to V _kj + δV / 2. δV is a preset value, for example, δV
Is set to about 1 V, the convergence coefficient α can be measured with an accuracy of about 1%. Figure 5 (A)
In the case shown in FIG. 5, V _kj + δV / 2 becomes as shown in FIG.

(74) The secondary electron detection amount S is read and is set as SH _j . Secondary electron detection amount SH _j becomes as shown in FIG. 5 (B).

[0046] (75) as a new SHT a plus SH _j to SHT.

(76) The values of j and m are compared.

(77) If j ≠ m, the phase j is incremented and the process returns to step 73.

(78) If j = m, the average SHT value SH = SHT / (m + 1) is calculated.

(79) The initial value 0 is substituted for the phase j, and the initial value 0 is substituted for the cumulative addition value SLT of the secondary electron detection amount S.

(80) Set the analysis voltage V to V _kj -δV / 2. V _kj −δV / 2 is as shown in FIG.

[0052] (81) reads the secondary electron detection amount S, which is referred to as SL _j. Secondary electron detection amount SL _j becomes as shown in FIG. 5 (B).

[0053] (82) as a new SLT a plus SL _j to the SLT.

(83) The values of j and m are compared.

(84) If j ≠ m, the phase j is incremented and the process returns to step 80.

(85) If j = m, the average value of SLT SL = SLT / (m + 1) is calculated.

(86) δS = SH−SL is calculated, and α +
Let κ (−δV / δS−α) be the new convergence coefficient α. That is, the convergence coefficient α which is conventionally treated as being constant is updated. Here, κ is a preset value such that 0 <κ ≦ 1.

[0058] (87) a _{V k + 1j = V kj +} α {(SH j + SL j) / 2-S L} VT j = VT j + V k + 1j is calculated for each of the j = 0 to m.

(88) In order to determine the end of the measurement, first, the difference VF _kj between the analysis voltage V _{k + 1j} and the noise component included in the analysis voltage V _kj and the phase j = 0 to m of the VF _kj are determined. following equation variance Va _k, calculated by _{VF kj = V k + 1j -V} kj Va k = (VF k0 2 + VF k1 2 + ··· + VF km 2) / (m + 1), following equation voltage resolution V _re , it is calculated by _{V re = 3 [(Va 0} + Va 1 + ··· + Va k) / {2 (k + 1) 2}] 1/2. Then, the voltage resolution V _re is compared with a preset value 3σ ₀ .

In the above voltage resolution calculation formula, (Va <sub>0
+ Va 1 + ··· + Va k</sub> ) / (k + 1) , the dispersion Va ₀
The average value of the to VA _k, also 2 ^{{2 (k + 1) 2} } is due to that it contains V _{k + 1j} in each of VF _kj and VF _{k + 1j.}

(89) If V _re > 3σ _0, it is determined that the voltage resolution is insufficient, the counter k is incremented, and the process returns to step 72.

(90) If V _re ≦ 3σ ₀ , an average analysis voltage VM _j = VT _j / (k + 1) is obtained for each of the phases j = 0 to m. The voltage at the measurement point is given by VM _j -V ₀ .

As described above, the voltage waveform can be measured more accurately than before.

[0064]

As described above, in the electron beam tester according to the present invention, during the measurement of the voltage waveform, the increment δV near the analysis voltage V _kj and the secondary electron detection amount S increase as the number of phase scans increases. convergence coefficient α based on the increment δS near _kj
Therefore, even if one measurement point is irradiated with an electron beam many times, the measurement point is charged, contamination is attached to the measurement point, the secondary electron detection amount S decreases, and the S curve changes. This has the effect that the voltage waveform can be measured more accurately than before.

According to the first aspect of the present invention, κ satisfying 0 <κ ≦ 1 is selected in accordance with the probability that the convergence coefficient α suddenly changes suddenly, so that the convergence coefficient α suddenly changes suddenly. Also has an effect that the convergence coefficient α is gradually updated to an accurate value without being affected so much. Further, since the average values SH and SL are used for δS, the accuracy of updating the convergence coefficient α is increased, and S _kj = (SH _j + SL _j ) /
Since 2, the secondary voltage does not need to be detected with the analysis voltage V _kj .

According to the second aspect of the present invention, there is an effect that it is possible to prevent the processing time from increasing due to unnecessarily large k.

According to the third aspect of the present invention, the voltage resolution V _re can be more accurately evaluated, and the final value of k can be determined more appropriately.

[Brief description of the drawings]

FIG. 1 is a principle configuration diagram of an electron beam tester according to the present invention.

FIG. 2 is a hardware configuration diagram of a main part of an electron beam tester according to one embodiment of the present invention.

FIG. 3 is a flowchart illustrating a voltage waveform measurement procedure.

FIG. 4 is a flowchart illustrating a voltage waveform measurement procedure.

FIG. 5 is a diagram provided for explanation of voltage waveform measurement.

FIG. 6 is a flowchart showing a voltage waveform measurement procedure according to a conventional method.

FIG. 7 is a flowchart showing a voltage waveform measurement procedure according to a conventional method.

FIG. 8 is an explanatory diagram of voltage waveform measurement.

FIG. 9 is a diagram showing a change in an S curve.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Electron beam irradiation apparatus 11 Electron gun 12A, 12B Condenser magnetic lens 13 Pulsing deflecting plate 14 Pulsing aperture 15 Deflector 16 Object magnetic field lens 17 Stage 18 Sample 191 Extraction grid 192 Control grid 193 Energy analysis grid 20 Secondary electrons Detector EB electron beam SE secondary electron

──────────────────────────────────────────────────続 き Continued on the front page (58) Fields surveyed (Int.Cl. ⁶ , DB name) H01L 21/66

Claims (4)

(57) [Claims] An electron beam irradiator (1) irradiates an electron beam (2) to a measurement point on a sample (3) and applies an analysis voltage V to secondary electrons (4) emitted from the irradiation point. detected by energy analyzer (5) through a secondary electron detector (6), the incremental analysis voltage for the secondary electrons detected amount of incremental δS at the point where the secondary electron detection amount S becomes the slice level S _L Is δV, the convergence coefficient α is α = −δV / δS,
In each phase j, converges the secondary electron detection amount S the slice level S _L, the secondary electron detecting amount in the k times of the phase scan after convergence and analysis voltage when the S _kj, V _kj respectively, V _{k + 1j} = seeking _{V kj + α (S kj -S} L) analyzed by (1) the voltage V _{k + 1j,} the difference between the value VM _j and the reference value V ₀ obtained by averaging the V _kj for k In an electron beam tester that sets a measurement voltage at the phase j, a convergence coefficient α is determined based on an increment δV near the analysis voltage V _kj and an increment δS near the secondary electron detection amount S _kj as k increases.
An electron beam tester comprising convergence coefficient updating means (7, 8) for updating the following. Wherein said convergence coefficient updating means (7, 8), in each phase j, and the secondary electrons (4) detecting the amount SH _j when the analysis voltage was V _kj + .DELTA.V / 2, the analysis voltage V _kj −δ
The secondary electron detection amount SL _j at V / 2 is obtained, and a value SH obtained by averaging the secondary electron detection amount SH _j with j and a value SL obtained by averaging the secondary electron detection amount SL _j with j are calculated. Then, α + κ (−δV / δS-α) is set as a new convergence coefficient α, where δS = SH-SL, κ is a constant satisfying 0 <κ ≦ 1, and S _kj = (SH _j + SL _j ) / 2. The electron beam tester according to claim 1, wherein the analysis voltage V _{k + 1j} is _obtained based on the above equation (2). 3. For each k, VF _kj = V _{k + 1j} -V
3. The electron beam tester according to claim 1, wherein a variance Va _k of _kj is calculated, and a final value of k is determined based on the variance Va _k and the value of k. The 4. A voltage resolution _{V re, V re = 3 [} (Va 0 + Va 1 + ··· + Va k) / {2 (k + 1) 2}] is calculated by ^1/2, the voltage resolution V _re is 4. The electron beam tester according to claim 3, wherein when the value becomes equal to or less than a set value, the final value of k is set.