JPS6267831A - Electron beam device - Google Patents

Abstract

PURPOSE:To make the measurement with high precision feasible by reducing the errors due to noise etc. by a method wherein analysis voltages are measured several times from at the even point of slice level to calculate the mean value thereof. CONSTITUTION:EB generating signals EBS 5'' are transmitted to an AD conversion circuit and a mean addition circuit 2 from a strobo unit 5 while the output voltage of the secondary electron detector 9 is converted into digital data to be added by the mean addition circuit 2 for calculating the mean value. When the mean additions are performed by the addition times N 2'' outputted from a control computer 1, the mean addition circuit 2 outputs a mean addition finish signal KEN 2' to a mean addition circuit 14, a unit control circuit 3 and a flip-flop 13. The flip-flop 13 stops the output of start signal ST 13' (e.g. L level) only when (e.g. H level) the mean addition finish signal KEN 2' and EF of finish flag 14' outputted from the mean addition circuit 14 are simultaneously transmitted so that the start signal ST 13' may be constantly transmitted to the mean addition circuit 2 not to output the mean addition finish signal KEN 2' but to repeat preceding procedures only.

Description

[Detailed Description of the Invention] [Summary] In an electron beam device, is the voltage always applied to the analyzer so that the amount of secondary electrons is constant? 1ilJ, and when the amount of secondary electrons becomes almost constant, the voltage of the analyzer is added and averaged. Thereby, even if the secondary electronic signal contains a lot of noise, the voltage of the object to be measured can be measured with high accuracy.

[Industrial application field]

The present invention relates to an electron beam device that measures the voltage of an irradiated object by irradiating it with an electron beam, and particularly relates to an electron beam device that measures the voltage of an irradiated object.
Control the analysis voltage '#11 so that the amount of secondary electrons is constant2
This invention relates to an electron beam device that measures the voltage of an irradiated object from an analysis voltage.

[Traditional technique]

Electron beam devices are often used as non-contact voltage measuring devices, for example, to measure wiring voltages in semiconductor ICs.

Generally, the above-mentioned electron beam apparatus calculates the voltage at the irradiation point of the electron beam by converting the amount of secondary electrons generated by irradiation with the electron beam from the analysis voltage that is to be kept constant.

FIG. 3 is a circuit diagram of a conventional electron beam device. A start signal ST generated by the control computer 1 is applied to the unit control circuit 3 and the averaging circuit 2. The unit control circuit 3 is supplied with a periodic clock from the IC driver 4 for instructing the measurement period, and outputs the periodic clock CLK to the strobe unit 5 when the aforementioned start signal is input.

Furthermore, as will be described later, the averaging circuit 2 is connected to the AD conversion circuit 10.
The addition and averaging processing of the digital data added from . Note that the averaging end signal KEN is cleared by this start signal.

The strobe unit 5 is synchronized with the periodic clock CLK.
EB (electron beam) pulse width 1 added from control computer 1
+, a blanking signal is applied to the EB blanker 6 in accordance with a signal instructing the delay time t2. The EB blanker 6 controls the passage of an electron beam emitted from an electron gun (not shown) through the EB blanker 6 using the blanking signal described above. That is, EB is pulsed by the blanking signal to become an EB pulse. And that EB
The pulses are converged by an electronic lens (not shown) and irradiated onto an integrated circuit (IC) 8, which is an object to be measured.

IC8 generates secondary electrons by the above-mentioned EB pulse. The secondary electrons are detected by the secondary electron detector 9, converted into a voltage value, and applied to the AD conversion circuit IO. AD conversion circuit 10. The EB generation signal EBS, that is, the electron beam generated from the strobe unit 5 is sent to the averaging circuit 2.
A timing signal indicating that EB is irradiated is added, and the AD conversion circuit 1 is synchronized with this EB generation signal EBS.
0 converts the analog voltage value of the secondary electron detector 9 into a digital voltage value and outputs it to the averaging circuit 2.

The averaging circuit 2 performs a process of adding (accumulating) the digital value added from the AD converting circuit 10, that is, a digital value proportional to the amount of secondary electrons, and dividing (averaging) by the number of additions. Data representing the number of additions N is added to the averaging circuit 2 from the control computer 1.

The averaging circuit 2 compares the number of times input data is added each time, and when they match, it performs the averaging process and then outputs the averaging end signal KEN. The averaging end signal KEN is applied to the unit control circuit 3, and the unit control circuit 3 outputs a stop signal to the strobe unit 5 to stop sending out the EB. In response to this stop signal, the strobe unit 5 applies a blanker voltage (voltage that does not allow the EB to pass) to the EB blanker 6 to stop EB irradiation. The averaging circuit 2 outputs the averaging value S to the feedback amount calculating circuit 11 almost at the same time as outputting the averaging end signal KEN, and the feedback amount calculating circuit 11 calculates (SL -3) Calculate Δ and output the calculation result to the analysis voltage determination circuit. Furthermore, the calculation result is outputted to the control computer 1 as well.

The analysis voltage determination circuit 12 uses the above-mentioned calculation results.

The voltage applied to the analyzer B is calculated via the DA converter 16 and a corresponding digital value is applied to the DA converter circuit 16. D
The A conversion circuit 16 converts the applied digital value into a corresponding analog voltage value and applies it to the 1 analyzer B.

The control computer 1 is configured so that the feedback amount calculation circuit 11 adds the addition average value S obtained from the addition and averaging circuit 2, and the control computer 1 determines whether to change the analysis voltage again and perform re-measurement. Make a determination. Note that this determination is a determination as to whether or not the additive average value S has reached a specific level value. When the average value does not reach a specific level value, the control computer 1 outputs a start signal ST and repeats the above-described operation again.

FIG. 4 is a characteristic curve diagram of the amount of secondary electron signal with respect to the analysis voltage of the conventional circuit.

Point So is the secondary electron signal amount S in the first measurement, and the analysis voltage (V) at that time is ■Ro. Since the point So is much higher than the slice level SL, measurement is performed again to find S+. This is also much higher than the slice level SL.

The measurement is carried out again at an analysis voltage of V, 2. At this time, the value of point S2 is lower than that of measurement points So and S+.

(SL-3) - Calculate Δ and repeat the analysis at vR3.

In this way, by sequentially repeating the secondary electron signal Sr
The value of l gradually approaches the slice level SL.

In the end, it becomes almost So', SL, so the analysis voltage at this time is ■. The voltage value of the wiring voltage can be calculated from n.

Incidentally, the object to be measured, that is, the IC 8 in FIG. 3, is configured to operate at a specific cycle by an IC driver, and the one-cycle clock is a clock representing the operation at this specific cycle. Therefore, by setting the delay time t2 value to a specific value, the voltage during a specific operation of the IC 8 can be measured, and the voltage can be measured by averaging the voltage.

[Problem that the invention seeks to solve]

When the secondary electron signal amount S approaches or exceeds a specific slice level SL, the voltage of the object to be measured is determined from the second analysis voltage. Conventionally, when the width of the EB pulse is narrow, the signal level is low as shown in FIG. 5, resulting in a secondary electron signal Y accompanied by noise.

For example, even if the voltage of the secondary electron signal becomes exactly equal to the slice level SL, it naturally has an error X due to the noise.

[Means for solving problems]

The present invention solves the above problems, and is characterized in that the secondary electron detection voltage output from the secondary electron detection means for detecting the secondary electrons generated by electron beam irradiation is constant. In the electron beam apparatus, the analysis voltage applied to the analyzer is controlled by an analysis voltage control means so that the voltage of the object to be measured is measured from the analysis voltage, and the secondary electron detection signal of the secondary electron detection means is specified. The present invention includes an adding and averaging circuit that adds the analysis voltage a specific number of times and obtains an average from when the voltage value reaches .

[For production]

The effect is 2 which is output from the secondary electron detection means.
The value of the analysis voltage applied to the analyzer is changed so that the next electron detection voltage becomes a specific value, and from when the specific value is reached, the averaging circuit 2 calculates the average of the subsequent data.

〔Example〕

The present invention will be described in detail below using one drawing.

FIG. 1 is a circuit diagram of an embodiment of the present invention.

Components that are the same as the circuit configuration diagram of the conventional system shown in FIG. 3 are given the same symbols and explanations will be omitted. The start clock SC output from the control computer 1' is connected to the flip-flop 13.
, and sets the flip-flop 13. This cent causes the flip-flop 13 to receive the start signal ST.
Output. With this start signal, the periodic clock CLK is applied to the strobe unit 5 via the unit control circuit 2 in response to the periodic clock output from the IC driver 4, as explained in the conventional circuit diagram of FIG. Unit 5 has a pulse width tl.

A blanking signal corresponding to the delay time t2 is output. Then, the EB pulse is applied to the sample IC8, and secondary electrons are generated and detected by a secondary electron detector. The EB generation signal EBS is sent from the strobe unit 5 to the AD conversion circuit 10. The output voltage of the secondary electron detector is converted into digital data and added in the averaging circuit 2 to obtain an average value. Control computer 1
When the averaging has been performed for the number of additions N output from the averaging circuit 14.', the averaging circuit 2 sends the averaging end signal KEN to the averaging circuit 14. Unit control circuit 3. flip flop 13
Output to. In the conventional circuit, this signal is applied only to the unit control circuit 3, but in the embodiment of the present invention, it is applied to the flip-flop 13 and the averaging circuit 14. Note *1 in 2 figures. *2. *3 is a connection symbol indicating that they are connected. The flip-flop 13 receives the averaging end signal KEN and the end flag EF output from the averaging circuit 14 (
For example, since the output of the start signal ST is stopped 2, for example, at the L level (for example, H level), the start signal ST is always applied to the averaging circuit 2, and the averaging end signal KEN is not output, and the above-mentioned operation is continued. repeat.

On the other hand, the averaging circuit 2 performs averaging in accordance with the number of additions N added by the control computer 1' and adds the average value S to the feedback calculation circuit 11.

The feedback amount calculation circuit 11 is the same as the conventional circuit described above, and calculates (S
L-3) Calculate Δ and output it to the 2-analysis voltage determination circuit 12' The 0-analysis voltage determination circuit 12' determines the analysis voltage from the variation obtained by the above-mentioned average value S, slice level SL, and convergence coefficient Δ. Determine the digital value of the voltage value to be applied.

It is output to the DA conversion circuit 16. The digital value is then converted into an analog voltage value by the DA conversion circuit 16 and applied to the analyzer B as an analysis voltage.

As mentioned above, since the averaging circuit 2 is always operating,
After the addition is performed a number of times, the analysis voltage changes and the voltage measurement operation is performed continuously.

On the other hand, the feedback amount calculation circuit 11 is also connected to the addition start determination circuit 15 (SL-
3) Output the Δ value. As mentioned above, the analysis voltage is changed and measurements are sequentially repeated so as to approach a specific slice level SL, so when multiple measurements are taken, the average value S, which is approximately equal to the slice level SL, is the average value. Since it is output from the circuit 2, the (SL-3) value is naturally close to zero. The addition start determination circuit 15 receives the determination amount Z added from the control computer 1' (SL-
3) Compare the Δ value and make 1 judgment in the range of 1z (SL-S) Δ
When a value is entered, an addition and averaging start signal is output to the addition and averaging circuit 14. As a result, the addition and averaging circuit 14 adds the analysis voltage value added from the 9 analysis voltage determination circuit 12' by the addition factor M added from the control calculation fil', and when the addition of the factor is completed, outputs the average value DATA to the control computer 1'. At the same time, the end flag IEF is transferred to flip-flop 1.
Output to 3. The flip-flop 13 receives the averaging end signal KEN output from the averaging circuit 2 as described above.
and the end flag EF of the averaging circuit 14 are added,
When these two signals are added (at H level), the flip-flop is activated, so the start signal ST is no longer output, and the measurement is completed. Note that the start clock SC is added to the addition averaging circuit 14 and the addition start determination circuit 15, and this is a drive signal for operating each circuit.

Through the above operation, after reaching a specific slice level value, the voltage values of the analyzer, which is constantly fed back and controlled, are added and averaged.

Even if there is a drop in SN due to a small signal, it is possible to accurately measure the voltage of the device under test (IC 8), for example.

FIG. 2 is a characteristic diagram showing the relationship between the number of measurements and the analysis voltage feedback amount 9 in the embodiment of the present invention. The horizontal axis represents the number of measurements, that is, the order number (for images) in which the result S averaged by the averaging circuit 2 was output, and the vertical axis represents the number of times (for images) calculated by the feedback amount calculating circuit 11.
SL-S) Analysis voltage determination circuit 1 according to the Δ value and its result
It represents the analysis voltage output from 2'.

The amount of analysis voltage feedback decreases sequentially from the first measurement, and the analysis voltage also decreases in the same way.

Then, the analysis feedback amount in the third measurement is less than the determination amount, and from this third measurement onwards, the analysis voltages output from the two-analysis voltage determining circuit 12' are averaged in the averaging circuit 14.

For example, addition starts from the averaging starting point P, but
Even if an error occurs due to the influence of noise at this time, it changes around the analysis voltage value that matches the slice level.
For example, by averaging 10 times, it is possible to obtain a correct analysis voltage that approximately matches the slice level.

〔Effect of the invention〕

As mentioned above, in the present invention, measurements are taken multiple times from the point where the analysis voltage matches the slice level, and the average value is obtained. Therefore, errors due to noise etc. are less likely to occur.1 The present invention is resistant to noise. , an electron beam device capable of highly accurate measurement can be obtained.

[Brief explanation of drawings]

FIG. 1 is a circuit configuration diagram of an embodiment of the present invention. FIG. 2 is a characteristic diagram of analysis voltage feedback amount and analysis voltage in the embodiment of the present invention. FIG. 3 is a circuit diagram of the conventional method. FIG. 4 is a characteristic curve diagram of the amount of secondary electron signal with respect to the analysis voltage. FIG. 5 is a characteristic curve diagram of the secondary electronic signal Y accompanied by noise. 2.14...Averaging circuit. 13...Flip-flop. 15... Addition start determination circuit. Tsuku 1 with funai λ1E suit I [Figure 2

Claims (2)

[Claims] (1) The analysis voltage applied to the analyzer is controlled by the analysis voltage control means so that the secondary electron detection voltage output from the secondary electron detection means that detects secondary electrons generated by electron beam irradiation is constant. In the electron beam device that measures the voltage of the object to be measured from the analysis voltage, the analysis voltage is added a specific number of times from when the secondary electron detection signal of the secondary electron detection means reaches a specific voltage value. An electron beam device characterized by having an averaging circuit for calculating an average. (2) Consists of an addition start determination circuit that determines whether the output of the feedback amount calculation circuit has entered a predetermined range, and a circuit that performs averaging processing of the output of the analysis voltage determination circuit after this output is turned on. 2. The electron beam device according to claim 1, wherein the wiring voltage is measured from the output of the averaging processing circuit.