JPH0654648B2 - Pattern size measurement method - Google Patents

Description

The present invention relates to a dimension measuring apparatus for measuring a fine pattern dimension of an electronic device such as a VLSI being manufactured mainly by using a charged beam.

[Conventional technology]

In the manufacturing process of VLSI, it is important to control the dimensions of resists, wirings, and the like, and as patterns become finer, devices for measuring pattern dimensions using a scanning electron microscope have come to be used. As such a device, there is a device disclosed in Japanese Examined Patent Publication No. 59-761. This device is a CRT
Two movable position markers are displayed so as to be superimposed on the scan image of the sample or the secondary electron signal waveform on the screen, and the distance such as the sample size is calculated from the interval between the markers. In the above method, the operator first selects a desired pattern to be measured while looking at the scan image, and switches the electron beam to the line scan mode. Two markers are displayed on the screen so as to overlap the secondary electron signal waveform obtained thereby. After the measurer adjusts the position of the marker so that the marker comes to the position to be measured, the distance is calculated from the distance between the markers and the magnification. Therefore, the measurer must specify the measurement place for each measurement point, and it has been impossible to continuously and automatically measure a large number of points.

To automatically set the slice level and measure the wiring width, convert the secondary electron signal level to a digital value, select the wiring portion, and measure. Conventionally, as shown in JP-A-58-214259, a voltage is externally applied by contact means,
There is a system that utilizes the fact that the amount of secondary electrons emitted from the electrode wiring differs depending on the potential, and binarizes it according to the level of the potential of the electrode wiring. In this case, the purpose is to observe the wirings of different potentials or the wirings of which the potentials have changed, such as distinguishing between 0V wiring and 5V wiring for the purpose of logic test or the like. Therefore, since voltage is applied from the outside for measurement, noise due to charge-up is less likely to occur during digitization. However, when measuring dimensions, the difference in secondary electron emission amount due to the material is measured without applying a voltage from the outside.Therefore, depending on the material and irradiation conditions, the secondary electron signal amount of the wiring part may be different from the base material. In some cases, a waveform as shown in FIG. 5 may be obtained which is almost equal to the secondary electron signal amount.
FIG. 5 shows an example of measurement of poly-Si wiring on SiO ₂ . In this case, the wiring and the SiO ₂ cannot be distinguished. Therefore, although L is originally a wiring and 1 is SiO ₂ , it may be erroneously recognized that 1 is a wiring.

[Problems to be solved by the invention]

When the poly-Si wiring is formed on the SiO ₂ as described above, the wiring and the SiO ₂ cannot be distinguished from each other, and the measurement result may cause the SiO ₂ and the wiring to be erroneously recognized. Further, when noise exceeding the slice level is added to this signal, it is not possible to know where to measure, and there is a drawback in that an interval different from the point to be measured is measured.

Furthermore, there is a stroboscopic scanning electron microscope that observes a scanning electron microscope image by externally applying a voltage to the wiring of an electronic device completed in the past and conducts an operation test by voltage contrast. However, this method has a drawback that a voltage must be applied from the outside by a contact type means and cannot be used for testing a device in the process of manufacture.

[Means for solving problems]

According to the present invention, when the difference in the contrast due to the material is small, the pattern size is measured by irradiating the second beam to emphasize the contrast, and without applying a voltage from the outside by a contact type means. , Non-contact detection of disconnection, leak, and short circuit between wirings.

[Action]

The present invention, when measuring the dimensions of a fine pattern such as an LSI, in the case of a combination of materials in which a signal contrast cannot be obtained, in order to clarify the difference between the materials and improve the measurement accuracy of the dimensions, a normal dimension measurement is performed. In addition to the electron optical lens barrel that generates the electron beam for performing the above, another electron optical lens barrel is prepared, and the measured pattern is irradiated with the first electron beam that is the accelerating voltage with the secondary electron emission ratio δ <1 and is charged. By increasing (providing a negative potential) the signal contrast, and irradiating the measured pattern with a second electron beam of an accelerating voltage that does not charge up and has a normal secondary electron emission ratio δ≈1, while vertically scanning the measured pattern. The generated secondary electrons are detected, and the dimension of the measured pattern is measured from the change in the obtained secondary electron signal. The double irradiation of the first electron beam and the second electron beam causes the measured pattern to be measured. And other patterns The ratio of the signal strengths of and becomes large, and the measurement accuracy is improved because it is less susceptible to noise.

〔Example〕

Next, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a configuration diagram showing a charged beam irradiation apparatus used in an embodiment of a pattern dimension measuring method of the present invention, FIG. 2 is an explanatory diagram of the measurement principle of the above embodiment, and FIG. 2 (a) is a diagram showing the measurement pattern. ,
(B) is a diagram showing a change in the secondary electron signal amount when the first electron beam is irradiated, (c) is a diagram showing a change in the secondary electron signal amount when the second electron beam is irradiated, FIG. 3 is an explanatory diagram of a procedure for testing an electronic device using the measuring method of the present invention, and FIG. 4 is a diagram showing a measuring principle of the above test,
(A) is a diagram showing a change in the amount of secondary electron signals when there is no short circuit or leakage between lines, and (b) is a diagram showing a change in the amount of secondary electron signals when there is a short circuit. Although the lens barrel of the first electron beam 1 will be described with reference to FIG. 1, the lens barrel of the second electron beam 2 has the same structure. Reference numeral 3 is a deflection electrode for deflecting an electron beam, 4 is a deflection power source, 5 is a secondary electron detector, 6 is an amplifier, and 7 is a CRT. 8 is an electronic device (wafer), 9 is a stage for mounting the electronic device, 10 is an objective lens for focusing the beam,
Reference numeral 11 is an objective lens power supply, and 13 is an acceleration power supply that accelerates the beam. 14 is a blanker for turning the beam on and off,
15 is a blanking power source and 12 is a blanking aperture. Reference numeral 16 is an electrostatic lens, and 17 is an electrostatic lens power source.
To operate the above device, first add the second wire to the wiring to be measured.
The electron beam 2 is deflected and irradiated. The accelerating voltage of the electron beam is negatively charged up by setting the accelerating voltage with the secondary electron emission ratio δ smaller than 1. As a result, the amount of secondary electron emission is made larger than in other places.
Next, the first electron beam 1 is line-scanned by applying a sawtooth wave or triangular wave voltage to the deflection electrode 3. As the acceleration voltage of the first electron beam, an acceleration voltage close to δ = 1 is used. The secondary electrons generated at this time are detected by the secondary electron detector 5, and are displayed on the CRT 7 as a change in the secondary electron signal with respect to the line scanning of the first electron beam 1. At this time, secondary electrons are also generated by the irradiation of the second electron beam 2, but when the same wiring is irradiated, the secondary electron signal by the irradiation of the second electron beam 2 is constant. A certain amount of signal will be obtained as the background level. In order to obtain only the secondary electron signal due to the irradiation (line scanning) of the first electron beam 1, the background level when the second electron beam 2 is irradiated when the first electron beam 1 is not irradiated is calculated. In advance, the signal amount is subtracted, or the first and second electron beams 1 and 2 are
The pulses may be emitted alternately as pulses, and the secondary electrons may be detected in accordance with the timing of the irradiation of the first electron beam 1. The method for measuring the pattern size is the same as the conventional one.
That is, the edge of the wiring is detected from the change in the secondary electron signal amount with respect to the line scanning of the first electron beam 1, and the wiring dimension is calculated from the pulse width and the magnification. To obtain the pulse width, set the slice level and set the secondary electron signal to 2
In addition to the method of performing binarization, two slice levels are set and the secondary electron signals are ternarized. Then, the arrangement of the ternarized signals causes signals such as foreign matter adhesion, noise, etc. There is a method described in the prior application for distinguishing and correcting signals and measuring pulse width.

Next, the measurement principle of the above embodiment will be described. The secondary electron emission ratio δ generally has a peak at an accelerating voltage of about several hundreds V, and decreases in an accelerating voltage region higher than that with an increase in the accelerating voltage. If δ> 1, more secondary electrons than the incident electrons are emitted, so the irradiated material is positive, δ <1.
If so, charge up negatively. If δ = 1, no charge-up will occur. For observing the image of the entire sample, usually, an accelerating voltage that does not cause charge-up is selected and scanning electron microscope observation or the like is performed. Depending on the accelerating voltage and the material, there is no difference in the amount of secondary electron emission between the wiring and the underlying material.
In some cases, the width of the wiring cannot be measured because the wiring cannot be distinguished from the underlying material. In this case, the measurement is performed by irradiating the second beam. FIG. 2 is a diagram for explaining the above principle.
(A) is a figure showing a measurement pattern, and a dotted portion shows wiring. (B) and (c) show changes in the amount of secondary electron signals with respect to a line scan perpendicular to the measurement pattern of the first electron beam. (B) shows the case where only the first electron beam is irradiated, and there is no difference in the amount of secondary electron emission between the wiring and the base material. In this state, point A of the pattern shown in (a) is irradiated with the second electron beam. Here, the first beam whose dimensions are to be measured has a low acceleration voltage, and the acceleration voltage of the second beam has a high acceleration voltage which charges up negatively. The wiring including the point A is negatively charged up by the second beam irradiation, and a large amount of secondary electrons are generated (c).
The change of the secondary electron signal amount with respect to the line scanning of the first electron beam as shown in FIG. Therefore, it becomes easy to distinguish the wiring and the base material.

In the above apparatus, the wiring portion is irradiated with the second beam and at the same time line scanning is performed with the first beam, and it is necessary to irradiate the same spot with the first and second beams.
The technique is disclosed in Japanese Patent Application No. 59-8614-6. Here, after irradiating the second beam and charging up,
This beam irradiation may be stopped and the first beam may be line-scanned to perform dimension measurement. In order to achieve the same purpose as the above-mentioned measurement, it is possible to switch and accelerate the accelerating voltage with a single lens barrel. In the method of changing the accelerating voltage, the irradiation position and the degree of adjustment of the lens change depending on the accelerating voltage. Although the sample having metal wiring on the underlying material has been described as an example, the pattern may be a pattern such as a resist on the insulating film or a resist on the metal film. It may be a wafer. Further, although electron beams are used as the first and second beams here, the second beam is a beam for negatively charging up, and may be a negatively charged charged beam. The first beam is for detection, and a charged beam having a small beam current, which does not easily cause charge-up due to beam irradiation, may be used. The irradiation of the charge-up beam is not limited to the spot, and line scanning along the wiring or planar scanning may be performed.

FIG. 3 is a diagram for explaining a procedure for testing an electronic device using the apparatus of the present invention, and a dotted portion shows wiring on an insulating film. This example is a method for measuring a short circuit or a leak between lines. First, the second beam 2 is connected to the wiring A
Irradiate a point. Then, the wiring including the point A and the wiring adjacent thereto are scanned by the first beam 1 perpendicularly to the wiring pattern as L ₁ . The accelerating voltage of the second beam 2 is a high accelerating voltage that causes negative charge-up, and the first beam 1 is an accelerating voltage that does not cause charge-up. The wiring including the point A is negatively charged up by the second beam, and if there is no short circuit or leak between the lines,
The potential at the point A is lower than that at the adjacent point B, and the amount of secondary electrons emitted is larger. However, if there is a short circuit, A and B will have substantially the same potential, and the amount of secondary electron emission will also be substantially equal.
Therefore, if there is no short circuit or leak between the lines, a change in the amount of secondary electron signal as shown in FIG. 4 (a) is obtained, and if there is a short circuit, the first electron beam as shown in FIG. 4 (b) is obtained. A change in the amount of secondary electron signal with respect to the line scanning is obtained. When there is a slight leak, the potentials A and B are not equal, but the difference is smaller than that shown in (a) above where there is no short circuit or leak. In order to detect this difference, a signal emphasizing short circuit or leak may be obtained by calculating the difference between when the second beam irradiation is on and when it is off. Here, the scanning position of the first beam does not have to pass above the point A, and may be deviated from the point A as indicated by L ₂ in FIG.

〔The invention's effect〕

As described above, in the pattern size measuring method according to the present invention, when the measured pattern is irradiated with the first electron beam having an acceleration voltage having a secondary electron emission ratio of less than 1, the measured pattern is charged to a negative voltage. At the same time, while irradiating with a second electron beam having an accelerating voltage at which the secondary electron emission ratio is approximately 1, it scans perpendicularly to the measured pattern, and the secondary electrons generated by the irradiation of the second electron beam are Detecting in synchronization with the scanning of the second electron beam, and measuring the dimension of the measured pattern from the detected change in the secondary electron signal, the dimension of the pattern with a small contrast difference between the wiring portion and the space portion is measured. , And non-contact means can detect line leaks, short circuits, and the like.

[Brief description of drawings]

FIG. 1 is a configuration diagram showing a charged beam irradiation apparatus used in an embodiment of a pattern dimension measuring method according to the present invention, FIG. 2 is an explanatory diagram of the measurement principle of the above-mentioned embodiment, and (a) is a diagram showing a measurement pattern. , (B) is a diagram showing changes in the amount of secondary electron signals during irradiation with the first electron beam, (c) is a diagram showing changes in the amount of secondary electron signals during irradiation with the second electron beam, and FIG. Is an explanatory view of a procedure for testing an electronic device using this embodiment, and FIG. 4 is a view showing a measurement principle of the above test. (A) is a secondary electron signal when there is no short circuit between lines and no leak. Change in quantity, (b)
Is a diagram showing a change in secondary electron signal amount when there is a short circuit, and FIG. 5 is a diagram for explaining a defect of the conventional technique. 1 ... Charged beam, 2 ... Charged beam 3 ... Deflection electrode, 5 ... Secondary electron detector 7 ... Cathode ray tube display device, 8 ... Electronic device

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inoue Akihei Fujinami, No. 3 Morinosato Wakamiya, Atsugi, Kanagawa Pref., Atsugi Telecommunications Research Laboratories, Nippon Telegraph and Telephone Corporation (72) Nobuo Shimazu, Morinosato Wakamiya, Atsugi, Kanagawa No. 56 (Reference) JP 58-201240 (JP, A) JP 59-169133 (JP, A) JP 60-180133 (JP, A) Special Kaisho 57-147857 (JP, A)

Claims (1)

[Claims] 1. A pattern to be measured is irradiated with a first electron beam having an acceleration voltage with a secondary electron emission ratio smaller than 1, and the pattern to be measured is charged to a negative voltage. While irradiating a second electron beam having an acceleration voltage of approximately 1, the scan is performed perpendicularly to the measured pattern, and secondary electrons generated by the irradiation of the second electron beam are synchronized with the scanning of the second electron beam. Then, the pattern dimension measuring method of measuring the dimension of the measured pattern from the change of the detected secondary electron signal.