JP4491882B2 - Microscope using deep ultraviolet light as light source - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a microscope using deep ultraviolet light as a light source, and more particularly to a microscope capable of limiting damage to samples by deep ultraviolet light.
[0002]
[Prior art]
When observing the microstructure of a sample with a microscope, the resolving power δ is
δ = λ / 2NA (1)
It is represented by Here, λ is the wavelength of the illumination light of the microscope, and NA is the numerical aperture of the objective lens. As shown in the equation (1), in order to increase the resolving power δ of the microscope, the wavelength λ of the illumination light may be shortened or the numerical aperture NA of the objective lens may be increased.
[0003]
When the observation target is a biological sample such as a cell, if the wavelength λ of the illumination light is shortened to the ultraviolet region or less, the biological sample itself is damaged by a photochemical reaction or the like. For this reason, shortening the wavelength λ of the illumination light is not very advantageous, and generally, the numerical aperture NA of the objective lens is increased to increase the resolving power δ.
[0004]
On the other hand, when the observation target is an inorganic substance such as a material and it is necessary to greatly improve the resolution δ, the numerical aperture NA of the objective lens is increased and the wavelength λ of the illumination light is shortened.
[0005]
For example, in the field of observing a semiconductor wafer or the like, the scale of a fine structure typified by an integrated circuit is steadily shrinking, and a repeat structure of a fine structure called a line & space in a semiconductor process is 0.25 μm. It has entered an area that is less than.
[0006]
In order to observe such a fine structure, in recent years, a microscope using deep ultraviolet light having a wavelength λ of 300 nm or less as illumination light is used. For example, λ = 266 nm which is a fourth harmonic of an Nd-YAG laser as a light source. Using a laser that continuously oscillates deep ultraviolet light and using an objective lens with a high numerical aperture of NA = 0.9, a resolution δ of about 0.10 μm is obtained.
[0007]
[Problems to be solved by the invention]
Thus, the resolution δ is greatly improved by making the wavelength λ of the illumination light deep ultraviolet, but at the same time, the problem of sample damage due to deep ultraviolet light cannot be ignored. That is, inorganic materials such as materials are less damaged by deep ultraviolet light than biological samples. For example, the observation target is a resist pattern on a semiconductor wafer, and the exposure wavelength of the resist is close to the wavelength of the illumination light of the microscope. In this case, if the amount of illumination light used for observation is large, damage to the resist pattern during the observation period cannot be ignored.
[0008]
In particular, in the case of a confocal laser scanning microscope, the laser light is focused on a very small area, so that the energy per unit area irradiated on the sample increases and the degree of damage to the sample increases.
[0009]
Therefore, an object of the present invention is to provide a microscope capable of limiting damage to a sample due to deep ultraviolet light in a microscope using deep ultraviolet as a light source.
[0010]
[Means for Solving the Problems]
In order to achieve the above object, one aspect of the present invention relates to a line width of a pattern provided at a predetermined position of an observation target in a microscope that acquires observation data by irradiating the observation target with deep ultraviolet light. When the line width of the pattern reaches a predetermined limit value, a control unit is provided that stops irradiation of the deep ultraviolet light onto the observation target.
[0011]
According to the present invention, when the line width of the pattern provided at a predetermined position of the observation target reaches a predetermined limit value, irradiation of the deep ultraviolet light to the observation target is stopped. It is possible to prevent damage as described above.
[0012]
As a preferred aspect of the above invention, when the line width of the pattern reaches a predetermined limit value, the control unit displays the observation data and the line width data of the pattern, and makes an observation to the operator. It is characterized by inquiring whether to continue.
[0013]
According to the present invention, when the line width of the pattern reaches a predetermined limit value, the operator is inquired about whether or not to continue the observation, so that it is possible to prevent accidental damage during the observation. Can do.
[0014]
Further, as a preferred aspect of the above invention, the control unit is connected to an external device capable of transmitting the acquired data, and when the line width of the pattern reaches a predetermined limit value, The line width data of the pattern is transmitted to the external device.
[0015]
According to the present invention, since information on a sample that has not been measured can be used in the next process, the reliability of the inspection process can be improved.
[0016]
Furthermore, in order to achieve the above object, another aspect of the present invention is generated by irradiating the observation target with deep ultraviolet light in a microscope that acquires observation data by irradiating the observation target with deep ultraviolet light. The progress speed of damage to be obtained is obtained by measuring the line width of the pattern provided at a predetermined position of the observation target, and the observation target is irradiated so that the progress speed of the damage becomes a predetermined progress speed. It has a control part which adjusts the intensity of deep ultraviolet light.
[0017]
According to the present invention, the amount of illumination light is adjusted while monitoring the progress of damage to the sample.There are a plurality of measurement points in the observation range, and when a considerable time is required for the measurement, All measurement points can be measured without exceeding the damage limit value.
[0018]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below with reference to the drawings. However, such an embodiment does not limit the technical scope of the present invention.
[0019]
FIG. 1 is a configuration diagram of a confocal laser scanning microscope according to an embodiment of the present invention. The confocal laser scanning microscope can form a so-called optical tomographic image by extracting only the image of the in-focus surface of the uneven sample by placing a minute aperture at the confocal position.
[0020]
In the confocal laser scanning microscope of FIG. 1, the laser light 102 emitted from the deep ultraviolet laser 101 passes through the shutter 103 and is adjusted to an appropriate light quantity by the neutral density filter in the neutral density filter switching unit 104. . Then, the light is reflected by the mirrors 121 and 122, and the beam diameter is expanded by the beam expander 105, so that the light beam 106 has a beam diameter that satisfies the pupil diameter of the objective lens 110.
[0021]
After passing through the beam splitter 107, the light beam 106 is two-dimensionally scanned in a direction perpendicular to each other by a two-dimensional scanner unit 108 having movable mirrors 123 and 124. Then, it is reflected by the mirror 125, passes through the relay lens 109, is collected by the objective lens 110, and forms an image as the minute spot light 112 on the sample 111.
[0022]
The minute spot light 112 is two-dimensionally scanned on the sample 111 and reflected by the surface of the sample 111. The reflected light passes through the objective lens 110, the relay lens 109, the mirror 125, and the two-dimensional scanner unit 108, and is reflected by the beam splitter 107 to become a stationary light beam 113.
[0023]
The stationary light beam 113 is condensed by the condenser lens 114, and only the light passing through the pinhole 115 is photoelectrically converted by the detector 116. The output signal of the detector 116 is converted into an image signal by the image processing device 117, and the image of the sample 111 is displayed on the image display 118.
[0024]
In the confocal laser scanning microscope, the pinhole 115 almost eliminates out-of-focus light. Therefore, if the sample 111 has irregularities, a so-called optical tomogram in which the sample 111 is in focus at a predetermined height is used. Can be observed clearly.
[0025]
The control unit 119 controls the image processing device 117 and closes the shutter 103 to close the depth when the damage to the sample 111 reaches a predetermined limit value in order to limit the damage to the sample 111 due to deep ultraviolet light. The irradiation of ultraviolet light is stopped to prevent the sample 111 from being damaged beyond the limit value.
[0026]
Further, the amount of deep ultraviolet light is controlled by the neutral density filter switching unit 104 to adjust the progress speed of damage to the sample 111. As a result, even when there are many measurement locations and it takes a long time to measure, it is possible to secure a measurement time during which the measurement at all the measurement locations can be completed before the damage reaches the limit value. The confocal laser scanning microscope is placed on the vibration isolation table 120 in order to guarantee high image quality.
[0027]
FIG. 2 is a configuration diagram of the collective illumination microscope according to the embodiment of the present invention. Since the collective illumination microscope irradiates the entire sample with uniform deep ultraviolet light, damage to the sample due to deep ultraviolet light can be reduced compared to a confocal laser scanning microscope that irradiates spot light. The collective illumination microscope is also called a Koehler illumination microscope.
[0028]
In the collective illumination microscope of FIG. 2, the laser light 202 emitted from the deep ultraviolet laser 201 passes through the shutter 203 and is adjusted to an appropriate amount of light by the neutral density filter in the neutral density filter switching unit 204. Then, the light is reflected by the mirrors 219 and 220, and the beam diameter is expanded by the beam expander 205, so that the light beam 206 has a beam diameter that satisfies the pupil diameter of the objective lens 209.
[0029]
The light beam 206 passes through the relay lens 207, is reflected by the beam splitter 208, and is irradiated onto the sample 210 as uniform illumination light 211 (solid line) by the objective lens 209. The reflected light 212 (broken line) from the sample 210 passes through the objective lens 209 and the beam splitter 208 and forms an image on a CCD (Charge Coupled Device) camera 214 by the second objective lens 213. The image on the CCD camera 214 is photoelectrically converted, converted into an image signal by the image processing device 215, and displayed on the image display 216.
[0030]
As in the case of the confocal laser scanning microscope, the control unit 217 closes the shutter 203 when the damage of the sample 210 reaches a predetermined limit value, and blocks the deep ultraviolet light irradiated on the sample 210. Prevent the sample from being damaged beyond the limit. Further, the amount of deep ultraviolet light is controlled by the neutral density filter switching unit 204 to adjust the time until the damage reaches the limit value. A batch illumination microscope is also placed on the vibration isolation table 218 to guarantee high image quality.
[0031]
Next, a first measurement flowchart in the embodiment of the present invention will be described with reference to FIG. In order to observe the sample with the microscope of the present embodiment, first, a specific observation range of the sample is displayed on the image display (step S1).
[0032]
FIG. 4 is an explanatory diagram of a sample observed with a microscope and an observation range. Here, a case where a resist pattern on the semiconductor wafer 301 is observed as a sample is shown. Although a resist pattern corresponding to the circuit pattern is formed on the semiconductor wafer 301, FIG. 4 shows resist patterns (black lines) having three types of line widths for explanation.
[0033]
In order to inspect whether or not the resist pattern is formed with a predetermined line width in the production process on the semiconductor wafer 301, a plurality of measurement points 305, 306, 307, 308, and 309 are usually set. Also, at least one damage monitor location 303 is provided to monitor damage to the resist pattern due to illumination light.
[0034]
Therefore, in the microscope, the range including the measurement locations 305, 306, 307, 308, 309 and the damage monitor location 303 is set as the observation range 302, and this observation range 302 is displayed on the image display to measure the width of the resist pattern. When the measurement location is set at a location other than the observation range 302, the observation range 302 of the microscope is moved to the measurement location for observation.
[0035]
As described above, there are a plurality of measurement points in the observation range 302, but each measurement point is an ultra-fine pattern in nanometer units, and therefore the focal length with respect to the objective lens is different even if there are minute irregularities. It often ends up. For this reason, focusing is performed for each specific measurement location to be measured (step S2), and the width of the resist pattern at that measurement location is measured (step S3).
[0036]
Here, an example of a method for measuring the width of the resist pattern in the observation range 302 is shown. FIG. 5 is a graph of the image signal intensity along one horizontal scanning line 304 in the observation range 302 shown in FIG.
[0037]
That is, the vertical axis indicates the image signal intensity as a percentage. For example, when the image signal intensity is digitally converted to 256 bits of 8 bits, the image signal intensity 0 is 0% and the image signal intensity 255 is 100%. And The horizontal axis represents the coordinates along the horizontal scanning line 304 of the image, that is, the sampling pixel position.
[0038]
In FIG. 5, the low image signal intensity portion (about 5%) corresponds to the width of the resist pattern. Therefore, if a predetermined threshold value 402 (50% in FIG. 5) is set for the image signal intensity and the intersection points 403 and 404 with the image signal intensity graph 401 are obtained, the horizontal axis positions 405 and 406 corresponding to the intersection points are read. Can do. The interval 407 between the horizontal axis positions 405 and 406 corresponds to the width 303 of the resist pattern.
[0039]
In this way, when the focus adjustment operation (preparation operation before measurement) is performed on the resist pattern and the width thereof is measured, the confocal laser scanning microscope scans the observation range 302 with the spot light of the deep ultraviolet laser, and collects them all at once. In the illumination microscope, the entire observation range 302 is irradiated with uniform deep ultraviolet laser light. Therefore, the resist pattern in the observation range 302 is damaged by the deep ultraviolet laser beam with the passage of the observation time in the focusing operation and the measurement operation, and the width thereof is reduced.
[0040]
Therefore, every time the width of the resist pattern at the measurement location is measured, the resist pattern at the damage monitor location 303 is focused and the width is measured (step S4), and the width of the resist pattern at the damage monitor location 303 is preset. It is determined whether or not the limit value has been reached (step S5).
[0041]
In this case, if the width of the resist pattern at the damage monitor location 303 has not reached the limit value (No), it is determined whether or not all measurement locations have been measured (step S6), and all measurement locations are measured. If not (No), the process proceeds to step S2 to focus on a new measurement location, and the measurement in the observation range 302 is continued (step S3-S6).
[0042]
On the other hand, if it is determined in step S6 that all the measurement points in the observation range 302 have been measured (Yes), it is determined whether or not all the observation ranges provided on the semiconductor wafer 301 have been observed (step S7). . In this case, when not observing the entire observation range (No), the process proceeds to step S1 to start observation of a new observation range (step S2-S6). If yes (Yes), the illumination light is blocked (step S8), and the observation is terminated.
[0043]
On the other hand, if it is determined in step S5 that the width of the resist pattern at the damage monitor location 303 has reached the damage limit value (Yes), the data of the width of the resist pattern that has been measured and the damage at the damage monitor location 303 The degree is displayed (step S9) and the operator is asked to determine whether or not to continue the measurement (step S10).
[0044]
In this case, when the operator decides to continue the measurement (Yes), the process proceeds to step S6, and the measurement in the observation range 302 is continued, but when the measurement is decided not to be continued (No), the measurement is performed. The completed resist pattern width data and data indicating the degree of damage are transmitted to the next inspection process or the like (step S11), and the process proceeds to step S7 to another observation range. It should be noted that the processing of the semiconductor wafer 301 for which measurement at all measurement points has not been completed is left to the operator's judgment in the next inspection process.
[0045]
As described above, in the microscope according to the present embodiment, whenever the width of the resist pattern in the observation range is measured, the width of the resist pattern at the damage monitor portion 303 is measured. When the width of the resist pattern at the damage monitor point 303 reaches a limit value stored in the control unit in advance, for example, 90% of the value before damage, the irradiation of the sample with the deep ultraviolet laser light is stopped. .
[0046]
Therefore, it can be prevented that damage proceeds during the observation of the sample and the sample that should be a good product becomes a defective product. In addition, since information about a sample that has not been measured is transmitted to the next process, the reliability of the inspection process can be improved.
[0047]
In this case, the image immediately before blocking the deep ultraviolet laser light is stored, and after the deep ultraviolet laser light is blocked, the stored image is repeatedly displayed. For this reason, the sample observation is not hindered.
[0048]
In the above embodiment, the damage monitor location 303 in the observation range 302 is one location. However, the measurement accuracy may be improved by taking a plurality of damage monitor locations and averaging the measured values. . Further, the line width of the damage monitor location 303 is measured every time the measurement location is measured, but the line width of the damage monitor location 303 may be measured every predetermined measurement time, for example, every 10 seconds.
[0049]
Next, a second measurement flowchart according to the embodiment of the present invention will be described with reference to FIG. In the present embodiment, the amount of illumination light is adjusted while monitoring the progress rate of sample damage. According to the present embodiment, when there are a plurality of measurement points within the observation range and a considerable time is required for the measurement, all the measurement points can be measured without exceeding the damage limit value. .
[0050]
In the present embodiment, prior to the measurement, the virtual damage rate is obtained from the measurement time required to measure a plurality of measurement points in the observation range and a preset damage limit value (step S21).
[0051]
The virtual damage speed will be described with reference to FIG. Here, as in the case of the first measurement method, the case where five measurement locations 305, 306, 307, 308, and 309 within the observation range 302 shown in FIG. 4 are measured will be described. In this case, it is assumed that a measurement time of, for example, about 1 minute is required to complete all the measurements in the observation range 302, and that damage to the sample is allowed up to 30% before the measurement.
[0052]
The vertical axis in FIG. 7 is the degree of damage of the sample expressed as a percentage of the value before damage, and the horizontal axis is the measurement time. In FIG. 7, a point 509 is obtained from a measurement time 503 (for example, 1 minute) required to measure five measurement points and a damage limit value of 30%, and the point 509 and the origin are connected. A straight line connecting the point 509 and the origin (indicated by a dotted line in FIG. 7) is a virtual damage straight line 501. The inclination of the virtual damage straight line 501 is the virtual damage speed.
[0053]
Next, as in the case of the first measurement method, the observation range 302 is displayed on the image display (step S22), and the measurement point is focused (step S23). Further, the width of the measurement location is measured (step S24), and the width is measured by focusing on the damage monitor location 303 (step S25).
[0054]
Next, in the present embodiment, an actually measured damage speed, which is the speed at which damage actually proceeds, is calculated from the time taken for measurement at one measurement point and the width of the damage monitor point 303 (step S26). The damage rate is compared with the virtual damage rate (step S27).
[0055]
In this case, if the measured damage rate is approximately equal to the virtual damage rate (Yes), it is considered that the intensity of the illumination light is appropriate and the measurement at all measurement points is completed before the sample damage reaches the limit value. . Accordingly, as in the case of the first measurement method, it is determined whether or not the widths of all the measurement points have been measured (step S29), and further, it is determined whether or not all the observation ranges have been observed ( Step S30) Continue the measurement. Further, when the observation of the entire observation range is finished, the illumination light is blocked (step S31).
[0056]
On the other hand, when it is determined in step S27 that the actually measured damage speed is not equal to the virtual damage speed (No), the intensity of the illumination light is adjusted by the neutral density filter (step S28). That is, when the actually measured damage speed is larger than the virtual damage speed, the intensity of the illumination light is too strong, and the widths of all measurement points cannot be measured until the damage of the sample reaches the damage limit value. Therefore, in this case, the intensity of the illumination light is reduced.
[0057]
On the other hand, when the actually measured damage speed is smaller than the virtual damage speed, the intensity of the illumination light is too weak, the SN ratio of the image signal intensity is lowered, and the required measurement accuracy cannot be ensured. Therefore, in this case, the intensity of the illumination light is increased.
[0058]
A change in the degree of damage in the sample in this case will be described with reference to FIG. The degree of damage at the damage monitor location 303 at the first measurement end time 505 is calculated, and a point 510 is plotted. In this case, the slope of the straight line connecting the origin and the point 510 is the actually measured damage speed. In the first measurement, the actually measured damage speed is larger than the virtual damage speed, and the measurement of all measurement points cannot be completed before reaching the damage limit value with the illumination light intensity as it is. Therefore, the intensity of illumination light is reduced by adjusting the neutral density filter.
[0059]
Next, the degree of damage at the damage monitor location 303 at the second measurement end time 506 is calculated, and a point 511 is plotted. In this case, the slope of the straight line connecting points 510 and 511 is the actually measured damage speed. The actually measured damage speed at the time of the second measurement is lower than the first time, and the point 511 approaches the virtual damage straight line 501.
[0060]
As described above, in this embodiment, every time each measurement location is measured, the width of the damage monitor location 303 is measured to calculate the damage rate, and the actually measured damage curve 504 is plotted. Then, since the dark filter is adjusted so that the actually measured damage curve 504 approaches the virtual damage straight line 501, the measurement at all the measurement points can be completed without exceeding the damage limit value.
[0061]
The protection scope of the present invention is not limited to the above-described embodiment, but covers the invention described in the claims and equivalents thereof.
[0062]
【The invention's effect】
As described above, according to the present invention, when the line width of the pattern provided at a predetermined position of the observation target reaches a predetermined limit value, the irradiation of the deep ultraviolet light to the observation target is stopped. It is possible to prevent damage beyond the limit value.
[0063]
In addition, according to the present invention, the amount of illumination light is adjusted while monitoring the progress rate of damage to the sample. Therefore, there are a plurality of measurement points in the observation range, and a considerable time is required for the measurement. In addition, all measurement points can be measured without exceeding the damage limit value.
[Brief description of the drawings]
FIG. 1 is a configuration diagram of a confocal laser scanning microscope according to an embodiment of the present invention.
FIG. 2 is a configuration diagram of a collective illumination microscope according to an embodiment of the present invention.
FIG. 3 is a first measurement flowchart according to the embodiment of the present invention.
FIG. 4 is an explanatory diagram of a sample to be observed and an observation range.
FIG. 5 is an explanatory diagram of width measurement based on image signal intensity.
FIG. 6 is a second measurement flowchart according to the embodiment of the present invention.
FIG. 7 is an explanatory diagram of a damage degree of a sample.
[Explanation of symbols]
101, 201 deep ultraviolet laser
103, 203 Shutter
104, 204 Neutral filter switching unit
105, 205 beam expander
107, 208 Beam splitter
108 2D scanner unit
109, 207 relay lens
110, 209 objective lens
111 and 210 samples
115 pinhole
116, 214 detector
117 and 215 Image processing equipment
118, 216 image display
119, 217 Controller
120, 218 vibration isolation table

Claims (4)

In a microscope that acquires observation data by irradiating the observation object with deep ultraviolet light,
A control unit that measures the line width of a pattern provided at a predetermined position of the observation target and stops irradiation of the deep ultraviolet light to the observation target when the line width of the pattern reaches a predetermined limit value A microscope characterized by comprising: In claim 1,
When the line width of the pattern reaches a predetermined limit value, the control unit displays the observation data and the line width data of the pattern, and asks an operator whether to continue observation. A microscope. In claim 1,
The control unit is connected to an external device capable of transmitting acquired data, and when the line width of the pattern reaches a predetermined limit value, the observation data and the line width data of the pattern are transmitted to the external device. A microscope characterized by being transmitted to an apparatus. In a microscope that obtains observation data by irradiating the observation object with deep ultraviolet light,
The progress speed of damage caused by irradiating the observation object with deep ultraviolet light is determined by measuring the line width of the pattern provided at a predetermined position of the observation object. A microscope comprising a control unit that adjusts the intensity of deep ultraviolet light applied to the observation target so that the traveling speed is reached.

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