JP2002237444A - Method of evaluating image-forming capability of charged-particle-beam aligner and charged-particle- beam aligner - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method of evaluating image-forming capability of a charged-particle-beam aligner, capable of realizing a highly precise measurement of a beam blur, and to provide a charged-particle-beam aligner to which the method is applicable. SOLUTION: A beam-limiting opening 5 is placed several mm-20 mm apart under a knife edge 1. The diameter of the beam-limiting opening 5 is designed such that an angle θ that views the opening edge 5a from the knife edge 1 is slightly larger than the convergent angle of the rectangular-shaped beam EB at a projection lens of a lower stage. When the rectangular-shaped beam EB that has passed through the projection lens of the lower stage is scanned on the knife edge 1, non-scattered electrons e1 and forward-scattered electrons e2, not absorbed by a knife-edge plate 2, pass to the downward direction. Then, these electron e1, e2 reach the beam-limiting opening 5, and the non-scattered electrons e1 pass through the opening 5, while the forward-scattered electrons e2 are mostly interrupted. Therefore, only the non-scattered electrons e1 are detected by an electron detector 6.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to a method for evaluating the imaging performance of a charged particle beam exposure apparatus used for lithography of semiconductor integrated circuits and the like, and a charged particle beam exposure apparatus to which the method can be applied. In particular, the present invention relates to a method for evaluating the imaging performance of a charged particle beam exposure apparatus capable of realizing highly accurate beam blur measurement.

[0002]

2. Related Art It is known that an electron beam drawing apparatus hardly improves throughput (processing speed). In contrast,
For the purpose of increasing the throughput of an electron beam lithography apparatus, development of an electron beam exposure apparatus (such as an EB stepper) for transferring and exposing a large area pattern collectively has been advanced.
In such an exposure apparatus, it is necessary to measure the blur of the electron beam, perform beam adjustment (calibration of various correction values such as focus, astigmatism, magnification, rotation, etc.) and evaluate the imaging performance. There is.

FIG. 5 is a perspective view schematically showing a beam blur measurement system of a conventional electron beam exposure apparatus. FIG. 6 is a side sectional view and a block diagram schematically showing the beam blur measurement system. FIG. 7 is a graph for explaining a measurement result in the beam blur measurement system.

At the most upstream portion of the electron beam exposure apparatus, a reticle having an illumination beam source and a measurement pattern (not shown) is arranged, and a rectangular having a knife edge 101 shown in FIGS. An opening is arranged. The electron beam emitted from the illumination beam source
The light beam is irradiated as a rectangular beam EB (transfer image of the reticle) on the rectangular opening having the number 01. Knife edge 101
An electronic detector (sensor) 105 is arranged below the electronic device. When the rectangular beam EB is scanned, the electrons hitting the non-opening (knife edge plate 100) of the knife edge 101 are absorbed when the knife edge plate is thick, and the electrons passing through the opening 102 are detected by the electron detector 105. Is done. However, if the knife edge plate is thin (eg,
(μm), most of the electrons hitting the knife edge plate 100 are transmitted while being scattered by the knife edge plate 100. In order to increase the geometric accuracy of the knife edge 101, it is advantageous that the knife edge plate 100 is thin. Hereinafter, the description will proceed assuming that the knife edge plate 100 is thin.

The electrons detected by the electron detector 105 are a non-scattered electron e1 passing through the opening 102 and a forward scattered electron e2 scattered and transmitted through the knife edge plate 100. The beam currents corresponding to these electrons e1 and e2 are amplified by a preamplifier 106, then converted into a rate of change with respect to time by a differentiating circuit 107, and the output waveform is converted to an oscilloscope 1
08 is displayed. Beam blur is measured from the output waveform, and beam adjustment (focus, astigmatism,
Calibration of various correction values such as magnification and rotation) and evaluation of the imaging performance are performed. In addition, as this kind of beam blur measurement method, there is, for example, Japanese Patent Application Laid-Open No. 10-289851, Japanese Patent Application No. 2000-12620, and the like.

[0006]

By the way, in the above-described beam blur measurement method, most of the forward scattered electrons e2, which do not originally want to reach the electron detector 105, are generated by the electron detector 1.
05, and the measurement contrast is deteriorated by the forward scattered electrons e2. That is, since the forward scattered electrons e2 become a noise source, as shown in FIG.
Since the detected current waveform W 'offset from the ideal detected current waveform W (waveform along the 0 level) is detected, the measurement accuracy deteriorates due to the influence of noise.

SUMMARY OF THE INVENTION The present invention has been made in view of such a problem, and a method for evaluating the imaging performance of a charged particle beam exposure apparatus capable of realizing highly accurate measurement of beam blur, and a charging method to which the method can be applied. An object of the present invention is to provide a particle beam exposure apparatus.

[0008]

In order to solve the above-mentioned problems, a method for evaluating the imaging performance of a charged particle beam exposure apparatus according to the present invention comprises the steps of: using a charged particle beam reticle having an original pattern to be transferred onto a sensitive substrate; A charged particle beam exposure apparatus that forms a transfer pattern by illuminating the charged particle beam that has passed through the reticle onto the sensitive substrate to form a transfer pattern, the method comprising: Surface position)
A reticle on which a pattern for measurement is formed is arranged, a knife edge opening for measurement is arranged at the position (image plane position) of the transfer pattern, and the knife edge is charged with a charged particle beam for measurement having passed through the pattern for measurement. Scanning, measuring the blur of the beam by detecting and processing the charged particle beam passing through the knife edge opening with a sensor,
At this time, at least a substantial portion of the charged particle beam that passes through the non-opening portion (knife edge plate) of the knife edge is removed in front of the sensor, and substantially only the charged particle beam that has passed through the knife edge opening is removed. Is incident on the sensor.

According to the present invention, since only the charged particle beam that has passed through the knife edge aperture is made incident on the sensor to determine the beam blur, the measurement contrast is not deteriorated and the beam blur can be measured with high accuracy. . Note that the beam blur can be measured usually by calculating the distance of the rising edge (12% to 88%) of the differential waveform of the detection current.

In the method for evaluating the imaging performance of a charged particle beam exposure apparatus according to the present invention, the knife edge may be an edge of a rectangular opening pattern formed on a thin film. By thinning the knife edge, a high-quality edge that is straight and has low edge roughness can be relatively easily formed. As such a thin film, it is preferable to use, for example, a Si thin film having a thickness of about 2 μm.

Further, in the method for evaluating the imaging performance of a charged particle beam exposure apparatus according to the present invention, a beam limiting aperture is provided between the knife edge and the sensor, and the knife edge is controlled by the beam limiting aperture. The charged particle beam transmitted through the plate can be blocked. By the beam limiting aperture, scattered charged particle beams (forward scattered electrons) transmitted through the knife edge can be almost completely blocked. As a result, a good detection waveform can be obtained with nearly ideal contrast.

Further, in the method for evaluating the imaging performance of the charged particle beam exposure apparatus according to the present invention, the angle at which the edge of the beam limiting aperture is viewed from the knife edge is slightly larger than the convergence angle of the charged particle beam. Thus, the opening width (opening diameter) of the beam limiting aperture can be selected. For example, when the acceleration voltage of the charged particle beam illumination is 100 kV and the convergence angle of the charged particle beam EB is 6 mrad, the angle from the knife edge to the edge of the beam limiting aperture is set to 6 to 10 mrad. In this case, 100% of non-scattered electrons pass and only 0.1% or less of forward scattered electrons pass. Therefore, measurement can be performed with almost perfect contrast.

A charged particle beam exposure apparatus of the present invention illuminates a reticle having an original pattern to be transferred onto a sensitive substrate with a charged particle beam, and projects a charged particle beam passing through the reticle onto the sensitive substrate to form an image. A charged particle beam exposure apparatus for forming a transfer pattern by using a knife edge for measurement having an opening and disposed at a position (image plane position) of the transfer pattern on the sensitive substrate; A beam limiting aperture disposed to block a charged particle beam scattered at a non-opening portion of the knife edge (knife edge plate); and a charged particle beam disposed below the beam limiting aperture and passing through the beam limiting aperture. And a beam blur measuring means for measuring blur of the beam based on the detection result of the sensor.

As a sensor of such a charged particle beam exposure apparatus, a Faraday cup, a semiconductor detector, or a combination of a scintillator and a photomultiplier can be used. By using these, it is possible to detect beam blur with extremely high sensitivity.

[0015]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a diagram schematically showing a configuration of a main part of an optical system and a configuration around a wafer stage of an electron beam exposure apparatus according to an embodiment of the present invention. FIG. 2 is a perspective view schematically showing a beam blur measurement system of the electron beam exposure apparatus according to one embodiment of the present invention. FIG. 3 is a side sectional view and a block diagram schematically showing the beam blur measurement system. FIG. 4 is a graph for explaining a measurement result in the beam blur measurement system.

At the top of FIG. 1, an illumination beam 12 and a reticle 11 are shown. The illumination beam 12 is emitted from an electron gun (not shown) and is shaped by an illumination optical system. The reticle 11 is a reticle (mask) for measurement, and has a rectangular opening 13 formed therein. The illumination beam 12 passes through the rectangular opening 13 of the reticle 11, and becomes a rectangular beam EB having a straight edge. At the time of normal transfer exposure, a reticle on which a device pattern to be transferred is formed is used.

Below the reticle 11, two stages of projection lenses 14, 15 are arranged. These projection lenses 1
Between 4 and 15, a contrast opening 17 is arranged. The rectangular beam EB formed by the rectangular opening 13 of the reticle 11 is converged by the upper projection lens 14,
A crossover is formed in the contrast opening 17. The contrast aperture 17 cuts a beam transmitted while being scattered by the reticle 11.

A wafer (sensitive substrate) stage 16 is arranged below the lower projection lens 15. On this stage 16, the knife edge 1 is arranged. The knife edge 1 is formed of a Si thin film (an example) having a thickness of about 2 μmn. By thinning the knife edge 1, a high-quality straight edge having a small edge roughness can be obtained relatively easily. The wafer stage 16 is also provided with a chuck (not shown) for mounting a wafer during normal transfer exposure.

As shown in FIGS. 2 and 3, below the knife edge 1, a beam limiting aperture 5 is arranged. The distance between the beam limiting aperture 5 and the knife edge 1 (h in FIG. 3) is about several mm to 20 mm. The aperture diameter of the beam limiting aperture 5 (reference d in FIG. 2) is such that the angle (reference θ in FIG. 2) from the knife edge 1 to the opening edge 5a is smaller than the convergence angle of the rectangular beam EB in the lower projection lens 15. The dimensions will be slightly larger. An example of this dimension d is 1
It is 00 to 200 μm. Aperture plate 5 of beam limiting aperture 5
b is a sufficiently thick (for example, 1 mm) conductive metal plate, and the electron beam hitting the aperture plate 5b is absorbed.

An electron detector (sensor) 6 is provided below the beam limiting aperture 5. This electron detector 6
It is composed of a Faraday cup, a semiconductor detector, or a combination of a scintillator and a photomultiplier. A preamplifier 7, a differentiating circuit 8, and an oscilloscope 9 are sequentially connected to the electronic detector 6.

In this electron beam exposure apparatus, when the rectangular beam EB that has passed through the lower projection lens 15 is scanned on the knife edge 1, electrons that are not absorbed by the knife edge plate 2 (unscattered electrons that have passed through the knife edge opening 3). Forward scattered electrons e2) scattered and transmitted through the knife edge plate 2 and the knife edge plate 2 pass downward. Next, these electrons e1 and e2 reach the beam limiting aperture 5, the non-scattered electrons e1 pass through the aperture 5, and most of the forward scattered electrons e2 are blocked. Therefore, the electron detector 6 below the beam limiting aperture 5 detects almost no scattered electrons e1.

The beam current of the unscattered electrons e1 detected by the electron detector 6 is plotted on the upper graph in FIG. 4B (detected current waveform).
Indicated by As shown in FIG. 4A, when the rectangular beam EB is scanned on the knife edge 1 in the direction of the arrow (right side),
The width (the amount of electrons) of the rectangular beam EB passing through the knife edge 1 increases, and the beam current detected by the electron detector increases. Therefore, the detected current waveform rises to the right as shown in the upper graph of FIG. This beam current is shown in FIG.
After that, the signal is amplified by the preamplifier 7 and converted by the differentiating circuit 8 into a change rate with respect to time.

The differentiated waveform output from the differentiating circuit 8 is shown in FIG.
(B) Shown on the lower side. The differential waveform becomes a rectangular wave W1 when the rectangular beam EB is an ideal beam without beam blur. However, actually, the waveform W
It becomes 2. Here, as clearly shown in FIG. 4C, a rising distance t of the waveform W2 is obtained in a range of 12% to 88% of the intensity of the differential waveform. By calculating the distance t, the beam blur can be measured. The output waveform of the differentiating circuit 8 is displayed on an oscilloscope 9. Based on the waveform displayed by the oscilloscope 9, beam adjustment (calibration of various correction values such as focus, astigmatism, magnification, rotation, etc.) and evaluation of imaging performance are performed.

Here, in the above electron beam exposure apparatus,
A specific numerical example of the angle θ (see FIG. 2) will be described.
When the acceleration voltage of the illumination beam 12 is 100 kV and the convergence angle of the rectangular beam EB in the projection lens is 6 mrad, the angle θ from the knife edge 1 to the opening edge 5 a of the beam limiting aperture 5 is set to 6 to 10 mrad. . In this case, 100% of the non-scattered electrons e1 pass and only 0.1% or less of the forward scattered electrons e2 pass. Therefore, measurement can be performed with almost perfect contrast.

[0025]

As is clear from the above description, according to the present invention, extremely accurate beam blur measurement can be performed. Furthermore, by adjusting the electron optical system and evaluating the imaging performance using the result of the beam blur measurement, the apparatus can be adjusted with extremely high accuracy. When a knife edge is formed on a thin film, a straight, high-quality edge with small edge roughness can be easily formed.

When a beam limiting aperture is provided between the knife edge and the sensor, the charged particle beam scattered by the knife edge plate can be blocked by the beam limiting aperture, and ideal detection can be performed with almost perfect contrast. Waveform can be obtained. When a Faraday cup, a semiconductor detector, or a combination of a scintillator and a photomultiplier is used as a sensor, extremely high-sensitivity beam blur detection can be performed.

[Brief description of the drawings]

FIG. 1 is a diagram schematically showing a configuration of a main part of an optical system and a configuration around a wafer stage of an electron beam exposure apparatus according to an embodiment of the present invention.

FIG. 2 is a perspective view schematically showing a beam blur measurement system of the electron beam exposure apparatus according to one embodiment of the present invention.

FIG. 3 is a side sectional view and a block diagram schematically showing the beam blur measurement system.

FIG. 4 is a graph for explaining a measurement result in the beam blur measurement system.

FIG. 5 is a perspective view schematically showing a beam blur measurement system of a conventional electron beam exposure apparatus.

FIG. 6 is a side sectional view and a block diagram schematically showing the beam blur measurement system.

FIG. 7 is a graph for explaining a measurement result in the beam blur measurement system.

[Description of Signs] 1 knife edge 2 knife edge plate 3 knife edge opening 5 beam limiting opening 5a opening edge 5b opening plate 6 electron detector (sensor) 7 preamplifier 8 differentiating circuit 9 oscilloscope 11 reticle 12 illumination beam 13 rectangular opening 14, 15 Projection lens 16 Wafer stage 17 Contrast aperture EB Rectangular beam e1 Non-scattered electron e2 Forward scattered electron

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) H01J 37/305 H01L 21/30 541E

Claims (5)

[Claims] A charged particle beam illuminates a reticle having an original pattern to be transferred onto a sensitive substrate, and forms a transfer pattern by projecting and imaging a charged particle beam passing through the reticle onto the sensitive substrate. A method for evaluating imaging performance in a line exposure apparatus, comprising: disposing a reticle on which a measurement pattern is formed at a position (object surface position) of the original pattern; and measuring a reticle at a position (image surface position) of the transfer pattern. By disposing a knife edge opening for, scanning the knife edge with a charged particle beam for measurement that has passed through the pattern for measurement, and detecting and processing a charged particle beam that has passed through the knife edge opening with a sensor The blur of the beam is measured. At this time, at least a substantial portion of the charged particle beam passing through the non-opening portion of the knife edge (knife edge plate) is positioned in front of the sensor. Eliminate, substantially, the evaluation method of the imaging performance of the charged particle beam exposure device only charged particle beam having passed through the knife-edge aperture, characterized in that is incident on the sensor. 2. The method according to claim 1, wherein the knife edge is an edge of a rectangular opening pattern formed on a thin film. 3. A beam limiting aperture is provided between the knife edge and the sensor, and the beam limiting aperture blocks a charged particle beam transmitted through the knife edge plate. 3. A method for evaluating the imaging performance of the charged particle beam exposure apparatus according to 2. 4. An opening width (opening diameter) of the beam limiting aperture is selected such that an angle from the knife edge to an edge of the beam limiting aperture is slightly larger than a convergence angle of the charged particle beam. The method for evaluating the imaging performance of a charged particle beam exposure apparatus according to claim 3, wherein: 5. A charged particle for illuminating a reticle having an original pattern to be transferred onto a sensitive substrate with a charged particle beam, and projecting and forming an image of the charged particle beam passing through the reticle on the sensitive substrate to form a transfer pattern. A line exposure apparatus, comprising: a knife edge for measurement having an opening disposed at a position (image plane position) of a transfer pattern on the sensitive substrate; and a knife edge having a knife edge disposed below the knife edge. A beam limiting aperture for blocking a charged particle beam scattered by a non-aperture (knife edge plate); a sensor disposed below the beam limiting aperture for detecting a charged particle beam passing through the beam limiting aperture; A charged particle beam exposure apparatus, comprising: a beam blur measuring unit that measures a beam blur based on the detection result of