JP5129535B2 - Photomask height measuring method and electron beam drawing apparatus having height measuring device - Google Patents

Description

  The present invention relates to a photomask surface height measurement method and an electron beam drawing apparatus having a height measurement device, and more particularly to a height measurement method and an electron beam drawing apparatus for specifying a height measurement position.

  When drawing a desired pattern using an electron beam on a photomask, in order to avoid problems such as misalignment of the drawing position, electron beam blur, etc., accurate height measurement of the surface of the photomask is performed as pre-processing. Need to do.

For example, as shown in Figure 7, when set to converge the electron beam B in i ₀ point on the ideal shape h ₀ of the photomask relative to the ideal shape h ₀ as actual shape h ₁ of the photomask If there is a height difference, the electron beam B converges at i ₁ point shifted by ΔX in the X-axis direction and ΔZ position in the Z-axis direction.

Further, as shown in FIG. 8, when the beam diameter of the electron beam B on the ideal surface s ₀ of the photomask is d ₀ , the actual position of the surface of the photomask is higher than the surface s ₀ by ΔZ ′. If the surface s _1, the beam diameter of the electron beam B on the photomask surface s ₁ at the time of irradiation with the electron beam B, so-called electron beam blur state becomes d ₁ extending from the d _0.

  In general, the photomask height is measured by irradiating the photomask surface with light from a light source, measuring the amount of light that converges on the element that receives the reflected light, and measuring the amount of movement of the photomask. This is performed by optical measurement in which the amount of displacement is converted and measured (for example, see Patent Document 1).

In this light measurement, before irradiating the light, as shown in FIG. 9, the optical axis of the light O was visually aligned with the position P to be measured using the microscope m in the air atmosphere A.
Japanese Patent Application Laid-Open No. 2003-303758 (claim 1)

  When performing height measurement and drawing by the light measurement, the inside of the electron beam drawing apparatus main body, such as a sample chamber provided with a stage for holding and moving a photomask, and an electron optical column must be maintained in vacuum.

  Thus, under the drawing condition in which the inside of the electron beam drawing apparatus is evacuated, the entire apparatus is distorted inward due to the atmospheric pressure, and this causes a disadvantage that the measurement position P shown in FIG. 9 is shifted. It was.

That is, as shown in FIG. 10, when the inside of the electron beam drawing apparatus main body D is evacuated to a vacuum atmosphere V, the outer wall of the electron beam drawing apparatus main body D is distorted inward and the air atmosphere on the photomask M due to the influence thereof. Since the measurement position P specified in the environment of A is shifted by ΔX ′ to the position of P ′, accurate drawing according to the height of the photomask M cannot be performed, resulting in a decrease in drawing accuracy. It was.

  Therefore, in view of the above problems, the present invention provides a photomask height measuring method capable of detecting a height measurement position under a drawing condition and an electron beam drawing apparatus capable of measuring the height. And

In order to solve the above problems, a photomask height measuring method according to the present invention is oblique to a photomask surface in order to draw a predetermined pattern using an electron beam on a photomask placed on a stage. A photomask height measurement method that measures the shape of the photomask surface by detecting the position of reflected light reflected from the photomask surface by irradiating light from a light source placed above with the optical axis aligned with a predetermined position. a is, the provided al is on the stage, a step of scanning by light irradiating the surface of the calibration mark reflectance of light different patterns are formed from the light source, the light quantity data detected by the scanning A step of specifying the position of the measurement point to measure the height in correspondence, and a process of specifying the position of the measurement point to measure the scanning and the height under the drawing condition The position of the measurement point corresponding to the predetermined light quantity data is compared before and after the drawing situation, the position deviation under the drawing situation is detected, and the position of the measurement point for measuring the height under the drawing situation is detected from this position deviation. Generating the correction data.

  According to this method, the shape of the pattern created on the calibration mark is detected by the light amount data obtained by scanning the light, and the height measurement position is specified by associating the light amount data with the position data. Even if the position data is shifted under a vacuum drawing state, correction data can be generated from the light amount data.

  As the position of the measurement point for measuring the height, a predetermined threshold is set for the light amount data detected by the scanning, a plurality of edge position data of data exceeding the threshold is detected, and each edge position data is weighted averaged. It may be calculated as follows.

  In addition, the position of the measurement point for height measurement is obtained by obtaining a differential value of the light amount data detected by the scanning, detecting a plurality of edge position data having differential values exceeding the predetermined threshold value, and calculating a weighted average of each edge position data. It may be calculated as follows.

An electron beam lithography apparatus capable of carrying out the photomask height measuring method includes a light source that irradiates light obliquely from above to a photomask surface placed on a stage, and light emitted from the light source. A light projecting lens that converges on the mask surface, a light receiving lens that receives the light reflected by the photomask surface, and a light position where the light converged by the light receiving lens enters and detects the position from the detection position of the reflected light An electron beam lithography apparatus comprising a photomask surface height measuring means having a detector, wherein the mark stage is provided on the stage and on which calibration marks on which patterns having different light reflectance are formed are placed When the surface shape of the calibration mark reflectance of light different pattern is formed by scanning by said height measuring means, position of the measurement points for the height measurement Is stored in correspondence with the light amount data detected by the scanning, and the position of the measurement point for the scanning and the height measurement is specified under the drawing condition, and the measurement corresponding to the predetermined light amount data is performed. The position of the point is compared before and after the drawing situation, the position deviation under the drawing situation is detected, and the generation means for generating the correction data of the position of the measurement point for measuring the height under the drawing situation is obtained from the position deviation. Anything is acceptable.

  As is clear from the above description, the photomask height measuring method and the electron beam drawing apparatus according to the present invention cause a positional shift when the position of the measurement point for height measurement is evacuated under the drawing condition. However, since it can be corrected, it is possible to accurately measure the height of the photomask and contribute to the improvement of the drawing accuracy.

  Referring to FIG. 1, reference numeral 1 denotes an electron beam drawing apparatus main body according to the present invention. The electron beam drawing apparatus main body 1 includes an electron gun 11 that irradiates a photomask M with an electron beam, various lenses 12a, 12b, 12c, 12d, and 12e such as a magnetic lens and an electric field lens, and a block that performs various deflections of the electron beam. An electron beam optical system comprising a ranking deflector 13a, a beam size changing deflector 13b, a beam scanning main deflector 13c, a beam scanning sub-deflector 13d, and two beam shaping apertures 14a and 14b. And a stage 16 on which the photomask is placed, and a sample chamber 15 that houses a mark table 17 on which a calibration mark placed on the stage 16 is placed separately from the photomask M.

  The stage 12 is driven in the X and Y directions by the stage drive circuit 13. The moving position of the stage 12 is measured by a position circuit 18 using a laser length meter or the like.

  The control computer 2 of the electron beam drawing apparatus main body 1 stores drawing data on a magnetic disk 21 that is a storage medium. The drawing data read from the magnetic disk 21 is temporarily stored in the pattern memory 22 for each frame area data composed of drawing positions and drawing graphic data. The pattern data for each frame area stored in the pattern memory 22 is analyzed by the pattern data decoder 23 and the drawing data decoder 24.

  The output of the pattern data decoder 23 is sent to the blanking circuit 25 as blanking data and to the beam shaper driver 26 as beam dimension data.

  Then, a predetermined deflection signal is applied from the beam shaper driver 26 to the beam size varying deflector 13b, thereby controlling the size of the electron beam.

The output of the drawing data decoder 24 is sent to the main deflector driver 27 and the sub deflector driver 28. Then, a predetermined deflection signal is applied from the main deflector driver 27 to the main deflector 13c, whereby the electron beam is deflected and scanned to a designated main deflection position. Further, a predetermined sub deflection signal is applied from the sub deflector driver 28 to the sub deflector 13d, thereby drawing inside the sub field.

In the present embodiment, a correction table 29 is provided for registering correction values for correcting the relative positional deviation between frames accompanying stage movement. In actual drawing, a correction value is set from the correction table 29 to the main deflector driver 27.

 Referring to FIG. 2, reference numeral 3 denotes a photomask height measuring unit of the electron beam lithography apparatus described with reference to FIG. The height measuring unit 3 employs optical measurement.

The height measurement unit 3 receives the light source 31 and the light Lr reflected on the photomask M and the light projection lens 32 for converging the light Li emitted from the light source 31 on the photomask M placed on the stage 16. A light receiving lens 33 that converges the light and a light position detector 34 that receives the light Lr converged by the light receiving lens 33 and detects the position of the light.

  From the position of the light detected by the optical position detector 34, height data is generated by the height data processing unit 20 on the surface of the photomask M, and this height data is fed back to the drawing process via the control computer 2. In addition, the drawing accuracy is improved.

  Incidentally, the calibration mark placed on the mark table 17 described with reference to FIG. 1 is normally used for detecting a deviation in sensitivity of the sub deflector 13d.

  In the present invention, the height measurement position is detected using the calibration mark and the height measuring unit 3. First, a pattern having a different light reflectance is created on the calibration mark, and the surface of the calibration mark on which the pattern is created is scanned by irradiating light from the light source 31 of the height measuring unit 3. At this time, a predetermined height measurement position when the height measurement unit 3 actually measures the height is specified.

  At this time, as shown in FIG. 3, the reflectance of the incident light Li varies depending on the height difference of the created pattern. By scanning each low reflectance area and high reflectance area formed on the calibration mark in the X and Y directions and detecting the reflected light Lr, the light quantity data of each area can be obtained. As shown, pattern data corresponding to the light amount data and the position data of the measurement point at which the height is measured is obtained. In the present embodiment, the pattern data is inscribed in the X-axis direction on the stage 16 with a 0.5 mm pitch, the Y-axis direction with a 0.5 mm pitch, and the Z-axis direction is the optical position of the height measuring unit 3. A PSD (Position Sensitive Detector) was used as the detector 34, and the output from this PSD (average value of two voltage values V1 and V2) was defined as the light quantity (V).

  As can be seen from FIG. 4, the position data measured by the height measuring unit 3 is specified by coordinates in the X and Y directions, and this position data corresponds to light amount data corresponding to the reflectance of the pattern.

  Incidentally, under an actual drawing situation, the inside of the electron beam drawing apparatus main body 1 in FIG. 1 is evacuated. At this time, the outer wall of the electron beam drawing apparatus main body 1 is distorted inward due to the relationship with atmospheric pressure, and due to the influence of this distortion, it is displaced to the specified height measurement position (in the X and Y directions shown in FIG. 4). Misalignment specified by coordinates) occurs.

  This positional deviation can be detected by fluctuations in light amount data corresponding to each position data. This is because when the height measurement unit 3 measures the specified height measurement position in a vacuum atmosphere, the light amount data corresponding to the shifted position data also varies. Therefore, by detecting the position of the light amount data corresponding to the specified original position data by the height measuring unit 3, it is possible to acquire the data of the difference, that is, the position shift data. Correction data for correcting the height measurement position in the vacuum atmosphere may be generated from the positional deviation data, and the specified height measurement position may be detected.

  Therefore, the height data processing unit 20 of the height measuring unit 3 of the electron beam lithography apparatus described in FIG. 2 scans the surface shape of the calibration mark, and the position of the measurement point for measuring the height is determined by the scanning. Storage means for storing in correspondence with the detected light quantity data, and specifying the position of the measurement point for scanning and height measurement under the drawing condition, and the position of the measurement point corresponding to the predetermined light quantity data Comparing before and after the drawing situation, a position deviation under the drawing situation is detected, and from this position deviation, a generation means for generating correction data of the position of the measurement point for measuring the height under the drawing situation is provided. That's fine.

  Hereinafter, two embodiments of the method for determining the predetermined height measurement position will be described with reference to the processing flowcharts of FIGS. 5 and 6.

  The first embodiment shown in FIG. 5 is a method for directly determining from measured light quantity data.

  First, patterns having different reflectances are formed on the calibration mark (S1). Next, the height measurement unit 3 scans the calibration mark to acquire data in which the light amount varies (S2). Here, a threshold value of the light amount data is set (S3), and position data corresponding to the light amount data exceeding the threshold value is detected (S4). A plurality of edge positions of the light amount data exceeding the threshold value are detected, and a weighted average is determined to determine a measurement position (S5).

  The second embodiment shown in FIG. 6 is a method of determining from the differential value of the measured light quantity data.

  As in the first embodiment, patterns having different reflectances are formed on the calibration mark (S′1), and the calibration mark is scanned (scanned) by the height measuring unit 3, and the data in which the amount of light varies is obtained. (S′2) A threshold value of the light amount data is set (S′3).

  Next, a differential value of the light quantity is obtained (S'4), and position data whose differential value is equal to or greater than the threshold value is detected (S'5). A plurality of edge positions of the position data equal to or larger than the detected threshold value are detected, and a weighted average is determined to determine a measurement position (S'6).

  According to the above method, when the height of the stage on which the photomask is placed varies by 1 mm due to distortion of the apparatus due to evacuation, if the incident angle of the irradiated light is 70 °, the measurement specified before evacuation Although the position will be displaced by 2.74 mm, it can be confirmed by actually measuring it. Therefore, it is possible to generate correction data for correcting the displacement of the measurement position due to the evacuation based on the displacement data.

  As described above, the method and the apparatus for generating the correction data of the height measurement position from the detected position deviation data of the height measurement position have been described. From the position deviation data of the detected height measurement position, Adjustment data for adjusting the position of the optical axis of the light source can be generated, and the irradiation position of the light source in the vacuum atmosphere can be automatically controlled based on the adjustment data to perform accurate height measurement.

The block block diagram which shows the outline of the electron beam drawing apparatus concerning this invention The figure which shows schematic structure of a height measurement part The figure which shows the state which scans a calibration mark by a height measurement part The figure which shows the pattern data which light quantity data and position data correspond Process flow chart for determining a predetermined height measurement position according to the first embodiment Process flow chart for determining a predetermined height measurement position according to the second embodiment Diagram showing misregistration of drawing position due to photomask height error Figure showing electron beam blur due to photomask height error A diagram schematically showing how to align the measurement position The figure which showed the state where the inside of the electron beam lithography system was evacuated schematically

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Electron beam control apparatus main body 2 Control computer 3 Height measurement part 16 Stage 17 Mark stand

Claims (4)

To draw a predetermined pattern using an electron beam on a photomask placed on the stage, light is emitted from a light source placed obliquely above the photomask surface with the optical axis aligned at a predetermined position. A photomask height measuring method for measuring the shape of the photomask surface by the detection position of the reflected light reflected by the photomask surface,
The provided al is on the stage, a step of scanning the surface of the calibration mark reflectance of light different patterns formed by light irradiated from the light source, high in correspondence with the light quantity data detected by the scanning Specifying the position of the measurement point to be measured, the step of specifying the position of the measurement point to be scanned and the height measurement under the drawing condition, and the position of the measurement point corresponding to predetermined light amount data A step of comparing before and after the drawing situation, detecting a position deviation under the drawing situation, and generating correction data of the position of the measurement point for measuring the height under the drawing situation from the position deviation. Photomask height measurement method. As the position of the measurement point for measuring the height, a predetermined threshold is set for the light amount data detected by the scanning, a plurality of edge position data of data exceeding the threshold is detected, and each edge position data is weighted averaged. The photomask height measuring method according to claim 1, wherein the photomask height is calculated by: The position of the measurement point for measuring the height is obtained by obtaining a differential value of the light amount data detected by the scanning, detecting a plurality of edge position data having differential values exceeding the predetermined threshold value, and weighting averaging the edge position data. photomask height measurement method according to claim 1 Symbol placement and calculates Te. A light source that irradiates light on the photomask surface placed on the stage obliquely from above, a light projection lens that converges the light emitted from the light source on the photomask surface, and the light reflected on the photomask surface An electron beam comprising a photomask surface height measuring means having a light receiving lens for receiving light and a light position detector for detecting the position from the detection position of the reflected light upon incidence of light converged by the light receiving lens A drawing device,
A mark base provided with a calibration mark provided with a pattern with different light reflectance provided on the stage and a surface shape of the calibration mark with a pattern with different light reflectance formed on the height. A storage unit that scans by the measuring unit and stores the position of the measurement point to measure the height in correspondence with the light amount data detected by the scanning, and measures the scanning and the height under a drawing condition. The position of the point is specified, the position of the measurement point corresponding to the predetermined light quantity data is compared before and after the drawing situation, the position deviation under the drawing situation is detected, and the height under the drawing situation is measured from this position deviation. An electron beam drawing apparatus comprising generation means for generating correction data for the position of a measurement point to be measured.

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