Slip evaluation method and charged particle beam lithography method

Abstract

This system accurately evaluates whether or not slippage occurs on the circuit board. [Solution] A slip evaluation method according to one aspect of the present invention includes the steps of: placing a calibration substrate having at least one mark formed on it on a movable stage in a charged particle beam lithography apparatus; measuring a first position of the mark while the stage is stopped; performing a slip-promoting stage operation with the acceleration of the object to be evaluated; measuring a second position of the mark while the stage is stopped after the slip-promoting stage operation; and calculating the slip amount of the calibration substrate based on the first and second positions. It is equipped with these features.

Description

Technical Field

[0005]

[0001] The present invention relates to a slip evaluation method and a charged particle beam lithography method.

Background Art

[0002] With the increasing integration of LSIs, the circuit linewidth required for semiconductor devices has been continuously miniaturized year by year. In order to form a desired circuit pattern on a semiconductor device, a method of reducing and transferring a high-precision original pattern formed on quartz onto a wafer using a reduction projection exposure apparatus is adopted. For the production of a high-precision original pattern, a so-called electron beam lithography technique, in which a resist is exposed by an electron beam drawing apparatus to form a pattern, is used.

[0003] In an electron beam drawing apparatus, a substrate is placed on support pins on a stage, and while moving the stage, the substrate is irradiated with an electron beam to draw a pattern. Since the substrate is simply placed on the support pins and is not fixed to the support pins, the inertial force acting on the substrate due to the acceleration and deceleration of the stage may exceed the frictional force generated between the substrate and the support pins, and the substrate may slip on the support pins. When the substrate slips on the support pins, a problem occurs in that the pattern drawing position accuracy decreases.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Patent Document 3

Summary of the Invention

Problems to be Solved by the Invention

[0005] The present invention aims to provide a slip evaluation method that can accurately evaluate whether or not slip occurs on a substrate, and a charged particle beam lithography method that performs drawing with a stage acceleration that does not cause slip. [Means for solving the problem]

[0006] A slip evaluation method according to one aspect of the present invention comprises the steps of: placing a calibration substrate having at least one mark formed on it on a movable stage in a charged particle beam lithography apparatus; measuring a first position of the mark while the stage is stopped; performing a slip-promoting stage operation with the acceleration of the object to be evaluated; measuring a second position of the mark while the stage is stopped after the slip-promoting stage operation; and calculating the amount of slip of the calibration substrate based on the first and second positions. [Effects of the Invention]

[0007] According to the present invention, the presence or absence of substrate slippage can be evaluated with high accuracy. [Brief explanation of the drawing]

[0008] [Figure 1] This is a schematic diagram of an electron beam lithography apparatus according to an embodiment of the present invention. [Figure 2] This is a plan view of the calibration substrate. [Figure 3] This is a cross-sectional view of the calibration substrate. [Figure 4] This is a flowchart illustrating the slip evaluation method according to the same embodiment. [Modes for carrying out the invention]

[0009] Embodiments of the present invention will be described below with reference to the drawings. In these embodiments, an electron beam configuration will be described as an example of a charged particle beam. However, the charged particle beam is not limited to an electron beam; an ion beam or the like may also be used.

[0010] Figure 1 is a schematic diagram of an electron beam lithography apparatus according to an embodiment of the present invention. The electron beam lithography apparatus includes an electron-optical tube 40, a lithography chamber 50, a control device 30, storage devices 34 and 35, a stage control unit 36, a detection amplifier 38, and the like. Inside the electron-optical tube 40 are an electron source 41, a blanking aperture 42, a first aperture 43, a second aperture 44, a blanking deflector 45, a shaping deflector 46, an objective deflector 47, an illumination lens CL, a projection lens PL, an objective lens OL, and the like.

[0011] A movable XY stage 52 is placed inside the drawing chamber 50. When pattern drawing is performed, the substrate 10 to be drawn is placed on the XY stage 52. For example, the substrate 10 is made of a glass substrate on which a light-shielding film such as a chromium film and a resist film are laminated.

[0012] The XY stage 52 is provided with multiple (for example, three) support pins 54, and the circuit board 10 is mounted on the support pins 54.

[0013] Furthermore, a mark M is installed and fixed on the XY stage 105 in an area separate from the area on which the substrate is placed. Mark M (fixed mark) is, for example, a metal cross mark.

[0014] A detector 56 is provided inside the drawing chamber 50 to detect backscattered electrons when the electron beam 49 is irradiated onto the mark M and the calibration substrate 20 (described later). The detection results from the detector 56 are transmitted to the control device 30 via the detection amplifier 38.

[0015] The electron beam 49 emitted from the electron source 41 illuminates the entire first aperture 43, which has a rectangular aperture, with the illumination lens CL. Here, the electron beam 49 is first shaped into a rectangle. The electron beam of the first aperture image that has passed through the first aperture 43 is then projected onto the second aperture 44 by the projection lens PL. The position of the electron beam of the first aperture image on the second aperture 44 is controlled by the shaping deflector 46, which can change the beam shape and dimensions. The electron beam of the second aperture image that has passed through the second aperture 44 is then focused by the objective lens OL and deflected by the objective deflector 47, and irradiated onto the target position on the substrate 10 on the XY stage 52.

[0016] The electron beam 49 is controlled by the blanking deflector 45 to pass through the blanking aperture 42 when the beam is on, and deflected so that the entire beam is shielded by the blanking aperture 42 when the beam is off. One electron beam shot consists of the electron beam that passes through the blanking aperture 42 from the beam off state to the beam on state and then to the beam off state. The irradiation time of each shot adjusts the amount of electron beam irradiation per shot onto the resist film on the surface of the substrate 10.

[0017] Each part of the electron beam lithography apparatus is controlled by the control device 30. The control device 30 has the functions of a lithography control unit 31, an acceleration setting unit 32, and a calculation unit 33. The lithography control unit 31 reads lithography data from the storage device 34 and generates apparatus-specific shot data by performing multiple stages of data conversion processing. The shot data defines the irradiation amount and irradiation position coordinates for each shot. Based on the shot data, the lithography control unit 31 controls the deflection amount of the objective deflector 47 and the movement amount of the XY stage 52 to change the irradiation position of the electron beam. In addition, based on the shot data, the lithography control unit 31 controls the deflection amount of the shaping deflector 46 to change the beam shape and dimensions. This makes it possible to irradiate the resist film on the substrate 10 with an electron beam that has a different shape and dimensions.

[0018] The acceleration setting unit 32 sets the acceleration of the XY stage 52. The stage control unit 36 controls the moving speed of the XY stage 52 so as to move at the set acceleration.

[0019] During the drawing process, an inertial force acts on the substrate 10 due to the acceleration and deceleration of the moving XY stage 52, and the substrate 10 may slip on the support pins 54. In the present embodiment, the calibration substrate 20 is placed on the support pins 54, the XY stage 52 is moved at a plurality of accelerations, the slip amount (displacement amount) of the calibration substrate 20 at each acceleration is evaluated, and the acceleration of the XY stage 52 at which no slip occurs is obtained.

[0020] FIG. 2 is a plan view of the calibration substrate 20 used for slip evaluation, and FIG. 3 is a cross-sectional view taken along line III-III of FIG. 2. The calibration substrate 20 includes a substrate body 22, a conductive film 24 (first conductive film), and a conductive film 26 (second conductive film) laminated in order. A plurality of marks 28 each formed of an opening penetrating through the conductive film 26 are regularly arranged. It is preferable that the plurality of marks 28 are arranged substantially uniformly as a whole so as not to be unevenly distributed on the substrate surface. Since the bottom surface of each mark 28 becomes the conductive film 24, charging of electrons can be avoided even when irradiated with an electron beam. Therefore, no unexpected error due to electron charging occurs. For example, the calibration substrate 20 and the ground member may be connected by bringing a grounded pin into contact with the conductive film 24 or the conductive film 26 from the upper surface side of the calibration substrate 20.

[0021] The mark 28 is, for example, in a cross shape. Further, as shown in FIG. 2, among the marks 28 formed on the calibration substrate 20, the three marks located at the center of the left end, the center of the right end, and the center of the upper end may be used as alignment marks 28A having a larger size (line width and length) than the other marks 28.

[0022] The conductive film 26 preferably uses a material with a higher reflectivity than the conductive film 24. As the material for the conductive film 26, tantalum (Ta), tungsten (W), platinum (Pt), or compounds thereof can be used; for example, boron-doped tantalum. As the material for the conductive film 24, chromium (Cr), titanium (Ti), vanadium (V), or compounds thereof can be used; for example, chromium nitride. However, the materials for conductive films 24 and 26 are not limited to the metal-containing materials described above, as long as they are conductive films with different reflectivity.

[0023] Since the conductive film 24 is exposed on the bottom surface of mark 28, and the surface of the area other than mark 28 is made of a conductive film 26 with a different reflectivity from the conductive film 24, the contrast of the reflected signal detected by scanning the calibration substrate 20 with an electron beam can be increased.

[0024] It is preferable to use low thermal expansion glass for the substrate body 22.

[0025] Next, the slip evaluation method according to this embodiment will be explained with reference to the flowchart shown in Figure 4.

[0026] First, the calibration substrate 20 is transported to the drawing chamber 50 of the electron beam lithography apparatus and placed on the support pins 54 of the XY stage 52 (step S1).

[0027] Step S2 adjusts the Z-direction (height) position of the calibration substrate 20 to focus the electron beam onto the surface of the calibration substrate 20. For example, with the XY stage 52 stopped, the electron beam is deflected by the objective deflector 47 to scan the mark 28 in the center of the calibration substrate 20, and the detector 56 detects backscattered electrons. The detector 56 outputs a backscattered electron signal indicating the intensity (amount) of the detected backscattered electrons to the control device 30 via the detection amplifier 38. The calculation unit 33 calculates the height and width of the scan waveform from the backscattered electron signal.

[0028] While changing the height of the calibration substrate 20, mark scanning, backscattered electron detection, and calculation of the scan waveform width and height are performed. When the focus is on the surface of the calibration substrate 20, the scan waveform width is minimized and the scan waveform height is maximized. Based on the calculated scan waveform width and height, the height of the calibration substrate 20 is adjusted to the focus position of the electron beam.

[0029] Next, the rotation and shift amounts when the calibration substrate 20 is placed on the XY stage 52 are calculated (step S3). For example, with the XY stage 52 stopped, the marks 28 on the calibration substrate 20 are scanned and backscattered electrons are detected. Among the marks 28, the alignment mark 28A is of a different size from the other marks 28, and therefore its scan waveform is also different. The calculation unit 33 detects the positions of the three alignment marks 28A from the scan waveform corresponding to the alignment mark 28A and the deflection amount of the electron beam. The calculation unit 33 calculates the rotation and shift amounts of the calibration substrate 20 from the positions of the three detected alignment marks 28A. It is found that each mark 28 is shifted from the design coordinates by the calculated rotation and shift amounts, and this is taken into consideration in the subsequent calculation of the position of the marks 28.

[0030] Next, with the XY stage 52 stopped, the marks 28 on the calibration substrate 20 are scanned (step S4). The detector 56 detects backscattered electrons, and the calculation unit 33 uses the detection results of the backscattered electrons to calculate the initial positions of multiple marks 28. For example, the positions of 3 marks 28 are calculated at predetermined intervals in the x-direction and 3 marks 28 at predetermined intervals in the y-direction, for a total of 9 marks (=3×3). The mark positions can be determined from the change in backscattered electron intensity and the stage position. At this time, the positions of the marks 28 are calculated taking into account the rotation and shift amounts of the calibration substrate 20 calculated in step S3.

[0031] Next, the amount of electron beam drift is measured (step S5). The XY stage 52 is moved to align mark M with the center position of objective lens OL, the electron beam is scanned over mark M, and the backscattered electrons are detected by the detector 56. The calculation unit 33 uses the beam profile based on the detection result of backscattered electrons and the stage position (position of mark M) to detect the beam irradiation position. The calculation unit 33 calculates the amount of deviation of the detected beam irradiation position from the reference position as the amount of drift.

[0032] The stage control unit 36 ​​controls the XY stage 52 and performs a slip-inducing stage operation with the acceleration set by the acceleration setting unit 32 (step S6). The slip-inducing stage operation is a stage operation that can cause the substrate to slip, and is, for example, a reciprocating stage operation that includes movement in the +X direction and movement in the -X direction.

[0033] After the slip-prompting stage operation is performed, the XY stage 52 is stopped and the marks 28 on the calibration substrate 20 are scanned (step S7). Similar to the calculation step for the initial mark position, the detector 56 detects backscattered electrons, and the calculation unit 33 uses the detection results of the backscattered electrons to calculate the positions of the multiple marks 28. At this time, the positions of the marks 28 are calculated considering the rotation and shift amounts of the calibration substrate 20 calculated in step S3 and the drift amount calculated in step S5.

[0034] If there are accelerations to be evaluated that have not undergone slip-inducing stage operation (step S8_No), the process returns to step S5. The process including drift measurement, slip-inducing stage operation, and mark position measurement (steps S5-S7) is performed for all accelerations to be evaluated.

[0035] After performing the slip-inducing stage operation for the acceleration of all evaluation targets (step S8_Yes), the calculation unit 33 calculates the amount of positional displacement (amount of substrate slip) for each acceleration (step S9).

[0036] This section describes the case where 16 types of accelerations, A1 to A16, are set sequentially and the slip-inducing stage operation is performed. The calculation unit 33 calculates the positional displacement amount F1 from the average difference between the design value and the measured value of the nine marks 28 after the slip-inducing stage operation with acceleration A1. This positional displacement amount F1 corresponds to the slip of the substrate caused by the slip-inducing stage operation with acceleration A1.

[0037] The calculation unit 33 determines the positional displacement F2 from the average of the differences between the design values ​​and measured values ​​of the positions of the nine marks 28 after the slip-prompting stage operation with acceleration A2. This positional displacement F2 is affected by the slip of the substrate due to the slip-prompting stage operation with acceleration A1 and the slip of the substrate due to the slip-prompting stage operation with acceleration A2. Therefore, the positional displacement (F2-F1) is calculated by subtracting the positional displacement F1 from the positional displacement F2. This positional displacement (F2-F1) corresponds to the slip of the substrate due to the slip-prompting stage operation with acceleration A2.

[0038] The calculation unit 33 calculates the displacement amount F3 from the average difference between the design value and the measured value of the nine marks 28 after the slip-prompting stage operation with acceleration A3. Similarly, the displacement amount (F3-F2) is calculated by subtracting the displacement amount F2 from the displacement amount F3. This displacement amount (F3-F2) corresponds to the slip of the substrate caused by the slip-prompting stage operation with acceleration A3.

[0039] Subsequently, the amount of substrate displacement due to the slip-prompting stage operation can be determined for each of the accelerations A4 to A16 in the same manner. Slip information showing the relationship between acceleration and the amount of substrate displacement (slip amount) is stored in the storage device 35.

[0040] The calculation unit 33 determines that if the amount of positional displacement is below a predetermined threshold (a value within a predetermined range), the substrate 10 will not slip at the acceleration used to perform the corresponding slip-prompting stage operation (the slip is at a level that does not pose an accuracy problem), and that this acceleration is usable when drawing patterns. Although there is a slight difference in the amount of slip between the calibration substrate 20 and the substrate 10 on which the product pattern is drawn due to differences in the center of gravity, material (coefficient of friction, etc.), flatness, etc., a high correlation is observed.

[0041] When the substrate 10 is placed on the XY stage 52 and the product pattern is drawn, the acceleration setting unit 32 sets the acceleration that has been determined to be usable during pattern drawing and moves the XY stage 52. This allows the pattern to be drawn with high precision using a stage acceleration that does not cause slippage.

[0042] As described above, according to this embodiment, the slip-inducing stage operation is performed with multiple stage accelerations, and the mark scan of the calibration substrate 20 is performed for each acceleration to determine the amount of shift in the mark position, thereby evaluating whether or not slip of the substrate has occurred. Furthermore, since drift measurement is performed before the slip-inducing stage operation and drift errors are removed when calculating the mark position, the amount of slip of the substrate can be determined with high accuracy.

[0043] One possible method involves drawing evaluation patterns using multiple stage accelerations and determining whether slip occurs from the drawing results, but this method is time-consuming due to the drawing, development, etching, and position measurement processes. In contrast, this embodiment eliminates the need for processes such as development and etching, allowing for rapid determination of whether or not slip occurs on the substrate.

[0044] In the above embodiment, an example was described in which the positions of nine marks 28 on the calibration substrate 20 are calculated and the average amount of positional deviation is determined. However, the number of marks 28 whose positions are calculated is not limited to nine, and the number can be adjusted according to the accuracy of the positional calculation.

[0045] In the above embodiment, an example was described in which 16 types of accelerations A1 to A16 are set in order to perform the slip-inducing stage operation. However, the slip-inducing stage operation may be performed multiple times with the same acceleration, and the average amount of slip may be calculated for each acceleration.

[0046] At least a portion of the control device 30 may be made up of hardware or software. If it is made up of software, a program that implements at least some of the functions of the control device 30 may be stored on a recording medium such as a flexible disk or CD-ROM, and loaded into a computer for execution. The recording medium is not limited to removable ones such as magnetic disks or optical disks, but may also be a fixed recording medium such as a hard disk drive or memory.

[0047] Furthermore, a program that implements at least some of the functions of the control device 30 may be distributed via communication lines such as the Internet (including wireless communication). In addition, the program may be encrypted, modulated, or compressed and distributed via wired or wireless lines such as the Internet, or stored on a recording medium.

[0048] Although a single-beam lithography system was described in the above embodiment, a multi-beam lithography system may also be used.

[0049] It should be noted that the present invention is not limited to the embodiments described above, and the components can be modified and implemented in practice without departing from the spirit of the invention. For example, the mark position may be measured by detecting an image using visible light. Also, the substrate does not necessarily need to be supported on support pins; it can be point-supported or surface-supported on the stage as appropriate. Furthermore, various inventions can be formed by appropriately combining the multiple components disclosed in the above embodiments. For example, some components may be deleted from all the components shown in the embodiments. Moreover, components from different embodiments may be appropriately combined. [Explanation of symbols]

[0050] 10 circuit boards 20 Calibration board 30 Control device 36 Stage Control Unit 40 Electro-optical microscope tube 50 drawing room 52 XY Stages 54 Support pins

Claims

1. A step of placing a calibration substrate on a movable stage within a charged particle beam lithography apparatus, on which at least one mark is formed, With the aforementioned stage stopped, the first position of the mark is measured, A process to induce slippage and perform stage movement at the acceleration to be evaluated, After the slip-prompting stage operation is performed, the second position of the mark is measured while the stage is stopped. A step of calculating the slip amount of the calibration substrate based on the first position and the second position, A slip evaluation method comprising the following features.

2. The slip evaluation method according to claim 1, wherein for each of the accelerations of multiple targets to be evaluated, the slip-promoting stage operation and the measurement of the second position are performed, and the amount of slip of the calibration substrate is calculated.

3. The slip evaluation method according to claim 2, wherein the amount of drift of the charged particle beam is measured for each of the multiple accelerations to be evaluated, and the second position of the mark is determined taking the amount of drift into consideration.

4. The slip evaluation method according to claim 1, wherein, with the stage stopped, a charged particle beam is scanned over a plurality of alignment marks formed on the calibration substrate, the positions of the plurality of alignment marks are measured, and the amount of rotation and the amount of shift of the calibration substrate placed on the stage are calculated based on the positions of the plurality of alignment marks.

5. A charged particle beam drawing method for drawing a pattern on a substrate to be drawn, wherein the slip evaluation method according to claim 2 is further characterized in that the stage is moved at an acceleration such that the slip amount of the calibration substrate falls within a predetermined range, while a charged particle beam is irradiated onto the substrate to be drawn.

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