Multibeam lithography method and multibeam lithography apparatus

Abstract

The beam is adjusted in response to changes in the current density distribution to suppress a decrease in drawing accuracy. [Solution] A multibeam drawing method according to one aspect of the present invention comprises the steps of: acquiring the current density distribution of a multibeam formed using a charged particle beam emitted from a charged particle source; and comparing the acquired current density distribution with a preset ideal shape of the current density distribution, and performing beam adjustment of the multibeam if the difference at a predetermined position is greater than a threshold.

Description

Technical Field

[0001] The present invention relates to a multi-beam drawing method and a multi-beam drawing apparatus.

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 has been 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] For example, there is a drawing apparatus using multi-beams. Compared with the case of drawing with a single electron beam, by using multi-beams, a large number of beams can be irradiated at once, so that the throughput can be significantly improved. In a multi-beam drawing apparatus, for example, an electron beam emitted from an electron source is passed through a shaping aperture array substrate having a plurality of apertures arranged in a matrix to form a multi-beam having a rectangular beam array shape. Each of the plurality of individual beams constituting the multi-beam is blanking-controlled, and the unshielded individual beam is deflected by a deflector and irradiated onto a desired position on the sample.

[0004] As an electron source of a multi-beam drawing apparatus, a thermionic emission type electron source having a cathode as a heater is used. In this electron source, electrons are emitted by heating the cathode. The emitted electrons are accelerated by an acceleration voltage and emitted as an electron beam.

[0005] Due to the consumption of the cathode or the like, the current density distribution of the electron beam emitted from the electron source changes. Therefore, the current density distribution within the multi-beam also changes, which may affect the pattern drawing accuracy.

Prior Art Documents

Patent Documents

[0006] [Patent Document 1] Japanese Patent Publication No. 2014-179383 [Patent Document 2] Japanese Patent Publication No. 2012-094614 [Patent Document 3] Japanese Patent Publication No. 2010-183004 [Overview of the Initiative] [Problems that the invention aims to solve]

[0007] The object of this invention is to provide a multi-beam lithography method and a multi-beam lithography apparatus that perform beam adjustment in response to changes in current density distribution and suppress a decrease in lithography accuracy. [Means for solving the problem]

[0008] A multibeam drawing method according to one aspect of the present invention comprises the steps of: acquiring the current density distribution of a multibeam formed using a charged particle beam emitted from a charged particle source; and comparing the acquired current density distribution with a preset ideal shape of the current density distribution, and performing beam adjustment of the multibeam if the difference at a predetermined position is greater than a threshold.

[0009] A multibeam lithography apparatus according to one aspect of the present invention comprises: a charged particle source that emits a charged particle beam; a multibeam forming unit that forms a multibeam using the charged particle beam; a current detector that detects the beam current of each beam of the multibeam; a calculation unit that calculates the current density distribution of the multibeam using the beam current; a determination unit that compares the calculated current density distribution with a preset ideal shape of the current density distribution and determines whether the difference at a predetermined position is greater than a threshold; a control unit that adjusts the beam of the multibeam if the difference is greater than a threshold; and a lithography unit that irradiates a substrate with the adjusted multibeam to draw a pattern. [Effects of the Invention]

[0010] According to the present invention, beam adjustment can be performed in response to changes in the current density distribution, thereby suppressing a decrease in drawing accuracy. [Brief explanation of the drawing]

[0011] [Figure 1] This is a schematic diagram of a multibeam lithography apparatus according to an embodiment of the present invention. [Figure 2] This is a plan view of a molded aperture array substrate. [Figure 3] This is a flowchart explaining the multibeam lithography method. [Figure 4] This is a flowchart explaining the feature extraction process. [Figure 5] This is a flowchart explaining beam limiting processing. [Figure 6] This figure shows an example of current density distribution measurement results. [Modes for carrying out the invention]

[0012] Figure 1 is a schematic diagram of a multi-charged particle beam lithography apparatus according to an embodiment of the present invention. In this embodiment, a configuration using an electron beam will be described as an example of a charged particle beam. However, the charged particle beam is not limited to an electron beam, and other charged particle beams such as ion beams may also be used.

[0013] This drawing apparatus comprises a drawing unit W that irradiates a substrate 24 to be drawn with an electron beam to draw a desired pattern, and a control unit C that controls the operation of the drawing unit W.

[0014] The imaging unit W includes an electro-optical lens barrel 2 and an imaging chamber 20. Inside the electro-optical lens barrel 2 are an electron source 4, an illumination lens 6, a molded aperture array substrate 8, a blanking aperture array substrate 10, a reduction lens 12, a limiting aperture member 14, an objective lens 16, a deflector 17, and the like.

[0015] In the drawing room 20, an XY stage 22 is arranged. On the XY stage 22, a substrate 24 to be drawn is placed. The substrate 24 to be drawn includes, for example, a wafer, a mask for exposure in which a pattern is transferred using a reduction projection exposure apparatus such as a stepper or a scanner using an excimer laser as a light source on the wafer, or an extreme ultraviolet exposure apparatus (EUV).

[0016] Also, on the XY stage 22, a current detector 40 such as a Faraday cup is arranged at a position different from the position where the substrate 24 is placed.

[0017] The control unit C has a control computer 32, a deflection control circuit 34, and a lens control circuit 36.

[0018] The control computer 32 has a drawing data processing unit 60,a drawing control unit 61,a feature amount calculation unit 62,a determination unit 63,a beam limiting unit 64,and a prediction unit 65. Each unit of the control computer 32 may be configured by hardware such as an electric circuit, or may be configured by software such as a program that executes these functions. When configured by software, a program that realizes these functions may be stored in a recording medium and read and executed by a computer including an electric circuit or the like.

[0019] Drawing data obtained by converting design data (layout data) into a format for a drawing device is stored in a memory device not shown. A drawing data processing unit 60 reads the drawing data from this memory device, performs a multi-stage data conversion process, and generates shot data. The shot data is generated for each pixel, and the drawing time (irradiation time) is calculated. For example, when no pattern is formed on a target pixel, since there is no beam irradiation, a drawing time of zero or an identification code indicating no beam irradiation is defined. Here, a maximum drawing time T (maximum exposure time) for one multi-beam shot is set in advance. It is preferable that the irradiation time of each actually irradiated beam is obtained in proportion to the calculated area density of the pattern. Also, it is preferable that the finally calculated irradiation time of each beam is set to a time corresponding to the corrected irradiation amount obtained by correcting the dimensional variation due to phenomena causing dimensional variations such as proximity effect, overlapping effect, and loading effect by the irradiation amount. Therefore, the irradiation time of each actually irradiated beam can be different for each beam. The drawing time (irradiation time) of each beam is calculated as a value within the maximum drawing time T. Further, the drawing data processing unit 60 generates irradiation time array data (shot data) arranged in the order of arrangement of each multi-beam for each multi-beam shot, with the irradiation time data of each calculated pixel as data for the beam that will draw the pixel.

[0020] A deflection control circuit 34 generates deflection amount data for deflecting a multi-beam using the irradiation time array data. A drawing control unit 61 outputs a control signal for performing a drawing process to a deflection control circuit 34 and a control circuit (not shown) for driving a drawing unit W. The drawing unit W draws a desired pattern on a substrate 24 using the multi-beam based on the control signal. Specifically, it operates as follows.

[0021] The electron beam 30 emitted from the electron source 4 illuminates the entire molded aperture array substrate 8 almost vertically through the illumination lens 6. Figure 2 is a conceptual diagram showing the configuration of the molded aperture array substrate 8. The molded aperture array substrate 8 has m rows (vertical y-direction) × n rows (horizontal x-direction) (m,n≧2) of apertures 80 formed in a matrix at a predetermined arrangement pitch. For example, 512 rows × 512 rows of apertures 80 are formed. Each aperture 80 is formed as a rectangle of the same dimensions and shape. Each aperture 80 may also be a circle of the same diameter.

[0022] The electron beam 30 illuminates the region of the molded aperture array substrate 8 that includes all of the apertures 80. As a portion of the electron beam 30 passes through each of these multiple apertures 80, a multi-beam system 30a to 30e is formed as shown in Figure 1.

[0023] The blanking aperture array substrate 10 has through-holes formed in accordance with the positions of each aperture 80 of the molded aperture array substrate 8, and a blanker consisting of a pair of electrodes is placed in each through-hole. The electron beams 30a to 30e passing through each through-hole are deflected independently by the voltage applied to the blanker. This deflection controls the blanking of each beam. The blanking aperture array substrate 10 performs blanking deflection on each beam of the multi-beam that has passed through the multiple apertures 80 of the molded aperture array substrate 8.

[0024] The multi-beams 30a to 30e that have passed through the blanking aperture array substrate 10 have their respective beam sizes and array pitches reduced by the reduction lens 12 and proceed toward the central aperture formed in the limiting aperture member 14. The electron beams deflected by the blanking aperture array substrate 10 have their trajectories displaced and move away from the central aperture of the limiting aperture member 14, where they are shielded. On the other hand, the electron beams that have not been deflected by the blanking aperture array substrate 10 pass through the central aperture of the limiting aperture member 14.

[0025] The limiting aperture member 14 shields each electron beam that has been deflected by the blanker of the blanking aperture array substrate 10 to the beam-off state. The beam that passes through the limiting aperture member 14 from the time the beam is turned ON until it is turned OFF constitutes one shot of electron beam.

[0026] The electron beams 30a to 30e that have passed through the limiting aperture member 14 are focused by the objective lens 16, forming a pattern image with the desired reduction ratio on the substrate 24. Each electron beam (the entire multi-beam system) that has passed through the limiting aperture member 14 is deflected in the same direction by the deflector 17 and irradiated onto the substrate 24.

[0027] Ideally, the multi-beams irradiated at once will be arranged at a pitch obtained by multiplying the array pitch of the multiple apertures 80 of the molded aperture array substrate 8 by the desired reduction ratio described above. This drawing device performs drawing operations using a raster scan method in which shot beams are irradiated in succession, and when drawing a desired pattern, the necessary beams are controlled to be turned ON by blanking control according to the pattern. When the XY stage 22 is moving continuously, the beam irradiation position is controlled by the deflector 17 so that it follows the movement of the XY stage 22.

[0028] The electron source is a thermionic emission type electron gun with the cathode as the heater. As the cathode wears down, the current density distribution of the electron beam emitted from electron source 4 changes. Therefore, the current density distribution of the multi-beam also changes, which can affect the drawing accuracy.

[0029] In this embodiment, the current density distribution of the multi-beam system is measured, and if the change is large, beam adjustment is performed to correct the current density distribution. Furthermore, if the current density distribution cannot be sufficiently corrected even with beam adjustment, the use of the beam with the reduced current density is restricted.

[0030] The multibeam lithography method according to this embodiment will be explained with reference to the flowchart shown in Figure 3.

[0031] The current density distribution is obtained by measuring the current of each beam in the multibeam (step S101). For example, the XY stage 22 is controlled to move the current detector 40 to the position where each beam of the multibeam is irradiated. Then, each individual beam constituting the multibeam is irradiated onto the current detector 40 one by one, and the current of each beam is measured. Alternatively, instead of a single beam, multiple beams from the surrounding area may be irradiated onto the current detector 40 together, and the current of the beam group may be measured.

[0032] The feature calculation unit 62 calculates the current density from the current amount of each beam and obtains the current density distribution. For example, a current density distribution like the one shown in Figure 6 is obtained. In this example, the current density is low at the four corners of the rectangular beam array multibeam. Also, there is a dip in the current density distribution in the center of the beam array.

[0033] The feature calculation unit 62 calculates the feature quantities of the current density distribution (step S102). The determination unit 63 determines whether the difference between the calculated feature quantities and the ideal value is less than or equal to a threshold (step S103). Details regarding the calculation of feature quantities and threshold determination will be described later.

[0034] If the difference is below the threshold (step S103_Yes) and drawing is to be performed (step S104_Yes), the pattern drawing process on the substrate 24 is performed (step S113). If it is not the right time to draw (step S104_No), the process returns to step S101. Alternatively, the process may wait until the drawing process begins.

[0035] If the difference is greater than the threshold (step S103_No), it is determined whether or not to perform beam adjustment (step S105). In the case of the cathode lifetime of electron source 4, beam adjustment is not performed (step S105_No), and beam limiting described later is performed (step S111).

[0036] When beam adjustment is performed (step S105_Yes), the lens control circuit 36 ​​adjusts the lens values ​​of the various lenses in the electro-optical lens barrel 2 (step S106). For example, the lens control circuit 36 ​​performs alignment adjustment so that the current density at the four corners of the multi-beam is increased.

[0037] After beam adjustment, the current density distribution is measured (step S107), feature quantities are calculated (step S108), and threshold determination is performed (step S109). Steps S107 to S109 are the same processes as steps S101 to S103.

[0038] If the difference between the calculated feature quantity and the ideal value becomes less than or equal to a threshold due to beam adjustment (step S109_Yes), the pattern drawing process is performed on the substrate 24 (step S113).

[0039] If the number of beam adjustments has not reached the upper limit (step S110_No), beam adjustment, measurement of current density distribution, feature calculation, and threshold determination (steps S106~S109) are repeated.

[0040] If the number of beam adjustments reaches a predetermined upper limit (step S110_Yes), the beam limiting unit 64 restricts the use of beams with low current density to beams that are not used for drawing (step S111). Details of this beam limiting will be described later.

[0041] The determination unit 63 determines whether drawing is possible with the use of some beams restricted (step S112). If drawing is possible (step S112_Yes), the pattern drawing process is performed on the substrate 24 (step S113). If it is determined that drawing is not possible, such as not being able to achieve the desired drawing speed (step S112_No), an alert is output (step S114).

[0042] Next, the calculation of features and threshold determination (steps S102, S103, S108, S109) will be explained according to the flowchart shown in Figure 4.

[0043] The location to monitor the current density within the multi-beam array is specified (step S201). For example, the four corners of a rectangular beam array are specified. If the current density distribution has been measured in advance and dips in current density other than the four corners are known, these dips are also specified. The four corners and dips are registered in the coordinate list to be monitored. The current density at the specified locations is calculated as a feature. If the number of beams for which beam current was measured in steps S101 and S107 of Figure 3 is small, data interpolation may be performed.

[0044] Step S202 compares the feature quantities of the current density distribution with the value of the current density at the monitor position in the ideal shape of the current density distribution (ideal value), and determines whether the difference is below a threshold. Here, the ideal shape of the current density distribution may be flat, a Gaussian distribution, or the initial shape of the current density distribution after the completion of the drawing device adjustment. When comparing the feature quantities with the ideal value, the current density distribution may be normalized.

[0045] If the difference is less than or equal to the threshold (step S202_Yes), the measured data of the measured current density distribution is stored in memory (not shown) (step S203).

[0046] The prediction unit 65 predicts the timing at which the difference between the feature quantity and the ideal value reaches a threshold by extrapolating the accumulated measurement data (step S204). If the number of days until the predicted timing is not less than a predetermined number (step S205_No), the process proceeds to step S104 or S113 in Figure 3. If the number of days until the predicted timing is less than a predetermined number (step S205_Yes), an alert is output (step S206), and the process proceeds to step S104 or S113 in Figure 3.

[0047] If a location where the difference is greater than the threshold is not registered in the coordinate list (steps S202_No, S207_No), it is determined whether or not to add it to the list (step S208). If it is added, the list is updated (steps S208_No, S209). Then, the process proceeds to step S105 or S110 in Figure 3.

[0048] Next, the beam limiting process (step S111 in Figure 3) will be explained following the flowchart shown in Figure 5.

[0049] The beam limiting unit 64 creates a difference map between the current density distribution created in step S101 or S107 and the ideal shape of the current density distribution (step S301).

[0050] The beam limiting unit 64 refers to the difference map and tentatively determines beams whose difference is greater than or equal to a predetermined value as limiting beams (step S302).

[0051] If the number of restricted beams provisionally determined in step S302 is less than or equal to the maximum number of restricted beams (step S303_Yes), the beam restriction unit 64 sets the provisionally determined restricted beams to permanently off restricted beams (step S304). The maximum number of restricted beams is determined considering drawing conditions, etc. Then, proceed to step S112 in Figure 3.

[0052] Thus, according to this embodiment, if the current density distribution of the multi-beam system deviates from the ideal shape, the beam is adjusted to bring it closer to the ideal shape. Furthermore, if the beam cannot be fully improved by beam adjustment due to factors such as the wear of the electron source cathode, the use of the beam is restricted. This suppresses a decrease in pattern drawing accuracy.

[0053] 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. 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]

[0054] 2. Electro-optical lens barrel 4 Electron source 6. Illumination Lens 8. Molded aperture array substrate 10 Blanking aperture array substrate 10 12 Reduction lens 12 16 Objective lenses 17 Deflector 20 Drawing room 22 XY Stages 24 circuit boards 40 Current detector

Claims

1. A process for obtaining the current density distribution of a multibeam formed using a charged particle beam emitted from a charged particle source, A step of comparing the acquired current density distribution with a preset ideal shape of the current density distribution, and if the difference at a predetermined position is greater than a threshold, performing beam adjustment of the multibeam, A multibeam lithography method comprising the following features.

2. The multibeam lithography method according to claim 1, wherein the ideal shape is flat or Gaussian.

3. The multi-beam drawing method according to claim 1 or 2, wherein the beam-adjusted multi-beam is irradiated onto a substrate to draw a pattern.

4. The current density distribution of the multi-beam obtained after the beam adjustment is compared with the ideal shape, and if the difference at the predetermined position is greater than a threshold, the beam corresponding to the predetermined position is set as a restricted beam. The multi-beam drawing method according to claim 1 or 2, wherein the multi-beams, which are controlled so that the beam set as the usage-restricted beam is always off, are irradiated onto a substrate to draw a pattern.

5. A charged particle source that emits a charged particle beam, A multibeam forming unit that forms a multibeam using the charged particle beam, A current detector for detecting the beam current of each beam in the multibeam, A calculation unit that calculates the current density distribution of the multi-beam using the beam current, A determination unit compares the calculated current density distribution with a preset ideal shape of the current density distribution and determines whether the difference at a predetermined position is greater than a threshold, When the difference is greater than a threshold, a control unit performs beam adjustment of the multibeam, A drawing unit that irradiates the substrate with the adjusted multi-beam to draw a pattern, A multibeam lithography system equipped with the following features.

6. The control unit includes a beam limiting unit that, as a result of comparing the current density distribution after beam adjustment with the ideal shape, sets the beam corresponding to the predetermined position as a restricted beam if the difference at the predetermined position is greater than a threshold. The multi-beam lithography apparatus according to claim 5, wherein the control unit controls the beam set as the usage-restricted beam to be kept off at all times.

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