Multi-charged particle beam lithography method, multi-charged particle beam lithography apparatus, and program

Abstract

Using the same pattern data, patterns with equivalent line width and shape are drawn on drawing devices of different generations and drawing methods. [Solution] A multi-charged particle beam drawing method for drawing a pattern with a desired resolution on a substrate on which a resist film has been formed using a multi-charged particle beam. In this method, the drawing area of ​​the substrate is virtually divided into a plurality of first mesh areas with a first mesh size, a first area density of the pattern is calculated for each first mesh area, a background dose is determined based on the desired resolution, the irradiation amount for each first mesh area is calculated using the background dose, the resolution threshold of the resist film, and the first area density, and the multi-charged particle beam is irradiated onto the substrate using the calculated irradiation amount.

Description

Technical Field

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

Background Art

[0002] With the high integration of LSIs, the circuit line width 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. The high-precision original pattern is drawn on a photomask by an electron beam drawing apparatus.

[0003] A drawing apparatus using a multi-beam can irradiate more beams at a time compared to the case of drawing with a single electron beam, so the throughput can be significantly improved. In a multi-beam drawing apparatus using a blanking aperture array substrate (blanking plate), which is a form of a multi-beam drawing apparatus, for example, an electron beam emitted from one electron source is passed through a shaping aperture array substrate having a plurality of openings to form a multi-beam (a plurality of electron beams). A blanking aperture array substrate is arranged downstream of the shaping aperture array substrate. The blanking aperture array substrate has electrode pairs for individually deflecting the beams, and an opening for beam passage is formed between the electrode pairs. By fixing one electrode of the electrode pair (blanker) at the ground potential and switching the other electrode between the ground potential and other potentials, blanking deflection of the passing electron beam is performed. The optical column of the multi-beam drawing apparatus is configured such that the electron beam deflected by the blanker is shielded and turned off, and the electron beam not deflected is irradiated onto the sample as an on-beam.

[0004] To reduce pattern drawing waiting times and increase productivity, it is being considered to use pattern data prepared for one multi-beam lithography system with multi-beam lithography systems of different generations or single-beam lithography systems.

[0005] However, due to differences in beam characteristics such as beam size and beam blur, multi-beam lithography systems and single-beam lithography systems of different generations exhibit different performance characteristics, including resolution. As a result, when using the same pattern data, the line width and shape of the drawn patterns can differ. [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] Japanese Patent Application Publication No. 5-308046 [Patent Document 2] Japanese Patent Publication No. 2001-118777 [Patent Document 3] Special Publication No. 2022-533790 [Patent Document 4] Japanese Patent Publication No. 2015-5729 [Overview of the project] [Problems that the invention aims to solve]

[0007] The present invention has been made in view of the above-mentioned conventional problems, and aims to provide a multi-charged particle beam lithography method, a multi-charged particle beam lithography apparatus, and a program that can draw patterns with equivalent line width and shape using the same pattern data, even with lithography apparatuses of different generations and drawing methods. [Means for solving the problem]

[0008] A multi-charged particle beam lithography method according to one aspect of the present invention is a multi-charged particle beam lithography method for drawing a pattern at a desired resolution on a substrate on which a resist film is formed using a multi-charged particle beam, wherein the drawing area of ​​the substrate is virtually divided into a plurality of first mesh areas with a first mesh size, a first area density of the pattern is calculated for each first mesh area, a background dose is determined based on the desired resolution, the irradiation amount for each first mesh area is calculated using the background dose, the resolution threshold of the resist film, and the first area density, and the multi-charged particle beam is irradiated onto the substrate using the calculated irradiation amount.

[0009] A multi-charged particle beam lithography apparatus according to one aspect of the present invention is a multi-charged particle beam lithography apparatus that draws a pattern with a desired resolution on a substrate on which a resist film is formed using a multi-charged particle beam, comprising: a rasterization unit that virtually divides the drawing area of ​​the substrate into a plurality of mesh areas with a predetermined mesh size and calculates the area density of the pattern for each mesh area; a background dose determination unit that determines a background dose based on the desired resolution; an irradiation dose calculation unit that calculates the irradiation dose for each mesh area using the background dose, the resolution threshold of the resist film, and the area density; and a drawing unit that irradiates the substrate with the multi-charged particle beam using the calculated irradiation dose.

[0010] A program according to one aspect of the present invention causes a computer to perform the following steps: virtually divide a drawing area of ​​a substrate on which a resist film to be patterned using a multi-charged particle beam is formed into a plurality of mesh areas of a predetermined mesh size; calculate the area density for each mesh area; determine a background dose based on the desired resolution; calculate the irradiation amount for each mesh area using the background dose, the resolution threshold of the resist film, and the area density; and control the drawing unit to irradiate the substrate with the multi-charged particle beam using the calculated irradiation amount.

Advantages of the Invention

[0011] According to the present invention, using the same pattern data, it is possible to draw patterns with equivalent line widths and shapes on drawing apparatuses with different generations and drawing methods.

Brief Description of the Drawings

[0012] [Figure 1] It is a schematic diagram of a multi-charged particle beam drawing apparatus according to an embodiment of the present invention. [Figure 2] It is a diagram showing a configuration example of a shaping aperture array substrate. [Figure 3] It is a diagram for explaining an example of a drawing operation. [Figure 4] It is a diagram showing an example of an irradiation region of a multi-beam and a drawing target pixel. [Figure 5] It is a graph showing the relationship between area density and SLA. [Figure 6] It is a graph showing the relationship between background dose and SLA. [Figure 7] It is a flowchart for explaining a drawing method according to the same embodiment. [Figure 8] It is a diagram showing an irradiation amount profile when background dose irradiation is not performed. [Figure 9] It is a diagram showing an irradiation amount profile when background dose irradiation is performed. [Figure 10] It is a diagram showing an irradiation amount profile according to the drawing method according to the same embodiment.

Modes for Carrying Out the Invention

[0013] Hereinafter, embodiments of the present invention will be described based on the drawings. In the embodiments, as an example of the charged particle beam, a configuration using an electron beam will be described. However, the charged particle beam is not limited to an electron beam, and an ion beam or the like may also be used.

[0014] FIG. 1 is a schematic configuration diagram of a drawing apparatus according to an embodiment. As shown in FIG. 1, the drawing apparatus 100 includes a drawing unit 150 and a control unit 160. The drawing apparatus 100 is an example of a multi-charged particle beam drawing apparatus.

[0015] The drawing unit 150 includes an electron optical lens barrel 102 and a drawing chamber 103. Inside the electron optical lens barrel 102, an electron source 201, an illumination lens 202, a shaping aperture array substrate 203, a blanking aperture array substrate 204, a reduction lens 205, a limiting aperture member 206, an objective lens 207, and a deflector 208 are arranged.

[0016] Inside the drawing chamber 103, an XY stage 105 capable of continuous movement is arranged. On the XY stage 105, a substrate 101 to be drawn during drawing is arranged. The substrate 101 is, for example, a mask blank on which resist is applied and nothing has been drawn yet. On the XY stage 105, a mirror 210 for measuring the position of the XY stage 105 is arranged.

[0017] The control unit 160 has a control computer 110, a memory 112, a deflection control circuit 130, a stage position detector 139, and storage devices 140, 142, 144 such as a magnetic disk device. These are connected to each other via a bus. Pattern data (drawing data) in which the layout of the graphic pattern to be drawn is defined is input from the outside and stored in the storage device 140.

[0018] The control computer 110 includes a target value input unit 50, a rasterization unit 52, a background dose determination unit 53, an irradiation dose calculation unit 54, an irradiation time calculation unit 55, and a drawing control unit 60. These functions may be implemented as hardware such as electrical circuits, or as software. If implemented as software, a program that implements at least some of the functions may be stored on a recording medium and loaded and executed by a computer having a CPU. The recording medium for storing the program 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. Information such as calculation results in the control computer 110 is stored in the memory 112 each time.

[0019] Figure 2 is a conceptual diagram showing an example configuration of a molded aperture array substrate 203. The molded aperture array substrate 203 has multiple openings 203a formed in a matrix at a predetermined arrangement pitch in both the vertical and horizontal directions. For example, 512 × 512 rows of openings 203a are formed in the vertical and horizontal (x,y directions). Each opening 203a is formed as a rectangle or circle of the same dimensions.

[0020] A portion of the electron beam 200 emitted from the electron source 201 passes through multiple apertures 203a, forming a multi-beam 20 containing multiple individual beams.

[0021] The blanking aperture array substrate 204 has through holes (openings) formed at positions corresponding to each aperture 203a of the molded aperture array substrate 203 shown in Figure 2, through which each individual beam passes. A set of electrodes for blanking deflection (blankers: blanking deflectors) is placed on either side of each through hole. A deflection voltage based on a control signal from the deflection control circuit 130 is applied to one of the two electrodes, and the other electrode is grounded.

[0022] Each individual beam passing through a hole is independently deflected by a blanker, and blanking control is performed. In this way, multiple blankers each perform blanking deflection for their respective individual beams.

[0023] Figure 3 is a conceptual diagram illustrating an example of a drawing operation. For example, as shown in Figure 3, the drawing area 30 of the substrate 101 is virtually divided into multiple stripe-shaped areas 32 with a predetermined width in the y direction.

[0024] First, the XY stage 105 is moved to adjust the position of the irradiation area 34 that can be irradiated with a single multi-beam 20 irradiation to the left edge of the first stripe area 32, or even further to the left, and then drawing begins. When drawing the first stripe area 32, the drawing progresses relatively in the +x direction by moving the XY stage 105, for example, in the -x direction. The XY stage 105 is moved, for example, continuously at a predetermined speed.

[0025] After the first stripe area 32 has been drawn, the stage position is moved in the -y direction to adjust the illumination area 34 so that it is relatively positioned in the y direction at the right edge of the second stripe area 32, or even further to the right. Then, the XY stage 105 is moved, for example, in the +x direction, to perform drawing in the -x direction in the same manner.

[0026] Drawing time can be reduced by alternating directions while drawing, such as drawing in the +x direction in the third stripe region 32 and in the -x direction in the fourth stripe region 32. However, drawing is not limited to alternating directions; each stripe region 32 may be drawn in the same direction. In a single shot, multiple shot patterns, up to the same number as the apertures 203a, are formed at once by the multi-beam formed by passing through each aperture 203a of the molded aperture array substrate 203.

[0027] Figure 4 shows an example of a multi-beam irradiation area and a pixel to be drawn. In Figure 4, the stripe area 32 is divided into multiple mesh areas 40, for example, by the beam size of the individual beams. Each mesh area 40 becomes a drawing pixel area (drawing position). In the example in Figure 4, the drawing area of ​​the substrate 101 is shown as being divided into multiple stripe areas 32, for example, in the y direction, by the size (shot size) of the irradiation area 34 that can be irradiated with one multi-beam 20 irradiation. Note that the width of the stripe area 32 is not limited to this, and may be, for example, n times the size of the irradiation area 34 (where n is an integer of 1 or more).

[0028] Within the irradiation area 34, multiple pixels 24 (beam irradiation positions) that can be irradiated with a single multi-beam 20 are shown. In other words, the pitch between adjacent pixels 24 becomes the pitch between each beam of the multi-beam. In the example in Figure 4, one sub-pitch area 26 is formed by a square area surrounded by four adjacent pixels 24 and containing one of the four pixels 24. Figure 4 shows the case where each sub-pitch area 26 consists of 4x4 pixels.

[0029] Next, the operation of the drawing unit 150 will be described. The electron beam 200 emitted from the electron source 201 (emission unit) illuminates the entire molded aperture array substrate 203 almost vertically by the illumination lens 202. As the electron beam 200 passes through each of the multiple openings 203a of the molded aperture array substrate 203, a multi-beam 20 containing multiple individual beams is formed. The beam array shape of the multi-beam 20 is, for example, rectangular. The multi-beam 20 passes through each corresponding blanker of the blanking aperture array substrate 204. Each blanker individually deflects the beam so that the beam is ON only during the calculated drawing time (irradiation time) and OFF otherwise.

[0030] The multi-beam 20 that has passed through the blanking aperture array substrate 204 is reduced by the reduction lens 205 and travels toward the central opening formed in the limiting aperture member 206. The electron beam that has been deflected by the blanking of the blanking aperture array substrate 204 to turn the beam OFF is moved away from the central opening of the limiting aperture member 206 and is shielded by the limiting aperture member 206. On the other hand, the beam that has not been deflected by the blanking of the blanking aperture array substrate 204 (the beam that has been deflected to turn the beam ON) passes through the central opening of the limiting aperture member 206.

[0031] The beam that has passed through the limiting aperture member 206, formed from the time the beam is turned ON until it is turned OFF, forms the beam for one shot. The multi-beam 20 that has passed through the limiting aperture member 206 is focused by the objective lens 207 to form a pattern image with the desired reduction ratio, and each beam (the entire multi-beam 20) is deflected in the same direction by the deflector 208 and irradiated onto the respective drawing positions (irradiation positions) on the substrate 101.

[0032] When the XY stage 105 is moving continuously, the beam drawing position (irradiation position) is tracked and controlled by the deflector 208 so that it follows the movement of the XY stage 105. A laser is shone from the stage position detector 139 toward the mirror 210 on the XY stage 105, and the position of the XY stage 105 is measured using the reflected light. Ideally, the multi-beams irradiated at one time will be aligned at a pitch obtained by multiplying the array pitch of the multiple apertures 203a of the molded aperture array substrate 203 by the desired reduction ratio described above.

[0033] The drawing device 100, during each tracking operation, irradiates a multi-beam, which becomes a shot beam, while sequentially shifting the drawing position, following the movement of the XY stage 105.

[0034] To improve the productivity of photomasks, it is sometimes necessary to use a multibeam lithography system of a different generation than the lithography system 100. However, because the resolution of the lithography pattern, such as the Dawes likelihood and SLA (Square Loss Area), differs between lithography systems of different generations, differences in the finished dimensions of the lithography pattern occurred when the same pattern data was used.

[0035] Here, SLA (Surface Area Latitude) is the area lost due to rounded corners when a rectangular pattern is drawn (or the area ratio of the lost portion relative to the design value). The larger the area density, the larger the SLA. The degree to which SLA changes with respect to area density differs between different generations of drawing devices.

[0036] Figure 5 shows examples of SLA for the lithography system 100 and an older generation multibeam lithography system (hereinafter referred to as the older generation machine). For example, the older generation machine is a lithography system with larger individual beam sizes and lower resolution than the lithography system 100. In Figure 5, the horizontal axis corresponds to area density, and the vertical axis corresponds to the SLA of the drawn pattern.

[0037] As shown in Figure 5, the SLA increases with increasing area density. Furthermore, the increase in SLA is greater for the older generation machine compared to the 100. For low area density, such as isolated patterns, the SLA is similar for the 100 and the older generation machine. As area density increases, the difference in SLA between the 100 and the older generation machine widens.

[0038] Thus, the resolution, such as SLA, differs between the drawing device 100 and the older generation machine. The inventors have found that the resolution can be changed not only by irradiating areas with patterns with a beam, but also by irradiating areas without patterns with a beam dose that does not resolve the pattern (hereinafter referred to as background dose). For example, as shown in Figure 6, the SLA increases with increasing background dose. The drawing device 100 according to this embodiment adjusts the background dose to match the resolution of the older generation machine and makes it possible to form patterns with the same (or similar) finished dimensions and shapes.

[0039] Resolution data, including data showing the relationship between area density and resolution as shown in Figure 5, and data showing the relationship between background dose and resolution as shown in Figure 6, for the drawing device 100, is obtained in advance through simulation and actual drawing and stored in the storage device 144.

[0040] Next, the drawing method according to the embodiment will be explained following the flowchart shown in Figure 7.

[0041] The target value input unit 50 accepts input of, for example, resolution information of an older generation machine, which will be the target value (step S1). For example, data showing the relationship between the pattern density and SLA of an older generation machine is input.

[0042] The rasterization unit 52 reads pattern data from the storage device 140, divides it into meshes according to the beam size of the individual beams, performs rasterization processing, calculates the proportion (area density) of the pattern contained in each mesh region (first mesh region), and creates an area density map (step S2). The area density map is stored in the memory 112.

[0043] The background dose determination unit 53 compares the target value with the resolution data stored in the memory device 144 and determines the background dose (step S3).

[0044] For example, the background dose determination unit 53 analyzes the pattern data to determine the area density of the pattern region, and for each area density, it calculates the difference between the resolution of the previous generation machine (SLA, etc.) and the resolution of the drawing device 100 when the background dose is zero, and determines a background dose corresponding to the calculated difference. The area density may be calculated for each mesh region, or for each region of a different size than the above mesh region, for example, for each region obtained by dividing the drawing region into a region larger than the above mesh region (second mesh region). For example, if a 50% line and space pattern is placed in a certain region, the difference in resolution at an area density of 50% is calculated, and the background dose is determined based on the difference.

[0045] The irradiation dose calculation unit 54 uses the area density defined in the area density map to calculate the incident irradiation dose (dose amount) to irradiate each mesh area (step S4).

[0046] Figure 8 shows the irradiation dose profile at the boundary between the patterned region and the unpatterned region when no background dose irradiation is performed. The incident amount applied to the resist is the sum of the incident irradiation dose Dose from the drawing device 100 and the backscattered irradiation dose W1 caused by the beam incidence. The backscattered irradiation dose W1 is calculated as the product of the area density P, the backscattering coefficient η, and the incident irradiation dose Dose. The edges of the patterned region are set to the threshold Dth at which the resist is resolved.

[0047] Figure 9 shows the irradiation dose profile when a background dose (BKGDose) is added in addition to the incident dose (Dose) shown in Figure 8. The incident dose delivered to the resist increases by the amount of the background dose (BKGDose) and the backscattered irradiation dose (W2) due to the background dose.

[0048] In this case, the areas exceeding the threshold Dth shift towards the non-patterned area, changing the pattern dimensions and making it impossible to draw a pattern of the desired dimensions.

[0049] Therefore, in this embodiment, as shown in Figure 10, an adjustment term is added to the incident irradiation dose so that even when background dose irradiation is performed, the point where the threshold Dth is exceeded does not shift.

[0050] Incident irradiation dose for resolving the pattern * This can be calculated using the following formula, taking background dose into account.

[0051] Dose * ={Dth-BKGDose·(1+η)} / (0.5+P·η)

[0052] The amount of incident charge applied to the resist is BKGDose·(1+η)+Dose * ·0.5·(erf(-x / σ)+1)+P·η·Dose * This is the result. x represents the position with the edge of the pattern region set to 0. Of the three terms in this equation, the first term, BKGDose·(1+η), corresponds to the background dose and the backscattered irradiation amount due to the background dose. Of the three terms, the last term, P·η·Dose * This is the incident irradiation dose required to resolve the pattern. * This corresponds to the amount of backscattered irradiation.

[0053] The irradiation dose calculation unit 54 calculates the irradiation dose. * The area density is multiplied by the area density defined in the area density map, and the background dose (BKGDose) is added to the result of the multiplication to calculate the incident irradiation amount required to irradiate each mesh area.

[0054] The irradiation time calculation unit 55 calculates the irradiation time t corresponding to the incident irradiation dose for each mesh region (step S5). The irradiation time t is calculated by dividing the incident irradiation dose by the current density. The irradiation time t is calculated as a value within the maximum irradiation time that can be irradiated in one shot of the multi-beam 20. The irradiation time data is stored in the storage device 142.

[0055] In the drawing process (step S6), the drawing control unit 60 rearranges the irradiation time data in shot order according to the drawing sequence. Then, it transfers the irradiation time data in shot order to the deflection control circuit 130. The deflection control circuit 130 outputs blanking control signals to the blanking aperture array substrate 204 in shot order, and also outputs deflection control signals to the deflector 208 in shot order. The drawing unit 150 draws a pattern on the substrate 101 using a multi-beam system with irradiation amounts calculated for each mesh region.

[0056] The pattern drawn on the substrate 101 will have a resolution similar to that of a pattern drawn with an older generation machine, making it possible to produce (almost) identical photomasks with the drawing device 100 and an older generation machine, thereby improving productivity.

[0057] In the above embodiment, the target value that the target value input unit 50 accepts is not limited to the resolution of an older generation multi-beam lithography system, but may also be the resolution of a single-beam lithography system. Furthermore, the background dose amount does not necessarily need to be calculated for each mesh area of ​​the entire surface, but may be determined only for the non-patterned areas. In addition, other known methods for calculating the background dose amount can be used. In that case, the irradiation dose for the newly determined patterned area is determined by the background dose amount of the non-patterned area, the resist resolution threshold, and the area ratio.

[0058] 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]

[0059] 50 Target value input section 52 Rasterization section 53 Background Dose Determination Unit 54 Irradiance calculation section 55 Irradiation time calculation unit 60 Drawing Control Unit 100 drawing device 110 Control Computer

Claims

1. A multi-charged particle beam lithography method for drawing a pattern with a desired resolution on a substrate on which a resist film has been formed using a multi-charged particle beam, The drawing area of ​​the substrate is virtually divided into a plurality of first mesh areas with a first mesh size, For each of the first mesh regions, the first area density of the pattern is calculated. The background dose is determined based on the aforementioned desired resolution. Using the background dose, the resolution threshold of the resist film, and the first area density, the irradiation dose for each of the first mesh regions is calculated. A multi-charged particle beam lithography method comprising irradiating the substrate with the multi-charged particle beam using the calculated irradiation dose.

2. The multi-charged particle beam drawing method according to claim 1, wherein the background dose is adjusted according to the first area density, or the second area density of the pattern calculated for each of a plurality of second mesh regions obtained by virtually dividing the drawing region with a second mesh size different from the first mesh size.

3. The multi-charged particle beam lithography method according to claim 1, wherein the background dose is determined based on the difference between the resolution when the background dose is zero and the target value.

4. The multi-charged particle beam lithography method according to claim 1, wherein the background dose is determined by referring to resolution data that shows the relationship between the background dose and the resolution, which has been acquired in advance.

5. A multi-charged particle beam lithography apparatus for drawing a pattern with a desired resolution on a substrate on which a resist film has been formed using a multi-charged particle beam, A rasterization unit that virtually divides the drawing area of ​​the substrate into a plurality of mesh areas with a predetermined mesh size and calculates the area density of the pattern for each mesh area, A background dose determination unit that determines the background dose based on the desired resolution, An irradiation dose calculation unit calculates the irradiation dose for each mesh region using the background dose, the resolution threshold of the resist film, and the area density. A drawing unit that irradiates the substrate with the multi-charged particle beam using the calculated irradiation dose, A multi-charged particle beam lithography system equipped with the following features.

6. The steps include: virtually dividing the drawing area of ​​a substrate on which a resist film to be patterned using a multi-charged particle beam is formed into multiple mesh areas with a predetermined mesh size; A step of calculating the area density for each of the aforementioned mesh regions, The steps include determining the background dose based on the desired resolution, A step of calculating the irradiation dose for each mesh region using the background dose, the resolution threshold of the resist film, and the area density. A step of controlling the drawing unit to irradiate the substrate with the multi-charged particle beam using the calculated irradiation dose, A program that causes a computer to execute something.

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