Cooling plate and charged particle beam writing device

Abstract

To provide a cooling plate with an excellent temperature averaging function and a charged particle beam drawing device that can efficiently cool a coil of an objective lens using the same.SOLUTION: The cooling plate includes a circular flat surface portion. On the flat surface portion, a spiral-shaped first refrigerant flow channel and a spiral-shaped second refrigerant flow channel located below the first refrigerant flow channel are formed so that they overlap each other. An inner circumferential flow channel of the first refrigerant flow channel is inclined to become gradually a lower level and connected to an inner circumferential flow channel of the second refrigerant flow channel.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a cooling plate and a charged particle beam writing apparatus. [Background technology]

[0002] As LSIs become more highly integrated, the circuit line width required for semiconductor devices is becoming finer every year. To form the desired circuit pattern on a semiconductor device, a method is adopted in which a high-precision original pattern (called a mask, or a reticle, especially when used in steppers and scanners) formed on quartz is reduced and transferred onto a wafer using a reduction projection exposure system. The high-precision original pattern is drawn using an electron beam drawing system, using so-called electron beam lithography technology.

[0003] An electron beam lithography system includes a lithography chamber that houses a stage on which a sample to be lithographed is placed, and an electron optical column connected to the lithography chamber. The electron optical column contains an electron gun that emits an electron beam, a deflector that deflects the beam to determine the beam irradiation position on the sample, and an objective lens that focuses the beam on the sample surface.

[0004] The objective lens is composed of a magnetic lens (electromagnetic lens) with a magnetic pole and a coil, and magnetic field lines created by passing a current through the coil leak into space through the pole piece, creating a magnetic field that functions as a lens for the electron beam. The objective lens is located at the bottom of the electron optical column, and generates heat when a current is passed through the coil, affecting the temperature distribution of the sample on the stage.

[0005] In conventional electron beam lithography systems, the heat generated by the objective lens coil is absorbed by cooling water via a cooling plate. However, a temperature gradient occurs inside the cooling plate during the heat absorption process by the cooling water, and this temperature gradient can have an effect on the temperature distribution in the sample.

[0006] To solve this problem, Patent Document 1 discloses a configuration in which a triple heat shield structure is provided between the coil cooling plate and the sample. However, with this configuration, it can be difficult to secure the space for the triple shield structure. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Japanese Patent Application Laid-Open No. 2011-66247 [Patent Document 2] Japanese Patent Publication No. 2020-145238 [Patent Document 3] Japanese Patent Application Laid-Open No. 2015-12057 [Patent Document 4] Japanese Patent Application Laid-Open No. 2000-208975 Summary of the Invention [Problem to be solved by the invention]

[0008] An object of the present invention is to provide a cooling plate with excellent heat uniformity, and a charged particle beam drawing apparatus that can efficiently cool the coil of an objective lens using this cooling plate. [Means for solving the problem]

[0009] A cooling plate according to one aspect of the present invention is a cooling plate having an annular flat portion, in which a first spiral refrigerant flow path and a second spiral refrigerant flow path located below the first refrigerant flow path are formed so as to overlap each other, and the inner flow path of the first refrigerant flow path is gradually inclined to become lower and is connected to the inner flow path of the second refrigerant flow path. [Effects of the Invention]

[0010] According to the present invention, the cooling plate can be uniformly heated, and the coil of the objective lens can be efficiently cooled. [Brief explanation of the drawings]

[0011] [Figure 1] 1 is a schematic diagram of an electron beam writing apparatus according to an embodiment of the present invention. [Figure 2] FIG. 2 is a cross-sectional view of an objective lens. [Figure 3] FIG. 2 is a perspective view of a coil cooling plate. [Figure 4] FIG. 4 is a cross-sectional view taken along line IV-IV in FIG. [Figure 5] FIG. 2 is a schematic diagram of a cooling water flow path. [Figure 6] FIG. 2 is a diagram illustrating the flow of cooling water. [Figure 7] FIG. 7A shows an example in which the entire flow path is an arc, and FIG. 7B shows an example in which a part of the flow path is an elliptical arc. [Figure 8] FIG. 10 is a diagram showing the simulation results of the temperature distribution on the lower surface of the coil cooling plate. [Figure 9] FIG. 10 is a cross-sectional view of a modified coil cooling plate. DETAILED DESCRIPTION OF THE INVENTION

[0012] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. In the embodiment, a configuration using an electron beam as an example of a charged particle 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.

[0013] Fig. 1 is a schematic diagram of an electron beam lithography apparatus according to this embodiment. The electron beam lithography apparatus 1 shown in Fig. 1 is an apparatus that can be installed in a clean room. The electron beam lithography apparatus 1 includes a evacuated lithography chamber 5 that houses a stage 3 on which a mask substrate 2, which is a sample to be lithographed, is placed, and an electron optical column 7 connected to the top of the lithography chamber 5. An electron beam 6 is emitted from an electron gun 4 provided in the electron optical column 7, and is irradiated onto the mask substrate 2 placed on the stage 3.

[0014] The stage 3 can be moved by a stage moving means 8. The stage 3 is provided with a mirror 9 for a laser interferometer 10. The laser interferometer 10 irradiates the mirror 9 with laser light, receives the light reflected from the mirror 9, and outputs a light reception signal to a position detection means (not shown). The position detection means detects the position of the stage 3 based on the signal from the laser interferometer 10.

[0015] The electron optical column 7 is provided with a deflector (not shown) that deflects the electron beam 6 and adjusts the shape of the electron beam 6 and the irradiation position on the mask substrate 2. In addition, an objective lens 20 that forms an image of the electron beam 6 on the mask substrate 2 is disposed at the bottom of the electron optical column 7.

[0016] A drawing control device (not shown) controls the position of the stage 3, the deflection amount of the deflector, etc., based on a drawing job that describes drawing conditions, etc., and performs drawing processing on the mask substrate 2.

[0017] 2 is a schematic longitudinal cross-sectional view of objective lens 20. Objective lens 20 is a magnetic lens (electromagnetic lens) and has a doughnut-shaped coil 21 and a yoke 22 that houses coil 21. Yoke 22 is made of a material with high magnetic permeability such as iron, and has a notch (pole piece 23) formed in one part.

[0018] Magnetic lines of force created by passing a current through the coil 21 leak into space via the pole piece 23, creating a magnetic field.

[0019] When a current is passed through the coil 21, the coil 21 generates heat. Therefore, a metal coil cooling plate 30 is disposed inside the yoke 22 to absorb the heat generated by the coil 21.

[0020] As shown in Figures 2 and 3, the coil cooling plate 30 has an annular flat portion 31 (bottom) and a cylindrical peripheral wall portion 32 that stands upward from the outer periphery of the flat portion 31. The annular shape may be, for example, a circular or elliptical ring. The coil 21 is placed on the flat portion 31. The outer periphery of the coil 21 is surrounded by the peripheral wall portion 32.

[0021] The lower surface of coil 21 contacts the upper surface of flat portion 31 via an insulating resin molding material. Similarly, the outer peripheral surface of coil 21 contacts the inner peripheral surface of peripheral wall portion 32 via the resin molding material.

[0022] Inside the flat portion 31, a cooling water flow path 40 is formed through which cooling water (refrigerant) for cooling the coil 21 flows.

[0023] The configuration of the cooling water flow path 40 will be described with reference to Fig. 4 to Fig. 6. Fig. 4 is a cross-sectional view taken along line IV-IV in Fig. 3. Fig. 5 is a schematic diagram of the cooling water flow path 40 in the flat portion 31. Fig. 6 is a diagram illustrating how the cooling water flows.

[0024] The cooling water flow path 40 has a two-layer structure including a spiral upper layer flow path 41 that goes around the annular flat portion 31, and a spiral lower layer flow path 42. Of the upper layer flow paths 41, the innermost flow path 41a is inclined so as to gradually lower (spiral-shaped) and is connected to the innermost flow path 42a of the lower layer flow path 42. The end of the outermost flow path 41b of the upper layer flow path 41 is bent upward and extends in the vertical direction within the peripheral wall portion 32, and a cooling water inlet 41c (see FIG. 3) is formed on the upper surface of the peripheral wall portion 32.

[0025] Of the upper layer flow passages 41 in the flat portion 31, the portions other than the innermost flow passage 41a are arranged at the same height.

[0026] The ends of the outermost flow passages 42b of the lower layer flow passages 42 are bent upward and extend in the vertical direction within the peripheral wall portion 32, and cooling water outlets 42c are formed on the upper surface of the peripheral wall portion 32. The lower layer flow passages 42 within the flat portion 31 are arranged at the same height.

[0027] The width W of the flow path (see FIG. 4) is about 30 mm, and the height H is about 2 mm. The interval D1 between the flow paths (the distance between the adjacent inner and outer flow paths) is about 1 mm. The interval D2 between the upper layer flow path 41 and the lower layer flow path 42 is about 1 mm. The upper layer flow path 41 and the lower layer flow path 42 have the same (constant) cross-sectional area of ​​the flow path.

[0028] The upper layer flow path 41 is located above the lower layer flow path 42, and the upper layer flow path 41 and the lower layer flow path 42 are formed so as to overlap each other.

[0029] Cooling water is introduced into the imaging apparatus from the outside through a path not shown and supplied to the cooling water inlet 41c. As shown in Fig. 6, the cooling water flows through the upper flow path 41 while circulating counterclockwise from the outer periphery to the inner periphery.

[0030] The cooling water flows down the innermost flow path 41a of the upper flow path 41 and enters the lower flow path 42, and then travels around the lower flow path 42 counterclockwise from the inner side to the outer side. The cooling water is discharged to the outside of the imaging apparatus through a path (not shown) connected to the cooling water outlet 42c.

[0031] Since a cooling water flow path is provided inside the flat portion 31 on which the coil 21 is placed, the coil 21 can be cooled efficiently.

[0032] Due to the heated coil 21, the temperature of the cooling water gradually increases as it flows through the cooling water flow path 40. Therefore, the closer the cooling water is to the cooling water inlet 41c, the lower the temperature of the cooling water, and the closer the cooling water is to the cooling water outlet 42c, the higher the temperature of the cooling water. In the coil cooling plate 30 according to this embodiment, the cooling water flows through the upper layer flow path 41 while circulating from the outer periphery to the inner periphery, and then flows through the lower layer flow path 42 provided directly below the upper layer flow path 41 while circulating from the inner periphery to the outer periphery.

[0033] Since the flow path close to the cooling water inlet 41c through which low-temperature cooling water flows is located directly above the flow path close to the cooling water outlet 42c through which high-temperature cooling water flows, the entire flat surface 31 of the coil cooling plate 30 is uniformly heated.

[0034] The upper flow path 41 and the lower flow path 42 are both spirally shaped and smoothly connected without any bends or sudden turns, which reduces pressure loss, increases the flow rate of cooling water, improves the heat transfer coefficient, and enables more efficient heat absorption.

[0035] In order to efficiently equalize the temperature across the entire flat surface 31 of the coil cooling plate 30, it is preferable to increase the overlapping area of ​​the upper flow path 41 and the lower flow path 42; for example, when viewed from above the coil cooling plate 30, it is preferable that 80% or more of the upper flow path 41 overlaps with the lower flow path 42 (covers the lower flow path 42).

[0036] As shown in Figures 7A and 7B, the upper layer flow path 41 and the lower layer flow path 42 have a portion that is an elliptical arc, compared to when the entire flow path is an arc. This increases the overlapping area of ​​the upper layer flow path 41 and the lower layer flow path 42 without creating straight sections or bends in the flow path, making this suitable for uniform heating of the flat portion 31 of the coil cooling plate 30.

[0037] 8 shows the simulation results of the temperature distribution on the underside of the flat portion 31 of the coil cooling plate 30 that cools the coil 21 (heat generating element) when a thermal fluid analysis was performed under the following simulation conditions. In the simulation, it was assumed that 85% of the upper flow path 41 overlapped with the lower flow path 42. ·Fluid name Water (specified temperature) Thermal conductivity: 0.019 [W / m K] ·Flow rate 5[L / min] Heat output of heating element: 45[W]

[0038] The color scale range of the analysis results shown in Fig. 8 is 0.5°C. The simulation confirmed that the temperature distribution (temperature difference between high-temperature and low-temperature areas) on the underside of the flat portion 31 of the coil cooling plate 30 was within approximately 0.4°C, and that the temperature was uniform. By uniformly heating the underside of the flat portion 31 of the coil cooling plate 30, the occurrence of temperature uniformity on the mask substrate 2 can be suppressed.

[0039] According to this embodiment, there is no need to provide a multiple heat shield structure between the coil cooling plate 30 and the mask substrate 2 as in the conventional configuration, which makes it possible to reduce the number of parts, save space, and reduce costs.

[0040] The coil cooling plate 30 can be manufactured by metal additive manufacturing, and is preferably made of a stainless steel alloy. Compared to copper, which is known to have high thermal conductivity, stainless steel has low thermal conductivity but high corrosion resistance, can be used for a long time, and is easy to manufacture. Furthermore, as described above, the coil cooling plate 30 can have a cooling water flow path located directly below the coil 21, so the coil 21 can be sufficiently cooled even when manufactured from stainless steel (or another metal with low thermal conductivity but high corrosion resistance).

[0041] The positions of the cooling water inlet 41c and the cooling water outlet 42c are not limited to the top surface of the peripheral wall portion 32, but may be formed on the side surface or bottom surface of the peripheral wall portion 32.

[0042] A cooling water flow path may also be formed within the peripheral wall portion 32 of the coil cooling plate 30 .

[0043] The coil cooling plate 30 may be configured without the peripheral wall portion 32. In this case, the cooling water inlet and the cooling water outlet may be formed on the outer peripheral surface of the annular flat portion 31.

[0044] A cooling water outlet may be provided at the end of the outermost flow path of the upper layer flow path 41, and a cooling water inlet may be provided at the end of the outermost flow path of the lower layer flow path 42, but it is preferable to provide the cooling water inlet in the upper layer flow path 41 closer to the coil 21 to be cooled.

[0045] The number of turns of the spiral upper flow passage 41 and the spiral lower flow passage 42 is not particularly limited, and may be determined based on the size of the flat portion 31, the width and height of the flow passage, the flow rate of the refrigerant, the amount of heat generated by the object to be cooled, and the like.

[0046] In the above embodiment, a two-layer structure cooling water flow path 40 including a spiral upper layer flow path 41 and a spiral lower layer flow path 42 has been described. However, as shown in FIG. 9, the cooling water flow path 40 may have a stacked structure of 2×n layers (n is an integer of 1 or more).

[0047] For example, if the cooling water flow path has a four-layer structure (n=2), a cooling water inlet is provided at the outermost peripheral part of the flow path in the first layer (top layer). The innermost peripheral part of the flow path in the first layer is inclined to gradually decrease in height and is connected to the innermost peripheral part of the flow path in the second layer. The outermost peripheral part of the flow path in the second layer is inclined to gradually decrease in height and is connected to the outermost peripheral part of the flow path in the third layer. The innermost peripheral part of the flow path in the third layer is inclined to gradually decrease in height and is connected to the innermost peripheral part of the flow path in the fourth layer (bottom layer). A cooling water outlet is provided at the outermost peripheral part of the flow path in the fourth layer.

[0048] Cooling water channels with a 2×n layer stack structure may be provided in m stages (m is an integer of 2 or greater). In this case, a cooling water inlet and a cooling water outlet are provided in each stage. For example, a cooling plate with two stages of four-layer cooling water channels has eight layers (=4 layers×2) of channels. A cooling water inlet is provided at the outermost periphery of the channel in the first layer. A cooling water outlet is provided at the outermost periphery of the channel in the fourth layer. The channel in the fourth layer is not connected to the channel in the fifth layer. A cooling water inlet is provided at the outermost periphery of the channel in the fifth layer. A cooling water outlet is provided at the outermost periphery of the channel in the eighth layer. By arranging four-layer channels in two stages in parallel, the pressure loss of the cooling water can be reduced compared to when eight-layer channels are connected in series. The number of channel layers of the cooling water channels in each stage may be the same or different.

[0049] The cooling water flow path 40 may have a laminated structure of 2×n+1 layers (n is an integer equal to or greater than 1), i.e., an odd number of layers equal to or greater than 3. When the cooling water flow path has a three-layer structure (n=1), a cooling water inlet is provided at the outermost peripheral portion of the flow path in the first layer (top layer). The innermost peripheral portion of the flow path in the first layer is gradually inclined downward and is connected to the innermost peripheral portion of the flow path in the second layer. The outermost peripheral portion of the flow path in the second layer is gradually inclined downward and is connected to the outermost peripheral portion of the flow path in the third layer. The innermost peripheral portion of the flow path in the third layer is shaped to extend from the bottom tangentially in a straight line or a smooth arc toward the cooling water outlet.

[0050] Cooling water flow paths having a laminated structure of 2×n+1 layers may be provided in m stages (m is an integer of 2 or more). A cooling water inlet and a cooling water outlet are provided in each stage. The number of flow path layers of the cooling water flow paths in each stage may be the same or different. The cooling water flow paths may include stages with an even number of flow path layers and stages with an odd number (3 or more).

[0051] Although the above embodiment has been described as a single-beam drawing apparatus, the drawing apparatus may be a multi-beam drawing apparatus.

[0052] In the above embodiment, a configuration for cooling the coil of the objective lens of a drawing device was described, but the cooling plate is not particularly limited to a specific object, and can be applied to various heat-generating components for which the impact on the temperature distribution of surrounding components needs to be suppressed.

[0053] If there is a surface above the heating element that needs to be uniformly heated, a cooling plate can be installed on the upper surface of the heating element. In this case, cooling water is supplied to the cooling plate from the outermost part of the cooling water flow path on the surface where the heating element is located.

[0054] The refrigerant flowing through the cooling water flow path 40 (refrigerant flow path) is not limited to water, and an aqueous solution produced by adding some substance to water to prevent deterioration of device components and raise the boiling point can be used. Fluorine-based refrigerants such as HFE (hydrofluoroether), FC (Fluorinert), and HFPE (H-Galden) can also be used.

[0055] The flat portion 31 may be configured in a cone shape that is inclined so that the level decreases toward the inner periphery. In this case, the upper layer flow path 41 has a spiral shape that is inclined so that the level decreases gradually from the cooling water inlet. On the other hand, the lower layer flow path 42 has a spiral shape that is inclined so that the level increases gradually from the connection point with the upper layer flow path 41 toward the cooling water outlet. The upper layer flow path 41 and the lower layer flow path 42 are inclined so that the level decreases toward the inner periphery.

[0056] The present invention is not limited to the above-described embodiments, and the components can be modified and embodied in practice without departing from the spirit of the invention. Furthermore, various inventions can be created by appropriately combining multiple components disclosed in the above-described embodiments. For example, some components may be omitted from all the components shown in the embodiments. Furthermore, components from different embodiments may be appropriately combined. [Explanation of symbols]

[0057] 2 Mask substrate 20 Objective Lens 21 Coil 30 Coil cooling plate 40 Cooling water flow path

Claims

1. A cooling plate having an annular planar portion, a first spiral refrigerant flow path and a second spiral refrigerant flow path located below the first refrigerant flow path are formed on the flat surface portion so as to overlap each other, a cooling plate in which an inner peripheral flow path of the first refrigerant flow path is inclined so as to gradually lower, and is connected to an inner peripheral flow path of the second refrigerant flow path;

2. The cooling plate according to claim 1 , wherein an inner peripheral flow path of the first refrigerant flow path is arranged to overlap a flow path of the second refrigerant flow path.

3. The cooling plate according to claim 1 , wherein a circulating direction of the coolant in the first coolant flow channel is the same as a circulating direction of the coolant in the second coolant flow channel.

4. a plurality of spiral-shaped coolant flow paths are formed on the flat surface, The cooling plate according to claim 1 , wherein an innermost or outermost flow path of each refrigerant flow path is connected to an upper or lower refrigerant flow path.

5. The flat surface portion has a plurality of spiral refrigerant flow paths formed in multiple stages, In each stage, the innermost or outermost circumferential flow path of each refrigerant flow path is connected to the refrigerant flow path on the upper or lower layer side, 2. The cold plate of claim 1, wherein a coolant inlet and an outlet are provided at each stage.

6. The cooling plate according to claim 1 , wherein the coolant flows from the outer periphery toward the inner periphery through a coolant flow path on the surface on which the heat generating element to be cooled is disposed.

7. a drawing chamber in which a stage for placing a substrate to be drawn is installed; an electron optical column connected to the writing chamber and including an emitter for emitting a charged particle beam, a deflector for deflecting the charged particle beam, and an objective lens for focusing the charged particle beam on the substrate; Equipped with the objective lens is an electromagnetic lens having a coil and a yoke inside which the coil is disposed, 7. A charged particle beam drawing apparatus, wherein the cooling plate according to claim 1 is provided in the yoke for cooling the coil.

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