Charged particle beam lithography apparatus and charged particle beam lithography method

Abstract

To prevent deterioration in beam position accuracy while operating a focus correction electrostatic lens with a positive bias.SOLUTION: A charged particle beam lithography device includes: an emitter that emits a charged particle beam; a first aperture that shapes the charged particle beam; an illumination lens that illuminates the first aperture with the charged particle beam; a second aperture that shapes the charged particle beam that has passed through the first aperture; a projection lens that projects the charged particle beam transmitted through the first aperture onto the second aperture; an objective lens that is a magnetic field type lens that focuses the charged particle beam transmitted through the second aperture; and an electrostatic lens that corrects the focus of the charged particle beam according to the surface height of a substrate to be drawn. The electrostatic lens is disposed within the objective lens, a positive voltage is applied to an electrode of the electrostatic lens, and the strength of the magnetic field of the objective lens at the upper end of the electrode is equal to or less than a predetermined value.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a charged particle beam drawing apparatus and a charged particle beam drawing method. [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] In electron beam lithography systems, the beam for each shot is focused onto the sample surface using an objective lens, and an electrostatic lens is used to dynamically correct the focus (dynamic focus) during lithography to accommodate unevenness on the sample surface. If the bias voltage applied to this electrostatic lens is negative, the number of fogging electrons increases, hindering improvements in the dimensional accuracy of the lithography pattern.

[0004] To suppress the effects of fogging electrons, it is preferable to apply a positive bias voltage to the electrostatic lens. However, when a positive bias voltage is applied to the electrostatic lens, secondary electrons (including backscattered electrons) from the sample surface are densely trapped on the beam trajectory, which can change the electron beam trajectory and degrade the beam position accuracy. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2000-113846 [Patent Document 2] Japanese Patent Application Laid-Open No. 2015-109323 [Patent Document 3] Japanese Patent Application Laid-Open No. 2001-93831 [Patent Document 4] Japanese Patent Application Laid-Open No. 2013-191841 [Patent Document 5] Japanese Patent Application Laid-Open No. 2013-168589 Summary of the Invention [Problem to be solved by the invention]

[0006] The present invention has been made in consideration of the above-described conventional situation, and an object of the present invention is to provide a charged particle beam drawing apparatus and a charged particle beam drawing method that prevent deterioration of beam position accuracy while operating a focus correction electrostatic lens with a positive bias. [Means for solving the problem]

[0007] A charged particle beam drawing apparatus according to one embodiment of the present invention comprises an emission unit that emits a charged particle beam, a first aperture that shapes the charged particle beam, an illumination lens that illuminates the charged particle beam onto the first aperture, a second aperture that shapes the charged particle beam that has passed through the first aperture, a projection lens that projects the charged particle beam that has passed through the first aperture onto the second aperture, an objective lens that is a magnetic lens that focuses the charged particle beam that has passed through the second aperture, and an electrostatic lens that corrects the focus of the charged particle beam to match the surface height of a substrate to be drawn, wherein the electrostatic lens is disposed within the objective lens, a positive voltage is applied to an electrode of the electrostatic lens, and the strength of the magnetic field of the objective lens at the upper end of the electrode is equal to or less than a predetermined value.

[0008] In the charged particle beam drawing apparatus according to one aspect of the present invention, at least a part of the electrode extends into a region where the strength of the magnetic field of the objective lens becomes greater than the predetermined value.

[0009] In the charged particle beam drawing apparatus according to one aspect of the present invention, the strength of the magnetic field of the objective lens at the lower end of the electrode is equal to or less than the predetermined value.

[0010] In one embodiment of the charged particle beam drawing apparatus of the present invention, the electrostatic lens has three stages of electrodes: an upper stage electrode, a middle stage electrode, and a lower stage electrode, and a voltage of 0 V is applied to the upper stage electrode and the lower stage electrode, and the positive voltage is applied to the middle stage electrode.

[0011] A charged particle beam writing method according to one aspect of the present invention comprises the steps of: emitting a charged particle beam; using an objective lens, which is a magnetic field lens, to focus the charged particle beam and irradiate the charged particle beam onto a substrate to be written to form a pattern; and using an electrostatic lens arranged within the objective lens to correct the focus of the charged particle beam to match the surface height of the substrate, wherein a positive voltage is applied to an electrode of the electrostatic lens and a current is supplied to a coil of the objective lens so that the strength of the magnetic field of the objective lens at the upper end of the electrode is equal to or less than a predetermined value. [Effects of the Invention]

[0012] According to the present invention, it is possible to prevent deterioration of beam position accuracy while operating a focus correction electrostatic lens with a positive bias. [Brief explanation of the drawings]

[0013] [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 perspective view of a first shaping aperture and a second shaping aperture. [Figure 3] 1 is a cross-sectional view of an objective lens and a focus correction electrostatic lens. [Figure 4] 10A and 10B are diagrams illustrating the magnetic field distribution of the objective lens and the position of the focus correction electrostatic lens. [Figure 5] FIG. 10 is a diagram illustrating a method for calculating a beam position deviation amount. [Figure 6] 10 is a graph showing the relationship between the strength of the magnetic field at the tip of the electrode of the focus correction electrostatic lens and the amount of beam position deviation. DETAILED DESCRIPTION OF THE INVENTION

[0014] Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

[0015] 1 is a schematic diagram of an electron beam lithography apparatus according to an embodiment of the present invention, which is a variable-shaping type lithography apparatus including a control unit 100 and a lithography unit 200.

[0016] The drawing unit 200 includes an electron lens barrel 220 and a drawing chamber 230. Inside the electron lens barrel 220, an electron gun 201, an illumination lens 202, a blanker 203, a first shaping aperture 204, a projection lens 205, a shaping deflector 206, a second shaping aperture 207, an objective lens 208, a deflector 209, and a focus correction lens 210 are arranged.

[0017] An XY stage 211 is disposed in the pattern writing chamber 230. A substrate 240 to be patterned is placed on the XY stage 211. A Z sensor 250 that detects the position of the substrate 240 in the height direction (Z direction) is disposed above the pattern writing chamber 230. The Z sensor 250 is composed of a combination of a light projector and a light receiver, and can measure the surface height of the substrate 240 by reflecting light emitted from the light projector on the surface of the substrate 240 and receiving this reflected light with the light receiver.

[0018] The height data detected by the Z sensor 250 is converted into digital data by the detection circuit 150 and then transferred to the control computer 110 .

[0019] When an electron beam B emitted from an electron gun 201 (emission unit) provided in an electron lens barrel 220 passes through a blanker (blanking deflector) 203, the blanker 203 switches whether or not the electron beam is irradiated onto a substrate.

[0020] The electron beam B is irradiated onto the entire first shaping aperture 204 having a rectangular opening 32 (see FIG. 2) by the illumination lens 202. By passing through the opening 32 of the first shaping aperture 204, the electron beam B is shaped into a rectangle.

[0021] The electron beam B of the first aperture image that has passed through the first shaping aperture 204 is projected onto the second shaping aperture 207 having the variable shaping aperture 34 (see FIG. 2) by the projection lens 205. At this time, the deflection of the first aperture image projected onto the second shaping aperture 207 is controlled by the deflector 206, and the shape and dimensions of the electron beam that passes through the variable shaping aperture 34 can be changed (variable shaping can be performed).

[0022] The electron beam B of the second aperture image that passes through the variable shaping opening 34 of the second shaping aperture 207 is focused by the objective lens 208 and the focus correction lens 210, deflected by the deflector 209, and irradiated onto the substrate 240 placed on the continuously moving XY stage 211.

[0023] The deflector 209 is composed of multiple stages of deflectors with different sizes of deflection areas. For example, it may be a two-stage configuration of a main deflector and a sub-deflector, or a three-stage configuration of a main deflector, a sub-deflector, and a sub-sub-deflector.

[0024] Electromagnetic lenses (magnetic lenses) are used for the illumination lens 202, the projection lens 205, and the objective lens 208. The focus correction lens 210 performs dynamic focus adjustment in response to height variations on the surface of the substrate 240, and an electrostatic lens is used for this lens.

[0025] 2 is a schematic diagram for explaining beam shaping by the first shaping aperture 204 and the second shaping aperture 207. The first shaping aperture 204 has a rectangular opening 32 formed therein for shaping the electron beam B.

[0026] In addition, second shaping aperture 207 is formed with variable shaping aperture 34 for shaping electron beam B, which has passed through aperture 32 of first shaping aperture 204, into a desired shape. The beam shape that has passed through both aperture 32 of first shaping aperture 204 and variable shaping aperture 34 of second shaping aperture 207 is written in a writing area of substrate 240 that is mounted on XY stage 211, which moves continuously.

[0027] 1, the control unit 100 includes a control computer 110, a deflection control circuit 120, a memory unit 130, a lens control circuit 140, and a detection circuit 150. Drawing data that serves as layout data is input from the outside and stored in the memory unit 130.

[0028] The control computer 110 has a shot data generation unit 111 and a writing control unit 112. Each unit of the control computer 110 may be configured with hardware such as an electric circuit, or may be configured with software. When configured with software, a program that realizes at least some of the functions of the control computer 110 may be stored in a recording medium and read and executed by a computer including an electric circuit. The recording medium is not limited to removable recording media such as a magnetic disk or optical disk, but may also be fixed recording media such as a hard disk drive or memory.

[0029] The shot data generation unit 111 reads the drawing data from the storage unit 130 and performs multiple stages of data conversion processing to generate shot data. The shot data includes information such as the shot shape, shot size, shot position, and shot time.

[0030] The writing control unit 112 transfers the shot data in shot order to the deflection control circuit 120. The deflection control circuit 120 uses the shot data to control the deflection amounts of the blanker 203, deflector 206, and deflector 209, and performs writing processing.

[0031] The lens control circuit 140 controls each lens provided in the drawing unit 200. For example, the lens control circuit 140 controls the amount of current applied to the coil of the objective lens 208. The lens control circuit 140 also controls the voltage applied to the focus correction lens 210 based on the surface height of the substrate 240 detected by the Z sensor 250.

[0032] Next, we will explain the configurations of the objective lens 208 and the focus correction lens 210. The objective lens 208 is an electromagnetic lens, and has a coil 208a and a yoke 208b that houses the coil 208a, as shown in Fig. 3. The yoke 208b is made of a material with high magnetic permeability, such as iron, and has a notch (pole piece 208c) formed in part of it.

[0033] Magnetic lines of force created by passing a current through coil 208a leak into space via pole piece 208c, creating a magnetic field.

[0034] The focus correction lens 210 is disposed inside the objective lens 208, for example, at the same height as the pole piece 208c. The focus correction lens 210 is an electrostatic lens and has three ring-shaped electrodes 210a, 210b, and 210c. A voltage of 0V is applied to the upper and lower electrodes 210a and 210c, and a positive voltage is applied to the middle electrode 210b, so that the focus correction lens 210 is operated with a positive bias.

[0035] When the electron beam is irradiated onto the substrate 240, secondary electrons (including electrons reflected by the substrate 240) generated by the electron beam entering the substrate 240 travel upward inside the electron column 220. These secondary electrons undergo spiral motion in the magnetic field of the objective lens 208. The orbital radius of the secondary electrons is small in regions where the magnetic field is strong and large in regions where the magnetic field is weak.

[0036] Furthermore, the secondary electrons increase in speed due to the influence of the voltage applied to the electrode 210b when they travel inside the electrode 210b of the focus correction lens 210. When the secondary electrons leave the electrode 210b, they decelerate and their speed decreases.

[0037] Even if the orbital radius of the secondary electrons is small, if the velocity is high, the density of the secondary electrons will be low and the effect on the trajectory of the electron beam output from the electron gun 201 will be small. Also, even if the velocity of the secondary electrons is low, if the orbital radius is large, the density of the secondary electrons will be low and the effect on the trajectory of the electron beam output from the electron gun 201 will be small.

[0038] On the other hand, if the orbital radius of the secondary electrons is small and the velocity is slow, the secondary electron density increases, which may change the trajectory of the electron beam output from the electron gun 201 and degrade the beam position accuracy. In other words, if the magnetic field in the region after passing through the electrode 210b is strong, the beam position accuracy may degrade.

[0039] Therefore, in this embodiment, as shown in Fig. 4, the upper end of electrode 210b of electrostatic lens 210 is configured to be located in a region where the strength of the magnetic field (axial magnetic field) is equal to or less than a predetermined value Bth. As a result, in a region where the magnetic field is strong and the orbital radius of the secondary electrons is small, the speed of the secondary electrons is high and the secondary electron density is low. In a region where the speed of the secondary electrons is slower after passing through electrode 210b, the magnetic field is weak, the orbital radius of the secondary electrons is large, and the secondary electron density is low.

[0040] Since it is possible to prevent the occurrence of areas with high secondary electron density, it is possible to prevent deterioration of the beam position accuracy. In addition, since the focus correction lens 210 is operated with a positive bias, it is possible to suppress the influence of fogging electrons.

[0041] The magnetic field strength Bth is set so that the positional deviation of the beam irradiation position is less than a predetermined value. The positional deviation Δpos of the beam irradiation position can be calculated using the formula shown in Figure 5. In Figure 5, ε0 is the dielectric constant of vacuum, Q is the charge amount of the region, m is the mass of the electron, and v r is the radial velocity of the secondary electrons, v Z is the z-direction velocity of the secondary electrons, L is territory The length of the region, h, is The upper end of the middle electrode 210b is the height from the surface of the substrate 240. Furthermore, kl is the reduction ratio of the objective lens 208, e is the elementary electron quantity, I is the beam current, V0 is the beam energy, η is the reflection efficiency, and Vs is the secondary electron energy. The emission angle of the secondary electrons was set to 45°.

[0042] Figure 6 shows the amount of misalignment calculated from this formula and the experimental values of the amount of misalignment. Figure 6 shows that the trends of the formula and the experimental values are almost the same.

[0043] By estimating the indefinite parameters from experimental values, the positional deviation Δpos can be calculated using the following formula: C is a proportionality constant. Δpos=C×B×I×h / V0

[0044] From this equation, for example, when the proportionality constant C is 100,000, the beam current I is 1 μA, the height h is 10 mm, and the beam energy V0 is 50 keV, it is found that the predetermined value Bth should be less than 0.05 T (tesla) to keep the positional deviation Δpos less than 1 nm. That is, by extending the electrode 210b of the electrostatic lens 210 to a region where the magnetic field strength is less than 0.05 T, the positional deviation of the beam irradiation position can be kept less than 1 nm. In other words, by adjusting the current supplied to the coil of the objective lens 208 so that the magnetic field strength at the upper end position of the electrode 210b of the electrostatic lens 210 is less than 0.05 T, the positional deviation of the beam irradiation position can be kept less than 1 nm.

[0045] In the above embodiment, it is preferable that the lower end of electrode 210b of electrostatic lens 210 is also located in a region where the magnetic field strength is equal to or less than predetermined value Bth. In other words, it is preferable that electrode 210b extends over the entire region where the magnetic field strength is greater than predetermined value Bth. The point where the magnetic field of objective lens 208 is strongest is between the upper and lower ends of electrode 210b.

[0046] In the above embodiment, a configuration using an electron beam has been described as an example of a charged particle beam, but the charged particle beam is not limited to an electron beam, and may be a beam using charged particles such as an ion beam.

[0047] Although the above embodiment has been described as an example of a drawing apparatus, the present invention can also be applied to an inspection apparatus that uses a charged particle beam.

[0048] 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]

[0049] 100 control section 110 Control computer 111 Shot data generation unit 112 Drawing control unit 140 Lens control circuit 150 Detection circuit 208 Objective Lens 210 Electrostatic Lens 250 Z sensor

Claims

1. an emission section that emits a charged particle beam; a first aperture for shaping the charged particle beam; an illumination lens for illuminating the charged particle beam onto the first aperture; a second aperture for shaping the charged particle beam transmitted through the first aperture; a projection lens that projects the charged particle beam that has passed through the first aperture onto the second aperture; an objective lens, which is a magnetic lens that focuses the charged particle beam that has passed through the second aperture; an electrostatic lens that corrects the focus of the charged particle beam in accordance with the surface height of the substrate to be drawn; Equipped with the electrostatic lens is disposed within the objective lens, a positive voltage is applied to an electrode of the electrostatic lens, and a portion of the objective lens where the magnetic field strength has a peak value is located below an upper end of the electrode; A charged particle beam lithography device that controls the strength of the magnetic field of the objective lens at the upper end of the electrode so that the amount of positional deviation of the beam irradiation position on the surface of the substrate, which is calculated using a calculation formula obtained from the relationship between the magnetic field strength of the objective lens at the upper end of the electrode, the beam current value of the charged particle beam, the beam energy, and the height of the upper end of the electrode from the surface of the substrate, which is determined in advance, is 1 nm or less.

2. a lens control circuit that controls the amount of current applied to the coil of the objective lens; 2. The charged particle beam lithography apparatus according to claim 1, wherein the lens control circuit controls the amount of current applied to the coil so that a magnetic field strength B of the objective lens at the upper end of the electrode becomes a value that satisfies the following equation, which includes an allowable upper limit Δpos of a positional deviation amount of the beam irradiation position on the surface of the substrate, a proportionality constant C that is experimentally determined in advance, a beam current I of the charged particle beam, a beam energy V0, and a height h of the upper end of the electrode from the surface of the substrate: Δpos=C×B×I×h / V0

3. the electrostatic lens has three stages of electrodes: an upper stage electrode, a middle stage electrode, and a lower stage electrode; 3. The charged particle beam drawing apparatus according to claim 1, wherein a voltage of 0 V is applied to the upper electrode and the lower electrode, and the positive voltage is applied to the middle electrode.

4. emitting a charged particle beam; a step of focusing the charged particle beam using an objective lens that is a magnetic lens and irradiating the charged particle beam onto a substrate to be written to form a pattern; correcting the focus of the charged particle beam in accordance with the surface height of the substrate using an electrostatic lens disposed within the objective lens; Equipped with Applying a positive voltage to the electrodes of the electrostatic lens; Controlling the portion of the objective lens having a peak value of magnetic field strength to be below the upper end of the electrode; A charged particle beam lithography method, comprising: controlling the strength of the magnetic field of the objective lens at the upper end of the electrode so that the amount of positional deviation of the beam irradiation position on the surface of the substrate, which is calculated using a calculation formula obtained from the relationship between the magnetic field strength of the objective lens at the upper end of the electrode, the beam current value of the charged particle beam, the beam energy, and the height of the upper end of the electrode from the surface of the substrate, which is calculated in advance, is 1 nm or less.

5. 5. The charged particle beam lithography method according to claim 4, wherein the amount of current applied to a coil of the objective lens is controlled so that a magnetic field strength B of the objective lens at the upper end of the electrode becomes a value that satisfies the following formula, which includes an allowable upper limit Δpos of a positional deviation amount of the beam irradiation position on the surface of the substrate, a proportionality constant C that is experimentally determined in advance, a beam current I of the charged particle beam, a beam energy V0, and a height h of the upper end of the electrode from the surface of the substrate: Δpos=C×B×I×h / V0

Images