Projection exposure apparatus for semiconductor lithography

Abstract

The invention relates to a projection exposure apparatus (1) for semiconductor lithography, comprising an optical correction element (20) and a means for at least partially irradiating an optically active region (22) of the correction element (20) by electromagnetic heating radiation (44.x), wherein the optical correction element (20) is equipped outside the optically active region (22) with at least one electrical heating element (25.x).

Description

[0001] This application claims priority to German patent application DE 10 2019 217 185.0, filed on 7 November 2019, the contents of which are incorporated herein by reference in their entirety. Technical Field

[0002] This invention relates to projection exposure equipment for semiconductor photolithography. Background Technology

[0003] Such equipment is used to fabricate extremely fine structures, particularly on semiconductor components or other microstructured parts. The operating principle of the equipment is based on the following: extremely fine structures, down to the nanometer scale, are fabricated by imaging the structure on a mask (so-called a master mask) onto the element to be structured (so-called a wafer) equipped with a photosensitive material. The minimum size of the fabricated structure depends directly on the wavelength of the light used. Recently, light sources with emission wavelengths in the range of several nanometers, for example, between 1 nm and 30 nm, particularly in the 13.5 nm region, have been increasingly used. This described wavelength range is also known as the EUV range.

[0004] In addition to using these systems, commercially established systems with wavelengths of 193 nm are also used to fabricate microstructured components. The introduction of the EUV range and the resulting possibility of fabricating even smaller structures has led to an increased demand for optical correction of systems with wavelengths of 193 nm. Simultaneously, increasing throughput to improve economic viability typically results in greater thermal loads, thus increasing thermally induced imaging aberrations.

[0005] To correct imaging aberrations, a manipulator comprising two parallel planes can be used, the surfaces of which are heated by electromagnetic heating radiation and cooled uniformly by an airflow passing between the parallel planes. The resulting locally tunable temperature distribution on the plates is converted into the desired wavefront effect to compensate for imaging aberrations by the temperature-dependent refractive index of the material used (e.g., quartz glass).

[0006] International patent application WO 2010 / 133231 A1, filed by the applicant and fully incorporated herein by reference, discloses a manipulator having two parallel planar plates with a cooling channel between them through which fluid, acting as a global radiator (i.e., for heat dissipation), flows. Local heating of the plates is caused by infrared irradiation, with the beam either incident on the surface of the cooling channel or on the plates, on opposite outer surfaces. The plates are locally heated by absorbing the beam. A disadvantage is that, particularly in the edge regions of the plates, irradiation can only occur at very small angles, leading to poor absorption and therefore insufficient heating in the edge regions. Summary of the Invention

[0007] The object of this invention is to provide a device that overcomes the aforementioned shortcomings of the prior art.

[0008] This objective is achieved by means of a device having the features of the independent claims. The dependent claims relate to advantageous developments and variations of the invention.

[0009] The projection exposure apparatus for semiconductor lithography according to the invention includes an optical correction element and a component that at least partially irradiates an optically active region of the correction element by electromagnetic heating radiation, wherein, according to the invention, the optical correction element is equipped with at least one electrically heated element outside the optically active region. The optical correction component can, for example, be arranged in the imaging optics unit of the projection exposure apparatus to correct imaging aberrations. For example, the component can be a laser, wherein the laser can be guided via an optical waveguide and thus can generate irradiation at one or more locations on the optical correction element. In this case, electromagnetic heating radiation can irradiate the optical correction element from one of its side surfaces (i.e., perpendicular to its optical axis) or onto one of the optically active surfaces of the optical correction element. The radiation can be at least partially absorbed by the material of the optical correction element, resulting in heating of the material. In this context, the optically active region should be understood as the area of ​​the optical correction element irradiated by the light used (i.e., the light used to image the structure of the mask master onto the wafer) during operation of the projection exposure apparatus. The optically active region can vary depending on the operating mode, with its maximum range defined by the optical design of the projection exposure apparatus.

[0010] In particular, the electric heating element can be exclusively arranged outside the optically active region, and no electric heating element is located in the optically active region.

[0011] The electric heating element may include a resistance wire, wherein the thickness of the resistance wire may be at least 1 μm, preferably at least 5 μm, and particularly preferably at least 10 μm. Because the resistance wire is arranged outside the optically active region, the thickness and height of the wire have no effect on optical imaging and can preferably be designed based on their effectiveness, electrical properties, and manufacturability.

[0012] Furthermore, the electric heating element can be arranged on the surface of the optical element. This has the advantage that the electric heating element does not obstruct the irradiation of the optically active region through the side surface of the optical correction element.

[0013] Furthermore, multiple electric heating elements can be arranged on the optical correction element, allowing for locally varying power densities of heating power. This enables the heating power of the electric heating elements to be adjusted based on the irradiation of the optical correction element by the laser and the heating caused by the light used, thus achieving a predetermined temperature profile within the optical correction element.

[0014] In particular, multiple heating elements can have different electrical properties. In the case of resistance wires, the latter can focus on the resistance of the wire, which is in turn affected by the diameter of the wire, the material of the wire, or the geometric length per unit area of ​​the wire. For example, the length per unit area can be increased by a zigzag arrangement and small distances between the zigzags of the resistance wire.

[0015] Furthermore, there can be open-loop / closed-loop control suitable for controlling multiple heating elements, which enables the achievement of locally different power densities for heating power.

[0016] Specifically, at least one temperature sensor can be present to detect the temperature of the optical correction element. Therefore, the required electrical heating power can be determined based on the detected temperature. Using multiple temperature sensors can advantageously improve the accuracy and speed of correction.

[0017] In one variant of the invention, the optical correction element may include at least one planar parallel plate. The planar parallel plate itself has no optical effects other than image shift in the case of tilted radiation transmission, and therefore exhibits neutral behavior in the case of uniform temperature distribution and vertical radiation transmission in the optical system.

[0018] Specifically, the optical correction element may comprise two planar parallel plates, with a fluid channel implemented between them. As an example, air can flow through the fluid channel, the temperature of which is advantageously lower than that of the optical correction element, thus the fluid can act as a heat sink. Therefore, some of the heat generated in the planar parallel plates due to irradiation by the light used, laser, and heating by electrically heated elements in the edge regions can be dissipated, and a temperature profile can be established while maintaining thermodynamic equilibrium within the plates. The two planar parallel plates can thus have an additional temperature profile, without heat being emitted to the imaging apparatus of the projection exposure device during the process.

[0019] In this case, the planar parallel plates can be arranged parallel to each other at a distance between 2 mm and 50 mm. This distance can depend in particular on the amount of fluid required for heat dissipation, or, if both planar parallel plates include electric heating elements, on their optical effects.

[0020] At least one planar parallel plate can have a thickness between 2 mm and 20 mm. The thickness can also depend on its optical effect, manufacturing requirements, mechanical stiffness, heat capacity, and the required correction effect of the optical correction element as a whole.

[0021] Furthermore, the material of the planar parallel plates and the wavelength of irradiation can be configured such that the average absorption rate of the achievable irradiation over the optically active region is at least 10 W, preferably at least 50 W, and particularly preferably at least 100 W. The absorption in the optically active region and thus the supplied heat can be increased depending on the cooling capacity of the fluid flowing between the planar parallel plates. The optical correction element is advantageously configured to have a thermally neutral effect relative to the interface of the imaging optical unit, meaning that the power supplied by the irradiation and electric heating elements does not exceed the power dissipated through fluid flow and the mechanical connection of the planar parallel plates. In this case, the heating power used to generate the temperature profile in the planar parallel plates can be independent of the thermally neutral power balance.

[0022] Specifically, the material of the planar parallel plate and the wavelength of the electromagnetic heating radiation can be configured such that the absorptivity is between 10% and 20% of the incident power per 100 mm of material. Therefore, absorption and thus heating of the entire optical element can be achieved at a maximum incident power of 100 watts, preferably 60 watts. The shaping of the electromagnetic heating radiation and the variation in the material's absorption properties allow for a constant power input with distance.

[0023] In addition, an electrical connecting strip may be provided for contacting the electric heating elements, and it may extend at least partially parallel to the fluid channel. The connecting strip connects the power source to the individual electric heating elements, which are preferably all connected to one side of the optical correction element to simplify accessibility and installation.

[0024] Furthermore, at least two, preferably all, electric heating elements can be connected to a common ground wire. This has the advantage of not requiring a dedicated ground wire for each electric heating element. Attached Figure Description

[0025] Exemplary embodiments and variations of the invention are explained in more detail below with reference to the accompanying drawings, in which:

[0026] Figure 1 The basic structure of a projection exposure apparatus to which the present invention can be applied is shown.

[0027] Figure 2 The basic details of the invention are shown in the diagram. Detailed Implementation

[0028] Figure 1An exemplary projection exposure apparatus to which the present invention can be applied is illustrated. The projection exposure apparatus 1 is used to image a structure on a substrate coated with a photosensitive material and typically made primarily of silicon, referred to as a wafer 2, for manufacturing semiconductor components such as computer chips. In this case, the projection exposure apparatus 1 generally includes an illumination device 3, a mask stage 4 for receiving and accurately positioning a mask equipped with the structure—a so-called mask master 5 (which determines the subsequent structure on the wafer 2), a wafer stage 6 for holding, moving, and accurately positioning the wafer 2, and an imaging device specifically having a projection lens 7 with a plurality of optical elements 8 held in the lens housing 10 of the projection lens 7 by means of mounting elements 9. The basic working principle in this case is to project an image of the structure introduced into the mask master 5 onto the wafer 2; the imaging is typically scaled down. The illumination device 3 provides a projection beam 11 in the form of electromagnetic radiation, which is required to image the mask master 5 onto the wafer 2. Lasers, plasma sources, etc., can be used as the source of this radiation. The optical elements in the illumination device 3 are used to shape the radiation so that when radiation is incident on the mask master 5, the projected beam 11 has desired properties regarding diameter, polarization, etc. An image of the mask master 5 is generated by the projected beam 11 and transferred from the projection lens 7 to the wafer 2 in a suitably reduced form, as explained above. In this case, the mask master 5 and the wafer 2 can move synchronously, such that during the so-called scanning operation, images of regions of the mask master 5 are projected onto corresponding regions of the wafer 2 virtually continuously. The projection lens 7 has multiple individual refractive, diffractive, and / or reflective optical elements 8, such as lens elements, mirrors, prisms, end plates, etc., which can be supplemented or replaced by, for example, the optical correction device 20 according to the invention.

[0029] The present invention can also be used in EUV equipment, which is not shown. The EUV equipment is configured in principle similar to the DUV equipment 1 described above, wherein the main reflector in the EUV equipment can be used as an optical element, and the light source of the EUV equipment emits radiation in the wavelength range of 5 nm to 100 nm, particularly 13.5 nm. In the case of the present invention used in an EUV equipment, the reflector is then heated outside its optically active region by an electrically heated element.

[0030] Figure 2 Detailed illustrations of the invention are shown, illustrating a device implemented as a thermal manipulator 20 in a plan view. The manipulator 20 includes optical elements implemented as two planar parallel plates 21.x. Figure 2The diagram only shows the lower portion 21.1 of two planar parallel plates 21.x that are functionally identical. The diagram shows a planar view of the surface 24 of the planar parallel plate 21.1 from above along the direction of the light used. The planar parallel plate 21.1 includes an optically active region 22, which is irradiated by radiation (not shown) used by the projection exposure apparatus. Furthermore, the optically active region 22 is irradiated by electromagnetic heating radiation implemented as a laser beam 44.x, which is coupled into the planar parallel plate 21.1 through its side surface 32.x. The laser beam 44.x is emitted by one or more lasers (not shown) and guided via an optical waveguide 41.x to an input coupling point 42.x at the side surface 32.x of the planar parallel plate 21.1. For example, an input coupling optical unit 43.x, implemented as a spherical lens element, is arranged at the input coupling point 42.x and shapes the laser beam 44.x, coupling it perpendicularly to the radiation used into the planar parallel plate 21.1. The planar parallel plate 21.1 is heated by absorption in its material. To enable localized heating, multiple laser beams 44.x are oriented such that they meet at an intersection 45.x in the optically active region 22 of the planar parallel plate 21.1, where the power density is doubled due to the absorption of the two laser beams 44.1 and 44.2. For clear reasons, Figure 2 Only the two laser beams 44.1 and 44.2 intersecting at intersection point 45 are illustrated. After the beams have passed through the planar parallel plate 21.1, they are absorbed by a light trap (not shown), and heat is dissipated so that excess energy does not heat other optical elements or other components, such as the mounting of the projection exposure device. The input coupling points 42.x can be arranged on all four sides of the planar parallel plate 21.x, in which case up to 200 laser beams can be coupled on each side, resulting in nearly 800 adjustable degrees of freedom for correcting imaging aberrations.

[0031] Compared to the optically active region 22, the region outside the optically active region 22—also referred to as the edge region 23—is heated by electric heating elements 25.x. Heating elements 25.x are arranged on the surface 24 of the lower planar parallel plate 21.1 and each includes a supply line 27.x, a heating structure 26.x, and a lead line 28.x. In the illustrated example, all leads 28.x of the heating elements 25.x are connected to a common ground line 29. In this case, the supply line 27.x is implemented with the resistance as low as possible to minimize undesirable heating in the region of the supply line 27.x. The same applies to the lead line 28.x and the ground line 29. The heating structure 26.x is arranged in the region requiring heating by the heating elements 25.x, distinguished by the increased resistance due to its small cross-section and / or different materials, and arranged in a tortuous form in specific regions on the surface 24 of the planar parallel plate 21.1. Therefore, the power density in the region of heating structure 26.x is several times higher than the power density in the regions of supply line 27.x, lead line 28.x, and ground line 29. Supply lines 27.x all originate from connecting strip 30, which is arranged in... Figure 2 On the right-hand side of the middle plane parallel plate 21.1. A fluid channel is formed between the lower plane parallel plate 21.1 and the upper plane parallel plate 21.2 (not shown), through which air flows as a cooling medium. The cooling airflow 31... Figure 2 The middle section is indicated by three arrows. For clarity, the side components of the cooling channel are not shown. Figure 2 The diagram shows a cooling medium that acts as a heat sink, further dissipating the power introduced by the laser beam 44.x and the electric heating element 25.x. This results in a thermally neutral effect relative to other optical elements in the projection optics unit, producing a temperature distribution only within the planar parallel plate. This temperature distribution generates a predetermined correction effect through the temperature dependence of the refractive index. In the illustrated example, the planar parallel plate 21.1 also includes four temperature sensors 33.x, which are arranged outside the optically active region 22 and... Figure 2 The diagram is only schematically illustrated by circles. Based on the values ​​detected by temperature sensor 33.x, the temperature distribution in the plate can be determined by open-loop or closed-loop control (not shown). This temperature distribution is used to determine the power introduced by electromagnetic heating radiation 44.x and electric heating element 25.x. The determined power is then passed to the open-loop or closed-loop control of the heating element and the laser, thus establishing a predetermined temperature distribution in the planar parallel plate 21.x.

[0032] List of reference numerals

[0033] 1. Projection Exposure Equipment

[0034] 2 chips

[0035] 3 lighting fixtures

[0036] 4. Mask Master Stage

[0037] 5. Mask Master

[0038] 6 chip stations

[0039] 7. Projection Lens

[0040] 8 Optical Components

[0041] 9 Installation components

[0042] 10 Lens housing

[0043] 11 Projection Beam

[0044] 20. Thermal control device

[0045] 21. Planar parallel plate (optical element)

[0046] 22 Optically active regions

[0047] 23 Edge Area

[0048] 24 Surface

[0049] 25.x Heating element

[0050] 26.x Heating Structure

[0051] 27.x Supply Line

[0052] 28.x Lead-out line

[0053] 29 Ground wire

[0054] 30 connecting strip

[0055] 31 Cooling airflow

[0056] 32.1-32.2 Side View

[0057] 33.1-33.4 Temperature Sensor

[0058] 41.1-41.10 Optical waveguides

[0059] 42.1-42.10 Input coupling points

[0060] 43.1-43.10 Input coupling optical unit

[0061] 44.1, 44.2 Laser beam (electromagnetic heating radiation)

[0062] 45 Intersection

Claims

1. A projection exposure apparatus (1) for semiconductor photolithography, comprising an optical correction element (20) and a component for at least partially irradiating an optically active region (22) of the correction element (20) by electromagnetic heating radiation (44.x), in, The optical correction element (20) is equipped with at least one electrically heated element (25.x) outside the optically active region (22). Multiple electric heating elements (25.x) are arranged on the optical correction element (20) to achieve locally different power densities of heating power, and The heating power of the electric heating element can be adjusted depending on the irradiation of the optical correction component by the laser and the heating caused by the light used. The optical correction element (20) includes at least one planar parallel plate (21.x), and a laser beam emitted by the laser is guided to the side surface of the planar parallel plate. The electric heating element (25.x) is arranged on the surface (24) of the planar parallel plate.

2. The projection exposure device (1) according to claim 1, in, The electric heating element (25.x) is exclusively arranged outside the optically active region (22) and no electric heating element (25.x) is located in the optically active region (22).

3. The projection exposure device (1) according to claim 1 or 2, in, The electric heating element (25.x) includes resistance wires (26.x, 27.x, 28.x).

4. The projection exposure device (1) according to claim 3, in, The thickness of the resistance wires (26.x, 27.x, 28.x) is at least 1 μm.

5. The projection exposure device (1) according to claim 3, in, The thickness of the resistance wires (26.x, 27.x, 28.x) is at least 5 μm.

6. The projection exposure device (1) according to claim 3, in, The thickness of the resistance wires (26.x, 27.x, 28.x) is at least 10 μm.

7. The projection exposure apparatus (1) according to claim 1 or 2, in, The plurality of electric heating elements (25.x) have different electrical properties.

8. The projection exposure apparatus (1) according to claim 1 or 2, in, There is an open-loop / closed-loop control suitable for controlling the plurality of electric heating elements (25.x), which enables locally different power densities of the heating power.

9. The projection exposure apparatus (1) according to claim 1 or 2, in, There is at least one temperature sensor (33.x) that detects the temperature of the optical correction element (20).

10. The projection exposure apparatus (1) according to claim 1 or 2, in, The optical correction element (20) includes two planar parallel plates (21.x) with a fluid channel between them.

11. The projection exposure apparatus (1) according to claim 10, in, The planar parallel plates (21.x) are arranged parallel to each other at a distance between 2 mm and 50 mm.

12. The projection exposure apparatus (1) according to claim 9, in, At least one planar parallel plate (21.x) has a thickness between 2 mm and 20 mm.

13. The projection exposure apparatus (1) according to claim 10, in, The material of the planar parallel plate (21.x) and the wavelength of the electromagnetic heating radiation (44.x) are configured such that the average absorption power of the electromagnetic heating radiation (44.x) over the optically active region (44.x) is at least 10W.

14. The projection exposure apparatus (1) according to claim 13, in, The average absorbed power is 50W.

15. The projection exposure apparatus (1) according to claim 13, in, The average absorbed power is 100W.

16. The projection exposure apparatus (1) according to claim 13, in, The material of the planar parallel plate (21.x) and the wavelength of the electromagnetic heating radiation (44.x) are configured such that the absorptivity is between 10% and 20% of the incident power per 100 mm of material.

17. The projection exposure apparatus (1) according to claim 10, in, An electrical connection strip (30) is provided for contacting the electric heating element (25.x), and it extends at least partially parallel to the fluid channel.

18. The projection exposure apparatus (1) according to claim 1 or 2, in, At least two electric heating elements (25.x) are connected to the common ground wire (29).

19. The projection exposure apparatus (1) according to claim 18, in, All electric heating elements (25.x) are connected to the common ground wire (29).

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