A method for measuring discharge current of excimer light source of deep ultraviolet lithography machine

Abstract

This invention proposes an embedded measurement method for the discharge current of an excimer light source in a deep ultraviolet lithography machine, belonging to the field of measurement technology. Utilizing a ceramic ring in the excimer light source of a deep ultraviolet lithography machine, which serves as high-voltage insulation and supports the conductive rod, two staggered, spaced through-holes are machined on the ceramic ring. Insulated wires are inserted into these holes to form a current coil structure. Current discharges from the peaking capacitor through the conductive rod to the electrodes. During the plasma formation between the cathode and anode, a signal is induced in the current coil. Two taps on the wire are connected to a coaxial connector. The coaxial line exits from the vent of the upper cavity, leading out the current coil signal. The induced signal is recorded by a data acquisition system through an attenuator and a matching load. A ferrite core passes through the coaxial line to suppress common-mode components, calibrating the ceramic ring current coil structure. The induced signal is then processed to obtain the discharge current.

Description

Technical Field

[0001] This invention belongs to the field of measurement technology, and in particular relates to an embedded measurement method for the discharge current of the excimer light source in a deep ultraviolet lithography machine. Background Technology

[0002] Excimer light sources (ArF 193 nm, KrCl 248 nm, etc.) are the core modules of deep ultraviolet lithography machines, and they play a decisive role in the output energy, electro-optic efficiency, stability, spot quality, and lifespan of the lithography machine.

[0003] Excimer light sources generate plasma through pulsed discharge in a characteristic atmosphere (a mixture of neon, argon, krypton, xenon, and fluorine in a certain proportion, at a pressure of several atmospheres). This plasma excites the working medium, forming excimer radiation luminescence. The high voltage of the pulsed power supply is input to a peaking capacitor connected in parallel with the discharge electrodes, charging both the peaking capacitor and the discharge electrodes. When the breakdown voltage threshold is reached, the working medium breaks down between the cathode and anode, forming plasma. The peak voltage of the excimer light source pulses reaches tens of kV, the characteristic discharge time is tens of nanoseconds, and the discharge current is above kA. The high voltage and strong current create an extremely complex electromagnetic environment.

[0004] Under high-energy, high-frequency conditions, excimer light sources are prone to diffusion-to-filamentary mode conversion. Partial discharge filaments and even arcs reduce the electro-optical efficiency and spot quality of the light source. Local hot spots accelerate the erosion of metal electrodes, introduce metallic impurities into the gas phase, and severely reduce the lifespan of the light source. Discharge current can reflect the operating status of the excimer light source. Combined with voltage waveform, discharge power and energy (rather than power supply output energy) can be calculated. Discharge current monitoring is crucial for understanding the operating status of the excimer light source and maintaining efficient coupling between the power supply and plasma energy.

[0005] The entire excimer light source module is housed within a fully sealed metal casing. The peaking capacitor is located inside the upper cavity above the discharge chamber and is connected to the cathode via a conductive rod. The ceramic ring serves as high-voltage insulation, supports the conductive rod, and withstands the stress of compressing the sealing ring, ensuring the sealing of the discharge chamber. The excimer light source has a very compact structure, with components spaced only a few millimeters (or even 1-2 millimeters) apart. Due to size limitations, it is difficult to embed existing current sensing devices, such as Rogowski coils and current transformers, resulting in the discharge current of the excimer light source in the operating deep ultraviolet lithography machine remaining unknown.

[0006] CN118444001A discloses a method for measuring the discharge current of a dual RC voltage divider, which measures the voltage across the electrodes and then calculates the current. However, this method cannot be used in space-constrained excimer light sources.

[0007] CN115473114B discloses a current sampling module for a laser pulse power supply, but it can only measure the power supply current and cannot actually measure the discharge current inside the discharge cavity.

[0008] CN101122619 discloses a flexible Rogowski coil for pulse current measurement, which has good applicability to measurement scenarios. However, it is difficult to adapt and install it within the millimeter gap inside the excimer light source, and the repeatability of the measurement also faces serious challenges.

[0009] CN108761164B discloses a hollow differential coil for pulse current measurement and its measurement method, but the coil is wound on a specific frame and cannot be used in the limited space of an excimer light source.

[0010] CN1442700A discloses a current measurement method based on a Faraday rotor and a Rogowski coil. However, it requires the measurement laser to pass through a discharge chamber. When the excimer light source outputs laser light, the measurement laser and the output laser coincide, which may prevent current measurement from being performed.

[0011] It can be observed that existing pulse current measurement methods are mostly based on coils with specific spatial configurations. These cannot be installed inside the excimer light source of a deep ultraviolet lithography machine, which is fully sealed with metal, has very small space between components, and has a very complex electromagnetic environment. Even if a flexible or compact design is adopted, it will inevitably interfere with the internal structure of the light source. If the installation is not done properly, high voltage and high current will cause catastrophic consequences of abnormal discharge inside the excimer light source, which is unacceptable in engineering practice. On the other hand, measurement methods based on optical principles are prone to interference with the light source output and are difficult to operate in semiconductor manufacturing processes. Summary of the Invention

[0012] To address the aforementioned technical problems, this invention proposes an embedded measurement method for the discharge current of an excimer light source in a deep ultraviolet lithography machine. This method addresses the extremely complex electromagnetic environment of the light source, characterized by its all-metal sealing, confined space, and high voltage and current, enabling online measurement of the discharge current without altering the existing structure of the excimer light source or interfering with its discharge state. The specific technical solution is as follows:

[0013] An embedded measurement method for the discharge current of an excimer light source in a deep ultraviolet lithography machine is disclosed. This method utilizes a ceramic ring in the excimer light source, which serves as a high-voltage insulator and supports the conductive rod. Several interlaced, spaced through-holes are machined into the ceramic ring. Insulated wires are inserted into these through-holes to form a current coil structure. Current flows from a peaking capacitor through the conductive rod to the cathode. During plasma formation between the cathode and anode, a signal is induced in the current coil. Two taps on the wire are connected to a coaxial connector. The coaxial line extends from the upper cavity, leading out the current coil signal. The induced signal is recorded by a data acquisition system through an attenuator and a matching load. A ferrite core passes through the coaxial line to suppress common-mode components. The ceramic ring current coil structure is calibrated, and the induced signal is processed to obtain the discharge current.

[0014] The present invention has the following beneficial effects:

[0015] This invention utilizes a ceramic ring within the excimer light source of a deep ultraviolet lithography machine, which serves as a high-voltage insulator and supports the conductive rod, to form a current sensor and achieve real-time embedded pulse current measurement without altering the design and structure of the excimer light source.

[0016] This invention solves the problem of real-time discharge current measurement in the all-metal enclosed cavity, confined space, and complex electromagnetic environment of the excimer light source in deep ultraviolet lithography machines, providing key support for the coupling of power supply and plasma energy and the monitoring of operating status of deep ultraviolet lithography machines. Attached Figure Description

[0017] Figure 1 This is a schematic diagram of the method of the present invention.

[0018] 1. Ceramic ring; 2. Through hole; 3. Wire; 4. Peaking capacitor; 5. Cathode; 6. Anode; 7. Coaxial connector; 8. Coaxial line; 9. Upper cavity; 10. Plasma; 11. Vent; 12. Attenuator; 13. Matching load; 14. Data acquisition system; 15. Ferrite core; 16. Discharge cavity; 17. Conductive rod; 18. Housing. Detailed Implementation

[0019] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention. Furthermore, the technical features involved in the various embodiments of this invention described below can be combined with each other as long as they do not conflict with each other. To achieve the above objectives, this invention adopts the following technical solution.

[0020] like Figure 1 As shown, this invention provides an embedded measurement method for the discharge current of an excimer light source in a deep ultraviolet lithography machine. It utilizes a ceramic ring 1, which serves as a high-voltage insulator and supports the conductive rod in the excimer light source of the deep ultraviolet lithography machine. Two interlaced through-holes 2 with a certain spacing are machined on the ceramic ring 1. Insulated wires 3 are inserted into the through-holes 2 to form a current coil structure. The current flows from the peaking capacitor 4 through the conductive rod 17 to the cathode 5. During the formation of plasma 10 between the cathode 5 and the anode 6, a signal is induced in the current coil. Two taps of the wire 3 are connected to a coaxial connector 7. A coaxial line 8 passes through the vent 11 of the upper cavity 9 to lead out the current coil signal. The induced signal is recorded by a data acquisition system 14 through an attenuator 12 and a matching load 13. A ferrite core 15 passes through the coaxial line 8 to suppress common-mode components, calibrating the current coil of the ceramic ring 1. The induced signal is then processed to obtain the discharge current.

[0021] A specific example is as follows:

[0022] Two rings of through holes 2 are machined on the ceramic ring 1 in an alternating pattern with a certain spacing. The number of holes in a single ring is 5-50, the distance between the two rings is 3-30 mm, and the diameter of the holes is 0.5-2.5 mm.

[0023] The insulation sheath of conductor 3 is made of silicone, polytetrafluoroethylene, or polyimide, with an insulation strength ≥1 kV. The conductor core is multi-core or single-core copper, and the outer diameter of the conductor is 0.4-2.4 mm. The conductors pass through the holes one by one to form a current coil.

[0024] Coaxial connector 7 is an MMXC female connector.

[0025] The coaxial cable 8 uses the RG316, with an MMXC male input and a BNC or SMA male output, ensuring that the coaxial cable input can pass through the housing vent and the output is compatible with the data acquisition system port.

[0026] Attenuator 12 can be used with any combination of attenuation values ​​from 1 to 30 dB. One feasible solution is: 3 dB + 6 dB + 10 dB + 20 dB. The attenuator with the smaller attenuation value is connected to the coaxial line output terminal.

[0027] Matching load 13 is a 50 Ω to 1 MΩ matching load, and the internal resistance of data acquisition system 14 is 1 MΩ, which can measure voltage signals with high amplitude and is not easily damaged; when the internal resistance of data acquisition system 14 is 50 Ω, the matching load is omitted, which is suitable for situations where pre-experiments have been carried out and it is determined that the measured signal will not exceed the range of data acquisition system; voltage probes can also be used to directly measure the output waveform of coaxial line, omitting attenuator and matching load.

[0028] Ferrite core 15 suppresses common-mode components. Multiple TDK ZCAT1325-0530 cores can be used, or multiple turns of coaxial line can be wound on a single TDK ZCAT3035-1330 core.

[0029] The data acquisition system 14 can use a high-bandwidth oscilloscope or data acquisition card (bandwidth ≥ 100 MHz, sampling rate ≥ 1GS / s); the data acquisition coefficients should share a common ground with the light source housing, and the overall system should be well grounded.

[0030] The response of the current coil is calibrated using a standard signal source or network analyzer to obtain the response coefficient C from the current signal to the voltage signal. The measured signal is then processed by subtracting the background and integrating to obtain the discharge current. The processing method is as follows:

[0031] Before measurement, obtain the background V when there is no discharge. b Then, the waveform V(t) during discharge is measured, where t is time and t0 is the measurement time 0. The discharge current I(t) passes through... The background introduces a linearly increasing term over time, and accurately obtaining the background is crucial for the current measurement in this invention.

[0032] The peaking capacitor 4, ceramic ring 1, conductive rod 17, cathode 5, anode 6, upper cavity 9, discharge cavity 16, housing 18, and vent 11 are proprietary structures of the excimer light source, and their parameters are determined by the lithography machine design; this invention does not impose any limitations on them. The peaking capacitor 4 and ceramic ring 1 are located in the upper cavity 9, while the conductive rod 17, cathode 5, and anode 6 are located in the discharge cavity 16. The upper cavity 9 and discharge cavity 16 are isolated, and the housing 18 is disposed outside the upper cavity 9 and discharge cavity 16.

[0033] The scope of protection of this invention is not limited to the current coil sensing structure with double turns arranged alternately on the ceramic ring 1. Structures with single turns, multi turns, or incense coils, or structures with multiple strands of wire wound together, are all within the scope of protection of this invention.

Claims

1. An embedded measurement method for the discharge current of an excimer light source in a deep ultraviolet lithography machine, characterized in that, A ceramic ring, which serves as a high-voltage insulator and supports the conductive rod in the excimer light source of a deep ultraviolet lithography machine, is used to fabricate several staggered, spaced through-holes on the ceramic ring. Insulated wires are inserted into these through-holes to form a current coil structure. Current flows from the peaking capacitor through the conductive rod to the cathode. During the formation of plasma between the cathode and anode, a signal is induced in the current coil. Two taps of the wire are connected to a coaxial connector, and the coaxial line extends from the upper cavity to extract the current coil signal. The induced signal is recorded by a data acquisition system through an attenuator and a matching load. A ferrite core passes through the coaxial line to suppress common-mode components. The ceramic ring current coil structure is calibrated, and the induced signal is processed to obtain the discharge current.

2. The embedded measurement method for discharge current of the excimer light source in a deep ultraviolet lithography machine according to claim 1, characterized in that, Two rings of through holes, spaced at a certain distance, are machined on a ceramic ring.

3. The embedded measurement method for discharge current of the excimer light source in a deep ultraviolet lithography machine according to claim 2, characterized in that, The number of holes in a single ring of two-ring through holes is 5-50, the distance between the two rings is 3-30 mm, and the diameter of the through hole is 0.5-2.5 mm.

4. The embedded measurement method for discharge current of excimer light source in a deep ultraviolet lithography machine according to claim 1, characterized in that, An insulated wire is threaded through a perforated ceramic ring to form a current coil.

5. The embedded measurement method for discharge current of the excimer light source in a deep ultraviolet lithography machine according to claim 4, characterized in that, The conductor insulation sheath is made of silicone, polytetrafluoroethylene, or polyimide, with an insulation strength ≥1 kV. The conductor core is multi-core or single-core copper, and the conductor outer diameter is 0.4-2.4 mm.

6. The embedded measurement method for discharge current of the excimer light source in a deep ultraviolet lithography machine according to claim 1, characterized in that, The coaxial connector is an MMXC female connector.

7. The embedded measurement method for discharge current of excimer light source in a deep ultraviolet lithography machine according to claim 1, characterized in that, The coaxial cable uses the RG316 connector, with an MMXC male input and a BNC or SMA male output.

8. The embedded measurement method for discharge current of excimer light source in a deep ultraviolet lithography machine according to claim 1, characterized in that, The attenuators use a combination of attenuation values ​​from 1 to 30 dB, with the attenuator with the smaller attenuation value connected to the coaxial cable output.

9. The embedded measurement method for discharge current of the excimer light source in a deep ultraviolet lithography machine according to claim 1, characterized in that, The matching load is 50 Ω to 1 MΩ, and the internal resistance of the data acquisition system is 1 MΩ.

10. The embedded measurement method for discharge current of the excimer light source in a deep ultraviolet lithography machine according to claim 1, characterized in that, The ferrite core uses a ZCAT1325-0530 core wound with one turn of coaxial line or multiple turns of coaxial line wound on a ZCAT3035-1330 core.

11. The embedded measurement method for discharge current of an excimer light source in a deep ultraviolet lithography machine according to claim 1, characterized in that, The data acquisition system uses a high-bandwidth oscilloscope or data acquisition card.

12. The embedded measurement method for discharge current of the excimer light source in a deep ultraviolet lithography machine according to claim 1, characterized in that, The wires are wound in a single turn, multiple turns, or in a coil shape.

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