Tin etching in an EUV source by inherent and surface wave plasma

Qerimi, Dren

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https://hdl.handle.net/2142/115451 Copy

Description

Title

Tin etching in an EUV source by inherent and surface wave plasma

Author(s)

Qerimi, Dren

Issue Date

2022-04-17

Director of Research (if dissertation) or Advisor (if thesis)

Ruzic, David N.

Doctoral Committee Chair(s)

Ruzic, David N.

Committee Member(s)

• Curreli, Davide
• Jurczyk, Brian
• Rovey, Joshua L.

Department of Study

Nuclear, Plasma, & Rad Engr

Discipline

Nuclear, Plasma, Radiolgc Engr

Degree Granting Institution

University of Illinois at Urbana-Champaign

Degree Name

Ph.D.

Degree Level

Dissertation

Keyword(s)

Plasma physics, semiconductor, tin etching, hydrogen radicals, hydrogen ions, Langmuir probe, Comsol, and Matlab modeling.

Abstract

The need for computing power grows every day as the amount of data increases due to automation process and computing need which expands over all aspects of life. For over five decades, the semiconductor industry has continued to advance and follow Moore’s law by increasing the numerical aperture and reducing the wavelength of optical lithography. Extreme ultraviolet light (EUV) has replaced 193nm excimer laser as the standard technique in lithography, thus decreasing the wavelength to 13.5nm. EUV light is generated by laser-produced plasma (LPP) when a laser beam hits molten tin, ionizing the tin to the 10+ state. A by-product of EUV plasma creation is tin debris, contaminating source surfaces and degrading collector optics' reflectivity. Thus, tin mitigation is one of the main challenges for manufacturers. Tin contamination lowers collector reflectivity, increasing the time needed to process a wafer. A potential solution is to employ an in-situ cleaning method that will not require any source downtime. Tin mitigation employs hydrogen radicals and ions, formed in a hydrogen plasma, to interact with tin to form tin hydride (SnH4) in the gaseous state, which can be removed through a pumping system. Surface wave plasma (SWP) technology developed at the University of Illinois generates high-density hydrogen radicals and ions, resulting in tin etch rates that are high enough to keep extreme ultraviolet (EUV) lithographic tools clean. An advantage of an SWP antenna is generating a high density of hydrogen radicals and hydrogen ions directly at the desired etching location. In-situ etching of tin enables the increased availability of EUV tools by maintaining the high reflectivity of the multilayer mirror of the collector. The SWP is characterized by low ion energies and low electron temperature. The multilayer mirror does not suffer damage from sputtering or implantation of hydrogen ions during operation. Here, experiments elucidating the fundamental processes of tin removal are conducted by varying pressure, power, surface temperature, and gas flow rate to observe the etch rate behavior. Our results have shown that the presence of hydrogen ions increases etch rates because ion bombardment weakens Sn–Sn bonds, which, in turn, allows for a higher rate of a chemical etching by the radicals. The ion bombardment reduces the number of radicals needed to etch a single tin atom to 102 –103. The linear SWP antenna yields plasma densities on the order of 1016 to 1017 m-3 and radical densities on the order of 1018 to 1019 m-3, allowing for greater utilization of ion etch enhancement. Three different antenna configurations, such as button, linear and circular antennas are embedded in the collector to test which geometry generates the most extensive surface coverage and etch rate. Etch rates of up to 270 nm/min have been achieved. The surface temperature of the samples is a principal factor in the etching process. The decrease in the surface temperature increases the etch rates and decreases the hydrogen desorption rates. In addition, a kinetic etch model is developed to explain the behavior of etch rates as a function of surface temperature. Furthermore, results from experiments performed in an Illinois NXE:3100 chamber will be discussed.

Graduation Semester

2022-05

Type of Resource

Thesis

Copyright and License Information

Copyright 2022 Dren Qerimi

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