Attachment (A) SOW Ion Beam Figuring.pdf

NSLS-II Enhanced Ion Beam Figuring system September 30, 2024

Statement of Work This project serves to enhance an existing enhanced Ion Beam Figuring (IBF) plasma system for the National Synchrotron Light Source II (NSLS-II) IBF group at Brookhaven National Laboratory (BNL) and seek to explore alternative IBF techniques.

IBF is a precision material removal technique for correction of shape errors on optical surfaces used in the final stages of optics fabrication. IBF utilizes ion beam / plasma milling as a non-contact process to reduce mechanical stress and surface damage, making it an ideal solution for high-precision applications. The results of this research will directly address limitations in IBF material removal rates at high spatial frequencies by utilizing an ion-optics system to increase beam current-density on the target surface in addition to the occluding aperture currently in use.

The main research output are: a final report of ion-optics simulations utilizing simulated beams from the KDC10 and KDC40 ion sources, construction, tests and delivery of an ion-beam-profiling diagnostic and a dedicated focusing ion-optics assembly for the KDC10 ion source, delivery of the designs of an atmospheric plasma discharge head and SiO2 or Si sample coupons with a best-effort-etching attempt.

Experimental results and simulations gathered in this project will be submitted for joint publications.

Background:

The NSLS-II IBF group has achieved sub-nanometer figure accuracy by integrating IBF coupled with in-house interferometry-and-profiler-based surface metrology to manufacture low-curvature hard X-ray mirrors [1]. The NSLS-II IBF group focuses on low-frequency shape error correction, which contains four aspects in the metrology and fabrication loops:

• Accurate metrology ensures precise measurement of surface deviations.

• Optimization of ion-beam dwell time at each individual path point to correct figure errors.

• Conversion of dwell-time to continuously varying IBF beam velocity over mirror surfaces that improves motion control for better surface generation.

• Inspection of height, slope, and roughness errors on X-ray mirror surfaces with cross-validation between profilometry and interferometry.

NSLS-II IBF group infrastructure is designed around a Kaufman & Robinson KDC 10 ion source with a beam diameter of 10 mm*, while shape error correction requires beam diameters that varies from 10 mm to 1mm feature sizes. To achieve IBF at this spatial frequency, beam diameter is limited by a graphite or tantalum occluding aperture located

ATTACHMENT A

~45mm in-front of the ion source with 10mm, 5 mm, 2.5 mm, and 1 mm pinhole diameters.

To maintain Gaussian beam profiles, pinhole-to-mirror-surface distance is varied between 10 mm, 5 mm, and 3 mm, respectively. The pinhole aperture reduces total beam current to the mirror surface by the ratio of the aperture to beam-source diameters, thus decreasing the IBF material removal rate by approximately 0.25, 6.2e-2, 1e-2, respectively.

The achieve removal rate is illustrated on figure 1 bottom. The NSLS-II IBF system utilized an ion source and pinhole that are mechanically translated over the mirror surface by an X-Y platform, shown in Fig 1.

Figure 1. Current NSLS-II IBF system. Argon ion beam is presently spatially restricted by a pinhole

(a) in a tantalum or graphite foil. Pinhole attenuates beam current proportional to geometric area between source beam and aperture

(b). IBF assembly is mechanically translated over mirror surface (c), a front view is shown on the left, and a top view is shown on the right.

Scope of Work 1st part: Proposed ion beam profiling diagnostic:

As shown on figure 1, the beam diameters on the substrate are measured by ion-milling a single point on the substrate and subsequently measuring the spatial dimensions of the removed material (Fig 1 bottom). The first part of this proposal focusses on developing a real time ion beam profiling diagnostic.

The main goal is to develop, construct, and test an ion beam profiler system, its associated controller, and a dedicated MATLAB operating code, and deliver one unit for the NSLS-II IBF system.

Deliverable (Detector Hardware & Data):

Development, construction and test of an ion beam profiler system, associated controller, and MATLAB operating code, and deliver one unit for the NSLS-II IBF system.

2nd part: Proposed ion optics simulations and Einzel lens system.

The second part of this proposal is dedicated to the simulation of the ion beam trajectories in Comsol (https://www.comsol.com) to optimize a dedicated Einzel lens (dimensions and biases) for the current KDC-10 and future KDC 40 ion sources. The goal is to optimize and construct an Einzel lens design and provide/test one unit for the NSLS-II IBF system. The overall size of this device should not exceed 50mm between the face of the ion source and the exit pinhole.

Deliverable (Lens Hardware & Data):

Use data from the 1st Part to develop a final report of COMSOL ion-optics simulations utilizing simulated beams from KDC10 and KDC40 ion sources, construction, tests and delivery of an ion-beam-profiling diagnostic.

3rd part: Test of a proof-of-principle atmospheric pressure plasma figuring system.

The third part of this proposal will focus on the exploration of an atmospheric micro plasma system figuring for Si and SiO2 substrates. The final system will be used on an X-Y gantry to scan the discharge plasma torch over a substrate.

The proposed system will be tested on SiO2 or silicon samples substrates to examine material removal and evaluate surface and sub-surface damage to the substrate.

Deliverable:

A complete atmospheric micro-plasma torch head, CAD designs of the torch head, and one or more SiO2 or Si sample coupons with a best-effort-etching attempt.

The timeframe for the completion of the proposed scope of work is spring 2025.

Experimental results and simulations gathered in this project will be submitted for joint publications.

[1] T. Wang et al., “Ion Beam Figuring System for Synchrotron X-Ray Mirrors Achieving Sub-0.2-µrad and Sub-0.5-nm Root Mean Square,” Nanomanufacturing and Metrology, vol. 6, no. 1, pp. 1–11, Dec. 2023, doi: 10.1007/S41871-023-00200-

X/FIGURES/17.

https://www.comsol.com/