X-ray Lithography (BL-7)

Introduction

Probable Application Field of the Beamline

Salient Features of the Beamline

Beamline Performance

Experimental Station

X-ray Mask

List of the Recent Users of the Beamline

Few Results

Contacts

Publications

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Indus Synchrotrons Utilization Division

Soft and Deep X-ray lithography beamline (BL-07)

Introduction

X-ray lithography is 1:1 proximity shadow printing process, which involves two dimensional image formation using an X-ray mask in contact with a photo resist and subsequent recording of the latent image on the resist. X-ray lithography using high intensity x-rays from synchrotron radiation (SR) sources (X-ray LIGA) is used for fabrication of high aspect ratio (10-500) microstructures. Lithography at the soft X-ray range (photon energies from 1 to 3 keV) known as soft x-ray lithography (SXRL) achieves patterns with high lithographic resolution (< 100nm). On the other hand, deep x-ray lithography (DXRL) is performed in hard X-ray region (> 4 keV), where few hundred microns of X-ray resist is exposed.

Soft and Deep X-ray lithography (SDXRL) beamline (BL-07) is a bending magnet based, high intensity beamline, is commissioned in April 2011. This beamline consist of two mirrors system, beam position monitors, slits, Be-winodow and an X-ray scanner as experimental station. Platinum coated silicon mirrors (100mm in width and 700mm in length) are installed on a precision manipulator for transporting X-ray beam in the desired energy window to the experimental station at a fixed height. The first mirror is plane for defining X-ray energy cutoff and the second mirror is torroidal for vertical focusing and horizontal collimation. Depending upon the depth of the structures required in photo resist, the beamline can be operated in high energy, low energy and high flux or edge absorber modified flux (power) modes.

  • Two mirror mode of operation : Energy band between 1.5-10keV is available for SXRL and DXRL process. Beam sizes are variable between 2mm (V) x 55 mm (H) to 10mm (V) x 80 mm (H) (depending on the energy band required during exposure).
  • Single mirror mode of operation : High energy and high flux, continuous energy spectrum from 5-10keV. Beam sizes is 10mm (V) x 100 mm (H).
  • White beam (No optics) mode of operation : High energy upto 40keV is available to creat high depth structures in photo resist. Beam sizes is 18mm (V) x 100 mm (H).

Probable application field of the beamline

  1. X-ray lithography process using soft x-ray and hard x-rays
  2. X-ray Irradiation process using white light and pink beam (spectral band of few keVs)
SDXRL10
Optical design of the SDXRL beamline
Mechanical design of the SDXRL beamline
Mechanical design of the SDXRL beamline

Salient Features of the beamline

Source

2.5GeV Indus-2, 1.5T Bending Magnet

Source sizes

σy = 232  µm,σx = 272  µm

Emittance

58 nmrad (horizontal) with 1% coupling

Energy range of the beamline

1.5 keV – 20 keV

Reflecting mirrors    

Two mirrors    (1 plane @ 16.2m and 1 torroidal @ 17m)

           

Pt coated Si-substrate with side-cooling arrangement

Mirror sizes   

100mm  x 650mm

Beamline acceptance

Horizontal 5 mrad and Vertical 0.83 mrad 4σ (@1.5 keV)

Beam size at sample

80-100 (Horizontal) x 2-10 (Vertical) mm2 (depending upon the beamline settings)

Angular Range         

0.16 – 2.0 degrees

Filters                                    

Be, C, Al etc.

Energy power spectrum offered by the beamline
Energy power spectrum offered by the beamline
 
Installed  view of two mirror system in optics hutch.
Installed view of two mirror system in optics hutch.

Beamline performance

Beamline performance
Wire scan obtained after two mirror system for direct synchrotron radiation
Wire scan obtained at 18m from source when mirrors are set for 3-10keV spectrum.

 

 

Beam size at experimental station

Experimental station

X-ray scanner is installed in experimental hutch. It scans the mask and resist assembly in vertical direction. It is possible to create three dimensional high aspect ratio microstructures in Poly Methyl Metha Acrylate (PMMA) and SU-8 using tilt and rotation module of x-ray scanner. IR camera images the temperature distribution of X-ray mask and resist. Temperature monitoring helps to prevent the degradation of resist and thus high quality of micro structures.

Features of X-ray Scanner
A  custom designed and developed X-ray scanner for mask-resist exposure

Exposure window

± 90 mm  (V), ± 40 mm  (H)

Exposure  Environment

Vacuum, He-gas, Air(inside chamber)

Mask-Substrate Size

Upto Circular Φ 100 mm and Square 100mm x 100mm

Photo resist thickness

1-5000 μm

Mask-Resist tilt and rotation

tilt 0-90°and rotation ± 180°

Gap between mask and resist

0-100 μm

Speed of scanning stage

1-30 mm/s

Alignment accuracy between mask and resist

~1 μm

 

Installed view of X-ray scaner systems in Experimental Hutch
Installed view of X-ray scaner systems in Experimental Hutch
 
20110621_1404.jpg
Inside view of x-ray scanner, showing the mounted x-ray mask and resist on goniometer.
 

X-ray Mask

A major ingredient required for performing x-ray lithography is x-ray mask. It consist of a low Z (atomic number) x-ray transparent material and high Z patterned absorbing material. We have developed two types of x-ray mask, (1) Gold absorber and polyimide based membrane fabricated using UV lithography and Gold electrodeposition for fine features (< 50 μm) and (2) Stainless Steel mask fabricated using UV lithography and chemical etching for coarse features (>50 μm).

DSC00965.JPG
Stainless steel x-ray mask
Gold based x-ray mask
Stainless steel x-ray mask

List of the recent users of the beamline

No.

Name of the  beamline user

Organisation

Details of experiment

1

Ms Jaishree Biswal

BARC, Mumbai

Synthesis of Gold nanoparticles using SR irradiation.

2

Mr Nilanjal Mishra

BARC, Mumbai

Synthesis of Gold, Silver nanoparticles using SR irradiation

3

Dr V K Suri and Dr R Balasubramanium

BARC, Mumbai

Fabrication of high speed bearing and associated structures

4

Mr V C Petwal

RRCAT, Indore

Evaluation of dose rates in lithography beamline using radiochromic film

5

Ms Asmita mallik

RRCAT, Inodre

Fabrication of electrophoratic device

6

Mr Prashad Shukla

VJTI, Mumbai

Fabrication of Micro reactor and Y micro mixer

7

Mr Swapnesh Panigrahi and Dr Sushil Mujumdar

TIFR, Mumbai

Fabrication of photonic crystal (micro cavities and micro pillars)

8

Mr Anish Kulkarni and Prof Suhas Joshi

IIT Bombay

Fabrication of Micro reactor

9

Rituraj Sharma

RGPV, Bhopal

Fabrication of micro fluidic device for Magneto-hydro-dynamic pump

10

Mr Prateek Sharma

Pt Ravishankar Univeristy, Raipur

Fabrication of micro fluidic device  for hydro-dynamic micro pump and micro valve

11

Dr Rahul Shukla

RRCAT, Indore

Fabrication of electrostatic actuators

12

Mr Vishal Dhamgaye

RRCAT, Indore

Fabrication of compound refractive lens

13

Dr P M Pawar, Prof Nitin Misal and team

SVERI, Pandharpur

Designing and fabrication of building blocks for microfluidic devices

14

Dr R K Sharma and Dr B D Pant

CEERI, Pilani

Development of THz structures and devices

Few Results

Quality structures consist of micro-fluidic channel, micro-pillars, micro-cavities, high speed bearings, compound refractive lens etc have been fabricated using SDXRL beamline.

Parabolic/cylindrical compound refractive lens (CRL) fabricated on PMMA resist with geometrical aperture of 400 μm, radius is 200 μm at apex and N (no of lens) = 1, 2, 5, 10, 20, 50 are fabricated. CRLs are designed for 9 keV x-ray energy. Wall thickness of the lens at the apex is ~ 15 μm and depth 150 μm. The maximum depth of CRLs ~800μm is achieved recently.

 

DSC01744.JPG

A microfluidc channel based on ferro hydrodynamics is fabricated on SU-8 with channel width of 400 μm and 600 μm and depth of 300-500 μm. Micro manipulation of Ferrofluid (Nickel ferrite nanoparticles dispersed in PEDG) is demonstrated. Ferrofluid speed is measured ~ 316 μm/s in a distace of 615 μm.

 

HOLE_02.TIF
Curved neck, tapered holes fabricated in PMMA using innovative exposure techniques. The top diameter of tapered curved neck holes is 200μm and bottom diameter is 100μm.

 

Micro-pillars are fabricated on SU-8 at BL-07, 200 μm in diameter, 170 μm  deep and 300μm pitch.

SDXRL beamline can be adopted to perform white beam experiments and beamline was used to synthesize nobel metal nanoparticles using white beam SR.

Contacts

Name Email Phone No
Sh. Vishal Prabhakar Dhamgaye,Beamline Incharge vishal (at) rrcat.gov.in +91-731- 2442123/2442141
Dr. G. S. Lodha,Head, X-ray Optics Section lodha (at) rrcat.gov.in +91-731-2442132

Publications

  1. V. P. Dhamgaye, B. Gowri Sankar, C. K. Garg and G. S. Lodha,
    Commissioning of Soft and Deep X-ray Lithography Beamline on Indus-2”,
    DAE-SSPS 2011, AIP Conf. Proc. 1447, 527 (2012).

  2. V. P. Dhamgaye and G. S. Lodha,
    “Fabrication of Compound Refractive Lens using Soft and Deep X-ray Lithography Beamline on Indus-2”,
    DAE-SSPS 2011, AIP Conf. Proc. 1447, 525 (2012).

  3. S. Chouksey, H. Nair, V. G. Sathe, V. Dhamgaye, M. Jaganath, A. K. Sinha, G. S. Lodha, Gurnam Singh,
    “Construction of Beamline Radiation Shielding Hutches for Indus-2 Synchrotron Radiation Source”,
    Proceedings Indian Particle Accelerator Conference (InPAC2011),New-Delhi (2011).

  4. M. K. Nayak, P. K. Sahani, Mukesh Khare, T. K. Sahu, P. Haridas, Vipin Dev, S. Dashora, Vishal Dhamgaye, G. Haridas and P. K. Sarkar,
    “Experimental investigation of Synchrotron and Bremsstrahlung hazards at Lithography beam line of Indus-2 SRS”,
    Conference on Accelerator Radiation Safety (CARS2011), Mumbai (2011)

  5. Nilanjal Misra, Jayashree Biswal, V. P. Dhamgaye, G. S. Lodha, S. Sabharwal,
    “A comparative study of gamma, electron beam, and synchrotron X-ray irradiation method for synthesis of silver nanoparticles in PVP”, 
    Applied Materials Letters, accepted manuscript (2012).
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