ELECTRON BEAM LITHOGRAPHY

Group 2: Trần Phúc Thành.

Cao Văn Phước.

Tống Văn Khoa.

OUTLINE

Introduction. Why E-beam lithography? Schematic of e-beam lithography. Lithography Process Advantages and disadvantages. Summary. References.

INTRODUCTION

- Electron beam lithography (often abbreviated as e-beam lithography) is the practice of emitting a beam of electrons in a patterned fashion across a surface covered with a film (called the resist), ("exposing" the resist) and of selectively removing either exposed or non-exposed regions of the resist ("developing").

- The purpose, as with photolithography, is to create very small structures in the resist that can subsequently be transferred to the substrate material, often by etching. It was developed for manufacturing integrated circuits, and is also used for creating nanotechnology architectures.

WHY E-BEAM LITHOGRAPHY

SCHEMATIC OF E-BEAM LITHOGRAPHY

ELECTRONIC GUN LENS

Lower resolution systems can use thermionic sources, which are usually formed from LaB6. However, systems with higher resolution requirements need to use field electron emission sources, such as heated W/ZrO2 for lower energy spread and enhanced brightness.

MAGNETIC LENS

A magnetic lens is a device for the focusing or deflection of moving charged particles, such as electrons or ions, by use of the magnetic Lorentz force. Its strength can often be varied by usage of electromagnets.

ELECTROSTATIC LENS- Sometime we aslo use electrostatic lens however, electrostatic lenses have more aberrations and so are not used for fine focusing.-Systems of electrostatic lenses can be designed in the same way as optical lenses.-Electrostatic lenses in an electron diffraction experiment.

Lithography process

Clean sample◦ Remove oils,

organics, etc (Acetone, IPA, ultrasonic)

Spin coating of photoresist on surface of film (positive or negative resist) substrate

Deposited film

Photoresist

Lithography process

E-beam lithography and develop

Etching (multi-step

processes) Evaporate metal

contacts

substrate

film

substrate

Deposited film

substrate

film

substrate

film

Direct writing with narrow beam Electron projection lithography using a mask

:EPL

Modes of operation

oIssues:

o Throughput of direct writing is very low : research tool or low pattern density manufacturing

o Projection stepper (EPL) is in development stage only (primarily by Nikon).

o Mask making is the biggest challenge for the projection method

o Back-scattering and second electron result in proximity effect –reduce resolution with dense patterns there is also the proximity effect

o Operates in high vacuum (10-6 –10-10 torr) –slow and expensive

Scanning Methods Raster Scan

The e-beam is swept across the entire surface, pixel by pixel

Beam is turned on and offBeam is scanned across

the entire surface

Vector Scan◦ The e-beam “jumps” from

one patterned area to the next

◦ Adjustments to the beam can also be made relatively easily

◦ It takes longer for the beam to settle, making it more difficult to

◦ maintain accurate placing for the beam

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Possible solution of low throughput: Scattering with angular limitation projection electron beam lithography (SCALPEL)

o Diffraction is not a limitation on resolution (l < 1 Å for 10-50 keV electrons)

o Resolution depends on electron scattering and beam optics the size of the beam, can reach ~ 5 nm

Resolution

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Issue associated with EBL: Proximity effect

In EBL the resolution is not limited by diffraction

In EBL backscattering causes the electron beam to broaden and expose a large volume of resist then expected.

The proximity effect places a limit on the minimum spacing between pattern feature.

Summary • The pattern is written directly onto the electron-sensitive resist (no mask is used) • More precise than photolithography or X-

Ray lithography • Used to make high-resolution masks for photolithography and X-Ray lithography • Beats the diffraction limit of light, minimum feature size around 5 nm

Very slow. Takes over 10 hours to scan across the entire surface of a wafer • Very costly. One e-beam system costs upwards of 5 to 10 MILLION dollars • Potential problems with electron scattering: –Electron energy: 100eV -> very slow, inefficient, damage the substrate –Electron energy: 10eV -> lower penetration depth and lower resolution

S.M. Sze, Semiconductor Devices, Physics and Technology, Willey, 2002.

C.Y. Chang and S.M. Sze, Eds., ULSI Technology, McGraw-Hill, 1996.

S.M. Sze, Ed., VLSI Technology, McGraw-Hill, 1988.

Nguyễn Đức Chiến, Nguyễn Văn Hiếu, Công nghệ chế tạo mạch vi điện tử, NXB Bách khoa, 2007.

 

References

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