T. C. Chu

High reflectance of reflective-type attenuated-phase-shifting masks for extreme ultraviolet lithography with high inspection contrast in deep ultraviolet regimes

Phase-shifting masks are a vital resolution enhance technique that will be used in extreme ultraviolet (EUV) lithography beyond the 20nm node. In this article, we demonstrate a structure for a reflective-type attenuated phase-shifting mask, which is based on a Fabry–Perot structure with common materials in EUV masks. The mask structure not only performs 180° phase shift with high reflectance at EUV wavelength, but also has high inspection contrast at deep ultraviolet (DUV) wavelength. The top layer of mask structures exhibits good conductivity, which can alleviate the charging effect during electron-beam patterning. The reflectance ratio of the absorber stack could be tuned from 32.6% (TaN∕SiO2∕Mo) to 4.4% (TaN∕SiO2∕TaN) by choosing different bottom layers and thickness. The inspection contrast could be raised to 99% with large thickness-control tolerance.

Novel bilayer bottom antireflective coating structure for high-performance ArF lithography applications

A novel bilayer bottom antireflective coating (BARC) structure composed of a commercial KrF lithography resist and an organic BARC film is demonstrated for ArF lithography. The diluted deep ultraviolet (248 nm) resist is high absorption at the 193 nm regime, which is suitable as bottom layer of bilayer BARC structures. While the deep ultraviolet organic BARC material is low absorption at the 193 nm regime, which is suitable as top layer of bilayer BARC structures. Such a bilayer BARC can have large thickness control tolerances over various highly reflective substrates. The measured swing effect is found significantly reduced by adding such a bilayer BARC on both aluminum and silicon crystal substrates. Reflectance can be reduced to less than 2% on other highly reflectance substrates such as copper, poly-silicon, tungsten silicide, and aluminum silicon. Such a process has several advantages: high performance, relatively inexpensive, large thickness control tolerance, low contamination, and easy film removal.

Characterizing Optical Properties of Self-Assembled Gold Nanoparticles for Surface Plasmon Resonance Device Applications

In this study, the optical constants of gold nanoparticles are evaluated for surface plasmon-based sensor applications. Using an effective medium approximation (EMA) and ellipsometry, approaches to monitor the self-assembly of gold nanoparticles are also demonstrated. Spectroscopic ellipsometric parameters measured (tan Ψ, cos Δ) before and after adding gold nanoparticles to a substrate are used to calculate the optical constants of gold nanoparticles. The film thickness is measured by grazing incidence X-ray reflectivity (XRR). The optical constants (refractive index, extinction coefficient) of gold nanoparticles can be obtained from the measured ellipsometric parameters and thickness. We also show that particles density can be well predicted and detected nondestructively by this method.

Fabrication of autocloned photonic crystals by using high-density-plasma chemical vapor deposition

The high-density-plasma chemical vapor deposition (HDP-CVD) method was demonstrated as an alternative to radio-frequency (rf) bias sputtering method for fabrication of “autocloned” photonic crystals. We successfully preserved periodic surface corrugation after deposition of multilayer stacks under appropriate chemical vapor deposition conditions. Freedom of the shaping process was increased by simply raising the bias power of the autocloning process, and thus created autocloned structures having a strong modulation of the effective refractive index in the lateral direction. The method allows photonic bands of autocloned photonic crystals to be designed with greater controllability and a simpler fabrication process. Furthermore, the HDP-CVD method has better step-coverage than the sputtering method and can be used to fabricate autocloning structures with small feature-sizes.

Low-dielectric constant bisbenzo(cyclobutene) and fluorinated poly(arylene)ether films as bottom anti-reflective coating layers for ArF lithography

In this article, we demonstrate a bottom anti-reflective coating (BARC) layer for ArF lithography. The anti-reflective layers are composed of a commercial low-dielectric constant bisbenzo(cyclobutene) (BCB)- and fluorinated poly(arylene)ether (FLARE)-based films. By adding an optimized etching hard-mask layer, reflectance of less than 1% at the resist/silicon substrate interface can be achieved. BCB and FLARE also have great potential to be used as BARC layers on highly reflective substrates for metal interconnect applications. It is easy to reduce reflectance without adding an extra BARC layer for patterning low-dielectric materials. It is convenient to use this BARC structure in ArF lithography. In this article, suitable etchingcharacteristics and thermal stability of BCB- and FLARE-based BARC layers are also described.

Diluted Low Dielectric Constant Materials as Bottom Antireflective Coating Layers for both KrF and ArF Lithography Processes

For reduction interconnect signal delay, low dielectric constant (K) materials are being introduced to replace conventional dielectrics in next generation IC technologies. In the advanced lithography processes, a bottom antireflective coating (BARC) layer for patterning low-K materials is essential. Nitride-based (silicon nitride, silicon oxynitride) films have been demonstrated to have suitable optical characteristics for both KrF and ArF lithography BARC applications. However, dielectric constants of nitride films are about 4/spl sim/8. Therefore, the nitride films should be removed after pattering low-K materials. Here we demonstrate low-K materials for both KrF and ArF lithography BARC applications. The antireflective layer is composed of diluted low-K materials, such as BCB, FLARE, and SiLK.

Thermal-flow techniques for sub-35 nm contact-hole fabrication in electron-beam lithography

In this article, we demonstrate that 200 nm contact-hole resist patterns can easily be shrunk to less than 35 nm after a simple thermal-flow procedure. The optimal thermal-flow temperature was determined by differential-scanning calorimetry and wafer-curvature measurement. The effects of postapplied baked temperature, thermal-flow temperature, baking time period, and pattern density were evaluated. The resist after thermal flow is more intact than during dry-etching processes. The resist can overcome the resist-thickness loss during the thermal-flow procedure.

Chemically amplified deep UV resists for electron-beam lithography applications

Chemically amplified resists have been widely used in deep UV optical lithography. In this paper, we characterized positive deep UV resists for high-resolution electron beam lithography applications. Results indicate this deep UV resist is very high sensitive and suitable for high throughput e-beam lithography applications. In general, deep UV resists are not suitable for sub-100 nm resolution lithography, except for strictly process control. After a simple thermal flow procedure, the trench-width can be easily down to 70 nm. It is also convenient to get a sub-70 nm contact hole pattern by utilizing commercial deep UV resists with this strategy. Many factors influence performance or resists such as soft bake, post exposure bake, exposure dose, and thermal flow, which are discussed and optimized. Suitable dry etching properties of deep UV resists are also characterized for pattern transfer.

Rapidly Selective Growth of Nanoparticles by Electron-Beam and Optical Lithographies with Chemically Amplified Resists

Rapidly and precisely selective growth of self-assembled nanoparticles using an electron-beam or optical exposure system with commercial chemically amplified resists was demonstrated. The required exposure dosage was lessthan 10 μc/cm 2 for patterning chemically amplified resists. By immersing the patterned resist sample in the nanoparticle colloidal solution, nanoparticles were selectively self-assembled on the (3-aminopropyl)trimethoxysilane layer, which was partially covered by the patterned resist layer. The selective growth area can be performed from several hundred micrometers to sub-50 nm. This method has great potential to be used for rapidly selective growth of various nanoparticles or nanomaterials.

High efficiency purification method for multi-walled carbon nanotubes

We remove the impurity and studied the reaction temperature and reagent and the purification methods for multiwalled carbon nanotubes (MWNTs). Defects within the MWNT structure can reduce the effective band overlap and therefore lead to an increase in the materials electrical resistivity. The main impurities in MWNT are iron particles, amorphous carbon, multishell carbon nanocapsules. The results obtained from Raman spectroscopy and thermogravimetric analysis explain that most defects such as metal or carbon defects can be purified by the proposed method.