Chang Ju Choi

Ar addition effect on mechanism of fluorocarbon ion formation in CF4/Ar inductively coupled plasma

Using a Langmuir probe and an energy-resolved ion mass spectrometer, gas-phase kinetics of fluorocarbon ions has been investigated as a function of the Ar percentage in a mixed CF4/Ar plasma. Spatially resolved electron energy distribution function, plasma potential, and ion density are measured in an inductively coupled plasma. As the Ar percentage increases, the average electron energy decreases while the electron density remains flat. The ion density also stays constant at low Ar percentages but increases over the Ar percentage larger than 63% mainly due to the increase of the Ar+ density. The plasma potential decreases as a result of the increase of Ar partial pressure, and this is confirmed by measuring the ion energy distributions of argon and fluorocarbon ions using the ion mass spectrometry. With the mass spectrometry, it is found that the most prominent ions, CF3+ and CF+, are formed predominantly by a process of dissociative ionization or radical ionization while CF2+ ions are formed dominantly ...

Use of neural networks to model low-temperature tungsten etch characteristics in high density SF6 plasma

A tungsten (W) etch process in a SF6 helicon plasma has been modeled using neural networks. The process was characterized by a 24−1 fractional factorial experimental design. The design factors that were varied include source power, bias power, chuck holder temperature, and SF6 flow rate. The responses modeled include etch rate, selectivity, anisotropy, and nonuniformity. With optical emission spectroscopy, spectra of radical F intensity were collected to investigate the etch mechanisms. High prediction accuracy was achieved in the etch models. The root mean-square prediction errors were 249 A/min, and 0.41, 0.16 and 0.83 for the etch rate, selectivity, anisotropy, and uniformity models, respectively. While exerting little impact on the selectivity, the temperature greatly affected the etch rate and anisotropy. In particular, the etch nonuniformity was improved at low temperature. Both the selectivity and nonuniformity were predominantly determined by the bias power. The anisotropy was inversely related to...

NEGATIVE ION FORMATION IN SIO2 ETCHING USING A PULSED INDUCTIVELY COUPLED PLASMA

The formation of negative ions in conjunction with their effect on SiO2 etching characteristics has been investigated within a CF4/Ar pulsed-power inductively coupled plasma. Electron energy distribution function in the pulsed plasma shows a narrow distribution compared with the CW mode. The average electron energy and electron density decrease greatly with decreasing duty ratio, which indicates that the high-energy electrons can be cooled effectively during afterglow time. By means of threshold ionization mass spectrometry, radical densities including CFx (x=1 to 3) and F are measured as a function of duty ratio and also correlated with the average energy and density of electrons. For negative ions, two major peaks, F- and CF3-, are formed predominantly through the electron attachment reactions during afterglow time. The possible mechanisms for the negative ion formation are proposed in the pulsed plasma. Additionally, the SiO2 etch rate decreases nearly linearly with decreasing duty ratio and microtrenching is suppressed by the reduction of charge accumulation on the sidewalls in the pulsed plasma.

EUV Mask Process Development and Integration

It becomes increasingly important to have an integrated process for Extreme UltraViolet (EUV) mask fabrication in order to meet all the requirements for the 32 nm technology node and beyond. Intel Corporation established the EUV mask pilot line by introducing EUV-specific tool sets while capitalizing on the existing photomask technology and utilizing the standard photomask equipment and processes in 2004. Since then, significant progress has been made in many areas including absorber film deposition, mask patterning optimization, mask blank and patterned mask defect inspection, pattern defect repair, and EUV mask reflectivity metrology. In this paper we will present the EUV mask process with the integrated solution and the results of the mask patterning process, Ta-based in-house absorber film deposition, absorber dry etch optimization, EUV mask pattern defect inspection, absorber defect repair, and mask reflectivity performance. The EUV resist wafer print using the test masks that are fabricated in the EUV mask pilot line will be discussed as well.

TaN-based EUV mask absorber etch study

Extreme ultraviolet lithography (EUVL) is one of the leading candidates for the next generation lithography. As the requirement on critical dimension (CD) and side wall profile control becomes ever stringent as minimum feature sizes keep shrinking following the Semiconductor Industry Association (SIA) roadmap, the patterning of the EUV mask absorber material, cost of ownership (COO) of mask, and the capability for defect free EUV masks become the crucial path in enabling the overall success of EUV lithography. The purpose of this study is to understand the etch characteristics in TaN-based EUV mask absorber etch, which will enable us to determine robust process condition in terms of CD performance and profile control. In this paper, CD bias performance in TaN-based EUV mask absorber etching is investigated within inductively coupled plasma (ICP) of fluorine-containing and chlorine-containing gas chemistries. The effects of etch parameters, such as plasma source power, bias power, and pressure, on the CD bias are evaluated through design of experiments (DOE). Some other etching characteristics like etch rate and selectivity are also correlated to the CD performance and etch profile to understand the basic etch mechanism in TaN etch. Latest etch results of the TaN-based absorber are also presented.

Plasma treatment after interconnect metal etch for recovery of plasma charge-induced damages

Plasma charge-induced damage has been investigated during metal interconnection in SrBi/sub 2/Ta/sub 2/O/sub 9/(SBT)-FeRAM device. The degradation of the ferroelectric characteristics, such as coercive voltage shift, was predominantly attributed to the metal etching that would inject electrons through the metal antenna and contacts. We also found that the degradation was not caused by a sputtering process in deposition of metal films or mechanical stress of patterned metal pads. To recover the plasma charge-induced damage, we suggest that a soft plasma treatment after metal plasma etching can neutralize charge-up of the electrons so that the degradation of electric properties is minimized.

Mechanism of Tungsten Atom Formation in Tungsten Etchback Using SF 6/Ar Helicon Plasma

The formation mechanism of tungsten (W) atoms in tungsten etching has been investigated with the SF 6 /Ar helicon plasma. The etch rate of W films decreases with increasing flow rate of Ar in the SF 6 /Ar gas mixture while the density of tungsten atoms increases as measured by optical emission spectroscopy. Tungsten films are rarely etched with pure Ar plasma. The density of tungsten atoms generated by a direct sputtering is much less than the one in SF6/Ar plasma. By comparing the etch rate with the relative intensity of W atom as a function of source power and bias power, it was found that tungsten atoms are mainly formed through the dissociation reaction of stable product, WF X (0 % x % 6), and further by electron impact. The loading effect in tungsten etchback can be suppressed by enhancing the redeposition of TiN V F. (y and z ≥ 0) by-products by increasing the source power. The suppression mechanism of the loading effect is investigated by an in situ monitoring of optical emission of tungsten atoms generated during overetching in tungsten etchback.

CD bias control with in-situ plasma treatment in EPSM photomask etch

As mask feature size decreases, etch bias control during Cr and shifter etch becomes more critical factor in Embedded Phase Shifter Mask (EPSM) mask making processes. Since the etching characteristics of the shifter materials, Molybdenum Silicide (MoSi), are sensitive to etching surface condition, Critical Dimension (CD) performance of the shifter layer strongly depends on incoming surface condition from Cr etch. In this paper, lateral etch component of MoSi etch was investigated as a function of various substrate conditions so that a new in-situ plasma treatment was suggested to control the CD bias during MoSi etch. The CD performance was characterized within the surface treatment plasmas and also correlated with some plasma parameters and substrate temperature. As a result, it was found that plasma surface modification could be an in-situ technique to better control the shifter CD in EPSM process and an essential option for redundancy tools in mask production environment.

Plasma-induced charging damage of a ferroelectric capacitor during interconnect metal etch

Plasma-induced charging damage of a SrBi/sub 2/Ta/sub 2/O/sub 9/ (SBT) ferroelectric capacitor has been investigated during interconnect metal etch in fabrication of ferroelectric random access memory (FeRAM). Pattern dependency and the effect of etch parameters such as RF bias power, microwave source power, and pressure on the ferroelectric capacitor were evaluated with a 256 cell array. The etch parameters affected strongly the voltage shift of hysteresis loops so that the degradation could be suppressed by optimized etch process conditions. To evaluate the mechanism of the voltage shift, effects of top and bottom electrode area of the capacitor were also studied.

Control of performance degradation induced by contact etching for a ferroelectric capacitor using a pulsed-power inductively coupled plasma

Using a pulsed-power inductively coupled plasma technique, etching characteristics for a SiO/sub 2/ film were investigated and applied to control the ferroelectric performance degradation induced by plasma etching when a ferroelectric capacitor structure is built to make a FeRAM device. It was found that the pulsed-power plasma helps to effectively suppress the degradation of the remanent polarization 2P/sub r/, an important ferroelectric parameter, compared with the conventional continuous wave plasma. The polarization degradation sensitivities were characterized as a function of the duty ratio and time-modulation frequency in the pulsed plasma mode and we observed a strong dependency of the polarization on the duty ratio. We also tried to understand how the plasma composition change in the pulsed-power mode is correlated with the electrical characteristics degradation of the ferroelectric capacitor by means of ion mass spectrometry.