Hiroshi Arimoto

Proximity effect correction using pattern shape modification and area density map for electron-beam projection lithography

A novel proximity effect correction algorithm using pattern shape modification and the area density map method for electron-beam projection lithography is proposed. This algorithm enables fast, accurate and self-consistent calculation of modified pattern sizes. The correctable minimum feature sizes for shape modification were investigated from two viewpoints, mask fabrication restriction and dose margin. The correctable minimum sizes are mostly determined by the dose margin requirement in the case of isolated and dense repeated patterns, implying that the tool resolution determines correctable minimum sizes. A special technique is required for isolated space patterns where the backscattering energy cannot be reduced by simple sizing. We have implemented an algorithm in which pattern densities at middle parts of large patterns are reduced by using a lines and spaces (L/S) pattern or mesh patterns for that case. Successful correction results down to 60 nm from the simulation and 100 nm from the experiment have been obtained.

Maskless ion beam writing of precise doping patterns with Be and Si for molecular beam epitaxially grown multilayer GaAs

We have developed a computer‐controlled ion beam writing system with 14‐bit resolution to operate a 100 kV maskless ion implanter combined with an MBE growth chamber for patterned impurity‐doped GaAs/AlGaAs multilayer growth. Performances of various functions of this new computer‐controlled, crystal growth system have been tested. (1) Ion species (Si++, Si+, Be++, Be+) are rapidly selected with minimum astigmatism. (2) Depth impurity doping geometry can easily be controlled by automatically selecting ion charges or semiautomatically changing accelerating voltage. (3) Ion beam diameter and position are precisely monitored and controlled. (4) Ion beam mark detection can be performed with submicron resolution over double layers. (5) Ion beam writing for maskless implantation can be done in arbitrary shapes over the 400 μm square field with assigned impurity, ion dose, and energy, while monitoring ion current and beam diameter. Using this system, we have demonstrated arbitrary pattern implantation and GaAs gr...

GaAs Growth Using an MBE System Connected with a 100 kV UHV Maskless Ion Implanter

A new molecular beam epitaxy (MBE) system coupled with a 100 kV maskless ion implanter via an ultrahigh vacuum (UHV) sample transfer module was constructed. This system can grow epitaxial layers with ion beam pattern-implantation without exposing a sample surface to the outer atmosphere. Buried Be implanted layers in MBE grown GaAs were fabricated using this apparatus. Because of the contamination-free UHV growth process, the photoluminescent intensity depth profile of the grown crystal showed no degradation at the interface where the MBE growth was interrupted for the ion implantation process.

Direct Evaluation of Gate Line Edge Roughness Impact on Extension Profiles in Sub-50-nm n-MOSFETs

In this paper, the impact of gate line edge roughness (LER) on two-dimensional carrier profiles in sub-50-nm n-MOSFETs was directly evaluated. Using scanning tunneling microscopy (STM), it was clearly observed that the roughness of extension edges induced by gate LER strongly depended on the implanted dose, pockets, and coimplantations. Impurity diffusion suppressed by a nitrogen (N) coimplant enhanced the roughness of the extension edges, which caused fluctuations in the device performance. The expected effect based on the carrier profiles measured by STM of the N coimplant on the electrical performance of the n-MOSFETs was verified

Focused Si Ion Implantation in GaAs

A 160-keV, submicron-focused Si ion implantation in MBE-GaAs was made using a 100 kV maskless implanter with a Au–Si–Be alloy ion source. Obtained Raman spectra indicated that compared with the implantation current densities of an unfocused ion beam, the higher current density (about 104 times greater) of the focused beam resulted in less implantation-induced and residual (after annealing up to 500°C) damage. Moreover, 850°C annealing led to a higher electrical activity of focused implanted Si-ions but almost the same optical quality of conventional implantation.

CHARGE BUILD-UP IN SI-PROCESSING PLASMA CAUSED BY ELECTRON SHADING EFFECT

We investigated the influence of electron temperature and rf bias on charge build‐up caused by electron shading in inductively‐coupled plasmas (ICP) at 2 to 40 mTorr in Ar. We used Si substrates covered with a 500‐nm‐thick SiO2 film which had a line‐and‐space pattern. We measured the electron and ion currents going into the Si substrate through the dielectric structure. When the pattern size decreases, the electron current through the dielectric structure is suppressed and the floating potential increases. We also measured the change in the floating potential of the sample as the electron temperature was increased. As the electron temperature is increased from 2 eV to 4 eV by controlling the gas pressures, the floating potential difference increases between samples with different pattern sizes. To investigate the influence of rf bias (13.56 MHz) on charge build‐up, we measured differences in the dc self‐bias voltage between samples with different pattern sizes. dc self‐bias voltage differences increase wi...

Flat-band voltage shifts in p-MOS devices caused by carrier activation in p/sup +/-polycrystalline silicon and boron penetration

We found that the annealing time dependence of the flat-band voltage (V/sub FB/) shift of a p/sup +/-polysilicon gate MOS diode is attributed to the activation of boron in the polysilicon instead of the boron penetration through the gate SiO/sub 2/. We identified the process window for p/sup +/-polysilicon gate pMOSFETs taking into account that boron is sufficiently activated in polysilicon without penetrating through the gate SiO/sub 2/.

Correction for local flare effects approximated with double Gaussian profile in ArF lithography

A method has been developed for correcting line width variations due to midrange flare with a scattering range of over a few tens of micrometers (which we call local flare). It is shown that the conventional single Gaussian point spread function (PSF) is not sufficient and that a double Gaussian point spread function is needed to explain the line width variation caused by local flare. The remaining errors after correction are discussed under the assumptions that the mask correction is linear with respect to local flare intensity and is independent of pattern layout considering the order of the local flare correction (LFC) and optical proximity correction (OPC). This simple sizing method can reduce the critical dimension (CD) variation regardless of whether LFC is done before or after OPC. The LFC performance was evaluated using actual 90-nm-node LSI data. A much faster correction time than that of OPC was achieved by introducing the area density map method. The CD variation due to local flare was reduced from 22 to 5 nm.

Growth-Interrupted Interfaces in Multilayer MBE Growth of Gallium Arsenide

Growth-interrupted interfaces in Molecular Beam Epitaxy (MBE) have been characterized by C-V measurements and secondary ion mass spectroscopy. Carriers were depleted around the interfaces depending on interruption conditions such as the background vacuum and the interrupted period. For the depleted samples, carbon was detected at the interfaces. This carbon contaminant deteriorated crystal quality at the interface and caused carrier depletion. Using the MBE system combined with a maskless ion implanter in ultrahigh vacuum (UHV), a selectively Si-implanted GaAs multilayer structure was grown without interface degradation.

Selective Si and Be implantation in GaAs using a 100 kV mass‐separating focused ion beam system with an Au–Si–Be liquid metal ion source

Submicron Si and Be ion beams have been implanted into GaAs using a 100 kV maskless ion implantation system with a liquid metal ion source which is capable of emitting double ion species (Si++ and Be++). Both ion beams are implanted at 160 keV with the dose of 1013 to 1014 cm−2. The feasibility of the focusing column was demonstrated by forming the submicron width of line patterns of alternative Si and Be doping in GaAs including a pn junction array. The linewidth of the ion implanted area has been evaluated by SEM, after selective etching of the annealed sample. It has been found that high dose implantation results in considerable lateral impurity spread of more than 1 μm even with the focused ion beams with a diameter of 0.1 μm. However, submicron width implantation turns out to be possible with relatively low doses or with shallow dopings.