Kun-Sik Park

Modeling etch rate and uniformity of oxide via etching in a CHF3/CF4 plasma using neural networks

Abstract An oxide film etched in a magnetically-enhanced CHF 3 /CF 4 plasma has been modeled using neural networks. The etch process was characterized with a 2 4−1 factorial experiment. The experimental factors and ranges include 20–80 sccm CHF 3 flow rate, 10–40 sccm CF 4 flow rate, 300–800 W radio frequency (RF) power, and 50–200 mTorr pressure. Radicals (F, CF 1 , and CF 2 ) measured with optical emission spectroscopy were related to etch responses. In the experiments conducted, increases in etch rate generally corresponded to decreases in nonuniformity. Etch nonuniformity was strongly dependent on RF power. The relative significance of polymer deposition and ion bombardment was separated and explained. The root-mean-squared prediction errors are 174 A/min and 0.425% for etch rate and etch nonuniformity models, respectively.

Modeling oxide etching in a magnetically enhanced reactive ion plasma using neural networks

Oxide films etched in a CHF3/CF4 plasma were qualitatively modeled using neural networks. The etching was conducted using a magnetically enhanced reactive ion etcher. A statistical 24-1 experimental design plus one center point was used to characterize relationships between process factors and etch responses. The factors that were varied include a radio frequency power, pressure, CHF3 and CF4 flow rates. The resultant nine experiments were used to train neural networks and trained networks were subsequently tested on eight experiments not belonging to the training data. A total of 17 experiments were thus conducted for modeling. Etch responses modeled are etch rate and etch profile. Root-mean-squared prediction errors of optimized models are 111 A/min and 3.50° for the etch rate and etch profile, respectively. Interaction effects between the factors were examined from the prediction models. Besides the dc bias, the F and CF2 intensities measured with an optical emission spectroscopy were related to the et...

Fabrication of low-cost submicron patterned polymeric replica mold with high elastic modulus over a large area

Low cost submicron patterning technique to fabricate a large area polymeric replica mold using an ultraviolet nanoimprint lithography (UV-NIL) technique is reported. A photo-curable polyurethane-acrylate (PUA) precursor was densified via UV light in order to form a solid polymeric replica mold and to maximise its stability, yet stable mechanical properties with different UV-exposure times were studied using a nanoindentation method as a function of the penetration depth during the loading–unloading cycles. The PUA replica mold demonstrated very high mechanical properties of hardness (0.15 GPa) and elastic modulus (2.7 GPa) due to the increased cross-linking density of the PUA precursor at an optimized UV-exposure time of 600 s. The PUA replica mold demonstrated potential for the fabrication of multi-scale line-and-space patterns with sizes of 350 nm or less with good uniformity and reproducibility over large areas. The replication of the polymeric mold with high durability and excellent mechanical properties can be economically valuable to physical contact nanolithography processes for the high throughput fabrication of micro- and nanodevices.

Siliconized silsesquioxane-based nonstick molds for ultrahigh-resolution lithography

A material approach to fabricating high-performance nonstick molds for manufacturing ultrahigh-resolution features ( 92% at 365 nm), high modulus and wide-range modulus tunability (0.757–4.192 GPa), high resistance to organic solvents (<1.2 wt%), low shrinkage (<3%), and high water contact angle (91–103°). The Si-SSQA–acrylic blends with a nonstick property were easily transferred to high-resolution replica molds with sub-25 nm features, a pitch of 25 nm and a height of 100 nm, even if the release agent was not modified onto the master. In addition, nonstick replica molds with a low concentration of uncross-linked (meth)acrylate showed the ability to duplicate ultrasmall nanostructures with a sub-8 nm parallel line, a pitch of 17 nm and a height of 6–7 nm. Furthermore, the Si-SSQA-based replica mold prevented the formation of bubble defects during imprinting owing to sufficient gas permeability.

Subthreshold characteristics of pentacene field-effect transistors influenced by grain boundaries

Grain boundaries in polycrystalline pentacene films significantly affect the electrical characteristics of pentacene field-effect transistors (FETs). Upon reversal of the gate voltage sweep direction, pentacene FETs exhibited hysteretic behaviours in the subthreshold region, which was more pronounced for the FET having smaller pentacene grains. No shift in the flat-band voltage of the metal-insulator-semiconductor capacitor elucidates that the observed hysteresis was mainly caused by the influence of localized trap states existing at pentacene grain boundaries. From the results of continuous on/off switching operation of the pentacene FETs, hole depletion during the off period is found to be limited by pentacene grain boundaries. It is suggested that the polycrystalline nature of a pentacene film plays an important role on the dynamic characteristics of pentacene FETs.

Control of pn-junction turn-on voltage in 4H-SiC merged PiN Schottky diode

We present numerical simulation results and experimental measurements that explain the physical mechanism behind the high critical voltage, Vcrit, required to turn on a pn junction in a merged PiN Schottky (MPS) diode. The 2D simulation of potential distribution within a unit MPS cell demonstrated that the potential gradient set by the Schottky junction raises the potential barrier formed at the pn junction, thereby increasing Vcrit. Based on this knowledge, we propose that changing the ratio of the Schottky contact and the p+ region area, as well as shallow p-doping of the Schottky interface, can be used to control the magnitude of Vcrit. We present simulation and measurement results that demonstrate the feasibility of our approach.

High-voltage 4H-SiC trench MOS barrier Schottky rectifier with low forward voltage drop using enhanced sidewall layer

In this paper, a 4H-SiC trench MOS barrier Schottky (TMBS) rectifier with an enhanced sidewall layer (ESL) is proposed. The proposed structure has a high doping concentration at the trench sidewall. This high doping concentration improves both the reverse blocking and forward characteristics of the structure. The ESL?TMBS rectifier has a 7.4% lower forward voltage drop and a 24% higher breakdown voltage. However, this structure has a reverse leakage current that is approximately three times higher than that of a conventional TMBS rectifier owing to the reduction in energy barrier height. This problem is solved when ESL is used partially, since its use provides a reverse leakage current that is comparable to that of a conventional TMBS rectifier. Thus, the forward voltage drop and breakdown voltage improve without any loss in static and dynamic characteristics in the ESL?TMBS rectifier compared with the performance of a conventional TMBS rectifier.

Ni-63 radioisotope betavoltaic cells based on vertical electrodes and pn junctions

3D Silicon pn junction betavoltaic cells are designed and fabricated with vertical electrode structure in this work. The betavoltaic cells consist of multiple vertical pn junctions generated by the vertical p-electrodes. The beta-particles from beta-emitting radioisotope Ni-63 are directly incident to the space charge region of vertically generated pn junctions without passing the neutral n or p region. The energy conversion from nuclear energy to electric energy occurs at the vertically generated space charge region. The electrical characteristics of betavoltaic cells having three different unit pn electrode spacing, i.e. 50, 110, and 190μm are demonstrated using electron beam irradiation in a scanning electron microscope (SEM). The Voc and Jsc as a function of pn spacing under 17keV and 30keV of acceleration voltage onto 1.2 × 1.2 mm2 of unit cell absorption area are presented in this paper.

Novel guard ring system design and implementation for punch-through protection toward the detector dicing edge with improved radiation tolerance and reduced dead area

A novel guard system has been proposed based on the experience of the development of Si Mini-Pad detectors for PHENIX Calorimeter at RHIC in BNL. The new GR system is a multi-guard-ring system with segmented n+ implants between them to prevent the punch-through of electric field through the GRs to reach the detector dicing edge. 2D processing and device simulations have shown that with this new GR system, one achieve 1) punch-through protection, 2) reduction of detector dead space, 3) it is detector manufacture/foundry independent regarding the SiO2 property, and 4) it can increase the detector radiation tolerance to a few times of Mrads. Simulations have shown that in the new GR system, the maximum electric field near the GR edges can be reduced by more than a factor of two, and the dead area can be reduced in the order. Further simulations will be performed to obtain optimum design in terms of n+ segmentation geometry, n+ dose, GR widths and numbers. The next engineering run of the Mini-pad detectors with the improved GR system is underway in the detector foundry, and test results will also presented.

Sub-22 nm silicon template nanofabrication by advanced spacer patterning technique for NIL applications

A spacer patterning technique using a poly-Si micro-feature and a SiO2 spacer has been demonstrated to achieve sub-22 nm structures with conventional semiconductor equipments. The sub-22 nm structures have been fabricated by a plasma etching of Si substrate with a spacer oxide mask of which dimension is accurately controlled by the deposited film thickness. The profile of the Si nano-feature was influenced by an O2 flow rate during Si etching in inductively coupled plasma (ICP). As the O2 flow rate was decreased, the etch profile was improved vertically even though the etch rate of Si was slightly decreased. We obtained a 6-inch Si template with both nano- and micro-features of positive shape used for a master mold in nanoimprint lithography (NIL). The nano-sized Si features showed 22-nm width and 145-nm height with the slope of 87°. Further size reduction by anisotropic wet etching with KOH solution was also investigated.