We numerically study surface-plasmon (SP) mediated semiconductor light-emitting diodes (LEDs) and show that
mediation of SPs can be useful for high power LEDs in their modulation speeds and directionalities. It has been reported
that SPs can drastically enhance internal quantum efficiencies and speeds of InGaN quantum-well (QW) LEDs by letting
them dominate spontaneous emission (SE) processes. Many experimental and theoretical studies have been conducted in
this context but most of the works have dealt SE into SPs and light extraction from excited SPs separately. In particular,
there is no theoretical analysis, to our knowledge, which simultaneously considers SE into SPs on a textured metal
surface along with its extraction to outside radiation. In this presentation, we numerically study InGaN QW LEDs which
consist of 1-D metallic gratings on a p-contact electrode and an adjacent single QW emitting green light by using finite-difference
time-domain (FDTD) method. We focus on the case where the first order diffraction of SPs produces
lightwaves propagating along the surface-normal direction. SP band-edge effect on SE rate, extraction of SPs into
internal-radiation, and angular directionality of final outside-radiation are analyzed. Practical enhancement of LED
performances are discussed on the basis of the simulation results.
Trichromatic LED backlights render higher color gamut and panel transmittance to liquid crystal displays (LCDs) than
yellow phosphor-converted white LED backlights can possibly do at their best. In realization, however, several technical
challenges arise, such as colour shift due to the ambient temperature change, decrease in brightness at elevated
temperature, an enlarged dead zone for colour mixing, minimizing the total number of chips and so on. In this work, we
designed and demonstrated a low-cost driving circuit that stabilizes brightness and colour coordinates of trichromatic
LED backlights using a thermistor as a temperature compensating element. By applying the temperature compensation,
the amounts of the brightness and colour shift were reduced to 54% and 51% of the uncompensated cases, respectively.
Ultra-compact silicon-photonic-crystal-waveguide-based thermo-optic and electro-optical Mach-Zehnder interferometers
have been proposed and fabricated. Thermal and electrical simulations and optical characterizations have been performed.
Experimental results were in good agreement with the theoretical predictions.
A method of writing long period grating and a model to explain light coupling between fundamental mode and cladding mode are presented. One athermal hermetic sealing approach is proposed to form hermetic sealing long period fiber grating. A long period fiber grating was designed and written for this experiment. Low temperature glass solder was introduced to seal around the fiber. The sealing and optical performance testing results are discussed.
Trichromatic LED backlights render higher color gamut and panel transmittance to the liquid crystal displays (LCDs) than yellow phosphor-converted white LED backlights can possibly do at their best. In realization, however, several technical challenges arise, such as color mixing, minimizing the total number of chips, and maintaining the color balance. We designed and demonstrated a backlight unit for 2.2 inch TFT LCD using two RGB 3-chip LEDs to assess the feasibility and the technical hurdles to overcome. The average brightness of the backlight is 2509cd/m2 at the input power of 200mW. The power efficiency is lower than but comparable to commercially available white LED backlights. The color gamut of the LC panel is increased from 53% to 78% when its conventional white LED backlight is replaced by the trichromatic LED backlight. Panel transmittance is expected to be enhanced as well by about 8%. The ambient temperature change was found to be the most significant cause of the color shift of the trichromatic LED backlight. The forward bias voltage can be used in the feedback, since it changes linearly with temperature.
As DRAM (Dynamic Random Access Memory) device continuously decreases in chip size, an increased speed and more accurate metrology technique is needed to measure CD (critical dimension), film thickness and vertical profile. Scatterometry is an optical metrology technique based on the analysis of scattered (or diffracted) light from periodic line and space grating and uses 2θ angular method (ACCENT Optical Technologies CDS-200). When a light source is irradiated into the periodic pattern, the scattered intensity signal of zero-th order as a function of incident angle is measured. By analyzing these scattered signals, various parameters of the periodic pattern such as CD, vertical profile, mapping of substrate structure, film thickness and sidewall angle can be determined. Advantages of scatterometry are that drastic decreased measuring time and acquirement of CD, vertical profile, film thickness and sidewall angle by just one measurement. In this paper we will discuss various applications of scatterometry to sub-100nm DRAM structures of straight line and space and curved line and space patterns. Details of the correlation with CD-SEM (Scanning Electron Microscope) of standard metrology tool and repeatability of measured CD values will be discussed. As diverse applications, results of in-field, in-wafer and wafer-to-wafer CD monitoring, STI (Shallow Trench Isolation) depth monitoring and matching of vertical profile with V-SEM (Vertical SEM) will be also presented.
Scatterometry is a novel optical metrology based on the analysis of light diffracted from a periodic sample. In the past the technology has been applied successfully to a variety of different grating types found in the manufacture of microelectronic devices. The scope of these applications, however, has been limited to structures that are singly periodic (periodicity = 1) in nature, i.e., gratings that are simple line and space structures with one periodic dimension. Rigorous coupled wave theory (RCWT), the underlying theory behind scatterometry measurements, can be applied to structures with a higher dimension of periodicity (periodicity > 1), although the computation is much more complex. In this paper we will discuss the application of scatterometry to structures with higher dimensions of periodicity, such as arrays of contact holes and DRAM cells. Details of the model, such as computation time and considerations for choosing a proper shape for the diffracting structures, will be presented. Sensitivity of the various parameters, such as the multiple critical dimensions and sidewall angles, will be discussed. Finally, results of measurements on contact hole and typical DRAM storage node patterns will be summarized. When compared to SEM, we will show correlation results that are greater than 0.9 for most applications, indicating that the technology can be applied successfully to such complicated structures. System matching between tools for these applications will also be discussed.
Currently it is very popular to use off-axis illumination technique for higher resolution with wider depth of focus. However there are several problems in the technique, one of which is deterioration of image quality induced by the non- uniform effective source distribution. If the intensity distribution on the illumination aperture lacks of spatial symmetry, each diffraction order beam impinging on the wafer surface has angularly asymmetric distribution. This makes the optical system have pattern size dependent telecentricity error. For a simple line or grouped lines it gives rise to only the pattern displacement with defocus which can hardly be detected unless there are any reference. But the periodic island type patterns which have discrete features and multiple pitch components in one direction can be bent and deformed asymmetrically with defocus. Asymmetric imaging for island type patterns gives rise to also the pattern CD asymmetry with defocus. We present schematic explanation of the effects of non-uniform effective source and the simulation result. We also investigated the phenomena in a high density DRAM cell active layer of 460 nm minimum pitch and characterized it by various approach.