With modern lithographic technology, a compact spectrometer is designed to include a blazed micro-grating with cylindrical concave grating profile. In order to restrict the sagittal beam divergence and to reduce the size of the spectrometer, the micro-grating is embedded inside a pair of planar mirrors used as a slab waveguide. In the simulations for the effect of the waveguide, we discover that the focal pattern distortion introduced by the waveguide causes a blunted and side-tailed peak in the spectrum. The distortion can be managed by allowing some gap between the edge of the waveguide and the image sensor. Such a configuration has greatly improved the resolving power of the micro-grating in this compact system.
There have been many researches regarding to the organic light-emitting diodes (OLEDs) with microcavity structures, in
order to enhance its output optical properties such as chromaticity and intensity. In the applications to the white-light
OLED (WOLED) and full color displays, the difficulty remains in the design of the optical length of the microcavity for
proper resonance. A typical microcavity structure consists of the dielectric quarter wave stacks (QWS) as a distributed
Bragg reflector (DBR) and the metal cathode to form a pair of mirrors. The organic and other material layers between the
mirrors plays the role of the cavity. It can only have one major resonance peak in the perpendicular view angle and degrade
the broad spectrum nature of the WOLED. Our study proposes the use of non-QWS mirror using thicker and higher-order
(greater integral multiple of the quarter wavelength) of the dielectric layers. We can have the multiple resonance peak
wavelengths to meet the WOLED requirement by introducing the reflection phase change of the dielectric stack mirror
at certain wavelengths. The proposed microcavity structure yields a desired shift to the white point in CIE chromaticity
for a typical green OLED. One of the potential applications of the microcavity with non-QWS mirror can be to make the
WOLED even closer to the CIE white point without worrying the doping process variation, which is a typical problem in
the WOLED. It greatly enhances the usability of the WOLED in various applications.
Many researches have been devoted to enhance the light extraction of light emitting diodes (LED). In some designs of
LEDs, an absorbing substrate cannot be avoided. To prevent the emitted light from being absorbed by the substrate, a
highly reflective mirror called distributed Bragg reflectors (DBR) is employed between the substrate and the active layers.
In addition, the DBR layers are doped to conduct current. In our study, we have n-GaAs as the substrate, n-AlGaAs /
AlAs as the DBR, multiple quantum wells (MQW) as the active layers, p-GaP as the window layer. The choices of the
dopant for the DBR are Si and Te. However, the resultant LEDs have different performance. The one doped with Si
in DBR (DBR:Si) performs poorly. Our investigation shows that the optical properties of DBR:Si degrade dramatically
because of the existence of AlGaInP (part of MQW) layer above and the subsequent high temperature annealing in p-GaP
layer growth. Either condition alone cannot yield the degradation. Conversely, the optical properties of DBR:Te do not
change significantly even though it undergoes the same processes to grow the subsequent layers. The result indicates
a sophisticated interaction between DBR:Si and AlGaInP layers during the high temperature annealing process for the
growth of p-GaP. The study provides the insight on the influence of the dopant to the optical properties of DBR in LED
devices.
The optical proximity effect (OPE) is one of the most serious problems, as the optical lithography is pushed into the smaller
feature size below the exposure wavelength. Some of the typical ways to solve this problem are to use the optical proximity
correction (OPC) and the phase shift mask (PSM). However, these sophisticated techniques increase the cost of making
masks, as well as the risk of getting defects on the masks. In this study we optimize the annular off-axis illumination (OAI)
conditions to reduce the Isolated-Dense bias (IDB), in order to improve the resolution and the depth of focus (DOF) as
a solution to fight for OPE. Through the simulation done with AIMS Fab 248 exposure system, the energy distribution
on the photo-resist is analyzed with the intensity distribution across the simulated exposure images. The optimization is
performed with the aid of Taguchi method. On the basis of the simulation analysis, the optimum optical parameters (the
numerical aperture NA, the degree of coherence Sigma, and the ratio of the inner and the outer radii of the rings Annular)
are selected to obtain the high resolution and enough DOF to reduce IDB value. The low IDB can be realized by using
optimal optical parameters before exposure processes, without using sophisticated OPC and PSM on the masks.
KEYWORDS: Photomasks, Semiconducting wafers, Critical dimension metrology, Scanning electron microscopy, Control systems, Etching, Optical testing, Process control, Deep ultraviolet, Diffusion
In the semiconductor process field, the control of the critical dimension (CD) is a major task, especially in the processes
of mask manufacturing and wafer exposure. One of the difficult problems is that sometimes the linewidth variation on
wafer is out of specification even though the linewidth on mask is in specification. The linewidth discrepancy may come
from the process control during the chrome film etching, which will influence the sidewall profile of the chrome film
pattern. The investigation begins with the analysis of the cross-section of the masks used in the 130-nm technology node
regarding the angular variation of the profile. Through the simulation done with AIMS fab 248 exposure system, the optical
energy distribution on the photoresist, affected by the sidewall angular variation of the mask, is analyzed with the intensity
distribution across the simulated exposure images. The result enables us to establish the process window of the exposure
latitude and the depth of the focus (DOF) for the acceptable linewidth variation (less than 4 nm.) The established process
window can help the engineers to avoid the linewidth discrepancy between the wafer and the mask, even with the inevitable
chrome sidewall angular variation of the mask.
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