A silicon micro-lens is proposed and analyzed when it is integrated into the photodiode for the application of a backside illuminated (BSI) image sensor (Pixel size is around 1 um). Due to the small dimension of the BSI pixel, each pixel of the image sensor receives from its adjacent pixels cross-talk (x-talk) due to large light incident angle and light diffraction, resulting in reduced sensor MTF and possible color artifacts. A silicon ulens formed between the photodiode and RGB color filter works as an inner lens to improve the focus of the light and guide it into its corresponding pixel, thus decreasing optical x-talk and reducing noise. Since the silicon ulens is integrated into the photodiode and could be doped as part of the photodiode, this design would eliminate any internal reflection caused by traditional inner micro lens solutions (made of Si oxide, Si nitride or polymer). ‘By color' anti-reflection coatings (ARC) on top of the silicon ulens can work as a versatile optical filter to compensate the light spectrum and angular mismatch. Our design and analysis provide a solution to improve the quantum efficiency (QE) and x-talk of the BSI image sensor and the QE enhancement for each pixel are discussed in detail.
Modern trends in camera module design for both mobile and DSC applications are driving the race to shrink pixel and
increase pixel array size. At the same time higher demands on the quality of color images - DSC-like quality for mobile
applications - require maintaining a large pixel capacity, quantum efficiency (QE), and sensitivity to preserve color
image quality. This becomes extremely difficult as the size of the pixel shrinks. This paper discusses the Common
Element Pixel Architecture (CEPA) for image sensors with small pixels as well as new pixel designs and process
changes, that have enabled a new generation of image sensors with high performance 2.2-μm, 1.75-μm, and smaller
pixels. Advanced algorithms of capturing the image help to overcome the challenges associated with the limited pixel
capacity of small pixels. The paper considers an HDR mode of operation for the small pixel and its effect on the image
quality. Achieving good color crosstalk performances is one of the big challenges in CMOS Image Sensors with small
pixels. The paper presents results of an experimental study of crosstalk for different pixel sizes, analyzes the effect of
crosstalk on the quality of color image and signal-to-noise ratio after color processing, and discusses ways of cross talk
reduction for small pixels.
Applying a method for direct on stepper measurement of aerial images, the quarter micron performance of an advanced deep UV excimer stepper is analyzed. The aerial images are compared to corresponding simulation results as well as data obtained on an aerial image measurement system (AIMS). The study includes three different mask types: standard chrome on glass, an attenuated and an alternating phase shifting mask. Substrate effects as well as laser spectral purity effects have been measured. In general, the data show that simulation and AIMS data represent an upper limit for the aerial image contrast, which may be degraded significantly under real world imaging conditions. Use of a bottom anti reflective layer and a new laser with improved spectral bandwidth result in optimum aerial images close to those measured on AIMS, but they are still worse than simulation results. Some examples of quarter micron resist profiles and process windows in a deep UV resist are shown that were obtained under these optimized conditions with an excimer laser stepper.