MRAM, a potential candidate of next generation or "universal" memory device, has been
in process development and targeted for production. This high density non-volatile
memory has a fast <20ns read/write cycle and unlimited endurance. Wordline layer is
important for writing. Using KrF tool capability only, this "line & contact hole" wordline
pattern must meet the challenge of aggressive pitch size shrinkage and process margin
requirements in order to deliver reliable writing efficiency. Thus, appropriate process
integration schemes demonstrating single exposure, double exposure and double
patterning are compared. A comprehensive study from mask layout simulation and its
cost to litho OL/CD process window experimental data analysis will be presented to
achieve potential high yield manufacturing goal of the critical wordline design and
Magneto-resistive Random Access Memory (MRAM), considered the leading candidate for the next generation of universal memory, has moved from research to pilot production. Commercialization of the MRAM devices in mobile computing, cell phones, portable recording and other playback devices, home computing, consumer electronics, enterprise computing and telecommunications, promise to bring in annual revenues exceeding $50 billion during the coming years. CD-SEM correlation of contact physical Critical Dimension to Magnetic Tunneling Junction (MTJ) resistance is critical for MRAM device performance. This paper focuses on a new two-dimensional metric that more accurately characterizes MTJ resistance by calculating total contact area of unique and complex structures. We consider the advantages of the Contact Area metric for measurement of complicated shapes. We illustrate that introduction of the new metric allows for improvement in process control for critical contacts.
Resolution enhancement techniques and higher NA exposure are employed to meet the lithography requirements imposed by aggressive shrinks to chip feature sizes. For certain critical levels, like storage and isolation patterning of DRAM devices, the capability to exactly reproduce the mask layout is limited. Severe corner rounding and line image shortening can occur. Such phenomena can be significant contributors to side effects like current leakage, inadequate retention time, stress, and perhaps yield loss. Our development work has shown that the use of Serif and Hammerhead structures can improve resolution printing. Moreover, better process latitude and CD control can be achieved. This paper gives an overview of these innovative techniques. It includes the consideration of different design layouts based on simulations, as well as mask making limitations e.g. mask inspection capability. The benefits of these techniques are discussed and illustrated with detailed lithographic performance data and SEM pictures.
Multiple contact hole resist samples from a variety of DUV resist suppliers, including both acetal and ESCAP chemistries are evaluated on an organic anti-reflective under layer (ARC) using an attenuated phase shift mask (APSM). One sample exhibited excellent surface inhibition and superior lithographic performance for patterning contact holes of 0.2 micrometers imaging size. For most of resists, the process windows are limited by unwanted sidelobe printing through focus. The sensitivity of sidelobe printing to focus can be attributed to lens aberrations. For the first time, we prose to use Depth-of-focus (DOF) loss PWLdof and Exposure latitude (EL) loss PWLel to characterize resists surface inhibition, as well discovered that DOF loss is a sensitive measure of surface inhibition. Similar lithographic performance is obtained from acetal and ESCAP based materials. The two ESCAP resists EB3 and EA2 have better oxide etch resistance than the acetal resist AC1. The top surface reticulation is observed on ESCAP resist EB3 and EA2 during the oxide etch, but not on the acetal resist AC1. 110 nm underexposed resolutions achieved with the resist EA4 at a mask size of 250 nm. Faster resists generally exhibit better resolution but have smaller process windows when side lobe printing is included as a criterion. Selection of a resist formulation for attenuated phase shift applications has to face a compromise between resolution, photospeed, process window and surface inhibition. Finally, ARC operational modes and optical properties had little effect on sidelobe printing, and optimization of PEB temperature is important in suppressing sidelobe printing.
The spectral sub-structures of XPM were measured using a high resolution optical spectral analysis system. The observation is in good agreement with the theoretical prediction. The oscillatory behavior of the XPM spectrum is suggested to be used for a high-bit all-optical XPM A/D converter. With the advent of ultrashort laser sources, it has been established that a light pulse can be used to control the properties of its own or another light pulse by using optical nonlinear processes in a material. This important property can be utilized for the future generation of high-speed optical computations and communications. Over the past several years, the operation of ultrafast optical logic gated using picosecond Sagnac Kerr Interferometer switch and phase conjugation gates have been successfully demonstrated. The third order nonlinear process cross-phase-modulation (XPM), in which the phase of a weak signal pulse is modulated by the index change induced by a strong pump pulse to produce the spectral broadening, provides a novel method to modulated the frequency of optical pulses at THz speed. We propose the ultrafast all optical A/D converter using XPM and report on measurements on the fine spectral structures of the XPM spectra of picosecond laser pulses using high resolution grating spectral analysis system. The observed substructure of the oscillatory XPM spectrum is suggested to be used for increasing the accuracy of all optical XPM A/D converters.