Organic light-emitting diode (OLED) display technology has been developing rapidly. A review of near-eye
applications indicates its utility and efficiency, especially in comparison to legacy technologies. Next-generation
designs now feature improved performance (significantly increased luminance and lifetime), further underscoring the
utility of this display technology for consumer, military and industrial applications. Consumer applications include
electronic gaming and personal entertainment. Military and industrial applications include situational awareness,
thermal imaging, and simulation & training. Recent development activity is already leading to new opportunities for
technological advances supporting a broader range of applications.
Active Matrix Organic Light Emitting Diode (AMOLED) displays are known to exhibit high levels of performance, and these levels of performance have continually been improved over time with new materials and electronics design. eMagin Corporation developed a manually adjustable temperature compensation circuit with brightness control to allow for excellent performance over a wide temperature range. Night Vision and Electronic Sensors Directorate (US Army) tested the performance and survivability of a number of AMOLED displays in a temperature chamber over a range from -55°C to +85°C. Although device performance of AMOLEDs has always been its strong suit, the issue of usable display lifetimes for military applications continues to be an area of discussion and research. eMagin has made improvements in OLED materials and worked towards the development of a better understanding of usable lifetime for operation in a military system. NVESD ran luminance degradation tests of AMOLED panels at 50°C and at ambient to characterize the lifetime of AMOLED devices. The result is a better understanding of the applicability of AMOLEDs in military systems: where good fits are made, and where further development is needed.
We present characterization of a full-color 852x3x600-pixel, active matrix organic light emitting diode (AMOLED) color microdisplay (eMagin Corporation's SVGA+ display) for environmentally demanding applications. The results show that the AMOLED microdisplay can provide cold-start turn-on and operate at extreme temperature conditions, far in excess of non-emissive displays. Correction factors for gamma response of the AMOLED microdisplay as a function of temperature have been determined to permit consistent luminance and contrast from -40°C to over +80°C. Gamma adjustments are made by a simple temperature compensation adjustment of the reference voltages of the AMOLED. The typical room temperature full-on luminance half-life of the SVGA+ full color display organic light emitting diode (OLED) display at over 3,000 hr at a starting luminance at approx. 100 cd/m2, translates to more than 15,000 hr of continuous full-motion video usage, based on a 25% duty cycle at a typical 50-60 cd/m2 commercial luminance level, or over 60,000 hr half-life in monochrome white usage, or over 100,000 hr luminance half-life in monochrome yellow usage at similar operating conditions. Half life at typical night vision luminance levels would be much longer.
Modern avionics systems are required to impart very large volumes of information about the aircraft's external environment, subsystems, operations, and navigation in real time with minimal impact on the pilot's ability to perform duties and minimal requirements for power and space. To achieve this, high resolution, high brightness displays are required, most often also requiring full color and full video rate. These displays should not demand much space or power and must be reliable, long-lived and able to operate in extreme environments, such as wide temperature ranges, large brightness ranges, and high acceleration and shock. Field emitter array based displays (FEDs) present the avionics community with an opportunity to obtain CRT-like performance in a thin, lighter weight, and more power efficient package. While cathodoluminescent is energy efficient, beam blocking shadow masks, heated filaments, and electromagnets waste most of the CRT's power. Row at a time addressing in FEDs lowers the peak current per pixel, decreases flicker, and increases phosphor life. There are also other opportunities made possible by FEDs such as built-in electronics subsystem capability, true matrix formatting, and an ability to distort arrays to correct for optics systems. Flat-panel displays utilizing field emission array-based technology offer such characteristics, and promise to do so with reduced cost when compared to alternative solutions.
Field emitter array-based display technology offers CRT-like characteristics in a thin flat-panel display with many potential applications for vehicle-mounted, crew workstation, and helmet-mounted displays, as well as many other military and commercial applications. In addition to thinness, high brightness, wide viewing angle, wide temperature range, and low weight, field emitter array displays also offer potential advantages such as row-at-a-time matrix addressability and the ability to be segmented.
Two approaches that control the overflow of silylated material that can occur subsequent to surface imaging of acid-hardened resists are introduced. Treatment of the resist surface with a cross-linking agent [bis(dimethylamino)dimethylsilane] prior to silylation can produce a surface layer with the physical integrity to constrain silylated material. Alternatively, the unexposed areas of the resist may be partially removed by development with a basic solution. The surface depressions thus produced allow volume expansion to occur during silylation without causing overflow.
Proc. SPIE. 1925, Advances in Resist Technology and Processing X
KEYWORDS: Deep ultraviolet, Etching, Image processing, Silicon, Manufacturing, Scanning electron microscopy, Very large scale integration, Reactive ion etching, Photoresist processing, Semiconducting wafers
Many approaches to surface imaging rely upon selective incorporation of silicon into an already imaged resist layer. SAHRTM (silylated acid hardened resist) obtains its selectivity by a lower rate of silicon incorporation into exposed and crosslinked areas, providing a positive tone image after RIE development. Two difficulties with the practical implementation of this approach have been the overflow of silylated material onto crosslinked areas, and reduced silicon incorporation in small openings. We have found that surface treatment with a bifunctional silylation agent (the `two gas process') can prevent overflow, and that removing part of the resist layer with dilute tetramethyl ammonium hydroxide (TMAH) (the `presilylation develop process') minimizes overflow and improves silicon incorporation in small features. With a predevelop step, feature size linearity is obtained below k1 equals 0.7, with uniformity and repeatability consistent with VLSI manufacturing practices.
Silicon field emitter arrays (FEAs) have been fabricated with a unique orientation dependent etching process and oxidation sharpening process to produce uniform and reproducible single point gated structures. Electron emission currents from these single silicon field emitters have exceeded 20 microamperes with extraction gate voltages less than 200 V. These pyramidal field emitters have a 'cone' angle of about 70 degrees with a tip radius of curvature of about 100 angstroms. The gate metallization has been formed from a variety of materials, notably platinum and polysilicon. Similar electron emission results have been operated continually in an unbaked vacuum system in the multi-microampere regime for over 600 hours without a change in their emission properties. Significant numbers of individually addressed field emitters can be fabricated on small silicon chips, and many chips can be fabricated on a silicon wafer, thereby making the cost per chip reasonably low. Microstructural Einzel lenses have also been fabricated with 5 pole electrodes as well as arrays of deflectors. The combination of the technology of microstructural field emission and microstructural lenses and deflectors offer a unique opportunity for nanolithography, novel devices, and electron/ion microscopy. Microstructurally Integrated Lens and Emitter Systems (MILES) offer the potential for massively parallel electron beam applications and electron/ion source redundancy.
In this paper, we describe the results of experiments performed using wafers having either phosphorous (POCl3) doped polysilicon, LPCVD silicon nitride, LPCVD silicon dioxide, LPCVD silicon dioxide over POCl3 doped polysilicon, evaporated aluminum, or CVD tungsten thin films, patterned with and without the use of deep UV anti-reflective coatings. The parameters of reflectance control, critical dimension control, focus/exposure latitude, and resist profiles were studied for line/space gratings and contacts. Incorporation of anti-reflective coatings was shown to be very beneficial for reducing the impact of highly reflective substrates, grainy surfaces, and topographical features encountered during deep UV imaging. The ARC process is independent of the substrate's reflectivity, allowing the same exposure dose for all substrates studied. Without ARC the optimum exposure dose for the same substrates varied over a 35% range. ARC also provides slightly increased exposure and focus windows for some substrates, and was shown to significantly improve linewidth control on rough substrates such as POCl3 doped polysilicon and tungsten. The grainy surface of the tungsten wafers was nearly impossible to pattern without the use of an anti-reflective coating; without ARC, there was virtually no process window (approximately 2 mJ/cm2) for retention of 0.50 micrometers features.
Contact structures represent some of the most challenging features to image using deep UV excimer laser lithography. A single resist process, exposure dose, and focal setting must compensate not only for variations in the reflectivities of gate (Le, polysilicon) and diffusion (i.e., oxide) substrates, but must deal with variations in underlying topographical features which create a non-uniform resist film over a non-planar imaging surface. Commercially available deep UV photoresists are negative toned, requiring the use of clear field photomasks for imaging of submicron contact structures. In this paper, we describe three strategies for enhancing the ability to image contact structures using currently available negative toned chemically amplified deep UV photoresists: (1) optimization of central exposing laser wavelength, (2) incorporation of anti-reflective coatings, and (3) optimization of resist film thickness for sidewall profile enhancement. These approaches should also enhance imaging of contacts using positive tone photoresists, once they are commercially available
A variety of analytical and process control techniques have been employed during process development activities for a 0.5 micrometers deep UV positive tone surface imaging process. Examples of applications of these methods for identification of primary positive tone surface imaging issues and process optimization for enhancement of ultimate resolution are described. Advantages and limitations for each technique are discussed.
Experiments were performed to quantify the central laser wavelength setting which provided optimum imaging performance for two generations of deep UV steppers: GCA ALS Laserstep and GCA XLS Laserstep. Significant performance enhancements resulted by adjusting the central wavelength setting of the ALS system by -0.23 nm from the original baseline wavelength (point of minimum distortion). The baseline wavelength of the more advanced lens of the XLS system was closer to optimum, with acceptable imaging performance parameters over a >0.04 nm band. Lens characterization methodologies are described.
A Monte-Carlo simulation program has been modified to allow specifying the specimen surface as a series of regions with arbitrary shape and composition. It also models the production of the secondary electron signal. This has been applied to a systematic series of experiments with 0.5 and 1.0 micrometers lines of photoresist, and compared to experimental measurements using an SEM. The qualitative agreement indicates that the model can be used to study the effects of variations in operating conditions such as accelerating voltage, as well as the effect of changes in specimen geometry or composition.
Techniques commonly used to determine silicon penetration depth during deep UV surface imaging lithography are compared to a method referred to as plasma etch 'staining.' This methodology is described in detail and the results compared and correlated to Rutherford Backscattering Spectroscopy (RBS) and ellipsometric (film swelling) measurements. Effects of the staining parameters on the resulting silicon depth are also discussed.
A combination of metrology techniques was employed to fine tune the wavelength setting of a 248 nm excimer laser stepper to optimize performance. Scanning electron microscopy was used to document local resolution, proximity effects, and astigmatism, while GCA SMARTSETR and electrical resistance techniques were used to examine full field effects. Using the combined metrology methodologies, the authors documented the decrease in proximity effect, improvement in resolution, and increase in absolute lens distortion with negative shifts in laser wavelength setting, with a slight differential in the setting required to minimize horizontal versus vertical proximity effect and astigmatism. A wavelength offset of -2.3 angstroms from the nominal stepper setup wavelength was determined to be the best operating wavelength for these applications.
As the feature size requirements of TJLSI devices continue to decrease below the practical limits of standard optical
metrology, alternate measurement methodologies will be utilized on a more routine basis during device fabrication. A
series of linewidth measurements of photoresist on polysilicon and etched polysilicon equal line/space gratings having
nominal linewidths ranging from 0.45 jim to 2.0 p.m has been performed using a variety of metrology techniques.
Features fabricated using a 248 nm deep UV laser stepper and 405 nm near UV stepper were used in the experiments.
Top-down low-voltage SEM measurements, electrical resistance measurements, confocal ultraviolet laser scanning
microscope profiles, and SEM measurements on cleaved cross sections are compared. By measuring a large number of
points on each line and die, the variability of the linewidths themselves, the measurement precision of the techniques, and
the measurement bias between the methods are isolated. Experimental procedures and measurement techniques are
described along with the resultant data.