Mask cost is a key challenge for the semiconductor industry and a major issue is the write times of e-beam pattern generators. DUV pattern generators can provide high throughput, but there is a cost and time involved in qualifying these tools for IC production. To minimize this time and cost, the masks from the DUV tool should have pattern fidelity similar to that of e-beam tools. This can be done with corner enhancements on an imaging DUV mask writer. Here, we describe such a corner enhancement scheme and present results for the 65-nm-node requirements. We demonstrate how the corner radius can be tuned in a range of radii with a negligible effect on the process latitude.
The first pattern generator, Sigma 7100, using the novel optical SLM (Spatial Light Modulator) technology is now shipping. This paper analyses the writing strategy, how the quality differs from that of a stepper/scanner, and some improvements in development for the next product, here called the SIGMA 7X. The improvements include higher NA, smaller grid size, optimized illumination for reduced proximity effects, and weak phase shifting. The use of embedded addition of corner enhancements is discussed. Finally there is a brief discussion of chrome as the absorber film in binary masks.
Grating coupled surface emitting lasers (GCSELs) are in- plane lasers monolithically integrated with grating outcouplers for beam shaping and image generation. Highly directional and efficient outcouplers can be formed using various grating and waveguide geometries. Beam shaping features are incorporated using a computer generated waveguide hologram that allows the wavefront of the emitted light to be tailored for the required beam shape. Requirements on the integrated in-plane laser include a wide and spatially coherent guided wave with a minimum of wavefront distortion and a stable emission wavelength. Promising lasers for this purpose are master-oscillator power-amplifier configurations as well as various kinds of unstable resonator designs. Here we present results from modeling and experiments on the key elements of GCSELs as well as fully integrated GCSELs of linear and circular geometries.
The modal performance of focusing circular grating-coupled surface-emitting lasers has been investigated. Both the effects of reducing the resonator diameter and introducing an unpumped indentation in the center of the resonator have been studied. We have found that inclusion of such an unpumped central indentation can greatly improve the spatial mode behavior, resulting in a very uniform near field intensity, single wavelength emission, and a focused spot size only 1.5 times the diffraction limit for a laser oscillating in the fundamental circular mode. Our measurements at different drive currents show that the modal behavior of the laser is stable up to at least three times the threshold current, and based on the near and far-field intensity distributions, the laser is possibly lasing simultaneously in two orthogonal first order circular modes. Reducing the resonator diameter of lasers without an unpumped central indentation does not offer similar improvement to the modal behavior.
A grating coupled surface emitting semiconductor laser consists of an in-plane laser with an integrated grating coupler that couples the light from the laser out of the waveguide and simultaneously shapes the emitted beam. Here we report on the progress towards a fully integrated grating coupled surface emitter. This includes: (1) grating outcouplers exhibiting more than 90% outcoupling efficiency through the use of optimized grating profiles and waveguide structures, (2) grating outcouplers possessing beam shaping capabilities through the use of computer generated waveguide holograms, and (3) grating based in-plane lasers producing wide and spatially coherent guided modes through the use of an unstable resonator design and mode selective feedback elements.
The surface emission efficiency of grating coupled surface emitters, defined as the fraction of the guided mode power incident on the grating outcoupler that is emitted into air, is limited by diffraction into the substrate. This paper presents results from experimental and theoretical studies of various techniques to suppress substrate emission from second order gratings while simultaneously enhance the emission into air. These techniques include optimized rectangular gratings, blazed asymmetric gratings, and laser structures incorporating multilayer reflectors below the waveguide to redirect light diffracted into the substrate. Optimized rectangular gratings exhibit more than 60% surface emission efficiency under appropriate detuning conditions. Blazed asymmetric gratings demonstrate a strong dependence of the surface emission efficiency on the orientation of the grating with respect to the propagation direction of the guided optical mode under both resonant and nonresonant conditions. Lasers with multilayer reflectors show promising performance with a precisely adjusted phase of the reflected wave. Techniques for fine tuning the phase difference between the reflected wave and the wave diffracted into air are discussed. The fabrication techniques used to fabricate the high quality gratings required for high performance surface emitters are also reviewed.
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