Hans Martinsson

Transverse mode selection in large-area oxide-confined vertical-cavity surface-emitting lasers using a shallow surface relief

Transverse mode selection has been introduced in a large area oxide-confined vertical-cavity surface-emitting laser (VCSEL) by etching a shallow (only 40-nm deep) surface relief. The circular relief pattern, intended for fundamental mode selection, selects low order modes, resulting in significantly reduced beam divergence (from 48/spl deg/ to 13/spl deg/ and less over the entire drive current range) and improved spectral purity (width of emission spectrum reduced from 5 to less than 0.3 nm) compared to VCSELs without surface relief. A maximum output power of 10 mW was measured.

Analog modulation properties of oxide confined VCSELs at microwave frequencies

Motivated by the need for affordable, high-performance fiber-optic microwave links in fiber-fed microcellular networks and radar systems, we have performed a comprehensive experimental evaluation of the microwave modulation characteristics of high-speed oxide-confined vertical cavity surface emitting lasers (VCSELs) emitting at 840 nm. VCSELs with different oxide aperture diameters, including both single- and multimode lasers, have been used to track the dependence on modal behavior. The study includes both static and dynamic characteristics, with an emphasis on those of major importance for analog modulation. This includes the small-signal modulation response (S/sub 11/ and S/sub 21/), the relative intensity noise (RIN), and the intermodulation distortion. From this, we determine the spurious free dynamic range, the impedance characteristics, and the speed limitations.

RET for optical maskless lithography

Due to the ever-increasing mask cost, Optical Maskless Lithography provides an attractive alternative to mask-based lithography, especially for low-volume runs. In order to offer a seamless mix-and-match solution with mask-based scanners, or a complete transfer from mask-based to maskless lithography, the imaging performance of a maskless tool must at least match the performance of a regular scanner. This paper reports results from simulations showing very good agreement with a mask-based scanner at the 65 nm design node, including semi-isolated lines of 50 nm (AttPSM), 45 nm (CPL), and 35 nm (phase edge). Due to a new enhanced rasterization, the results show minor or no influence at all from the pixel grid. The results also indicate that a maskless tool can use the same OPC model as a mask-based scanner, including phase-shifting.

Numerical optimization of the single fundamental mode output from a surface modified vertical-cavity surface-emitting laser

The effects of etching a shallow surface relief in the top mirror of an oxide confined vertical-cavity surface-emitting laser, for the purpose of selecting the fundamental mode, have been investigated by numerical simulations. A quasi-3-D model has been implemented which self-consistently accounts for optical, electrical, and thermal effects. The design has been optimized for maximum single fundamental mode output and the limiting mechanisms have been studied. The results are also compared with experimental values and the effects of limitations in fabrication precision are investigated.

Single-mode power dependence on surface relief size for mode-stabilized oxide-confined vertical-cavity surface-emitting lasers

We have studied the mode behavior of oxide-confined vertical-cavity surface-emitting lasers (VCSELs) with a surface relief for fundamental mode selection. The dependence of single-mode power on the surface relief diameter was measured and compared with numerically calculated values. VCSELs with diameters of 9 and 12 /spl mu/m were equipped with surface reliefs with diameters in the range 4-10 /spl mu/m. The results show that there exists an optimum relief diameter for each VCSEL size. A maximum single-mode power of 2.2 mW was achieved for a 9-/spl mu/m-diameter VCSEL with a 4-/spl mu/m-diameter surface relief.

Single- and multimode VCSELs operating with continuous relief kinoform for focussed spot-array generation

We report the use of both single- and multimode VCSELs operating at 850 nm as the illumination source for a continuous-relief diffractive optical element (DOE) fabricated in resist on quartz. The system produces a 4/spl times/4 array of focussed spots from a single optical input. The uniformity error was found to be /spl sim/10% in all cases, and the overall system efficiency /spl sim/35% A single spot-coupling efficiency of 70% into a multimode fiber placed 20 mm from the DOE was also measured.

Nonlinear distortion and dynamic range of red (670 nm) oxide confined VCSELs

The analog modulation properties of oxide confined InGaAlP vertical cavity surface emitting lasers (VCSELs) emitting in the visible region (670 nm) are investigated. Two VCSELs with different oxide aperture sizes (10 and 18 /spl mu/m) were measured. The larger VCSEL exhibits a spurious free dynamic range as high as 92-100 dB/spl middot/Hz/sup 2/3/ in the frequency range 0.1-3 GHz while the smaller VCSEL exhibits a dynamic range of 88-94 dB/spl middot/Hz/sup 2/3/ in the same frequency range.

Transparent corner enhancement scheme for a DUV pattern generator

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.

Rasterizing for SLM-based mask making and maskless lithography

In high fidelity SLM-based mask making and maskless lithography, a high performance rasterizer with high capability is of utmost importance. The rasterizer must be capable, not only to convert the vector format input data to a bitmap suitable for the SLM in fractions of seconds, but also to perform image adjustments in terms of edge placement and edge acuity. This paper presents a new rasterizing algorithm with built-in capability to remove virtually all influence of the finite pixel size on lithographic performance, even for printed features down to the size less than 2 pixels. The rasterizer allows the SLM to mimic the performance of any phase-shifted reticle, including strong phase-shifting and chromeless lithography. In addition, with SLM-based mask making and maskless lithography, it is possible to switch between completely different printing modes (binary, weak and strong phase-shifting, or CPL) between consecutive exposures, without the need for reticle and wafer re-alignment. The result is improved image fidelity, smaller printed features relative to the pixel grid, and flexible powerful phase-shifting capabilities.

Monolithic integration of continuous-relief diffractive structures with vertical-cavity surface-emitting lasers

In this work, we have studied the transfer of diffractive optical elements (DOEs), originally made in resist, into GaAs for monolithic integration with vertical-cavity surface-emitting lasers (VCSELs). The DOEs are blazed gratings and Fresnel lenses, and have been fabricated on the back surface of bottom emitting VCSELs using electron-beam lithography or replication by hot embossing in resist followed by a quick-dry etch step. Diffraction efficiency was measured to be 81% in the first order of diffraction for the blazed grating.