III-V semiconductor devices typically use structures grown layer-by-layer and require passivation of sidewalls by vertical etching to reduce leakage current. The passivation is conventionally achieved by sealing the sidewalls using polymer and the polymer needs to be planarized by polymer etch-back method to device top for metal interconnection. It is very challenging to achieve perfect planarization needed for sidewalls of all the device layers including the top layer to be completely sealed. We introduce a novel hard-mask-assisted self-aligned planarization process that allows the polymer in 1-3 μm vicinity of the devices to be planarized perfectly to the top of devices. The hard-mask-assisted process also allows self-aligned via formation for metal interconnection to device top of μm size. The hard mask is removed to expose a very clean device top surface for depositing metals for low ohmic contact resistance metal interconnection. The process is robust because it is insensitive to device height difference, spin-on polymer thickness variation, and polymer etch non-uniformity. We have demonstrated high yield fabrication of monolithically integrated optical switch arrays with mesa diodes and waveguide electroabsorption modulators on InP substrate with yield > 90%, high breakdown voltage of > 15 Volts, and low ohmic contact resistance of 10-20 Ω.
Potential transmission problems for polymeric pellicle membranes at 157 nm have led to alternative designs incorporating ultra-thin modified fused silica, i.e., so-called 'hard pellicles.' The mechanical characteristics of hard pellicles are unique. Forces can be generated between the pellicle frame and the patterned reticle during bonding because of misalignment and warpage. These forces create out-of-plane distortions of the reticle, which can subsequently induce in-plane distortions. Also, since the hard pellicle is an optical element, its deflection can be a source of error. In addition, because the reticle is rapidly repositioned during exposure, vibration of the pellicle could be excited by stage motion. It is important, therefore to understand the structural and modal response of the composite pellicle / reticle system. Experimental analyses were conducted to determine changes in the reticle and hard pellicle profiles (out-of-plane) due to bonding. Finite element modeling was used to support the experimental study, as well as identify the gravitational distortions of the pellicle. A modal analysis was also performed on the hard pellicle after bonding. The experimental measurements and finite element results were in excellent agreement, both for mode shapes and vibration frequencies.
In this paper we present studies on the optical transmittance of modified fused silica substrates subject to mask making dry etch and wet clean processes, mask handling, and photon chemical clean. Using a custom built nitrogen purged in-situ transmittance measurement system with a 172-nm Xe Excimer lamp photon chemical clean unit we have achieved measured transmittance up to 87% because of the removal of surface contamination. We concluded from the experiments that: (1) Transmittance of the as-shipped mask substrate is lower than that after the photon chemical clean, (2) Chromium dry etch not only caused a transmittance loss but also made the transmittance uniformity worse, (3) Acidic wet clean must be done after the Chromium etch to recover transmittance loss and uniformity problem due to contamination introduced in Chromium etch, (4) Long time storage (more than 30 days) and short term handling (a few minutes) in ambient condition both degrade transmittance. We found that in-situ transmittance measurement after the photon chemical clean is needed in order to eliminate the transmittance measurement uncertainty due to surface contamination
The development of pellicles for 157 nm lithography includes not only the determination of appropriate materials, but also the minimization of pellicle-induced distortions contributing to overlay error. In particular, the attachment of the pellicle to the reticle surface can cause both out-of-plane and in-plane distortions (OPD and IPD) which contribute to pattern placement errors. This research focused on identifying the mechanical characteristics of thin-film pellicles, and the effect of bonding the pellicle frame to the reticle. Several different pellicle designs and films were analyzed and compared, using experimental, analytical, and finite element (FE) methods. The pellicle film stress was determined via two experimental procedures. The first, a resonant frequency test, identified the natural frequencies and mode shapes. The film stress values were subsequently determined from their relation to the frequencies. In the second procedure, static measurements of the displaced shape due to applied loads were taken using an MTI Fotonic Sensor. The film stresses from these independent measurements were between 200 and 300 kPa. The effect of the pellicle bonding was determined interferometrically by measuring the change in OPD of the reticle. The OPD values corresponded to IPD magnitudes of approximately 10 to 20 nm. These distortions were also simulated with FE models to replicate the mounting process. Using these methods, alternative mounting schemes, procedures, and materials can be developed, tested, and analyzed to reduce distortions in future designs.
Localized resist heating effects that occur during electron beam (e-beam) patterning of optical masks can lead to critical dimension (CD) errors. These errors are due to unexpected resist development or underdevelopment, which is related to the temperature history of the resist. Eliminating this source of error requires a knowledge of the localized temperature history and how resist properties are impacted by elevated temperatures. Computer simulations of electron beam patterning of an optical mask can address the temperature history of the localized heating not possible through experimentation. Presented are the results of a study to determine the feasibility of using finite element (FE) analysis to predict these thermal effects. Two models were created to demonstrate its capabilities. The first shows that FE modeling is capable of high spatial resolution temperature profiles. The second demonstrates that FE models can be programmed to run complete patterning simulations.
157-nm lithography has gained significant momentum and worldwide support as the post-193 nm technology. Due to higher absorption at shorter wavelength, however, there are several critical issues including materials and reticle handling at 157-nm. These key technical areas are being studied at Intel in collaboration with worldwide industrial and academic partners. In this paper, we will report the progress on 157-nm specific mask technology development.
Intel is aggressively pursuing the use of 157 nm lithography for the 0.1 mm patterning node. Two areas of concentration have been in photoresist and reticle materials development. Over the six months, we have seen considerable progress in new materials development in both areas. In the photoresist area, the use of ultra-thin resists of currently used chemistries appear to be capable of providing short-term layer development and tool testing patterning capability. We have obtained imaging results using a 0.5 NA Schwartzchild optics system. Our best result to data show 70-80 nm lines printed on a pitch of 180 nm. While this small field system has considerably immature optics, it can be used effectively to do basic resist development. In the area of reticle materials development, we have seen considerable improvement in the reduction of OH in blank materials, resulting in higher transmission. We expect to see substrates with greater than 80 percent transmission within the next year at the current rate of accelerated progress. Furthermore, we are not seeing any major processing differences with these new blank materials. Overall, we have seen an accelerated pace of learning in materials development for both resist and new blank materials. Overall, we have seen an accelerated pace of learning in materials development for both resist and reticle materials for 157 nm lithography.