Search

Diffraction patterns of two different contact arrays of 0.32 μm pitch are investigated using the AIMS TM tool and analyzed using Fourier analysis. We introduce a simple method to analytically predict the pupil pattern for an arbitrary periodic mask feature. A circular illuminator is split up into components that produce varying amount of interference at the wafer plane and it is shown that contrast can be enhanced by excluding certain parts of this illuminator. The optimized illuminator depends only on stepper parameters and mask geometry.

Feature distortion, linewidth variation, and line-end shortening in lithographic pattern transfer seriously affect circuit performance. These so-called optical proximity effects are both optical and process related. Optical proximity correction (OPC) aims at minimizing these effects by pre-distorting the patterns of the mask. In this article, we present several approaches to OPC and the application of OPC to linewidth control in patterning the gate level of microprocessors.

The unique aspects of x-ray lithography that make it attractive for the sub-100nm domain include: a highly localized, sharply peaked point-spread function, leading to minimal proximity effects; absence of spurious scattering; an intrinsic resolution below 30 nm; compatibility with all pattern geometries; and parallel exposure (i.e., compatibility with volume production). The major problem areas are: the mask-sample gap (less than 5 @mm for linewidths below 70 nm), and absorber stress, which must be near zero to avoid mask distortion. Nanometer-level pattern placement and alignment are considered achievable by means of spatial-phase-locked e-beam lithography and interferometric-broad-band imaging, respectively. The efficacy of x-ray nanolithography has been demonstrated via the fabrication of a variety of sub-100 nm-featured quantum-effect devices, Si MOSFETs, and grating-based optoelectronic devices. In the event that the small gaps required of proximity x-ray nanolithography prove unacceptable in manufacturing, x-ray projection using arrays of zone plates appears to be the only approach that can employ the optimal wavelengths (i.e., ~1 nm or 4.5 nm) and achieve deep sub-100 nm resolution. A scheme is proposed that employs an array of zone plates in a pattern generator mode.

We report on recent advances in the fabrication of quantum-effect devices using x-ray nanolithography. A novel scheme for gap control during the mask replication process was developed that uses capacitance sensing in a feedback loop. The capacitance between two masks is measured and held constant through control of the pressure between them. This scheme can be used to maintain the masks at a gap as small as 1 @mm, thus reducing penumbra and diffraction. This capacitive feedback method, used in mask-to-mask replication can, in principle, also be used for mask-to-substrate exposures and is thus an additional element in an x-ray nanolithography technology for sub-70nm features.