No abstract

This paper reports on the design, fabrication and evaluation of solid immersion blazed-phase diffractive optics for near-infrared radiation of wavelength 1064 nm. The practical application of enhancing the analysis of integrated circuits using scanning laser microscopy through the silicon substrate is demonstrated. A general design technique using computer generated holography (CGH) is developed to create a numerical program that calculates the structure required for spherical wavefront reconstruction through a silicon substrate into any user-defined pattern. Fabrication of the blazed-phase structure with a diffraction efficiency of 87.9% is achieved in a single-process step by using a combination of the focused ion beam to implant gallium atoms according to the phase pattern, followed by reactive-ion etching using CHF 3 chemistry. The implant conditions and etch times are experimentally adjusted to achieve a continuous blazed-phase profile with the required height of 440 nm with a minimum implant spacing of 140 nm. The imaging capability of the solid immersion blazed-phase lens is compared to a binary-phase lens with a diffraction efficiency of 38.8%, where the more efficient blazed design results in a corresponding improvement with image contrast. The complete technique is then extended to the reconstruction of multiple focal points and ring patterns, to produce analysis techniques that use phase contrast to produce differential images between each focal point from the same diffractive optic. Analysis results are presented that demonstrate lateral resolutions up to 3.5 times better than without the diffraction optic and the capability of selectively removing of specific spatial frequencies from repetitive integrated circuits.

In this paper we present a new method to increase the lateral resolution available in laser scanning failure analysis tools. By fabricating a diffractive lens on the back side of the die, the area of the circuit of interest, directly underneath the lens, may be studied with a lateral resolution up to 3.5 times better than without the lens. This method is easily implemented with standard equipment already present in most failure analysis laboratories, and overcomes some significant problems encountered with alternative resolution enhancing schemes.