High precision non-destructive grating assessment techniques

This paper proposes an entirely new technique based on the measurement of the reflectance using the commercially available Nanometrics Nanospec Microarea Gauge. Using the Nanospec reflectance system it is possible to combine high resolution fields with ease of operation, low cost and the ability to assess patterns in a variety of substrates. The structure of a semiconductor distributed feedback (DFB) laser is detailed. A definition is given of the grating top:groove parameter which is an important consideration in the manufacture of the precision gratings which are etched into the waveguide layer. These gratings have carefully chosen pitches which can be as small as 0.2 μm. The studies detailed in the paper have centred around the control of a high precision electron lithography process, used to generate the diffraction gratings in DFB lasers