  We present an interdigitated capacitor trimming technique for fine-tuning the
resonance frequency of superconducting microresonators and increasing the
multiplexing factor. We first measure the optical response of the array with a
beam mapping system to link all resonances to their physical resonators. Then a
new set of resonance frequencies with uniform spacing and higher multiplexing
factor is designed. We use simulations to deduce the lengths that we should
trim from the capacitor fingers in order to shift the resonances to the desired
frequencies. The sample is then modified using contact lithography and
re-measured using the same setup. We demonstrate this technique on a 112-pixel
aluminum lumped-element kinetic-inductance detector array. Before trimming, the
resonance frequency deviation of this array is investigated. The variation of
the inductor width plays the main role for the deviation. After trimming, the
mean fractional frequency error for identified resonators is -6.4e-4, with a
standard deviation of 1.8e-4. The final optical yield is increased from 70.5%
to 96.7% with no observable crosstalk beyond -15 dB during mapping. This
technique could be applied to other photon-sensitive superconducting
microresonator arrays for increasing the yield and multiplexing factor.
