Optical probing from the backside of an integrated circuit (IC) is a powerful failure analysis technique but raises serious security concerns when in the hands of attackers. For instance, attacks using laser voltage probing (LVP) allow direct reading of sensitive information being stored and/or processed in the IC. Although a few sensor-based countermeasures against backside optical probing attacks have been proposed, the overheads (fabrication cost and/or area) are considerable. In this paper, we introduce nanopyramid structures that mitigate optical probing attacks by scrambling the measurements reflected by a laser pulse. Nanopyramid structure is applied to selected areas inside an IC that requires protection against optical probing attacks. The fabrication of nanopyramids is CMOS compatible and well established for photovoltaic applications. We design the nanopyramid structure in ICs, develop the LVP attacking model, and perform optical simulations to analyze the impact of nanopyramids on LVP. According to the simulation results, the nanopyramid can disturb the optical measurements enough to make LVP attacks practically infeasible. In addition, our nanopyramid countermeasure has no area overheads and works in a passive mode without consuming any energy.