On-chip metal deformation measurements: A capacitive approach

Abstract

Abstract The large mismatch in thermal expansion coefficients of silicon and the plastic encapsulants available today introduces severe stress at the chip surface which might lead to stress-induced displacements of metallization paths. The sensor discussed here has been designed to measure such displacements and consists of four Si-implanted electrodes in a symmetrical configuration. These electrodes carry sinusoidal signals of identical amplitude and frequency, but with phase shifts of 0, 90, 180 and 270 degrees respectively. At the centre a MOS electrode is deposited on top of the SiO 2 layer. When this electrode is situated in the central position it will have identical capacitive couplings with all four implanted electrodes and there will be no net signal in the electrode. However, when the electrode is moved from its central position the capacitive couplings will be out of balance. This means that the metal electrode will sense a net signal whose amplitude is proportional to the magnitude of the displacement while the phase is proportional to the direction of displacement.