Non-contact and nanometer-scale measurement of PN junction depth buried in Si wafers using terahertz emission spectroscopy

Buried channel array transistors enable fast and high-density integrated devices. The depth of the PN junction and carrier dynamics at the depletion layer in silicon wafers have a crucial influence on their performance and reliability. Therefore, rapid and non-contact/non-destructive inspection tools are necessary to accelerate the semiconductor industry. Despite the great efforts in this field, realizing a technique to probe the junction depth and carrier dynamics at the PN junction inside wafers remains challenging. Herein, we propose a new approach to access PN junctions embedded in wafers using terahertz (THz) emission spectroscopy. THz emission measurements and simulations demonstrate that the amplitude and polarity of THz emissions reflect the junction depth and carrier dynamics at the PN junctions. It allows us to evaluate the junction depth non-destructively with nanometer-scale accuracy, surpassing the limits of traditional techniques. Laser-induced THz emission spectroscopy is a promising method for the sensitive and non-contact/non-destructive evaluation of Si wafers and will benefit the modern semiconductor industry.