Arvind Srivastava

UV-activated room-temperature gas sensing mechanism of polycrystalline ZnO

The effects of UV illumination on the electronic properties and gas sensing performance of ZnO are reported. It is found that UV light improves the sensitivity and the sensor response and recovery rate. By investigating the photoresponse behavior of ZnO, we observe that the electrons generated by UV light promote the adsorption of oxygen and form the photoinduced oxygen ions [O2−(hv)]. These ions [O2−(hv)] are responsible for the room-temperature gas sensing phenomena and promise enhanced sensor performance through further optimization.

Ultrasound holography for noninvasive imaging of buried defects and interfaces for advanced interconnect architectures

Imaging high resolution subsurface defects nondestructively in advanced interconnect structures and devices is a challenge and no known metrology tools are available to identify such defects in a nondestructive way at nanometer level. Monitoring these defects necessitate the understanding of their growth mechanism of these interconnects as well as defect formation. We report here the application of scanning near field ultrasound holography by imaging buried defects in copper interconnects and low-K dielectric materials. Defects in these copper lines such as voids and delaminations appear as regions of dark contrast in ultrasound holography imaging due to large acoustic impedance mismatch at the voids. Identification of these buried defects in these interconnect architectures in a nondestructive way will open up unique opportunities in using this technique to detect subsurface defects and material imperfections.

Nanomechanoelectronic signal transduction scheme with metal-oxide-semiconductor field-effect transistor-embedded microcantilevers

We explore various metal-oxide-semiconductor field-effect transistor (MOSFET)-embedded microcantilever designs to assess their performance as an efficient nanomechanoelectronic signal transduction platform for monitoring deflection in microcantilever-based phenomena such as biochemical sensing and actuation. The current-voltage characteristics of embedded MOSFETs show current noise in the nanoampere range with a large signal-to-noise ratio sufficient to provide measureable output signal. The change in drain current with cantilever deflection is consistent with the effect of stress on carrier mobility and drain current reported in previous studies, validating that the MOSFET cantilevers can directly transduce deflection of a microcantilever into reproducible change in electrical signal.

Probing Buried Defects in Extreme Ultraviolet Multilayer Blanks Using Ultrasound Holography

Imaging high-resolution subsurface defects nondestructively in Mo-Si multilayer (ML) blanks used in extreme ultraviolet lithography is a challenge and no known metrology tools are available to identify such defects in a nondestructive way. The understanding of their growth mechanism during ML deposition necessitates the monitoring of these defects, which can then lead to fabricating defect-free ML blanks. Here, we report for the first time, a unique and novel application of scanning near-field ultrasound holography (SNFUH) in nondestructive imaging of high-resolution e-beam patterned lines and bumps buried under Mo/Si ML film stacks used for ultraviolet lithography. Our results indicate the successful identification of buried defects under ML blanks using SNFUH.

Microcantilever array with embedded metal oxide semiconductor field effect transistor actuators for deflection control, deflection sensing, and high frequency oscillation

A batch fabricated microcantilever array with embedded metal oxide semiconductor field effect transistor (MOSFET) is demonstrated to behave as an actuator as well as a strain sensor. Actuation is made possible through MOSFET self-heating effect and metal-silicon bimaterial thermal expansion mismatch. Precise cantilever deflection is achieved with gate modulated saturation current. Controllable deflection and oscillation are demonstrated, with amplitude of 212 nm measured through laser interferometry near first resonant frequency. Higher amplitude is attainable through higher bias. Such in situ actuation and sensing promises to have applications ranging from nanolithography to microfluidic mixing, among others, which require precise and controllable nanoscale deflection.

Thickness Resonance Acoustic Microscopy for Nanomechanical Subsurface Imaging

A nondestructive scanning near-field thickness resonance acoustic microscopy (SNTRAM) has been developed that provides high-resolution mechanical depth sensitivity and sharp phase contrast of subsurface features. In SNTRAM technology, we excited the sample at its thickness resonance, at which a sharp change in phase is observed and mapped with a scanning probe microscopy stage in near field to provide nanometer-scale nanomechanical contrast of subsurface features/defects. We reported here the remarkable subsubsurface phase contrast and sensitivity of SNTRAM by exciting the sample with a sinusoidal elastic wave at a frequency equal to the thickness resonance of the sample. This results in a large shift in phase component associated with the bulk longitudinal wave propagating through the sample thickness, thus suggesting the usefulness of this method for (a) generating better image contrast due to high S/N of the transmitted ultrasound wave to the other side of the sample and (b) sensitive detection of local variation in material properties at much better resolution due to the sharp change in phase. We demonstrated that the sample excited at the thickness resonance has a more substantial phase contrast and depth sensitivity than that excited at off-resonance and related acoustic techniques. Subsurface features down to 5-8 nm lateral resolution have been demonstrated using a standard sample.