Kishou Kaneko

Highly reliable BEOL-transistor with oxygen-controlled InGaZnO and Gate/Drain offset design for high/low voltage bridging I/O operations

Reliability of BEOL-transistors with a wide-gap oxide semiconductor InGaZnO (IGZO) film, integrated on LSI Cu-interconnects, is intensively discussed in terms of application to on-chip bridging I/Os between low and high voltage interactive operations (Fig. 1). Oxygen control in the thin IGZO film was found to be important to stabilize the device characteristics. A conventional IGZO tends to contain deep-level donor-states, which cause temperature and bias instabilities. The oxygen control in IGZO reduces these deep donor-states to improve operation instability. A gate/drain offset structure effectively suppresses the hot-carrier generation, resulting in a stable operation at high Vd bias condition (∼20V). The oxygen-controlled IGZO and gate/drain offset structure are important for making the BEOL-transistors applicable to high/low voltage I/Os bridging.

Operation of functional circuit elements using BEOL-transistor with InGaZnO channel for on-chip high/low voltage bridging I/Os and high-current switches

Functional circuit elements based on novel BEOL-transistors with a wide-band-gap oxide semiconductor InGaZnO (IGZO) film are integrated onto LSI Cu-interconnects, and their operations are demonstrated. High-current comb-type transistors show excellent Ion/Ioff ratio (>;108) and high-Vd operation with linear area dependence, realizing area-saving compact high-current BEOL switches. Successful operation of voltage-controlled inverter switches with high-Vd enables on-chip bridging I/Os between high/low voltage on conventional Si system LSIs. Setting the gate-to-drain offset design to just 0.1μm realizes +20V enhancement of the breakdown voltage to ~60V with excellent safety operation at around Vd=50V due to the wide-band-gap characteristics.

High on/off-ratio P-type oxide-based transistors integrated onto Cu-interconnects for on-chip high/low voltage-bridging BEOL-CMOS I/Os

A new P-type amorphous SnO thin-film transistor with high I_on/I_off ratio of >10⁴ is developed, for the first time, as a component to complement N-type IGZO transistors for on-chip voltage-bridging BEOL-CMOS I/Os on conventional Si-LSI Cu-interconnects (Fig. 1). Dedicated low-temperature (<;400°C) oxide-semiconductor processes are implemented to overcome several integration challenges (Fig. 2) with only one-mask addition using standard BEOL process tools (Fig. 3). We demonstrate high I_on/I_off ratio of >10⁴ and high-V_d capability (|V_bd|>40V) with gate-to-drain offset structure, showing superior properties over the previously reported values (Table 1). The SnO transistor is suited for the BEOL-CMOS I/O, which gives standard LSIs a special add-on function to control high voltage signals directly in smart society applications.

Microstructure Control of Low-Loss Ni–Zn Ferrite by Low-Temperature Sputtering for On-Chip Magnetic Film

Low-loss oxide magnetic film of Ni–Zn ferrite (Ni0.5Zn0.5Fe2O4) is deposited by RF magnetron sputtering at a low temperature (300 °C), applicable for integration in advanced LSIs with Cu/low-k interconnects. To control the film microstructure, or its essential magnetic and electrical properties, (1) selection of a buffer layer as a diffusion barrier under the ferrite film and (2) control of the O2/Ar gas ratio in the sputtering chamber are key factors. A thin TaN buffer layer provides the Ni–Zn ferrite film with a highly preferential (311) orientation, resulting in high saturation magnetization. In addition, the thin TaN buffer has a sufficiently good barrier property to be practical for integration of the magnetic film into Cu/low-k interconnects. Oxygen addition to Ar sputtering gas realizes both high (311) crystallization and high resistivity (ρ=10 MΩ cm), which are essential for low-loss properties. Simulation of the on-chip inductor with the magnetic film suggests that the high-ρ magnetic film is suitable for high-efficiency on-chip inductors with GHz ranges.

A Novel Multilayered Ni?Zn-Ferrite/TaN Film for RF/Mobile Applications

A novel multilayered Ni–Zn-ferrite/TaN (MFT) film is developed for RF/mobile complementary metal oxide semiconductor (CMOS) applications. The Ni–Zn ferrite (Ni0.5Zn0.5Fe2O4) film is deposited by low-temperature RF magnetron sputtering technique applicable for conventional low-k/Cu interconnects in advanced CMOS LSI. In the MFT film, a stacking unit of thin Ni–Zn-ferrite and thin TaN is laminated to enhance the ferrite (311)spinel orientation close to the magnetization easy axis of the ferrite. The saturated magnetization (Ms) increased 50% referred to the single-layer Ni–Zn-ferrite/TaN, and the coercivity (Hc) decreased one-fifth desirable for the high speed switching. By physical-based modeling, it is proved that the fraction of the (311)-orientation region in the total ferrite thickness is very important to improve the magnetic properties. In addition to the high resistivity (ρ=10 MΩ cm) to suppress eddy current loss, the MFT film is effective to confine and enhance the magnetic field in the on-chip inductor in GHz range, suitable for RF/mobile applications.