Takeshi Ohmori

Negative charge injection to a positively charged SiO2 hole exposed to plasma etching in a pulsed two-frequency capacitively coupled plasma in CF4/Ar

As microchips become smaller, the threat of damage to the device elements of Si semiconductors by charging during plasma etching will become significant. It will be of first importance to establish a plasma-etching technique that does not involve charging, i.e., “charging-free plasma processing.” Here, we utilize the effect of negative charge acceleration under a double layer in order to neutralize the charge inside a microstructure exposed to plasma etching. We have constructed a dual measurement system consisting of an emission in an interface and a contact hole charging on a SiO2 wafer during etching in two-frequency capacitively coupled plasma (2f-CCP) in CF4/Ar and pure Ar. A reduction in charging voltage is measured in the pulsed operation both of the plasma power source and of the wafer bias in the 2f-CCP in electronegative gases, CF4/Ar.

Diagnostics for low-energy electrons in a two-frequency capacitively coupled plasma in Ar

An experimental procedure to investigate the spatiotemporal characteristics of electrons in the vicinity of mean energy in a radiofrequency plasma is proposed by using optical emission and absorption spectroscopy in Ar. The method employs optical kinetics of long-lived metastable atom Ar(1s5) and short-lived excited Ar(2p9). The electron density distribution ne(z,t) is demonstrated in a typical condition in a two-frequency capacitively coupled plasma, excited at 100MHz and biased at 500kHz in pure Ar. The density shows almost time independent characteristics in the bulk plasma and a strong time dependence in the sheath in front of the bias electrode.

Negative charge injection to a wafer in a pulsed two-frequency capacitively coupled plasma for oxide etching; diagnostics by emission-selected computerized tomography

In order to develop charging-free plasma processing, we investigated the function of negative charge injection to a SiO2 wafer, during etching in a pulsed two-frequency capacitively coupled plasma under various external conditions in CF4/Ar at low pressures, by using emission-selected computerized tomography. The formation of a negatively-charged layer by an excess negative charge in the interface close to the wafer and the degree of acceleration of negative charges were experimentally estimated through the spatiotemporal characteristics of the net excitation rate of the short-lived Ar(2p1) used as a probe. A bias pulse operation with a single positive component at the wafer during the off-phase of very high frequency (100 MHz) plasma production resulted in the most efficient formation of the negatively-charged layer close to the wafer. The influence of the external plasma conditions on the negatively-charged layer is observed in detail.

Time-Resolved Measurement of Charging on Hole Bottoms of SiO2 Wafer Exposed to Plasma Etching in a Pulsed Two-Frequency Capacitively Coupled Plasma

We experimentally demonstrate a time chart of the shading either of electrons or positive ions on a topologically patterned wafer exposed to plasma etching by synchronized measurements of bottom-charging potential in a SiO2 hole, current components incident on the wafer, and optical emission CT in the interface in a pulsed two frequency capacitively coupled plasma. The present paper gives a history of charging affected dynamically by an instantaneous electrical response on the bottom.