Yong-Hyuk Lee

Characteristics of He/O2 atmospheric pressure glow discharge and its dry etching properties of organic materials

In this study, the characteristics of atmospheric low temperature plasmas generated by capillary electrodes with capillary dielectrics were investigated for the application of microelectronic cleaning processes. The characteristics of the plasmas were studied as a function of capillary aspect ratios, input power, electrode distance, He/O 2 gas flow rate, etc., using a high voltage probe, current probe, and optical emission spectroscopy (OES). The voltage between the electrodes increased with the increase of input power, the increase of electrode distance, the decrease of He flow rate, and the increase of O 2 flow rate. The increase of the voltage has led to unstable filamentary discharge from the stable capillary discharge. The use of electrodes with capillary dielectrics instead of a conventional dielectric barrier electrode (the electrode covered with non-capillary dielectric) not only decreased the electrode voltage, therefore, increased the stability of the plasma but also increased the discharge current and, therefore, the intensity of the plasma. Increased ionization and dissociation of the plasma species could be observed by OES with the increase of input power in He/O 2 mixtures. However, with the increase of O 2 flow rate in a constant He flow rate, the emission peaks from He decreased due to the increased electron consumption by oxygen while the emission peaks from O 2 + and O increased due to the increased ionization and dissociation rates with the increase of oxygen concentration in the He/O 2 gas mixtures. Also, using a He/O 2 gas mixture, organic materials such as photoresist could be successfully removed with the average etch rates higher than 200 nm/min.

Etching mechanism of (Ba, Sr)TiO3 films in high density Cl2/BCl3/Ar plasma

(Ba, Sr)TiO3 (BST) thin films have attracted great interest as new dielectric materials of capacitors for ultralarge-scale integrated dynamic random access memories such as 1 or 4 Gbit. In this study, inductively coupled BCl3/ Cl2/Ar plasmas was used to etch BST. The Cl2/(Cl2+Ar) was fixed at 0.2, and the BST thin films were etched by adding BCl3. The characteristics of the plasmas were estimated using optical emission spectroscopy (OES). The change of Cl, B radical density was measured by OES as a function of BCl3 percentage in Cl2/Ar. The cross section of BST thin films and residue remaining after the etch was investigated by scanning electron microscopy. The chemical reactions between BST and Cl2 and the surface of BST films etched with different BCl3/Cl2/Ar gas mixing ratios were investigated using x-ray photoelectron spectroscopy.

Characteristic of a dielectric barrier discharges using capillary dielectric and its application to photoresist etching

Abstract In this study, atmospheric pressure plasmas were generated using a dielectric barrier discharge equipment using capillary dielectric materials and the characteristics of the plasmas and the surface cleaning rate were studied as a function of He/O 2 gas mixture and electrode material. The use of capillary dielectric instead of blank dielectric increased the plasma density by effectively using the voltage sustained in the dielectric for accelerating electrons at the capillary holes, therefore, by forming ion beam-like plasmas at the holes in addition to typical dielectric barrier discharges. The addition and increase of oxygen into He decreased the plasma density monotonically due to the increased charge neutralization; however, oxygen atoms increased initially and showed a maximum with the increase of oxygen. The etch trend of photoresist, therefore the cleaning rate of organic materials, was related to that of oxygen atoms in the plasma. As capillary dielectric materials, the use of ceramics instead of Teflon showed higher photoresist etch rate with higher radical and plasma densities due to the higher sustaining voltage at the air gap between the electrodes.

Effects of inductively coupled plasma conditions on the etch properties of GaN and ohmic contact formations

Abstract In this study, n-GaN was etched using inductively coupled Cl 2 /H 2 plasmas and the effects of plasma conditions on the etch properties, surface composition and ohmic contact formation were investigated as a function of gas composition using OES (optical emission spectroscopy), SEM (scanning electron microscope), XPS (X-ray photoelectron spectroscopy), AES (Auger electron spectroscopy) and TLM (transmission line method). The addition of hydrogen to Cl 2 plasma decreased GaN etch rate and changed the surface composition from Ga-rich to N-rich. Etched profiles were near vertical with a smooth sidewall, however, the pure Cl 2 case showed the most anisotropic etch profile. Specific contact resistivity was increased with increasing hydrogen percent in Cl 2 /H 2 , however, most of contact resistivities of the contacts fabricated on the GaN etched with Cl 2 /H 2 (≤75% H 2 ) were less than those fabricated on the non-etched GaN.

The Effect of N2 Flow Rate in He/O2/N2 on the Characteristics of Large Area Pin-to-Plate Dielectric Barrier Discharge

In this study, the effects of N2 flow rate in the He/O2/N2 gas mixture on the characteristics of a pin-to-plate dielectric barrier discharge (DBD) having the size of 100 mm ×1000 mm have been investigated for the application to flat panel display processing such as photoresist ashing. The pin-to-plate DBD showed about 70–120% higher photoresist ashing rate at the same applied voltage compared to the conventional DBD. The addition of 3 slm of N2 to He(10 slm)/O2(3 slm) showed the highest photoresist ashing rate of about 580 nm/min for the pin-to-plate DBD at 12 kV of AC voltage. The increase of N2 flow rate in He/O2 gas mixture up to 3 slm appeared to increase the density of N2+ ions and N2 metastables while the oxygen atomic density appeared to decrease continuously. The increase of photoresist ashing rate with the increase of N2 flow rate up to 3 slm was related to the increase of the substrate surface temperature by the increased collision of N2+ ions and N2 metastables with the substrate.

Properties and applications of a modified dielectric barrier discharge generated at atmospheric pressure

An atmospheric pressure plasma was generated using a modified dielectric barrier discharge with the power electrode composed of multi-pins (i.e., a pin-to-plate type) instead of a conventional blank plate (i.e., a DBD-type), and the discharge and the photoresist etching characteristics were compared with those produced by the DBD-type at various He/O2 mixtures. The pin-to-plate type showed a higher discharge current and a higher power consumption than the DBD-type at a given voltage. Therefore, the pin-to-plate type appeared to be more efficient than the conventional DBD-type. In addition, when the photoresist etch rate was examined, the pin-to-plate showed higher etch rates than the DBD-type at various He/O2 mixtures. For the He/O2 mixture, both types showed the maximum photoresist etch rate at a certain He/O2 mixture. Using a gas mixture of 3 slm of O2 and 10 slm of He, a maximum photoresist etch rate of 340 nm/min and 260 nm/min could be obtained using the pin-to-plate type and the DBD-type, respectively, at 10 kV AC for an electrode size of 500 mm×50 mm. No physical damage was observed on the metal lines of the TFT-LCD devices after photoresist etching under the above conditions.

Evaluation of fluorinated polyimide etching processes for optical waveguide fabrication

Fluorinated polyimides have attracted much attention as potential materials for optical waveguide fabrication due to their high thermal stability, humidity resistance, as well as low optical loss in the wavelength region of optical communications. For the fabrication of optical waveguide structures, reactive ion etching (RIE) has been widely used. According to our study, the highest etch rate obtained with vertical profile for RIE of fluorinated polyimides with O 2 plasma was 300 nm/min. Inductively coupled plasma (ICP) etching of Ultradel® 9020D fluorinated polyimide has been conducted to obtain waveguide channels with higher etch rate and more vertical profile than is possible with RIE. The etch rate and the etch profile have been investigated as a function of ICP power, r.f. chuck power, O 2 flow rate, and chamber pressure. Etch rates of 1700 nm/min to 2200 nm/min with vertical profile and smooth sidewall were obtained by ICP etching at an ICP power of 500 W, r.f. chuck power of 150 W to 350 W, chamber pressure of 5 mTorr and O 2 flow rate of 40 sccm. Under these conditions there was no appreciable change in the etch rate with chamber pressure in the range 5-20 mTorr.

A Study of Electrical Damage to a-Si:H Thin Film Transistor during Plasma Ashing by a Pin-to-Plate Type Atmospheric Pressure Plasma

In this study, the effect of the plasma ashing of the photoresist on a-Si:H thin film transistor (TFT) devices carried out using an atmospheric pressure plasma on the electrical damage to the TFT devices was investigated. By exposing the TFT devices to the plasma with a photoresist ashing rate of about 860 nm/min for up to 120 s, their electrical characteristics were significantly degraded, possibly due to charge trapping in the SiNx of the passivation layer and gate insulator and to bond breaking in a-Si:H. The degradation of the field effect mobility, Ioff, and Ion/Ioff ratio of the devices is believed to be mostly related to the bond breaking in the a-Si:H and charge trapping caused by the UV radiation, while the change in the threshold voltage appears to be mostly related to the surface charging caused by the charged species in the plasma. The damaged TFT devices, however, could be fully repaired by conventional annealing in a furnace at 290°C in N2 for 60 min.