We examined the etch characteristics of SiO2 contact holes which have the sizes of 0.3–1.2 μm in a C4F8+H2 electron cyclotron resonance plasma etching system. We varied the chamber pressure (3–7.5 mTorr), microwave power (300–800 W), gas mixing ratio, bias voltage (100–300 V) and bias frequency (100 –800 kHz) as the experimental parameters to investigate the reactive ion etching (RIE) lag. The RIE lag improved, as the bias voltage increased and this RIE lag improvement was thought to be due to the increase of ion energy incident on the substrate. The RIE lag also improved as the chamber pressure decreased and this improvement is due to the increase of ion current density as the chamber pressure decreases. When we increased the bias frequency from 100 to 800 kHz maintaining the same bias voltage, the RIE lag improved considerably. We calculated energy distribution of ions striking the rf biased substrate using Monte Carlo particle-in-cell method to understand this phenomenon. The ion energy distributions are bimodal when the bias frequencies are below 1 MHz, but as the bias frequency increases from 100 kHz to 1 MHz, the low energy part decreases and the high energy part increases, and it is suggested that this change of ion energy distribution is responsible for the RIE lag improvement with the bias frequency increase.

The formation of a particulate cloud was examined by the laser light scattering method with the diamondlike carbon film deposited wafer on the cathode in a radio frequency ͑rf͒ excited Ar plasma. A laser sheet and a medium speed camera were used to obtain the time-resolved images of the moving particulates in the afterglow. When the rf power is turned off, the direction and the characteristic time of the particulate density decaying are highly dependent on experimental conditions such as electrode temperature and gas flow rate. The particulates move to the cold surface with a constant velocity due to the balanced thermophoretic force and the viscous drag force by background neutral molecules. The drift velocity of the particulates is linearly dependent on the temperature difference between the electrodes, and a simplified model is used to explain the experimental result. The dependence of the afterglow particulate behavior on experimental conditions suggests that proper control of the temperature profile and the gas flow direction in the plasma reactor can reduce particulate contamination on the substrate.

The behavior of particulates in a capacitively coupled, 13.56 MHz radio frequency (rf) excited CH4 plasma was investigated by time-resolved laser light scattering (LLS). The ballistic motion of the large particulates causes the LLS signal to fluctuate with peaks at the plasma sheath boundary. In an Ar plasma with a substrate which had been coated by diamondlike carbon film in the CH4 plasma process, a quasistatic particulate cloud formed and the LLS signal, the self-bias voltage, and the optical emission oscillated slowly, all with the same period. Also, the shape of the particulate cloud changed periodically. The time variation of the particulate’s mean size in the cloud was obtained by the angular dissymmetry measurement of scattered light intensities. The behavior of the particulates seemed to depend on the particulate size. The time-resolved plasma potential obtained from the heated, fast scanning Langmuir probe indicates that the formation of particulates influences the plasma state. The optical microscope and scanning electron microscopy were used to observe the morphology and the size of the particulates. Transmission electron microscopy and electron probe x-ray microanalysis studies indicate that they have an armorphous structure. Together with the observation of the collected particulates, the results of LLS studies showed that two different groups of particulates are generated in CH4 plasma. The optical emission spectra of the particulate-contaminated Ar plasma and the normal clean Ar plasma were obtained and compared. The difference between the two spectra indicates that the mean energy of the secondary electrons which come out of the powered electrode changes as a result of the interaction with the particulate cloud formed around the plasma-sheath boundary. The distribution of the particulate cloud was highly dependant on the rf power. The ion drag force due to the ambipolar diffusion flux from the central high plasma density region to the wall is thought to play an important role in particulate cloud distribution. A modified turn-off process is suggested to prevent particulates from falling on the wafer surface.

One of the important issues for the deep-submicron shallow trench isolation process is profile control in the trench etch process for voidless gap filling with the chemical vapor deposition oxide. We examined the effects of some additive gases such as N2 or He–O2 (30% O2) on the trench slope to obtain an optimized trench profile with a commercial magnetron enhanced reactive ion etching system. It was found that the thickness of deposited film on the trench sidewall was highly related to the trench slope. As the film thickness increases, the trench profile becomes more tapered. The thickness of the sidewall film was directly proportional to the amount of the additive gases, N2 and He–O2. As the amount of He–O2 increases in the Cl2+HBr+He–O2 chemistry, the etch rate of silicon nitride decreases and the ratio of the silicon etch rate to the silicon nitride etch rate drastically increases. Scanning electron microscopy shows thick film deposits on the trench sidewall during the trench etch process. To know the chemical constituents in the deposited film on the sidewall, an angle-resolved x-ray photoelectron spectroscopy (XPS) was used. XPS results reveal that the deposited film on the trench sidewall is composed of SiOx in Cl2+HBr+He–O2 and SiOxNy in Cl2+HBr+N2. Cl or Br were not detected in our XPS measurements because the absorbed Cl or Br might react with water vapor to form HCl(g) or HBr(g) and grow SiOx when the samples are exposed to air. An aspect ratio dependence of the trench sidewall slope was observed. Usually the dense patterns are more vertical than the isolated patterns.

Particulate formation in the reactive ion etching process of SiO2 with a CF4/H2 plasma was studied with the laser light scattering (LLS) method. The LLS onset time decreases drastically as the hydrogen percentage increases which indicates that the particulate formation was stimulated by the increase of the unsaturated fluorocarbon species as a result of the hydrogen addition. The onset time was also dependent on the substrate material. The measured onset time with a Si wafer was shorter than that with a SiO2 wafer. The onset time decreases very rapidly with the increase of the radio frequency (rf) power. A decrease of the LLS peak intensity was observed with the square wave modulation process of rf power. The change of the etch rate and the LLS peak intensity according to the change of the duty ratio shows that the optimal process condition, which satisfies high selectivity, high etch rate, and low particulate growth level, can be obtained with the rf modulation method. In the rf modulation process, both an increase in the off period and a decrease in the on period resulted in a decrease of the LLS signal in the particulate trap. It was observed that a change in the off period has a more pronounced effect on the change of the LLS signal intensity.