P. J. Matsuo

Chemical dry etching of silicon nitride and silicon dioxide using CF4/O2/N2 gas mixtures

The chemical dry etching of silicon nitride (Si3N4)and silicon nitride (SiO2) in a downstream plasma reactor using CF4, O2, and N2 has been investigated. A comparison of the Si3N4 and SiO2 etch rates with that of polycrystalline silicon shows that the etch rates of Si3N4 and SiO2 are not limited by the amount of fluorine arriving on the surface only. Adding N2 in small amounts to a CF4/O2 microwave discharge increases the Si3N4 etch rate by a factor of 7, but leaves the SiO2 etch rate unchanged. This enables etch rate ratios of Si3N4 over SiO2 of 10 and greater. The Si3N4 etch rate was investigated with respect to dependence of tube length, tube geometry, and lining materials. Argon actinometry has shown that the production of F atoms in the plasma is not influenced by the addition of N2 to the discharge. Mass spectrometry shows a strong correlation between the Si3N4 etch rate and the NO concentration. X‐ray photoelectron spectra of the silicon nitride samples obtained immediately after the etching proces...

Patterning of fluorine-, hydrogen-, and carbon-containing SiO2-like low dielectric constant materials in high-density fluorocarbon plasmas: Comparison with SiO2

Successful pattern transfer of 0.36–0.62 μm features into fluorinated silicon dioxide, hydrogen silsesquioxane (HSQ), and methyl silsesquioxane (MSQ) has been demonstrated in a transformer coupled plasma (TCP) source using fluorocarbon feedgas chemistries. These films have a lower dielectric constant than conventional SiO2. It is this property that makes them attractive for implementation in future integrated circuit technology. The etching of these novel dielectrics was compared to conventional SiO2. We have observed that the different chemical makeup of these SiO2-like dielectrics does not affect the etching when weakly polymerizing gases are used, such as CF4. In this case, the etch rate is primarily dependent on the ion energy. For more polymerizing chemistries, like CHF3 or C3F6/H2 gas mixtures, x-ray photoelectron spectroscopy analysis showed that an increasing steady state fluorocarbon film thickness limits the ion and neutral flux at the interface of the various dielectrics. It is suggested that, ...

REMOTE PLASMA ETCHING OF SILICON NITRIDE AND SILICON DIOXIDE USING NF3/O2 GAS MIXTURES

The etching of silicon nitride (Si3N4) and silicon dioxide (SiO2) in the afterglow of NF3 and NF3/O2 microwave discharges has been characterized. The etch rates of both materials increase approximately linearly with the flow of NF3 due to the increased availability of F atoms. The etch rate of Si3N4 is enhanced significantly upon O2 injection into the NF3 discharge for O2/NF3 ratios of 0.3 and higher, whereas the SiO2 etch rate is less influenced for the same flow ratios. X-ray photoelectron spectroscopy of processed Si3N4 samples shows that the fluorine content of the reactive layer, which forms on the Si3N4 surface during etching, decreases with the flow of O2, and instead oxidation and nitrogen depletion of the surface occur. The oxidation of the reactive layer follows the same dependence on the flow of O2 as the etch rate. Argon actinometry and quadrupole mass spectrometry are used to identify reactive species in the etching of both materials. The atomic fluorine density decreases due to dilution as O...

Role of N2 addition on CF4/O2 remote plasma chemical dry etching of polycrystalline silicon

The remote plasma chemical dry etching of polycrystalline silicon was investigated using various CF4/O2/N2 gas compositions. The effects of O2 and N2 addition on the etch rate and surface chemistry were established. Admixing O2 to CF4 increases the gas phase fluorine density and increases the etch rate by roughly sevenfold to a maximum at an O2/CF4 ratio of 0.15. The addition of small amounts of N2 (N2/CF4=0.05) can again double this etch rate maximum. Strong changes in surface chemistry were also seen as a result of N2 addition to CF4/O2. Real-time ellipsometry and atomic force micro-roughness measurements reveal that nitrogen addition at low O2/CF4 ratios leads to the smoothing of surfaces, but to increased oxidation at high O2/CF4 ratios. Based on etch rate data and gas phase species analysis, we propose that NO plays an important role in the overall etching reaction. Variable tube lengths separated the reaction chamber from the discharge. These tubes were lined with either quartz or Teflon liners. In ...

Surface science issues in plasma etching

Pattern transfer by plasma-based etching is one of several key processes required for fabricating silicon-based integrated circuits. We present a brief review of elementary plasma-etching processes on surfaces and within integrated-circuit microstructures-and an overview of recent work in our laboratory on plasma-etching aspects of the formation of self-aligned contacts to a polysilicon layer through a SiO 2 layer and a Si 3 N 4 etch-stop layer. The work illustrates the richness of associated surface science issues that must be understood and controlled in order to most effectively achieve plasma-based pattern transfer.

High-density plasma patterning of low dielectric constant polymers: A comparison between polytetrafluoroethylene, parylene-N, and poly(arylene ether)

The pattern transfer of SiO2 hard masks into polytetrafluoroethylene, parylene-N, and poly(arylene ether) (PAE-2) has been characterized in an inductively coupled plasma source. Selected results obtained with blanket parylene-AF4 films are included in this work. These dielectrics offer a relatively low dielectric constant (k∼2–3) and are candidate materials for use as intra- and interlayer dielectrics for the next generations of high-speed electronic devices. Successful patterning conditions were identified for Ar/O2 and N2/O2 gas mixtures. It was found that the formation of straight sidewalls in Ar/O2 discharges relies on the redeposition of oxygen-deficient etch products on the feature sidewall. Furthermore, the etch rates of parylene-N, parylene-F, and PAE-2 for blanket and patterned films could be captured by a semiempirical surface coverage model, which balances the adsorption rate of oxygen and the ion-induced desorption rate of oxygenated etch products.

Characterization of Al, Cu, and TiN surface cleaning following a low-K dielectric etch

The cleaning of Al, TiN, and Cu blanket samples was investigated in a high density inductively coupled plasma reactor, and compared with results for silicon. After simulating the dielectric overetch exposure of these substrates to a CHF3 discharge, an in situ O2 plasma clean and subsequent Ar+ premetal sputter clean were performed and evaluated using ellipsometry and x-ray photoelectron spectroscopy. Following the fluorocarbon exposure, significant C and F residues were observed. Exposure to a O2 plasma clean greatly reduced this contamination. Subsequent treatment with an Ar+ sputter further reduced the thickness of the modified surface layer. Comparisons of the cleaning results with silicon suggest an efficient cleaning procedure, especially in the cases of copper and titanium nitride. The response of several blanket, oxide-like low-K dielectrics to the O2 plasma treatment were also studied and compared to SiO2. While a fluorinated SiO2(SiOF) exhibited SiO2-like stability, deep modifications were observ...

Highly selective etching of silicon nitride over silicon and silicon dioxide

A highly selective dry etching process for the removal of silicon nitride (Si3N4) layers from silicon and silicon dioxide (SiO2) is described and its mechanism examined. This new process employs a remote O2/N2 discharge with much smaller flows of CF4 or NF3 as a fluorine source as compared to conventional Si3N4 removal processes. Etch rates of Si3N4 of more than 30 nm/min were achieved for CF4 as a source of fluorine, while simultaneously the etch rate ratio of Si3N4 to polycrystalline silicon was as high as 40, and SiO2 was not etched at all. For NF3 as a fluorine source, Si3N4 etch rates of 50 nm/min were achieved, while the etch rate ratios to polycrystalline silicon and SiO2 were approximately 100 and 70, respectively. In situ ellipsometry shows the formation of an approximately 10-nm-thick reactive layer on top of the polycrystalline silicon. This oxidized reactive layer suppresses etching reactions of the reactive gas phase species with the silicon.

Surface etching mechanism of silicon nitride in fluorine and nitric oxide containing plasmas

The etch rate of silicon nitride (Si3N4) in the afterglow of fluorine-containing plasmas is strongly enhanced when both nitrogen and oxygen are added to the remote discharge. This effect is attributed to the formation of nitric oxide (NO), which we identify as a highly reactive precursor for the etching of Si3N4. The Si3N4 etch rate, surface oxidation, and the depletion of the surface of N atoms show a linear dependence on the NO density. In order to determine the products of the NO reaction at the Si3N4 surface, mass spectrometry was performed in immediate proximity to the surface with a specially designed movable sampling orifice. Both SiF4 and N2 are identified as primary etch products, but a smaller amount of N2O was also detected. Based on our results, we suggest that NO enhances the removal of N from the Si3N4 surface by the formation of gaseous N2, and leaving behind an O atom, while the overall surface oxidation remains very low, and the reactive layers are very thin. This modified surface reacts ...

Effect of capacitive coupling on inductively coupled fluorocarbon plasma processing

This article describes results obtained using various plasma and surface diagnostics in a study of inductively coupled fluorocarbon plasmas in which the amount of capacitive coupling was systematically varied. It is found that the plasma density decreases while the electron temperature increases as the amount of capacitive coupling is increased at a constant source power level. The rate at which the dielectric coupling window is eroded is found to scale with both the peak-to-peak rf voltage and the ion current density, and the dielectric window erosion is found to influence the resulting plasma gas-phase chemistry. The changes in plasma electrical and chemical characteristics have a large impact on the surface processes occurring in inductively coupled fluorocarbon plasmas such as fluorocarbon deposition, fluorocarbon etching, SiO2 etching and Si etching. Further, we show how the selective SiO2-to-Si etch process changes with varying capacitive coupling.