B. E. E. Kastenmeier

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...

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.

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 ...

Gas utilization in remote plasma cleaning and stripping applications

Nitrogen trifluoride (NF3) is a likely candidate to replace perfluorocompounds (PFCs) in stripping and reactor cleaning applications. In this article, the performance of NF3 for the etching of silicon, silicon dioxide (SiO2), and silicon nitride (Si3N4) is compared with that of CF4, C2F6, and C3F8. The performance measures emphasized in this article are the dissociation efficiency of the parent molecule in the discharge, the etch rate, and the gas utilization. The destruction efficiency of NF3 in the discharge as determined by mass spectrometry is typically 100%. The maximum destruction of the PFC gases for the parameters used in this investigation is approximately 75% for CF4, and can approach 100% for C2F6 and C3F8. The removal rates for NF3 obtained at optimum settings of O2 addition and microwave power are significantly higher than those for PFC gases. The gas utilization, which describes the degree of conversion of the parent molecules into etch products and is defined in this article, is also higher...

Silicon etching in NF3/O2 remote microwave plasmas

The etching of silicon in remote microwave discharges fed with NF3/O2 has been investigated. In situ ellipsometry and x-ray photoelectron spectroscopy (XPS) were used to monitor surface effects, while mass spectrometry was used to monitor the gas phase dynamics. Varying the microwave power from 600 to 1400 W has little effect, due to the near complete dissociation of the NF3, even at lower powers. For discharges containing pure NF3, the poly-Si etch rate increases linearly with NF3 flow. When a low proportion of O2 (O2/NF3=0.1) is added to the discharge, the etch rate increases quickly to its maximum of ∼700 nm/min. With further O2 addition, this etch rate decreases below that observed for pure NF3 processing. The fluorine concentration in the processing region decreases for all O2 additions by a dilution effect. For pure NF3 discharges, XPS measurements reveal 1–2 nm thick, highly fluorinated reaction layers with a gradual loss of fluorine content as the NF3 flow is increased. Specimens processed with bo...

Chemical downstream etching of silicon–nitride and polycrystalline silicon using CF4/O2/N2: Surface chemical effects of O2 and N2 additives

By comparing the etching characteristics of silicon and silicon nitride in CF4/O2/N2 microwave downstream plasmas we demonstrate clearly how low concentrations of energetic species can play a dominant role in remote plasma processing: Injection of 5% N2 to a CF4/O2 plasma increases the silicon nitride etch rate by a factor of 7, while not significantly affecting the bulk composition of the discharge. Downstream injection of N2 is ineffective. Using surface spectroscopies we directly show a dramatic enhancement of the reactivity of fluorine and oxygen atoms with silicon and silicon–nitride surfaces upon N2 injection to the discharge. Our results can be explained by the production of energetic metastable species in the discharge region which transport energy to the gas‐surface interface.

Study of plasma-surface interactions : chemical dry etching and high-density plasma etching

We report results of the characterization of the plasma - surface interactions of silicon and silicon dioxide in fluorocarbon discharges using real-time ellipsometry and post-plasma multi-technique surface analysis for chemical dry etching (CDE) and high-density plasma etching (HDPE). We show that changes of the gas composition in CDE causes major changes in silicon surface chemistry and etching behaviour. For low-pressure HDPE we investigate the influence of power deposition into the discharge and bias voltage and bias power at the wafer on the surface chemical changes of silicon and .