碳氟等离子体中CF2对SiO2，Si3N4和Si刻蚀的作用

The CF2 density and etch rate of SiO2, Si3N4 and Si are investigated as a function of gas pressure and O2 flow rate in fluorocarbon plasma. As the pressure increases, the self-bias voltage decreases whereas the SiO2 etch rate increases. Previous study has shown that SiO2 etch rate is proportional to the self-bias voltage. This result indicates that other etching parameters contribute to the SiO2 etching. Generally, the CF2 radical is considered as a precursor for fluorocarbon layer formation. At a given power, defluorination of fluorocarbon under high-energy ion bombardment is a main source of fluorine for SiO2 etching. When more CF2 radical in plasma, SiO2 etch rate is increased because more fluorine can be provided. In this case, CF2 is considered as a reactant for SiO2 etching. The etch rate of Si3N4 and Si is mainly determined by the polymer thickness formed on its surface which is dominated by the CF2 density in plasma. Etching results obtained by varying O2 flow rate also support the proposition.     

Dry etching of new phase-change material Al_(1.3)Sb_3Te in CF_4/Ar plasma

正The dry etching characteristic of Al_(1.3)Sb_3Te film was investigated by using a CF_4/Ar gas mixture.The experimental control parameters were gas flow rate into the chamber,CF_4/Ar ratio,the O_2 addition,the chamber background pressure,and the incident RF power applied to the lower electrode.The total flow rate was 50 sccm and the behavior of etch rate of Al_(1.3)Sb_3Te thin films was investigated as a function of the CF_4/Ar ratio,the O_2 addition,the chamber background pressure,and the incident RF power.Then the parameters were optimized.The fast etch rate was up to 70.8 nm/min and a smooth surface was achieved using optimized etching parameters of CF_4 concentration of 4%,power of 300 W and pressure of 80 mTorr.     

Reactive-ion etching of Ge2Sb2Te5 in CF4/Ar plasma for non-volatile phase-change memories

Etching of Ge₂Sb₂Te₅ (GST) is a critical step in the fabrication of chalcogenide random access memories. In this paper, the etch characteristics of GST films were studied with a CF₄/Ar gas mixture using a reactive-ion etching system. We observed a monotonic decrease in etch rate with decreasing CF₄ concentration indicating its importance in defining the material removal rate. Argon, on the other hand, plays an important role in defining the smoothness of the etched surface and sidewall edge acuity. We have studied the importance of gas mixture and RF power on the quality of the etched film. The smoothest surfaces and most vertical sidewalls were achieved using a CF₄/Ar gas mixture ratio of 10/40, a background pressure of 80 mTorr, and power of 200 W.     

用于非易失性相变存储器中Si2Sb2Te5在CF4/Ar等离子体下的反应离子刻蚀

Phase change random access memory（PCRAM） is one of the best candidates for next generation nonvolatile memory,and phase change Si₂Sb₂Te₅ material is expected to be a promising material for PCRAM.In the fabrication of phase change random access memories,the etching process is a critical step.In this paper,the etching characteristics of Si₂Sb₂Te₅ films were studied with a CF₄/Ar gas mixture using a reactive ion etching system.We observed a monotonic decrease in etch rate with decreasing CF4 concentration,meanwhile,Ar concentration went up and smoother etched surfaces were obtained.It proves that CF4 determines the etch rate while Ar plays an important role in defining the smoothness of the etched surface and sidewall edge acuity.Compared with Ge₂Sb₂Te₅, it is found that Si₂Sb₂Te₅ has a greater etch rate.Etching characteristics of Si₂Sb₂Te₅ as a function of power and pressure were also studied.The smoothest surfaces and most vertical sidewalls were achieved using a CF₄/Ar gas mixture ratio of 10/40,a background pressure of 40 mTorr,and power of 200 W.     

Influence of temperature on the etching rate of SiO2 in CF4 + O2 plasma

The plasmochemical etching of SiO₂ in CF₄ + O₂ plasma is considered. During the experiment SiO₂ films are etched in CF₄ + O₂ plasma at temperatures of 300 and 350 K. The dependences of plasmochemical etching rates of SiO₂ on O₂ content in the feed are measured. The experimental measurements are compared with theoretical calculations. The obtained theoretical results are used to predict the real dimensions of etched trenches. It is found that decrease in temperature reduces lateral undercutting due to decreased desorption of formed SiF₄ molecules from the sidewalls.     

Mechanism of selective Si3N4 etching over SiO2 in hydrogen-containing fluorocarbon plasma

This paper describes the mechanism of selective Si₃N₄ etching over SiO₂ in capacitively-coupled plasmas of hydrogen-containing fluorocarbon gas, including CHF₃, CH₂F₂ and CH₃F. The etch rate of Si₃N₄ and SiO₂ is investigated as a function of O₂ percentage in all plasma gases. Addition of O₂ in feed gases causes plasma gas phase change especially H density. The SiO₂ etch rate decreases with increase of O₂ percentage due to the decline of CF_x etchant. The Si₃N₄ etch rate is found to be strong correlated to the H density in plasma gas phase. H can react with CN by forming HCN to reduce polymer thickness on Si₃N₄ surface and promote the removal of N atoms from the substrate. Thus the Si₃N₄ etch rate increases with H intensity. As a result, a relative high selectivity of Si₃N₄ over SiO₂ can be achieved with addition of suitable amount of O₂ which corresponds to the maximum of H density.     

Influence of activated polymer on the etching rate of SiO2 in CF4 + H2 plasma

The reactive ion etching (RIE) of SiO₂ in CF₄ + H₂ plasma is considered. The influence of activated polymer on the RIE rate of SiO₂ in CF₄ + H₂ plasma is determined by extrapolation of experimentally measured kinetics of the etching rate. It is found that the increased surface coverage by CF₂ radicals suppresses the RIE rate of SiO₂ in CF₄ + H₂ plasma during the initial stages of the etching process. The formation of activated polymer becomes pronounced when adsorbed CF₂ radicals are slowly activated. The activated polymer intensifies the etching reaction and enhances the etching rate. At the same time, the activated polymer intensifies the polymerization reactions. The increased surface coverage by the polymer suppresses the RIE rate of SiO₂ in CF₄ + H₂ plasma at later stages of the etching process.     

On the etching mechanism of ZrO2 thin films in inductively coupled BCl3/Ar plasma

The etching mechanism of ZrO₂ thin films in BCl₃/Ar plasma was investigated using a combination of experimental and modeling methods. It was found that an increase in the Ar mixing ratio causes the non-monotonic behavior of the ZrO₂ etch rate which reaches a maximum of 41.4 nm/min at about 30-35% Ar. Langmuir probe measurements and plasma modeling indicated the noticeable influence of a BCl₃/Ar mixture composition on plasma parameters and active species kinetics that results in non-linear changes of both densities and fluxes for Cl, BCl₂ and . From the model-based analysis of surface kinetics, it was shown that the non-monotonic behavior of the ZrO₂ etch rate can be associated with the concurrence of chemical and physical pathways in ion-assisted chemical reaction.     

Characterization of the CH4/H2/Ar high density plasma etching process for HgCdTe

High density plasma etching of mercury cadmium telluride using CH₄/H₂/Ar plasma chemistries is investigated. Mass spectrometry is used to identify and monitor etch products evolving from the surface during plasma etching. The identifiable primary etch products are elemental Hg, TeH₂, and Cd(CH₃)₂. Their relative concentrations are monitored as ion and neutral fluxes (both in intensity and composition), ion energy and substrate temperature are varied. General insights are made into surface chemistry mechanisms of the etch process. These insights are evaluated by examining etch anisotropy and damage to the remaining semiconductor material. Regions of process parameter space best suited to moderate rate, anisotropic, low damage etching of HgCdTe are identified.     

Dry etching characteristics of In1-x-y Ga x Al y as alloys in CCl2F2:Ar and CH4:H2:Ar discharges

The etching characteristics of InGaAlAs alloys lattice-matched to InP were investigated using low pressure (1 mTorr) electron cyclotron resonance CH₄:H₂:Ar or CCl₂F₂:Ar discharges with additional radiofrequency biasing of the samples. Using CCl₂F₂:Ar discharges with ≥250V negative bias it is possible to obtain equi-rate etching of the material for all compositions between In_0.53Ga_0.47As and In_0.52Al_0.48As. At lower bias values, formation of A1F₃ on the surface leads to an inhibition of the etch rates. By making use of the differential etch rates of InGaAlAs layers of different compositions in CH₄:H₂:Ar mixtures, it is possible to choose dc bias values that allow one to stop the etching at a pre-selected depth in a multi-layer structure. For example, for -150 V bias, one can etch through In_0.53Ga_0.47As, In_0.53Ga_0.40Al_0.07As and Ino.53Ga_0.30Al_0.17As layers, and stop at an underlying layer with composition In_0.53Ga_0.20Al_0.27As.     

Patterning of Ge2Sb2Te5 phase change material using UV nano-imprint lithography

DRAM is the most commonly used memory due to many advantages such as high speed and easy manufacturability owing to its simple structure, but is volatile. On the other hand, flash memory is non-volatile, but has other disadvantages such as slow speed, short lifetime, and low endurance for repetitive data writing. Compared to DRAM and flash memory, PRAM (Phase-change Random Access Memory), which is a non-volatile memory using a reversible phase change between amorphous and crystalline state, has many advantages such as high speed, high sensing margin, low operating voltage, and is being pursed as a next generation memory. Being able to pattern and etch phase change memory in nanometer scale is essential for the integration of PRAM. This study uses the Nano-Imprint Lithography (NIL) for patterning the PRAM in nanometer scale which is believed to be a future lithography technology that will replace the conventional Photo Lithography. Si wafers coated with SiO₂ were used as substrates, and Ge₂Sb₂Te₅ (GST) films with the thicknesses of 100 nm were deposited by RF sputtering. Poly-benzylmethacrylate based polymer patterns were formed using NIL on the surface of GST films, and the GST films were etched using Cl₂/Ar plasma in an Oxford ICP (inductively coupled plasma) etcher.