APC技术在刻蚀工艺过程控制中的研究进展

APC是一个多层次的控制系统,其包含了实时的设备及工艺控制和非实时的RtR控制。APC引入等离子体刻蚀过程控制可极大提高等离子刻蚀机的使用效率和产品成品率,适应当前深亚微米半导体工艺技术发展的需求。针对等离子体刻蚀机及其刻蚀工艺过程控制的需求,本文分别从实时控制和RtR控制两个不同层次展开了论述,讨论了APC技术的发展趋势。     

Profile control in high aspect ratio contact hole etching by a capacitively coupled plasma source

Two types of masking methodologies for high aspect ratio deep contact hole etching, photo-resist (PR) masks only and poly-silicon hard masks (poly-HM), have been applied and studied. In order to understand the variation of plasma chemistries, the optical emission spectroscopy has been used to characterize the reactions of plasma etching. A novel technique for bowing-free 0.1-μm deep contact hole etching using either PR or poly-HM has been developed. It has been demonstrated that a straight vertical profile of deep contact hole can be obtained by controlling two process factors: polymer deposition rates and ion extraction energy. The step-by-step control of top and bottom powers in the capacitively coupled plasma has been found to be an effective method to avoid profile bowing and tapering in the etching process. The deep contact holes with aspect ratio >30 and profile angle of 89.8° have been obtained.     

等离子体刻蚀过程中的FTIR监控技术

采用傅里叶红外光谱仪(FHR)和MCT红外探测器可以构成原位的FTIR测量系统,可应用于在电感耦合等离子体刻蚀机中进行的硅刻蚀工艺.文中对反应腔室腔壁状态对刻蚀过程的影响,以及在硅晶片表面反应层的变化进行了详细的研究.实验表明:采用含F化合物对反应腔室进行清洗会改变反应腔室的状态,在腔室内壁状态达到稳定之前会对刻蚀速率的一致性造成扰动.硅片表面反应层中的化学组成变成了以CF为主的薄膜层,对刻蚀过程的有一定的抑制作用.     

Inductively coupled plasma etching of HgCdTe

The high-density inductively coupled plasma (ICP) etching technique has been applied to HgCdTe. The HgCdTe etch rate was studied as a function of key process variables commonly used in high-density plasma etching: chamber pressure, direct current (DC) bias, and ICP-source power. Mesa profiles were characterized using scanning electron microscopy (SEM), and the profiles for the process conditions used were found to be compatible with fabrication procedures for HgCdTe infrared focal-plane arrays (FPAs). The etch uniformity was measured to be better than 5% over a diameter of 6-in.     

Nanoscale structure formation by plasma etching

Process of isotropic plasma etching of polysilicon to form nanostructures has been developed and optimized. Dependences of the technological characteristics of the isotropic plasma etching process of polysilicon on its operational parameters have been obtained. The results were to form nanowire silicon field effect transistors and a sensitive vibro-resonant nanoelement for an atom mass sensor.     

Optical detector to monitor plasma etching

A simple photodetector has been developed to monitor plasma etching of polysilicon, pyrolytic silicon nitride and reactive plasma deposited silicon nitride.     

Virtual plasma equipment model: a tool for investigating feedbackcontrol in plasma processing equipment

As microelectronics device feature sizes continue to shrink and wafers continue to increase in size, it is necessary to have tighter tolerances during the fabrication process to maintain high yields. Feedback control has, therefore, become an important issue in plasma processing equipment design; comprehensive plasma equipment models linked to control algorithms would greatly aid in the investigation and optimal selection of control strategies. This paper reports on a numerical plasma simulation tool, the virtual plasma equipment model (VPEM), which addresses this need to test feedback control strategies and algorithms on plasma processing equipment. The VPEM is an extension of the hybrid plasma equipment model which has been augmented by sensors and actuators, linked together through a programmable controller. The sensors emulate experimental measurements of species densities, fluxes, and energies, while the actuators change process parameters such as pressure, inductive power, capacitive power, electrode voltages, and mole fraction of gases. Controllers were designed using a response surface based methodology. Results are presented from studies in which these controllers were used to compensate for a leak of N₂ into an Ar discharge, to stably control drifts in process parameters such as pressure and power in Ar and Ar/Cl₂, and to nullify the effects of long term changes in wall conditions in Cl₂ containing plasmas. A new strategy for improving the ion energy flux uniformity in capacitively coupled discharges using feedback control techniques is also explored     

等离子体刻蚀工艺中的OES监控技术

采用光学发射光谱(OES)原位检测技术,对等离子体刻蚀机中的等离子体状态进行实时监控,讨论了其在故障诊断、分类、刻蚀终点的判断及控制方面的应用。实验平台为在新研发的高密度等离子体刻蚀机,采用化学气体HBr/Cl₂为刻蚀气体进行多晶硅刻蚀工艺实验,实验过程中所采集的OES数据通过PCA法进行分析,得到与刻蚀过程相关的特征谱线。实验结果表明：OES技术适合于深亚微米等离子体刻蚀工艺过程的终点检测及故障诊断。最后就OES技术未来发展面临的挑战进行了讨论。     

Damaged depth in GaAs processed by Ar plasma etching

The damaged depths in GaAs processed by Ar plasma etching under various applied radio-frequency (RF) voltages and Ar pressures in a parallel-plate type apparatus were studied. The damaged depth was evaluated in terms of the chemically etched thickness at which the photoluminescence intensity recovers. The damaged depth decreased as the applied radio frequency peak voltage was decreased. The depth was extraordinarily deep in the lower radio frequency voltage region. The effect of Ar pressure on damaged depth was small in the range from 1 to 10 Pa.<>     

Hydrogen etching for semiconductor materials in plasma doping experiments

The etching effects of hydrogen plasma for semiconductor materials including single crystalline silicon, polycrystalline silicon, silicon dioxide, and aluminum in plasma immersion ion implantation (PHI) doping experiments have been investigated. Etching can alter device structure and affect implant profile and dose. The effects of varying different PIII process parameters such as pulse potential, pulse repetition frequency, and substrate temperature are presented. The experimental data show that the spontaneous etching by hydrogen radicals enhanced by ion bombardment is responsible for the etching phenomena that occurs at the material surface. A model is used to calculate the retained implant dose and impurity profile when the etching effect is considered.     

Polarisation control in VCSELs by elliptic surface etching

850 nm-wavelength vertical-cavity surface-emitting lasers (VCSELs) with an elliptical shallow surface relief having various aspect ratios and orientations have been fabricated. Using appropriate etch dimensions, VCSELs of up to 12.5 μm active diameter are forced to operate on the fundamental mode for a certain current range. By aligning the longer axis of the etched ellipse with the [011] or [011¯] crystal axis, the polarisation of the fundamental mode is pinned accordingly with a polarisation suppression ratio of ~30 dB     

Antireflective structures in CdTe and CdZnTe surfaces by ECR plasma etching

A rigorous coupled-wave analysis procedure has been used to design structures which can be embedded in Cd(Zn)Te surfaces to make them antireflective in the 8–14 m spectral region. Gray scale lithography was used to produce these patterns in photoresist layers. High fidelity transfer of patterns into Cd(Zn)Te surfaces was accomplished by utilizing an electron cyclotron resonance plasma with etch selectivity values in the range of 6.7–13.3. Transmission values at patterned surfaces were measured to be as high as 99.3%.     

Electrical endpoint detection of VLSI contact plasma etching

A precise, in situ monitor of plasma contact etching is described. This method of electrical endpoint detection provides a dc electrical current which is proportional to the total open contacts and gives more than an order of magnitude improvement in signal-to-noise ratio over optical techniques. Endpoint detection is clearly deserved for total contact areas of less than 0.3 percent of a 3-in wafer. Using this method, contact resistances and leakage currents for both p+-n and n+-p junctions, are compatible to that of wet-etched or dry-etched contacts.     

The influence of plasma etching on trap levels in InP

Electroreflectance (ER) and deep level transient spectroscopy (DLTS) were carried out to characterize the effects of CF₄ plasma etching on defect levels in InP. Different chamber gas pressures were conducted to study effects on the etching result. Similar ER spectra were obtained from the starting InP wafer and the wafer after plasma etching plus rapid thermal annealing (RTA) which showed good restoration of material properties by RTA. Two impurity of structural related features, T1 and T2, were observed from these ER spectra at energy positions about 0.112 and 0.178 eV below bandgap. Two trap levels, El and E2, with activation energy 0.15 and 0.55 eV, were detected from the initial wafer by DLTS. Trap El may correlate with the Tl and T2 levels observed by ER. Similar traps were found in plasma etched samples after rapid thermal annealing with one of the DLTS peaks labeled E2 shifted to the higher temperature side as the plasma etching chamber pressure increased. We identified El to be a residual electron trap from material growth and E2 to be an interface trap arising from Schottky diode fabrication.     

Carbon etching with a high density plasma etcher

Generating suitable passivation on the carbon sidewall is a major challenge facing carbon etching especially for films thicker than 500 nm. Patterning carbon hard mask stacks for sub 90 nm technologies was tested for three different O₂-based chemistries using an inductively coupled plasma etch tool. The results show that the etched carbon profiles are highly dependant upon the O₂ flow and the total time of the etch process. Extended over etch times quite often initiates lateral etching and rapid loss of profile and critical dimension. An HBr/O₂/N₂ chemistry has been shown to provide the best options for profile control and more resistance to profile loss during extended over etching than the other chemistries which were tested during this study.     

小型等离子清洗/刻蚀机的应用

综述了等离子体产生的原理、小型等离子清洗/刻蚀机的特点以及在各加工行业的应用,特别是其在科学研究领域的独特功能:等离子清洗、刻蚀、等离子镀、等离子涂覆、等离子灰化和表面改性等;论述了小型等离子清洗/刻蚀机在TEM、SEM、电镜等方面的特殊应用,并讨论了等离子处理的特殊性及其在现代科学研究中的不可替代性。     

High selectivity plasma etching of InN over GaN

Etch selectivities for InN over GaN as high as 40 and 100 are achieved in BBr₃/Ar and BI₃/Ar, respectively, under inductively coupled plasma conditions. Previous work on Cl₂-based plasma chemistries has produced selectivity in the reverse direction, i.e., GaN over InN, and therefore the introduction of these new Br₂- and I₂-based mixtures facilitates device fabrication involving double heterostructures of GaN/In_xGa_1−xN/GaN. Selectivities up to 10 for InN over the common mask materials SiO₂ and SiN_x were obtained in both BI₃ and BBr₃.     

Aspect-ratio-independent anisotropic silicon etching in a plasma chemical cyclic process

The conditions of implementation of aspect-ratio-independent etching (ARIE) are given for a two-stage etching/passivation process in an SF₆/C₄F₈ plasma. It is shown experimentally that the ARIE etching is achieved by extension of the stage of passivation and/or reduction of the energy of ions at the stage of etching. These phenomena lead to prolonged removal of the fluorocarbon film, which affects the dependence of the etching rate on the aspect ratio of the groove. A model of cyclic etching is presented that takes into account the aspect dependences of the processes on the groove bottom, namely, Si etching and deposition and removal of the fluorocarbon film. The simulation results correlate satisfactorily with the experimental data. Limitations of implementation of ARIE etching are discussed.     

Contamination of silicon and oxidized silicon wafers during plasma etching

Neutron activation analysis has been used to study the type and level of contamination of silicon and oxidized silicon wafers exposed to various plasmas used in silicon device processing. Silicon wafers exposed to plasmas in a reactor previously used to remove SiN passivation layers from Au metallized wafers were found to be heavily contaminated with Au (up to ∼10¹⁴ atoms/cm²). Au contamination of oxidized silicon wafers similarly treated was two to three orders of magnitude smaller regardless of whether SiO₂ etched faster or slower than Si in the plasmas used. Wet chemical cleaning of contaminated Si subsequent to plasma exposure was relatively ineffective in removing residual Au. This is interpreted as indicating indiffusion of Au during plasma exposure of Si. Exposure to a polymer forming plasma reduced the level of Au contamination of Si by nearly two orders of magnitude due to effective “sealing” of reactor surfaces by polymer film. Further, the level of contamination of Si was observed to decrease by over two orders of magnitude with usage time of the reactor during a 300-day time period when no Au containing materials were introduced into the reactor.     

A novel two-step etching to suppress the charging damages duringmetal etching employing helicon wave plasma

A two-step etching has been performed to eliminate the plasma charging damages during helicon-wave plasma metal etching without selectivity loss. This technique utilized a normal etching recipe to remove the Al film followed by an optimized etching recipe for the overetching step. By increasing the bias power and decreasing the source power, the optimum etching recipe can target the plasma more directionally and reduce the Al charging damages. Eventually, the damage mechanism was also reported