Plasma etching technologies such as reactive ion etching (RIE), isotropic etching, and ashing/plasma cleaning are the currently used booster technologies for manufacturing all silicon devices based on the scaling law. The needs-driven conversion from the wet etching process to the plasma/dry etching process is reviewed. The progress made in plasma etching technologies is described from the viewpoint of requirements for the manufacturing of devices. The critical applications of RIE, isotropic etching, and plasma ashing/cleaning to form precisely controlled profiles of high-aspect-ratio contacts (HARC), gate stacks, and shallow trench isolation (STI) in the front end of line (FEOL), and also to form precise via holes and trenches used in reliable Cu/low-k (low-dielectric-constant material) interconnects in the back end of line (BEOL) are described in detail. Some critical issues inherent to RIE processing, such as the RIE-lag effect, the notch phenomenon, and plasma-induced damage including charge-up damage are described. The basic reaction mechanisms of RIE and isotropic etching are discussed. Also, a procedure for designing the etching process, which is strongly dependent on the plasma reactor configuration, is proposed. For the more precise critical dimension (CD) control of the gate pattern for leading-edge devices, the advanced process control (APC) system is shown to be effective.

https://iopscience.iop.org/article/10.1143/JJAP.47.1435/pdf

Developments of Plasma Etching Technology for Fabricating Semiconductor Devices

Etching yields of SiO2 have been determined for F+, CFx+ (x=1,2,3) ion irradiation with energy ranging from 250 to 2000 eV using a mass-analyzed ion-beam apparatus that can irradiate a single species ion to sample surfaces under an ultrahigh vacuum condition. The etching yield of CFx+ (x=1,2,3) was enhanced by the chemical effects of the ions, and both carbon and fluorine atoms from the incident ions were significant reactants. For lower energies, the etching yield increased with increasing ion energy. Above 1000 eV, the etching yield was gradually saturated with increasing ion energy. In the low ion energy region, steady etching did not occur, and an amorphous fluorinated carbon (a-C:F) film was deposited on the SiO2 surface. The ion energy region in which a-C:F film deposition occurred decreased with increasing fluorine atoms in incident CFx+ (x=1,2,3) ions.

Etching yield of SiO2 irradiated by F+, CFx+ (x=1,2,3) ion with energies from 250 to 2000 eV

The effect of radio-frequency bias on electron density in an inductively coupled plasma reactor was measured using a wave cutoff probe, over a wide range of conditions in pure Ar, pure CF4, and 50%–50% mixtures of Ar∕CF4, at pressures of 0.7–4.0Pa (5–30mTorr), bias frequencies of 10–30MHz, bias voltages up to 750V, and inductive source powers of 50–300W. Also, at selected experimental conditions, comparisons with Langmuir probe measurements were made. Two types of bias-induced changes in electron density were detected. First, at high source powers, we observed a bias-induced decrease in electron density, which had a slow time response (several minutes), a linear dependence on bias voltage, and little or no dependence on bias frequency or pressure. This decrease is a gas composition effect caused by etch or sputter products liberated from the wafer surface. Second, at low source powers, we observed a faster, bias-induced increase in electron density, which was proportional to the bias frequency and the squ...

The effects of radio-frequency bias on electron density in an inductively coupled plasma reactor

In plasma etching for microelectronics fabrication, a sheath electric field accelerates ions into the substrate so they strike at normal incidence, contributing energy and reactive species to enable anisotropic etch profiles. The energy of the bombarding ions is typically controlled coarsely with a sinusoidal bias voltage applied to the substrate electrode, producing a broad bimodal ion energy distribution (IED) at the substrate. By systematically tailoring the shape of the waveform, the energies and relative fluxes of the two IED peaks are varied independently over a 100–500 eV range in a fluorocarbon-based helicon plasma, while silicon dioxide and photoresist etch rates are monitored. A 100 eV IED peak was combined with a higher energy peak, with the energy and relative flux of the high energy group as variables in the experiment. A relatively small contribution of high energy ions is found to lead to considerable etch rate enhancement, higher than predicted by a linear combination of single-peak etch rates at the two energies. Because high energy ion bombardment is known to suppress fluorocarbon deposition, it seems likely that changes in surface chemical composition in their presence enhances the contribution of lower energy ions to etching reactions.

https://iopscience.iop.org/article/10.1088/0963-0252/18/2/025009/pdf

Energy distribution of bombarding ions in plasma etching of dielectrics

Plasma etching of thin films is essential for microelectronics manufacturing. With current feature sizes of 35 nm in production and processes for smaller devices being developed, the sidewall roughness is within the order of magnitude of the gate length of the device, and therefore significantly impacts the devices' performance. In this paper we review the modelling of the surface profile evolution in plasma etching. Both two-dimensional (2D) and three-dimensional (3D) models have been developed using a number of representations and solution algorithms. String algorithms and the method of characteristics use a segmented string which is incrementally advanced. Level-set representations describe the profile evolution as a moving interface in response to a velocity field. Cellular representations in which the area or volume domain is divided into discrete cells have been used with flux and surface kinetics based on Monte Carlo calculations. We discuss our work in the modelling of profile evolution with surface roughening using a 3D cellular Monte Carlo simulation. The formation of perpendicular and parallel ripple formation on planar surfaces as a function of ion bombardment incidence angle and the transformation from perpendicular to parallel as etching progresses has been modelled. The smoothing and/or roughening of resist masks has been demonstrated along with the pattern transfer of roughness into the underlying layers being etched.

https://iopscience.iop.org/article/10.1088/0022-3727/42/19/194014/pdf

Review of profile and roughening simulation in microelectronics plasma etching

To clarify the origins of high selectivity in SiO2-to-SiN etching in fluorocarbon gas plasma, mass-analyzed CFx+ (x=1,2,3) ions with a definite kinetic energy of 250–2000eV were irradiated on SiN and SiO2 surfaces. Selectivity in SiO2-to-SiN etching varies greatly for different CFx+ ions. For CF3+ ions, the etch yield of SiN is almost the same as that of SiO2, causing poor selectivity. For CF+ ions, on the other hand, the etch yield of SiN is much smaller than that of SiO2. An amorphous fluorinated carbon (a-C:F) film grows without any neutral radicals on the SiN surface at energies below 1250eV and on the SiO2 surface at energies below 500eV due to CF+ ion irradiation. The difference in threshold energy of a-C:F film deposition causes high selectivity in SiO2-to-SiN etching. Slight etching of substrate films first takes place at the initial stage of deposition, then etching stops, and a homogeneous a-C:F film is grown. Accumulated carbons during the initial etching reaction modify the surface reaction la...

Mass-analyzed CFx+ (x=1,2,3) ion beam study on selectivity of SiO2-to-SiN etching and a-C:F film deposition

We have studied both the etching of SiO2 film and the growth of an amorphous fluorinated carbon (a-C:F) film by mass-analyzed fluorocarbon ion irradiation. This experiment was done in an ultrahigh vacuum with a pressure of 10−7 Pa even during irradiation. When using a carbon monoflouride (CF1+) ion with an energy of 300 eV to irradiate, it was found that SiO2 film a few nm thick was initially etched away. Then, an a-C:F film was continuously deposited on the SiO2 surface as the ion dose exceeded about 5×1016 cm−2. Using in situ x-ray photoelectron spectroscopy analysis, it was determined that carbon accumulates on the surface at this early stage as the ion dose increases, so that this transition is resulted by the surface modification on which the CF1+ ion itself irradiates the SiO2 surface. Especially in highly ionized fluorocarbon plasmas, surface conditions such as the carbon concentration affect possibly etching performance.

Transitional change to amorphous fluorinated carbon film deposition under energetic irradiation of mass-analyzed carbon monofluoride ions on silicon dioxide surfaces

Ken-ichi Yanai

Papers

Etching yield of SiO2 irradiated by F+, CFx+ (x=1,2,3) ion with energies from 250 to 2000 eV

Mass-analyzed CFx+ (x=1,2,3) ion beam study on selectivity of SiO2-to-SiN etching and a-C:F film deposition

Transitional change to amorphous fluorinated carbon film deposition under energetic irradiation of mass-analyzed carbon monofluoride ions on silicon dioxide surfaces