Dry etching for submicron structures

The fabrication of the FeRAM requires the development of etching processes for ferroelectric thin films and electrodes as well as deposition processes. But different etching methods have different impacts such as resolution and process-induced damages. In this paper, reactive ion etching (RIE) and ion beam etching (IBE) for ferroelectric thin films and Pt electrodes have been studied in details. Different silicon-based ferroelectric thin films and their corresponding electrodes have been etched successfully. To compensate the possible oxygen loss caused by the etching process, the samples should be annealed in O2 at 550°C for 30 min after RIE and IBE etching.

: A microcavity surface emitting (SE) laser is very attractive for future optoelectronic applications such as optical parallel processing and optical interconnections. In order to realize such a low threshold SE laser, micro-fabrication providing a low damage etch is one of important issues. We have introduced a reactive ion etch (RIE) and reactive ion beam etch (RIBE) technique to fabricate a tiny dielectric multilayer reflector and micro-resonator for surface emitting lasers. In most of SE laser structures, a SiO2/TiO2 dielectric multilayer reflector or semiconductor multilayer mirror is used as high reflective mirrors. However, it has been difficult to fabricate the microcavity with steep side walls by wet chemical etching since each material has different etching rates. Dry etch techniques for multilayer structures, especially for GaInAsP/InP semiconductors, have not been fully studied.

Two kinds of ion beam etching techniques, Ar gas ion beam etching (IBE) and oxygen gas reactive ion beam etching (RIBE), were used for adhesion enhancement of the PI/Cu and Cu/PI interface, respectively.Ar gas IBE on Cu followed by deposition of PI film on the modified Cu surface can double the adhesion strength of spin-coated PI on Cu compared with unmodified Cu. The adhesion enhancement is due to increasing the surface contact area of the rough Cu surface to PI. However, a corrosion reaction happens at the polyamic acid (PAA) and Cu interface, resulting in the dissolution of Cu into the PI film and Cu oxide layer growth during curing of PI film. A Cr layer between Cu and spin-coated polyamic acid(PAA) is necessary to keep the Cu from dissolving in PAA and diffusing into PI. Ar IBE modification on Cu followed by deposition of a thin Cr layer on the modified Cu surface is recommended to enhance the adhesion strength of spin-coated PI on Cr.O2 RIBE on PI followed by evaporation of Cu on a modified PI increases the peel strength of Cu/PI by more than 25 times. The maximum peel strength of Cu on the PI modified by O2 RIBE is almost 70 grams/mm. The increase of adhesion is due to the mechanical interlocking of a unique structure of modified PI - a grass-like structure. This structure occurs because of the inhomogeniety of PI film - the presence of ordered and disordered phases in a PI film. In addition, the Cu/PI interface exhibits stability with thermal cycling and humidity, because the adhesion enhancement is mostly due to a mechanical effect and not a chemical effect. The diffusion of Cu into PI at various temperatures is not significant. Typically, Cu atoms can diffuse up to 300 at 400 °C in 1 hour. Another advantage of O2 RIBE on PI is the capability of enhancing the adhesion of the second PI layer on a first PI layer.These technologies allow the precise control of the adhesion strength of the PI/Cr/Cu and Cu/PI interfaces by independent variation of the beam energies, ion doses and angle of beam incidence. Also the ion source is easily installed in the same vacuum chamber for Cr and Cu evaporation. This provides low cost and simple operation.

The excellent anisotropy of the reactive Ion BeM eTCHING(RIBE) process, its fairly high etch rate and the perfectly smooth etched surface have made it a desirable tool for III-V eletronic and optoeletronic device fabrication. The properties of a microwave excited ion source have been examined, the influence of the various parameters and the etch affect of various gases in Chemical Assisted Ion Beam Etching(CAIBE) have been studied. Application to the fabrication of lasers have demostrated that the initial reluctance to accept such a process for semiconductor device etching was not justified.

Reactive Ion Beam Etching (RIBE) has been found to be an extremely useful technique for fabricating highly anisotropic ferroelectric device structures, particularly nonvolatile random access (NVRAM) memory devices, which are difficult to etch by other dry etching methods. The application of ion beam equipment to this field has been limited in the past by the use of standard Kaufman type ion sources, which have very short cathode lifetimes when operated with the reactive gases which are used to attain enhanced selectivity. This problem is solved by using the RF inductively coupled ion source described here. Etch results on ferroelectric PZT and Pt electrodes are presented for the RF source and compared with results for a Kaufman filament ion source. It is shown that RF RIBE with fluorocarbon gases provides higher etch selectivity for the ferroelectric (up to about 4:1 PZT/Pt) combined with relatively high etch rates (650 A/min for PZT at 500 eV). A complete practical ion beam process for patterning ferroelectric device structures is then described, incorporating the ferroelectric RIBE step. Highly anisotropic etched features are shown.

Dry etching and overgrowth process techniques have been developed for the fabrication of InGaN inner stripe laser diodes. The dry etch damage at the etched surface and the overgrown interface was estimated using X-ray photoelectron spectroscopy (XPS) and Rutherford backscattering spectrometry (RBS). As a result, the etch damage at the overgrown interface was shown to be repaired during the overgrowth. Groove stripes formed on the GaN layer by reactive ion beam etching (RIBE) were overgrown by GaN using metalorganic chemical vapor deposition (MOCVD). The morphology of the overgrown surface was observed by scanning electron microscopy (SEM). The grooves of widths less than 10 µm were buried completely at 1100°C and smooth, flat surfaces were obtained. We have fabricated the InGaN inner stripe (IS) lasers and reported on the first pulsed lasing operation of InGaN inner stripe lasers, fabricated by dry etching and overgrowth techniques.

Dry etching utilizing showered electron beam assisted etching

A number of current and future optoelectronic components require the creation of waveguides in LiNbO3. In order to accomplish this, trenches between one and ten microns deep must be patterned into the LiNbO3 substrate. We have demonstrated the formation of near-vertical, smooth-walled trenches up to ten microns deep using Ar ion beam etching (IBE) and Ar/CHF3 reactive ion beam etching (RIBE) processes. Both Ar IBE and Ar/CHF3 RIBE processes can achieve etching rates of up to 100 nm/minute. Our patented RIBE process [K. E. Williams, et al. U.S. Patent No. 6,238,582 (29 May 2001)] has the additional advantage of providing up to a 5:1 selectivity for etching the LiNbO3 over a photoresist mask. The collimated beam available with IBE and RIBE allows control over feature profiles and redeposition removal. Using a combination of RIBE and a multiangle process, the sidewall angle and smoothness of the mask have been transferred into LiNbO3 substrates to depths between one and ten microns. This depth range can be expanded in either direction if an appropriate mask can be fabricated.

We measured the chlorine plasma characteristics in reactive ion beam etching (RIBE) and chemically assisted ion beam etching (CAIBE) process. In the CAIBE process, the energy peak of Cl+ ionized by Ar+ appears in the energy range of 50–70 eV and this Cl+ energy peak increases with an increase of Ar+ energy. We observed that the excited state Cl2 density in CAIBE is lower than that in RIBE as measured by appearance mass spectrometry (AMS).

Reactive ion beam etch (RIBE) is one of the most important dry etching techniques for microfabrication of semiconductor devices such as microsized vertical-cavity surface-emitting lasers (VCSELs) which have a side-etched shape near the bottom of mesas We think the side-etch is caused due to the temperature rise by ion irradiation. In this paper, the measurement of surface temperature by using a radiation thermometer is carried out, in-situ during RIBE. We propose a multistep RIBE to improve etching profiles in order to alleviate the temperature rise. In this experiment, we used a high-vacuum RIBE system which has an electron cyclotron resonance-type ion source.

Reactive ion beam etching (RIBE) offers intrinsic interest as an etch technique and its comparatively low operating pressure (10-4 torr in the bombardment chamber) allows the application of ion beam based surface analytical techniques to monitor the surface during etching. We report here on the RIBE of tungsten with a reactive ion beam generated from a carbon tetrafluoride (CF4)/argon (Ar) gas mixture.

Argon and reactive ion beam etching for SAW devices

Ion incidence angle-dependent pattern formation on AZ® 4562 photoresist by reactive ion beam etching

Shaping of laser light intensities by using Diffractive Optical Elements allows the adaption of the incident light to its application. Fused silica is used where for example UV-light or high temperatures are mandatory. For high diffraction efficiency the quality of the etched surface areas is important. The investigation of different process parameters for Ion Beam and Reactive Ion Etching reveals that only Ion Beam Etching provides surfaces with optical quality. Measurements of the influence of the surface quality on the diffraction efficiencies prove that the surfaces generated by Reactive Ion Etching are not suitable. Due to the high selectivity of the process Reactive Ion Etching is nevertheless a reasonable choice for the fabrication of Diffractive Optical Elements. To improve the quality of the etched surfaces a post processing with Ion Beam Etching is developed. Simulations in MATLAB display that the angle dependent removal of the surface during the Ion Beam Etching causes a smoothing of the surface roughness. The positive influence of a post processing on the diffraction efficiency is outlined by measurements. The ion beam post processing leads to an increase of the etching depth. For the fabrication of high efficient Diffractive Optical Elements this has to be taken into account. The relation is investigated and transferred to the fabrication of four-level gratings. Diffraction efficiencies up to 78 % instead of the ideal 81 % underline the practicability of the developed post processing.

ABSTRACTDry etching characteristics of GaN using reactive ion beam etching (RIBE) were studied. Etching profile, etching rate and etching selectivity to a photoresist (PR) mask were investigated as a function of various etching parameters. Characteristics of chemically assisted reactive ion beam etching (CARIBE) and RIBE were compared at varied mixtures of CH4 and Cl2. A highly anisotropie etching profile with a smooth surface was obtained for tilted RIBE with Ch at room temperature. Etching selectivity to a PR was dramatically improved in RIBE and CARIBE when a volume fraction of CH4 to the mixture of CH4 and Ch was larger than 0.83.