Deep Trench Etching Research Articles

Micro chamber for cellar analysis integrated with negligible dead volume sample injector

A micro chamber integrated with an extremely low dead volume sample injector for real-time monitoring of living cell was developed. By means of the combination of isotropic etching and deep trench etching using CCP–RIE and ICP–RIE, the sample injector with negligible dead volume of less than 0.05 nl is realized. Using fabricated devices, the reproducible sample injection of the order of 1 nl was obtained. Biological cell culture of rat mast cell was also performed in the fabricated micro chamber.

The Novel Junction Termination Method Employing Shallow Trench

We propose a novel junction termination method employing shallow silicon trenches filled with silicon dioxide, which decreases the junction termination radius by 23% while maintaining the identical breakdown voltage. The shallow silicon trenches filled with silicon dioxide and P+ FLRs (Field Limiting Rings) in the proposed structure reduced the electric field concentration in the P+ cathode due to the low dielectric constant of the silicon dioxide. We fabricated the proposed structure in silicon wafers and measured its breakdown voltage. The proposed junction termination method does not require any complex fabrication process such as a deep silicon trench or silicon bevel edge etching. The junction termination radius of the proposed structure employing three trenches was decreased by 23% compared with that of the conventional FLR employing three P+ FLRs. The breakdown voltage of the proposed structure with four trenches was 664V, which is 86% of the ideal parallel-plane breakdown voltage.

Deep dry etching of borosilicate glass using fluorine-based high-density plasmas for microelectromechanical system fabrication

For the fabrication of microelectromechanical system devices, deep trench etching of borosilicate glass (Corning 7740) has been investigated using SF6/Ar inductively coupled plasma. Since borosilicate glass contains metal elements which produce nonvolatile fluorides, dry etching of its smooth surface is a difficult issue. In this article, requisite conditions for etching glass with a smooth surface and high mask selectivity have been discussed on the basis of the results of a comprehensive experimental study of the effects of substrate bias power and Ar addition on the removal of involatile fluoride residues deposited via the backscattering of etch products in the vicinity of the substrate surface. Under optimized etching conditions, deep trench etching of borosilicate glass to 32 μm depth and 15 μm width has been accomplished using 3-μm-thick chrome metal masks.

High aspect ratio via etching conditions for deep trench of silicon

Deep trench etching of silicon was investigated as a function of platen power, operational pressure and the SF6:C4F8 gas flow rate. Their effects on the etch rate, etch profile and scallops were also studied. As the platen power was increased from 5 to 30 W, the etch rate was increased from 0.54 to 2.51 μm/min. However, the etch rate was decreased at platen power higher than 30 W. As the pressure was increased from 10 to 25 mTorr, the etch rate was increased from 1.93 to 2.69 μm/min but the etch rate was decreased at the pressure higher than 35 mTorr. As the SF6:C4F8 gas flow rate was increased from 50:50 to 200:160 sccm, the etch rate was increased from 1.91 to 2.31 μm/min and at the SF6:C4F8 gas flow rate of 260:220 sccm, it was decreased to 2.21 μm/min.

Enhanced wavelength tuning of an InGaAsP-InP laser with a thermal-strain-magnifying trench

We have used temperature-dependent strain from differential thermal expansion to increase the temperature tuning rate, dλ/dT, of the modal wavelength of an InP-based laser. The effectiveness of the strain may be further enhanced with a deep trench etch beneath the laser waveguide. We have obtained a 50% increase in the tuning rate, without degradation of the threshold current, and a maximum increase of 86%.

A bulk micromachined vibratory lateral gyroscope fabricated with wafer bonding and deep trench etching

A bulk micromachined vibratory lateral gyroscope, which is fabricated with Silicon-glass wafer bonding and deep trench etching, has been developed. By using entirely symmetric springs, drive mode and sense mode frequencies of the gyroscope are matched precisely, which is important to improve sensitivity. The gyroscope has a large mass and capacitance, and its thermal–mechanical noise floor is estimated to be about 0.05°/h/Hz 1/2.

Highly accurate cell projection mask for applications to sub-130 nm patterning

In this article, we introduce the constraints of cell projection mask (CPM) design for application to sub-0.13 μm patterning and the modified fabrication technology for the highly accurate CPM. First, we investigated the constraints of CPM design such as Coulomb interaction and proximity effect. Especially, in order to reduce beam blur effect, we applied mask bias and optimized shot size that could be obtained by calculated space margin and experiment. Second, we made highly accurate CPM using modified fabrication technology, which included deep trench etching process with oxide barrier, the stacked protection layer, and effective cleaning process. The minimum feature size achievable in this technology is 1 μm, corresponding to 0.04 μm on a wafer due to 1/25 reduction ratio of cell projection e-beam lithography system. Using CPM made by above process, we successfully defined 0.08 μm lines-and-spaces and 0.1 μm contact hole patterns with a standard deviation of 0.005 μm. In addition, we also compared the lithographic performance of the CPM samples with 20- and 10-μm-thick diaphragms. According to our results, thin CPM has more advantages than a thick one in view point of fabrication and low electron transmittance of sidewall.

12 kV low current cascaded light triggered switch on one silicon chip

A new insulation technique for lateral high voltage switch devices has been developed. Applying deep trench etching, backside etching and wafer dicing completely insulated silicon islands have been generated on wafer level. Each island contains a photo bipolar transistor to allow an optical control of the device. The transistors have been connected in line to achieve blocking voltages of 12 kV. The entire chip size of the HV device is about 30 mm^2.

Microfabricated ultrasensitive piezoresistive cantilevers for torque magnetometry

New types of piezoresistive cantilevers for torque magnetometry have been microfabricated and tested. The design is optimized to detect the flexion and torsion of the cantilever corresponding to a torque in two directions, which is induced by a microscopic magnetic sample mounted on the lever surrounded by an external magnetic field. The high sensitivity (up to ≈10 −14 N m) of the device is achieved by its special geometrical design featuring cantilever legs with only 3-μm-wide beams. The microfabrication process makes use of silicon-on-insulator wafers for precise etch-stop of a novel deep-trench etch process from the backside to fabricate the individual chips. One cantilever version has an integrated metal loop for absolute calibration of the sensor within 1%. The loop can also be used to actuate the lever mechanically. Owing to their small dimension and mass, the new devices feature ultrahigh sensitivity combined with short response time, which allows the characterization of microscopic magnetic samples with very high resolution.

Design and fabrication of an angular microactuator for magnetic disk drives

Angular electrostatic microactuators suitable for use in a two-stage servo system for magnetic disk drives have been fabricated from molded chemical-vapor-deposited (CVD) polysilicon using the HexSil process. A 2.6-mm-diameter device has been shown to be capable of positioning the read/write elements of a 30% picoslider over a /spl plusmn/1-/spl mu/m range, with a predicted bandwidth of 2 kHz. The structures are formed by depositing polysilicon via CVD into deep trenches etched into a silicon mold wafer. Upon release, the actuators are assembled onto a target wafer using a solder bond. The solder-bonding process will provide easy integration of mechanical structures with integrated circuits, allowing separate optimization of the circuit and structure fabrication processes. An advantage of HexSil is that once the mold wafer has undergone the initial plasma etching, it may be reused for subsequent polysilicon depositions, amortizing the cost of the deep-trench etching over many structural runs and thereby significantly reducing the cost of finished actuators. Furthermore, 100-/spl mu/m-high structures may be made from a 3-/spl mu/m deposition of polysilicon, increasing overall fabrication speed.

Fabrication of high aspect ratio structures using chlorine gas chopping technique

This article reports on the development of dry etching technology which will offer the potential to fabricate high aspect ratio structures in silicon for Micro Electro Mechanical Systems (MEMS) fabrication, using chlorine chemistry. In this study, we report about our investigations on the etching mechanisms using gas chopping technique. Chlorine with BCl3, as chopping gas for scavenging was the basis for deep trench etching in silicon. A conventional planar RIE (Reactive Ion Etching) reactor has been used. We optimised the process parameters as per our reactor's configuration to have compromise for best selectivity, anisotropy and high etch rates, which was obtained at BCl3 gas chopping time of 2 to 4 minutes, with DC-bias of −200 to −300 Volts.

Etching technology for chromatography microchannels

Half-circular channels, to be used for gas chromatography, were etched isotropically using a mixture of HF, HNO 3 and H 2O. Two wafers with half-circular channels were bonded on top of each other to yield channels with a circular cross-section. During etching the so-called “loading effect” was encountered: the etch rate depends on the local structure density. To solve this, extra structures were placed around the channels to create an equal structure density over the wafer and so prevent irregularities in channel width. To eliminate the alignment problems that arise when bonding two wafers with isotropically etched channels together, a method which combines deep trench etching, passivation and isotropic etching was developed to construct channels under the surface of a wafer.

Deep trench etching in silicon with fluorine containing plasmas

Single crystal silicon was etched with mixtures of SF 6, CBrF 3, Ar and O 2, using different electrode materials to obtain deep trenches. The etch rates, both vertically and horizontally increase when the relative flow of SF 6 increases. When using aluminium or stainless steel electrodes, the amount of SF 6 has to be limited to 10% of the total flow of fluorine containing gases to obtain wall profiles with an angle of over 80°. However, in all these cases considerable surface roughness is observed. A solution to this problem is the use of a graphite electrode, which permits the use of SF 6 as the sole halogen containing gas to obtain vertical walls. Depending on the Ar addition, processes with good anisotropy and without surface roughness can be obtained.

Selectivity and Si-load in deep trench etching

Time dependent measurements of etch rates and mask erosion rates for a variety of different features were carried out utilizing 0.25μm ground rule masks with different silicon loads. A small loading effect for the silicon etching and a strong secondary loading effect for the mask erosion were observed leading to a time dependent selectivity. RIE lag effects for oval trenches and long grooves were quantified by least square fits. Both feature types have essentially the same etch rate and RIE lag.

Rapid plasma etching of silicon, silicon dioxide and silicon nitride using microwave discharges

Microwave plasma discharges of CF4, SF6 and CHF3 at high pressures (0.5-1.5 Torr) have been used for rapid etching of silicon, silicon dioxide and silicon nitride suitable for single-wafer etching applications. Etch rates and selectivities have been studied as a function of pressure, gas flow and the amount of O2 as the additive gas. Extremely high etch rates of 2.0-3.6 mu m min-1 and 5.0 mu m min-1 for silicon, obtained respectively in an CF4 and a CF4+20% O2 plasma can be useful for deep-trench etching applications. Formation of a sidewall passivation layer in silicon at high CF4 pressure ( approximately=1.2 Torr) gives rise to good etching anisotropy. The variation of etch selectivity between SiO2 and Si3N4 has been studied as a function of gas flow rates in SF6 plasma. The formation of a thin fluorocarbon polymer film on the etching surface in a CHF3 plasma, which has resulted in selective etching of SiO2 over Si3N4, has been observed by X-ray photoelectron spectroscopy.

Characterization of a Trench Etching Process Using CBrF3 and Optimal Emission Spectroscopy of the Plasma

AbstractDry processes for deep silicon trench etching using CBrF3 were studied. The experiments were done in a single‐wafer reactive ion etcher in a low frequency and a high frequency mode. By optical emission spectroscopy of the CBrF3 plasma relative Br‐, F‐, CF3‐, and Br+ concentrations were measured as a function of applied frequency, pressure and power. Finally, in connection with d.c. bias voltage measurements some aspects of the etching mechanism are discussed.

Redeposition during Deep Trench Etching

In reactive ion etching, redeposited materials from the plasma and the trench can significantly alter the trench profile. A simple model, which takes into account simultaneous ion‐assisted etching and redeposition mechanisms, is presented. Using this model, a computer simulation, based on the string‐point model, is performed on the evolution of a deep trench profile. The redeposited materials from the plasma and the trench region, coupled with a moving boundary scheme, allow the shape evolution of the etching profile to be computed. The computer simulation shows that defected ions, polymer deposition, and polymer sputtering are important factors in determining the etching profile of silicon trench. Under significant bombardment of deflected ion on the sidewalls of the trench, the redeposited material from the trench is found to be more effective in blocking the etching of the sidewalls during trench etching.

Fabrication of GaAs/GaAlAs transport devices using a deep submicron trench etching technique

This paper demonstrates a submicron trenching technique for defining low-dimensional electron systems in GaAs/GaAlAs heterostructures for transport measurements. A variety of electron systems can be defined between trenches as narrow as 200 nm etched into a suitable heterostructure. The use of narrow trenches gives the advantages of high resolution, simplicity, and flexibility, and also avoids the complications associated with negative resists and lift-off techniques. Using the trenching technique, we have fabricated Aharonov–Bohm ring devices with a Schottky gate over the entire ring. At 0.4 K, these devices exhibit clear interference effects which are dependent on the gate bias.

Trench Etches in Silicon with Controllable Sidewall Angles

This paper describes the role of the temperature of the silicon wafer in controlling a deep trench etch sidewall angle and also the etch rate. In addition, we discuss the role of pressure in controlling etch rate and selectivity. This work was performed in a Tegal 1500 Test Bench. The temperature of the wafer could be held fixed as a function of time at any temperature between 20° and 200°C. Our chemistry is chloroform, with and as additives. We have found that the sidewall angle of the trench (the angle that the sidewall makes with a normal to the wafer surface) could be varied continuously from about 32° at 40°C to 7° at 190°C. The sidewalls are typically planar and relatively smooth. The bottom of the etch becomes increasingly planar as sidewall angle decreases. In order for the above processes to occur, there must be a small flow of through the chamber, e.g., 3–5 sccm. Results from the simulation code SAMPLE suggest that the rate of deposition of a material on the etch surface can control sidewall angle. We theorize that a chlorinated hydrocarbon polymer is being deposited, and that the wafer temperature is controlling the rate of deposition of the polymer. In addition to sidewall angle, for zero , increasing wafer temperature over the range stated above can cause the etch rate to increase with increasing temperature by 1800 Å/min at a nominal etch rate of 4000 Å/min. By adding to the gas mixture, the etch rate becomes insensitive to temperature. By increasing the total gas pressure to 1.2 torr, an etch rate of 8000 Å/min has been obtained, with an attendant selectivity in excess of 15.

Microfabrication Technologies for Advanced VLSI Devices

ABSTRACTRecent progress in microfabrication technologies for advanced VLSI devices, such as 16M and 64MDRAM, is presented. First, an EB delineator with a vector-scanned VSB on a moving stage has been developed for printing 0.25 μm patterns employing PMMA, high dose exposure, and 50 KeV EB. Optical lithography also has been extended toward lower submicron geometry. A Krf excimer laser reduction projection system, using a quartz/CaF2 lens, resolves successfully 0.35 μm patterns. Ga field ion beam technology has been developed with new applications in fuse-cutting of redundancy and in optimizing sense amplifier by cutting transistor gates in the SRAM device. For fine line etching technology, collimated reactive ions produced by 10−3 Torr magnetron discharge achieves deep Si trench etching and tapered Al etching by using a polymer deposition process in addition to the original thin sidewall film. Finally, a damage-free excimer laser etching process has been developed which can etch n+ poly-Si with resist mask and with pattern transfer using an optics down to 0.5 μm and 0.9 μm resolutions respectively.