摘要:

Hydrogen concentration depth profiles in as‐deposited and annealed chemical vapor deposited silicon oxide [2% P glass, 8% P glass, tetraethylorthosilicate (TEOS), phosphorous‐doped TEOS and plasma oxide] films were measured using the nuclear reaction profiling technique with a 6.4 MeV15N ion beam. The H2/Ar annealing of 450 °C for 60 min in furnace and the rapid thermal annealing at 1000 °C for 60 s in O2or H2/Ar were carried out. It is found that hydrogen concentration is in the range 1021–1022per cm3in as‐deposited films. Annealing at high temperatures, even in hydrogen containing medium, lowers the hydrogen concentration in all films. The hydrogen concentration gradually increased with time when the films were left in the room environment. The electrical properties of the oxide are found to be related to the presence of hydrogen. The observed correlation between the flatband voltage and the hydrogen concentration is presented and discussed.

ISSN:1071-1023    

DOI:10.1116/1.584173

出版商:American Vacuum Society    

年代:1988

数据来源: AIP

摘要:

Polyimides are finding increased use in integrated circuits as a dielectric and protective layer. Its low dielectric constant, ease of application, and ability to planarize the surfaces, permit their incorporation into very large scale integrated and ultra‐large scale integrated circuit processing. However, there is no single polyimide available which possesses high‐temperature stability at temperature>300 °C. A newer class of polymers called polyimidesiloxane (SIM‐2000), resulting from the modification of polyimides by special equilibrated silicone blocks, has been found superior to commercial polyimides especially with respect to their high‐temperature stability. In this paper, we present the results of our investigation of the high‐temperature stability of a few polyimidesiloxane materials spun on various substrates including Si, SiO2, and Al.

ISSN:1071-1023    

DOI:10.1116/1.584174

出版商:American Vacuum Society    

年代:1988

数据来源: AIP

摘要:

The threshold voltage of GaAs metal–semiconductor field effect transistors (MESFET’s) can be controlled by the use of buried gates. The controlling mechanism is through the alloying reaction between the gate material and the GaAs substrate. Although this can be done by choosing suitable annealing conditions, the alloying reaction may continue to proceed if the operating temperature of the device is high and/or for long‐device field service. To overcome this problem a Ni–W alloy is chosen as the gate metallization. The idea here is to utilize the concentration dependence of the interfacial reactivity between the Ni–W alloy and the GaAs to limit the alloying reaction. Below 400 °C Ni leaches out of the Ni–W alloy to react with the GaAs, and W does not participate in the reaction. As Ni leaches out, the composition of W at the interface increases and this appears to choke off the reaction, resulting in a self‐limiting reaction for buried gates. We found that a thin‐Pd (20 Å) layer placed at the GaAs/NiW interface is helpful in improving the interfacial reaction uniformity. It was found that the threshold voltage of GaAs MESFET’s can be adjusted to any desired value using this approach. After the desired threshold voltage has been obtained, the mean value of the threshold voltage of 30 field effect transistors (FET’s) is found to stabilize to ±5 mV with a standard deviation of ±27 mV at a temperature of 235 °C for a period of at least 90 h. The activation energies for the change in threshold voltage at different stages of anneal have also been estimated.

ISSN:1071-1023    

DOI:10.1116/1.584154

出版商:American Vacuum Society    

年代:1988

数据来源: AIP

摘要:

We have investigated the temperature dependence of threshold voltage (Vth) ofn‐channel GaAs metal–semiconductor field effect transistors with different gate materials and structures. It is found thatVthincreases by 0.3–0.4 V as temperature decreases from 350 to 80 K. TheVthversus temperature relationship is approximately linear. The amount ofVthshift is independent of channel length from 0.8 to 3 μm and it does not strongly depend on the gate material used. SimilarVthincreases are observed for different channel doping methods, such as ion implantation and molecular‐beam epitaxy growth. Different GaAs substrates only show a small effect on theVthtemperature dependence. Calculations show that Fermi‐level shift and energy‐gap expansion with decreasing temperature account for only a fraction of the observed change inVth. Our measurements indicate that the extraVthshift is not mainly due to deep‐level traps within the channel. Results fromC–Vmeasurements on metal/GaAs diodes suggest that build‐in voltage changes with temperature are principally responsible for theVthshift.

ISSN:1071-1023    

DOI:10.1116/1.584155

出版商:American Vacuum Society    

年代:1988

数据来源: AIP

摘要:

Micromechanical structures can be made by selectively etching sacrificial layers from a multilayer sandwich of patterned thin films. This paper reviews this technology, termed surface micromachining, with an emphasis on polysilicon microstructures. Micromechanical characteristics of thin‐film microstructures critically depend on the average residual stress in the film, as well as on the stress variation in the direction of deposition. The stress in low‐pressure chemical vapor deposition polysilicon varies with deposition temperature, doping, and annealing cycles. Applications of surface micromachining to fabricate beams, plates, sealed cavities, and linear and rotary bearings are discussed.

ISSN:1071-1023    

DOI:10.1116/1.584158

出版商:American Vacuum Society    

年代:1988

数据来源: AIP

摘要:

The performance of submicron devices and circuits for the coming decade is advancing at a rapid pace. The emerging requirements to probe the internal nodes of these ultrafast, small and dense circuits give rise to great challenges for high‐speed electron beam testing. In this paper, we review the steps of advancing the electron beam testing to achieve simultaneously: 5‐ps temporal resolution, 0.1‐μm spot size, and 3 mV/Hz1/2voltage sensitivity. The newly developed instrument, called the picosecond photoelectron scanning electron microscope, is capable of measuring the state‐of‐the art bipolar and field‐effect transistor circuits.

ISSN:1071-1023    

DOI:10.1116/1.584159

出版商:American Vacuum Society    

年代:1988

数据来源: AIP

摘要:

We have fabricated and tested lateral‐surface‐superlattice (LSSL) and quasi‐one‐dimensional (Q1D) devices on a modulation‐doped GaAs/GaAlAs heterostructure. The LSSL consists of a 0.2‐μm‐period (0.1‐μm nominal linewidth) Ti/Au grating or grid on top of the GaAlAs layer, forming a Schottky barrier which presents a tunable periodic potential modulation to the electrons traveling from source to drain. The grating gate was fabricated using x‐ray lithography to define the grating lines in poly(methylmethacrylate), and deep‐UV lithography to expose gate contact pads, followed by lift‐off of Ti/Au. Plots of the source–drain current as a function of the grating‐gate bias showed distinct plateaulike features at 4.2 K, providing evidence of a superlattice effect, that is, electron backdiffraction. Minor modifications of the fabrication process permitted Q1D and grid‐gate devices to be made. These also showed the expected structure in the conductance.

ISSN:1071-1023    

DOI:10.1116/1.584161

出版商:American Vacuum Society    

年代:1988

数据来源: AIP

摘要:

The hybrid lithography of a 280‐keV Si++focused ion beam (FIB) and a 20‐keV shaped electron beam (EB) has been applied to fabricate a mushroom‐shaped gate for a high electron mobility transistor. In this process, a resist in the gate region is reduced to ∼0.2 μm by an FIB lithography (corresponding to ‘‘top‐gate’’ formation), and then the center of the top gate is exposed by the EB (corresponding to ‘‘bottom‐gate’’ formation). For a thin resist, patterns with smaller dimensions are more easily delineated by an EB exposure than for a thick resist. A 0.2‐μm pattern can be obtained by using a shaped EB system with a high throughput. The radiation damage is neglected due to the use of EB for the bottom‐gate formation.

ISSN:1071-1023    

DOI:10.1116/1.584162

出版商:American Vacuum Society    

年代:1988

数据来源: AIP

摘要:

Implantation with finely focused beams of dopant ions scanned under computer control enables laterally graded doping profiles to be formed. A 150‐nm‐diam beam of silicon ions from a gold–silicon–beryllium liquid metal ion source has been used to fabricate GaAs metal–semiconductor field effect transistors (MESFET’s) incorporating a number of different laterally graded doping profiles. It is seen experimentally that, when compared with uniformly implanted devices, these MESFET’s display increased available output power and transductance.

ISSN:1071-1023    

DOI:10.1116/1.584175

出版商:American Vacuum Society    

年代:1988

数据来源: AIP

摘要:

Specific issues related to achieving high device performance in extremely small channel length field effect transistor circuits are discussed. Ultrahigh resolution electron beam lithography is needed to obtain the ultrashort channels which are key for fast devices, and for the important gate area, double‐layer poly(methylmethacrylate) for lift‐off of a metal reactive ion etching mask has proven to be a suitable technique. Good level to level overlay and dimensional control in the contact process allow miniaturization of all device elements, in particular, reduction of the distance between source/drain contacts and optimization of the contact size and geometry. These are key factors in minimizing parasitic effects. The design considerations are discussed and the fabrication techniques are described which resulted in devices with a maximum measured transconductance of 910 mS/mm at 77 K for a 70‐nm gate device, exhibiting the clearest evidence so far for electron velocity overshoot, and unloaded ring oscillators with 13‐ps switching time per stage.

ISSN:1071-1023    

DOI:10.1116/1.584181

出版商:American Vacuum Society    

年代:1988

数据来源: AIP