Dale M. Brown

Silicon carbide UV photodiodes

SiC photodiodes were fabricated using 6 H single-crystal wafers. These devices have excellent UV responsivity characteristics and very low dark current even at elevated temperatures. The reproducibility is excellent and the characteristics agree with theoretical calculations for different device designs. The advantages of these diodes are that they will operate at high temperatures and are responsive between 200 and 400 nm and not responsive to longer wavelengths because of the wide 3-eV bandgap. The responsivity at 270 nm is between 70% and 85%. Dark-current levels have been measured as a function of temperature that are orders of magnitude below those previously reported. Thus, these diodes can be expected to have excellent performance characteristics for detection of low light level UV even at elevated temperatures. >

SiC MOS interface characteristics

It is well known that SiC can be thermally oxidized to form SiO/sub 2/ layers. And Si MOSFET ICs using thermally grown SiO/sub 2/ gate dielectrics are the predominant IC technology in the world today. However the SiC/SiO/sub 2/ interface has not been well characterized as was the case for Si MOS in the early 1960s. This paper presents data which for the first time characterizes the SiC/SiO/sub 2/ interface and explains one of the previously unexplained abnormalities observed in the characteristics of SiC MOSFETs. >

Nitrogen-implanted SiC diodes using high-temperature implantation

6H-SiC diodes fabricated using high-temperature nitrogen implantation up to 1000 degrees C are reported. Diodes were formed by RIE etching a 0.8- mu m-deep mesa across the N/sup +//P junction using NF/sub 3//O/sub 2/ with an aluminum transfer mask. The junction was passivated with a deposited SiO/sub 2/ layer 0.6 mu m thick. Contacts were made to N/sup +/ and P regions with thin nickel and aluminum layers, respectively, followed by a short anneal between 900 and 1000 degrees C. These diodes have reverse-bias leakage at 25 degrees C as low as 5*10/sup -11/ A/cm/sup 2/ at 10 V.<<ETX>>

Silicon carbide MOSFET technology

Abstract The research and development activities carried out to demonstrate the status of MOS planar technology for the manufacture of high temperature SiC ICs will be described. These activities resulted in the design, fabrication and demonstration of the worlds first SiC analog IC—a monolithic MOSFET operational amplifier. Research tasks required for the development of a planar SiC MOSFET IC technology included: characterization of the SiCSiO2 interface using thermally grown oxides; high temperature (350°C) reliability studies of thermally grown oxides; ion implantation studies of donor (N) and acceptor (B) dopants to form junction diodes; epitaxial layer characterization; device isolation methods; and finally integrated circuit design, fabrication and testing of the worlds first monolithic SiC operational amplifier IC. High temperature circuit drift instabilities at 350°C were characterized. These studies defined an SiC depletion model MOSFET IC technology and outlined tasks required to improve all types of SiC devices.

Platinum silicide ohmic contacts to shallow junctions in silicon

Ohmic contact to shallow pn+ and np+ junctions in silicon were studied. Thin layers (∼200 A) of platinum were sputter deposited and reacted with the silicon substrate at 590 °C to result in the stable PtSi silicide. In a self‐registered process, aqua regia was used to etch the unreacted platinum. An Al‐0.9% Si alloy has been used for final metallization. A small contact area of 3×3 μm2 was chosen so as to be in accordance with the current level of integration. A four‐terminal Kelvin‐resistor structure has been utilized to accurately measure the contact resistance. The effect due to the dopant concentration was studied at the implant dose range of 1–8×1015 cm−2. Van der Pauw sheet resistance measurements, secondary ion mass spectroscopy, and Rutherford backscattering experiments were all performed in order to characterize the shallow junctions and the silicide‐silicon interface. Predeposition and in‐situ etching resulted in considerable improvement in the measured specific contact resistance. Values well w...

Boron‐implanted 6H‐SiC diodes

Ion implanted planar p‐n junctions are important for silicon carbide discrete devices and integrated circuits. Conversion to p‐type of n‐type 6H‐SiC was observed for the first time using boron implantation. Diodes were fabricated with boron implants at 25 and 1000 °C, followed by 1300 °C post‐implant annealing in a furnace. The best diodes measured at 21 °C exhibited an ideality factor of 1.77, reverse bias leakage of 10−10 A/cm2 at −10 V, and a record high (for a SiC‐implanted diode) breakdown voltage of −650 V.

Refractory metal silicon device technology

Abstract Films 2000–5000 A thick of Mo or W deposited over thin films of thermally grown SiO 2 are shown to be effective high temperature diffusion masks against both phosphorous and boron. These metal films may be precisely patterned and their diffusion masking properties can be used to define the source and drain regions of MOSFETs. In this manner, self-registered MOSFETs can be fabricated with a portion of the diffusion masking metal film acting as the gate electrode. Using P or B doped deposited glasses as diffusion sources, n or p channel enhancement mode MOSFETs were made by diffusion through the exposed thin SiO 2 film into p and n type Si to form source and drain junctions. Contact was subsequently made by etching holes through the oxide layers to the source and drain regions and to the refractory metal gate electrode buried within the oxide layers. These devices exhibit channel mobilities between 200 and 300 cm 2 /V-sec at gate voltages about 10 V above threshold. The stability of MOS structures processed in a similar manner has been measured. After being stressed at ±6 × 10 5 V / cm and 250°C for 15 hr, these devices exhibited shifts in their CV characteristics less than 200 mV.

FREEZE‐OUT CHARACTERISTICS OF THE MOS VARACTOR

Experimental MOS C(V) data are obtained in the temperature range over which majority carriers are substantially frozen out (40° − 70°K). These are compared with calculated curves and other calculated curves are presented to show the effect of impurity concentration and compensation. The C(V) curves are characterized by a secondary minimum in capacitance near the flat band bias.

The P-channel refractory metal self-registered MOSFET

In this paper p-channel self-registered Mo gate MOSFET fabrication techniques are described and tested. Excellent p-channel devices resulted. Device characteristics including junction characteristics, threshold, stability, effective channel mobilities, and Si-SiO 2 interface studies are examined and compared with theoretical predictions. Simple processing steps yielded FETs whose threshold is predictably controlled by the intrinsic properties of Mo and the Si-SiO 2 system. Effective mobility theory matches the data at low fields, but at high fields theory predicts values that are too low. Similarly constructed integrated circuits are T2L compatible with excellent threshold reproducibility and exhibit stability during accelerated temperature-bias life testing.

Growth of Bismuth‐Antimony Single‐Crystal Alloys

Homogeneous crystals of Bi‐Sb solid solutions are difficult to grow, but are important for the basic understanding of the electron transport properties and band structure of these materials. The problems arise from (1) the low melting temperature (approximately 300°C) which makes it difficult to achieve a large thermal gradient at the crystal growing interface; (2) the small liquid diffusion coefficient which was estimated to be between 2 and 3×10−5 cm2/sec at 300°C; and (3) a segregation coefficient so large (5–10) as to favor growth of undesirable cellular substructure. Under existing theories of crystal growth, the conditions necessary for producing crystals with Sb compositions from 5% to 14% free of macro‐ and micro‐inhomogeneity are described. A zone‐melting technique was used to grow the crystals with temperature gradients in the molten zone about 60°C/cm and growth rates between 1.6 and 0.4 mm/h. The degree of homogeneity was determined by etching studies, chemical analysis, and electron beam micr...