Showing papers by "Robert M. Wallace published in 1997"

SiO2 film thickness metrology by x-ray photoelectron spectroscopy

Abstract: Silicon dioxide films grown by industrial thermal furnace, rapid thermal, and low-pressure thermal methods were measured by x-ray photoelectron spectroscopy, transmission electron microscopy (TEM), spectroscopic ellipsometry, and capacitance–voltage analysis. Based on TEM measurements, the photoelectron effective attenuation lengths in the SiO2 and Si are found to be 2.96±0.19 and 2.11±0.13 nm, respectively. The oxide physical thicknesses (range from 1.5 to 12.5 nm) as measured by all above techniques are in good agreement. The electrical thickness is noted to be slightly thicker than the physical thickness.

Fluorinated coating for an optical element

Abstract: A protective cover (10) for an optical device, such as a spatial light modulator or an infrared detector or receiver. The cover (10) has an optically transmissive window (11), which has a coating (12) on one or both of its surfaces. The coating (12) is made from a halogenated material, which is deposited to form a chemical bond with the surface of the window (11).

Controlled growth of SiO2 tunnel barrier and crystalline Si quantum wells for Si resonant tunneling diodes

Abstract: Two methods for producing Si-oxide barriers upon which crystalline Si layers can be grown are presented. One method entails oxide island nucleation on a clean vicinal Si(001) surface. The second method makes use of void formation in ultrathin oxides on the Si(100) surface at elevated temperatures. Either method results in an oxide barrier which is porous and the exposed Si within these pores can serve as a way to seed c-Si overgrowth. We demonstrate that it is feasible to grow crystalline Si overlayers on top of such porous oxide barriers, while on the continuous Si-oxide surface, only amorphous or nanocrystalline Si layer overgrowth can be achieved. The controlled oxide growth and Si overgrowth on the oxide can find possible applications in Si-based resonant tunneling devices, optoelectronics, and other Si-based nanoelectronics.

In situ Si flux cleaning technique for producing atomically flat Si(100) surfaces at low temperature

Abstract: We have developed a method for removing oxides and producing atomically flat Si(100) surfaces with single atomic height steps using a Si flux cleaning technique. By introducing a Si flux in the range 1.0–1.5 A/s at the onset of an SiO2 thermal desorption step as low as 780 °C, scanning tunneling microscopy (STM) and atomic force microscopy images reveal smooth surfaces with atomically flat terraces with an rms roughness of 0.5 A and single-step heights of 1.4 A. STM reveals that A- and B-type steps are present across the entire area of the scanned surface. Desorption of the surface oxide layer with Si fluxes below this range results in rougher surfaces with pits ∼50 A deep and 1000 A across. For Si fluxes above this range, no pits are seen but atomic steps are not visible on the surface.

Method for thin film deposition on single-crystal semiconductor substrates

Abstract: A method of preparing a surface for and forming a thin film on a single-crystal silicon substrate is disclosed. One embodiment of his method comprises forming an oxidized silicon layer (which may be a native oxide) on at least one region of the substrate, and thermally annealing the substrate in a vacuum while supplying a silicon-containing flux to the oxide surface, thus removing the oxidized silicon layer. Preferably, the thin film is formed immediately after removal of the oxidized silicon layer. The silicon-containing flux is preferably insufficient to deposit a silicon-containing layer on top of the oxidized silicon layer, and yet sufficient to substantially inhibit an SiO-forming reaction between the silicon substrate and the oxidized silicon layer. The method of the invention allows for growth or deposition of films which have exceptionally smooth interfaces (less than 0.1 nm rms roughness) with the underlying silicon substrate at temperatures less than 800° C., and is ideally suited for deposition of ultrathin films having thicknesses less than about 5 nm.

Protonic nonvolatile field effect transistor memories in Si/SiO/sub 2//Si structures

Abstract: A low-voltage, radiation-tolerant, nonvolatile field effect transistor (NVFET) memory involving proton motion in SiO/sub 2/ is illustrated in both bulk Si and silicon-on-insulator devices. We discuss a mechanism by which the protons are created in the oxide layer by a forming gas anneal. At low temperature (T<250/spl deg/C), the H/sup +/ is largely "imprisoned" in the buried SiO/sub 2/ layer; i.e., the ions are sandwiched between the two encapsulating Si layers. The Si layers can be either c-Si or poly-Si, thus the technology is compatible with standard Si processing. The protons can be reliably and controllably drifted from one interface to another without any noticeable degradation in the signal past 10/sup 6/ cycles. Under an unbiased condition, the net proton density is not significantly affected by radiation up to at least 100 krad (SiO/sub 2/). Last, we compare many of the properties of the NVFET to commercial flash nonvolatile memories.

Improvements in or relating to semiconductors

Abstract: A method of preparing a surface for and forming a thin film on a silicon substrate is disclosed. One embodiment of his method comprises forming an oxidized silicon layer (which may be a native oxide) on at least one region of the substrate, and thermally annealing the substrate in a vacuum while supplying a silicon-containing flux to the oxide surface, thus removing the oxidized silicon layer. Preferably, the thin film is formed immediately after removal of the oxidized silicon layer. The silicon-containing flux is preferably insufficient to deposit a silicon-containing layer on top of the oxidized silicon layer, and yet sufficient to substantially inhibit an SiO-forming reaction between the silicon substrate and the oxidized silicon layer. The method of the invention allows for growth or deposition of films which have exceptionally smooth interfaces (less than 0.1 nm rms roughness) with the underlying silicon substrate at temperatures less than 800°C, and is ideally suited for deposition of ultrathin films having thicknesses less than about 5 nm.

Low temperature process for post-etch defluoridation of metals

Abstract: An integrated circuit fabrication process in which residual fluorine contamination on metal surfaces after ashing is removed by exposure to an NH3 /O2 plasma.

Improvements in or relating to integrated circuits

Abstract: An integrated circuit fabrication process in which residual flourine contamination on metal surfaces after ashing is removed by exposure to an NH3/O2 plasma.

Method to produce ultrathin porous silicon-oxide layer

Abstract: A method for producing a porous film on a silicon substrate is described. The substrate 14 is placed in a vacuum chamber in the presence of oxygen at specified pressure and temperature for a period of time to form a thin oxide film 10 thereon. Then the conditions in the chamber are altered so that voids 14 of a desired dimension are formed in the oxide film 10. Alternatively, a substrate 20 is subjected to specific conditions in the vacuum chamber whereat oxide islands 22 nucleate on the surface. As the islands grow, they eventually cover most of the surface leaving voids 24 of the desired size.