V. I. Rudakov

Forming through channels in silicon substrates

A new method of silicon processing, based on the selective electrochemical etching of p+-type regions formed in an n-type matrix by thermal migration of aluminum, is proposed. A special advantage offered by this technique is the possibility of obtaining through channels with a cross section of arbitrary shape and a characteristic transverse size ranging from 20 to 200 μm.

Features of CoSi2 phase formation by two-stage rapid thermal annealing of Ti/Co/Ti/Si(100) structures

A method of cobalt disilicide (CoSi2) layer formation proceeding from a Ti(8 nm)/Co(10 nm)/Ti(5 nm)/Si(100) (substrate) structure prepared by magnetron sputtering is described. The initial structure was subjected to two-stage rapid thermal annealing (RTA) in nitrogen, and the samples after each stage were studied by the time-of-flight secondary-ion mass spectrometry, Auger electron spectroscopy, scanning electron microscopy, and energy-dispersive X-ray spectroscopy. The RTA-1 stage (550°C, 45 s) resulted in the formation of a sacrificial surface layer of TiNxOy, which gettered residual impurities (O, C, N) from inner interfaces of the initial structure. After the chemical removal of this TiNxOy layer, the enrichment with cobalt at the RTA-2 stage (830°C, 25 s) led to the formation of a low-resistance CoSi2 phase.

Evolution of Dopant Concentration from a Gaussian Profile in a Nonuniform Temperature Field

An exact analytical solution to the dopant diffusion equation for a temperature field with nonzero uniform gradient is obtained in the case of a Gaussian initial doping profile.

Control of the formation of ultrathin CoSi2 layers during the rapid thermal annealing of Ti/Co/Ti/Si(100) structures

The initial Ti(8 nm)/Co(10 nm)/Ti(5 nm) structures formed on the Si(100) substrate by magnetron sputtering were subjected to two-stage rapid thermal annealing (RTA) in the nitrogen ambient. The samples of the structures were controlled using the time-of-flight SIMS, the Auger spectroscopy, scanning electron microscopy, X-ray dispersion microprobe analysis, and measurements of the layer resistance at each stage of annealing. At the RTA-1 stage (550°C, 45 s), a sacrificial layer formed on the surface. This layer consisted of the titanium (oxy)nitride coating, into which the residual impurities (O, C, and N) were forced out, and the transient Co-Si-Ti(TiO,TiN) layer with a high cobalt content and a low (trace) titanium content. After the selective removal of this sacrificial layer, the surface composition corresponded to monosilicide CoSi, which transformed into the highly conductive CoSi2 phase at the RTA-2 stage (830°C, 25 s).

Formation of the TiN/CoSi2 system by rapid thermal annealing of a Co/Ti/Si structure

An Auger-spectroscopy investigation is conducted into the formation of the TiN/CoSi2 system by rapid thermal annealing of a Co/Ti/Si structure in a nitrogen atmosphere. Two different directions of temperature gradient under annealing are considered. It is established that TiN/CoSi2 formation occurs only when the temperature on the coated side of the specimen grows with depth. The influence of different factors is discussed.

Effect of the doping level on temperature bistability in a silicon wafer

The influence of the doping level on the effect of the temperature bistability in a silicon wafer upon radiative heat transfer between the wafer and the elements of the heating system is studied. Theoretical transfer characteristics are constructed for a silicon wafer doped with donor and acceptor impurities. These characteristics are compared with the transfer characteristics obtained during heating and cooling of wafers with the hole conduction (with dopant concentrations of 1015, 2 × 1016, and 3 × 1017 cm−3) and electron conduction (with impurity concentrations of 1015 and 8 × 1018 cm−3) in a thermal reactor of the rapid thermal annealing setup. It is found that the width and height of the hysteresis loop decrease with increasing dopant concentration and are almost independent of the type of conduction of the silicon wafer. The critical value of the impurity concentration of both types is 1.4 × 1017 cm−3. For this concentration, the loop width vanishes, and the height corresponds to the minimal value of the temperature jump (∼200 K). The mechanism of temperature bistability in the silicon wafer upon radiative heat transfer is discussed.

Annealing effect on the formation of high-k dielectric in the W/ultrathin HfO2/Si-substrate system

Using a method of high-frequency magnetron sputtering, the structures W(150 nm)/HfO2(5 nm)/Si(100) were prepared and were further annealed either at 500°C in vacuum for 30 min or in an atmosphere of argon at 950°C for 12 s. Study of the capacitance-voltage characteristics of these structures showed that high-temperature annealing leads to a decrease in the maximum specific capacitance in accumulation (from 4.8 × 10−6 to 3.2 × 10−6 F/cm2) and dielectric constant (from 27 to 23). Using time-of-flight secondary-ion mass spectrometry, it is established that growth of a WOx phase at the W/HfO2 interface and a HfSixOy silicate phase at the HfO2/Si (100) interface occurs during annealing. In addition, the total thickness of the intermediate oxide layer exceeds the thickness of the initial HfO2 film by 30%.

Formation and investigation of cobalt silicide ultrathin layers in Ti/Co/Ti-, TiN/Ti/Co-, and TiN/Co-on-silicon structures

The formation of ultrathin CoSi2 layers in Ti(8 nm)/Co(10 nm)/Ti(5 nm), TiN(18 nm)/Ti(2 nm)/Co(8 nm), and TiN(18 nm)/Co(8 nm) systems magnetron-sputtered on the Si(100) surface is studied. The systems are subjected to two-step rapid thermal annealing. In between the annealing steps, the “sacrificial” layer is chemically removed and the second and third systems are additionally covered by a 17-nm-thick amorphous silicon (α-Si) layer. In the course of the fabrication process, the structures are examined using time-of-flight secondary-ion (cation) mass spectrometry, Auger electron spectroscopy, and scanning electron microscopy combined with X-ray energy dispersion microanalysis. It is shown that the above complex of analytical investigation provides efficient physical control of ultrathin silicide layer formation.

Influence of optical properties of the SOI structure on the wafer temperature during rapid thermal annealing

Optical characteristics are compared theoretically, and temperature differences of the Si wafer with the B-doped SOI structure and substrate wafer are evaluated during rapid thermal annealing. It is shown that under identical annealing conditions and temperatures above 800 K, the difference in their temperatures can reach ∼30 K. We studied the dependence of the total emissivity and temperature of the wafer with the SOI structure on the concentration of the doping impurity in the Si layer. The method of the quantitative analysis of variations of the wafer temperature under invariable annealing conditions depending on the variations of emissivity of its surfaces is suggested.

Formation of thin-film HfO2/Si(100) structures by high-frequency magnetron sputtering

The results of X-ray structural investigations and current-voltage measurements of the HfO2/Si(100) structures are presented. The HfO2 films of 50 nm thickness were deposited in a Si substrate by high-frequency magnetron sputtering in argon plasma and subjected to rapid thermal annealing at 500, 700, and/or 800°C in the Ar or O2 ambient. It is shown that the HfO2 films become polycrystalline after annealing. The presence of various crystalline phases in them and the form of the I–V characteristics of the Al/HfO2/Si(100) test structures strongly depend on the growth conditions and the gas ambient during the rapid thermal annealing. It is established that the HfO2 films deposited at a high-frequency bias at a substrate of −7 V during the growth and then passed through rapid thermal treatment in the O2 ambient at 700°C have the highest breakdown voltages.