Yu. I. Denisenko

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.

The structure of thermomigration channels in silicon

We have studied deep and through channels formed in n-Si wafers by means of thermal migration of thin discrete aluminum zones. The region of thermal migration channels was investigated using selective chemical etching of silicon in combination with secondary ion mass spectrometry for the analysis of impurity distributions. It is established that the channels are surrounded by two distinct peripheral shells.

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).

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.

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.

Formation of W/HfO2/Si gate structures using in situ magnetron sputtering and rapid thermal annealing

The W(150 nm)/HfO2(5 nm)/Si(100) structures prepared in a single vacuum cycle by rf magnetron sputtering were subjected to rapid thermal annealing in argon. It is found that at an annealing temperature of 950°C, the tungsten oxide WOx phase and the hafnium silicate HfSixOy phase grow at the W/HfO2 and HfO2/Si(100) interfaces, respectively. Herewith, the total thickness of the oxide layeris 30% larger than that of the initial HfO2 film. In addition, a decrease in the specific capacitance in accumulation Cmax and in the dielectric constant k (from 27 to 23) is observed. At an annealing temperature of 980°C, intensive interaction between tungsten and HfO2 takes place, causing the formation of a compositionally inhomogeneous HfxSiyWzO oxide layer and further decrease in Cmax. It is shown that a considerable reduction in the leakage currents occurs in the W/HfO2/X/Si(100) structures, where X is a nitride barrier layer.

Investigation into the diffusion of boron, phosphorus, and arsenic in silicon during annealing in a nonisothermal reactor

The influence of the temperature gradient on the diffusion of boron, phosphorus, and arsenic during annealing of silicon in a nonisothermal lamp reactor in the second and minute ranges is investigated experimentally and theoretically. Parameters of the thermodiffusion process are determined: for the boron diffusion in the second range, the effective diffusivity Deff ∼ 10−12 cm2/s and the effective measured heat of transport Qmeff* ∼ 103–104 eV. The results are interpreted based on the equations of nonequilibrium thermodynamics.

Formation and properties of ultrathin layers for fabrication of SOI MOS nanotransistor elements

The methods of manufacturing and properties of elements of the SOI MOS nanotransistor such as the gate/gate dielectric, source/drain regions and ohmic contacts have been considered. The HfO2(50 nm)/Si (100) and W/HfO2(4 nm)/Si (100) gate structures have been fabricated using the radio-frequency magnetron sputtering method. It is shown that the crystalline structure of the HfO2 films and their electrical characteristics (breakdown voltage) are interrelated. To produce ultrashallow source/drain regions, a high-dose plasma-immersion boron ion implantation is used. In the process of the rapid thermal annealing of the implanted layers, a substantial reduction in the boron amount near the surface of the SOI structure is detected. The CoSi2 ohmic contacts were made using the Ti(8 nm)/Co(10 nm)/Ti(5 nm) structures formed on a Si substrate of (100) orientation. It is established that the CoSi2 film formed as a result of two-stage annealing possesses a surface resistance of ∼20 Ohm/□.