Shigetoshi Takayanagi

The effects of the recoil‐implanted oxygen in Si on the electrical activation of As after through‐oxide implantation

The effects of the recoil‐implanted oxygen resulting from high‐dose As implantations into (111) Si through a thin SiO2 film on the electrical activation have been studied in the dose range 1015–1016 ions/cm2. The concentration profiles of total electrically active As and recoil‐implanted oxygen have been measured and compared with each other. It was found that the electrically active As profiles derived from the measured resistivity by assuming published data of mobility which are characteristic of defect‐free silicon show an apparent fall‐off in the surface region for the implantation with doses above 5×1015 ions/cm2. It is shown that the apparent fall‐off in the profiles is caused by both the reduction of the mobility and net carrier concentration in the case of 800 °C anneal, while the former is the main cause in case of 1000 °C anneal. By comparing the mobility profiles with the measured concentration profiles of the recoil‐implanted oxygen, the marked reduction of the mobility is shown to occur in the region where the oxygen concentration exceeds ∼1020/cm3. From the analysis of the depth distribution of the defects remaining in Si after annealing, it was demonstrated that the region is confined to the thin layer where the anomalous high‐density defects are present. For the As implantation with a dose less than 1015 ions/cm2, however, the recoil‐implanted oxygen is likely to have little influence on the electrical activation of the implanted As in the temperature range studied.

Electrical properties of Si heavily implanted with boron molecular ions

High dose implantations of boron molecular ions such as BF+2 and BCl+2 ions in Si have been investigated in an attempt to form shallow P+ layers in the dose range 1×1015–1×1016 ions/cm2, in comparison with those of boron. For BF+2 implants it was found that both the effective surface carrier density Ns and junction depth Xj in Si after 1000°C anneal tend to completely saturate at doses above 5×1015 ions/cm2, while they tend to increase for B+ implants. From profile measurements of total and electrically active boron it was clarified that the additional implantation of BF+2 ions in excess of 5×1015 ions/cm2 results in the accumulation of inactive boron atoms particularly around the surface region. Junction depths in Si resulting from BF+2 implants are generally shallower than those resulting from B+ implants. For BCl+2 implants the values of Ns are generally much lower than those for BF+2 and B+ implants.

The concentration profiles of projectiles and recoiled nitrogen in Si after ion implantation through Si3N4 films

The concentration profiles of ion‐implanted boron, phosphorus, and arsenic, and recoil‐implanted nitrogen atoms after ion implantation through Si3N4 films on Si have been measured using secondary ion mass spectrometry. The concentration profiles of the implanted ions in Si after ion implantation through Si3N4 films were found to agree with those implanted into bare Si within experimental errors, with the exception of a shifting of the concentration peak position. The concentration profiles of recoil‐implanted nitrogen in Si are generally composed of high‐concentration regions with steeply decaying distributions near the silicon surface and the exponential tails whose slopes are independent of ion mass, energy, dose, and film thickness. The concentration level of recoil‐implanted nitrogen and maximum penetration range relative to the implanted ion range depend strongly on ion mass, film thickness, and ion energy. It was demonstrated that the concentration profiles for recoiled nitrogen in Si calculated usi...

The Concentration Profiles of Phosphorus, Arsenic and Recoiled Oxygen Atoms in Si by Ion Implantation into SiO2–Si

The concentration profiles of phosphorus, arsenic and recoiled oxygen in Si after high dose implantations through SiO2 films have been measured using Secondary Ion Mass Spectrometry (SIMS). The characteristics such as the standard deviation or the slopes of the exponential tails of the concentration profiles of the projectiles were found to agree with those directly implanted into bare Si within experimental errors, with the exception of a shifting of the concentration peak position. The concentration level and the maximum penetration depth in Si for recoiled oxygen relative to the projectiles are discussed in correlation with ion mass, ion energy and SiO2 film thickness.

Depth distribution of knock‐on nitrogen in Si by phosphorus implantation through Si3N4 films

The concentration profiles of phosphorus and knock‐on nitrogen in silicon after phosphorous implantations into Si3N4‐Si systems have been investigated by using secondary ion mass spectrometry (SIMS). The tails were found on the phosphorus distribution in silicon after the implantation through Si3N4 films. The concentration profiles of knock‐on nitrogen in silicon have been determined by measuring both the in‐depth profiles of knock‐on nitrogen and those of nitrogen after additional nitrogen implantation into a bare silicon embedded with knock‐on nitrogen. The concentration profiles of knock‐on nitrogen show a very high concentration near the surface and extending tails. It was found that the tails were observed at the deeper portion in silicon as energy increased, for a given Si3N4 layer.

Electrical properties of Si implanted with As through SiO2 films

The effects of the recoil implantation of oxygen on the electrical properties of Si heavily implanted with As through SiO2 films have been investigated as a function of annealing temperature, in correlation with the crystal orientation. The concentration profiles of the electrically active As in Si have been compared with those of total As and recoil implanted oxygen measured by secondary‐ion mass spectrometry. It is shown that at temperatures between 650 and 850 °C, both the restriction in the electrical activation and the reduction of mobility are observed in the region where the oxygen concentration exceeds ∼1020 O/cm3 in (111) ‐oriented Si, while the recoil implantation of oxygen has much less influence on the electrical properties of Si in (100) ‐oriented Si. At 1000 °C the only effect of the recoil implantation is the reduction of mobility in the surface region in (111) ‐oriented Si. The analysis of the defect structures by transmission electron microscopy indicates that the defects in (111) ‐orient...

A 2Kx8-bit static MOS RAM with a new memory cell structure

A 2K/spl times/8-bit static MOS RAM with a new memory cell structure has been developed. The memory cell consists of six devices including four MOSFETs and two memory load resistors. Two load resistors are fabricated in the second-level polysilicon films over the polysilicon gate MOSFET used as the driver. Thus the memory cell area is determined only by the area of four MOSFETs. By applying the new cell structure and photolithography technology of 3 /spl mu/m dimensions, the cell area of 23/spl times/27 /spl mu/m and the chip area of 3.75/spl times/4.19 mm have been realized. The RAM is nonclocked and single 5 V operation. Access time of about 150 ns is obtained at a supply current of 120 mA.

Asymmetrical Profiles of Ion Implanted Phosphorus in Silicon

The concentration profiles of phosphorus implanted into amorphous Si at energies ranging from 150 to 300 keV have been studied by using Secondary Ion Mass Spectrometry (SIMS). It is found that the phosphorus profiles in amorphous Si deviate from Gaussian distributions in the surface region. The concentration profiles are shown to be well fitted by the joined half-Gaussian distributions using the values of the projected ranges, the standard deviations and the third central moments obtained from the measured profiles. The experimental projected ranges are about 10 to 15% smaller than those theoretically calculated. From the data of the projected ranges measured, the electronic stopping power coefficient is evaluated to be 1.4KL.

A 2K×8-bit static RAM

High density 2K×8-bit fully static RAM has been developed. Memory cell size of 23×27µm results in the chip size of 3.75×4.19mm, which is nearly equal to that of existing 4K-bit static RAMs. High packing density is realized by layout of 3µm photolithography and double-level polysilicon process permitting fabrication of memory load resistors upon driver MOSFETs.

Annealing Behaviors of Phosphorus Implanted in Silicon

Annealing behavior of phosphorus implanted in silicon has been studied using secondary ion mass spectrometry.