Tetsuo Yamaji

Reduction of transient boron diffusion in preamorphized Si by carbon implantation

Boron diffusion in preamorphized Si is studied as a function of dose of carbon ion implantation. The boron was implanted at 20 keV with a dose of 1×1015 cm−2, and carbon was implanted at 60–90 keV. The preamorphized depth was 230 nm. It is shown that transient enhanced diffusion occurs even in the preamorphized region without C+ implantation. The diffusion constant is larger than the standard one by about one order of magnitude in the case of 1000 °C annealing for 15 s. This enhancement is eliminated by C+ implantation at a dose of about 1015 cm−2. This implantation also reduces the defects at the amorphous/crystal interface. These findings indicate that the implanted carbon acts as a sink of excess interstitials.

Elimination of secondary defects in preamorphized Si by C+ implantation

In preamorphization of Si, secondary defects formed at the original amorphous/crystal (a/c) interface were studied as a function of the dose of carbon ion implantation. The preamorphized depth was 230 nm. The carbon was implanted at 78 or 90 keV at 2×1012–2×1015/cm2. The size and density of dislocation loops near the a/c interface decreased with increasing C+ dose. The C+ implantation at a dose of 1×1015/cm2 reduced the density of atoms bound by dislocation loops from 5.9×1014/cm2 to 2.6×1013/cm2. At C+ doses higher than about 1×1015/cm2, additional defects with a diameter of less than about 5 nm were observed. These defects are SiC agglomerates that act as a sink for excess self‐interstitials, which results in a reduction in the density of secondary defects.

A New Mechanism of Failure in Silicon p + /n Junction Induced by Diffusion Barrier Metals

The mechanism of failure of p+/n and n+/p junctions under Al-Si/TiN/Ti and Al-Si/ZrN/Zr systems at contact holes has been investigated. When the total force of the barrier metal in the metallization system, which is defined as the product of the film stress and the film thickness, is larger than 3×105 dyn/cm, the junction leakage current increases on p+/n diodes, but not on n+/p diodes after annealing at 500°C. This increase is caused by the formation of dislocation loops in p+-Si. The formation depends on the annealing temperature, the total force of barrier metal and the B concentration.

Thermal Stability of Interconnect of TiN/Cu/TiN Multilayered Structure

The etching process for a Cu interconnect with self-aligned deposition of a thick sidewall film has been developed. This sidewall film acts as a barrier layer to prevent Cu from corrosion and oxidation during the subsequent process, such as formation of a passivation film. Using this etching process, the Cu interconnect of a TiN/Cu/TiN multilayered structure in a submicron feature is formed. Resistivity for the Cu interconnects is about 2 µ Ω cm, and it does not change on annealing up to 700° C. Diffusion of impurities into Cu is not observed up to 800° C annealing. Therefore, the structure of the Cu interconnect, that is, Cu covered with TiN and the thick sidewall film, is suitable for the ULSI process.

Diffusion of ion‐implanted phosphorus within thermally grown SiO2 in O2 ambient

Phosphorus, implanted into thermally grown SiO2, was diffused in O2 ambient, and the phosphorus distribution was analyzed by secondary ion‐mass spectrometry. A profile of the highly doped phosphorus revealed enhanced diffusion in its high‐concentration region (above about 1×1019 cm−3). An empirical diffusion model, in which phosphorus diffusivity depends on local phosphorus concentration, is proposed. Numerical simulations using this model give well‐matched profiles to the SIMS data, and parameters for the model are determined. The concentration‐dependent diffusivity is ascribed to the formation of P=O bond in SiO2 layer, and to the resulting loosening of SiO2 network or increase of liquid phase with increasing phosphorus concentration. It was also found that the diffusivity becomes less dependent on phosphorus concentration with increasing annealing temperature.

Suppression of migration in Al conductors by lowering deposition temperature in plasma CVD SiN passivation

Storage tests at elevated temperatures and electromigration tests were performed on aluminum (Al) conductors covered with silicon nitride passivation deposited at low temperature by plasma enhanced chemical vapor deposition (CVD). It was shown that the migration such as stress induced voiding and electromigration can be reduced by lowering the deposition temperature of the passivation layer. The discontinuity failure by voiding is reduced and leads to increased lifetimes. The generation of notchlike voiding is also reduced. Improvements were attributed to the reduction of thermally induced stress in Al conductors at test temperatures. The plasma silicon nitride passivation deposited at low temperature was preferable as a candidate for passivation layers in devices with submicron Al conductors.<<ETX>>

Time‐dependent diffusion of ion‐implanted arsenic in thermally grown SiO2

Arsenic implanted into thermally grown SiO2 was diffused in ambients of O2 and N2, and arsenic distributions in the SiO2 were analyzed with secondary ion mass spectrometry (SIMS). Arsenic was implanted at energies between 40 and 70 keV with a dose of 1×1015 cm−2 and diffused at temperatures between 1000 and 1100 °C. The profiles revealed retarded diffusion in the high‐concentration region (>1×1019 cm−3) in both ambients. It was found that for N2 annealing the diffusion in the low‐concentration region (<1×1019 cm−3) is highly enhanced in the early annealing stage and gradually reduced with annealing time, and that this time‐dependent diffusion depends on the implantation energy and annealing temperature. Arsenic diffusivities and related parameters were extracted by fitting numerically calculated profiles to SIMS data. The time‐dependent diffusion was attributed to the diffusion of interstitial arsenic and its reaction with the SiO2 network.

Influence of annealing ambients on ZrSi2 formation

Abstract The formation of zirconium silicide was studied in many kinds of annealing ambients, i.e., Ar-H 2 , Ar-O 2 , N 2 -O 2 , Ar-N 2 -O 2 , and Ar-air. When the ambient involves both N 2 and O 2 , such as Ar-N 2 -O 2 and N 2 -O 2 , in the range of [N 2 ]/([N 2 ] +[O 2 ])>0.9, the film resistivity becomes higher than that of the Ar-O 2 case, even at the same O 2 concentration. This is because a thick ZrO x N y layer is formed on the ZrSi 2 layer. When the ratio of [N 2 ]/([N 2 ] + [O 2 ]) in the Ar-N 2 -O 2 ambient is less than 0.9, the films are partially peeled off from the substrate. The resistivity of a film annealed in the Ar-air ambient is very high at even a few ppm O 2 . This is because the film peels off and then the oxidation of the peeled film is accelerated by a small amount of H 2 O in air.

Effects of contact-hole-etching damage on aluminum chemical vapor deposition

The effects of contact-hole-etching damage on aluminum (Al) chemical vapor deposition (CVD) have been investigated. When Si wafers were etched by reactive ion etching (RIE) under the conditions of contact hole etching, two kinds of damage were observed on the etched surface; i.e., an amorphized layer at a depth of 30 A and a contaminated (carbon, oxygen, and fluorine) layer at a depth of 100 A. Aluminum deposited on the as-etched wafer had granular structure and the grains were not connected with each other, which indicates that the growth of Al is suppressed by the damages. The effect of these damages was be removed by annealing at 1050°C or etching at a depth of 30 A (slight etching). In both cases, the amorphized layer was disappeared by recrystallization or was removed by etching, but the contaminated layer still remained. Therefore, it is concluded that the nucleation of Al is suppressed by the amorphized layer, but not by the contaminated layer. When this slight etching is made after contact hole etching, perfect contact hole filling with Al can be achieved by selective CVD.

Modeling of Mechanism of Leakage in a Shallow p+/n Junction Formed by Preamorphization

A model of the leakage induced by preamorphization is developed, assuming that the depth profile of excess interstitials making up dislocation loops is equal to the profile before annealing and that it is approximated by Gaussian distribution. It has been confirmed that this model well reproduces experimental data. Furthermore, Ge+ preamorphization was compared with Si+ in detail. An advantage of Ge+ preamorphization over Si+ has been confirmed in a wider range of conditions than in our previous report. A 0.08-µm-deep p+/n junction whose leakage current is less than 1×10-8A/cm2 is fabricated with a 40-nm-thick amorphous layer formed by Ge+ implantation.