Leonard M. Rubin

Evaluation of high dose, high energy boron implantation into Cz substrates for epi-replacement in CMOS technology

We implanted high energy boron to create a heavily doped ground plane in Cz wafers in order to replace p/p/sup +/ episubstrates in deep submicron complementary metal-oxide semiconductor (CMOS) technology. Devices manufactured on Cz wafers with a 1.5 or 1.6 MeV, 1/spl times/10/sup 15/ cm/sup -2/ boron implanted ground plane have superior latch-up immunity as compared to devices on epiwafers. Improvements in latch-up suppression were observed for all isolation spacings. Diode leakage was lower in high dose buried-layer substrates than in episubstrates, while gate oxide integrity was equivalent. For the first time, buried layer substrates have been shown to duplicate or exceed the performance of episilicon simultaneously for all relevant CMOS transistor and circuit parameters.

On the FinFET extension implant energy

The need of an ultrashallow junction technology for the extension of p-FinFETs has been investigated by integrated process and device simulations. For devices with 60 nm physical gate length, whose extensions are activated in a low thermal-budget process (spike anneal), it is found that the I/sub off/-I/sub on/ performance is invariant with respect to the extension implant energy. Nevertheless, the short-channel behavior worsens. This can be remedied by adding spacers to both sides of the gate before the extension implant, resulting in virtually identical dc characteristics and speed. Devices with gate lengths of 18 nm and below require dopant activation with negligible diffusion. Under those circumstances the short channel behavior of the FinFET is limited by the lateral straggle of the ion implant. Spacers may remedy what is otherwise poor short channel behavior due to a relatively high energy extension implant. However, this comes at the price of drastically worse drive current at a fixed off-current.

Process control issues for retrograde well implants for narrow n+/p+ isolation in CMOS

Shallow trench isolation (STI) is being scaled down in both width and depth to increase device packing densities. Critical to the success of interwell isolation is the accurate placement of the n-well/p-well junction in the center of the region below the STI oxide. Zero degree implants avoid shadowing effects from resist features but can reduce process robustness due to channeling-induced profile variations. The shape of dopant profiles near 0° tilt vary significantly with tilt angle changes too small to control on even advanced ion implanters. We modeled 150nm devices with a 380nm n+/p+ spacing and show that these profile variations lead to significant shifts in transistor threshold voltage and n-well to n+ leakage. We calibrated our simulator with SIMS data to accurately model transistor and interwell breakdown performance for 0° well implants for the first time. We also modeled the same structures made with implants at 3° tilt using quad repositioning. Low angle quad implants for retrograde wells eliminate shadowing effects while delivering superior process robustness as compared to 0° well implants.

Properties of ultralow energy boron implants using octadecaborane

The material properties of junctions formed by implanting ultralow energy octadecaborane (B18H22+) followed by spike and flash annealings are reported. Along with providing significant drift mode beam current improvements at sub-1-keV energies, the B18H22 implants form an amorphous layer due to the large mass of the material. The authors have found that the thickness of the amorphous layer is dependent on the beam current of the implant, and that upon millisecond annealing, results in a shallow junction that is free of end-of-range damage. The authors have also investigated other issues critical to integrating B18H22 into standard complementary metal-oxide semiconductor processing. Dose retention and sputtering of silicon have been examined using secondary-ion-mass spectroscopy for implants ranging from 50eVto2keV. Of considerable concern is the ability to effectively strip photoresist from wafers without removing dopant that is placed within 1–2nm of the surface. The use of fluorine-free downstream ashin...

Fluorine-enhanced boron diffusion in germanium-preamorphized silicon

Silicon wafers were preamorphized with 60 keV Ge+ or 70 keV Si+ at a dose of 1×1015 atoms∕cm2. F+ was then implanted into some samples at 6 keV at doses ranging from 1×1014 to 5×1015 atoms∕cm2, followed by B+11 implants at 500 eV, 1×1015atoms∕cm2. Secondary-ion-mass spectrometry confirmed that fluorine enhances boron motion in germanium-preamorphized materials in the absence of annealing. The magnitude of boron diffusion scales with increasing fluorine dose. Boron motion in as-implanted samples occurs when fluorine is concentrated above 1×1020atoms∕cm3. Boron atoms are mobile in as-implanted, amorphous material at concentrations up to 1×1019atoms∕cm3. Fluorine directly influences boron motion only prior to activation annealing. During the solid-phase epitaxial regrowth process, fluorine does not directly influence boron motion, it simply alters the recrystallization rate of the silicon substrate. Boron atoms can diffuse in germanium-amorphized silicon during recrystallization at elevated temperatures with...

Impact of extension implant energy purity and angle on the electrical characteristics of a 65nm device technology

We show that a significant fraction of the overlap in advanced logic technologies originates in the as-implanted dopant profile. As a consequence, small changes in the as-implanted profile have a large impact on device characteristics. We have developed a virtual, high-performance, planar, bulk, 65nm technology that we use as a platform to investigate the impact of imperfections in the extension implant stemming from (1) contamination of the beam with higher energy ions and (2) angular alignment of the incident ion beam to the wafer. We find that a deceleration ratio of 7 and an energy contamination equal to 1% of the total dose double the off current. Small (of the order 1°) beam steering of the incident beam as seen by the wafer leads to large changes in on current (of the order of 20%) and speed. Steering that results in shadowing of the source has a far larger impact than drain-side shadowing. This can be alleviated significantly by a quad implant, provided the tilt angle is sufficiently large, on the...

A universal ion implantation model for all species into single-crystal silicon

A physically based model for ion implantation of any species into single crystal silicon has been developed, tested and im- plemented in the ion implant simulator, UT-MARLOWE. In this model, an interpolation scheme, based on mathematical proper- ties of ion-target interatomic potential, was employed and imple- mented to calculate the scattering process. Using this scheme, the resulting energy, direction and momentum of the ion and target can be derived from the existing scattering tables of UT-MARLOWE without calculating the entire scattering process. The method has advantages in terms of both accuracy and computational efficiency, as well as significantly reduced cost of code development. The im- purity profiles and damage profiles predicted by the model simu- lations have been compared with secondary ion mass spectroscopy (SIMS) and Rutherford backscattering spectrometry (RBS), and excellent agreement with experimental data has been achieved.

Tilted ion implantation as a cost-efficient sublithographic patterning technique

Tilted ion implantation (TII) is experimentally demonstrated to be a promising approach to pattern features smaller than pre-existing mask features on the surface of a wafer substrate. A key to this approach is a substantial change in the etch rate of a thin masking layer by TII. Fifteen degrees-tilted Ar+ implantation into a 10 nm-thick thermally grown silicon dioxide (SiO2) masking layer at a dose of 3 × 1014 cm−2 enhances its etch rate in dilute hydrofluoric acid solution by a factor of approximately 9. The features defined by TII are shown to be self-aligned to the pre-existing mask features and to have critical dimensions that can be adjusted by changing the implant tilt angle (θ) and/or geometrical dimensions of the pre-existing mask features. In this work, trenches of width as small as ∼9 nm and sub-20 nm holes are achieved by TII-enhanced patterning.

n‐LDD Ultra‐Shallow Extension Formation Using Cold and Carbon Ion Implantation

The sheet resistivity and junction depths of P implants with and without Ge PAI implants and C co‐implants were compared. Phosphorus activates well under RTA+LSA annealing conditions, but junction depths did not reach the 15 nm target. Arsenic junctions achieved the junction depth target but with higher sheet resistance. NMOS junction depth was determined to depend heavily on both channeling and transient enhanced diffusion of phosphorus. Combining Ge and C co‐implants reduced junction depths to a much larger degree than either species alone. The substitution of the C7H7 molecule for monomer C or the reduction of implant temperature to as low as −40 °C had little effect on the overall sheet resistivity and junction depth. It is possible to eliminate the Ge‐PAI for n‐LDD if C co‐implant energy and dose could be modified. The low implant temperature technique could help the formation of amorphous layer from C co‐implant, for which the implant dose and energy need to be tailored in order to reduce junction l...

Effect of carbon codoping on boron diffusion in amorphous silicon

The effect of carbon codoping on boron diffusion in amorphous silicon is investigated during low temperature annealing. The diffusivity of boron is unaffected by carbon codoping, but the fraction of mobile boron is observed to increase with increasing carbon concentration. A concomitant reduction in boron clustering is also observed at higher carbon coimplant concentrations, consistent with a change in the local trap concentration. This is consistent with carbon possibly acting as a trap site for boron and thereby changing the size and dynamics of the boron cluster formation.