Hiroshi Onoda

Cluster carbon implants — Cluster size and implant temperature effect

In this paper we present results for amorphous layer thickness and interface roughness for various cluster carbon ions as well as monomer carbon implants for various doses implanted at different implant temperatures. The effect of cluster size, implant dose, implant dose rate and wafer implant temperatures are discussed based on Spectroscopic Ellipsometry, TEM and RBS/channeling techniques.

High dose dopant implantation to heated Si substrate without amorphous layer formation

Enhancement of transistor drivability with suppressing short channel effect is a mandatory requirement for device scaling. In order to address the requirement, transistor structure transition from 2D bulk planar to SOI or 3D FinFET structures is now proceeding[1-3]. In FinFET structures, high dose tilt implantations are used in source drain extension formation. This implantations cause amorphization of Si fins, and there exists an issue here for difficulty in regrowth of amorphized Si fins during successive activation annealing. For further scaling, fin width becomes narrower, and regrowth from crystal channel also cannot be much expected. Amorphized Si fin cannot be easily regrown to Si fin top during activation annealing, resulting in twin formation and/or poly crystal[4] as shown in the schematic figure (Fig.1). In addition, memory devices also have almost the same transistor structure. Shrinking active Si areas in transistors of flash memory embedded in surrounding STI oxide is similar structure as tall Si fin in FinFET structures. Doping with ion implantation causes narrow active Si areas amorphous, and regrowth to the active Si top is also becoming difficult. Doping without Si amorphization is a challenge for further scaling of transistors both in logic devices and memory devices. This paper reports high dose doping by using implantation to heated Si substrates. Crystalline quality, depth profiles and resistance of As+, P+ and BF2+ implanted Si at elevated temperatures have been investigated. It will be shown that high dose doping without amorphization, and also low resistance of implanted regions after annealing can be successfully embodied.

Suppression of phosphorus diffusion using cluster Carbon co-implantation

Phosphorus transient enhanced diffusion (TED) is caused by interstitial diffusion mechanism. It is important for the efficient suppression of phosphorus diffusion that some carbons could be located on lattice point in the initial stage of re-growth during annealing and trap interstitial Silicon. Carbon co-implantation after Germanium, pre-amorphization implantation (PAI) is applied for the applications of n+/p junction formation and the effects of Carbon co-implantation are reported. In our experiments it is shown that suppression of Phosphorus diffusion could be achieved with conventional rapid thermal annealing (RTA) by using cluster Carbon (C16Hx+, C7Hx+) co-implantation for the self-amrphization. Our experimental data suggests that cluster carbon co-implantation enable to suppress phosphorus diffusion without germanium pre-amorphous implantation. In this paper the characteristics of cluster Carbon co-implantation after RTA are introduced from experimental results which were obtained by secondary ion mass spectroscopy (SIMS) measurement, transmission electron microscopy (TEM) and sheet-resistance measurement.

Carrier activation in cluster boron implanted Si

Boron retained dose and carrier activation after spike RTA in Cluster B<inf>18</inf>⁺ (Octadecaborane : B<inf>18</inf>H<inf>11</inf>⁺) implanted Si have been investigated comparing with BF<inf>2</inf> beamline implanted Si. The retained dose estimated by SIMS depth profile integration is higher in B<inf>18</inf> samples. In the same implant set dose, carrier concentrations in B<inf>18</inf> samples show almost twice compared with BF<inf>2</inf> samples although mobilities are almost the same in both samples. This means that activation ratio of B<inf>18</inf> sample is much higher compared with that of BF<inf>2</inf> sample. This is one of the advantages of cluster ion implantation.

Improvement of productivity by cluster ion implanter: CLARIS

The cluster ion beam implanter named CLARIS has been developed for beyond 45nm device production use, which is characterized by the high productivity, high effective low energy high current, and preciseness of incident beam angle and dose uniformity. For the USJ process application, a cluster beam co-implantation is introduced. Carbon cluster co-implantation and the boron cluster beam implantation productivity are evaluated from a COO and CoC view point and compared with the conventional high current implanter.

Effects of cluster carbon implantation at low temperature on damage recovery after rapid thermal annealing

Cluster C implantation at low temperature has been studied in terms of amorphous Si (a-Si) formation and elimination of B implanted induced end of range defects (EORDs). Thickness of a-Si can be controlled by C equivalent energy and dose. Monomer C never creates a-Si layer at less than 1E15/ cm² at 25°C implant. Dose increase and temperature decrease starts to create a-Si layer. On the other hand, cluster C7 implant creates a-Si layer at less than 5E14/cm² dose even at 25°C, and −30°C implant increases the a-Si thickness by around 7∼8nm in each C dose. A large amount of EORDs remain in cluster B10 25°C implant sample after RTA at 950°C. The situation does not change a lot with B10 −30°C implant. On the other hand, cluster C7 co-implant with B10 at 25°C, however, greatly reduces EORD density. EORD free can be realized in C7 co-implant with B10 at −30°C. Cluster C7 co-implant at −30°C assists the EORD elimination. Sheet resistance of cluster C and B10 co-implanted at −30°C sample is remarkably low compared with only B10 implanted sample. It can be concluded that cluster C implantation at −30°C is very effective for eliminating EORDs and obtaining high carrier activation.

Optimization of implant and anneal processes

A method of choosing a coupled pair of a doping process and an annealing process that is optimized on the basis of the R<inf>s</inf>·x<inf>j</inf> figure of merit. Differential Hall effect evaluations are used to measure 1/µ<inf>def</inf>, the defect scatter contribution to the mobility. Supressing 1/µ<inf>def</inf> leads to optimization of the doping process-annealing process couple.

Damage control with cluster ion implantation

Ion implantation is doping process for manufacturing semiconductor. Doping process contains not only implanting doping atoms at a controlled depth profile but also making damages caused by collisions between ions and silicon crystal atoms, knock-on silicon atoms and silicon crystal atoms. A characteristic of doping atoms such as boron, phosphorous and arsenic is well known because it is easy to measure its resistivity and depth profile. On the other hand it is difficult to measure damages. The damage consist vacancies and interstitials in silicon crystals. We have to measure nothing and same atoms in the same crystal atoms. In order to measure damages characteristics we have to fabricate transistor devices, because damages region after thermal budget is too small to measure.

Microwave and RTA annealing of phos-doped, strained Si(100) and (110) implanted with molecular Carbon ions

Effects of microwave (MWA) at ≈500 C and rapid-thermal annealing at 600 to 1000 C are compared for phosphorous-doped, strained Si(100) and (110) implanted with molecular Carbon (C7H7) ions. Substitutional Carbon levels at 1.44% were achieved for P-doped, C7 implanted strained nMOS S/D type junctions with MWA.

Phosphorous transient enhanced diffusion suppression with cluster carbon co-implantation at low temperature

Low temperature cluster carbon co-implantation was applied for phosphorous activation enhancement and transient enhanced diffusion (TED) suppression. The dependence of phosphorous activation and TED on 1) carbon energy, 2) dose and 3) substrate temperature have been investigated. 1) Implanted carbon depth compared with phosphorous depth was optimized for better phosphorous TED suppression and phosphorous activation. 2) Junction depth and sheet resistance (Rs) were evaluated as a function of carbon dose. 3) Amorphous layer thickness was controlled by cooling down the substrate temperature and the influence on TED and activation was evaluated. Finally shallow junction with low Rs has been achieved using low temperature cluster carbon co-implantation.