Conventional Beam-line Ion Implantation Research Articles

Plasma Doping of InGaAs at Elevated Substrate Temperature for Reduced Sheet Resistance and Defect Formation

Plasma doping (PLAD), a high-throughput ion implantation technique capable of achieving ultrashallow junctions and conformal doping of 3-D structures such as fin field-effect transistors, is investigated as an alternative to conventional beam-line ion implantation for InGaAs at advanced technology nodes. The PLAD at an elevated substrate temperature (ET-PLAD) is studied and reported for InGaAs for the first time. The ET-PLAD can give lower sheet resistance than room-temperature PLAD due to enhanced dopant incorporation. More crucially, an ET can help to prevent amorphization. After dopant activation anneal, residual corner defects are observed in small fins that are amorphized during plasma ion implantation, whereas fins that remain crystalline during plasma ion implantation are free of corner defects.

Effect of $\hbox{B}_{2}\hbox{H}_{6}$ Plasma Doping on the Shallow Trench Isolation in CMOS Image Sensor Device

We evaluate the electrical and optical properties of a complementary metal-oxide-semiconductor (CMOS) image sensor with shallow trench isolation (STI) sidewall doped by plasma-doping (PLAD) method using B2H6. PLAD can be used to fabricate an STI sidewall junction depth shallower than that fabricated using conventional beamline ion implantation. The use of B2H6 for the STI sidewall doping by PLAD facilitates the concurrent doping of numerous hydrogen atoms around the STI sidewall, thus improving the optical properties, such as temporal noise, crosstalk, and saturation, of the 1.75-μm pixel CMOS image sensor. Although the dark current performance was slightly degraded, it could be improved under more heavily doped conditions.

Advantage of Plasma Doping for Source/Drain Extension in Bulk Fin Field Effect Transistor

The impact of plasma doping (PD) on the formation of source/drain extension (SDE) is demonstrated for a p-type bulk fin field effect transistor (FinFET). The impurity distribution in a narrow fin (15 nm) was analyzed with atom probe tomography (APT) and secondary ion mass spectroscopy (SIMS). The lateral distribution of boron in the Si fin by the PD is similar to the case with conventional beam-line ion implantation (BL). However, the vertical distribution of boron by the PD is much steeper than that by the conventional BL. TCAD simulations show that the driving current of the FinFET fabricated by the PD is 34% higher than that of the FinFET fabricated by the BL under the same off-leakage current. Therefore, the PD is a key technology for fabricating the SDE of narrow bulk-FinFETs in the future.

SIMS/ARXPS—A New Technique of Retained Dopant Dose and Profile Measurement of Ultralow-Energy Doping Processes

A newly developed surface analysis technique, which combines secondary ion mass spectrometry with angle-resolved X-ray photoelectron spectroscopy, was used to achieve more accurate results of the retained impurity doses and profiles for ultralow-energy implants, including conventional beamline implant and plasma immersion ion implantation (PIII). Using this method, it has been found that the B <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> H <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6</sub> (diborane) PIII demonstrates thicker native oxide and much more B dose loss during rapid thermal processing and surface-cleaning treatments than conventional beamline ion implantation, due to the higher surface B concentration. In order to match the electrical parameters of the device, PIII must consider higher nominal dose to compensate the B loss.

Comparison of tribological behaviour and biocompatibility of Ti6Al4V alloy after ion implantation or thermal oxidation

AbstractThis paper describes improvements of the tribological properties and the biocompatibility of Ti6Al4V alloy implanted by oxygen plasma immersion (PIII) in comparison with other treatments like thermal oxidation, conventional beamline ion implantation (II) of nitrogen and a combination of both thermal oxidation and II of nitrogen.Ball‐on‐disc friction and wear tests were performed to investigate the modifications introduced for each treatment. Biocompatibility tests were carried out by controlling Al and V ion migration in a Hank's solution simulating the human body fluid. The reported results indicate that PIII provide a promising method to improve the characteristics of the Ti6Al4V alloy to be used in human body implants. (© 2008 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

Ultra shallow P+/N junctions using plasma immersion ion implantation and laser annealing for sub 0.1 μm CMOS devices

Classical beam line ion implantation is limited to low energies and cannot achieve P+/N junctions requested for <45nm ITRS node. RTA (rapid thermal annealing) needs to be improved for dopants activation and damage reductions. Spike annealing process also induces a large diffusion mainly due to TED (transient enhanced diffusion).Compared to conventional beam line ion implantation limited to a minimum energy implantation of 200eV, plasma immersion ion implantation (PIII) is an emerging technique to get ultimate shallow profiles (as-implanted) due to no lower limitation of energy and high dose rate. On the another hand, laser thermal processing (LTP) allows to obtain very shallow junction with no TED, abrupt profile and activated depth control.In this paper, we show the implementation of the BF3 PIII associated with the LTP. Ions from BF3+ plasma have been implanted in 200mm n-type silicon wafers with energies from 100eV to 1keV and doses from 3E14 to 5E15at/cm2 using PULSION® (IBS PIII prototype). Then, wafers have been annealed using SOPRA VEL 15 XeCl excimer lasers (l=308nm, 200ns, 15J/pulse) with energy density from 1 to 2.5J/cm2 and 1, 3 or 10 shots. The samples have been characterized at CEA LETI by secondary ion mass spectrometry (SIMS) combined with four points probe sheet resistance measurements.

Co-axial ECR plasma system for radioactive ion implantation

A pulsed, co-axial electron cyclotron resonance (ECR, 2.45 GHz) plasma reactor was designed and tested to demonstrate the feasibility of plasma-based radioactive ion implantation (32P radioisotope). The geometry of the reactor was designed to produce an efficient implantation of cylindrical implants. Therefore, the reactor is cylindrical in shape, and is equipped with a cylindrical grid in a co-axial geometry. The plasma is created between the wall and the grid; the plasma surrounds the implant, allowing for a radial implantation. A 1 ms microwave pulse creates a plasma in argon, which sputters material from a radioactive cathode. A fraction of the radioisotopes is then ionized, and the ions are implanted into negatively biased metal samples. The plasma was characterized by means of electrostatic probes, giving spatial evaluations of the electron temperature, plasma potential and electron density. Titanium samples were implanted with 32P during a study that aimed at optimizing the position of the radioactive sputter cathode in the plasma. From an analysis of the distribution of the radioactive fragments, we deduce that the plasma potential has a marked effect on the ion trajectories. In particular, it provides a more uniform implantation distribution than one would otherwise expect. For plasma densities ∼8 × 1010 cm−3, implantation efficiencies as high as 1% are measured; this is about 100 times higher than conventional beam-line ion implantation.

Efficiency of plasma-based ion implantation of radioisotopes (32P)

Radioactive phosphorus (32P) can be implanted in biomedical devices using plasma-based ion implantation (PBII). A pulsed ECR (2.45 GHz) coaxial argon plasma reactor has been developed in which the radioisotopes are implanted into a negatively biased target. A 1 ms microwave pulse creates the plasma, which sputters material from a sputter target. A fraction of the radioisotopes is then ionized and the ions are implanted into a negatively biased cylindrical titanium implant. The theory underlying plasma-based radioisotope ion implantation is described in this article and the calculations are compared to experimental results for different plasma conditions and sputtering target positions. This study confirms the importance of radioactive source positioning and the impact of high plasma densities when using a PBII reactor. Implantation efficiency rates of about 1% are measured, which is about 100 times higher than conventional beam-line ion implantation.

Semiconductor applications of plasma immersion ion implantation technology

Many semiconductor integrated circuit manufacturing processes require high dose of implantation at very low energies. Conventional beam line ion implantation system suffers from low beam current at low energies, therefore, cannot be used economically for high dose applications. Plasma immersion ion implantation (PIII) is emerging as a potential technique for such implantations. This method offers high dose rate irrespective of implantation energy. In the present study nitrogen ions were implanted using PIII in order to modify the properties of silicon and some refractory metal films. Oxidation behaviour of silicon was observed for different implantation doses. Diffusion barrier properties of refractory barrier metals were studied for copper metallization.

Damage in hydrogen plasma implanted silicon

The damage and defects created in silicon by hydrogen plasma immersion ion implantation (PIII) are not the same as those generated by conventional beamline ion implantation due to the difference in the ion energy distribution and lack of mass selection in PIII. Defect generation must be well controlled because damage in the implanted and surface zones can easily translate into defects in the silicon-on-insulator structures synthesized by the PIII/wafer bonding/ion-cut process. The defect formation and its change with annealing temperature were investigated experimentally employing channeling Rutherford backscattering spectrometry, secondary ion mass spectrometry, and atomic-force microscopy. We also calculated the damage energy density of the three dominant hydrogen species in the plasma (H+, H2+, and H3+) as well as displacement of silicon atoms in the silicon wafer. H2+ creates the most damage because its damage energy density is very close to the silicon threshold energy. The effects of atmospheric gaseous impurities unavoidably coimplanted from the overlying plasma are also modeled. Even though their concentration is usually small in the plasma, our results indicate that these gaseous impurities lead to significant silicon atom displacement and severe damage in the implanted materials.

Modeling of incident particle energy distribution in plasma immersion ion implantation

Plasma immersion ion implantation is an effective surface modification technique. Unlike conventional beam-line ion implantation, it features ion acceleration/implantation through a plasma sheath in a pulsed mode and non-line-of-sight operation. Consequently, the shape of the sample voltage pulse, especially the finite rise time due to capacitance effects of the hardware, has a large influence on the energy spectra of the incident ions. In this article, we present a simple and effective analytical model to predict and calculate the energy distribution of the incident ions. The validity of the model is corroborated experimentally. Our results indicate that the ion energy distribution is determined by the ratio of the total pulse duration to the sample voltage rise time but independent of the plasma composition, ion species, and implantation voltage, subsequently leading to the simple analytical expressions. The ion energy spectrum has basically two superimposed components, a high-energy one for the majority of the ions implanted during the plateau region of the voltage pulse as well as a low-energy one encompassing ions implanted during the finite rise time of the voltage pulses. The lowest-energy component is attributed to a small initial expanding sheath obeying the Child-Langmuir law. Our model can also deal with broadening of the energy spectra due to molecular ions such as N2+ or O2+, in which case each implanted atom only carries a fraction (in this case, half) of the total acceleration energy.

In situ sample temperature measurement in plasma immersion ion implantation

Plasma immersion ion implantation (PIII) is an excellent surface modification technique because it is not restricted by the line-of-sight limitation that plagues conventional beamline ion implantation. However, the lack of in situ monitoring has hampered wider acceptance of the technique in industry. It is known that the implantation temperature has a large influence on the surface properties of the treated specimens in addition to the more obvious parameters such as implantation voltage, pulse duration, pulsing frequency, and so on. Direct measurement of the target temperature is complicated by the sample high voltage as well as by interference from the electromagnetic field and plasma. In this article, we present a novel interference-free, in situ temperature measurement technique employing a shielded thermocouple directly attached to the sample stage. Our experiments show that the setup can monitor the target temperature in real time, even under severe arcing conditions. Our results also indicate that in a hot filament glow discharge radiation heating is quite small, and sample heating is primarily caused by ion bombardment during the PIII cycles. The new design will open up other possibilities such as in situ dose monitoring if, for example, the thermocouple is replaced by a Faraday cup.

Simulation of dose uniformity for different pulse durations during inner surface plasma immersion ion implantation

Without the line-of-sight limitation, plasma immersion ion implantation (PIII) emulates conventional beam-line ion implantation in inner surface modification of industrial components. However, dose uniformity on the inner surface is critical. Inner surface PIII of a cylindrical bore is modeled using a two-dimensional fluid model. It is found that the retained dose is not uniformly distributed on the inner surface and the maximum dose is observed away from the edge. The exact location of the maximum dose, which varies with the implant pulse duration, is closer to the center when the pulse width is longer. The maximum relative difference of the retained dose along the interior also depends on the implant pulse duration. It is smaller for a longer pulse duration after a threshold value has been exceeded.

Special modulator for high frequency, low-voltage plasma immersion ion implantation

Plasma immersion ion implantation is a burgeoning surface modification technique and not limited by the line-of-sight restriction plaguing conventional beam-line ion implantation. It is therefore an excellent technique to treat interior surfaces as well as components of a complex shape. To enhance the implant uniformity and increase the thickness of the modified layer, we are using a high frequency, low-voltage process to achieve high temperature and dose rate to increase the thickness of the modified layer. The low voltage conditions also lead to a thinner sheath more favorable to conformal implantation. In this article, we will describe our special modulator consisting of a single ended forward converter with a step-up transformer. The modulator is designed to operate from 5 to 35 kHz and the output voltage is adjustable to an upper ceiling of 5000 V that is deliberately chosen to be our voltage limit for the present experiments. We will also present experimental data on SS304 stainless steel materials elucidating the advantages of our modulator and high frequency, low-voltage experimental protocols.

Treatment uniformity of plasma immersion ion implantation studied with three-dimensional model systems

Plasma immersion ion implantation is a rapidly developing technique for ion-beam treatment of materials, mainly metals and semiconductors. This technique was developed initially to circumvent the line-of-sight restrictions of conventional beam-line ion implantation. In contrast to the latter, the treatment of three-dimensional samples does not require complicated manipulation of the workpiece and ion beam. With this concept, knowledge of treatment homogeneity is of particular importance for the further development of plasma immersion ion implantation. In the present paper, homogeneity measurements of model systems are discussed. Silicon wafer segments mounted on wedge-shaped and V-shaped sample holders with different edge angles (30° to 120°), and on a U-shaped sample holder (trench), were treated by plasma immersion ion implantation with argon ions of −45 kV high-voltage pulses. The samples were analysed for lateral implantation concentration by Rutherford backscattering spectrometry measurements. The results show that, for wedge-shaped samples, gradients in concentration of implanted argon by a factor of up to six develop, depending on the process parameters. In the case of trenches, differences of more than an order of magnitude between the implantation concentrations of the side walls and bottom of the trench were found.

Modification of mechanical and chemical surface properties of metals by plasma immersion ion implantation

Plasma immersion (ion) implantation (PII) was developed a decade ago for modifying mechanical and chemical surface properties of metals. In analogy to conventional beam-line ion implantation, it uses energetic ions, mostly nitrogen, that are implanted in the near-surface region of a material. A sample is enveloped by a plasma and subjected to negative high-voltage pulses. In the electrical field, the ions are accelerated to high energies and incorporated into the sample. This process takes place at all sides of the sample simultaneously without requiring ion beam and sample manipulation, in contrast to beam-line ion implantation. The present review discusses the fundamentals of PII and its most important features. The influence of the most important process parameters such as implantation dose, ion density, pulse repetition rate, and sample temperature on hardness and wear resistance and on corrosion resistance of metals and alloys such as mild steel, stainless steel, nickel, aluminium and titanium alloys is discussed.

Improvement of the wear and corrosion resistance of oil pump materials using plasma immersion ion implantation

A typical oil pump used in oil wells consists of a piston column, piston sleeve and ball valve. The working environment in an oil field is harsh and unforgiving, and the piston column in the oil pump is very vulnerable to wear and corrosion. Hence, improving the wear and corrosion resistance of the piston which is made of 45 # steel is critical to the efficiency and profitability of oil companies. Even though ion implantation is an effective means to enhance the surface properties of the materials, the irregular shape and large dimension of the column make conventional beamline ion implantation very difficult. As the technique of plasma immersion ion implantation circumvents this line-of-sight restriction, it is a suitable technique to improve the wear and corrosion resistance of the components in an oil pump. A treatment process involving RF plasma nitriding and ion beam enhanced deposition (IBED) has been developed. The microhardness, mass loss due to wear, and coefficient of friction of the untreated and treated samples were measured. A salt fog test was also conducted to evaluate the resistance against rusting. The results indicate that the treatment improves the wear and corrosion resistance of the 45 # steel samples significantly, and that the combined RF plasma nitriding and IBED process is more effective than a single RF plasma nitriding step.

Lateral implantation homogeneity of wedge-shaped samples treated by plasma immersion ion implantation

Plasma immersion ion implantation (PIII) is a rapidly developing technique for ion implantation in metallurgical and semiconductor applications. In contrast to conventional beam-line ion implantation, the treatment of three-dimensional samples does not require complicated workpiece and ion beam manipulation. However, recent results have shown that, in addition to the shape of the workpiece, treatment homogeneity is strongly dependent on process parameters such as ion density and gas pressure. Knowledge of homogeneity is of great importance for the further development of PIII. In the present paper, homogeneity measurements of a model system are discussed. Wedge-shaped silicon specimens with different angles (30 ° to 90 °) were treated by plasma immersion ion implantation with argon ions with 45 kV high-voltage pulses. The samples were analyzed for lateral implantation concentration by Rutherford backscattering measurements. The implanted concentration, the projected range and their gradient are a strong function of the edge angle. The results show that for acute angles (30 °), gradients in implantation concentration up to a factor five develop.

Homogeneity measurements of plasma immersion ion-implanted complex-shaped samples

It is commonly accepted, that one of the favourable features of plasma immersion ion implantation in comparison to conventional beam-line ion implantation is its ability to treat non-planar samples without complicated workpiece and beam manipulation. Therefore, it is of particular interest to study the homogeneity of PIII treatment of three-dimensional bodies. In the present paper, homogeneity measurements are of PIII treated model systems are discussed. Wedge-shaped specimens (V- and D-shaped) with different angles made of silicon were treated by plasma immersion ion implantation with argon ions. The voltage pulse heights ranged between 30 and 45 kV. The samples were analysed for retained implantation dose by lateral Rutherford backscattering measurements. These show that large gradients in implantation dose develop under the chosen PIII conditions. An explanation for these gradients is a misalignment of electric field lines, crooked near the edges of samples, and ion trajectories, due to the inertia of the ions.

Plasma immersion ion implantation for metallurgical and semiconductor research and development

Plasma Source Ion Implantation, also termed Plasma Immersion Ion Implantation, is a rapidly developing material modification technique for treating the near-surface regions of various kinds of materials. It makes use of high-energy ions which are accelerated by a high voltage pulse from a plasma which wraps the workpiece to be treated. The ions are implanted into the material causing effects similar to those of conventional beam-line ion implantation. Research and development of plasma immersion ion implantation has focused in two main fields, treatment of metals for improved wear and corrosion performance, and modification of semiconductors. The paper discusses examples from both fields, with nitrogen PIII of steels and aluminum, and modification of thin metal films. From the semiconductor field, trenchwall doping, ultra-shallow doping with boron, and oxygen ion implantation for SIMOX formation is treated.