Joseph D. Sweeney

Properties of Diboron Tetrafluoride (B2F4), a New Gas for Boron Ion Implantation

Currently, boron trifluoride, BF3, is the primary feed gas for boron implantation in manufacturing of semiconductor devices. However, BF3 molecule is difficult to ionize and fragment, and therefore only a small fraction is is converted into B+ ions that can be used for ion implantation. This results in low B+ beam currents even at relatively high extraction currents, which can limit process throughput and system performance. The problem is particularly severe at low energies. ATMI has demonstrated that use of diboron tetrafluoride, B2F4, as a feed gas for boron implantation may offer advantages over BF3. It has been shown that B2F4 is capable of generating higher B+ and BF2+ beam currents at lower ion source power settings, and that the molecule can be used on the existing installed base of implanters without any major equipment modifications.

High-efficiency, high-productivity boron doping implantation by diboron tetrafluoride (B 2 F 4 ) gas on Applied Materials solar ion implanter

Ion implantation is known for its precise control and reproducibility of doping, enabling it to become one of the main approaches for high-efficiency cell manufacturing in the solar industry. Among the dopant materials, boron doping often represents the largest challenge to productivity as the efficiency of the traditional doping material, boron trifluoride (BF3), is always low. This paper presents a high-efficiency and high-productivity solution for boron doping on an Applied Materials solar ion implanter by using diboron tetrafluoride (B2F4) as a replacement gaseous boron source material for BF3. Both the B+ beam current and source life effects were evaluated. With optimized source parameters and beam tuning, the solar implanter with B2F4 has demonstrated significant improvements for both B+ beam current performance and source lifetime.

Germanium ion implantation efficiency improvement with use of germanium tetrafluoride

Ion implantation of germanium in silicon wafers is often troubled by reduced ion source life due to use of germanium tetrafluoride (GeF₄) as a source material. The problem is mainly due to tungsten re-deposition, a result of a fluorine-induced halogen cycle initiated within the ion source. The halogen cycle is particularly pronounced in the case of GeF₄ by easy fragmentation of the molecule, as well as low utilization of germanium due to wide isotopic distribution of natural abundance GeF₄. Through isotopic enrichment of ⁷²GeF₄, benefits such as enhanced ion implantation beam current, lower gas flow, and longer source life can be achieved versus natural GeF₄. Additional benefits can be realized when using mixtures of GeF₄ with hydrogen (H₂). Data are presented that show the effect of H₂ content on beam current as well as on tungsten transport. Lastly, thermodynamics and stability results are presented for a single cylinder mixture of GeF₄ with H₂.

Investigation into Methods to Improve Ion Source Life for Germanium Implantation

Germanium tetrafluoride has long been the standard dopant gas of choice for germanium implantation processes. While this material maintains several positive attributes (e.g., it is a nonflammable gas that is easily delivered to an ion source), its use can result in extremely short ion source lifetimes. This is especially the case for the situation when an ion implanter runs solely or predominantly GeF4. Presented here is an examination of various potential solutions to the short source life problem, some of which enable significant improvement.

Carbon implantation performance improvement by using carbon monoxide (CO) gas on applied materials VIISta HCS implanter

Carbon implant has become one of the major co-implant steps in the fabrication of advanced semiconductor devices due to its proven effectiveness in controlling and reducing Transient Enhanced Diffusion (TED) in ultra-shallow junction formation. Carbon dioxide (CO₂) is still widely used as the feed gas for carbon implantation. However, it is well known that the high concentration of oxygen from CO₂ causes many problems, including oxidation of the implant arc chamber components, which leads to rapid performance degradation of the source. Phosphine (PH₃) is often used as a dilution gas to minimize the oxidation effect from CO₂. However, its use usually results in a reduction of the C⁺ beam current, thereby negatively impacting the tools productivity. In this paper, carbon monoxide (CO) is presented as an alternative carbon doping gas replacing CO₂ or CO₂ with PH₃ dilution (referred to as CO₂/PH₃ throughout this paper). CO is shown to exhibit distinct performance improvements compared to CO₂/PH₃ on the Applied Materials VIISta HCS high current implanter. Significant improvement in C⁺ beam current and source life with CO gas is noted.

Comparison of SAGS I vs. SAGS II delivery systems in emerging implantation technologies

The International Fire Code has classified Subatmospheric Gas Delivery Systems (SAGS) technologies into two main categories: SAGS Type I and SAGS Type II systems. SAGS Type I delivery systems both store and deliver gases at subatmospheric pressures. An example of this technology is ATMI’s Safe Delivery Source (SDS®) adsorbent based cylinder. SAGS Type II delivery systems store fluids at high pressure and utilize mechanical devices internal to the cylinder to deliver the gas at subatmospheric pressures. Typical mechanical devices used to enable subatmospheric delivery are either set point regulators or mechanical capillary based systems. This paper focuses on how these delivery systems perform against the unique requirements of traditional beam line ion implantation as well as solar and flat panel applications. Specifically, data are provided showing the capability of these systems with respect to flow rate, residual gas left within the cylinder, and cylinder end-point flow and delivery pressure dynamics.

Atomic layer deposition of boron-containing films using B2F4

Ultrathin and conformal boron-containing atomic layer deposition (ALD) films could be used as a shallow dopant source for advanced transistor structures in microelectronics manufacturing. With this application in mind, diboron tetrafluoride (B2F4) was explored as an ALD precursor for the deposition of boron containing films. Density functional theory simulations for nucleation on silicon (100) surfaces indicated better reactivity of B2F4 in comparison to BF3. Quartz crystal microbalance experiments exhibited growth using either B2F4-H2O for B2O3 ALD, or B2F4-disilane (Si2H6) for B ALD, but in both cases, the initial growth per cycle was quite low (≤0.2 A/cycle) and decreased to near zero growth after 8–30 ALD cycles. However, alternating between B2F4-H2O and trimethyl aluminum (TMA)-H2O ALD cycles resulted in sustained growth at ∼0.65 A/cycle, suggesting that the dense –OH surface termination produced by the TMA-H2O combination enhances the uptake of B2F4 precursor. The resultant boron containing films we...

Gas cylinder release rate testing and analysis

There are varying cylinder technologies employed for the storage of gases, each resulting in a potentially different hazard level to the surroundings in the event of a gas release. Subatmospheric Gas delivery Systems Type I (SAGS I) store and deliver gases subatmospherically, while Subatmospheric Gas delivery Systems Type II (SAGS II) deliver gases subatmospherically, but store them at high pressure. Standard high pressure gas cylinders store and deliver their contents at high pressure. Due to the differences in these cylinder technologies, release rates in the event of a leak or internal component failure, can vary significantly. This paper details the experimental and theoretical results of different Arsine (AsH3) gas cylinder release scenarios. For the SAGS II experimental analysis, Fourier Transform Infrared Spectroscopy (FTIR) was used to determine the spatial concentration profiles when a surrogate gas, CF4, was released via a simulated leak within an ion implanter. Various SAGS I and SAGS II cylind...

Source and beam performance improvement for carbon implantation with carbon monoxide (CO) gas

Carbon co-implantation has been widely adopted for better Ultra-Shallow Junction formation in the fabrication of advanced semiconductor devices. Currently, carbon dioxide (CO2) is the primary feed gas for carbon implantation. The primary disadvantage of CO2 is the high oxygen content, which causes significant oxidation of the implant source components resulting in rapid degradation of the source performance. Usually the C+ beam starts to degrade quickly while running continuously with carbon dioxide. Also, some other species’ implants, especially boron, are significantly affected after a short duration of CO2 usage. Carbon monoxide (CO) is described here as an alternative carbon source material to CO2. In our testing, CO has demonstrated significant improvements compared to CO2 for both source life and beam performance. Additionally, this paper describes a subatmospheric delivery option for CO. The cylinder package with reliability information is provided.Carbon co-implantation has been widely adopted for better Ultra-Shallow Junction formation in the fabrication of advanced semiconductor devices. Currently, carbon dioxide (CO2) is the primary feed gas for carbon implantation. The primary disadvantage of CO2 is the high oxygen content, which causes significant oxidation of the implant source components resulting in rapid degradation of the source performance. Usually the C+ beam starts to degrade quickly while running continuously with carbon dioxide. Also, some other species’ implants, especially boron, are significantly affected after a short duration of CO2 usage. Carbon monoxide (CO) is described here as an alternative carbon source material to CO2. In our testing, CO has demonstrated significant improvements compared to CO2 for both source life and beam performance. Additionally, this paper describes a subatmospheric delivery option for CO. The cylinder package with reliability information is provided.

Optimization of Xenon Difluoride Vapor Delivery

Xenon difluoride (XeF2) has been shown to provide many process benefits when used as a daily maintenance recipe for ion implant. Regularly flowing XeF2 into the ion source cleans the deposits generated by ion source operation. As a result, significant increases in productivity have been demonstrated. However, XeF2 is a toxic oxidizer that must be handled appropriately. Furthermore, it is a low vapor pressure solid under standard conditions (∼4.5 torr at 25 °C). These aspects present unique challenges for designing a package for delivering the chemistry to an ion implanter. To address these challenges, ATMI designed a high‐performance, re‐usable cylinder for dispensing XeF2 in an efficient and reliable manner. Data are presented showing specific attributes of the cylinder, such as the importance of internal heat transfer media and the cylinder valve size. The impact of mass flow controller (MFC) selection and ion source tube design on the flow rate of XeF2 are also discussed. Finally, cylinder release rate...