Sharad Yedave

ATMI’s Ion Implant Process Efficiency Research Laboratory (IIPERL)

We describe an ion source test stand recently installed by ATMI, and show data illustrative of the research being carried out at the new facility.

The Development of In‐Situ Ion Implant Cleaning Processes

Considerable gains in implanter utilization efficiency can be attained with in‐situ cleaning of deposited material, particularly in and around the ion source. Different methods of in‐situ cleaning are described, and we discuss the relative merits of several chemical reagents. We introduce XeF2, a new and promising reagent for in‐situ cleaning and present some preliminary experiments showing its ability to etch dopant materials. We also show that in some cases etching by XeF2 can be selective with respect to ion source construction materials such as tungsten.

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.

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...

Surface Analytics in Support of the Development of Static AutoClean™—an In‐Situ Cleaning Process for Ion Implanters

Static AutoClean™ is a new in‐situ cleaning strategy in development at ATMI® that enables increased process efficiency and safety in the ion implantation process. Like the Dynamic in‐situ AutoClean technology previously introduced and released by ATMI, Static AutoClean utilizes XeF2 chemistry for in‐situ cleaning of hazardous contaminants and deposits. Static AutoClean, however, is targeted towards cleaning areas of the beam‐line (like electrode insulators or source bushings) where cleaning efforts using Dynamic AutoClean may not be sufficient. An explanation of this cleaning strategy and results showing its effectiveness will be presented in a separate paper at this conference (S. Yedave et al.). This paper presents the surface analytical data and methods used to understand and evaluate the effectiveness of Static AutoClean in removing contaminants from surfaces within the source vacuum chamber. Energy Dispersive Spectroscopy (EDS) was used to track the magnitude and spatial distribution of contaminants ...

Development of “Static” In‐Situ Implanter Chamber Cleaning

Since the introduction of XeF2 in‐situ cleaning, its use in production implanters has been mainly focused on cleaning ion sources by flowing the cleaning vapor through the source arc chamber. This has been called “Dynamic” in‐situ cleaning. “Static” in‐situ cleaning is a different method under development at ATMI which allows an entire vacuum chamber and its contents to be cleaned. The chamber is filled to a pressure of 1–3 Torr of XeF2 vapor, which reacts with deposited material on all internal surfaces, and the reaction by‐products are then pumped away. When applied to the source vacuum chamber, the Static cleaning method allows cleaning vapor to contact components, such as the HV bushing and the manipulator assembly, which may not be adequately cleaned with the Dynamic method. Recently, ATMI has installed a prototype Static in‐situ cleaning system on an in‐house Ion Source Test Stand in Danbury, CT. This paper will describe the prototype cleaning system and process and its applicability to production i...

Hydrogen Selenide (H2Se) Dopant Gas for Selenium Implantation

With the continued scaling of semiconductor devices, controlling contact resistance becomes more and more challenging. Selenium (Se) ion implantation is noted in the literatures to effectively reduce contact resistance in NMOS transistors by lowering the electron Schottky barrier height (SBH). A suitable selenium source feed material is required and can be in solid form, such as selenium oxide (e.g. SeO2), or in gas form, such as hydrogen selenide (H2Se). Solid source materials in general suffer from relatively longer setup times and concern of re-deposition of the dopant, whereas hydrogen selenide gas stored at high pressure poses safety and handling issues. In this paper, we present performance and usage data associated with a subatmospheric source of H2Se, including beam setup, Se+ beam current, beam stability, and source conditions. Material properties, as well as the subatmospheric delivery source are also described.