SPECIALTY CHEMICALS AND ENGINEERED MATERIALS | WHITE PAPER Enriched 11Boron Trifluoride and Hydrogen Mixture for Performance Improvement on Applied Materials E-500 Implanter Authors: Barry Chambers – Entegris; Francisco E. Cruz Jr. – ABB Switzerland Ltd INTRODUCTION — Abstract A focus of the semiconductor industry – Historically, the semiconductor industry has experienced different on advanced devices and equipment is expected, periods of increased production as well as a reduction in capacity, but many fabs are also at full capacity with legacy depending on the end-user product demand. However, one con- node technology. This results in hundreds of older stant throughout this time has been the need for efficiency and generation ion implanter tools still being used for optimization of the production tools. In times of high production volume, equipment utilization with maximum process availability semiconductor manufacturing processing. The is essential. When demand is low other factors may influence key expectation for better yields and lower cost of own- metrics, but to be competitive, manufacturing must still maintain ership is always important no matter the technology efficient operations. node. Fluoride gases, including BF3, have a long As the Internet of Things (IOT) continues to expand the use of history of poor ion source life performance due semiconductor devices, a portion of these devices need leading to tungsten transport from halogen cycling inside edge technology to be effective. There is also a segment of the the arc chamber. This paper will demonstrate semiconductor market that still can use legacy node devices. Maximizing the equipment performance of legacy implanters the advantages of mixing only hydrogen (H ) with 2 through the use of gas mixtures, is the focus of this paper. enriched 11Boron Trifluoride to increase source life on an Applied Materials (Varian) E-500 ion implant Customers of semiconductor devices look for the lowest cost of ownership and best quality, independent of technology node. tool. The use of a single subatmospheric cylinder Entegris’ Vacuum Actuated Cylinder (VAC®) Enriched 11Boron to provide this benefit, makes converting from pure 11 11 Trifluoride ( BF3) and Hydrogen (H2) mixture ( BF3/H2) has pro- 11Boron Trifluoride to the Entegris 11Boron Trifluoride vided source life improvement and lower cost of ownership on mixture simple, easy to maintain, and safe. current implant tool models.1 This paper will explore the bene- 11 fits of using BF3/H2 on older generation equipment as well. Keywords – Ion Implant, Dopant, VAC, Boron Trifluoride, BF3, Hydrogen, H2, Productivity, Beam Current, Source Life. CONFIGURATION OF OLDER MODEL IMPLANTERS Applied Materials (Varian) E-500 Implanter — The E-500 implanter used in this study was config- Control System and Gas Box Compatibility ured as a standard E-500 implanter with Bernas style source and a gas box that holds four cylinders. The In these implanter models, software systems use results of a comparison of 11BF3 and VAC 11BF /H microprocessors mainly for analog and digital selec- 3 2 mixture demonstrated improved source life and tion of the gas dopant and flow rate control. In some lower cost of ownership using the 11BF /H mixture. cases, software or hard-wired interlocks pre- 3 2 vented the gas control system from having any flexibility beyond flowing gas from a single cylinder. This limitation presents an issue as co-flowing multiple TUNGSTEN TRANSPORT DUE TO HALOGEN CYCLING gases into the ion source is not possible without — significant hardware and software retrofits. These This paper presents the results of improving source retrofits are not always available on older tools. life by utilizing a mixture of 11BF /H , however, it Therefore, to gain the performance bene- 3 2 should be noted that ion source performance is fits that are enabled with 11BF /H mixtures, which will 3 2 similarly improved when employing the same be described later in this paper, it is imperative that approach on other fluoride dopants, such as GeF4 the solution be in the form of a precision mixture in and SiF4. The presence of fluorine in the arc cham- a single cylinder. The Entegris 11BF /H product which 3 2 ber allows fluorine radicals to be created in the ion was used to generate the data presented in this paper plasma. These radicals etch the relatively cooler was a single cylinder containing an optimized mixture tungsten or molybdenum arc chamber walls or liner concentration for this application. and deposit the tungsten or molybdenum on the hotter filament in the ion source.2 The transport of Along with control system limitations in older gen- the tungsten material from the arc chamber to the eration implanters, previous semiconductor device filament increases the mass of the filament. When requirements were limited to the typical primary the filament mass increases, the filament power dopants of arsine, phosphine and boron. The stand- supply cannot sufficiently heat the filament. This ard gas box allowed four cylinders to be installed. limits the generation of electrons needed to sustain 11 Again, the Entegris BF3/H2 product is designed to the ion source plasma. work in older gas boxes, by replacing the single boron 11 The addition of inert gases to enhance cathode cylinder with a single BF3/H2 mixture cylinder. sputtering has very little effect on cathode weight For high volume semiconductor manufacturing, change. Just using hydrogen will achieve equivalent the use of co-flow gases to control tungsten trans- cathode weight changes of non-fluorine gases.3 11 port is critical, though the mechanism by which this Adding the correct amount of H2 in the BF3 gas control is achieved is complex. To provide optimal cylinder creates a mixture that provides enough beam performance, interactions between primary gas hydrogen to combine with the fluorine radicals and co-flow gas need to be understood, and precise thereby reducing tungsten transport, but not stop tuning and adjustments to electrical settings of the arc it completely. This allows some tungsten to deposit chamber need to be performed. Ion mass spectrum on the cathode and replace cathode mass loss during analysis is required to maximize the desired ion frag- non-fluorine gas operation. The introduction of other ments, while minimizing the generation of unwanted gas species in addition to the primary dopant and 4 ions.3 Legacy implanters do not have the control H2 may needlessly complicate the gas mixture. systems to manage these complex interactions of co-flow gases, or require expensive upgrades if available. 2 11 Without the 11BF3 /H2 mixture, the metal that deposits BF3/H2 RESULTS on the filament during the tungsten transport mech- — anism, does not deposit evenly. This results in incon- Key performance metrics for ion implantation include sistent mass across the filament such that there are 11 many process aspects which BF3/H2 successfully regions which have additional tungsten and other passed. The equipment related parameters are the areas that have eroded tungsten. Providing the correct focus of this report. amount of H2 to balance the radical fluorine but not contribute to filament erosion is critical to ensuring Beam current performance can affect equipment optimized source life performance. throughput, and impact process module cycle time. A comparison of the beam current data over time During the product development phase, highly suggest no change in beam performance as shown controlled experiments focused on the effects in Fig 3. The vertical line on sample 16 is the date 11 of tungsten transport were studied. During these the material supply changed from 11BF3 to BF3/H2. 11 experiments, the arc chamber component weight The use of a two-sample t-test to compare the BF3 11 changes were analyzed as a function of the mixture mean beam current and the BF3/H2 mean beam concentration in order to gain insight on the source current, revealed the two means were not signifi- life performance.4 In preparing the mixture for this cantly different (p=0.774). application, testing was completed to understand 1 the hydrogen concentration which would provide + BF₃/H₂ Spectrum BF BF₂+ the best performance.2 0.75 11 0.5 B+ VAC BF3/H2 QUALIFICATION PLAN + — Beam Current (mA) F With all process material changes, process quali- 0 fication testing is required to ensure there is no 285 11 14 17 20 23 26 29 32 35 38 41 44 47 50 Atomic Mass Unit unintended impact to device parameters. In the testing presented in the following sections, the Figure 1. AMU spectrum qualification plan included verifying beam spectrum, sheet resistance, source lifetime and comparing the 280 Sheet resistance 11 ® 11 Identified results with VAC BF3/H2 to Entegris’ SDS 3 BF3. 275 equipment issue The initial qualification test was to run an Atomic 270 Mass Spectrum (AMU) scan to verify that there were m 265 Oh no unexpected changes with 11BF /H ; the results 3 2 260 are shown in Fig 1. The process team’s analysis con- 11 255 firmed that the standard BF3/H2 recipe showed only expected isotopes. Hydrogen, which is an active 250 195 13 17 21 25 29 33 37 41 45 49 53 57 61 component of the mixture, was almost undetectable. Samples The next qualification step was to check Sheet Figure 2. Sheet resistance Resistance (Rs). Several months of baseline Rs data 11 1.4 was compared to test results after installing BF3/H2. The vertical line by sample 17 in Figure 2 identifies the 1.2 Beam current trend 11 point in time where the BF3/H2 cylinder was installed. 1.0 The outlier values have been identified by comment 0.8 boxes with an assignable cause not related to 11BF /H . 3 2 0.6 Analysis by the process team found no significant 0.4 change to sheet resistance after the introduction Beam Current (mA) 11 0.2 of BF3/H2.