Suresh Biligiri, Vice President Rorze Automation 07/08/14 Managing Oxide growth, on in-process storage wafers for cost & yield impact Suresh Biligiri, Vice President Rorze Automation 07/08/14

Agenda Introduction Impact of undesired oxidation on wafers Cost & process sensitivity trends Impact of undesired oxidation on wafers Bare wafer stocker with nitrogen purge oxygen concentration data (Static & dynamic) Oxide growth data Wafer cleaning per wafer pass costs Oxide growth mitigation Conclusion                    

Introduction Cost trend with technology node migration:One of the key drivers of cost is the increasing sensitivity of process that requires tight control and management of process variables. Source: International Business Strategies (IBS)

Impact of undesired oxidation The variation in oxide thickness can dictate the yield of process and product quality resulting in large spread in the speed and power consumption of integrated circuits especially with the device shrinkage below 32 nm. (References: S. Borkar et al., "Parameter Variations and Impact on Circuits and Micro-architecture", DAC, 2003, pp. 338-342 & article IMPACT OF STRAIN AND CHANNEL THICKNESS ON PERFORMANCE OF BIAXIAL STRAINED SILICON MOSFETs by Neha Sharan, Ashwani K.Rana in International Journal of VLSI design & Communication Systems (VLSICS) Vol.2, No.1, March 2011, DOI : 10.5121/vlsic.2011.2106 61).

Level of Process Sensitivity References: S. Borkar et al., "Parameter Variations and Impact on Circuits and Micro-architecture", DAC, 2003, pp. 338-342

Impact of undesired Oxide growth A typical wafer goes through a clean cycle prior to wafer move. Chemical waste handling costs are involved to handle, treat and dispose If the oxide growth levels are uncertain Metrology of wafer before wafer move is required adding costs to the process. If the oxide growth has exceeded the specification Re-cleaning required, adding direct cleaning, handling & tool related costs Impact of re-clean, due to stringent environmental controls and corporate responsibility in green initiatives, the cost of handling the waste chemicals will have a cost impact greater than the first cleaning. Each time a wafer is handled, the risk of yield loss increases impacting cost When a fab utilization is approaching Max. feasible, the re-clean adds opportunity costs and a negative impact on production volumes.

oxide growth mitigation Oxide growth studies were conducted in a fab in US, using a Rorze bare wafer stocker (BWS 1600 N2) Here wafers are stored in a nitrogen purged environment The wafers are stored in Rorze designed POD’s that minimizes nitrogen usage while also minimizing wafer interaction with ambient air (oxygen & water) during wafer handling Wafers are stored in different locations in the tool to ensure the stored wafer environment is uniform A set of wafers are also stored in open fab environment Wafers are measured

Bare wafer stocker with N2 purge Rorze BWS3200 N2

Bare wafer stocker with N2 purge Rorze BWS1600 N2

Wafer storage environment View from rear of Rorze BWS1600/3200 N2

O2 concentration during purge

O2 concentration during handling

Oxide growth data Oxide data obtained using “Rudolph S3000A” system

Oxide growth measurements BWS600 BWS1600/3200 N2 Data obtained using “Rudolph S3000A” on Day1, 3, 6, 7 10, 14 & 21

wafer cleaning per wafer pass cost Cost per wafer pass pass using DI water based cleaning only: $1.90* per wafer pass - 300mm wafer Cost per wafer using standard chemicals without the IPA: $2.30* per wafer pass – 300mm wafer Cost per wafer pass using standard chemicals + IPA: $ 3.60* per wafer pass– 300mm wafer – This includes the reprocess cost of IPA Source: Data reference provide by Mr. Rob Randhawa of Planar Semiconductor, based on Sematech model that takes into account the cost of materials, capital tool costs, uptime in the fab etc. * These cost figures are likely higher now as data is not current

Annual cost of re-cleaning Annual cost of wafer reclean @ Cleaning Process Cost/Wafer ($) 10K Wafers/Mo 20K Wafers/Mo 30K Wafers/Mo 40K Wafers/Mo Clean with DI Water only $1.90 $228,000 $456,000 $684,000 $912,000 Clean with Std Chemicals & No IPA $2.30 $276,000 $552,000 $828,000 $1,104,000 Clean with std. chemical + IPA $3.60 $432,000 $864,000 $1,296,000 $1,728,000 Source: SEMATECH model provided by Mr. Rob Randhawa, Planar Semiconductors

Oxide growth mitigation Ensure the cleaning does not leave residue that could cause/accelerate oxidation Eliminate or minimize wafer exposure to moisture and oxygen in process & handling Minimize wafer delays in between process Minimize storage times Minimize wafer interaction with Oxygen and water during storage

Other oxide growth mitigation Bottom purge load-ports that can keep the nitrogen flow in to the LP while wafers are on the process tool minimizing wafer interaction with O2 & H2O Shower type load-ports that can be a stand alone tool that will purge the LP with N2 for short term handling This does not require special FOUP OR FOSB and can be done on standard FOUP & FOSB Rorze has patent pending products that actually keeps a wafer under nitrogen flow even while handling if required

Conclusions Undesired wafer Oxidation is becoming a major issue as we are approaching atomic layers for process thickness HF strip/cleaning to rid of undesired oxide layer is limited on advanced nodes which can cause yield loss or device loss Oxide growth mitigation options are available including while handling each wafer in and out of process while in opened FOUP Adoption of new Nitrogen purge technologies pays for itself Estimated cost savings of minimum of about $900K per year to over $1.7 million per year based on number of wafer pass/ wafer re-clean and type of cleaning

Conclusion Thank YOU