The Making of an ASICThe process of designing and productionising a mixed signal application specific integrated circuit with SWINDON Silicon Systems www.swindonsilicon.co.uk
SWINDON Silicon SystemsAnalogue and mixed signal ASICs | A completely integrated service | From design concept through to production supply Founded 1978 Fab-less business model Full turnkey design and supply offering 2010 - £18M turnover 70 employees 2010 – shipped 34 million tested devices HQ Design + Testing Centre Production ATE test facility Full device characterisation capability Obsolescence guarantee TS 16949 Accreditation Just 1 hour from London Heathrow
ContentsThe Design Process An informative guide Specification to the process ofDesign and Layout designing and productionising a Processing mixed signal Evaluation application specific integrated circuitTest Development with Qualification SWINDON Silicon Production Systems
The Design Process - Part 1 The ASIC Development Process provides a proven roadmap for complete Product Development1. Application Review 4. Initial Design & Layout – Complete Critical Circuits design – Review of your system requirements – Complete preliminary ASIC Floor Plan – Establish ASIC requirements – Complete Built-In Test features2. ASIC Quotation 5. Critical Design Review – Non-Recurring Engineering (NRE) – Review Critical Circuit performance – Estimated Unit Price (in Production) – Report physical layout status – Development Schedule 6. Final Design & Layout – Complete Cell Level designs3. Preliminary Design Review – Complete Top Level design – Review Block Diagram – Simulate over temperature | voltage – Establish Specification – Complete Design Rule Checks (DRCs) – Establish Packaging Requirements – Complete Layout Vs. Schematic (LVS) – Prepare Test Plans – Establish Test Requirements – Review Schedule – Establish target Die Size – Establish Fabrication Process
The Design Process – Part 2 The ASIC Development Process provides a proven roadmap for complete Product Development7. Final Design Review 10. Prototype Evaluation Review Simulations SWINDON tests Prototype at wafer probe Review Test Plans SWINDON tests Prototype in package Review Physical Layout Customer evaluates Prototype Proceed to Fabrication8. Prototype Fabrication 11. Prototype Acceptance Review ASIC performance versus Specification Mask Fabrication Reliability Testing Review Silicon Fabrication Yield Analysis Review9. Test Program Development Proceed to Production Prototype Test Program Preliminary Production Test Program
The Importance of SpecificationThe specification phase is an extremelyimportant part of the design process asany errors that occur here will bemagnified further down the process.That is why SWINDON assists itscustomers in developing the systemsspecification and advises as to what canbe achieved on chip.The full ASIC specification is thenproduced by the relevant SWINDONtechnical lead engineer and this will besigned off by all parties concerned.This extensive process can usually takebetween 4 and 12 weeks depending uponthe complexity of the device that is beingdesigned.
The Specification Process1. Review of the system schematics, block diagrams and specifications.2. Develop an understanding of the design challenges, operating environment and regulatory requirements3. Understand the final product (not just the ASIC) including any certification requirements such as IEC, TS compliance.4. Produce an ASIC block diagram and full specification that states full operational parameters and pin out and any required external components.5. Identify board level architectural trade- offs that lead to most cost effective silicon integration.
Design – A simplistic example1 • Assign Technical Lead, Project Manager and Design Team2 • Determine process3 • System level design, block specification and Floor plan4 • Block level design/simulation and IP block insertion5 • Design for Test (DFT)6 • Synthesis and verification7 • Layout8 • DRC and LVS9 • Takeout
1. Design and Layout • A Top Down design approach is adopted for the Project • Partitioning the chip into Functional blocksSystem level • Defining their functionality and writing a specification fordesign block each blockspecification • Writing a behavioural model (analogue or digital), which is used to verify that the design meets its requirements. • Writing a simulation plan which describes the method of proving the design correctness • A top level chip floor plan is produced that defines the area and shape of each functional block. Along with its interconnection to other blocks. The block areas are design Floor plan goals for each block. These terms will be assessed and the floor plan updated as the project progresses.
2. Design and LayoutFor mixed signal designs there are 2 procedures run in parallel: Analogue | Digital • Analogue Design • Circuit blocks are designed at the transistor level and simulated using a HSPICE compatible simulator. • Simulation results are verified against the block specification and the VerilogA behavioural model. • Digital Design Block level design / • Writing a synthesizable RTL (register simulation transfer level) description (either on Verilog or VHDL) of the device. • Writing a behavioural model, which is used to verify that the design meets its requirements. • Writing a verification plan and a corresponding verification environment which describes and implements the method of proving the design correctness
3. Design and Layout • The RTL description is verified against the behavioural model. • This approach reduces the probability of the design error since no RTLVerification designer tests his own code.
4. Design and Layout • Most mixed signal ASIC designs are complex require built in assistance in order to be able to production test effectively. These preparations are called DFT (design for test). • For the analogue sections it is important that key signals can be observed in the analogue blocks. This may require the routing of internal test points to device pads. • For the Digital section of the design DFT techniques include:Design for Test • Scan path insertion - a methodology of linking all registers into one long shift register (scan path). This can (DFT) be used to check small parts of design instead of the whole design (the latter being almost always impossible). • BIST (built-in self test) - a device used to check RAMs. After being triggered it feeds specific test patterns to the RAM module, reads back and compares results. • ATPG (automatic test pattern generation) - a method of creating test vectors for scan paths and BIST automatically. Most modern EDA tool chains incorporate such a feature.
5. Design and Layout • The synthesizable and verified RTL undergo logic synthesis. The synthesized reads RTL input, user-specified constraints and aSynthesis cell library from the foundry. The output of the synthesis process is a gate-level netlist. • The netlist must undergo formal verification to prove that RTL and netlist are equivalent. Netlist • Preliminary timing results after synthesis are analyzed, critical paths are checked against the project performance requirements. If needed, the RTL description, constraints or Checks synthesis options are modified, and the synthesis is repeated.
6. Design and Layout • Analogue • This often requires hand crafting of the layout at a transistor level to construct customised analogue functions . • The size and shape being dictated by the floorplan. These blocks can subsequently be interconnected at the top level. • On completion of the blocks the circuits will be back- extracted and resimulated in order to account for layout parasitics. • DigitalLayout • When timing constraints are finally met, the design proceeds to the layout, which consists of floorplanning, placement and routing. • Some other important tasks are performed at this step, including clock tree insertion.
7. Design and Layout • The last stage before tape out includes the following checks: • DRC (design rule check) is a check that the layout DRC conforms to the foundry-specific rules.and LVS • LVS (layout versus schematic) is a formal equivalence check between the post-synthesis netlist and the final layout. • At last the resulting layout in GDSII format is handed to the semiconductor fabrication plant (foundry).Tapeout • This process is called tape out.
1. Wafer ProcessingThe Czochralski Process – A typical wafer is made out of extremely pure silicon that is grown into mono- crystalline cylindrical ingots (boules) up to 300 mm (slightly less than 12 inches) in diameter using the Czochralski process. – These ingots are then sliced into wafers about 0.75 mm thick and polished to obtain a very regular and flat surface. – Once the wafers are prepared, many process steps are necessary to produce the desired semiconductor integrated circuit. In general, the steps can be grouped into two major parts: Front-end-of-line (FEOL) processing Back-end-of-line (BEOL) processing
2. Wafer ProcessingDeposition Removal processes – Any process that grows, coats, or – Any that remove material from the otherwise transfers a material onto wafer either in bulk or selectively and the wafer. consist primarily of etch processes, – Available technologies consist of either wet etching or dry etching. • Physical vapour deposition (PVD) – Chemical-mechanical planarisation • Chemical vapour deposition (CVD) (CMP) is also a removal process used • Electrochemical deposition (ECD) between levels. • Molecular beam epitaxy (MBE) • More recently, atomic layer deposition (ALD) …among others.
3. Wafer ProcessingPatterning – The series of processes that shape or alter the existing shape of the deposited materials and is generally referred to as lithography. – For example, in conventional lithography, the wafer is coated with a chemical called a photoresist. The photoresist is exposed by a stepper, a machine that focuses, aligns, and moves the mask, exposing select portions of the wafer to short wavelength light. – The unexposed regions are washed away by a developer solution. After etching or other processing, the remaining photoresist is removed by plasma ashing.Modification of electrical properties – Historically consisted of doping transistor sources and drains originally by diffusion furnaces and later by ion implantation. – These doping processes are followed by furnace anneal or in advanced devices, by rapid thermal anneal (RTA) which serve to activate the implanted dopants. – Modification of electrical properties now also extends to reduction of dielectric constant in low-k insulating materials via exposure to ultraviolet light in UV processing (UVP).
4. Wafer Processing - FEOLFEOL processing – The formation of the transistors directly in the silicon. The raw wafer is engineered by the growth of an ultrapure, virtually defect-free silicon layer through epitaxy. – In the most advanced logic devices, prior to the silicon epitaxy step, tricks are performed to improve the performance of the transistors to be built. – One method involves introducing a straining step wherein a silicon variant such as silicon-germanium (SiGe) is deposited. Once the epitaxial silicon is deposited, the crystal lattice becomes stretched somewhat, resulting in improved electronic mobility. – Another method, called silicon on insulator technology involves the insertion of an insulating layer between the raw silicon wafer and the thin layer of subsequent silicon epitaxy. This method results in the creation of transistors with reduced parasitic effects.Gate oxide and implants – Front-end surface engineering is followed by: growth of the gate dielectric, traditionally silicon dioxide (SiO2), patterning of the gate, patterning of the source and drain regions, and subsequent implantation or diffusion of dopants to obtain the desired complementary electrical properties. – In dynamic random access memory (DRAM) devices, storage capacitors are also fabricated at this time, typically stacked above the access transistor.
5. Wafer Processing - BEOLMetal Layers – Once the various semiconductor devices have been created, they must be interconnected to form the desired electrical circuits. – This occurs in a series of wafer processing steps collectively referred to as BEOL (not to be confused with back end of chip fabrication which refers to the packaging and testing stages). – BEOL processing involves creating metal interconnecting wires that are isolated by dielectric layers. – The insulating material was traditionally a form of SiO2 or a silicate glass, but recently new low dielectric constant materials are being used. – These dielectrics presently take the form of SiOC and have dielectric constants around 2.7 (compared to 3.9 for SiO2), although materials with constants as low as 2.2 are being offered to chipmakers.
6. Wafer Processing - BEOLInterconnect – Synthetic detail of a standard cell through four layers of planarized copper interconnect, down to the polysilicon, wells and substrate. – More recently, as the number of interconnect levels for logic has substantially increased due to the large number of transistors that are now interconnected in a modern chip, the timing delay in the wiring has become significant prompting a change in wiring material from aluminium to copper and from the silicon dioxides to newer low-K material. – As the number of interconnect levels increases, planarization of the previous layers is required to ensure a flat surface prior to subsequent lithography. Without it, the levels would become increasingly crooked and extend outside the depth of focus of available lithography, interfering with the ability to pattern.
7. Processing – Prototyping There are two methods of prototyping the first silicon MPW |MLMMulti Product Wafer (MPW)• Shared silicon technology for the parallel processing of several devices on one wafer• Delivery of dies or ceramic samples Benefits: • Development charges significantly reduced Disadvantages: • Fixed start dates and lead times • Only a small number of untested samples available • No volume production with these masks
8. Processing – Prototyping There are two methods of prototyping the first silicon MPW |MLMMulti Level Mask (MLM)• 4 mask levels drawn on the same reticule• Mask costs reduced down to 1/4 for all technology nodes Benefits: • Flexible tape-in dates • Start-stop options and design revisions possible Disadvantages: • No volume production with these masks
9. Processing – Wafer ThinningWafer Thinning – A semiconductor device fabrication step during which wafer thickness is reduced to allow for stacking and high density packaging of integrated circuits (IC). – ICs are being produced on semiconductor wafers that undergo a multitude of processing steps. The silicon wafers predominantly being used today have diameters of 20 and 30 cm. They are roughly 750 μm thick to ensure a minimum of mechanical stability and to avoid warping during high-temperature processing steps. – The backside of the wafers are ground prior to wafer dicing (where the individual microchips are being singulated). Wafers thinned down to 75 to 50 μm are common today. The process is also known as ‘Backlap’ or Wafer backgrinding‘.
10. Processing – Wafer DicingWafer Dicing – The process by which die are separated from a wafer of semiconductor following the processing of the wafer. The dicing process can be accomplished by scribing and breaking, by mechanical sawing (normally with a machine called a dicing saw) or by laser cutting. Following the dicing process the individual silicon chips are encapsulated into chip carriers . – During dicing, wafers are typically mounted on dicing tape which has a sticky backing that holds the wafer on a thin sheet metal frame. Once a wafer has been diced, the pieces left on the dicing tape are referred to as die, dice or dies. These will be packaged in a suitable package or placed directly on a printed circuit board substrate as a "bare die". The area that has been cut away are called die streets which are typically about 75 micrometres (0.003 inch) wide. – The die created may be any shape generated by straight lines, but they are typically rectangular or square shaped.
1. Packaging - DevelopmentEarly Flat Packs – The earliest integrated circuits were packaged in ceramic flat packs, which continued to be used by the military for their reliability and small size for many years. Commercial circuit packaging quickly moved to the dual in-line package (DIP), first in ceramic and later in plasticPGA & LCC – In the 1980s pin counts of VLSI circuits exceeded the practical limit for DIP packaging, leading to pin grid array (PGA) and leadless chip carrier (LCC) packages. Surface mount packaging appeared in the early 1980s and became popular in the late 1980s, using finer lead pitch with leads formed as either gull- wing or J-lead, as exemplified by small-outline integrated circuit — a carrier which occupies an area about 30 – 50% less than an equivalent DIP, with a typical thickness that is 70% less. This package has "gull wing" leads protruding from the two long sides and a lead spacing of 0.050 inches.Small Outline Integrated Circuits – Small-outline integrated circuit (SOIC) and Plastic leaded chip carrier (PLCC) packages. In the late 1990s, plastic quad flat pack (PQFP) and thin small-outline packages (TSOP) became the most common for high pin count devices, though PGA packages are still often used for high-end microprocessors.
2. Packaging – BGD | SiPBall grid array (BGA) packages – Have existed since the 1970s. Flip-chip Ball Grid Array packages, which allow for much higher pin count than other package types, were developed in the 1990s. – In an FCBGA package the die is mounted upside-down (flipped) and connects to the package balls via a package substrate that is similar to a printed-circuit board rather than by wires. – FCBGA packages allow an array of input- output signals (called Area-I/O) to be distributed over the entire die rather than being confined to the die periphery.System in a Package (SiP) – When multiple dies are stacked in one package, it is called SiP, for System In Package, or three-dimensional integrated circuit. – When multiple dies are combined on a small substrate, often ceramic, its called an MCM, or Multi-Chip Module.
3. Packaging – QFN Part 1QFN – Flat no-leads packages such as QFN (quad- flat no-leads) and DFN (dual-flat no-leads) physically and electrically connect integrated circuits to printed circuit boards. Flat no-leads, also known as MicroLead Frame, is a surface-mount technology, one of several package technologies that connect ICs to the surfaces of PCBs without through-holes. – Flat no-lead is a near chip scale package plastic encapsulated package made with a planar copper lead frame substrate. Perimeter lands on the package bottom provide electrical connections to the PCB. – Flat no-lead packages include an exposed thermal pad to improve heat transfer out of the IC (into the PCB). Heat transfer can be further facilitated by metal vias in the thermal pad. The QFN package is similar to the quad-flat package, and a ball grid array.
4. Packaging – QFN Part 2QFN packages – Two types of QFN packages are common: air-cavity QFNs, with an air cavity designed into the package, and plastic-moulded QFNs with air in the package minimized. Plastic Moulded QFN – Less-expensive plastic-moulded QFNs usually limited to applications up to ~2–3 GHz. – It is usually composed of just 2 parts, a plastic compound and copper lead frame, and does not come with a lid. Air-cavity QFN – In contrast, the air-cavity QFN is usually made up of 3 parts; a copper lead frame, plastic-moulded body (open, and not sealed), and either a ceramic or plastic lid. – It is usually more expensive due to its construction, and can be used for microwave applications up to 20–25 GHz.QFN packages can have a single row of contacts or a double row of contacts.
5. Packaging – Flip ChipFlip chip | C4 – Flip chip, also known as Controlled Collapse Chip Connection or its acronym, C4, is a method for interconnecting semiconductor devices, such as IC chips and Microelectromechanical systems (MEMS), to external circuitry with solder bumps that have been deposited onto the chip pads. – The solder bumps are deposited on the chip pads on the top side of the wafer during the final wafer processing step. In order to mount the chip to external circuitry (e.g., a circuit board or another chip or wafer), it is flipped over so that its top side faces down, and aligned so that its pads align with matching pads on the external circuit, and then the solder is flowed to complete the interconnect. – This is in contrast to wire bonding, in which the chip is mounted upright and wires are used to interconnect the chip pads to external circuitry.
6. Packaging – Flip Chip ProcessIntegrated circuits are created on the wafer Pads are metalized on the surface of the chips Solder dots are deposited on each of the pads Chips are cut Chips are flipped and positioned so that the solder balls are facing the connectors on the external circuitry Solder balls are then re-melted (typically using hot air reflow) Mounted chip is “under-filled” using an electrically-insulating adhesive
ASIC Initial EvaluationJoint Evaluation – Device evaluation is conducted by both the SWINDON design team and also the customer. – The design team will evaluate the device as a stand alone component and the customer will evaluate the device within it’s system. – It is preferably conducted on identical evaluation boards and set up in order to be able to accurately correlate results.Initial evaluation: - Power up. Turn on the power supply and check the mains fuse has not blown, if not check current consumption in key modes. Check functionality either, optimistically, everything at once or block by block then a full functional test. Look at the performance aspects (accuracy, speed, settling time etc.) that are key performance aspects to the chip for a few samples at room temperature..
ASIC Full EvaluationFunctional and Parametric – Once the initial checking has been completed then a full evaluation (functional and parametric) against the specification is then carried out. – This is conducted over the environmental window (temperature and voltage), over a limited number of samples (5 to 10), all according to the evaluation schedule. T – his schedule should be in existence well before the initial prototype chips arrive at the respective companies.Parallel Testing – In parallel samples will go to the test department so that ATE development can proceed. – This will need a large number of samples to be tested to ensure that the functional and parametric yield is up to expectation.
ASIC Test Development Part 1The Test Development phase Consists of developing the tests for the state of the art ASICs. It is conducted in close co-operation with the design team to develop DFT strategies, test methods, verify test structures through simulation and generate test vectors.This phase covers the following areas: 1. Structural tests - Develop test vectors for ATPG/JTAG/IDDQ. 2. Memory Tests - Develop test vectors for embedded memories. 3. Develop tools to support Failure analysis and Yield enhancement teams to physically located failure locations on the chip. 4. Mixed-signal tests - Develop test vectors for on-chip PLLs, DACs, ADCs, and other analog/RF blocks. 5. Functional tests - Develop broadside functional/Fmax test vectors for embedded controllers and DSP cores. 6. Behavioural Modelling - Develop analog models (DAC, ADC, PLL, up/down converters and amplifiers) for pre-silicon verification and test vector generation.
ASIC Test Development Part 2Automatic Test Equipment (ATE ) – The aim is for the implementation of these test vectors and methodologies on Automatic Test Equipment (ATE) during first silicon debug, characterization, and production. – The required skills to perform this critical function includes; Strong knowledge of DFT: ATPG, JTAG, IDDQ, At-speed ATPG, fault simulation, fault analysis. Knowledge of Iddq test techniques and At-speed ATPG including transition and path delay Strong knowledge of test bench development, simulation debug, behavioural model development.
ASIC Test Development Results• Bespoke Test Regime – The results of this work in a bespoke test regime for the ASIC under test and includes; Fully automated wafer and package level test Fully automated, online test and QA procedures 100% wafer level test, each device 100% package level test, each package Real-time yield statistics Wafer and package level tests correlated 100% Datalog, each device Tri temperature test PPM field failure rate sub 1ppm
ASIC Production The production of the ASIC comprises many aspects of areas that have already been covered.1. Production Acceptance Review 5. Package Testing – Prototypes are reviewed for – Packages are typically tested at CSS Production Suitability – Test Program is Custom Made2. Wafer Fabrication – Delivery in rails, tape & reel or – Production Orders from Silicon waffle packs (die) Fabricator 6. Production Reports3. Wafer Probe – Probe and Package Test Data is – Die are tested at wafer level at CSS analysed by Quality Engineering – Test Program is Custom Made for and your ASIC – Yield and Statistical Process Control – Key Product Characteristics (KPCs) information is available to ASIC are collected for Statistical Process customers. Control 7. Order Fulfilment and Logistics4. Packaging Forecasting – A wide variety of packages are – Supply Chain Management available, as well as die delivery – Support functions
Fulfilment and Logistics In-house capabilitiesIt is hugely preferential if your ASIC supplier has many of the fulfilment and logisticscapabilities in house. This will provide a much more risk averse supply chain andSWINDON offers the complete service. From forecasting to shipping… Supply Chain Warehousing OrderForecasting Management Manufacturing / Shipping Management
Fulfilment and Logistics Support FunctionsThe support functions that your ASIC supplier provides can be critical in order for yourcompany to perform to its highest level. SWINDON offers the highest support…. Environmental Warranty and Resource Operations FinancialsHealth and Safety Returns Management Support
10 Reasons why… SWINDON makes a good choice for your next ASIC projectDesign and productionisation expertiseGained over 30 years of successful projectsFixed development costs and unit pricesDesign ownershipProduction supplyIn house wafer probe and ATE production testLifetime product supportFinancial stabilityQualityPartnership Approach
• We have a full range of resources from case histories to planning checklists• Please visit our web site www.swindonsilicon.co.uk• Or contact us Headquarters & Design Centre Swindon Silicon Systems Limited Radnor Street Swindon Wiltshire SN1 3PR United Kingdom Tel: +44 (0) 1793 649400 email: email@example.com