Achieving high-yielding designs in the state of the art, VLSI
Very-large-scale integration is the process of creating integrated circuits by combining thousands of transistors into a single chip. VLSI began in the 1970s when complex semiconductor and communication technologies were being developed. The microprocessor is a VLSI device.The first semiconductor...
technology has become an extremely challenging task due to the miniaturization as well as the complexity of leading-edge products. The design methodology called design for manufacturability
) includes a set of techniques to modify the design of integrated circuit
An integrated circuit or monolithic integrated circuit is an electronic circuit manufactured by the patterned diffusion of trace elements into the surface of a thin substrate of semiconductor material...
s (IC) in order to make them more manufacturable, i.e., to improve their functional yield, parametric yield, or their reliability.
Traditionally, in the prenanometer era, DFM consisted of a set of different methodologies trying to enforce some soft (recommended) design rules regarding the shapes and polygons of the physical layout of an integrated circuit
Integrated circuit layout, also known IC layout, IC mask layout, or mask design, is the representation of an integrated circuit in terms of planar geometric shapes which correspond to the patterns of metal, oxide, or semiconductor layers that make up the components of the integrated circuit.When...
. These DFM methodologies worked primarily at the full chip level. Additionally, worst-case simulations at different levels of abstraction were applied to minimize the impact of process variations on performance and other types of parametric yield loss. All these different types of worst-case simulations were essentially based on a base set of worst-case (or corner) SPICE
SPICE is a general-purpose, open source analog electronic circuit simulator.It is a powerful program that is used in integrated circuit and board-level design to check the integrity of circuit designs and to predict circuit behavior.- Introduction :Unlike board-level designs composed of discrete...
device parameter files that were intended to represent the variability of transistor performance over the full range of variation in a fabrication process.
Taxonomy of yield loss mechanisms
The most important yield loss models (YLMs) for VLSI ICs can be classified into several categories based on their nature.
- Functional yield loss is still the dominant factor and is caused by mechanisms such as misprocessing (e.g., equipment-related problems), systematic effects such as printability or planarization problems, and purely random defects.
- High-performance products may exhibit parametric design marginalities caused by either process fluctuations or environmental factors (such as supply voltage or temperature).
- The test-related yield losses, which are caused by incorrect testing, can also play a significant role.
Design for manufacturability
After understanding the causes of yield loss, the next step is to make the design as resistant as possible. Techniques used for this include:
- Substituting higher yield cells where permitted by timing, power, and routability.
- Changing the spacing and width of the interconnect wires, where possible
- Optimizing the amount of redundancy in internal memories.
- Substituting fault tolerant (redundant) vias in a design where possible
All of these require a detailed understanding of yield loss mechanisms, since these changes trade off against one another. For example, introducing redundant vias
A via is a vertical electrical connection between different layers of conductors in a physical electronic circuit.- In IC :In integrated circuit design, a via is a small opening in an insulating oxide layer that allows a conductive connection between different layers. A via on an integrated circuit...
will reduce the chance of via problems, but increase the chance of unwanted shorts. Whether this is good idea, therefore, depends on the details of the yield loss models and the characteristics of the particular design.
- Electronic design automation
Electronic design automation is a category of software tools for designing electronic systems such as printed circuit boards and integrated circuits...
- Critical area
-Aviation:In aviation, a critical area refers to a designated area of an airport that all aircraft must remain clear of when another aircraft is inbound on an ILS approach. The critical area should be avoided when the weather is less than or equal to 2 miles visibility or less than or equal to...
- Reliability engineering
Reliability engineering is an engineering field, that deals with the study, evaluation, and life-cycle management of reliability: the ability of a system or component to perform its required functions under stated conditions for a specified period of time. It is often measured as a probability of...
- Six Sigma
Six Sigma is a business management strategy originally developed by Motorola, USA in 1986. , it is widely used in many sectors of industry.Six Sigma seeks to improve the quality of process outputs by identifying and removing the causes of defects and minimizing variability in manufacturing and...
- Statistical process control
Statistical process control is the application of statistical methods to the monitoring and control of a process to ensure that it operates at its full potential to produce conforming product. Under SPC, a process behaves predictably to produce as much conforming product as possible with the least...