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Adaptable IC Manufacturing systems for the 21st century
MICROELECTRONIC ENGINEERING
ELSEVIER
Microelectronic
Engineering 25 (1994) 131-137
Adaptable IC Manufacturing Systems for the 21st Century Krishna C. Saraswat Department of Electrical Engineering Stanford University, Stanford, CA 95304. USA
Abstract The semiconductor industry is currently facing a number of challenges. The capital costs of IC factories and the cost of developing technology are increasing at a faster rate than the revenues. In addition, demand for ICs is fragmenting into lower volume and more differentiated markets. The current chip manufacturing approach is establishing megafactories for slow mass production of commodity products. To remain competitive alternative design and manufacturing techniques will have to be developed with flexible factories for rapid production of multiple products in different technologies. At Stanford University we have built a large interdisciplinary program aimed at exploring radically different semiconductor manufacturing opportunities. The approach is to build a highly flexible computer controlled manufacturing facility - the Programmable Factory and in parallel with this factory, a suite of simulation tools the Virtual Factory which emulate all functions of the real factory. Economic modeling suggests that such approach may offer more economical small or large scale production, higher flexibility to accommodate many products on several processes, and faster turnaround to hasten product innovation.
1. INTRODUCTION The future success of IC companies will demand rapid innovation, rapid product introduction and ability to react quickly to a change in the technological and business climate of microelectronics. These technological advances in integrated electronics will require
development of flexible manufacturing technology for electronic systems. However, the current chip manufacturing approach is establishing megafactories for mass production of commodity products, as opposed to flexible factories for rapid production of multiple products in different technologies. Alternative manufacturing techniques will have to be developed to remain competitive [ 11. For the past three decades, the semiconductor industry has made immense progress in increasing component densities, decreasing feature sizes and increasing device structure complexity. This progress in VLSI has been achieved through advances in equipment and fabrication technology, resulting in enormous economic benefits for commodity products, for which manufacturing of one kind of chip is done in large quantities. This increased complexity in devices, circuits and technology has resulted in increasingly higher cost of the fabrication facility. This is shown clearly in Figure 1. During the last three decades a 4-mask fabrication process requiring about 25 major steps and a 1 million dollar factory has evolved into a 15 to 20 mask process requiring about 300 steps and a 500 million dollar factory. About 75% of the cost to set up a factory can be attributed to the equipment [2] and with each new generation of the equipment, the average cost per machine has increased by at least 30% [3]. Although the cost per piece of equipment has increased by about 30% per generation, the added complexity of processes requires more pieces of equipment to achieve the same throughput. Thus the total cost of equipment in fabs more than doubles per generation. If this trend continues, well before the turn of the century the entry cost to set up a manufacturing facility will be well in excess of 1 billion dollars [2,3]. There have been enormous advances in circuit design techniques which have contributed to the success of microelectronics. The number of designs manufactured in a year has steadily increased. In 1975 about 200 designs were manufactured worldwide. The number increased to about 2,000 by 1980, to about 12,000 by 1986, and is expected to be in excess of 0167-9317/94/$07.00 0 1994 SSDI0167-9317(94)00009-.I
Elsevier Science B.V. All rights reserved.
132
K.C. Saraswat
I Adaptable
IC manufacturing
systems
100,000 in early the nineties. Whereas in 1975 most of them were produced in large quantities, except for a few commodity chips the number of chips produced per design has steadily decreased. This trend projected to the year 2000 clearly indicates that a company will be required to manufacture many designs and varying in volumes from a few thousand chips to many millions over the life cycle of the design. 500
*
A t
NEC tigubishi
l
Motorola ,Q&VFujitsu
t
; 3
500
”
.
12~.10 mask. 1 OOK
I
m
0
!
1965
i
l
I
I
1970
1975
i
I
I
I
I
1980
c
-m
I
1985
I
1990
I
1995
2000
YEAR
Figure 1. Cost of establishing a factory vs. year for a state-of-the-art chip fabricated that year In the conventional mass manufacturing approach the process development largely relies on experimental techniques as was the case for circuits couple of decades ago. As a result the cost of developing the next generation technology is reaching in excess of $ 100 million and the time from inception to market has increased to about 5 years [4]. This methodology will not be suitable for supporting a flexible manufacturing environment to produce multiple products in multiple technologies. As we look to the 21Sf century it is clear that the conventional mass manufacturing approach has limitations with regard to the economic production of small quantities, faster speed of realization of innovations, faster turnaround time in manufacturing, and research on innovative tools and processes. 2. STANFORDS’ VISION FOR MANUFACTURING
IN THE 21ST CENTURY
At Stanford University we have built a large interdisciplinary program aimed at exploring radically different semiconductor manufacturing opportunities. Manufacturing plants today are characterized by enormous capital costs and inflexibility. They are built to serve one or two generations of technology and usually a narrow product base. New technology development is very expensive and largely empirically done. Competition in such an environment is heavily capital investment driven. Ten years ago, chip designers were facing similar investment problems since new designs were largely hand crafted. Many observers felt that few VLSI applications would be able to justify design costs. The CAD revolution changed all that. Our view is that a similar revolution, driven by the same ideas, can revolutionize manufacturing. The approach [5] as shown in Fig. 2 is to build a highly flexible computer controlled manufacturing facility - the Programmable Factory and in parallel with this factory, a suite of simulation tools the Virtual Factory which emulate all functions of the real factory. Controlling both of these and integrating them is the Manufacturing Automation.
K.C. Saraswat I Adaptable IC manufacturing systems
Df;S%tWJ
F!!iEsF
Library of Circuit modules
Library of Device modules
\ circuit synttleais
133
Library of process modules J ProCesS
1 Devke
technology synthesis Equipment Process Devke circuit Factory
\Lateral Geometries \
\
Vertical Geometries Process Flow 1
/
IC Technology Synthesis
P==r
for MultIpie Products in Multiple technoiogles Single wafer programmable equipment, Cm for speclfkation, monitoring, control and diagnosb Sensors for in-situ measurements
Figure 2. Programmable and virtual factory for design and adaptable IC Manufacturing in the 21st century. The Virtual Factory consists of a hierarchy of models including equipment, processes, devices and circuits to describe the chips that are built in the factory, and a set of factory performance and physical plant models which describe the factory itself. To the extent that these models represent reality, the Virtual Factory can be used to design processes, to assess the manufacturability of a process, to optimize factory throughput, to predict delivery times on products and for a host of other applications. In a very real sense, the Virtual Factory provides the same capability for the process designer and the plant manager, that today’s CAD tools provide for the circuit designer. The same productivity enhancements that have occurred in the chip design area through these tools, should be possible in the manufacturing area. The Programmable Factory is a concept which seeks to emulate the enormous power of abstraction that is possible in a stored program computer. If the factory can be made sufficiently flexible and if that flexibility can be invoked by a stored “program”, then we can build upon the considerable experience of computer science to multiply human productivity. The approach is to develop the “program” which will build chips largely by using the Virtual Factory (Fig. 2). That “program” is, of course, the same representation which drives the emulation of the factory in the Virtual Factory. Secondly, if we can create a new class of multi-function equipment (Fig. 2) which replaces several single-function equipment and simplifies the overall process at the same time, then we open the possibility of making factories affordable to a much larger number of enterprises. Coupled with the automation tools being developed in this program, we seek to empower designers with the ability to create a much larger variety of new products. Finally, if we can instrument these factories sufficiently well to tighten the feedback loop on diagnosis and control, we open the opportunity to dramatically reduce the learning cycle of manufacturing.
134
3. VIRTUAL
K.C. Saraswat
/ Adaptable
IC manufacturing
system.\
FACTORY
The traditional approach to new product or process development in many areas of engineering has been experimental--real experiments on real materials in real laboratories. When a field of science is in its infancy, this approach is likely to be the only possibility. In such cases, other approaches such as using simulation tools simply do not make sense because the physical models needed for simulation do not exist. As an industry matures, simulation becomes more of a possibility because the industry is based more and more on solid physical understanding of the processes it uses and the products it develops. One might conclude from this that it is possible to simulate only those things which have been built because it is only after the experimental work has been done that we have complete physical understanding. However, this is clearly not the case. In the VLSI area all new circuits today are fully simulated before they are built. This has resulted in a high probability of obtaining first pass success on new designs. It is also common today for new semiconductor device structures to be simulated before they are built and for structures to be optimized in this way. In the first two decades of the semiconductor industry, chip designs were handcrafted, hand checked and individually guided through the manufacturing process by a small cadre of very skilled people. There were projections made towards the end of this period, in the late 197Os, that custom ICs would never become pervasive in systems because there were simply not enough skilled people available to design such chips and not enough skilled people available to shepherd the designs through manufacturing. What changed, of course, was the introduction of modern computing tools into the design process. These tools both leveraged the creativity of the small number of skilled designers and opened up the design opportunity for a vastly larger number of individuals who had system ideas but little experience in translating them into silicon. The net result has been that the cost of designing a given function in silicon has dropped dramatically in the past decade making possible the megachips we see today. Such a revolution has not occurred in semiconductor manufacturing. In fact, exactly the opposite has happened. Rather than a proliferation of the technology, there has been a consolidation. Rather than costs going down, they have gone up enormously. Rather than the systems community having access to the latest technology, they generally today design in a fixed technology which is at least one and perhaps two generations behind the state-of-the-art. Increasingly, U.S. systems companies are dependent on overseas suppliers for the critical components their systems need. We believe that the solution to this problem is exactly the same as the solution to the design problem of the 1970s. Modem computing techniques can make a major difference in our ability to manufacture chips economically. They can also make a major difference in our ability to get the latest technology into new systems. The Virtual Factory is one of the keys to doing this. The Virtual Factory consists of a hierarchy of models including equipment, processes, devices and circuits to describe the chips that are built in the factory, and a set of factory performance and physical plant models which describe the factory itself. To the extent that these models represent reality, the Virtual Factory can be used to design processes, to assess the manufacturability of a process, to optimize factory throughput, to predict delivery times on products and for a host of other applications. In a very real sense, the Virtual Factory provides the same capability for the process designer and the plant manager, that today’s CAD tools provide for the circuit designer. The same productivity enhancements that have occurred in the chip design area through these tools, should be possible in the manufacturing area.
KC. Saraswat I Adaptable IC manufacturing systems 4. PROGRAMMABLE
135
FACTORY
In the conventional Mass Manufacturing Systems (MMS) approach the processing is optimized by performing each step in the fabrication process on a separate piece of equipment, by processing identical wafers in large batches. The variation is reduced by in-process and end-of-process monitoring and statistical process control by feeding the information to subsequent runs. Wafer batching inhibits the use of in-situ monitoring and real-time control. Since there are several process parameters to optimize, statistical techniques require hundreds of wafers to be processed. In the MMS approach it is difficult to accelerate the learning curve. In addition, there are difficulties in efficiently tracking and scheduling wafers when the variety of part numbers is very large. This is an impediment in the production of small quantities of a large variety of chips fabricated using different technologies. It is also an impediment to rapid prototyping of chips, where it is desirable to accelerate the learning cycle for innovative devices and processes. These problems may make alternative Adaptable Manufacturing Systems (AMS), in contrast to conventional MMS, more attractive for semiconductor manufacturing. At Stanford, we are developing concepts of a programmable factory, an alternative AMS approach to IC fabrication, which may offer more economical small or large scale production, higher flexibility to accommodate many products on several processes, and faster turnaround to hasten product innovation. This approach is based on a new generation of flexible multifunctional equipment with extensive use of computer integrated manufacturing (CIM) to further enhance the flexibility. In this approach the new type of multiprocessing equipment quickly processes one semiconductor wafer at a time, performs several process steps in-situ in contrast to the conventional alternative of slowly processing many wafers simultaneously and one step per equipment (Fig. 3). Single wafer processing enables the use of in-situ monitoring and real-time control. The process equipment is also modular, with common mechanical and electronic interfaces. Such modularization and standardization is expected to decrease the amount and expense of equipment that must be purchased for existing fabs to upgrade to new generations of technology. Extensive use of CIM for specification, monitoring, control, and information management should make switching between processes faster and more reliable, should increase the ease by which large numbers of different products could simultaneously be routed and tracked through the factory, and maximize equipment utilization.
SINGLE CHAMBER MULTlPROCESSlNG EGUIPMBNT
MULTI CHAMBER CLUSTER TOOL
MANUFACTURING SYSTW ..
Figure 3. Concept of a microfactory with multiprocessing equipment
136
K.C. Saraswat
I Adaptable
IC manufacturing
This approach is demonstrated through the Rapid Thermal Multiprocessing (RTM) reactor (Fig. processing and several other process environments in multilayer in-situ growth and deposition of dielectrics,
systems
development of a novel single wafer 4). The RTM combines rapid thermal a single chamber, with applications for semiconductors and metals.
By doing extensive integration of computers and related technology for specification, communication, execution, monitoring, control, and diagnosis (Fig. 4) we demonstrate the programmable nature of the RTM. For equipment and process control a variety of new sensors for real-time measurements of wafer temperature and thin film thickness have been developed and a model based control system has been developed. The overall control design includes a model based real-time control system, a supervisory discrete event control system, and a model based AI system for monitoring and diagnosis. A computer process specification system has been developed to accurately specify the manufacturing process. The specification is communicated to RTM to automatically reconfigure the equipment parameters and execute the recipes. Users can access the reactor from X-terminals connected to the lab ethernet and, with a multiple window control interface they can specify, run and monitor processes.
LABORATORY CIM SYSTEM
DISTRIBUTED INFORMATlON SYSTEMS (DIB)
ETHERNET
COYYUNiChDN v *
AGENTS *
DlSCRETE EVENT BUPERVIBOR CONTROL BVSTEY
t YODEL BASED REAL TIME CONTROL BVBTEY 4
RAPW)THERMAL YUL-EBBW4G REACTOR
_wChmbur
B E
_mPf!?‘ii 0” Floi Pii.&~ Pix
; o R s
Figure 4. Schematic of the Rapid Thermal monitoring and real-time control.
Multiprocessing
-
AIBVSTEY MONITORING AND DIAGNOSEi
reactor and CIM for specification,
The overall system is very flexible for in-situ multiprocessing because it allows rapid cycling of ambient gases, temperature, pressure, etc. It allows several processing steps to be done sequentially in-situ, while providing sufficient flexibility to allow optimization of each processing step.
Implications Our modeling [6,7] suggests that the key differences between an AMS factory and a conventional MMS factory would be shorter product development times, shorter manufacturing times, smaller inventories, economies of scale available at lower fab capacities, less time spent retooling equipment to change products, more different products simultaneously in the fab, product competition based on functionality rather than price, and
K.C. Saraswat I Adaptable IC manufacturing systems
137
longer equipment lifetimes. Compared to an AMS factory, the MMS factory would be much larger, focus on achieving economies of scale on standardized products, and would use equipment more directly evolved from contemporary conventional equipment. This approach is likely to extend the lifetime of equipment across multiple product generations, and also decrease size-related inefficiencies of smaller fabs. These features should diminish the relatively large firms’ competitive advantages that come from their access to greater amounts of capital. In addition, it would probably increase the competitive importance of design and design software, compared to product manufacturing cost. Finally,
the AMS methodology also allows implementation of a smaller factory - a factory - a megufactory without paying any penalty and with all the advantages of the flexibility offered by this approach.
microfactory - which is scalable to a larger conventional
Acknowledgment: This work was supported by Semiconductor Research Corporation and Texas Instruments through the MMST program funded by AIR FORCE/DARPA. The author is thankful to the Manufacturing Science Group at Stanford University - 39 students, 18 senior staff, 11 faculty, and several industrial visitors, for making this research successful.
References [l] W.E. Steinmueller, “The Economics of Alternative Integrated Circuit Manufacturing Technology: A Framework and Appraisal,” Center for Economic Policy Research, Stanford University, Stanford, CA. May 15, 1991 [2] G. B. Larrabee, “The Intelligent Microelectronics Factory of the Future,” IEEE/SEMI Znt. Semiconductor Manufacturing Science Symp. ‘9 1, Burlingame, CA, May 20-22, 199 1, p 30. [3] C.R. Deininger, “Fabs of the Year 2000,” Extended Abstracts, SRC Techcon ‘90, San Jose, CA. October 1990, pp. 276-278. [4] C. Barrett, ” ” Symp. VLSI Technology, Kyoto, Japan, May 1993. [5] S. C. Wood’and K. C. Saraswat. “Modeling the Performance of Cluster-Based Fabs.” Proc. International Semiconductor Manufacturing Science Symposium, San Francisco, California. May 20, 1991, pp. 8 - 14. [6] K. C. Saraswat, S. C. Wood, J. D. Plummer and P. Losleben “Programmable Factory for Adaptable IC Manufacturing,” Symp. VLSI Technology, Kyoto, Japan, May 1993. [7] Samuel C. Wood and Krishna C. Saraswat, “Factors Affecting the Economic Performance of Cluster-Based Fabs,” Proc. Third International Symposium of ULSI Science and Technology, the Electrochem. Sot., Washington, D.C., May 9, 1991, pp. 551 - 565.
ELSEVIER
Microelectronic
Engineering 25 (1994) 131-137
Adaptable IC Manufacturing Systems for the 21st Century Krishna C. Saraswat Department of Electrical Engineering Stanford University, Stanford, CA 95304. USA
Abstract The semiconductor industry is currently facing a number of challenges. The capital costs of IC factories and the cost of developing technology are increasing at a faster rate than the revenues. In addition, demand for ICs is fragmenting into lower volume and more differentiated markets. The current chip manufacturing approach is establishing megafactories for slow mass production of commodity products. To remain competitive alternative design and manufacturing techniques will have to be developed with flexible factories for rapid production of multiple products in different technologies. At Stanford University we have built a large interdisciplinary program aimed at exploring radically different semiconductor manufacturing opportunities. The approach is to build a highly flexible computer controlled manufacturing facility - the Programmable Factory and in parallel with this factory, a suite of simulation tools the Virtual Factory which emulate all functions of the real factory. Economic modeling suggests that such approach may offer more economical small or large scale production, higher flexibility to accommodate many products on several processes, and faster turnaround to hasten product innovation.
1. INTRODUCTION The future success of IC companies will demand rapid innovation, rapid product introduction and ability to react quickly to a change in the technological and business climate of microelectronics. These technological advances in integrated electronics will require
development of flexible manufacturing technology for electronic systems. However, the current chip manufacturing approach is establishing megafactories for mass production of commodity products, as opposed to flexible factories for rapid production of multiple products in different technologies. Alternative manufacturing techniques will have to be developed to remain competitive [ 11. For the past three decades, the semiconductor industry has made immense progress in increasing component densities, decreasing feature sizes and increasing device structure complexity. This progress in VLSI has been achieved through advances in equipment and fabrication technology, resulting in enormous economic benefits for commodity products, for which manufacturing of one kind of chip is done in large quantities. This increased complexity in devices, circuits and technology has resulted in increasingly higher cost of the fabrication facility. This is shown clearly in Figure 1. During the last three decades a 4-mask fabrication process requiring about 25 major steps and a 1 million dollar factory has evolved into a 15 to 20 mask process requiring about 300 steps and a 500 million dollar factory. About 75% of the cost to set up a factory can be attributed to the equipment [2] and with each new generation of the equipment, the average cost per machine has increased by at least 30% [3]. Although the cost per piece of equipment has increased by about 30% per generation, the added complexity of processes requires more pieces of equipment to achieve the same throughput. Thus the total cost of equipment in fabs more than doubles per generation. If this trend continues, well before the turn of the century the entry cost to set up a manufacturing facility will be well in excess of 1 billion dollars [2,3]. There have been enormous advances in circuit design techniques which have contributed to the success of microelectronics. The number of designs manufactured in a year has steadily increased. In 1975 about 200 designs were manufactured worldwide. The number increased to about 2,000 by 1980, to about 12,000 by 1986, and is expected to be in excess of 0167-9317/94/$07.00 0 1994 SSDI0167-9317(94)00009-.I
Elsevier Science B.V. All rights reserved.
132
K.C. Saraswat
I Adaptable
IC manufacturing
systems
100,000 in early the nineties. Whereas in 1975 most of them were produced in large quantities, except for a few commodity chips the number of chips produced per design has steadily decreased. This trend projected to the year 2000 clearly indicates that a company will be required to manufacture many designs and varying in volumes from a few thousand chips to many millions over the life cycle of the design. 500
*
A t
NEC tigubishi
l
Motorola ,Q&VFujitsu
t
; 3
500
”
.
12~.10 mask. 1 OOK
I
m
0
!
1965
i
l
I
I
1970
1975
i
I
I
I
I
1980
c
-m
I
1985
I
1990
I
1995
2000
YEAR
Figure 1. Cost of establishing a factory vs. year for a state-of-the-art chip fabricated that year In the conventional mass manufacturing approach the process development largely relies on experimental techniques as was the case for circuits couple of decades ago. As a result the cost of developing the next generation technology is reaching in excess of $ 100 million and the time from inception to market has increased to about 5 years [4]. This methodology will not be suitable for supporting a flexible manufacturing environment to produce multiple products in multiple technologies. As we look to the 21Sf century it is clear that the conventional mass manufacturing approach has limitations with regard to the economic production of small quantities, faster speed of realization of innovations, faster turnaround time in manufacturing, and research on innovative tools and processes. 2. STANFORDS’ VISION FOR MANUFACTURING
IN THE 21ST CENTURY
At Stanford University we have built a large interdisciplinary program aimed at exploring radically different semiconductor manufacturing opportunities. Manufacturing plants today are characterized by enormous capital costs and inflexibility. They are built to serve one or two generations of technology and usually a narrow product base. New technology development is very expensive and largely empirically done. Competition in such an environment is heavily capital investment driven. Ten years ago, chip designers were facing similar investment problems since new designs were largely hand crafted. Many observers felt that few VLSI applications would be able to justify design costs. The CAD revolution changed all that. Our view is that a similar revolution, driven by the same ideas, can revolutionize manufacturing. The approach [5] as shown in Fig. 2 is to build a highly flexible computer controlled manufacturing facility - the Programmable Factory and in parallel with this factory, a suite of simulation tools the Virtual Factory which emulate all functions of the real factory. Controlling both of these and integrating them is the Manufacturing Automation.
K.C. Saraswat I Adaptable IC manufacturing systems
Df;S%tWJ
F!!iEsF
Library of Circuit modules
Library of Device modules
\ circuit synttleais
133
Library of process modules J ProCesS
1 Devke
technology synthesis Equipment Process Devke circuit Factory
\Lateral Geometries \
\
Vertical Geometries Process Flow 1
/
IC Technology Synthesis
P==r
for MultIpie Products in Multiple technoiogles Single wafer programmable equipment, Cm for speclfkation, monitoring, control and diagnosb Sensors for in-situ measurements
Figure 2. Programmable and virtual factory for design and adaptable IC Manufacturing in the 21st century. The Virtual Factory consists of a hierarchy of models including equipment, processes, devices and circuits to describe the chips that are built in the factory, and a set of factory performance and physical plant models which describe the factory itself. To the extent that these models represent reality, the Virtual Factory can be used to design processes, to assess the manufacturability of a process, to optimize factory throughput, to predict delivery times on products and for a host of other applications. In a very real sense, the Virtual Factory provides the same capability for the process designer and the plant manager, that today’s CAD tools provide for the circuit designer. The same productivity enhancements that have occurred in the chip design area through these tools, should be possible in the manufacturing area. The Programmable Factory is a concept which seeks to emulate the enormous power of abstraction that is possible in a stored program computer. If the factory can be made sufficiently flexible and if that flexibility can be invoked by a stored “program”, then we can build upon the considerable experience of computer science to multiply human productivity. The approach is to develop the “program” which will build chips largely by using the Virtual Factory (Fig. 2). That “program” is, of course, the same representation which drives the emulation of the factory in the Virtual Factory. Secondly, if we can create a new class of multi-function equipment (Fig. 2) which replaces several single-function equipment and simplifies the overall process at the same time, then we open the possibility of making factories affordable to a much larger number of enterprises. Coupled with the automation tools being developed in this program, we seek to empower designers with the ability to create a much larger variety of new products. Finally, if we can instrument these factories sufficiently well to tighten the feedback loop on diagnosis and control, we open the opportunity to dramatically reduce the learning cycle of manufacturing.
134
3. VIRTUAL
K.C. Saraswat
/ Adaptable
IC manufacturing
system.\
FACTORY
The traditional approach to new product or process development in many areas of engineering has been experimental--real experiments on real materials in real laboratories. When a field of science is in its infancy, this approach is likely to be the only possibility. In such cases, other approaches such as using simulation tools simply do not make sense because the physical models needed for simulation do not exist. As an industry matures, simulation becomes more of a possibility because the industry is based more and more on solid physical understanding of the processes it uses and the products it develops. One might conclude from this that it is possible to simulate only those things which have been built because it is only after the experimental work has been done that we have complete physical understanding. However, this is clearly not the case. In the VLSI area all new circuits today are fully simulated before they are built. This has resulted in a high probability of obtaining first pass success on new designs. It is also common today for new semiconductor device structures to be simulated before they are built and for structures to be optimized in this way. In the first two decades of the semiconductor industry, chip designs were handcrafted, hand checked and individually guided through the manufacturing process by a small cadre of very skilled people. There were projections made towards the end of this period, in the late 197Os, that custom ICs would never become pervasive in systems because there were simply not enough skilled people available to design such chips and not enough skilled people available to shepherd the designs through manufacturing. What changed, of course, was the introduction of modern computing tools into the design process. These tools both leveraged the creativity of the small number of skilled designers and opened up the design opportunity for a vastly larger number of individuals who had system ideas but little experience in translating them into silicon. The net result has been that the cost of designing a given function in silicon has dropped dramatically in the past decade making possible the megachips we see today. Such a revolution has not occurred in semiconductor manufacturing. In fact, exactly the opposite has happened. Rather than a proliferation of the technology, there has been a consolidation. Rather than costs going down, they have gone up enormously. Rather than the systems community having access to the latest technology, they generally today design in a fixed technology which is at least one and perhaps two generations behind the state-of-the-art. Increasingly, U.S. systems companies are dependent on overseas suppliers for the critical components their systems need. We believe that the solution to this problem is exactly the same as the solution to the design problem of the 1970s. Modem computing techniques can make a major difference in our ability to manufacture chips economically. They can also make a major difference in our ability to get the latest technology into new systems. The Virtual Factory is one of the keys to doing this. The Virtual Factory consists of a hierarchy of models including equipment, processes, devices and circuits to describe the chips that are built in the factory, and a set of factory performance and physical plant models which describe the factory itself. To the extent that these models represent reality, the Virtual Factory can be used to design processes, to assess the manufacturability of a process, to optimize factory throughput, to predict delivery times on products and for a host of other applications. In a very real sense, the Virtual Factory provides the same capability for the process designer and the plant manager, that today’s CAD tools provide for the circuit designer. The same productivity enhancements that have occurred in the chip design area through these tools, should be possible in the manufacturing area.
KC. Saraswat I Adaptable IC manufacturing systems 4. PROGRAMMABLE
135
FACTORY
In the conventional Mass Manufacturing Systems (MMS) approach the processing is optimized by performing each step in the fabrication process on a separate piece of equipment, by processing identical wafers in large batches. The variation is reduced by in-process and end-of-process monitoring and statistical process control by feeding the information to subsequent runs. Wafer batching inhibits the use of in-situ monitoring and real-time control. Since there are several process parameters to optimize, statistical techniques require hundreds of wafers to be processed. In the MMS approach it is difficult to accelerate the learning curve. In addition, there are difficulties in efficiently tracking and scheduling wafers when the variety of part numbers is very large. This is an impediment in the production of small quantities of a large variety of chips fabricated using different technologies. It is also an impediment to rapid prototyping of chips, where it is desirable to accelerate the learning cycle for innovative devices and processes. These problems may make alternative Adaptable Manufacturing Systems (AMS), in contrast to conventional MMS, more attractive for semiconductor manufacturing. At Stanford, we are developing concepts of a programmable factory, an alternative AMS approach to IC fabrication, which may offer more economical small or large scale production, higher flexibility to accommodate many products on several processes, and faster turnaround to hasten product innovation. This approach is based on a new generation of flexible multifunctional equipment with extensive use of computer integrated manufacturing (CIM) to further enhance the flexibility. In this approach the new type of multiprocessing equipment quickly processes one semiconductor wafer at a time, performs several process steps in-situ in contrast to the conventional alternative of slowly processing many wafers simultaneously and one step per equipment (Fig. 3). Single wafer processing enables the use of in-situ monitoring and real-time control. The process equipment is also modular, with common mechanical and electronic interfaces. Such modularization and standardization is expected to decrease the amount and expense of equipment that must be purchased for existing fabs to upgrade to new generations of technology. Extensive use of CIM for specification, monitoring, control, and information management should make switching between processes faster and more reliable, should increase the ease by which large numbers of different products could simultaneously be routed and tracked through the factory, and maximize equipment utilization.
SINGLE CHAMBER MULTlPROCESSlNG EGUIPMBNT
MULTI CHAMBER CLUSTER TOOL
MANUFACTURING SYSTW ..
Figure 3. Concept of a microfactory with multiprocessing equipment
136
K.C. Saraswat
I Adaptable
IC manufacturing
This approach is demonstrated through the Rapid Thermal Multiprocessing (RTM) reactor (Fig. processing and several other process environments in multilayer in-situ growth and deposition of dielectrics,
systems
development of a novel single wafer 4). The RTM combines rapid thermal a single chamber, with applications for semiconductors and metals.
By doing extensive integration of computers and related technology for specification, communication, execution, monitoring, control, and diagnosis (Fig. 4) we demonstrate the programmable nature of the RTM. For equipment and process control a variety of new sensors for real-time measurements of wafer temperature and thin film thickness have been developed and a model based control system has been developed. The overall control design includes a model based real-time control system, a supervisory discrete event control system, and a model based AI system for monitoring and diagnosis. A computer process specification system has been developed to accurately specify the manufacturing process. The specification is communicated to RTM to automatically reconfigure the equipment parameters and execute the recipes. Users can access the reactor from X-terminals connected to the lab ethernet and, with a multiple window control interface they can specify, run and monitor processes.
LABORATORY CIM SYSTEM
DISTRIBUTED INFORMATlON SYSTEMS (DIB)
ETHERNET
COYYUNiChDN v *
AGENTS *
DlSCRETE EVENT BUPERVIBOR CONTROL BVSTEY
t YODEL BASED REAL TIME CONTROL BVBTEY 4
RAPW)THERMAL YUL-EBBW4G REACTOR
_wChmbur
B E
_mPf!?‘ii 0” Floi Pii.&~ Pix
; o R s
Figure 4. Schematic of the Rapid Thermal monitoring and real-time control.
Multiprocessing
-
AIBVSTEY MONITORING AND DIAGNOSEi
reactor and CIM for specification,
The overall system is very flexible for in-situ multiprocessing because it allows rapid cycling of ambient gases, temperature, pressure, etc. It allows several processing steps to be done sequentially in-situ, while providing sufficient flexibility to allow optimization of each processing step.
Implications Our modeling [6,7] suggests that the key differences between an AMS factory and a conventional MMS factory would be shorter product development times, shorter manufacturing times, smaller inventories, economies of scale available at lower fab capacities, less time spent retooling equipment to change products, more different products simultaneously in the fab, product competition based on functionality rather than price, and
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longer equipment lifetimes. Compared to an AMS factory, the MMS factory would be much larger, focus on achieving economies of scale on standardized products, and would use equipment more directly evolved from contemporary conventional equipment. This approach is likely to extend the lifetime of equipment across multiple product generations, and also decrease size-related inefficiencies of smaller fabs. These features should diminish the relatively large firms’ competitive advantages that come from their access to greater amounts of capital. In addition, it would probably increase the competitive importance of design and design software, compared to product manufacturing cost. Finally,
the AMS methodology also allows implementation of a smaller factory - a factory - a megufactory without paying any penalty and with all the advantages of the flexibility offered by this approach.
microfactory - which is scalable to a larger conventional
Acknowledgment: This work was supported by Semiconductor Research Corporation and Texas Instruments through the MMST program funded by AIR FORCE/DARPA. The author is thankful to the Manufacturing Science Group at Stanford University - 39 students, 18 senior staff, 11 faculty, and several industrial visitors, for making this research successful.
References [l] W.E. Steinmueller, “The Economics of Alternative Integrated Circuit Manufacturing Technology: A Framework and Appraisal,” Center for Economic Policy Research, Stanford University, Stanford, CA. May 15, 1991 [2] G. B. Larrabee, “The Intelligent Microelectronics Factory of the Future,” IEEE/SEMI Znt. Semiconductor Manufacturing Science Symp. ‘9 1, Burlingame, CA, May 20-22, 199 1, p 30. [3] C.R. Deininger, “Fabs of the Year 2000,” Extended Abstracts, SRC Techcon ‘90, San Jose, CA. October 1990, pp. 276-278. [4] C. Barrett, ” ” Symp. VLSI Technology, Kyoto, Japan, May 1993. [5] S. C. Wood’and K. C. Saraswat. “Modeling the Performance of Cluster-Based Fabs.” Proc. International Semiconductor Manufacturing Science Symposium, San Francisco, California. May 20, 1991, pp. 8 - 14. [6] K. C. Saraswat, S. C. Wood, J. D. Plummer and P. Losleben “Programmable Factory for Adaptable IC Manufacturing,” Symp. VLSI Technology, Kyoto, Japan, May 1993. [7] Samuel C. Wood and Krishna C. Saraswat, “Factors Affecting the Economic Performance of Cluster-Based Fabs,” Proc. Third International Symposium of ULSI Science and Technology, the Electrochem. Sot., Washington, D.C., May 9, 1991, pp. 551 - 565.