- Email: [email protected]
Glasses in microelectronics
Journal of Non-Crystalline Solids 73 (1985) 409-411 North-Holland, Amsterdam
409
GLASSES IN MICROELECTRONICS Rao R. T U M M A L A I B M Corporation, East Fishkill, N Y 12524, USA
1. Introduction This paper deals with the technology of glass for microelectronic applications. It will specifically address those applications in which glass is being used today and those areas in which glass could be used in the year 2004. The problems and prospects in essence for glass technology as it pertains to electronic applications are the themes.
2. Glass applications Over the last twenty years, glass materials have found their way into a wide variety of applications. Starting with the need to passivate silicon devices which required the formation of defect-free films of low temperature and low expansion glasses as well as glasses to meet similar but active need for display and substrate applications to glasses that are used to hermetically seal to such materials and applications as soda-lime-silica for displays, ferrites for storage applications, and molybdenum for printers. In addition, perhaps in more volume than any other single application, glass is used today as a densifying aid to sinter metals and ceramics at lower temperatures and to higher densities than otherwise practical. Glass for electro-optic communications is perhaps one of the fastest growing areas. In most of these applications, the starting technology is one of particulate technology and the end result is a material that is mechanically sound.
3. General requirements Scientific understanding and technology are necessary to meet all the above applications to make glass products that are: 0022-3093/85/$03.30 © Elsevier Science Publishers B.V. (North-Holland Physics Publishing Division)
410
R.R. Tummala / Glasses in microelectronics
Table 1 Typical electronic glass and glass-ceramic dielectric films Required
Process
Today
Monosized/uniform Max. packing density Stability rheology packing
fine particle synthesis $ dispersion in organic binders
variable
No defects Reproducible Visco elastic Complete organic removal No defects
film formation $
defects variability too thick defects poor mechanical strength
Fine grained Smoothness
densification microstructure control nucleation and crystallization control Problems reproducibility - thermal - electrical - mechanical reliability dimensional control
aqueous systems not as stable
(1) (2) (3) (4)
Reproducible. Reliable. Defect-free. High performing. These are the primary microelectronic requirements. Glassy materials capable of forming thin and thick film structures (500 A - 500 # m ) with a wide variety of electrical, thermal, magnetic and mechanical properties are the challenging needs of the industry for the next two decades.
4. C u r r e n t p r o b l e m s
If we assume that glass could be used as a dielectric with a buried c o n d u c t o r within which are carriers of a transmission signal of an electronic device, the processes that are used today in fabricating such devices and the problems associated with these are shown in table 1. The improvements required in each of the major process steps through scientific and technological studies outlined in table 2 are the areas that are expected to provide m a x i m u m leverage. The single most important problem limiting the use of glass and glassceramics is the adequacy of mechanical properties of commercial glasses. Sinterable glasses and glass-ceramics with mechanical strengths approaching that of polycrystalline alumina are the materials of the twenty-first century in microelectronics.
R.R. Tummala / Glasses in microelectronics
411
Table 2 Critical problems: areas of maximum leverage Particulate technology Organic-inorganic reactions Sintering- microstructural control Interfaces
Glass-to-metal bonding Fracture and wear Thin film dry process glassy insulators
5. Prospects At the current pace of scientific understanding of those factors limiting the mechanical strength of glass together with the technological innovations that have come about to date and will exponentially emerge, vitreous-based substrates replacing crystalline ceramics will become a reality by the year 2000. Defect-free thin films of multi-component glasses tailored specifically for electrical and thermal properties will become commercial, primarily due to technological innovations in depositing such films in defect-free condition at commercially acceptable deposition rates using ion beam, CVD, laser CVD. sol gel, sputtering and others. These technologies, therefore, will replace the particulate technology that is commercially practiced today. However, since the particulate technology is expected to stay with us for the next decade or so, attention is required in generating particles of uniform size and surface chemistry which could be dispersed in a suitable organic system to form the most stable and maximum packing thick films. Sintering of these films in such an atmosphere that allows the initial coalescence of particles and the subsequent saturation of the particle boundaries with a gas which will diffuse out fast enough to collapse the bubbles in a subsequent atmosphere in which the partial pressure of the first gas is zero, is an area of great technological interest. However, all these processes should proceed subsequent to organic burn-off at as low a temperature as the glass transition temperature. Bonding of such highly conductive metals as copper which is both chemically and thermally incompatible with most borosilicates, alumino-silicates and other glasses of interest to electronic packaging needs to be commercially explored.
409
GLASSES IN MICROELECTRONICS Rao R. T U M M A L A I B M Corporation, East Fishkill, N Y 12524, USA
1. Introduction This paper deals with the technology of glass for microelectronic applications. It will specifically address those applications in which glass is being used today and those areas in which glass could be used in the year 2004. The problems and prospects in essence for glass technology as it pertains to electronic applications are the themes.
2. Glass applications Over the last twenty years, glass materials have found their way into a wide variety of applications. Starting with the need to passivate silicon devices which required the formation of defect-free films of low temperature and low expansion glasses as well as glasses to meet similar but active need for display and substrate applications to glasses that are used to hermetically seal to such materials and applications as soda-lime-silica for displays, ferrites for storage applications, and molybdenum for printers. In addition, perhaps in more volume than any other single application, glass is used today as a densifying aid to sinter metals and ceramics at lower temperatures and to higher densities than otherwise practical. Glass for electro-optic communications is perhaps one of the fastest growing areas. In most of these applications, the starting technology is one of particulate technology and the end result is a material that is mechanically sound.
3. General requirements Scientific understanding and technology are necessary to meet all the above applications to make glass products that are: 0022-3093/85/$03.30 © Elsevier Science Publishers B.V. (North-Holland Physics Publishing Division)
410
R.R. Tummala / Glasses in microelectronics
Table 1 Typical electronic glass and glass-ceramic dielectric films Required
Process
Today
Monosized/uniform Max. packing density Stability rheology packing
fine particle synthesis $ dispersion in organic binders
variable
No defects Reproducible Visco elastic Complete organic removal No defects
film formation $
defects variability too thick defects poor mechanical strength
Fine grained Smoothness
densification microstructure control nucleation and crystallization control Problems reproducibility - thermal - electrical - mechanical reliability dimensional control
aqueous systems not as stable
(1) (2) (3) (4)
Reproducible. Reliable. Defect-free. High performing. These are the primary microelectronic requirements. Glassy materials capable of forming thin and thick film structures (500 A - 500 # m ) with a wide variety of electrical, thermal, magnetic and mechanical properties are the challenging needs of the industry for the next two decades.
4. C u r r e n t p r o b l e m s
If we assume that glass could be used as a dielectric with a buried c o n d u c t o r within which are carriers of a transmission signal of an electronic device, the processes that are used today in fabricating such devices and the problems associated with these are shown in table 1. The improvements required in each of the major process steps through scientific and technological studies outlined in table 2 are the areas that are expected to provide m a x i m u m leverage. The single most important problem limiting the use of glass and glassceramics is the adequacy of mechanical properties of commercial glasses. Sinterable glasses and glass-ceramics with mechanical strengths approaching that of polycrystalline alumina are the materials of the twenty-first century in microelectronics.
R.R. Tummala / Glasses in microelectronics
411
Table 2 Critical problems: areas of maximum leverage Particulate technology Organic-inorganic reactions Sintering- microstructural control Interfaces
Glass-to-metal bonding Fracture and wear Thin film dry process glassy insulators
5. Prospects At the current pace of scientific understanding of those factors limiting the mechanical strength of glass together with the technological innovations that have come about to date and will exponentially emerge, vitreous-based substrates replacing crystalline ceramics will become a reality by the year 2000. Defect-free thin films of multi-component glasses tailored specifically for electrical and thermal properties will become commercial, primarily due to technological innovations in depositing such films in defect-free condition at commercially acceptable deposition rates using ion beam, CVD, laser CVD. sol gel, sputtering and others. These technologies, therefore, will replace the particulate technology that is commercially practiced today. However, since the particulate technology is expected to stay with us for the next decade or so, attention is required in generating particles of uniform size and surface chemistry which could be dispersed in a suitable organic system to form the most stable and maximum packing thick films. Sintering of these films in such an atmosphere that allows the initial coalescence of particles and the subsequent saturation of the particle boundaries with a gas which will diffuse out fast enough to collapse the bubbles in a subsequent atmosphere in which the partial pressure of the first gas is zero, is an area of great technological interest. However, all these processes should proceed subsequent to organic burn-off at as low a temperature as the glass transition temperature. Bonding of such highly conductive metals as copper which is both chemically and thermally incompatible with most borosilicates, alumino-silicates and other glasses of interest to electronic packaging needs to be commercially explored.