Low-temperature bonding process
View Patent ↗The invention relates to a process for assembling a first element that includes at least one first wafer, substrate or at least one chip, and a second element of at least one second wafer or substrate, involving the formation of a surface layer, known as the bonding layer, on each substrate, at least one of these bonding layers being formed at a temperature less than or equal to 300° C.; conducting a first annealing, known as degassing annealing, of the bonding layers, before assembly, at least partly at a temperature at least equal to the subsequent bonding interface strengthening temperature but below 450° C.; forming an assembling of the substrates by bringing into contact the exposed surfaces of the bonding layers, and conducting an annealing of the assembled structure at a bonding interface strengthening temperature below 450° C.
1. A method for bonding two surfaces at low temperatures comprising:
forming at a low temperature a first bonding layer on a first substrate and a second bonding layer on a second substrate, wherein at least one of the first substrate or the second substrate comprises one or more components, micro-components or circuits, wherein the first bonding layer and the second bonding layer each have an exposed surface, and the formation of each bonding layer is done at a low temperature that is less than or equal to 300° C.;
conducting a first annealing of the first and second bonding layers on the first and second substrates for a first annealing time period, wherein the first annealing is conducted up to and at an annealing temperature that is higher than the low temperature of formation of each bonding layer and is at least 350° C. but less than 450° C. and for a time which does not deleteriously affect the components, micro-components or circuits;
assembling the annealed first and second substrates to form a structure by bringing into contact the exposed surfaces of the first bonding layer and the second bonding layer; and
conducting a second annealing of the first and second bonding layers of the bonded first and second substrates after assembling the structure, with the second annealing conducted at a second temperature of at least 350° C. and lower than or at most equal to the first annealing temperature,
wherein the second annealing is conducted at a temperature and time which does not deleteriously affect the components, micro-components or circuits, and
wherein the annealings provide a bonding interface between the substrates that has a bonding energy of at least 4 J/m 2 .
2. The method according to claim 1 , wherein the first annealing is conducted for a time sufficient to remove contaminants from the bonding layers.
3. The method according to claim 1 , wherein at least one of the bonding layers is formed by a Plasma Enhanced Chemical Vapor Deposition or a Low Pressure Chemical Vapor Deposition.
4. A method for bonding two surfaces at low temperatures comprising:
forming at a low temperature a first bonding layer on a first substrate and a second bonding layer on a second substrate, wherein at least one of the first substrate or the second substrate comprises one or more components, micro-components or circuits, wherein the first bonding layer and the second bonding layer each have an exposed surface, and at least one of the bonding layers is formed at a temperature less than or equal to 250° C. and the formation of the other bonding layer is done at a low temperature that is less than or equal to 300° C.;
conducting a first annealing of the first and second bonding layers on the first and second substrates for a first annealing time period, wherein the first annealing is conducted at an annealing temperature that is higher than the low temperature of formation of each bonding layer and is at least 350° C. but less than 450° C. and for a time which does not deleteriously affect the components, micro-components or circuits;
assembling the annealed first and second substrates to form a structure by bringing into contact the exposed surfaces of the first bonding layer and the second bonding layer; and
conducting a second annealing of the first and second bonding layers of the bonded first and second substrates after assembling the structure, with the second annealing conducted at a second temperature of at least 350° C. and lower than or at most equal to the first annealing temperature,
wherein the second annealing is conducted at a temperature and time which does not deleteriously affect the components, micro-components or circuits, and
wherein the annealings provide a bonding interface between the substrates that has a bonding energy of at least 4 J/m 2 .
5. The method according to claim 1 , wherein at least one of the bonding layers is an oxide or a nitride material.
6. The method according to claim 5 , wherein at least one of the bonding layers is a silicon oxide.
7. The method according to claim 1 , wherein the second annealing is a bonding interface strengthening annealing conducted at a temperature (Tr) below 400° C.
8. The method according to claim 7 , wherein the temperature of the first annealing increases at a rate between 1° C./min and 5° C./min to provide a temperature ramp.
9. The method according to claim 1 , wherein the first annealing time period lasts between 10 minutes and 5 h.
10. The method according to claim 9 , wherein the first annealing time period lasts between 30 minutes and 2 h.
11. The method according to claim 1 , which further comprises preparing the surfaces of the first bonding layer and the second bonding layer for bonding before assembling the first and second substrates.
12. The method according to claim 11 , wherein the preparing of the surfaces is by chemical-mechanical polishing, wherein the contacting of the exposed surfaces of the first bonding layer and the second bonding layer produces bonding by molecular adhesion.
13. The method according to claim 1 , wherein one of the first substrate and first bonding layer or the second substrate and second bonding layer are cut into one or more chips.
14. The method according to claim 1 , which further comprises; cutting of one of the substrates into one or more chips before assembling the first and second substrates to form a structure so that individual chips may be assembled with the other substrate, wherein at least one of the substrates or chips are made of a semiconductor material.
15. A method for bonding two surfaces at low temperatures comprising:
forming at a low temperature a first bonding layer on a first substrate and a second bonding layer on a second substrate, wherein at least one of the first substrate or the second substrate comprises one or more components, micro-components or circuits, wherein the first bonding layer and the second bonding layer each have an exposed surface, and the formation of each bonding layer is done at a low temperature that is less than or equal to 250° C.;
conducting a first annealing of the first and second bonding layers on the first and second substrates for a first annealing time period, wherein the first annealing is conducted at an annealing temperature that is higher than the low temperature of formation of each bonding layer and is at least 350° C. but less than 450° C. and for a time which does not deleteriously affect the components, micro-components or circuits, and the first annealing comprises an initial temperature that is increased at a rate between 1° C./min and 5° C./min to provide a temperature ramp up to the first annealing temperature, and wherein the first annealing time period lasts between 10 minutes and 5 h;
assembling the annealed first and second substrates to form a structure by molecular bonding by bringing into contact the exposed surfaces of the first bonding layer and the second bonding layer; and
conducting a second annealing of the first and second bonding layers of the bonded first and second substrates after assembling the structure, with the second annealing conducted at a second temperature of at least 350° C. and lower than or at most equal to the first annealing temperature,
wherein the second annealing is conducted at a temperature and time which does not deleteriously affect the components, micro-components or circuits; and
wherein the annealings provide a bonding interface between the substrates that has a bonding energy of at least 4 J/m 2 .
16. The method according to claim 1 , wherein at least one of the bonding layers is an oxide or nitride material; wherein at least one of the substrates is made of a semiconductor material and wherein the bonding between the first and second bonding layers at the bonding interface is of molecular adhesion type.
17. The method according to claim 4 , wherein at least one of the bonding layers is an oxide or nitride material; wherein at least one of the substrates is made of a semiconductor material and wherein the bonding between the first and second bonding layers at the bonding interface is of molecular adhesion type.
18. The method according to claim 15 , wherein at least one of the bonding layers is an oxide or nitride material and wherein at least one of the substrates is made of a semiconductor material.
19. A method for increasing bond strength and reducing contaminants when bonding two semiconductor substrates, which comprises:
forming a first bonding layer on a first substrate and forming a second bonding layer on a second substrate, wherein at least one of the substrates comprises one or more components, micro-components or circuits, wherein the first bonding layer and the second bonding layer each have an exposed surface, and the formation of each bonding layer is done at a temperature that is less than or equal to 300° C.;
conducting a first annealing of each of the first and second substrates for a first annealing time period and up to a first annealing temperature of at least 350° C. but less than 450° C. to degas contaminants from the substrates;
assembling the annealed first and second substrates to form a structure by molecular bonding by bringing into contact the exposed surfaces of the first and second bonding layers; and
conducting a second annealing of the bonded first and second substrates at a second temperature that is at least 350° C. but below 450° C., wherein the second annealing temperature does not exceed the first annealing temperature;
wherein the annealings provide a bonding interface between the substrates that has a bonding energy of at least 4 J/m 2 and without a reduction in porosity of the bonding layers; and
wherein the first and second annealings are conducted at a temperature and time which does not deleteriously affect the components, micro-components or circuits.
20. The method according to claim 19 , wherein at least one of the bonding layers is an oxide or nitride material and wherein at least one of the substrates is made of a semiconductor material.