Method for the production of thin substrates
View Patent ↗A method is provided for producing a thin substrate with a thickness below 750 microns, comprising providing a mother substrate, the mother substrate having a first main surface and a toughness; inducing a stress with predetermined stress profile in at least a portion of the mother substrate, said portion comprising the thin substrate, the induced stress being locally larger than the toughness of the mother substrate at a first depth under the main surface; such that the thin substrate is released from the mother substrate, wherein the toughness of the mother substrate at the first depth is not lowered prior to inducing the stress. The method can be used in the production of, for example, solar cells.
1. A method for producing a thin substrate with a thickness of less than about 750 microns, comprising:
providing a mother substrate, said mother substrate having a main surface and a toughness; and
inducing a stress with a predetermined stress profile in at least a portion of said mother substrate, said portion comprising a thin substrate, said induced stress being locally larger than the toughness of said mother substrate at a first depth under the main surface, such that said thin substrate is released from said mother substrate at the first depth, wherein the toughness of the mother substrate at the first depth is not lowered prior to inducing the stress, wherein the first depth is determined by at least one of tuning properties of a stress inducing mechanism and dimensions of a stress inducing mechanism, wherein the stress inducing mechanism is formed by providing at least one layer of stress induction material with at least one predetermined stress induction mechanism on said mother substrate and actuating said at least one stress induction mechanism, wherein tuning properties of a stress inducing mechanism and dimensions of a stress inducing mechanism comprise tuning properties of the stress induction material and dimensions of the stress induction material, and wherein said mother substrate has a side surface and said at least one layer of stress induction material partially extends on and is directly in contact with said side surface of said mother substrate.
2. The method according to claim 1 ,
wherein the mother substrate has a shape of a cylinder.
3. The method according to claim 1 , wherein said stress is induced by creating a different expansion or a different contraction of said at least one layer of stress induction material and said mother substrate.
4. The method according to claim 3 , wherein said at least one layer of stress induction material has a first thermal expansion coefficient and said mother substrate has a second thermal expansion coefficient, wherein said first thermal expansion coefficient is larger than said second thermal expansion coefficient, and wherein the method further comprises applying a general temperature step for inducing the stress in at least a portion of said mother substrate, wherein said temperature step is a negative temperature step.
5. The method according to claim 3 , wherein said at least one layer of stress induction material has a first thermal expansion coefficient and said mother substrate has a second thermal expansion coefficient, wherein said first thermal expansion coefficient is smaller than said second thermal expansion coefficient, and wherein the method further comprises applying a general temperature step for inducing the stress in at least a portion of said mother substrate, wherein said temperature step is a positive temperature step.
6. The method according to claim 1 , wherein the set of at least one layer of stress induction material comprises at least two layers, wherein a bond between said two subsequent layers of stress induction materials, a first layer of stress induction material, and said mother substrate is strong enough to withstand said induced stress.
7. The method according to claim 1 , wherein said at least one layer of stress induction material is able to withstand said stress without breaking and without plastic deformation.
8. The method according to claim 1 , wherein said at least one layer of stress induction material is flexible.
9. The method according to claim 1 , further comprising, before inducing said stress, a step of temporarily bonding said at least one layer of stress induction material to a stretchable carrier substrate, wherein said stretchable carrier substrate is resistant to at least one of said at least one stress inducing mechanism and said induced stress.
10. The method according to claim 1 , further comprising a step of removing at least a portion of said at least one layer of stress induction material, thereby releasing said stress from said thin substrate.
11. The method according to claim 1 ,
wherein said main surface is concave shaped.
12. The method according to claim 1 , wherein providing a mother substrate comprises providing a silicon mother substrate and wherein inducing a stress comprises screen printing a metal layer atop the silicon mother substrate, annealing the silicon mother substrate with metal layer and allowing the silicon mother substrate with metal layer to cool, whereby the silicon mother substrate and the metal layer each undergo a thermal contraction, leading to a high stress field in the silicon mother substrate due to a mismatch in a coefficient of thermal expansion between the metal layer and the silicon mother substrate, causing the metal layer to peel off the silicon mother substrate with a thin layer of silicon from the mother substrate attached thereto.
13. The method according to claim 12 , wherein a thickness of the thin layer of silicon is less than 750 microns.
14. The method according to claim 13 , wherein the metal is Ag or Al.
15. The method according to claim 14 , wherein the silicon is p-type multi-crystalline silicon, and wherein the silicon mother substrate with metal layer are annealed at a temperature above 700° C. for a few seconds.