METHOD OF WAFER ASSEMBLY BY MOLECULAR BONDING
The present description concerns a method of manufacturing a first wafer, intended to be assembled to a second wafer by molecular bonding, including the successive steps of: forming a stack of layers at the surface of a substrate; and successive chemical etchings of the edges of said layers from the layer of the stack most distant from the substrate, across a smaller and smaller width.
1 . A method, comprising:
forming a stack of layers on a surface of a substrate; and
performing successive chemical etchings of respective edges of respective layers of the stack of layers on the substrate, the successive chemical etchings including:
a first chemical etching of a first respective layer of the stack of layers furthest away from the substrate; and
a final chemical etching of a second respective layer of the stack of layers closet to the substrate.
2 . The method according to claim 1 , wherein the chemical etching of each layer of the stack of layers includes exposing an etching solution to the respective edge to be etched of the respective layer.
3 . The method according to claim 1 , wherein a distance between the respective edges of two successive respective layers in the stack ranging from 30 μm to 200 μm.
4 . The method according to claim 1 , wherein the successive chemical etchings of the respective edges is followed by forming a step structure of the substrate on a contour of the substrate.
5 . The method according to claim 4 , wherein forming the step structure further includes forming the step structure by chemical etching.
6 . The method according to claim 1 , wherein at least one of the successive chemical etchings includes utilizing a hydrogen fluoride solution.
7 . The method according to claim 1 , wherein at last one of the successive chemical etchings includes utilizing a solution including hydrogen fluoride and nitric acid.
8 . The method according to claim 1 , wherein at least one of the successive chemical etchings includes utilizing a solution including at least one of tetramethylammonium hydroxide, of tetraethylammonium hydroxide, or of ammonia.
9 . The method according to claim 4 , wherein forming the step structure further includes forming the step structure by mechanical abrasion.
10 . The method according to claim 4 , wherein the step structure is formed in the substrate down to a depth in the range from 5 μm to 20 μm.
11 . A method, comprising:
processing a first wafer, the processing including:
forming a stack of layers on a surface of a substrate;
performing successive chemical etchings of respective edges of respective layers of the stack of layers on the substrate, the successive chemical etchings including:
a first chemical etching of a first respective layer of the stack of layers furthest away from the substrate; and
a final chemical etching of a second respective layer of the stack of layers closet to the substrate; and
bonding the first wafer to a second wafer by molecular bonding.
12 . The method according to claim 11 , further comprising thinning the first wafer after the bonding of the first wafer to the second wafer by molecular bonding.
13 . A device, comprising:
a first wafer including:
a substrate having a surface and a first edge;
a center axis transverse to the surface of the substrate; and
a stack of layers at the surface of the substrate, the stack of layers including:
a first layer on the surface of the substrate, the first layer having a second edge; and
a second layer on the first layer, the second layer having a third edge further away from the second edge than the first edge in a first direction transverse to the center axis.
14 . The device according to claim 13 , wherein at least one layer of the stack of layers is a semiconductor layer.
15 . The device according to claim 13 , wherein at least one layer of the stack of layers of the stack is a dielectric layer.
16 . The device according to claim 13 , wherein the substrate includes a step structure at the first edge.
17 . The device of claim 16 , wherein:
the substrate includes a thickness extending in a second direction transverse to the first direction; and
the step structure including a depth extending in the second direction, the depth being less than the thickness.
18 . The device according to claim 13 , wherein the stack of layers and the substrate have a staircase structure.
19 . The device according to claim 13 , further comprising a second wafer coupled to the first wafer.
20 . The device of claim 19 , wherein the second wafer is molecularly coupled to the stack of layers of the first wafer.