Semiconductor structure including bottom isolation and method for manufacturing the same
A semiconductor structure includes: a first fin portion and a second fin portion; a first device and a second device which are respectively disposed on front surfaces of the first and second fin portions, each of the first and second devices including a source/drain portion; an isolation portion disposed to separate the first fin portion from the second fin portion and to separate the first device from the second device; and a hard mask portion disposed beneath a back surface of the isolation portion, and including a main region and two sidewall regions that are respectively located at two opposite sides of the main region so as to separate the main region from the first and second fin portions. The sidewall regions are made of a material different from that of the isolation portion. The main region is made of a material different from the material of the sidewall regions.
1 . A method for forming a semiconductor structure, comprising:
forming a patterned structure which includes a first fin portion and a second fin portion each of which has a front surface and a back surface opposite to the front surface along a first direction, the first fin portion and the second fin portion being spaced apart from each other in a second direction different from the first direction;
a first device and a second device which are respectively disposed on the front surface of the first fin portion and the front surface of the second fin portion, each of the first device and the second device including a source/drain portion, and
an isolation structure disposed to separate the first fin portion and the second fin portion from each other and to separate the first device and the second device from each other;
recessing the isolation structure from a back surface of the isolation structure to form a recess such that the isolation structure is formed into an isolation portion; and
forming a hard mask portion in the recess, the hard mask portion including a main region and two sidewall regions that are respectively located at two opposite sides of the main region in the second direction, so as to separate the main region from the first fin portion and the second fin portion, the two sidewall regions being made of a first insulating material different from a material of the isolation portion, the main region being made of a second insulating material different from the first insulating material of the two sidewall regions.
2 . The method as claimed in claim 1 , wherein formation of the hard mask portion includes:
depositing a first insulating layer along the back surface of each of the first fin portion and the second fin portion and along an inner surface of the recess, the first insulating layer including the first insulating material;
depositing a second insulating layer on the first insulating layer, the second insulating layer including the second insulating material;
removing horizontal portions of the second insulating layer such that two vertical portions of the second insulating layer are left in the recess and are spaced apart from each other in the second direction;
removing portions of the first insulating layer which are exposed from the two vertical portions of the second insulating layer such that the first insulating layer is formed into the two sidewall regions of the hard mask portion; and
forming a third insulating layer to fill the recess, the third insulating layer including the second insulating material, such that the two vertical portions of the second insulating layer and the third insulating layer together serve as the main region of the hard mask portion.
3 . The method as claimed in claim 1 , further comprising:
forming a dielectric layer to cover the back surface of each of the first fin portion and the second fin portion; and
forming a backside via which extends through the dielectric layer and the second fin portion and which is connected to the source/drain portion of the second device.
4 . The method as claimed in claim 1 , further comprising:
forming a dielectric layer to cover the back surface of each of the first fin portion and the second fin portion, the dielectric layer having a back surface spaced apart from the back surface of each of the first fin portion and the second fin portion;
forming a hole which penetrates the dielectric layer and the second fin portion so as to expose the source/drain portion of the second device, an inner surface of the hole having a hole-bottom portion which is defined by the source/drain portion of the second device and a lateral portion which interconnects the back surface of the dielectric layer and the hole-bottom portion;
depositing a silicon nitride layer along the inner surface of the hole, the silicon nitride layer having a first portion on the hole-bottom portion and a second portion on the lateral portion;
removing the first portion of the silicon nitride layer so as to expose the source/drain portion of the second device; and
forming a backside via in the hole, such that the backside via is connected to the source/drain portion of the second device.
5 . The method as claimed in claim 4 , wherein:
the second portion of the silicon nitride layer has two vertical parts and a horizontal part between the two vertical parts;
during the removal of the first portion of the silicon nitride layer, the horizontal part of the second portion of the silicon nitride layer is removed so as to permit one of the two sidewall regions of the hard mask portion to be exposed from the two vertical parts of the second portion of the silicon nitride layer; and
after forming the backside via, the two vertical parts of the second portion of the silicon nitride layer and the one of the two sidewall regions of the hard mask portion cooperatively separate the backside via from the isolation portion.
6 . The method as claimed in claim 1 , wherein the first insulating material of the two sidewall regions is different from a material of the silicon nitride layer.
7 . The method as claimed in claim 1 , wherein the first insulating material of the two sidewall regions includes an electrically insulating metal oxide.
8 . The method as claimed in claim 1 , wherein the hard mask portion has a surface flush with the back surface of one of the first fin portion and the second fin portion.
9 . A method for forming a semiconductor structure, comprising:
forming a first fin portion and a second fin portion on a substrate, each of the first fin portion and the second fin portion having a front surface and a back surface opposite to the front surface along a first direction which is normal to a lower surface of the substrate, and being elongated in a second direction different from the first direction, the first fin portion and the second fin portion being spaced apart from each other along a third direction different from the first direction and the second direction;
forming a trench isolation on the substrate between the first fin portion and the second fin portion;
forming a first device and a second device respectively on the front surface of the first fin portion and the front surface of the second fin portion, each of the first device and the second device including a source/drain portion;
forming a first dielectric layer on the trench isolation between the source/drain portion of the first device and the source/drain portion of the second device, the first dielectric layer and the trench isolation together constituting an isolation structure which has a front surface and a back surface opposite to the front surface along the first direction;
removing the substrate so as to expose the back surface of each of the first fin portion, the second fin portion and the isolation structure; and
forming a hard mask portion which extends from the back surface of the isolation structure into the isolation structure.
10 . The method as claimed in claim 9 , wherein the hard mask portion includes a main region and two sidewall regions that are respectively located at two opposite sides of the main region in the third direction so as to separate the main region from the first fin portion and the second fin portion, the two sidewall regions being made of a material different from a material of the isolation structure and a material of the main region.
11 . The method as claimed in claim 10 , wherein each of the two sidewall regions has a vertical part and a horizontal part which is connected to an end of the vertical part, the horizontal part of one of the two sidewall regions extending toward the horizontal part of another one of the two sidewall regions.
12 . The method as claimed in claim 11 , wherein the horizontal part of each of the two sidewall regions is in contact with the back surface of the isolation structure.
13 . The method as claimed in claim 12 , further comprising:
forming a second dielectric layer on the first fin portion, the second fin portion and the hard mask portion opposite to the first dielectric layer; and
forming a backside via which extends through the second dielectric layer and the second fin portion such that the backside via is brought into connection with the source/drain portion of the second device.
14 . The method as claimed in claim 13 , further comprising:
forming a silicon nitride re-deposition layer to separate the backside via from the second fin portion and the isolation structure.
15 . The method as claimed in claim 14 , wherein
the backside via has a wider portion and a narrower portion, the narrower portion being disposed between the wider portion and the source/drain portion of the second device, the wider portion having a dimension in the third direction greater than a dimension of the second fin portion in the third direction, the backside via further having a transition portion between the wider portion and the narrower portion, and
the silicon nitride re-deposition layer is discontinuous so as to permit the transition portion to be in direct contact with the hard mask portion.
16 . A method for forming a semiconductor structure, comprising:
forming a first fin portion and a second fin portion, the first fin portion and the second fin portion extending lengthwise along a first direction and being spaced apart from each other by a trench isolation in a second direction different from the first direction;
forming a first device and a second device respectively on the first fin portion and the second fin portion, each of the first device and the second device including two source/drain portions which are spaced apart from each other in the first direction, and a channel portion extending between the two source/drain portions;
forming a gate portion over the channel portion of the first device and the channel portion of the second device, the gate portion extending lengthwise along the second direction over the trench isolation;
forming an inter-layer dielectric layer on the trench isolation and the two source/drain portions of each of the first device and the second device, the inter-layer dielectric layer and the trench isolation together constituting an isolation structure;
forming a hard mask portion in the isolation structure such that the hard mask portion is spaced apart from the gate portion through the isolation structure, the hard mask portion including a main region and two sidewall regions that are respectively located at two opposite sides of the main region in the second direction so as to separate the main region from the first fin portion and the second fin portion, the two sidewall regions being made of a material different from a material of the isolation structure and a material of the main region; and
forming a backside via which extends through the second fin portion such that the backside via is brought into connection with one of the two source/drain portions of the second device.
17 . The method as claimed in claim 16 , wherein each of the two sidewall regions has an L-shaped cross-section.
18 . The method as claimed in claim 16 , wherein
the backside via has a wider portion and a narrower portion, the narrower portion being disposed between the wider portion and the one of the two source/drain portions of the second device,
the wider portion has a dimension in the second direction greater than a dimension of the second fin portion in the second direction, and
the narrower portion has a dimension in the second direction that is not greater than the dimension of the second fin portion in the second direction.
19 . The method as claimed in claim 18 , wherein
the channel portion is spaced apart from a corresponding one of the first fin portion and the second fin portion in a third direction different from the first direction and the second direction,
the gate portion is disposed to surround the channel portion of each of the first device and the second device,
each of the first device and the second device further includes two inner spacers which are spaced apart from each other in the first direction, and which are disposed between the channel portion and a corresponding one of the first fin portion and the second fin portion, such that the gate portion is separated from the two source/drain portions respectively through the two inner spacers, and
the narrower portion has a dimension in the first direction greater than a dimension of the one of the two source/drain portions of the second device in the first direction such that the narrower portion partially lands on one of the two inner spacers of the second device.
20 . The method as claimed in claim 19 , wherein the gate portion has
a first gate part extending into the trench isolation of the isolation structure along the first direction, and having a middle region and two end regions at two opposite sides of the middle region in the second direction, a dimension of the middle region in the first direction being smaller than a dimension of each of the two end regions in the first direction, and
two second gate parts respectively disposed over the channel portion of the first device and the channel portion of the second device, each of the two second gate parts having a maximum dimension in the first direction that is greater than the dimension of the middle region of the first gate part in the first direction such that each of the two second gate parts partially overlaps the two inner spacers of a corresponding one of the first device and the second device in the third direction.