S-contact for SOI
Systems, methods, and apparatus for an improved protection from charge injection into layers of a device using resistive structures are described. Such resistive structures, named s-contacts, can be made using simpler fabrication methods and less fabrication steps. In a case of metal-oxide-semiconductor (MOS) field effect transistors (FETs), s-contacts can be made with direct connection, or resistive connection, to all regions of the transistors, including the source region, the drain region and the gate.
1. A device comprising:
a silicon-on-insulator (SOI) substrate, the SOI substrate comprising:
a high resistivity semiconductor substrate comprising silicon;
a single layer trap rich layer overlying and in contact with the silicon of the high resistivity semiconductor substrate;
an insulation layer overlying and in contact with the trap rich layer; and
an active layer overlying and in contact with the insulation layer;
a transistor fabricated on the SOI substrate, the transistor comprising a transistor contact; and
a first metal line connecting the transistor contact to a first metal contact,
wherein the first metal contact extends through the active layer and through the insulation layer and makes a resistive contact with the silicon of the high resistivity semiconductor substrate through the trap rich layer.
2. The device according to claim 1 , wherein the first metal contact extends through the active layer and through the insulation layer so as to at least contact the trap rich layer to make the resistive contact.
3. The device according to claim 1 , wherein the transistor contact is a source contact, a drain contact, or a gate contact.
4. The device according to claim 1 , wherein an effective contact resistance between the first metal contact and the high resistivity semiconductor substrate is in a range of 0.2 to 20 G-ohm.
5. The device according to claim 1 , wherein the first metal contact extends through the active layer and through the insulation layer to make contact with the trap rich layer at a depth corresponding to a desired resistance value coupled between the first metal contact and the high resistivity semiconductor substrate.
6. The device according to claim 5 , wherein the depth is substantially equal to zero.
7. The device according to claim 1 , wherein the resistive contact with the silicon of the high resistivity semiconductor substrate is through a resistance provided by a thickness portion of the trap rich layer not penetrated by the first metal contact.
8. The device according to claim 1 , wherein a resistivity value of the high resistivity semiconductor substrate is in a range of 3,000 to 20,000 ohm-cm.
9. The device according to claim 1 , wherein a resistivity value of the high resistivity semiconductor substrate is greater than 3,000 ohm-cm.
10. The device according to claim 1 , further comprising a second metal line that resistively connects another transistor contact to the high resistivity semiconductor substrate, wherein the second metal line connects the other transistor contact to a second metal contact, and wherein the second metal contact extends through the active layer and through the insulation layer and makes a resistive contact with the silicon of the high resistivity semiconductor substrate through the trap rich layer.
11. The device according to claim 1 , wherein the first metal line comprises copper extending from the transistor contact to the first metal contact, wherein the first metal contact comprises tungsten extending through the active layer and through the insulation layer, and wherein the transistor is one of: a) an N-type metal-oxide-semiconductor field effect transistor (NMOSFET), or b) a P-type metal-oxide-semiconductor field effect transistor (PMOSFET).
12. The device according to claim 1 , wherein the first metal contact extends through the active layer at an isolation region formed in the active layer.
13. The device according to claim 12 , wherein the isolation region is a shallow trench isolation (STI) region.
14. The device according to claim 1 , wherein the insulation layer is an insulation buried oxide (BOX) layer.
15. A method for providing a discharge path to a silicon-on-insulator (SOI) transistor, the method comprising:
(i) forming the SOI transistor on a SOI substrate that comprises a high resistivity semiconductor substrate comprising silicon;
(ii) forming a transistor contact of the SOI transistor;
(iii) forming a first metal line connecting the transistor contact to a first metal contact;
(iv) extending the first metal contact through an active layer and through an insulation layer of the SOI substrate to make a resistive contact with the silicon of the high resistivity semiconductor substrate through a trap rich layer of the SOI substrate; and
(v) based on the resistive contact, providing a resistive discharge path to the SOI transistor.
16. The method according to claim 15 , wherein the resistive contact with the high resistivity semiconductor substrate is through a resistance provided by a thickness portion of the trap rich layer not penetrated by the first metal contact.
17. The method according to claim 15 , wherein the extending comprises extending the first metal contact through the active layer and through the insulation layer so as to at least contact the trap rich layer to make the resistive contact.
18. The method according to claim 15 , wherein the first metal contact extends through the active layer at an isolation region of the active layer.
19. The method according to claim 15 , wherein the SOI transistor is formed in active regions of the active layer, wherein the active layer overlies and is in contact with the insulation layer, wherein the insulation layer overlies and is in contact with the trap rich layer, and wherein the trap rich layer overlies and is in contact with the high resistivity semiconductor substrate.
20. The method according to claim 15 , wherein the insulation layer is an insulation buried oxide (BOX) layer, wherein the first metal line comprises copper extending from the transistor contact to the first metal contact, and wherein the first metal contact comprises tungsten extending through the active layer and through the insulation layer of the SOI substrate.
21. The device according to claim 1 , further comprising one or more additional metal contacts that each extends through the active layer and through the insulation layer and each makes a respective resistive contact with the high resistivity semiconductor substrate through the trap rich layer, wherein a number of the one or more additional metal contacts is based on a desired equivalent resistance between the one or more additional metal contacts and a bottom surface of the high resistivity semiconductor substrate away from the insulation layer.