TILTED IMPLANT FOR POLY RESISTORS
A semiconductor device having a substrate, a dielectric layer, a polycrystalline silicon (“poly”) resistor, a drain, and a source is disclosed. After implantation, the poly resistor may have a lateral doping profile with two peaks, one near each edge of the poly resistor, and a trough near the middle of the poly resistor. Such a doping profile can allow the poly resistor to have a resistance that is insensitive to small variations in critical dimension of the poly resistor. The resistance of the poly resistor may be determined by the doping dose of the tilted implant used to form the poly resistor. The tilted implant may be used to form the drain and the source of a transistor substantially simultaneously as forming the poly resistor.
1 . A method of manufacturing a semiconductor device, comprising:
forming a dielectric layer on a substrate;
forming a polycrystalline silicon (“poly”) layer on the dielectric layer;
forming a patterned masking layer on the poly layer;
etching a portion of the dielectric layer and a portion of the poly layer using the patterned masking layer to form a remaining portion of the dielectric layer and a remaining portion of the poly layer; and
implanting dopants at a tilted angle into the remaining portion of the poly layer to form a poly resistor and into the substrate to form lightly-doped drain regions,
wherein the patterned masking layer prevents implantation of dopants into the remaining portion of the poly layer through a top surface of the patterned masking layer during the implanting.
2 . The method of claim 1 , wherein the dopants comprise p-type dopants.
3 . The method of claim 2 , wherein the p-type dopants comprise boron ions.
4 . The method of claim 3 , wherein implanting the boron ions further comprises using a doping dose of greater than or equal to 8×10 13 ions/cm 2 .
5 . The method of claim 3 , wherein implanting the boron ions further comprises using a doping energy level of greater than or equal to 10 keV.
6 . The method of claim 3 , wherein implanting the boron ions further comprises using four rotations.
7 . The method of claim 2 , wherein the dopants further tilted implant comprises implanting comprise boron fluoride ions.
8 . The method of claim 7 , wherein implanting the boron fluoride ions further comprises using a doping dose of greater than or equal to 8×10 13 ions/cm 2 .
9 . The method of claim 7 , wherein implanting the boron fluoride ions further comprises using a doping energy level of greater than or equal to 60 keV.
10 . The method of claim 7 , wherein implanting the boron fluoride ions further comprises using four rotations.
11 . The method of claim 1 , wherein the dopants comprise n-type dopants.
12 . The method of claim 1 , wherein the tilted angle is 35 degrees.
13 . The method of claim 1 , wherein forming the patterned masking layer comprises forming a nitride layer.
14 . A semiconductor device, comprising:
a substrate;
a dielectric layer on the substrate; and
a poly resistor on the dielectric layer;
wherein the poly resistor was formed using a tilted implant.
15 . The device of claim 14 , wherein operation of the tilted implant results in the poly resistor having a lateral doping concentration profile with two peaks, one near each edge of the poly resistor, and with a trough near the middle of the poly resistor.
16 . The device of claim 15 , wherein the lateral doping profile with two peaks causes the poly resistor to have a resistance that is insensitive to small variations in a critical dimension of the poly resistor.
17 . The device of claim 16 , wherein the critical dimension is greater than or equal to 0.25 μm.
18 . The device of claim 14 , wherein the poly resistor has a resistance that is determined by a doping dose of the tilted implant.