Method for fabricating multiple transistor devices on a substrate with varying threshold voltages
First Claim
1. A method for fabricating multiple transistor devices on a substrate with a plurality of threshold voltages, comprising:
- forming a first device in a substrate, the first device including a screen layer with a first dopant concentration, a threshold voltage layer with a second dopant concentration less than the first dopant concentration, and a substantially undoped epitaxial channel with a first thickness thereon, the screen layer, threshold voltage layer, and undoped epitaxial channel of the first device underlying a first gate;
forming a second device in the substrate electrically isolated from the first device, the second device having a screen layer with a third dopant concentration, a threshold voltage layer with a fourth dopant concentration less than the third dopant concentration, and a substantially undoped epitaxial channel with a second thickness thereon, the screen layer, threshold voltage layer, and undoped epitaxial channel of the second device underlying a second gate, the second thickness being different than the first thickness such that the first and second devices have different threshold voltages;
wherein a top surface of the substantially undoped epitaxial channel of the first device is substantially coplanar with a top surface of the substantially undoped epitaxial channel of the second device adjacent respective gates of the first and second devices.
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Abstract
Fabrication of a first device on a substrate is performed by exposing a first device region, removing a portion of the substrate to create a trench in the first device region, forming a screen layer with a first dopant concentration in the trench on the substrate, and forming an epitaxial channel on the screen layer having a first thickness. On or more other devices are similarly formed on the substrate independent of each other with epitaxial channels of different thicknesses than the first thickness. Devices with screen layers having the same dopant concentration but with different epitaxial channel thicknesses have different threshold voltages. Thus, a wide variety of threshold voltage devices can be formed on the same substrate. Further threshold voltage setting can be achieved through variations in the dopant concentration of the screen layers.
505 Citations
12 Claims
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1. A method for fabricating multiple transistor devices on a substrate with a plurality of threshold voltages, comprising:
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forming a first device in a substrate, the first device including a screen layer with a first dopant concentration, a threshold voltage layer with a second dopant concentration less than the first dopant concentration, and a substantially undoped epitaxial channel with a first thickness thereon, the screen layer, threshold voltage layer, and undoped epitaxial channel of the first device underlying a first gate; forming a second device in the substrate electrically isolated from the first device, the second device having a screen layer with a third dopant concentration, a threshold voltage layer with a fourth dopant concentration less than the third dopant concentration, and a substantially undoped epitaxial channel with a second thickness thereon, the screen layer, threshold voltage layer, and undoped epitaxial channel of the second device underlying a second gate, the second thickness being different than the first thickness such that the first and second devices have different threshold voltages; wherein a top surface of the substantially undoped epitaxial channel of the first device is substantially coplanar with a top surface of the substantially undoped epitaxial channel of the second device adjacent respective gates of the first and second devices. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 12)
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10. A method for fabricating multiple transistor devices on a substrate with a plurality of threshold voltages, comprising:
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forming a first device in a substrate, the first device including a screen layer with a first dopant concentration, a threshold voltage layer with a second dopant concentration less than the first dopant concentration, and a substantially undoped epitaxial channel with a first thickness thereon, the screen layer, threshold voltage layer, and undoped epitaxial channel of the first device underlying a first gate; forming a second device in the substrate electrically isolated from the first device, the second device having a screen layer with a third dopant concentration, a threshold voltage layer with a fourth dopant concentration less than the third dopant concentration, and a substantially undoped epitaxial channel with a second thickness thereon, the second thickness being different than the first thickness such that the first and second devices have different threshold voltages, the screen layer, threshold voltage layer, and undoped epitaxial channel of the second device underlying a second gate, wherein a top surface of the substantially undoped epitaxial channel of the first device is substantially coplanar with a top surface of the substantially undoped epitaxial channel of the second device adjacent respective gates of the first and second devices; and forming a third device in the substrate electrically isolated from the first device, the third device having a threshold voltage that is set using a method that does not include a screen layer.
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11. A method for fabricating multiple transistor devices on a substrate with a plurality of threshold voltages, comprising:
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forming a first device in a substrate, the first device including a screen layer with a first dopant concentration and a substantially undoped epitaxial channel with a first thickness thereon; forming a second device in the substrate electrically isolated from the first device, the second device having a screen layer with a first dopant concentration and a substantially undoped epitaxial channel with a second thickness thereon, the second thickness being different than the first thickness such that the first and second devices have different threshold voltages; and forming a third device in the substrate electrically isolated from the first device, the third device having a threshold voltage that is set using a method that does not include a substantially undoped epitaxial channel.
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Specification