MOS transistor with low-k spacer to suppress capacitive coupling between gate and source/drain extensions

• US 6,107,667 A
• Filed: 09/10/1998
• Issued: 08/22/2000
• Est. Priority Date: 09/10/1998
• Status: Expired due to Term

• Current Assignee: Advanced Micro Devices SDN Berhad (Advanced Micro Devices, Inc.)
• Original Assignee: Advanced Micro Devices, Inc.
• Inventors: An, Judy Xilin, Yu, Bin, Liu, Yowjuang W.
• Primary Examiner(s): Tran, Minh Loan
• Assistant Examiner(s): NGUYEN, CUONG QUANG
• Application Number:
  US09/151,146
• Time in Patent Office: 712 Days
• Field of Search: 257/380-384, 257/410-412, 257/345, 257/401-408, 257/506, 257/900, 438/282-289, 438/299-305, 438/228
• US Class Current: 257/408
• CPC Class Codes: H01L 21/28123 Lithography-related aspects, e.g. sub-lithography lengths; Isolation-related aspects, e.g. to solve problems arising at the crossing with the side of the device isolation; Planarisation aspects
• CPC Class Codes: H01L 21/28194 by deposition, e.g. evaporation, ALD, CVD, sputtering, laser deposition H01L21/28202 takes precedence
• CPC Class Codes: H01L 29/42376 characterised by the length or the sectional shape
• CPC Class Codes: H01L 29/4983 with a lateral structure, e.g. a Polysilicon gate with a lateral doping variation or with a lateral composition variation or characterised by the sidewalls being composed of conductive, resistive or dielectric material
• CPC Class Codes: H01L 29/51 Insulating materials associated therewith for MIS structures on thin film semiconductor H01L29/4908
• CPC Class Codes: H01L 29/6653 using the removal of at least part of spacer, e.g. disposable spacer
• CPC Class Codes: H01L 29/66545 using a dummy, i.e. replacement gate in a process wherein at least a part of the final gate is self aligned to the dummy gate
• CPC Class Codes: H01L 29/6659 with both lightly doped source and drain extensions and source and drain self-aligned to the sides of the gate, e.g. lightly doped drain [LDD] MOSFET, double diffused drain [DDD] MOSFET
• CPC Class Codes: Y10S 257/90 MOSFET type gate sidewall insulating spacer

Abstract

A method for making a ULSI MOSFET includes establishing a void in a field oxide layer on a silicon substrate and filling the center of the void with a gate electrode. A high-k gate insulator is sandwiched between the gate electrode and the substrate. Around the void, a low-k gate spacer is formed, with the gate spacer being disposed directly above the source and drain extensions of the MOSFET.

Claims

1. A semiconductor device made in accordance with the steps comprising of:

establishing a channel region, a source region, a drain region, a source extension and a drain extension within a surface of a substrate;

forming a field oxide layer over the surface of the substrate;

establishing a gate void in the field oxide layer defining a wall above the substrate, wherein the gate void is above the channel region, source extension and drain extension;

forming a gate oxide within the gate void on the surface of the substrate;

disposing a gate spacer in the gate void against the wall over the gate oxide and above the source extension and drain extension, wherein the gate spacer has a void over the channel region of the substrate;

removing the gate oxide above the channel region of the substrate;

placing a gate insulator over the channel region of the substrate in the gate spacer void, wherein the gate insulator has a high dielectric coefficient;

disposing a gate electrode in the gate spacer void so that the gate spacer is disposed between the wall and the gate electrode and the gate insulator is between the gate electrode and the substrate;

removing the gate spacer and gate oxide to form a void between the wall and the gate electrode and exposing the substrate between the wall and the gate insulator;

forming a protective layer in the void between the wall and the gate electrode, so that the protective layer coats the wall, the gate electrode and the substrate between the wall and the gate insulator;

filling part of the void between the wall and the gate electrode with a low dielectric coefficient spacer, so that the low dielectric coefficient spacer is separated from the wall and the substrate and at least part of the gate electrode by the protective layer.

2. A digital processing apparatus incorporating the semiconductor device of claim 1.

3. A semiconductor device comprising:

at least one field effect transistor (FET) comprising;

a silicon substrate, comprising a substantially undoped channel region, a source region, a drain region, a source extension, and a drain extension;

a field oxide layer extending over the entire source region and drain region, wherein the field oxide layer is in contact with the silicon substrate, and wherein the field oxide layer has an aperture passing completely through the field oxide layer over the source extension, drain extension, and channel so that the field oxide layer does not extend over the channel, and wherein the field oxide layer has a thickness, and wherein part of the field oxide layer forms a wall surrounding the aperture;

a high-k gate insulator disposed on the substrate above the channel region within the aperture in the field oxide layer and forming a space between the high-k gate insulator and the field oxide layer;

a gate electrode covering the high-k gate insulator within the aperture in the field oxide layer and forming a space between the gate electrode and the field oxide layer;

a protective layer coating the wall of the field oxide layer and the silicon substrate surface, and the gate electrode within the aperture, so that the protective layer coats the silicon substrate surface in the space between the high-k gate insulator and the field oxide layer, above the source and drain extensions; and

a low-k gate spacer being disposed within the aperture of the field oxide layer and above the source and drain extensions in the space between the gate electrode and the field oxide layer, so that the field oxide layer does not extend over the low-k gate spacer, and connected to the part of the protective layer coating the wall of the field oxide layer and the part of the protective layer coating the source extension and drain extension of the silicon substrate and the part of the protective layer coating the gate electrode so that the low-k gate spacer is separated from the field oxide layer, the gate electrode, and the silicon substrate by the protective layer.

4. The device of claim 3, further comprising an electrode cap disposed over the gate electrode and gate spacer.

5. The semiconductor device, as recited in claim 3, wherein the protective layer surrounds the low-k spacer on three sides.

6. The semiconductor device, as recited in claim 5, wherein the protective layer is U-shaped.