Method of forming layered polysilicon filled contact by doping sensitive endpoint etching

• US 4,829,024 A
• Filed: 09/02/1988
• Issued: 05/09/1989
• Est. Priority Date: 09/02/1988
• Status: Expired due to Fees

• Current Assignee: Motorola, Inc. (Motorola Solutions, Inc.)
• Original Assignee: Motorola, Inc. (Motorola Solutions, Inc.)
• Inventors: Swenson, Mark S., Madan, Sudhir K., Klein, Jeffrey L., Poon, Stephen S.
• Primary Examiner(s): Hearn, Brian E.
• Assistant Examiner(s): NGUYEN, TUAN H
• Application Number:
  US07/239,919
• Time in Patent Office: 249 Days
• Field of Search: 437/189, 437/192, 437/193, 148/DIG. 19, 357/51, 357/71, 357/59 F, 357/68
• US Class Current: 438/14
• CPC Class Codes: H01L 21/28525 the conductive layers comprising semiconducting material H01L21/28518, H01L21/28537 take precedence
• CPC Class Codes: H01L 21/32137 of silicon-containing layers
• CPC Class Codes: H01L 21/76879 by selective deposition of conductive material in the vias, e.g. selective C.V.D. on semiconductor material, plating plating on semiconductors in general H01L21/288

Abstract

A semiconductor process is provided for the formation of a very low resistance contact. After a straight wall contact is formed conventionally above a silicon substrate, a blanket metal barrier layer is deposited. A plurality of planar polysilicon layers are deposited above the metal barrier layer. The polysilicon layers have varying doping levels and are etched away. A byproduct gas of the etch reaction is monitored and the transition between polysilicon layers can be accurately noted. In this way, a layer of doped polysilicon is left above the metal barrier in the contact region. Metal may then be patterned over the entire structure to provide a low resistance reliable contact.

Claims

1. A method of forming a layered polysilicon contact, comprising the steps of:

providing a substrate material with a doped diffusion region in a portion of the substrate material and at a top surface of the substrate material;

depositing a layer of electrically insulating material above the substrate material and doped diffusion region;

forming a contact fill region with substantially vertical sidewalls by removing a portion of insulating material to expose a portion of a top surface of the doped diffusion region;

forming a first layer of a first metal over both the layer of electrically insulating material and the top surface of the doped diffusion region;

forming a layer of a metal barrier material over the layer of first metal;

depositing a first layer of polysilicon having an impurity added thereto above the layer of metal barrier material;

depositing a second layer of polysilicon having substantially less impurity added thereto above the first layer of polysilicon;

depositing a third layer of polysilicon having the impurity added thereto above the second layer of polysilicon;

etching away the second and third layers of polysilicon and maintaining the first layer of polysilicon; and

forming a second layer of a second metal above the first layer of polysilicon substantially above the contact fill region.

2. The method of claim 1 wherein the first layer of polysilicon is maintained after etching away the second and third layers of polysilicon by monitoring photoemissions provided from a chemical reaction used to etch the second and third layers of polysilicon.

3. The method of claim 1 wherein the metal barrier material is titanium nitride.

4. The method of claim 1 wherein the layer of electrically insulating material is dual layer comprising a layer of borophosphosilicate glass formed over a layer of undoped oxide.

5. The method of claim 1 wherein the third layer of polysilicon is deposited to a substantially larger thickness than the first and second layers of polysilicon.

6. The method of claim 1 wherein the first and second metals are the same metal material.

7. A method of forming a polysilicon contact, comprising the steps of:

providing a silicon substrate having a diffusion region contained therein and extending along a portion of a top surface of the substrate, said contact to provide electrical connectivity to the diffusion region;

depositing a layer of electrically insulating material above the substrate and diffusion region;

forming a contact fill region by removing a portion of the layer of electrically insulating material to expose a portion of a top surface of the substrate;

depositing a layer of a first metal over both the electrically insulating material and the exposed top surface of the substrate;

forming a layer of titanium nitride over the layer of metal;

depositing polysilion above the layer of titanium nitride to completely fill said contact fill region, said polysilicon having at least two zones of differing impurity concentrations;

selectively etching by a predetermined chemical reaction each of the at least two zones of polysilicon until etching to an endpoint indicating a zone of polysilicon immediately above the layer of titanium nitride adjacent the contact fill region, said endpoint being detected by monitoring a ratio of a product produced from the predetermined reaction and a reactant used in the predetermined reaction and detecting a variation in the ratio when said endpoint is reached; and

forming a layer of a second metal above the polysilicon which is not etched and substantially above the contact fill region.

8. The method of claim 7 wherein the layer of electrically insulating material is a dual layer of borophosphosilicate glass over a layer of undoped oxide.

9. The method of claim 7 wherein the ratio is a ratio of a chemical compound containing fluorine and a chemical compound containing chlorine.

10. The method of claim 7 wherein the first and second metals are the same metal material.