Process for forming low sheet resistance polysilicon having anisotropic etch characteristics

• US 4,561,907 A
• Filed: 07/12/1984
• Issued: 12/31/1985
• Est. Priority Date: 07/12/1984
• Status: Expired due to Term

• Current Assignee: Bruha Raicu
• Original Assignee: Applied Materials Incorporated Santa Clara CA
• Inventors: Raicu, Bruha
• Primary Examiner(s): Roy, Upendra
• Application Number:
  US06/630,091
• Time in Patent Office: 537 Days
• Field of Search: 148/1.5, 148/187, 148/175, 29/571, 29/576 B, 357/59, 357/91, 156/643, 156/646
• US Class Current: 438/301
• CPC Class Codes: H01L 21/2686 using incoherent radiation
• CPC Class Codes: H01L 21/32055 Deposition of semiconductive layers, e.g. poly - or amorphous silicon layers
• CPC Class Codes: H01L 21/32137 of silicon-containing layers
• CPC Class Codes: Y10S 148/004 Annealing, incoherent light
• CPC Class Codes: Y10S 438/934 Sheet resistance, i.e. dopant parameters

Abstract

A method for forming highly doped, low sheet resistance, anisotropically etched polysilicon using heat pulse annealing and plasma etching. The combination of low sheet resistance and anisotropic etch behavior is provided by heat pulse annealing for a time which corresponds to a characteristic transition region of the sheet resistance-annealing time curve.

Claims

1. A method for treating polysilicon material to provide low sheet resistance and anisotropic dry etching characteristics, comprising doping the polysilicon material using impurities selected from n-type and p-type impurities;

heating the polysilicon material at a selected temperature using rapid thermal annealing so that the time rate of change of the sheet resistance of the polysilicon material describes a region of relatively constant slope having at least a portion thereof characterized by an annealing time span which is associated with anisotropic etching of the polysilicon material; and

terminating annealing at a time within the time span.

2. A method for treating polysilicon material to provide low sheet resistance and anisotropic plasma etching characteristics, comprising doping the polysilicon material using impurities selected from n-type and p-type impurities;

heating the polysilicon material at a selected temperature using rapid thermal annealing so that the time rate of change of the sheet resistance of the polysilicon material describes a transition to a relatively shallowly sloped plateau region, the transition region and adjoining portion of the plateau region being characterized by an annealing time span which is associated with anisotropic etching of the polysilicon material; and

terminating annealing at a time within the time span.

3. A method of treating a layer of polysilicon material to provide low sheet resistance and anisotropic plasma etching characteristics, comprising forming a composite comprising the polysilicon layer on a support;

doping the layer of polysilicon using impurities selected from n-type and p-type impurities;

inserting the composite into a rapid heating chamber adapted for heating one or more wafers simultaneously; and

heating the layer of polysilicon material in the chamber at a temperature of at least about 1100°

C. for a time within the range of between about five and thirty seconds.

5. The polysilicon treatment method of claim 3 or 4 wherein the resulting polysilicon sheet resistance is ≦

17 ohms per square and the plasma etch anisotropy is ≦

0.2.

6. The polysilicon treatment method of claim 3 or 4 wherein the temperature is equal to or greater than about 1200°

C. and the resulting polysilicon sheet resistance is ≦

7 ohms per square and the plasma etch anisotropy is ≦

0.1.

7. The polysilicon treatment method of claim 3 or 4 wherein the temperature is equal to or greater than about 1200°

C. and the resulting polysilicon sheet resistance is ≦

7 ohms per square, the plasma etch anisotropy is ≦

0.1 and the polysilicon is doped by implanting at least a surface-adjacent region thereof to a concentration ≧

10²⁰ cm^-3.

8. The polysilicon treating method of claim 3 or 4 wherein the etching step is plasma etching using a chlorinated etching gas.

9. The polysilicon treating method of claim 3 or 4 wherein the etching step is plasma etching and the eteching gas comprises HCl.

10. The polysilicon treatment method of claim 7 wherein the impurities implanted are n-type impurities selected from one of phosphorous, antimony and arsenic.

11. The polysilicon treatment method of claim 7 wherein the annealing temperature is within the approximate range 1100°

C.-1200°

C. and the associated annealing time span is ≲

20 seconds.

12. The polysilicon treatment method of claim 10 wherein the implantation step is performed at a dose within the approximate range 10¹⁶ -10¹⁷ ions per cm².

4. A method of treating a layer of polysilicon material to provide low sheet resistance and anisotropic plasma etching characteristics, comprising forming a composite comprising the polysilicon layer on a wafer;

doping the layer of polysilicon to a concentration ≧

10²⁰ cm^-3 using impurities selected from n-type and p-type impurities;

inserting the composite into a rapid radiant heating chamber adapted for heating one or more wafers simultaneously; and

heating the layer of polysilicon material in the chamber at a temperature of at least about 1100°

C. for a time within the range of between about five and thirty seconds.

13. A method of treating a layer of polysilicon material to provide low sheet resistance and an anisotropic plasma etching profile, comprising forming a composite comprising the layer of polysilicon on a semiconductor wafer;

implanting at least a selected depth of the polysilicon material to a concentration ≧

10²⁰ cm^-3 of impurities selected from n-type and p-type impurities;

inserting the layer of polysilicon material into a rapid thermal annealing chamber adapted for heating one or more wafers simultaneously;

heating the polysilicon material in the chamber at a temperature of at least about 1100°

C. using rapid thermal annealing so that the time rate of change of the sheet resitivity of the polysilicon material describes a transition region to a relatively shallowly sloped plateau region, the transistion region and adjoining portion of the plateau region being characterized by an associated annealing time span of between about five and thirty seconds and by anisotropic etching of the polysilicon material when annealed for a time within the time span;

terminating annealing at a time within the time span, positioning an etching mask over the polysilicon; and

etching the polysilicon in the presence of the mask using plasma etching.

14. A method for forming a polysilicon gate of precisely controlled side profile on a substrate, comprising forming a composite structure comprising a layer of polycrystalline silicon on the substrate;

implating the silicon with impurities to a surface conecntration of at least about 10²⁰ cm^-3 ;

inserting the composite into a rapid thermal annealing chamber adapted for heating one or more such composites simultaneously;

heating the composite in the chamber of at a temperature greater than about 1100°

C. and for a time of between about five and thirty seconds to provide a sheet resistance ≦

17 ohms per square and a selected aspect ratio ≦

0.1 during ecthing;

etching the silicon in the presence of an etching mask using plasma etching to pattern the silicon to a desired configuration and the selected profile aspect ratio; and

doping the substrate structure using the polysilicon as a deposition mask.

15. The method of claim 14 wherein prior to the implanting step, a layer of silicon dioxide is formed on the silicon to lower the implantation dose required to achieve the selected sheet resistance value.

16. A method for treating polysilicon material to provide low sheet resistance and anisotropic plasma etching characteristics comprising doping the polysilicon material to a concentration of at least about 10²⁰ cm^-3 using impurities selected from n-type and p-type impurities;

and heating the polysilicon material using rapid thermal annealing at a temperature of at least about 1100°

C. for a time within the range five seconds to thirty seconds.