Interferometric endpoint determination in a substrate etching process

• US 20040087152A1
• Filed: 11/01/2002
• Published: 05/06/2004
• Est. Priority Date: 11/01/2002
• Status: Active Grant

• Current Assignee: Applied Materials Incorporated
• Original Assignee: Applied Materials Incorporated
• Inventors: Lian, Lei, Davis, Matthew F.
• Granted Patent: US 7,306,696 B2
• Time in Patent Office: Days
• US Class Current: 438/689
• CPC Class Codes: G01B 11/0675 using interferometry
• CPC Class Codes: G01B 11/0683 measurement during deposition or removal of the layer
• CPC Class Codes: H01J 37/32935 Monitoring and controlling tubes by information coming from the object and/or discharge
• CPC Class Codes: H01J 37/32963 End-point detection

Abstract

In determining an endpoint of etching a substrate, light that is directed toward the substrate is reflected from the substrate. A wavelength of the light is selected to locally maximize the intensity of the reflected light at an initial time point of the etching process. The reflected light is detected to determine an endpoint of the substrate etching process.

Claims

1. A method of etching a substrate having a mask thereon, in a process zone, the method comprising:

(a) selecting a wavelength of light that provides a local maximum of intensity when light having the wavelength is reflected from the substrate;

(b) etching the substrate by exposing the substrate to an energized gas in the process zone while the substrate is exposed to light having the selected wavelength;

(c) detecting light reflected from the substrate that has the selected wavelength and generating a signal; and

(d) evaluating the signal to determine an endpoint of the substrate etching process.

2. A method according to claim 1 wherein (a) comprises changing a wavelength of a light directed onto, or reflected from, the substrate until a local maximum of an intensity of the light reflected from the substrate is detected.

3. A method according to claim 1 wherein (a) comprises directing a broadband spectrum of light at the substrate, detecting a reflectance spectrum of the light reflected from the substrate, and selecting a local maximum of the reflectance spectrum.

4. A method according to claim 1 wherein (a) comprises computing a wavelength for which the additional distance from a detection point, of a path of light that passes through a thickness of the mask and is reflected from an interface between the mask and the substrate, in comparison to a path of light that is reflected from the surface of the mask, is approximately an integral multiple of the wavelength.

5. A method according to claim 1 wherein (a) comprises determining a wavelength of light such that an internal reflection of the light from an interface between the mask and substrate, and a surface reflection of the light from the mask surface, are substantially in phase.

6. A method according to claim 1 wherein the substrate comprises a patterned overlying material and an underlying material, and further comprising:

(1) determining a reflectance spectrum of a substrate that is substantially absent an overlying material; and

(2) in (c), normalizing the intensity of the detected light that is reflected from the substrate by an intensity of the reflectance spectrum at the wavelength of the light reflected from the substrate.

7. A method according to claim 1 further comprising selecting a wavelength of light at which the mask is substantially permeable to light having the wavelength.

8. A method according to claim 7 wherein the mask comprises a nitride, and whereby, when a first portion of light having the wavelength is reflected from the surface of the mask and another portion of the light passes through the nitride mask and is reflected from the interface between the mask and the substrate, the interface and surface reflections of the light are substantially in phase upon emerging from the substrate.

9. A method according to claim 8 wherein the substrate comprises polysilicon exposed between features of a nitride mask comprising silicon nitride, wherein (b) comprises providing an energized gas capable of etching the polysilicon, and wherein in (a) the wavelength of the light is from about 220 to about 300 nm.

10. A substrate etching method comprising:

(a) placing a substrate in a process zone, the substrate comprising polysilicon exposed between features of a mask comprising silicon nitride;

(b) providing an energized gas in the process zone that is capable of etching the polysilicon;

(c) detecting an intensity of light that is reflected from the substrate at a wavelength of from about 220 to about 300 nm; and

(d) evaluating the detected light intensity to determine an endpoint of an etching of the substrate,

whereby at an initial time during etching of the substrate, light having the wavelength generates a local maximum in intensity, when a first portion of light having the wavelength is reflected from the surface of the silicon nitride mask and another portion of the light is reflected from the interface between the silicon nitride mask and the polysilicon, and the interface and surface reflections of the light are substantially in phase upon emerging from the substrate.

11. A substrate etching apparatus comprising:

(a) a chamber comprising;

(1) a substrate support;

(2) a gas distributor to introduce an etchant gas into the chamber;

(3) a gas energizer to energize the etchant gas to etch the substrate;

(4) a gas exhaust port;

(b) a light wavelength selector capable of determining a wavelength by;

(1) changing a wavelength of a light reflected from the substrate until a local maximum of an intensity of the light reflected from the substrate is detected;

(2) computing a wavelength of light that provides a local maximum of intensity when light having the wavelength is reflected from the substrate;

or

(3) retrieving a stored predetermined wavelength of light that provides a local maximum of intensity when light having the wavelength is reflected from the substrate;

(c) a light detector adapted to detect an intensity of the light having the determined wavelength that is reflected from the substrate, and generate a signal; and

(d) a controller to receive and evaluate the signal to determine an endpoint of the etching process.

12. An apparatus according to claim 11 wherein the light wavelength selector comprises a diffraction grating to change the light through a sequence of wavelengths until a local maximum of the intensity is detected.

13. An apparatus according to claim 11 wherein the light wavelength selector comprises a bandpass filter to filter the signal from the light detector to detect preselected wavelengths of the reflected light.

14. An apparatus according to claim 11 wherein the light wavelength selector comprises program code to compute a wavelength of light that provides a local maximum of intensity when light having the wavelength is reflected from the substrate.

15. An apparatus according to claim 11 wherein the controller comprises a memory, and wherein the light wavelength selector comprises a portion of the memory of the controller having the wavelength stored therein.

16. An apparatus according to claim 11 wherein the substrate has a mask thereon, and wherein the light wavelength selector determines a wavelength of light that is selected such that when a first portion of light having the wavelength is reflected from the surface of the mask and another portion of the light passes through the mask and is reflected from the interface between the mask and the substrate, and the interface and surface reflections of the light are substantially in phase upon emerging from the substrate.

17. An apparatus according to claim 11 wherein the substrate comprises polysilicon exposed between features of a mask comprising silicon nitride, and wherein the light wavelength selector determines a wavelength of from about 220 to about 300 nm.

18. A substrate etching apparatus comprising:

(a) a chamber comprising;

(1) a substrate support;

(2) a gas distributor to introduce an etchant gas into the chamber;

(3) a gas energizer to energize the etchant gas to etch the substrate;

(4) a gas exhaust port;

(b) a light wavelength selector to determine a wavelength of a light that is reflected from the substrate and that is from about 220 to about 300 nm;

(c) a light detector adapted to detect an intensity of the light reflected from the substrate and generate a signal; and

(d) a controller to receive and evaluate the signal to determine an endpoint of the etching process.

19. A substrate etching apparatus comprising:

(a) a chamber comprising;

(1) a substrate support;

(2) a gas distributor to introduce an etchant gas into the chamber;

(3) a gas energizer to energize the etchant gas to etch the substrate;

(4) a gas exhaust port;

(b) means for selecting a wavelength of light that provides a local maximum of intensity when light having the wavelength is reflected from the substrate;

(c) a light detector adapted to detect an intensity of the light reflected from the substrate and generate a signal; and

(d) a controller to receive and evaluate the signal to determine an endpoint of the etching process.

20. A method of determining an endpoint of etching a substrate, the method comprising:

(a) directing a light toward the substrate, whereby the light is reflected from the substrate;

(b) before (a), determining a wavelength of the light to locally maximize the intensity of the reflected light at an initial time point of an etching process conducted on the substrate; and

(c) detecting the reflected light to determine an endpoint of the substrate etching process.

21. A method according to claim 20 wherein (b) comprises scanning the light through a sequence of wavelengths until a local maximum of the intensity of the reflected light is detected.

22. A method according to claim 20 comprising etching a substrate having a mask thereon, wherein (b) comprises selecting a wavelength such that the additional distance of a path of an interface reflection passing through the mask, in comparison to a path of a surface reflection reflected from the mask, is approximately an integral multiple of the selected wavelength to cause the interface and surface reflections to be substantially in phase when they emerge from the substrate.

23. A method according to claim 20 wherein (a) comprises directing, toward the substrate, a light having a wavelength of from about 220 to about 300 nm.