Apparatus and method for monitoring and controlling thickness of a crystalline layer

Patent metadata

Field	Value
Publication number	US-9574285-B2
Application number	US-201414566085-A
Country	US
Kind code	B2
Filing date	Dec 10, 2014
Priority date	Dec 10, 2014
Publication date	Feb 21, 2017
Grant date	Feb 21, 2017

Abstract

An apparatus to monitor thickness of a crystalline sheet grown from a melt. The apparatus may include a process chamber configured to house the melt and crystalline sheet; an x-ray source disposed on a first side of the crystalline sheet and configured to deliver a first beam of x-rays that penetrate the crystalline sheet from a first surface to a second surface opposite the first surface, at a first angle of incidence with respect to the first surface; and an x-ray detector disposed on the first side of the crystalline sheet and configured to intercept a second beam of x-rays that are generated by reflection of the first beam of x-rays from the crystalline sheet at an angle of reflection with respect to the first surface, wherein a sum of the angle of incidence and the angle of reflection satisfies the equation λ=2d sin θ.

First claim

What is claimed is:

1. An apparatus to monitor thickness of a crystalline sheet grown from a melt, comprising:
a process chamber configured to house the melt and the crystalline sheet;
an x-ray source disposed on a first side of the crystalline sheet and configured to deliver a first x-ray beam that penetrates a thickness of the crystalline sheet from a first surface to a second surface opposite the first surface; and
an x-ray detector disposed on the first side of the crystalline sheet and configured to intercept a second x-ray beam that is generated by reflection of the first x-ray beam from a group of crystallographic planes that extend through the thickness of the crystalline sheet,
wherein λ=2d sin θ,
where λ is a wavelength of at least some x-rays of the first x-ray beam, d is a spacing between adjacent crystallographic planes of the group of crystallographic planes, and θ is an angle of incidence of the at least some x-rays with respect to the group of crystallographic planes.

2. The apparatus of claim 1 , further comprising:
a crucible configured to contain the melt;
a heating system to provide heating to the melt;
a crystallizer configured to generate a crystallization front of the crystalline sheet at a surface of the melt; and
a crystal puller configured to draw the crystalline sheet at a pull rate along the surface of the melt.

3. The apparatus of claim 2 , further comprising a controller configured to:
receive a measurement signal from the detector indicative of the thickness of the crystalline sheet between the first surface and the second surface; and
responsive to the measurement signal, send at least one control signal to adjust operation of at least one of: the heating system, crystallizer, and crystal puller.

4. The apparatus of claim 1 , wherein the melt is silicon, and wherein a thickness of the crystalline sheet is less than 2 mm.

5. The apparatus of claim 1 , wherein the x-ray source is configured to generate monochromatic radiation, wherein λ is less than 1 Å.

6. The apparatus of claim 1 , wherein the x-ray source is configured to generate polychromatic radiation.

7. The apparatus of claim 1 , wherein the group of crystallographic planes is oriented at a non-zero angle with respect to the first surface.

8. The apparatus of claim 1 , wherein the detector comprises a planar detector surface configured to form an x-ray image of the second x-ray beam, wherein a height of the x-ray image along a first direction of the planar detector surface is proportional to a thickness of the crystalline sheet between the first surface and second surface, and wherein a width of the x-ray image along a second direction of the planar detector surface is proportional to a width of the crystalline sheet.

9. The apparatus of claim 1 , further comprising:
an entrance enclosure configured to conduct the first x-ray beam from the x-ray source to the process chamber under vacuum; and
an exit enclosure configured to conduct the second x-ray beam from the process chamber to the detector under vacuum.

10. An apparatus to control crystalline sheet grown from a melt, comprising:
a process chamber configured to house the melt and crystalline sheet;
a thickness monitoring system, comprising:
an x-ray source configured to deliver a first x-ray beam that penetrates the crystalline sheet through a thickness of the crystalline sheet from a first surface to a second surface opposite the first surface;
an x-ray detector configured to intercept a second x-ray beam that is generated by Bragg diffraction of the first x-ray beam from a group of crystallographic planes that extend through the thickness of the crystalline sheet; and

a control system coupled to the detector and configured to:
receive a measurement signal from the detector indicative of a thickness of the crystalline sheet between the first surface and the second surface; and
responsive to the measurement signal, send at least one control signal to adjust at least one of: heating rate of the melt, cooling rate at a crystallization region of the melt, and pulling rate of the crystalline sheet.

11. The apparatus of claim 10 , further comprising:
a crucible configured to contain the melt;
a crystallizer configured to generate a crystallization front of the crystalline sheet at a surface of the melt, wherein the crystalline sheet has an initial thickness downstream of the crystallizer;
a melt back heater to melt back a fraction of the initial thickness; and
a crystal puller configured to draw the crystalline sheet at a pull rate along the surface of the melt, wherein the at least one control signal is operative to adjust operation of at least one of: the crystallizer, melt back heater, and crystal puller.

12. The apparatus of claim 10 , wherein the x-ray source is configured to generate monochromatic radiation, wherein λ is less than 1 Å.

13. The apparatus of claim 10 , wherein the x-ray source is configured to generate polychromatic radiation.

14. The apparatus of claim 10 , wherein the group of crystallographic planes is oriented at a non-zero angle with respect to the first surface.

15. The apparatus of claim 10 , wherein the detector comprises a planar detector surface configured to form an x-ray image of the second x-ray beam, wherein a height of the x-ray image along a first direction of the planar detector surface is proportional to the thickness of the crystalline sheet between the first surface and second surface, and wherein a width of the x-ray image along a second direction of the planar detector surface is proportional to a width of the crystalline sheet.

16. The apparatus of claim 10 , wherein the controller is configured to determine from the measurement signal at least one of: a single point thickness of the crystalline sheet, an average thickness of the crystalline sheet, a thickness profile of the crystalline sheet, and a thickness variation of the crystalline sheet.

17. The apparatus of claim 10 , further comprising:
an entrance enclosure configured to conduct the first x-ray beam from the x-ray source to the process chamber under vacuum; and
an exit enclosure configured to conduct the second x-ray beam from the process chamber to the detector under vacuum.

18. A method for controlling thickness of a crystalline sheet, comprising:
crystallizing the crystalline sheet on a surface of a melt using a crystallizer wherein the crystalline sheet has an initial thickness downstream of the crystallizer;
pulling the crystalline sheet away from the crystallizer along a pull direction;
directing a first x-ray beam to the crystalline sheet, wherein the first x-ray beam is configured to penetrate the crystalline sheet through a thickness of the crystalline sheet from a first surface to a second surface opposite the first surface; and
intercepting at an x-ray detector a second x-ray beam that is generated by Bragg diffraction of the first x-ray beam from a group of crystallographic planes that extend through the thickness of the crystalline sheet.

19. The method of claim 18 , further comprising:
forming an image of the second x-ray beam on the x-ray detector; and
determining a sheet thickness t of the crystalline sheet from a height h of the image, where h is proportional to t.

20. The method of claim 18 , further comprising;
receiving a measurement signal indicative of the thickness of the crystalline sheet; and
sending a control signal to adjust one or more of: the crystallizing, the pulling, and melting back of the crystalli

Assignees

• Varian Semiconductor Equipment Ass Inc

Inventors

• Sinclair Frank
• Kellerman Peter L

Classifications

• C30B15/26 Primary

  using television detectors; using photo or X-ray detectors · CPC title

• C30B15/06

  Non-vertical pulling · CPC title

• C30B29/06

  Silicon · CPC title

• G01N23/207

  Diffractometry using detectors, e.g. using a probe in a central position and one or more displaceable detectors in circumferential positions · CPC title