Diffractive optical elements and methods of making the same

• US 20040020892A1
• Filed: 07/30/2002
• Published: 02/05/2004
• Est. Priority Date: 07/30/2002
• Status: Active Grant

• Current Assignee: Avago Technologies International Sales Pte Limited (Broadcom, Inc.)
• Original Assignee: Avago Technologies General IP PTE Limited (Broadcom, Inc.)
• Inventors: Matthews, James Albert, Grubbs, Wayne H.
• Granted Patent: US 6,905,618 B2
• Time in Patent Office: Days
• US Class Current: 216/2
• CPC Class Codes: B82Y 10/00 Nanotechnology for information processing, storage or transmission, e.g. quantum computing or single electron logic
• CPC Class Codes: G02B 5/18 Diffraction gratings holographic optical elements G02B5/32, G03H; integrally combined with optical fibres G02B6/02057; for coupling light guides G02B6/34; integrally combined with optical integrated light guides G02B6/12; grating systems G02B27/44
• CPC Class Codes: G02B 5/1857 using exposure or etching means, e.g. holography, photolithography, exposure to electron or ion beams
• CPC Class Codes: G21K 1/062 Devices having a multilayer structure
• CPC Class Codes: G21K 2201/067 Construction details

Abstract

Diffractive optical elements and methods of making the same are described. In one aspect, a diffractive optical element is made by forming a multilayer structure comprising multiple amorphous silicon phase shift layers having respective thicknesses selected so that the diffractive optical element is operable to phase shift infrared light within an operative wavelength range. The amorphous silicon phase shift layers are separated by respective silicon dioxide etch stop layers having respective thicknesses of about 5 nm or less. Layers of the multilayer structure are serially masked and etched to form a multi-step optical structure. In another aspect, a diffractive optical element is made by forming a multilayer structure comprising multiple etch layers separated by respective etch stop layers selectively etchable with respect to the etch layers. One or more of the etch and etch stop layers are substantially opaque to light within an operative wavelength range. Opaque layers are converted into substances substantially transparent to light within the operative wavelength range. Layers of the multilayer structure are serially masked and etched to form a multi-step optical structure.

Claims

1. A method of forming a diffractive optical element, comprising:

forming a multilayer structure comprising multiple amorphous silicon phase shift layers having respective thicknesses selected so that the diffractive optical element is operable to phase shift infrared light within an operative wavelength range and being separated by respective silicon dioxide etch stop layers having respective thicknesses of about 5 nm or less; and

serially masking and etching layers of the multilayer structure to form a multi-step optical structure.

2. The method of claim 1, wherein each etch stop layer has a thickness of about 2 nm or less.

3. The method of claim 1, wherein forming the multilayer structure comprises depositing amorphous silicon phase shift layers by chemical vapor deposition.

4. The method of claim 3, wherein the amorphous silicon phase shift layers are deposited by low pressure chemical vapor deposition.

5. The method of claim 3, wherein the amorphous silicon phase shift layers are deposited at a temperature below about 600°

C.

6. The method of claim 1, wherein forming the multilayer structure comprises thermally growing silicon etch stop layers on respective phase shift layers.

7. The method of claim 6, wherein the silicon dioxide etch stop layers are thermally grown in steam at a temperature below about 600°

C.

8. The method of claim 1, wherein forming the multilayer structure comprises depositing silicon dioxide etch stop layers on respective phase shift layers.

9. The method of claim 8, wherein the silicon dioxide etch stop layers are deposited by chemical vapor deposition.

10. The method of claim 1, further comprising converting amorphous silicon phase shift layers in the multi-step optical structure into silicon dioxide phase shift layers.

11. The method of claim 1, further comprising forming over the multi-step optical structure a layer substantially reflective of radiation within the operative wavelength range.

12. The method of claim 1, further comprising imprinting the multi-step optical structure into a relatively soft material to transfer a diffraction pattern into the relatively soft material.

13. A diffractive optical element, comprising a multi-step structure including multiple amorphous silicon phase shift layers having respective thicknesses selected to phase shift infrared light within an operative wavelength range and being separated by respective silicon dioxide etch stop layers having respective thicknesses of about 5 nm or less.

14. A method of forming a diffractive optical element, comprising:

forming a multilayer structure comprising multiple etch layers separated by respective etch stop layers selectively etchable with respect to the etch layers, one or more of the etch and etch stop layers being substantially opaque to light within an operative wavelength range;

converting opaque layers into substances substantially transparent to light within the operative wavelength range; and

serially masking and etching layers of the multilayer structure to form a multi-step optical structure.

15. The method of claim 14, wherein etch layers and etch stop layers are characterized by mutual etch selectivity.

16. The method of claim 14, wherein each etch stop layer has a thickness of about 5 nm or less.

17. The method of claim 14, wherein etch layers are formed of amorphous silicon and etch stop layers are formed of silicon dioxide.

18. The method of claim 17, wherein forming the multilayer structure comprises depositing amorphous silicon etch layers by chemical vapor deposition.

19. The method of claim 18, wherein the amorphous silicon etch layers are deposited by low pressure chemical vapor deposition.

20. The method of claim 18, wherein the amorphous silicon etch layers are deposited at a temperature below about 600°

C.

21. The method of claim 17, wherein forming the multilayer structure comprises thermally growing silicon dioxide etch stop layers on respective amorphous silicon etch layers.

22. The method of claim 21, wherein the silicon dioxide etch stop layers are thermally grown in steam at a temperature below about 600°

C.

23. The method of claim 17, wherein forming the multilayer structure comprises depositing silicon dioxide etch stop layers on respective amorphous silicon etch layers.

24. The method of claim 23, wherein the silicon dioxide etch stop layers are deposited by chemical vapor deposition.

25. The method of claim 17, wherein converting opaque layers comprises converting amorphous silicon etch layers in the multi-step optical structure into silicon dioxide layers.

26. The method of claim 14, wherein etch layers are formed of silicon dioxide and etch stop layers are formed of silicon.

27. The method of claim 26, wherein forming the multilayer structure comprises oxidizing an upper portion of an amorphous silicon layer to form a silicon dioxide etch layer and an underlying silicon etch stop layer.

28. The method of claim 27, wherein oxidizing the upper portion of the amorphous silicon layer comprises thermally growing a silicon dioxide cap layer on a top portion of the amorphous silicon layer and subsequently thermally oxidizing the remaining upper portion of the amorphous silicon layer.

29. The method of claim 28, wherein the cap layer is thermally grown at a temperature below about 600°

C. and the remaining upper portion is thermally oxidized at a temperature above about 600°

C.

30. The method of claim 29, wherein converting opaque layers comprises thermally oxidizing silicon etch stop layers in the multi-step optical structure.

31. The method of claim 14, further comprising forming over the multi-step optical structure a layer substantially reflective of radiation within the operative wavelength range.

32. The method of claim 14, further comprising imprinting the multi-step optical structure into a relatively soft material to transfer a diffractive pattern into the relatively soft material.