Composite hard mask for the etching of nanometer size magnetic multilayer based device

• US 7,696,551 B2
• Filed: 09/20/2007
• Issued: 04/13/2010
• Est. Priority Date: 09/20/2007
• Status: Active Grant

• Current Assignee: Taiwan Semiconductor Manufacturing Company Limited
• Original Assignee: MagIC Technologies Inc (TDK Corporation)
• Inventors: Zhang, Tom, Zhang, Adam, Kula, Witold, Torng, Chyu-Jiuh, Xiao, Rongfu
• Primary Examiner(s): Menz; Douglas M
• Application Number:
  US11/901,999
• Publication Number:
  US 20090078927A1
• Time in Patent Office: 936 Days
• Field of Search: 257/295, 257/421, 438/3
• US Class Current: 257/295
• CPC Class Codes: H10N 50/01 Manufacture or treatment
• CPC Class Codes: Y10T 428/24736 Ornamental design or indicia

Abstract

A composite hard mask is disclosed that enables sub-100 nm sized MTJ cells to be formed for advanced devices such as spin torque MRAMs. The hard mask has a lower non-magnetic metallic layer such as Ru to magnetically isolate an overlying middle metallic spacer such as MnPt from an underlying free layer. The middle metallic spacer provides a height margin during subsequent processing to avoid shorting between a bit line and the MTJ cell in the final device. An upper conductive layer may be made of Ta and is thin enough to allow a MTJ pattern in a thin overlying photoresist layer to be transferred through the Ta during a fluorocarbon etch without consuming all of the photoresist. The MTJ pattern is transferred through the remaining hard mask layers and underlying MTJ stack of layers with a second etch step using a C, H, and O etch gas composition.

Claims

1. A composite hard mask used for the fabrication of a MTJ cell in a MRAM device, comprising:

(a) a lower non-magnetic metallic layer formed on a free layer in a MTJ stack of layers, said non-magnetic metallic layer essentially magnetically isolates said free layer from an overlying metallic spacer and has an etch rate substantially higher than an overlying upper conductive layer during an etch process comprised of one or more gases having a C, H, and O composition;

(b) a middle metallic spacer that has an etch rate substantially lower than an overlying upper conductive layer during a fluorocarbon etch process that selectively removes portions of the upper conductive layer, and has an etch rate substantially higher than an overlying conductive layer during an etch process comprised of one or more gases having a C, H, and O composition; and

(c) an upper conductive layer that has a substantial etch rate in regions exposed to a fluorocarbon etch but has a substantially high etch resistance to an etch process comprised of one or more gases having a C, H, and O composition.

2. The composite hard mask of claim 1 wherein the lower non-magnetic metallic layer is comprised of Ru, Ti, Zr, Mg, or NiFeHf and has a thickness of about 20 to 50 Angstroms.

3. The composite hard mask of claim 1 wherein the middle metallic spacer is comprised of MnPt, Cu, Mg, Ru, Ti, Pd, Zr, or NiCr and has a thickness from about 200 to 600 Angstroms.

4. The composite hard mask of claim 1 wherein the upper conductive layer is comprised of Ta or TaN and has a thickness between about 200 and 400 Angstroms.

5. A MTJ cell, comprising:

(a) a seed layer formed on a substrate;

(b) an anti-ferromagnetic (AFM) layer on the seed layer;

(c) a pinned layer on the AFM layer;

(d) a tunnel barrier layer formed on the pinned layer;

(e) a free layer disposed on the tunnel barrier layer; and

(f) a composite hard mask formed on the free layer, said composite hard mask is comprised of;

(1) a lower non-magnetic metallic layer formed on the free layer, said lower non-magnetic metallic layer is comprised of Ru, Ti, Zr, Mg, or NiFeHf and magnetically isolates the free layer from an overlying metallic spacer;

(2) a middle metallic spacer made of MnPt, Cu, Mg, Ru, Ti, Pd, Zr, or NiCr, said middle metallic spacer has a different composition than the lower non-magnetic metallic layer; and

(3) an upper conductive layer comprised of Ta or TaN.

6. The MTJ cell of claim 5 wherein the lower non-magnetic metallic layer has a thickness from about 20 to 50 Angstroms.

7. The MTJ cell of claim 5 wherein the middle metallic spacer has a thickness of about 200 to 600 Angstroms.

8. A method of forming a MTJ cell in a memory device, comprising:

(a) sequentially forming a MTJ stack of layers comprising a seed layer, AFM layer, pinned layer, tunnel barrier layer, and a free layer on a substrate;

(b) forming a composite hard mask on the free layer, said composite hard mask is comprised of;

(1) a lower non-magnetic metallic layer formed on said free layer, said non-magnetic metallic layer essentially magnetically isolates said free layer from an overlying metallic spacer and has an etch rate substantially higher than an overlying upper conductive layer in regions exposed to a subsequent etch process comprised of one or more gases having a C, H, and O composition;

(2) a middle metallic spacer that has an etch rate substantially lower than an overlying upper conductive layer in regions exposed to a subsequent fluorocarbon etch process, and has an etch rate substantially higher than an overlying conductive layer in regions exposed to a subsequent etch process comprised of one or more gases having a C, H, and O composition; and

(3) an upper conductive layer that has a substantial etch rate in regions exposed to a subsequent fluorocarbon etch, and has a substantially high etch resistance to an etch process comprised of one or more gases having a C, H, and O composition;

(c) sequentially coating a bottom anti-reflective coating (BARC) and a photoresist layer on the upper conductive layer, and then patterning said photoresist layer to form a plurality of features having MTJ easy-axis and hard-axis dimensions;

(d) transferring said plurality of features through the upper conductive layer with a first etching step comprised of a fluorocarbon gas;

(e) removing said photoresist layer and BARC with an oxygen ashing step; and

(f) transferring said plurality of features through the middle metallic spacer, lower non-magnetic metallic layer, and through the MTJ stack of layers with a second etching step comprised of one or more gases that provide a C, H, and O etchant composition.

9. The method of claim 8 wherein the lower non-magnetic metallic layer is comprised of Ru, Ti, Zr, Mg, or NiFeHf and has a thickness of about 20 to 50 Angstroms.

10. The method of claim 8 wherein the middle metallic spacer is comprised of MnPt, Cu, Mg, Ru, Ti, Pd, Zr, or NiCr and has a thickness from about 200 to 600 Angstroms.

11. The method of claim 8 wherein the upper conductive layer is comprised of Ta or TaN and has a thickness between about 200 and 400 Angstroms.

12. The method of claim 8 wherein the photoresist layer has a thickness between about 1000 and 3000 Angstroms to enable sub-100 nm features to be formed.

13. The method of claim 8 wherein fluorocarbon gas in the first etching step is comprised of CF₄, C₂F₆, C₄F₈, CHF₃, or CH₂F₂, a RF source power of about 200 to 600 Watts and a RF bias power of about 20 to 80 Watts.

14. The method of claim 8 wherein the second etching step is performed in a different process chamber than the first etching step or oxygen ashing step.

15. The method of claim 8 wherein the second etching step is comprised of CH₃OH, C₂H₅OH, and CO/NH₃, a RF source power of about 800 to 1800 Watts, and a RF bias power of about 500 to 1500 Watts.

16. The method of claim 8 wherein the exposed regions of the upper conductive layer etch at least 10 times faster than the middle metallic layer during the first etching step.

17. The method of claim 8 wherein exposed regions of the middle metallic layer, lower non-magnetic metallic layer, free layer, pinned layer, AFM layer, and seed layer etch at least 8 times faster than the upper conductive layer during the second etching step.

18. A composite hard mask used for the fabrication of a MTJ cell in a MRAM device, comprising:

(a) a lower non-magnetic metallic layer made of Cu, Mg, Ti, Pd, Zr, or NiCr formed on a free layer in a MTJ stack of layers, said non-magnetic metallic layer has an etch rate substantially lower than an overlying upper conductive layer during a fluorocarbon etch process that selectively removes portions of the upper conductive layer, and has an etch rate substantially higher than the overlying conductive layer during an etch process comprised of one or more gases having a C, H, and O composition; and

(b) an upper conductive layer made of Ta or TaN that has a substantial etch rate in regions exposed to a fluorocarbon etch but has a substantially high etch resistance to an etch process comprised of one or more gases having a C, H, and O composition.

19. The composite hard mask of claim 18 wherein the lower non-magnetic metallic layer has a thickness from about 200 to 600 Angstroms.

20. The composite hard mask of claim 18 wherein the upper conductive layer has a thickness between about 200 and 400 Angstroms.

21. A MTJ cell, comprising:

(a) a seed layer formed on a substrate;

(b) an anti-ferromagnetic (AFM) layer on the seed layer;

(c) a pinned layer on the AFM layer;

(d) a tunnel barrier layer formed on the pinned layer;

(e) a free layer disposed on the tunnel barrier layer; and

(f) a composite hard mask formed on the free layer, said composite hard mask is comprised of;

(1) a lower non-magnetic metallic layer formed on the free layer, said lower non-magnetic metallic layer is comprised of Cu, Ti, Zr, Mg, Pd, or NiCr; and

(2) an upper conductive layer made of Ta or TaN.