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Novel in Situ Dry Etch End Point Monitoring for MRAM Applications

IP.com Disclosure Number: IPCOM000125336D
Original Publication Date: 2005-Jun-20
Included in the Prior Art Database: 2005-Jun-20
Document File: 2 page(s) / 496K

Publishing Venue

Siemens

Related People

Juergen Carstens: CONTACT

Abstract

The following text is about the production of a MRAM (Magnetoresistive Random Access Memory) tunnel junction device. The patterning of the magnetic/non-magnetic MRAM-layers is usually based on dry etching. An optimal etch sequence for the tunnel junction element consists of a hard mask (usually 1000A of TaN or TiN thick) open process, a patterning of a magnetic free layer (e.g. 30A NiFe or CoFeB) with a precise etch stop on a thin tunnel barrier layer (e.g. 15A Al2O3). This precise etch stop on or in the tunnel barrier is essential to get required device performance and is a subject to be solved by the idea described below. The method can be used for any dry etch tool, which needs precise control of endpoint when etching magnetic layers (e.g. GMR (Giant Magneto Resistance)). The methods used up to date give imprecise etch-control: - Use of conventional end point signals from the optical absorption data of the etched species in the chamber - Time based etching (= guessing) - Use of certain sequences of materials and etch chemistry to allow proper window for etch selectivity The method uses in situ monitoring of the remaining free layer thickness during the etch process based on well known MOKE (Magneto Optical Kerr Effect - in short: light, which is reflected on the surface of a magnetic material, will result in the rotation of the polarization plane or a change in the intensity of the reflected light, depending on the amount and the direction of the magnetization).

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Novel in Situ Dry Etch End Point Monitoring for MRAM Applications

Idea: Dr. Ulrich Klostermann, FR-Corbeil-Essonnes; Dr. Chanro Park, FR-Corbeil-Essonnes

The following text is about the production of a MRAM (Magnetoresistive Random Access Memory) tunnel junction device. The patterning of the magnetic/non-magnetic MRAM-layers is usually based on dry etching. An optimal etch sequence for the tunnel junction element consists of a hard mask (usually 1000A of TaN or TiN thick) open process, a patterning of a magnetic free layer (e.g. 30A NiFe or CoFeB) with a precise etch stop on a thin tunnel barrier layer (e.g. 15A Al2O3). This precise etch stop on or in the tunnel barrier is essential to get required device performance and is a subject to be solved by the idea described below.

The method can be used for any dry etch tool, which needs precise control of endpoint when etching magnetic layers (e.g. GMR (Giant Magneto Resistance)).

The methods used up to date give imprecise etch-control:

- Use of conventional end point signals from the optical absorption data of the etched species in the chamber

- Time based etching (= guessing)

- Use of certain sequences of materials and etch chemistry to allow proper window for etch selectivity

The method uses in situ monitoring of the remaining free layer thickness during the etch process based on well known MOKE (Magneto Optical Kerr Effect - in short: light, which is reflected on the surface of a magnetic material, will result in the rotation of the polarization plane or a change in the intensity of the reflected light, depending on the amount and the direction of the magnetization).

This method allows not only in situ monitoring of the thickness of the remaining magnetic material, but also to obtain magnetic properties of the free layer or reference system (e.g. Switching Field, Neel Coupling Field). The method gives fast and real time feedback on surface properties, because it uses data from the surface directly and not from the chamber. This extremely enhances the etch control of magnetic materials. It is even possible to assess the remaining thickness of non-magnetic layers (depending of the used magnetic/non magnetic ma...