MAGNETORESISTIVE RANDOM ACCESS MEMORY AND METHOD OF MANUFACTURING THE SAME
A magnetoresistive random access memory (MRAM), including a bottom electrode layer on a substrate, a magnetic tunnel junction stack on the bottom electrode layer, and a top electrode layer on the magnetic tunnel junction stack, wherein the material of top electrode layer is titanium nitride, and the percentage of nitrogen in the titanium nitride gradually decreases from the top surface of top electrode layer to the bottom surface of top electrode layer.
The present invention generally relates to a magnetoresistive random access memory, and more specifically, to a magnetoresistive random access memory with particular composition of top electrode.
2. Description of the Prior ArtMagnetoresistance (MR) effect has been known as a kind of effect caused by altering the resistance of a material through variation of outside magnetic field. The physical definition of such effect is defined as a variation in resistance obtained by dividing a difference in resistance under no magnetic interference by the original resistance. Currently, MR effect has been successfully utilized in production of hard disks thereby having important commercial values. Moreover, the characterization of utilizing GMR materials to generate different resistance under different magnetized states could also be used to fabricate magnetoresistive random access memory (MRAM) devices, which typically has the advantage of keeping stored data even when the device is not connected to an electrical source.
The aforementioned MR effect has also been used in magnetic field sensor areas including, for example, electronic compass components used in global positioning system (GPS) of cellular phones for providing information regarding moving location to users. Currently, various magnetic field sensor technologies such as anisotropic magnetoresistance (AMR) sensors, giant magnetoresistance (GMR) sensors, magnetic tunnel junction (MTJ) sensors have been widely developed in the market. Nevertheless, nowadays MRAM still suffer many problems resulted from processes, such as the problem of tail bit performance. How to come up with an improved device to resolve these issues has become an important task in this field.
SUMMARY OF THE INVENTIONIn order to improve the performance of tail bits in magnetoresistive random access memory (MRAM), the present invention hereby provides a MRAM structure with particular composition of top electrode to prevent etchant penetrating through the top electrode and damaging the magnetic tunnel junction (MTJ) thereunder.
One aspect of the present invention is to provide a magnetoresistive random access memory cell, which includes a substrate, a bottom electrode layer on the substrate, a magnetic tunnel junction stack on the bottom electrode layer, and a top electrode layer on the magnetic tunnel junction stack, wherein a material of the top electrode layer is titanium nitride, and a percentage of nitrogen in the titanium nitride gradually decreases from a top surface of top electrode layer to a bottom surface of top electrode layer.
Another aspect of the present invention is to provide a method of fabricating magnetoresistive random access memory, which includes steps of providing a substrate, forming a bottom electrode layer, a magnetic tunnel junction stack and a top electrode layer sequentially on the substrate, wherein a material of the top electrode layer is titanium nitride, and a percentage of nitrogen in the titanium nitride gradually decreases from a top surface of top electrode layer to a bottom surface of top electrode layer, and patterning the bottom electrode layer, the magnetic tunnel junction stack and the top electrode layer into multiple magnetoresistive random access memory cells.
These and other objectives of the present invention will no doubt become obvious to those of ordinary skill in the art after reading the following detailed description of the preferred embodiment that is illustrated in the various figures and drawings.
The accompanying drawings are included to provide a further understanding of the embodiments, and are incorporated in and constitute apart of this specification. The drawings illustrate some of the embodiments and, together with the description, serve to explain their principles. In the drawings:
It should be noted that all the figures are diagrammatic. Relative dimensions and proportions of parts of the drawings have been shown exaggerated or reduced in size, for the sake of clarity and convenience in the drawings. The same reference signs are generally used to refer to corresponding or similar features in modified and different embodiments.
DETAILED DESCRIPTIONReference now be made in detail to exemplary embodiments of the invention, which are illustrated in the accompanying drawings in order to understand and implement the present disclosure and to realize the technical effect. It can be understood that the following description has been made only by way of example, but not to limit the present disclosure. Various embodiments of the present disclosure and various features in the embodiments that are not conflicted with each other can be combined and rearranged in various ways. Without departing from the spirit and scope of the present disclosure, modifications, equivalents, or improvements to the present disclosure are understandable to those skilled in the art and are intended to be encompassed within the scope of the present disclosure.
It should be readily understood that the meaning of “on,” “above,” and “over” in the present disclosure should be interpreted in the broadest manner such that “on” not only means “directly on” something but also includes the meaning of “on” something with an intermediate feature or a layer therebetween, and that “above” or “over” not only means the meaning of “above” or “over” something but can also include the meaning it is “above” or “over” something with no intermediate feature or layer therebetween (i.e., directly on something).
Further, spatially relative terms, such as “beneath,” “below,” “lower,” “above,” “upper,” and the like, may be used herein for ease of description to describe one element or feature's relationship to another element(s) or feature(s) as illustrated in the figures. The spatially relative terms are intended to encompass different orientations of the device in use or operation in addition to the orientation depicted in the figures. The apparatus may be otherwise oriented (rotated 90 degrees or at other orientations) and the spatially relative descriptors used herein may likewise be interpreted accordingly.
Please refer to
An inter-metal dielectric (IMD) layer 102, a stop layer 104 and an inter-layer dielectric (ILD) layer 106 are formed sequentially on the substrate 100. The material of inter-metal dielectric layer 102 is preferably ultra low-k material, such as porous silicon oxide carbides (SiOC). The material of stop layer 104 is preferably nitrogen doped carbide, silicon nitride or silicon carbonitride (SiCN), etc, and the material of inter-layer dielectric layer 106 is preferably tetraethoxysilane (TEOS), but not limited thereto, wherein metal layers 108 and contact plugs 110 may be formed respectively in the inter-metal dielectric layer 102 and the inter-layer dielectric layer 106 by using single damascene process or dual damascene process. The metal layer 108 and the contact plug 110 may be embedded in the inter-metal dielectric layer 102, the stop layer 104 and the inter-layer dielectric layer 106 and electrically connect with each other. The material of metal layer 108 and contact plug 110 may be selected from the combination of tungsten (W), copper (Cu), aluminum (Al), titanium aluminum (TiAl) alloy and cobalt-tungsten-phosphorous (CoWP) alloy, etc, but not limited thereto.
Please refer again to
In the embodiment, the material of top electrode layer 116 is titanium nitride, which preferably has a composition gradient. That is, the composition of titanium nitride in entire top electrode layer 116 is not uniform. More specifically, the percentage of nitrogen in the titanium nitride of top electrode layer 116 would preferably and gradually decreases from the top surface (exposed surface) of top electrode layer 116 to the bottom surface (the surface adjoining the magnetic tunnel junction stack 114) of top electrode layer 116, while the percentage of titanium in the titanium nitride of top electrode layer 116 would preferably and gradually increase from the top surface of top electrode layer 116 to the bottom surface of top electrode layer 116. In other words, the portion adjacent to the bottom surface of top electrode layer 116 or adjacent to the interface between the top electrode layer 116 and the magnetic tunnel junction stack 114 is preferably provided with higher concentration distribution of titanium or lower concentration distribution of nitrogen, while the portion adjacent to the top surface of top electrode layer 116 is preferably provided with higher concentration distribution of nitrogen and lower concentration distribution of titanium, wherein the percentage of nitrogen in the titanium nitride of top electrode layer 116 is greater than 0% and less than 50%. Detailed function of composition gradient in the titanium nitride of top electrode layer 116 will be explained in later embodiment.
Thereafter, as shown in
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In the embodiment of present invention, the dual damascene recesses 128 on the MRAM region and the dual damascene recesses on logic region (not shown) are intended to be formed in the same processes. Regarding the devices on the logic region, a wet etch process would be additionally performed after the dual damascene recesses are formed in order to remove polymer byproduct and TiN-based hard mask layer exposed from the recesses. The etchant used in this wet etch process, such as DuPont's EKC residue remover series combined with hydrogen peroxide solution, has quite high etching power to titanium nitride and oxide thereof. Moreover, the titanium nitride layer is generally grown in the form of column-like polycrystalline structure. This type of titanium nitride layer has high surface toughness, with multiple inherent pinhole defects extending directly downward to the bottom of titanium nitride layer between the crystalline columns. For this reason, the aforementioned wet etch process used to remove the hard mask on logic region would simultaneously remove a part of TiN-based top electrode layer 116 on the MRAM region. The etchant may even further penetrate to the bottom of top electrode layer 116 and damage underlying magnetic tunnel junction stack 114, so that the ferromagnetic layer in the magnetic tunnel junction stack 114 would lose its ferromagnetism. This phenomenon especially causes the issue of tail bits failure.
In the present invention, the advantage of having a TiN composition gradient in the top electrode layer 116 is that the magnetic tunnel junction stack 114 may be prevented from the damage by the wet etch process. The principle of this prevention lies in that the less the nitrogen composition in the titanium nitride, its crystal form is closer to compact metal form rather than polycrystalline form. That is, the grain size and surface toughness of the titanium nitride will be smaller and the pinhole defects will be fewer. Through the design of less nitrogen percentage in the TiN composition of top electrode layer 116 in portion closer to the magnetic tunnel junction stack 114, the etchant is not easy to penetrate through the magnetic tunnel junction stack 114, so that the underlying magnetic tunnel junction stack 114 may be prevented from the damage by the etchant.
Thereafter, as shown in
According to the process method in aforementioned embodiment, the present invention hereby provides a novel magnetoresistive random access memory cell 118. As shown in
In addition to the aforementioned characteristics of TiN composition gradient, in other embodiment, other features may be added to the MRAM to improve the protection effect for magnetic tunnel junction stack. Please refer to
Those skilled in the art will readily observe that numerous modifications and alterations of the device and method may be made while retaining the teachings of the invention. Accordingly, the above disclosure should be construed as limited only by the metes and bounds of the appended claims.
Claims
1. A magnetoresistive random access memory cell, comprising:
- a substrate;
- a bottom electrode layer on said substrate;
- a magnetic tunnel junction stack on said bottom electrode layer; and
- a top electrode layer on said magnetic tunnel junction stack, wherein a material of said top electrode layer is titanium nitride, and a percentage of nitrogen in said titanium nitride gradually decreases from a top surface of top electrode layer to a bottom surface of top electrode layer.
2. The magnetoresistive random access memory cell of claim 1, wherein said percentage of nitrogen in said titanium nitride is greater than 0% and less than 50%.
3. The magnetoresistive random access memory cell of claim 1, further comprising a hard mask layer disposed on said top electrode layer, wherein a material of said hard mask layer is tantalum or tantalum nitride.
4. The magnetoresistive random access memory cell of claim 1, further comprising an etch stop layer disposed between said top electrode layer and said magnetic tunnel junction, wherein a material of said etch stop layer comprises ruthenium or ruthenium oxide.
5. The magnetoresistive random access memory cell of claim 4, wherein said etch stop layer is a layer stack of alternating ruthenium layers and ruthenium oxide layers.
6. The magnetoresistive random access memory cell of claim 1, wherein said magnetic tunnel junction layer comprises seed layer, pinned layer, reference layer, tunneling barrier layer, free layer, and metal spacer.
7. A method of fabricating magnetoresistive random access memory, comprising:
- providing a substrate;
- forming a bottom electrode layer, a magnetic tunnel junction stack and a top electrode layer sequentially on said substrate, wherein a material of said top electrode layer is titanium nitride, and a percentage of nitrogen in said titanium nitride gradually decreases from a top surface of top electrode layer to a bottom surface of top electrode layer; and
- patterning said bottom electrode layer, said magnetic tunnel junction stack and said top electrode layer into multiple magnetoresistive random access memory cells.
8. The method of fabricating magnetoresistive random access memory of claim 7, wherein said percentage of nitrogen in said titanium nitride is greater than 0% and less than 50%.
9. The method of fabricating magnetoresistive random access memory of claim 7, further comprising a hard mask layer disposed on said top electrode layer, wherein a material of said hard mask layer is tantalum or tantalum nitride.
10. The method of fabricating magnetoresistive random access memory of claim 7, further comprising an etch stop layer disposed between said top electrode layer and said magnetic tunnel junction, wherein a material of said etch stop layer comprises ruthenium or ruthenium oxide.
11. The method of fabricating magnetoresistive random access memory of claim 10, wherein said etch stop layer is a layer stack of alternating ruthenium layers and ruthenium oxide layers.
12. The method of fabricating magnetoresistive random access memory of claim 7, wherein said magnetic tunnel junction layer comprises seed layer, pinned layer, reference layer, tunneling barrier layer, free layer, and metal spacer.
Type: Application
Filed: Aug 5, 2019
Publication Date: Jan 21, 2021
Inventors: Hui-Lin Wang (Taipei City), Chen-Yi Weng (New Taipei City), Chin-Yang Hsieh (Tainan City), Yi-Hui Lee (Taipei City), Ying-Cheng Liu (Tainan City), Yi-An Shih (Changhua County), Jing-Yin Jhang (Tainan City), I-Ming Tseng (Kaohsiung City), Yu-Ping Wang (Taoyuan City), Chien-Ting Lin (Hsinchu City), Kun-Chen Ho (Tainan City), Yi-Syun Chou (Taipei City), Chang-Min Li (Yunlin County), Yi-Wei Tseng (New Taipei City), Yu-Tsung Lai (Tainan City), JUN XIE (Singapore)
Application Number: 16/531,129