JP5085637B2 - Dry etch stop process to eliminate electrical shorts in MRAM device structure - Google Patents

Description

  This application claims priority from US Provisional Application No. 60 / 783,157 entitled "Dry Etch Stop Treatment to Eliminate Electrical Shorts in MRAM Device Structures" filed March 16, 2005. This patent is incorporated herein by reference.

  The present invention relates generally to semiconductor fabrication, and more particularly to fabricating device structures containing metal-insulator-metal stacked thin film stacks for use in magnetic tunnel junction devices and memory devices.

Metal-insulator-metal stacks are used as storage elements in memory devices such as magnetic random access memory (MRAM). The memory element for MRAM technology is a patterned structure of multilayer material, usually composed of a stack of different materials such as NiFe, CoFe, PtMn, Ru, etc. and like AI ₂ O ₃ or MgO A material similar to a simple insulator can be included. A typical stack can contain at most 10 or more layers of these materials, some of which are non-magnetic materials, some are magnetic materials, one or Two are insulating materials. The insulating film in this specification is defined as an oxide or metal nitride layer that exhibits high electrical resistance in a bulk form. In order to fabricate storage elements, it is necessary to deposit material layer by layer in the form of an overlying blanket film, form a patterned layer of photoresist, and etch the film into a suitable structure. .

  Ion beam milling or ion beam etching processes are used to remove the magnetoresistive material. Ion beam milling, however, is a physical milling process. Areas not protected by the mask are removed by ion bombardment. The ion bombardment is removed by sputtering or peeling off the unprotected material. Ion beam milling is less selective in operation and the portion of the stack near the border of the mask edge or MRAM cell body can be easily damaged.

  Chemical etching techniques have also been used to selectively remove portions of the deposited layer. Examples of the etching technique include a dry etching technique and a wet etching technique.

  One drawback of current etching techniques is that the profile of the MRAM structure is susceptible to electrical shorts across the thin tunnel junction. The vertical separation between the upper magnet layer above the insulating dielectric tunnel layer and the lower magnet layer below this tunnel layer is inadequate to prevent electrical shorts.

U.S. Provisional Application No. 60 / 783,157 US Pat. No. 6,673,675 US Pat. No. 6,677,165 US Pat. No. 6,653,704 US Pat. No. 6,024,885 US Pat. No. 5,650,958

  Embodiments of the present invention relate, inter alia, to the fabrication of magnetic tunnel junction (MTJ) devices in which the tunnel barrier layer functions as a stop layer during plasma overetching of the top magnetic layer. The resulting MTJ device exhibits excellent electrical isolation across the tunnel barrier layer.

  In another embodiment, the gas used during plasma overetching preferably excludes halogen gases containing species that result in highly selective etching of the top magnetic layer compared to the tunnel barrier layer. By introducing oxygen into the gas, process reproducibility is improved.

  In yet another embodiment, a fluorine-chlorine gas mixture is used to partially etch the magnet layer overlying the tunnel barrier layer.

Finally, another embodiment relates to a corrosive plasma treatment with He and H ₂ gases before or during photoresist mask stripping. Optionally, after the stripping step, a water washing treatment and He and H ₂ dehydration firing can be used.

  The present invention is based in part on the development of a patterning method for fabricating magnetic tunnel junction (MTJ) devices for use in magnetic random access memory (MRAM) devices. As further described herein, a very important aspect of the present invention is that the MTJ device prepared by the method of the present invention has superior electrical properties between the magnet layers in contact with the dielectric tunnel layer compared to current technology. The separation is obtained.

  A typical MRAM structure in which the MTJ is accommodated is shown in FIG. The MRAM structure is a composite stack of a magnetic film, a conductive film, and an insulating film on a substrate. In FIG. 1, specific components of a typical MRAM structure are shown, a multi-layer pinning comprising layers such as substrate 10, barrier layer 12, bottom contact layer 14, CoFe, Ru, NiFe, IrMn, and PtMn. Magnet structure 16, dielectric tunnel layer 18 such as alumina or MgO, switchable magnet layer 20 (NiFe, CoFe, CoNiFe, CoFeB, etc.), and upper contact layer 22 (Ta, Tan, Ti, TiN, W, etc.) ).

  A pattern layer of hard mask layer 24, anti-reflective coating 26, and photoresist 28 is also shown in FIG. The photoresist layer 28 masks one or more of the underlying layers underneath the photoresist for etching so that portions of the underlying layer not protected by the resist layer can be etched away. Photosensitive materials commonly used by those skilled in the art of electrical device fabrication. The antireflective film 26, typically 30 to 800 mm thick, is typically used to absorb radiation and form an optically opaque film to enhance the contrast of the imaging resist. The ARC coating substantially reduces the reflection of incident light onto the overlapping PR mask layer. This prevents overexposure of the photoresist material. The hard mask layer 24 is generally used in device fabrication as an intermediate mask transfer layer. In use, using the photoresist as a dry etch mask, transfer the pattern to one or more of the hard mask and possibly the underlying layer, and then using the photoresist using the hard mask layer as a mask. The pattern is transferred to the remaining lower layer that is not formed. Rigid masks such as silicon dioxide and silicon nitride are commonly used as a means to improve mask durability relative to photoresist or to allow processing at temperatures above the softening point of the polymeric photoresist layer Use it.

  The magnetic stack structure is generally formed on the substrate 10. The substrate 10 can include any structure having an exposed surface. This structure consists of silicon wafer, silicon on insulator (SOI), silicon on sapphire (SOS), aluminum titanium carbide (AlTiC) doped and undoped semiconductor, III-V or II-VI group semiconductor, base semiconductor base Preferably, the structure is used in the manufacture of semiconductor devices such as silicon epitaxial layers supported by and other semiconductor structures. The semiconductor does not have to be mainly composed of silicon. The semiconductor can be silicon germanium, germanium, or gallium arsenide. This structure can be a non-semiconductor such as glass or polymer. Substrate 10 can include embedded electronic devices such as transistors, diodes, capacitors, and resistors, or any other device or circuit element used with a magnetic multilayer stack.

  It will be appreciated that for the exemplary multi-layer MRAM structure shown in FIG. 1 in which the MTJ is housed, the particular layers forming the multi-layer structure, such as materials and their arrangement, may vary. MTJ and MRAM structures are known in the art, for example, US Pat. No. 6,673,675 to Yates et al. Entitled “Method of Fabricating MRAM Devices Using Chemical Mechanical Polishing”. US Pat. No. 6,677,165 to Lu et al., Entitled “Magnetoresistive Random Access Memory (MRAM) Cell Patterning”, “Tunnel Junction Memory Cells and Phase Transition Controlling Current to Cells US Pat. No. 6,653,704, granted to Gurney et al. Entitled “Magnetic Memory with Materials”, US Pat. No. 6,024, assigned to Pendharkar et al., Entitled “Method of Patterning Magnetic Films” No. 885, and US patents granted to Gallagher et al., Entitled “Magnetic Tunnel Junction with Controlled Magnetic Response”. Are described in No. 5,650,958, all of these patents are incorporated herein by reference.

  It should be understood that the orientation of the magnetic film stack can be reversed with respect to the order shown in FIG. That is, the orientation of the film structure allows the film stack to be deposited in reverse order, the upper contact layer and the free magnet layer are below the dielectric tunnel layer, and the multilayer pinned layer and the antiferromagnetic layer are from the dielectric tunnel layer. It can be as provided above. The magnetic film stack can also include a plurality of magnetic tunnel junctions oriented to deposit the free layer above or below the dielectric tunnel layer, and within the scope of the method of the present invention. It should also be understood that it can remain.

  In one simplified embodiment shown in FIG. 2, the MTJ stack includes a substrate 101, a lower contact layer 14, a fixed lower magnet layer 16, a dielectric tunnel layer 18, a switchable upper magnet layer 21, and an upper contact layer 22. Including. The stack structure is patterned with a photoresist layer 28. This simplified structure will be used in the following description of the preferred embodiment of the present invention.

  The etching stop processing sequence of the present invention is shown in FIGS.

  FIG. 3 illustrates the processing sequence of the present invention, depositing a magnetic stack (100), patterning PR (102), etching one or both of the hard mask layer and the top contact layer (104), A portion of the upper magnet layer is removed using a reactive etching process (106). After reactive etching 106 of the top magnet layer, the MTJ device structure is directly subjected to the etch stop process of the present invention (108), or an etch comprising first a DI cleaning process, a PR strip, and a plasma-based etch process. A processing sequence and then an etching stop process of the present invention is performed (108).

In one embodiment shown in FIG. 3 where the etch stop process 108 of the present invention is performed immediately after the reactive partial etch 106 of the top magnet, once the MTJ device structure has been patterned, the device moves on to subsequent processes (114). . In a second embodiment where the etch stop process 108 of the present invention is performed immediately after the reactive partial etch 106 of the upper magnet, the device is subjected to a series of processes to prevent corrosion. When exposed to chlorine- and bromine-containing etch chemistries, the magnetic film can cause adverse reactions when removed from the device vacuum under ambient conditions and when the film to be etched is subsequently exposed to moisture. is there. Based on the sensitivity of the membrane, various sequences have been developed to prevent harmful corrosive reactions as shown in FIG.
In one embodiment of the method of the present invention using a corrosion prevention process and using the corrosion process after etch stop 108 on the tunnel layer, the corrosion process sequence comprises a DI cleaning process and a subsequent photoresist strip. / Corrosion treatment 112. In a second embodiment of the method of the present invention using an anti-corrosion treatment and using the anti-corrosion treatment after the etch stop 108 on the tunnel layer, the anti-corrosion treatment sequence includes the photoresist stripping / corrosion treatment 112 and The DI water cleaning process 110 is performed next.

  In one embodiment shown in FIG. 3, the etch stop process 108 of the present invention is not performed immediately after the reactive partial etch 106 of the upper magnet, but rather, the corrosion processes 110 and 112 are performed first. In the first embodiment shown in FIG. 3 where the etch stop process of the present invention is not performed immediately on the reactive partial etch 106 of the upper magnet, the MTJ device structure is formed on the tunnel layer before the etch stop 108 of the present invention. A DI water cleaning process 110 is performed, followed by a photoresist stripping / corrosion process 112. In a second embodiment of the method of the present invention in which the etch stop process 108 of the present invention is not performed immediately after the reactive partial etch 106 of the upper magnet, the device is subjected to a photoresist strip / corrosion process 112 and then Before the etching stop 108 of the present invention on the tunnel layer, a DI water cleaning process is performed.

  FIG. 4 illustrates the processing sequence of the present invention, in which a magnetic stack is deposited (100), PR is patterned (102), and the hard mask is etched (103). After the hard mask etching 103, the MTJ device structure is subjected to a photoresist stripping process (107), or a reactive etching 105 is performed to remove the upper contact layer, and a reactive etching process 106 is performed to perform a part of the upper magnet. Remove. In the first embodiment of the method of the present invention in which the hard mask etching process 103 is followed by the photoresist stripping process 107, after the photoresist process 107, the MTJ device is subjected to a reactive etching 105 to remove the upper contact layer. Then, a reactive etching process 106 is performed to remove a part of the upper magnet. Performing a hard mask etch process 103, followed by a reactive etch process 105 to remove the upper contact layer, and a reactive etch process 106 to remove a portion of the upper magnet. In the embodiment, the photoresist stripping process 107 is next performed on the MTJ device.

  Performing a combination of resist stripping 107 and reactive etching process 105 to remove the upper contact layer and 106 and removing a portion of the upper magnet, and then performing an etch stop process 108 directly on the MTJ device, or First, a corrosion process sequence comprising a DI cleaning process and a plasma-based corrosion process 113 is performed, and then an etching stop process 108 of the present invention is performed.

  In one embodiment shown in FIG. 4, the etch stop process 108 of the present invention is performed immediately after the reactive partial etch 106 of the upper magnet or after the photoresist strip process 107 preceded by the reactive partial etch 106 of the upper magnet. Once the MTJ device structure patterning is complete, the device moves to subsequent processing 114. In the second embodiment, the etch stop process 108 of the present invention is performed immediately after the reactive partial etching 106 of the upper magnet, or after the photoresist stripping process 107 preceded by the reactive partial etching 106 of the upper magnet, A series of treatments are performed to prevent corrosion. When magnetic films are exposed to chlorine-containing and bromine-containing etching chemicals, adverse reactions may occur under ambient conditions when the device is removed from vacuum and when the film to be etched is subsequently exposed to moisture . Based on the sensitivity of the membrane, various sequences have been developed to prevent harmful corrosion reactions as shown in FIG.

  In one embodiment of the method of the present invention using a corrosion prevention treatment and using the corrosion treatment after the etch stop 108 on the tunnel layer, the corrosion prevention treatment sequence is followed by a DI water cleaning treatment. And a plasma-based corrosion treatment 112. In a second embodiment of the method of the present invention using a corrosion protection treatment and using the corrosion protection treatment after an etch stop 108 on the tunnel layer, the corrosion prevention treatment sequence comprises a plasma-based corrosion prevention treatment 112, and It is comprised from the DI water washing process 110 performed after that.

  In one embodiment shown in FIG. 4, the etch stop process 108 of the present invention is not performed immediately after the reactive partial etch 106 of the upper magnet, but rather the corrosion prevention processes 110 and 113 are performed first. In the first embodiment shown in FIG. 4 where the etch stop process of the present invention is not performed immediately after the reactive partial etch 106 of the upper magnet, the MTJ device structure is formed on the tunnel layer before the etch stop 108 of the present invention. Then, a DI water cleaning process 110 is performed, and then a plasma-based corrosion process 113 is performed. In a second embodiment of the method of the present invention where the etch stop process 108 of the present invention is not performed immediately after the reactive partial etch 106 of the upper magnet, the device is subjected to a plasma-based corrosion process 113 and then the tunnel layer. Before the etching stop 108 of the present invention above, a DI water cleaning process is performed.

  Two approaches to subsequent processing 114 as shown in FIGS. 3 and 4 are shown in FIGS. 5a and 5b. These figures illustrate two specific methods that specifically take advantage of the attendant functionality provided by the etch stop process step 108 of the present invention.

In FIG. 5a, spacers are used to passivate the sidewalls of the MTJ device structure to prevent electrical shorts during subsequent processing. Sidewall spacers are used in conjunction with the etch stop process as described by the etch stop process 108 shown in FIGS. FIG. 5a illustrates a preferred embodiment of subsequent processing steps that follow the etch stop process 108 of the present invention shown in FIGS. In this preferred embodiment, the subsequent process 114 described in FIGS. 3 and 4 completes the method or bottom magnet / bottom contact etch 134, then the DI water clean process step, and then plasma based corrosion protection. To perform the process 142, it consists of a spacer dielectric deposit 130, a spacer etch 132, and a bottom magnet / bottom contact etch 134. Alternatively, the plasma-based corrosion protection process 142 can precede the DI water cleaning process, as shown in FIG. 5a, before the device 150 continues with further processing.
In FIG. 5b, an alternative approach to subsequent processing 114 is shown, in which an insulating hard mask layer such as silicon dioxide or silicon nitride is deposited (120), the photoresist is patterned (122), and the hard mask is etched. (124) Strip the photoresist (126) and etch the magnet and bottom contact (128). In this approach, photoresist patterning is performed by applying a silicon dioxide or silicon nitride hard mask layer to the vertical sidewalls generated from the initial hard mask etch 103, top contact etch 105, reactive top magnet etch 106, and etch stop process 108. It extends beyond the side. The lateral extension of the hard mask 120 beyond the vertical sidewalls is such that during the photoresist patterning 122, the initial hard mask, top contact and upper magnet sidewalls are covered with the hard mask layer 120 after the hard mask layer etch 124. It should be something that remains untouched.

Layers containing MRAM stacks or other magnetic device structures are deposited using techniques used by those skilled in the art of film deposition (100). The film can be deposited by physical vapor deposition, chemical vapor deposition, atomic layer deposition, nanolayer deposition, atomic layer deposition, evaporation, and other techniques. The film in the stack can also be deposited in one form by one of these methods and subsequently modified in the second chamber. An alumina (Al ₂ O ₃ ) dielectric can be formed, for example, by depositing a layer of aluminum and then oxidizing the aluminum to form alumina. Similarly, MgO can be formed by depositing a layer of magnesium and then oxidizing the magnesium to form MgO.

  A photoresist deposition and patterning step 102 is used to create a pattern that forms an MTJ or MRAM stack. Although not shown in the simplified MRAM stack example of FIG. 2, an anti-reflective coating can be used with the photoresist to improve pattern transfer accuracy. In addition, a hard mask layer can be incorporated between the photoresist and the top contact layer. Hard mask layers such as silicon dioxide and silicon nitride can be used. Alternatively, the thickness of the conductive top contact layer can be such that it can serve the dual purpose of the hard mask and top contact layer. FIG. 2 shows a simplified MRAM stack structure after magnetic stack deposition 100 and subsequent photoresist patterning 102.

In a preferred embodiment, the hard mask layer and top contact layer are patterned using common techniques used by those skilled in the art (103). An example of a common process for reactively etching a silicon oxide hard mask, if any, is to use a mixture of CF ₄ , CHF ₃ , and Ar. Oxide etching is widely introduced in the literature. Similarly, an example of a commonly used method chemistry for reactive etching of the top conductor layers 104, 105 is the use of an Ar / Cl ₂ mixture. Metal contact layer etching is also widely published in the literature. Oxide and nitride hard masks and metal contact layers have been used for many years and the techniques used to remove these layers will be apparent to those skilled in the art. A simplified MRAM stack structure after contact etching is shown in FIG.

Removal of the magnetic layers in a magnetic multilayer stack is not well established in the art. The use of a method that is particularly well suited for the top magnet layer reactive etch 106 in combination with the etch stop process 108 is within the scope of the present invention. This method 106 of the present invention uses chlorine-containing gases such as Cl ₂ , BCl ₃ , and HCl and fluorine-containing gases such as CF ₄ , SF ₆ , and CHF ₃ to remove a portion of the upper magnet layer. Consists of a gas mixture. Alternatively, gas molecules containing Cl and F atoms can be used. The ratio of chlorine containing gas to fluorine containing gas should be in the range of 2: 1 to 20: 1. The general processing conditions of the reactive etching stage 106 revealed in the “Spectra®” inductive coupling processing module manufactured by “Tegal Corporation” are as follows: 400 W 13.56 MHz rf power, 20 W 450 kHz rf power applied to the substrate, 40 sccm Cl ₂ , 8 sccm CF ₄ , and ₄ mT processing pressure. A simplified MRAM stack structure after magnet layer reactive etching 106 is shown in FIG.

  The inclusion of fluorine as an additive in the chlorine-containing etching process produces a smooth etched surface (as shown in FIG. 8) and a very thin film of magnetic material that remains after the upper magnet reactive etching stage 106. It is known to prevent the diffusion of chlorine species in the inside. The use of a fluorine / chlorine containing gas mixture makes it possible to remove the upper magnet layer within 5 to 25 inches of the interface between the remaining upper magnet layer and the lower dielectric tunnel layer.

  In a preferred embodiment of the top magnet reactive etching process 106 of the present invention, the remaining top magnet layer is transferred to a subsequent processing step such as an etch stop process 108, a DI water wash process 110, or a PR strip / corrosion process 112. Previously, it will be etched as close as possible to the interface between the remaining upper magnet layer 20 and lower dielectric layer 18 without penetrating the tunnel dielectric layer near the feature. In a preferred embodiment, when the upper magnet layer 20 is etched uniformly, the lower dielectric layer 18 is not broken anywhere on the wafer during the upper magnet layer reactive etch 106, as shown in FIG.

However, in one embodiment of the method of the present invention, when the upper magnet layer 20 is completely removed, the lower dielectric layer 18 is breached, but not in close proximity to the patterned MTJ stack (see FIG. 9). In this embodiment of the method of the present invention, the top magnet layer etch 106 performs the following gases or gas mixtures: Cl ₂ , Cl ₂ / Ar, Cl ₂ / CF ₄ , Cl ₂ / CHF ₃ , Cl ₂ / Ar. , BCl ₃ / Cl ₂ , BCl ₃ / Cl ₂ / Ar, BCl ₃ / HBr, BCl ₃ / HBr / Ar, NH ₃ , HN ₃ / CO. Removed.

In another embodiment, the top magnet layer 20 is completely removed, the bottom dielectric layer 18 is also removed outside the immediate sloped area of the patterned MTJ stack, and all or part of the bottom magnet layer 16 and the bottom All or part of the contact layer 14 is removed. (See FIG. 10.) The attendant advantage of this embodiment is that the complete MRAM structure is patterned with a single mask, ie, no subsequent processing step 114 is required. In this embodiment of the method of the present invention, the top magnet layer etch 106 performs the following reaction gases and gas mixtures: Cl ₂ , Cl ₂ / Ar, Cl ₂ / CF ₄ , Cl ₂ / CHF ₃ , Cl ₂ / Etching process containing one or more of Ar, BCl ₃ / Cl ₂ , BCl ₃ / Cl ₂ / Ar, BCl ₃ / HBr, BCl ₃ / HBr / Ar, NH ₃ , HN ₃ / CO Is removed.

The remainder of the top magnet layer that is not removed in the reaction step 106 in the above-described embodiment is then used in a preferred embodiment using an etch stop process 108 comprising a mixture of a non-reactive gas such as argon and an oxidizing gas such as oxygen. The dielectric of the tunnel barrier layer functions as a stop layer. In a preferred embodiment, the inert gas flow rate is generally in the range of 10 to 350 sccm and the oxygen-containing gas flow rate is in the range of 0.02 to 0.15 sccm. The actual flow rate of the oxygen-containing gas may vary depending on the flow rate of the inert gas, the selection of the oxygen-containing gas, and the type of plasma system used. A general method 108 used in a “Spectra®” inductively coupled etch module manufactured by “Tegal Corporation” is as follows for a 200 mm diameter silicon substrate: a source coil Above, 100 W 13.56 MHz rf frequency power, 20 W 450 kHz rf power applied to the substrate, 350 sccm Ar, 0.08 sccm O ₂ , 10 mT processing pressure. The conditions previously indicated for the etch stop sputter process stage 108 result in ~ 90: 1 sputter selectivity between NiFe and alumina in processing the “Spectra ICP” process module manufactured by “Tegal Corporation”. It is an object to provide an exemplary set of conditions that have been found. (See FIG. 11)

  A variety of processing conditions and chamber configurations can be used to obtain results with high selectivity between the top magnet material and the dielectric. Two factors that should be considered when achieving high selectivity are control of the ratio of inert gas to oxygen-containing gas in the processing chamber and operation of the method at low bias power levels. These two elements are described in more detail in the following paragraphs.

In a preferred embodiment, the etch stop process requires high selectivity (> 5: 1) between the upper magnet layer 20 and the lower dielectric layer 18. The upper magnet layer 20 is expected to be etched at a rate that is at least five times the rate at which the lower dielectric layer 18, eg, Al ₂ O ₃ is etched. Accurate control of the NiFe / CoFe etch rate is possible due to the significant differences in the sputtering threshold between NiFe and CoFe and the thresholds of metal oxides such as Al ₂ O ₃ and MgO. Experiments were performed to confirm these phenomena using a “Spectran®” processing module manufactured by “Tegal Corporation” (Petaluma, Calif.).

  Specifically, NiFe and CoFe sputtering rates were measured with a single layer test wafer and alumina etch rates were measured with an alumina / NiFe test structure. The test structure consisted of a substrate with a NiFe layer deposited on the substrate and a very thin layer of alumina on NiFe (˜15 cm). The measured alumina etch rate represented the thin film properties believed to be seen in the stack containing the magnetic tunnel junction.

  As is apparent from the graph of FIG. 12, a significant difference was observed between the onset of sputtering for the magnetic alloy and that of alumina. A significant difference was further observed in etch rate tests performed on alumina / NiFe test structures at bias power levels from 10 W to 25 W, where the alumina was not etched appreciably. According to these observations, under certain processing conditions, significant amounts of NiFe and CoFe can be etched away from the TMR stack, while only a small amount of alumina is removed in the same amount of time.

  The resulting device profile after the preferred embodiment of the reactive etch stage 106 and etch stop process 108 as shown in FIGS. 7, 9, and 10 is shown in FIGS. 13, 14, and 15. FIG. . In each of these embodiments, the remaining metal film of the upper magnet layer 20 after the reactive etching step 106 is removed from the lower dielectric layer 18. Removal of the upper magnet layer 20 remaining after the reaction stage 106 with a low bias non-reactive etch stop 108 provides superior electrical isolation over other known methods without damaging the lower dielectric layer 18. . Geometric isolation is obtained in each of the three embodiments of the method of the present invention without the attendant risks of electrical shorts known to limit the device performance of structures incorporating MTJ stacks. The excellent electrical separation between the upper magnet layer 20 and the lower magnet layer 16 is also at a processing stage that is crucial to produce a reliable device without the associated risks associated with using corrosive chemicals. This is achieved by the method of the present invention.

  The typical process conditions for etch stop 108 shown above are intended to represent processes that have been found to obtain exceptionally high selectivity between NiFe or CoFe and alumina. . Variations in the processing conditions within the “Spectra” reactor can be used within the scope of the etch stop process 108 of the present invention.

  A first stage of removing the entire upper magnet layer using a mixture of chlorine and fluorine containing gases and a second stage of using a mixture of inert and oxygen containing gases to stop on the dielectric tunnel layer. Similar processes utilizing one or both approaches are used to generate plasma to produce devices from other inductively coupled plasma reactors, capacitively coupled plasma reactors, electron cyclotron resonance reactors, and magnetic films. However, these processes are still within the scope of the process of the present invention. Furthermore, the use of a mixture of inert gas and oxygen-containing gas to use the dielectric layer as an etch stop without the initial step of removing the entire upper magnet layer using a mixture of chlorine and fluorine containing gases. The scope of the method of the present invention.

The high selectivity of the exemplary embodiment for the etch stop 108 described above between NiFe and alumina is observed with a gas mixture of argon and oxygen. The use of one or both of the alternative inert and oxidizing components of the preferred embodiment of the argon / oxygen gas mixture used to reveal a NiFe / alumina selectivity of ˜90: 1 in the etch stop process 108 is The range of methods. For example, helium, neon, krypton, and nitrogen can provide an inactive component of the etch stop process 108 when used in place of or in combination with argon. Similarly, oxygen substitutes such as N ₂ O, NO, CO, and CO ₂ can produce an oxidizing component of the etch stop process 108, particularly when used in place of or in combination with oxygen. . Alternatively, within the scope of the method of the present invention, the oxygen-containing gas is excluded by controlling the oxygen concentration in the etching chamber by a method other than the intentional introduction of the oxygen-containing gas, as described in the following paragraphs. can do.

  When a magnetic layer containing a transition metal such as NiFe is plasma sputtered with an inert sputtering gas such as Ar, adjusting the amount of oxygen in the plasma chamber may affect the etching selectivity with respect to the lower layer alumina. It has been clarified that it can be done. That is, higher NiFe / alumina selectivity can be achieved by controlling the flow rate of oxygen entering the plasma chamber. In one embodiment of this plasma overetch process, it is necessary to reduce background oxygen to a level that does not affect the etch process while reintroducing oxygen into the plasma chamber in a simultaneously measurable and controllable manner. . Sources of background oxygen that can enter the plasma chamber include, for example, (1) sputtering of oxygen-containing internal chamber components, (2) oxygen in the air, (3) degassing action from chamber material, and (4) There are other processing modules in the processing system.

When reducing uncontrolled background oxygen in the chamber, the selectivity between NiFe and alumina can be optimized by reintroducing a very small amount (eg, ˜0.08 sccm) of oxygen into the chamber. . One technique for reintroducing oxygen uses two separate carrier gas sources connected to the chamber. The first source supplies an Ar / O ₂ 2 gas mixture containing 99.9% Ar and 0.1% O ₂ to the plasma chamber, while the second source is parallel to the chamber. A gas containing 100% Ar is supplied. When reintroducing oxygen into the plasma chamber, it is preferable to reduce the basic pressure of the chamber to ˜0.001 mT or less. Furthermore, the sputtering of the surface of the internal chamber parts should be minimized or controlled. For example, the inductive power supply should be low (100W to 200W) to minimize window sputtering. An excessive amount of oxygen in the chamber can slow down the etch rate of the metal magnetic film and can cause a reduction in selectivity between the magnet layer and the dielectric layer.

  Alternatively, in the second technique, oxygen is introduced into the processing chamber through an orifice separating the oxygen source and the processing chamber. The orifice is sized such that enhanced sputtering selectivity is created between the upper magnetic film and the tunneling dielectric by the flow of the oxygen-containing gas when the inert gas is mixed.

  Other means of introducing a controlled level of oxygen into the inert gas to achieve the conditions necessary to selectively etch the magnetic material on the dielectric layer can also be used within the scope of this patent. In such an embodiment, sputtering of the inner surface of the oxygen-containing material in the plasma reactor can be used as the oxygen source. In this embodiment, the surface of the upper magnetic layer is etched by conventional means such as a mass flow controller or needle valve so as to obtain selective removal between the magnetic and tunneling dielectric layers. An inert gas such as argon is introduced in a volume that produces a mixture of active gas and oxygen-containing species. The processing conditions are adjusted to remove the magnetic material at a rate of> 5 Å / min and to remove the dielectric layer at a rate of <1 Å / min.

  In another embodiment of the invention, the level of oxygen-containing gas is achieved by controlling the escape of atmospheric gas entering the vacuum chamber. Plasma-based semiconductor fabrication processes are typically performed in the range of 0.1 to 1000 millitorr. At conditions below these atmospheric pressures, oxygen can be inadvertently introduced through imperfect seals, through porous materials, and from outgassing of parts of the process quality. The rate of leakage can be easily measured with conventional plasma processing equipment.

  In this embodiment, the surface of the upper magnetic layer is etched by conventional means such as a mass flow controller or needle valve so as to obtain selective removal between the magnetic and tunneling dielectric layers. An inert gas such as argon is introduced in a volume that produces a mixture of active gas and oxygen-containing species. Controlled through conventional means to remove the magnetic material at a rate of> 5 Å / min and produce the required mixture of inert gas and oxygen-containing species to the extent that the dielectric layer is removed at a rate of <1 Å / min. Techniques for controlling oxygen-containing leakage from the atmosphere in combination with the introduction of an inert gas stream are within the scope of the present invention.

  The process of removing the photoresist and preventing corrosion, ie 112 in FIG. 3, 113 in FIG. 4, 142 in FIG. 5a, and 126 and 142 in FIG. 5b, should be compatible with the magnetic film structure. The use of a hydrogen-containing gas mixture suitable for resist removal and preventing corrosion that can result from exposure of the MRAM film stack to halogen-containing etch chemistries is within the scope of the present invention. In a preferred embodiment, the magnetic film stack is exposed to a hydrogen-containing plasma to remove the photoresist and / or to prevent corrosion when exposed to ambient conditions. Hydrogen is introduced into the processing chamber with a mixture of hydrogen and an inert gas such as helium, neon, argon, or nitrogen.

1 is a diagram of an exemplary MRAM structure having a magnetic tunnel junction. FIG. FIG. 3 is a simplified MRAM structure with a magnetic tunnel junction. It is a figure of the MRAM processing sequence of this invention. It is a figure of the MRAM processing sequence of this invention. It is a figure of the MRAM processing sequence of this invention. It is a figure of the MRAM processing sequence of this invention. FIG. 4 is a diagram of an MRAM stack structure after top contact patterning. FIG. 4 is a diagram of an MRAM stack structure after a reactive magnet layer etching step. It is a figure of the MRAM stack structure after reactive magnet layer etching. FIG. 5 is an illustration of an embodiment of the MRAM patterning sequence of the present invention in which the tunnel dielectric layer is not broken near the feature but is broken in areas not near the mask feature. FIG. 4 is a diagram of an embodiment of the MRAM patterning sequence of the present invention that intentionally etches the magnetic stack layer with a graded profile during a reactive etch step prior to the etch stop process. The two peaks in the plot indicate the removal of the two NiFe layers, and the time between the two peaks indicates the time required to remove the 15% alumina layer, obtained from the process used to generate the graph. FIG. 6 is a plot of light emission signal intensity plots obtained during etching of a 50ÅNiFe / 15Åalumina / 50ÅNiFe stack structure with a NiFe to alumina etch selectivity greater than 90: 1. It is a graph of the etching sputter | spatter rate of CoFe, NiFe, and an alumina. FIG. 7 is a diagram of an MRAM stack structure after reactive magnet layer etching (see FIG. 6) and etch stop treatment. FIG. 8 is a diagram of the MRAM stack structure after reactive magnet layer etching (see FIG. 7) and etch stop treatment. FIG. 9 is a diagram of the MRAM stack structure after reactive magnet layer etching (see FIG. 8) and etch stop treatment.

Explanation of symbols

100 Process for depositing magnetic stack 102 Process for patterning PR 108 Etching stop process of the present invention

Claims (15)

A method of fabricating a magnetic junction memory device, comprising:
(A) preparing a substrate;
(B) forming an insulating layer on the substrate;
(C) forming an upper metal layer on the insulating layer;
(D) selectively removing the upper metal layer relative to the underlying insulating layer;
Including
The selective removal process includes application of a bias to the substrate by a bias power between sputtering thresholds of the upper metal layer and the insulating layer.
A method characterized by that.   The method according to claim 1, wherein the selective removal treatment is performed in a non-reactive gas atmosphere. The method of claim 1, wherein the step of selectively removing the upper metal layer further comprises a physical sputter process using a mixture of non-reactive gas and less than 1% oxygen-containing gas. . A method of fabricating a magnetic junction memory device, comprising:
(A) preparing a substrate;
(B) forming an insulating layer on the substrate;
(C) forming an upper layer on the insulating layer;
(D) selectively removing the upper metal layer relative to the underlying insulating layer;
Including
The selective removal process includes a physical sputter process using a mixture of non-reactive gas and less than 1% oxygen-containing gas.
A method characterized by that. Prior to the step of selectively removing the upper metal layer,
(Cl) removing a portion of the upper metal layer using a mixture of a fluorine-containing gas and a chlorine-containing gas;
The method according to claim 1 or 3, further comprising the step of:   6. The method of claim 5, wherein the ratio of chlorine containing gas to fluorine containing gas is in the range of 2: 1 to 20: 1. 6. The non-reactive gas is Ar, He, Ne, Kr, N ₂ , or Xe, or any combination thereof, according to claim 2, claim 3, claim 4, or claim 5. Method. The oxygen-containing _{gas, O, O 2, N 2} O, NO, air, CO, or method of claim 3, claim 4, or claim 5, wherein any combination thereof.   The mixture of non-reactive gas and oxygen-containing gas is introduced through a first flow controller and non-reactive gas is introduced through a second flow controller. Item 6. The method according to Item 5.   6. The non-reactive gas is in the range of 10 to 350 sccm, and the oxygen-containing gas is in the range of 0.02 to 0.15 sccm. the method of.   6. A method according to claim 3, 4 or 5, wherein an oxygen-containing gas is introduced into the process from sputtering of a solid source of oxygen-containing solids.   6. The method of claim 1, 3, 4, or 5, further comprising forming a lower metal layer under the insulating layer.   6. The method of claim 1, 3, 4, or 5, wherein the insulating layer comprises aluminum oxide, magnesium oxide, or any insulating oxide.   The top metal layer comprises a magnetic layer, part of an MRAM stack structure, or one or more layers of NiFe, CoFe, CoNiFe, and CoFeB. Item 6. The method according to item 4 or item 5. The chlorine-containing gas includes Cl ₂ , BCl ₃ , HCl, atomic chlorine-containing gas, or any combination thereof,
The fluorine-containing gas includes CF ₄ , SF ₆ , CHF ₃ , atomic fluorine-containing gas, or any combination thereof.
6. The method of claim 5, wherein:

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