WO2011071028A1

WO2011071028A1 - Method for processing laminated electrode

Info

Publication number: WO2011071028A1
Application number: PCT/JP2010/071861
Authority: WO
Inventors: 一誠東條; 直志山本; 英男大野; 正二池田
Original assignee: 株式会社アルバック; 国立大学法人東北大学
Priority date: 2009-12-08
Filing date: 2010-12-07
Publication date: 2011-06-16
Also published as: JP5587911B2; TW201131644A; JPWO2011071028A1

Abstract

Either at least one halogen gas selected from the group comprising CF4, C2F6, C3F6, C3F8, C4F6, C4F8, C5F8, Cl2, BCl3, SiCl4, HBr, and HI, or a mixed gas of the halogen gas and at least one inert gas selected from the group comprising N2, Ne, Ar, and Xe is used as an etching gas in a process for etching the upper electrode film layer (Eu) of a bottom electrode (E) and a process for etching the bottom electrode film layer (Eb) of the same. A gas comprising at least an oxygen gas is used as an etching gas in a process for etching the middle electrode film layer (Em) of the same.

Description

Multilayer electrode processing method

The present invention relates to a method of processing a laminated electrode formed by laminating a plurality of conductive films, for example, a method of processing a lower electrode of a magnetoresistive element used in a magnetoresistive random access memory (MRAM).

Conventionally, a multi-layered element having a tunnel magnetoresistive effect, a so-called magnetoresistive element is known. The magnetoresistive element is used as a magnetoresistive head for writing data to the hard disk and reading the written data from the hard disk, or as a storage medium of a magnetoresistive random access memory (MRAM) which is a storage element using magnetism. It is used.

In the method of manufacturing a magnetoresistive element described in Patent Document 1, first, a metal film serving as a lower electrode of the element is formed. Next, on this metal film, a free magnetic layer laminate having a three-layer structure in which a nonmagnetic layer is sandwiched between two free magnetic layers, a nonmagnetic layer, and a three layer in which a nonmagnetic layer is sandwiched between two pinned magnetic layers The pinned magnetic layer stack having the structure and the antiferromagnetic layer are stacked in this order. That is, a multilayer film structure is formed on the lower electrode. Then, a resist is applied to the upper surface of the multilayer film structure, and the resist is patterned according to a desired shape of the magnetoresistive element. Thereafter, the multilayer structure is sequentially etched downward by ion milling according to the patterned resist.

JP 2003-101097 A

By the way, after the magnetoresistive element is formed through the above-described processes, the lower electrode of the laminated structure electrically connected to the lower layer of the magnetoresistive element may be processed into a predetermined shape. With reference to FIGS. 5A and 5B, the processing steps of the lower electrode will be described. As shown in FIG. 5A, the lower electrode E and the magnetoresistive element MR are formed on the support substrate SS. The entire magnetoresistive element MR and the upper surface of the lower electrode E on which the magnetoresistive element MR is laminated. The resist PR is applied to the whole. The resist PR is patterned into a predetermined shape. Next, anisotropic etching is performed from above the resist PR. This etching is performed in the order of the upper layer electrode film Eu, the intermediate layer electrode film Em, and the lower layer electrode film Eb constituting the lower electrode E by ion milling in the same manner as the magnetoresistive element MR.

Here, the etching by ion milling is to obtain a desired shape by physically scraping an object by causing an inert gas such as argon to collide with the object to be etched. Therefore, etching is possible regardless of the constituent material of the object to be etched.

However, since ion milling is a method of physically removing an object to be etched in this way, when etching the lower electrode E, the metal material of the lower electrode E shaved by ion milling is released as metal particles. The The metal particles adhere to the upper surface of the lower electrode E, particularly to the side wall of the resist PR that covers the entire magnetoresistive element MR. The amount of the metal particles adhering to the resist PR is increased by the progress of ion milling, and as shown in FIG. 5B, most of the resist PR covering the magnetoresistive element MR is formed by the film-like metal adhering Er. It will be covered.

Such metal deposit Er remains in a state of being connected to the lower electrode E even after the resist PR is removed along with the completion of ion milling. That is, the ion milling residue is attached to the lower electrode E. Therefore, an insulating film such as silicon dioxide is formed so as to cover the magnetoresistive element MR and the lower electrode E, and an upper electrode electrically connected to the upper layer of the magnetoresistive element MR is formed via this insulating film. However, the upper electrode and the lower electrode E may be electrically connected by the metal deposit Er, that is, the residue. That is, the residue that short-circuits the upper electrode and the lower electrode may deteriorate the yield for manufacturing the magnetoresistive element.

In addition, the problem that the residue derived from the etching target adheres to the etching target is not limited to the case where the lower electrode included in the magnetoresistive random access memory as described above is etched by ion milling. Even when an electrode of an apparatus or the like is etched by ion milling, it is generally seen in common.

The present invention has been made in view of the above-described conventional situation, and an object of the present invention is to suppress generation of a residue derived from a material for forming an electrode when etching a laminated electrode made of a metal material. An object of the present invention is to provide a method for processing a laminated electrode.

One aspect of the present invention is a lower electrode film made of any one of a metal selected from the group consisting of Ta, Ti, Mo, Ga, and W, an oxide of the metal, and a nitride of the metal; With respect to a laminated electrode in which an intermediate layer electrode film made of any one selected from the group consisting of Ru and Cr and an upper layer electrode film made of the same constituent material as the lower layer electrode film are laminated in this order, the upper layer Provided is a laminated electrode processing method in which each electrode film is processed in order from the upper electrode film by reactive ion etching using a resist formed on the electrode film as a mask. In the step of etching the upper electrode film and the step of etching the lower electrode film, CF ₄ , C ₂ F ₆ , C ₃ F ₆ , C ₃ F ₈ , C ₄ F ₆ , C ₄ F ₈ , C _{5 are used.} At least one halogen-based gas selected from the group consisting of F ₈ , Cl ₂ , BCl ₃ , SiCl ₄ , HBr, HI, and at least one inert gas selected from the group consisting of N ₂ , Ne, Ar, Xe In the step of etching the intermediate layer electrode film, any one of a mixed gas of a gas and the halogen-based gas is used as an etching gas, and a gas containing at least an oxygen gas is used as an etching gas.

According to the above method, ions generated from the etching gas react with the metal element constituting the electrode film to generate a highly volatile metal compound. This metal compound is less adherent to the resist than the corresponding metal itself. Therefore, the residue derived from the etching of the laminated electrode can be suppressed.

In one example, the intermediate layer electrode film is made of Ru. In the step of etching the intermediate layer electrode film, oxygen gas, CF ₄ , C ₂ F ₆ , C ₃ F ₆ , C ₃ F ₈ , C ₄ F _{6 are used.} , C ₄ F ₈ , C ₅ F ₈ , Cl ₂ , BCl ₃ , SiCl ₄ , a mixed gas of at least one halogen gas selected from the group consisting of HBr, and oxygen gas, the halogen gas, and N ₂ Any one of a mixed gas with at least one inert gas selected from the group consisting of Ne, Ar, and Xe is used as an etching gas.

In one example, the intermediate layer electrode film is made of Cr, and in the step of etching the intermediate layer electrode film, oxygen gas, CF ₄ , C ₂ F ₆ , C ₃ F ₆ , C ₃ F ₈ , C ₄ F _{6 are used.} , C ₄ F ₈ , C ₅ F ₈ , Cl ₂ , BCl ₃ , SiCl ₄ , a mixed gas of at least one halogen-based gas, and oxygen gas, the halogen-based gas, N ₂ , Ne Any one of a mixed gas with at least one inert gas selected from the group consisting of Ar, Xe is used as an etching gas.

Since the resist used for processing the laminated electrode is generally made of an organic substance, the resist is also etched by reacting with an oxygen gas used as an etching gas during the etching process of the intermediate layer electrode film. On the other hand, in the etching process of the intermediate layer electrode film using the halogen-based gas, the etching selectivity with respect to the resist is larger than that in the process using the oxygen gas. Therefore, in the etching process of the intermediate layer electrode film, by using a mixed gas of oxygen gas and halogen-based gas or a mixed gas of oxygen gas, halogen-based gas and inert gas, the etching amount of the intermediate layer electrode film is reduced. The amount of resist etching can be further reduced. That is, the influence of the etching process on the laminated electrode can be suppressed.

In one example, in the step of etching the intermediate layer electrode film, the etching is terminated when a part of the lower layer electrode film is exposed, and in the step of etching the lower layer electrode film, the remaining on the lower layer electrode film The lower electrode film is etched together with a part of the intermediate electrode film.

The resist is used to control the electrode shape after etching, and is generally made of an organic material. Therefore, in the etching of the intermediate layer electrode film using oxygen gas, the etching of the resist proceeds significantly as compared to the etching of the upper layer electrode film and the lower layer electrode film, which is etching without using oxygen gas. If the etching time of the intermediate layer electrode film is lengthened, the amount of etching of the resist increases due to such oxygen, and the shape of the resist may be deteriorated in the etching of the lower layer electrode film performed following the etching of the intermediate layer electrode film. There is.

Therefore, by ending the etching of the intermediate layer electrode film when a part of the lower layer electrode film is exposed, it is possible to shorten the time during which the resist is exposed to oxygen gas. At this time, a part of the intermediate layer electrode film to be etched remains on the lower layer electrode film. Such a small amount of the intermediate layer electrode film is formed of the halogen-based gas in the etching process of the lower layer electrode film. It can be removed by etching. Therefore, it is possible to suppress the shape failure of the laminated electrode after etching while suppressing the shape failure of the resist.

In one example, the step of etching the intermediate electrode film is performed at a pressure of 0.1 Pa or more and 10 Pa or less.
In the intermediate layer electrode film etching step, the resist etching rate may be higher than the intermediate layer electrode film etching rate depending on the conditions. That is, if the etching selectivity of the intermediate layer electrode film is 1 or less, the etching of the resist proceeds more than the intermediate layer electrode film, and most of the resist is etched before the completion of the etching of the intermediate layer electrode film. There is a possibility that the laminated electrode cannot be formed into a desired shape.

Here, the inventors of the present application perform the step of etching the intermediate layer electrode film at a pressure set to 0.1 Pa or more and 10 Pa or less, thereby bringing the etching selectivity of the intermediate layer electrode film to the resist close to 1, and The selectivity of the interlayer electrode film to the resist during dry etching of the layer electrode film was improved. That is, according to the above method, resist etching during the etching of the intermediate layer electrode film can be suppressed.

In one example, the resist covers the entire magnetoresistive element formed on the upper electrode film, and the laminated electrode is a lower electrode of the magnetoresistive element.
As in the above method, the processing method can be employed as a method of processing the lower electrode of the magnetoresistive element. Therefore, if the residue of the material constituting the lower electrode can be suppressed during processing of the lower electrode, the lower electrode and the magnetoresistive element placed on the upper surface of the lower electrode are electrically connected in an unintended manner. In addition, it is possible to suppress a short circuit between the lower electrode and the upper electrode, and as a result, it is possible to suppress a deterioration in yield in manufacturing a device having a magnetoresistive element.

Schematic of the plasma etching apparatus for processing a laminated electrode. The partially broken top view of the process board | substrate by which reactive ion etching is carried out in the said plasma etching apparatus. FIG. 3 is a cross-sectional view of the substrate of FIG. 2 taken along line 3-3. (A) (b) (c) (d) Sectional drawing which shows the processing method of the laminated electrode which concerns on embodiment. (A) (b) Sectional drawing which shows the processing method of the conventional laminated electrode.

Hereinafter, an embodiment in which a method for processing a laminated electrode according to the present invention is applied to reactive ion etching performed in a plasma etching apparatus will be described with reference to FIGS.
FIG. 1 shows a schematic configuration of a plasma etching apparatus in which reactive ion etching is performed. As shown in FIG. 1, a quartz plate 12 that seals a plasma generation space 11 a that is an internal space of the chamber body 11 is attached to the upper opening of the chamber body 11 of the plasma etching apparatus 10. 11 and the quartz plate 12 constitute a vacuum chamber. The plasma generation space 11a is depressurized to a predetermined pressure by an exhaust unit such as a vacuum pump (not shown). The chamber body 11 is connected to a chamber temperature adjustment mechanism 11b that adjusts the temperature of the chamber body 11 by supplying temperature adjustment water during the etching process.

In the plasma generation space 11a, a substrate stage 13 for supporting a processing substrate S that is an object of plasma etching processing is disposed. The substrate stage 13 is electrically connected to a bias high frequency power source 21 via a bias matching circuit 20. The high frequency power output from the bias high frequency power source 21 is impedance-matched by the bias matching circuit 20 so that the reflected wave from the load side becomes small, and is applied to the processing substrate S via the substrate stage 13. The A ring-shaped protection member 14 that surrounds the outer periphery of the processing substrate S is disposed on the wafer mounting surface of the substrate stage 13. The protective member 14 is made of, for example, glassy carbon having high resistance to chlorine-based or iodine-based plasma, and has a function of protecting the outer peripheral portion of the substrate stage 13 from the plasma generated in the plasma generation space 11a. is doing. Furthermore, a stage temperature adjustment mechanism 22 that adjusts the temperature of the processing substrate S placed thereon to a predetermined temperature is connected to the substrate stage 13. When the etching process is performed in the plasma etching apparatus 10, the temperature of the processing substrate S is adjusted through temperature control water supplied by the stage temperature control mechanism 22 according to the processing conditions. can do.

The structure of the processing substrate S will be described with reference to FIGS. In the support substrate SS that is a support base of the processing substrate S, a plurality of element regions C in which active elements and passive elements are provided are virtually divided. On the upper surface of the support substrate SS, a lower electrode E in which three layers of metal films are laminated so as to spread over the entire element region C is formed. In each element region C, one magnetic tunnel junction element MTJ having a known structure is provided on the uppermost layer of the lower electrode E one by one. The entire magnetic tunnel junction element MTJ is covered with the resist PR. Each resist PR also covers a part of the corresponding element region C. More precisely, in the uppermost metal film in the lower electrode E in the element region C, a region other than the portion etched by the plasma etching apparatus 10 (FIG. 1) is covered with the resist PR.

Referring to FIG. 3, the sectional structure of the processing substrate S will be described. A lower electrode E made of a three-layer metal film is stacked on the support substrate SS. In the illustrated example, the lower electrode E includes a lowermost layer, that is, a lower electrode film Eb, an intermediate layer, that is, an intermediate layer electrode film Em, and an uppermost layer, that is, an upper layer electrode film Eu. The lower electrode film Eb is a metal film made of a metal selected from the group consisting of tantalum (Ta), titanium (Ti), molybdenum (Mo), gallium (Ga), and tungsten (W), or a nitride of these metals. Alternatively, a metal compound film made of a metal compound selected from the group consisting of oxides. The intermediate layer electrode film Em is made of ruthenium (Ru) or chromium (Cr). The upper electrode film Eu is made of the same material as that of the lower electrode film Eb. Each of these three metal films has a thickness of 2 nm to 30 nm. The upper electrode film Eu and the lower electrode film Eb have the same thickness, and the intermediate electrode film Em is configured to be thinner than the upper electrode film Eu and the lower electrode film Eb. The metal constituting the upper electrode film Eu and the lower electrode film Eb has reactivity with one or more halogen elements of fluorine (F), chlorine (Cl), bromine (Br), and iodine (I). . The metal constituting the intermediate layer electrode film Em has reactivity with oxygen. Note that the lower electrode film Eb has a function of improving the adhesion with the support substrate SS and a function of improving the crystal orientation of the intermediate layer electrode film Em. Further, the intermediate layer electrode film Em has a function of reducing the electrical resistance of the entire lower electrode E and a function of improving the crystal orientation and flatness of the upper layer electrode film Eu. The upper electrode film Eu has a function of improving the flatness and crystal orientation of the magnetic tunnel junction element MTJ and a function of improving the adhesion with the intermediate layer electrode film Em.

The magnetic tunnel junction element MTJ is formed on the upper surface of the upper electrode film Eu in the lower electrode E. This magnetic tunnel junction element MTJ is an element having a known multilayer structure. A plurality of layers for forming the magnetic tunnel junction element MTJ are stacked on the upper surface of the lower electrode E, and patterned into a predetermined shape by etching or milling to form the magnetic tunnel junction element MTJ. The magnetic tunnel junction element MTJ is covered with a resist PR. The resist PR is applied to the entire lower electrode E and then patterned in accordance with the final shape of the lower electrode E. The resist PR functions as an etching mask for etching the lower electrode E into a predetermined shape. The resist PR is appropriately selected according to the design rule of the magnetic tunnel junction element MTJ, and is made of a heat-resistant resin material such as phenol resin or imide resin.

In addition to the etching process in the plasma etching apparatus 10 (FIG. 1), the processing substrate S having such a configuration includes an upper electrode connected to the lower electrode E through a subsequent process, for example, the magnetic tunnel junction element MTJ. A magnetoresistive element, which is a memory element using magnetism, is formed in each of the element regions C through the forming process and the like, and a random access memory consisting of a plurality of element regions C, so-called MRAM is constructed. become.

On the other hand, a double-winding high-frequency loop antenna 30 is disposed above the quartz plate 12 shown in FIG. 1, and between the high-frequency loop antenna 30 and the quartz plate 12, the high-frequency loop antenna 30 and A coaxial loop-shaped permanent magnet 31 is disposed in parallel with the surface of the quartz plate 12. The high-frequency loop antenna 30 is electrically connected to a discharging high-frequency power source 41 via a discharging matching circuit 40. The high-frequency power output from the discharge high-frequency power supply 41 is impedance-matched by the discharge matching circuit 40 so that the reflected wave from the load side becomes small, similarly to the high-frequency power output from the bias high-frequency power supply 21. Applied to the high-frequency loop antenna 30. The high frequency loop antenna 30 applies a high frequency electric field to the plasma generation space 11a. The induction electric field generated by the high-frequency electric field generates an etching gas plasma in the plasma generation space 11a. At this time, the permanent magnet 31 forms a static magnetic field in a direction substantially orthogonal to the current flowing through the high-frequency loop antenna 30 in the plasma generation space 11a. Further, between the quartz plate 12 and the permanent magnet 31, a planar electrode 32 having substantially the same diameter as the quartz plate 12 is disposed in parallel with the surface of the quartz plate 12. The planar electrode 32 is electrically connected to the discharging high-frequency power source 41 via the variable capacitor 42 and the discharging matching circuit 40. Such a planar electrode 32 has a function of forming a uniform electric field on the inner surface of the quartz plate 12, and is made of, for example, a linear metal material.

A halogen-based gas supply unit 50, an inert gas supply unit 51, and an oxygen gas supply unit 52 are connected to the chamber body 11. The halogen-based gas supply unit 50, the inert gas supply unit 51, and the oxygen gas supply unit 52 supply the halogen-based gas, the inert gas, and the oxygen gas to the plasma generation space 11a at controlled timings, respectively. The halogen-based gas, the inert gas, and the oxygen gas are etching gases for the plasma etching process.

Note that the halogen-based gas supplied from the halogen-based gas supply unit 50 is used alone or mixed with an inert gas supplied from the inert gas supply unit 51 to form the upper electrode film Eu and the lower electrode film Eb. Used in the etching process. In one example, in the etching process of the upper electrode film Eu and the lower electrode film Eb, the oxygen gas supply unit 52 stops supplying oxygen gas.

The oxygen gas supplied from the oxygen gas supply unit 52 is mixed with the halogen-based gas supplied from the halogen-based gas supply unit 50 and used in the etching process of the intermediate layer electrode film Em. In the etching process of the intermediate layer electrode film Em, oxygen gas, halogen-based gas, and inert gas supplied from the inert gas supply unit 51 may be used as etching gas.

Incidentally, the halogen-based gas reacts with a metal material that is a constituent material of the upper electrode film Eu and the lower electrode film Eb, that is, one selected from the group consisting of tantalum, titanium, molybdenum, gallium, and tungsten. A gas that generates volatile metal halide is employed.

Preferred halogen-based gases are listed. For example, as a compound of fluorine (F), carbon tetrafluoride (CF ₄ ), tetrafluoroethylene (C ₂ F ₄ ), hexafluoroethane (C ₂ F ₆ ), hexafluoropropene (C ₃ F) ₆ ), octafluoropropane (C ₃ F ₈ ), hexafluorobutadiene (C ₄ F ₆ ), octafluorocyclobutane (C ₄ F ₈ ), and octafluorocyclopentene (C ₅ F ₈ ). . The chlorine (Cl) compound includes simple chlorine (Cl ₂ ), boron trichloride (BCl ₃ ), and silicon tetrachloride (SiCl ₄ ). The bromine (Br) compound includes hydrogen bromide ( Further, examples of the compound of HBr) and iodine (I) include hydrogen iodide (HI). One or more halogen-based gases are supplied from the halogen-based gas supply unit 50. Examples of the inert gas include nitrogen (N ₂ ) gas, neon (Ne) gas, argon (Ar) gas, and xenon (Xe) gas. One or more inert gases are supplied from the inert gas supply unit 51.

The plasma etching apparatus 10 is provided with a control unit 60 for controlling the plasma etching process. The control unit 60 is connected to the substrate stage 13, the bias matching circuit 20, the bias high frequency power source 21, the discharge matching circuit 40, the discharge high frequency power source 41, and the variable capacitor 42, and the conditions for the plasma etching process Various control signals based on the above are supplied to each unit.

For example, the control unit 60 refers to the plasma etching processing conditions stored in the storage area of the control unit 60. Then, a temperature control signal corresponding to this processing condition is supplied to the stage temperature adjustment mechanism 22 of the substrate stage 13 to control the temperature of the processing substrate S.

The controller 60 supplies a bias high-frequency power control signal corresponding to the processing conditions to the bias high-frequency power supply 21 to control the bias high-frequency power applied to the processing substrate S.
The control unit 60 supplies a discharging high-frequency power control signal to the discharging high-frequency power source 41 based on the processing conditions, and applies the discharging high-frequency power from the discharging high-frequency power source 41 to the high-frequency loop antenna 30. The frequency of the discharging high-frequency power is controlled to 13.56 MHz, for example.

In the etching process of the upper electrode film Eu and the lower electrode film Eb, the control unit 60 uses the halogen-based gas alone or the mixed gas of the halogen-based gas and the inert gas according to the processing conditions. A flow rate control signal for supplying a flow rate suitable for the metal material of the electrode film Eb is supplied to the halogen-based gas supply unit 50 or to the halogen-based gas supply unit 50 and the inert gas supply unit 51. In this way, in the etching process of the upper electrode film Eu and the lower electrode film Eb, the gas at the optimum flow rate is supplied from the halogen-based gas supply unit 50 or from the halogen-based gas supply unit 50 and the inert gas supply unit 51. In the etching process of the intermediate layer electrode film Em, the controller 60 uses oxygen gas alone, a mixed gas of oxygen gas and halogen-based gas, or a mixed gas of oxygen gas, halogen-based gas, and inert gas. Depending on the processing conditions, a flow rate control signal for supplying a flow rate suitable for the metal material of the intermediate layer electrode film Em is supplied to the oxygen gas supply unit 52, or to the oxygen gas supply unit 52 and the halogen-based gas supply unit 50, or The oxygen gas supply unit 52, the halogen-based gas supply unit 50, and the inert gas supply unit 51 are supplied. Thus, in the etching process of the intermediate layer electrode film Em, the oxygen gas supply unit 52, the oxygen gas supply unit 52 and the halogen-based gas supply unit 50, or alternatively, the oxygen gas supply unit 52, the halogen-based gas supply unit 50, and A gas having an optimum flow rate is supplied from the inert gas supply unit 51.

The controller 60 adjusts the capacitance of the variable capacitor 42 to an optimum value within the range of 10 pF to 100 pF, and the reaction product during etching adheres to the inner surface of the quartz plate 12 in a film form. Suppress. In addition, if it is the structure which expresses such a function, this variable capacitor 42 can also be changed into a variable choke.

Under the control of the control unit 60, the plasma etching apparatus 10 first supplies an etching gas to the plasma generation space 11a according to various etching processing conditions, and then supplies a high frequency power for discharge according to the above conditions to the high frequency loop. A high frequency magnetic field corresponding to the high frequency power is applied to the antenna 30 to form the plasma generation space 11a. The induction electric field generated by the high frequency magnetic field turns the etching gas supplied to the plasma generation space 11a into plasma. Thereafter, when the high-frequency power source for bias 21 applies high-frequency power to the processing substrate S, a bias voltage corresponding to the high-frequency power is applied to the processing substrate S, so-called active species in plasma formed in the plasma generation space 11a, so-called A predetermined region of each layer of the lower electrode E is etched in the thickness direction of the processing substrate S by the etchant.

Next, etching of the lower electrode E (FIGS. 2 and 3) will be described in detail with reference to FIG. FIG. 4 shows only a single element region C on the processing substrate S as a representative.
First, the processing substrate S is carried into the plasma generation space 11 a of the plasma etching apparatus 10 from a carry-out / unload port (not shown) and placed on the substrate stage 13. The temperature of the chamber main body 11 is maintained at 100 ° C. to 150 ° C. by the chamber temperature adjusting mechanism 11b. The temperature of the substrate stage 13 is maintained at 20 ° C. to 100 ° C., for example, 20 ° C. by the stage temperature adjusting mechanism 22. The chamber body 11 and the substrate stage 13 are maintained at the above temperatures from the start to the end of the etching process of the lower electrode E.

Next, one or more halogen-based gases are supplied from the halogen-based gas supply unit 50 to the plasma generation space 11a, and one or more inert gases are supplied from the inert gas supply unit 51 to the plasma generation space 11a. Is done. Each flow rate of the halogen-based gas and the inert gas is adjusted to 2 sccm to 100 sccm. Thereafter, the internal pressure of the plasma generation space 11a is adjusted to 0.1 Pa to 10 Pa.

Then, for example, 800 W of power is applied to the high-frequency loop antenna 30 from the discharge high-frequency power source 41. Thereby, plasma derived from the halogen-based gas is induced in the plasma generation space 11a.

Thereafter, a bias power is applied to the processing substrate S placed on the substrate stage 13 by applying, for example, 50 W of power from the bias high-frequency power source 21 to the substrate stage 13. As described above, when the bias power is applied to the processing substrate S, as shown in FIG. 4A, the halogen-based gas GA containing ionized ions, dissociated active species, or molecules is moved to the processing substrate S side. The surface region that is drawn and is not covered with the resist PR in the upper electrode film Eu of the lower electrode E is etched. The metal constituting the upper electrode film Eu to be etched reacts with the halogen-based gas GA, and the metal halide shown in Table 1 is generated and released into the plasma generation space 11a. For example, when the metal element constituting the upper electrode film Eu is Ta and the halogen-based gas GA is CF ₄ , volatile tantalum pentafluoride ([TaF ₅ ] ₄ ) is generated. For example, when the metal element constituting the upper electrode film Eu is Ti and the halogen gas GA is CF ₄ , volatile titanium trifluoride (TiF ₃ ) or titanium tetrafluoride (TiF) ₄ ) is generated.

Since these metal halides are more volatile than the corresponding metal single substance, they are difficult to adhere to the processing substrate S. In the etching process of the upper electrode film Eu, the resist PR covering the magnetic tunnel junction element MTJ is also slightly etched. However, the etching selectivity of the metal material of the upper electrode film Eu with respect to the resist PR is as high as 2.5. Therefore, reactive ion etching reduces the etching amount of the resist PR with respect to the etching amount of the upper electrode film Eu, compared with a method such as ion milling that shows almost the same etching selectivity regardless of the material. Can do. That is, the reactive ion etching can maintain the state in which the magnetic tunnel junction element MTJ is covered with the resist PR, and reliably suppress the etching of the magnetic tunnel junction element MTJ. The inert gas is supplied to the plasma generation space 11a at the same time as the halogen-based gas GA mainly for the purpose of adjusting the pressure in the plasma generation space 11a and for stabilizing the plasma generated in the plasma generation space 11a. ing.

When the etching process is performed under the above conditions, the etching rate of the upper electrode film Eu is about 5 nm / sec to about 15 nm / sec. If the thickness of the upper electrode film Eu is, for example, 30 nm and the etching rate is 5 nm / sec, it can be estimated that the etching of the upper electrode film Eu is completed in 6 seconds. In this embodiment mode, the etching amount of each layer is controlled by the etching time. In the etching process of the upper electrode film Eu, a longer time obtained by adding a time margin (also referred to as overetching time) to the estimated etching completion time obtained by the above division is set as the etching time of the upper electrode film Eu. For example, when the estimated etching completion time obtained by dividing the film thickness by the etching rate is 6 seconds, the etching time of the upper electrode film Eu is set to 7 seconds, which is longer than the estimated etching completion time. The time margin is determined in advance by experiments or the like so that a portion of the upper electrode film Eu does not remain after etching due to the etching rate, film thickness non-uniformity, error, etc. in the processing substrate S surface. That is, the etching time of the upper electrode film Eu is determined so as to over-etch the upper electrode film Eu. When this etching time has elapsed, the etching of the upper electrode film Eu is completed.

Next, oxygen gas is supplied from the oxygen gas supply unit 52 to the plasma generation space 11a. The flow rate of this oxygen gas is adjusted to 2 sccm to 100 sccm, similar to the halogen-based gas GA and the inert gas. At this time, the supply of the inert gas to the plasma generation space 11a may be stopped. Thereafter, the internal pressure of the plasma generation space 11a is adjusted to 0.1 Pa to 10 Pa.

Since application of electric power to the high-frequency loop antenna 30 and the processing substrate S is continued under the same conditions as in the etching process of the upper electrode film Eu, at least oxygen gas and halogen-based gas are supplied to the plasma generation space 11a. Then, as shown in FIG. 4B, the oxygen gas GB and the halogen-based gas GA are drawn into the processing substrate S side, and are covered with the upper electrode film Eu and the resist PR in the intermediate layer electrode film Em. Unexposed surface areas are etched. During this etching, the oxygen gas GB and the halogen-based gas GA react with the metal material constituting the intermediate layer electrode film Em, and as shown in Table 2, the metal element and the halogen-based gas constituting the intermediate layer electrode film Em. Alternatively, a compound based on oxygen gas is generated. For example, when the metal element constituting the intermediate layer electrode film Em is Ru and the halogen-based gas is CF ₄ , volatile ruthenium trifluoride (RuF ₃ ) or ruthenium hexafluoride (RuF). ₆ ) Furthermore, ruthenium dioxide (RuO ₂ ) and ruthenium tetroxide (RuO ₄ ) are generated in the plasma generation space 11a. In addition, for example, when the metal element constituting the intermediate layer electrode film Em is Cr and the halogen-based gas is CF ₄ , volatile chromium difluoride (CrF ₂ ) or chromium pentafluoride ( CrF ₅ ) and further chromium trioxide (CrO ₃ ) are generated in the plasma generation space 11a.

As shown in Table 2, by etching the intermediate layer electrode film Em with the oxygen gas GB and the halogen-based gas GA, various metal halides and metal oxides are generated and released into the plasma generation space 11a. However, since these metal halides and metal oxides are more volatile than the corresponding single metal, they are difficult to adhere to the processing substrate S.

Here, since the resist PR covering the magnetic tunnel junction element MTJ is an organic substance, the resist PR can be etched by reacting with an oxygen gas supplied as an etching gas during the etching process of the intermediate layer electrode film Em. The inventors of the present application measured the pressure dependency of the rate at which the resist PR is etched and the pressure dependency of the rate at which the intermediate layer electrode film Em is etched. If the pressure range is 0.1 Pa to 10 Pa, It has been found that the etching rate of the intermediate layer electrode film Em is higher than the etching rate of the resist PR regardless of the constituent material of the intermediate layer electrode film Em and the constituent material of the resist PR. Therefore, in this etching process of the intermediate layer electrode film Em, by adjusting the internal pressure of the plasma generation space 11a to 0.1 Pa to 10 Pa, the etching selection ratio of the intermediate layer electrode film Em to the resist PR is further increased, and the resist PR Minimize removal.

Further, since the halogen-based gas GA having an etching selection ratio with respect to the resist PR larger than that of the oxygen gas GB is used as the etching gas for the intermediate layer electrode film Em, the resist PR with respect to the etching amount of the intermediate layer electrode film Em is used. The amount of etching can be further reduced, and consequently the influence on the magnetic tunnel junction element MTJ can be suppressed. However, both ruthenium and chromium have the same etching rate when the oxygen gas GB is used than the etching rate when the halogen-based gas GA is used when the conditions other than the etching gas are the same. Is double. Therefore, the etching gas in the etching process of the intermediate layer electrode film Em is a mixed gas of the halogen-based gas GA and the oxygen gas GB rather than the halogen-based gas GA alone in order to suppress the lengthening of the etching time. It is preferable.

Further, when the etching process of the intermediate layer electrode film Em is performed under the above conditions, the etching rate is about 1 nm / sec to 5 nm / sec. If the thickness of the intermediate layer electrode film Em is, for example, 10 nm and the etching rate is 2 nm / sec, it can be estimated that the etching of the intermediate layer electrode film Em is completed in 5 seconds. Similar to the etching process for the upper electrode film Eu, the etching amount of the intermediate electrode film Em is controlled by the etching time. However, the etching time of the intermediate layer electrode film Em is set to the same time as the estimated etching completion time described above. For example, when the estimated etching completion time obtained by dividing the film thickness by the etching rate is 5 seconds, this estimated etching completion time is set as the etching time of the intermediate layer electrode film Em. That is, no time margin is added to the estimated etching completion time. Therefore, when the etching time of the intermediate layer electrode film Em has elapsed, a part or all of the lower layer electrode film Eb is exposed, and the intermediate layer electrode film Em may partially remain on the processing substrate S. Thus, the amount of etching of the resist PR by oxygen gas is reduced as much as possible.

Thus, when the etching process time of the intermediate electrode film Em elapses, the lower electrode film Eb is etched under the same conditions as in the etching process of the upper electrode film Eu. That is, the halogen-based gas GA from the halogen-based gas supply unit 50 and the inert gas from the inert gas supply unit 51 are supplied to the plasma generation space 11a. Thereby, as in the etching process for the upper electrode film, the halogen-based gas GA is drawn into the processing substrate S side, whereby the lower electrode film Eb is etched as shown in FIG. By this etching, a volatile metal halide shown in Table 1 is generated, and the metal halide is released into the plasma generation space 11a.

When switching from the etching process for the intermediate layer electrode film Em to the etching process for the lower layer electrode film Eb, plasma generation is performed as in the case of switching from the etching process for the upper layer electrode film Eu to the etching process for the intermediate layer electrode film Em. It is only necessary to change the gas type supplied to the space 11a and its internal pressure. However, if the oxygen gas used as the etching gas during the etching of the intermediate layer electrode film Em remains even during the etching of the lower layer electrode film Eb, the oxygen drawn into the processing substrate S side and the metal of the lower layer electrode film Eb Reacts to produce a metal oxide.

The volatility of these metal oxides is higher than the volatility of the corresponding metal, but lower than the volatility of metal halides. Therefore, the metal oxide may adhere to the processing substrate S, and may remain on the processing substrate S as a so-called etching residue after a series of etching processes on the lower electrode E is completed. If this residue remains as an impurity in the completed MRAM, the function of the MRAM may be impaired.

Therefore, in order to suppress such a metal oxide residue, when switching from the etching process for the intermediate layer electrode film Em to the etching process for the lower layer electrode film Eb, from the time of the etching time of the intermediate layer electrode film Em, Until the oxygen gas used as the etching gas during the etching process is completely exhausted from the plasma generation space 11a, the supply of power to the processing substrate S is stopped, and further, the supply of power to the high-frequency loop antenna 30 is stopped. You may do it. That is, the supply of the high frequency power from the bias high frequency power supply 21 to the substrate stage 13 may be stopped, and the supply of the high frequency power from the discharge high frequency power supply 41 to the high frequency loop antenna 30 may be stopped. Thereby, it is possible to suppress the lower electrode film Eb from being oxidized by the oxygen gas and to suppress the generation of the residue.

When the etching process of the lower electrode film Eb is performed under the same conditions as the etching process for the upper electrode film Eu, the etching rate and the etched thickness are equal between the upper electrode film Eu and the lower electrode film Eb. . Therefore, originally, if the film thickness of the lower electrode film Eb is 30 nm and the etching rate is 10 nm / sec, for example, the etching time of the lower electrode film Eb is similar to the etching process of the upper electrode film Eu. If the estimated etching completion time is set to 4 seconds obtained by adding a time margin (overetching time), the lower electrode film Eb should also be etched completely. However, as described above, at the start of the etching process for the lower electrode film Eb, there is a possibility that the unetched intermediate electrode film Em remains on the lower electrode film Eb. Moreover, for the ruthenium or chromium of the intermediate layer electrode film Em, the etching rate for the halogen-based gas GA used as the etching gas for the lower layer electrode film Eb is about 10% (2 nm / sec × 0.10) of the etching rate for the oxygen gas. And very small. Therefore, even if the thickness of the remaining intermediate layer electrode film Em is only about 10% of the initial thickness (for example, 3 nm), the remaining intermediate layer electrode film Em is completely removed by the halogen-based gas GA. It takes about 15 seconds to complete. Therefore, the etching time of the etching process for the lower electrode film Eb is set to 20 seconds, which is five times the etching time of the upper electrode film Eu. Thereby, even if the intermediate layer electrode film Em is not completely etched, the etching of the lower layer electrode film Eb including the remaining intermediate layer electrode film Em can be completed.

Thus, the upper layer electrode film Eu, the intermediate layer electrode film Em, and the lower layer electrode film Eb are each etched by the reactive ion etching process, thereby covering the magnetic tunnel junction element MTJ as shown in FIG. The lower electrode E can be processed into a desired shape without accompanying residues resulting from etching on the resist PR.

Thus, the three-layer metal film (upper electrode film Eu, intermediate electrode film Em, lower electrode film Eb) of the lower electrode E is etched by so-called reactive dry etching. The metal constituting these metal films reacts with the corresponding etching gas to generate a volatile metal compound. Any of the metal compounds thus produced has a higher volatility than a single metal constituting the metal film, or oxides or nitrides thereof, and therefore hardly adheres to the metal film or the processing substrate S. That is, the residue resulting from the etching of the lower electrode E can be suppressed.

As described above, according to the laminated electrode processing method of the present embodiment, the effects listed below can be obtained.
(1) During the etching process of the lower electrode E made of a three-layer metal film, the upper electrode film Eu, the intermediate electrode film Em, and the lower electrode film Eb were used with various gases having reactivity with these metal films. Etching is performed by dry etching, so-called reactive dry etching. Thereby, even when any of these upper layer electrode film Eu, intermediate layer electrode film Em, and lower layer electrode film Eb is etched, the reaction between the various gases and the metal constituting these metal films proceeds, and these Is produced. Any of the metal compounds generated in this manner has higher volatility than the simple substance of the metal constituting the metal film, or its oxide or nitride itself, so that it may adhere to the metal film or the processing substrate S. Becomes lower. That is, the residue resulting from the etching of the lower electrode E can be suppressed.

(2) During the etching process for the intermediate layer electrode film Em, the internal pressure of the plasma generation space 11a was set to 0.1 to 10 Pa. Thereby, the etching selectivity of the intermediate layer electrode film Em with respect to the resist PR can be further increased.

(3) When performing the etching process of the intermediate layer electrode film Em, a mixed gas of the halogen-based gas GA and the oxygen gas GB is used as an etching gas. Thereby, prolonged etching time can be suppressed.

(4) At the time of switching from the etching process for the intermediate layer electrode film Em to the etching process for the lower layer electrode film Eb, the oxygen gas used as the etching gas during the etching process is changed from the time when the etching time of the intermediate layer electrode film Em has elapsed. The supply of power to the processing substrate S was stopped until the generation space 11a was completely exhausted. As a result, it is possible to suppress the lower electrode film Eb from being oxidized by the oxygen gas, and consequently to suppress the adhesion of the metal oxide to the processing substrate S, in other words, the generation of etching residues.

(5) The etching time for the intermediate layer electrode film Em is set as a time obtained by dividing the film thickness of the intermediate layer electrode film Em by the etching rate, and the etching time for the upper layer electrode film Eu is set as the etching time for the lower layer electrode film Eb. 10 times was set. Thereby, the etching of the lower layer electrode film Eb including the remaining intermediate layer electrode film Em can be completed from the state in which a part of the intermediate layer electrode film Em remains on the lower layer electrode film Eb layer. Therefore, it is possible to reduce the time during which the resist PR is exposed to oxygen gas, as compared with an aspect in which all of the intermediate layer electrode film Em to be etched is removed by the etching for the intermediate layer electrode film Em. . Therefore, it becomes possible to suppress the shape defect of the laminated electrode after etching while suppressing the shape defect of the resist PR.

In addition, the said embodiment can also be suitably changed and implemented as follows.
The plasma etching apparatus 10 may not include the permanent magnet 31 and the planar electrode 32. The plasma etching apparatus 10 may be configured such that the high-frequency loop antenna 30 is wound around the side wall of the chamber body 11 and the permanent magnet 31 is provided outside the high-frequency loop antenna 30. Even in such a plasma etching apparatus, a permanent magnet may not be provided.

The above various temperatures, more precisely, the temperature of the processing substrate S during the etching process, the temperature of the chamber body 11, the high frequency power applied to the high frequency loop antenna 30 during the etching process, and the high frequency power applied to the processing substrate S are: Not limited to the above range, it is appropriately selected according to the thermal and electrical resistance of various elements constituting the processing substrate S.

-Even if the etching selectivity of the upper electrode film Eu and the lower electrode film Eb with respect to the resist PR and the etching selectivity of the intermediate layer electrode film Em with respect to the resist PR are small, the film thickness of the resist PR is sufficiently thick to compensate for this. The processed substrate S may be configured such that the pressures of various gases such as a halogen-based gas, an inert gas, and an oxygen gas are set in a range different from the above range.

The two metal films of the upper electrode film Eu and the lower electrode film Eb constituting the lower electrode E are formed to have the same thickness, and the intermediate electrode film Em is thinner than these two layers. To have. However, the upper layer electrode film Eu, the lower layer electrode film Eb, and the intermediate layer electrode film Em may have the same film thickness.

At the time of switching from the etching process for the intermediate layer electrode film Em to the etching process for the lower layer electrode film Eb, the oxygen gas used as the etching gas during the etching process is changed from the time when the etching time of the intermediate layer electrode film Em has elapsed. The supply of power to the processing substrate S is stopped until the exhaust from 11a is completed, and further, the supply of power to the high-frequency loop antenna 30 is stopped. Not limited to this, the gas type supplied to the plasma generation space 11a and its internal pressure may only be changed in the same manner as when switching from the etching process for the upper electrode film Eu to the etching process for the intermediate electrode film Em. .

・ Each of the three layers of metal film of the lower electrode E was etched in a single vacuum chamber. However, the etching is not limited to this, and the etching of the upper electrode film Eu and the lower electrode film Eb and the etching of the intermediate electrode film Em may be performed in separate vacuum chambers. In this case, the plasma etching apparatus 10 includes two vacuum chambers, that is, a vacuum chamber in which the etching process for the upper electrode film Eu and the lower electrode film Eb is performed, and a vacuum chamber in which the etching process for the intermediate layer electrode film Em is performed. It is good also as an apparatus provided with what is called a multi-chamber apparatus. Further, by using two apparatuses having a single vacuum chamber, such as the plasma etching apparatus 10, the etching process for the upper electrode film Eu and the lower electrode film Eb and the etching process for the intermediate electrode film Em are separated. You may make it implement in a vacuum chamber.

In the etching process of the intermediate layer electrode film Em, the etching selection ratio of the intermediate layer electrode film Em to the resist PR can be made sufficiently high, or the thickness of the resist PR can be set even if the resist PR is etched. In the case where it is possible to increase the thickness so as not to affect the magnetic tunnel junction element MTJ covered thereby, the etching rate of the intermediate electrode film Em and its layer are the same as in the etching of the upper electrode film Eu. You may make it set as etching time more than the estimated etching completion time computed from thickness. As a result, when the lower layer electrode film Eb is etched, the upper layer intermediate layer electrode film Em is surely etched. Therefore, the etching time of the lower layer electrode film Eb is set equal to the etching time of the upper layer electrode film. Will be able to.

・ So-called organic resist PR made of organic material was used. Not limited to this, a so-called inorganic resist made of an inorganic material may be used. This makes the resist difficult to be etched by oxygen gas, so the etching time of the intermediate layer electrode film Em is set to a time longer than the estimated etching completion time calculated from the etching rate and the layer thickness. It is possible to ensure that the film Em is etched.

· The lower electrode E has a structure in which a magnetic tunnel junction element MTJ which is a magnetoresistive element using a tunnel magnetoresistive effect is connected. The structure is not limited to this, and a magnetoresistive element that does not use the magnetoresistive effect may be connected to the lower electrode E.

The method of the reactive ion etching process is not limited to the processing of the lower electrode of the MRAM, but may be used for processing of other stacked electrodes having the same configuration as the lower electrode E.

Claims

A lower electrode film made of any one of a metal selected from the group consisting of Ta, Ti, Mo, Ga, and W, an oxide of the metal, and a nitride of the metal, and a group made of Ru and Cr A laminated electrode formed by laminating any one of the selected intermediate layer electrode film and the upper layer electrode film made of the same constituent material as the lower layer electrode film in this order was formed on the upper layer electrode film. A method of processing a laminated electrode in which each electrode film is processed in order from the upper electrode film by reactive ion etching using a resist as a mask,
In the step of etching the upper electrode film and the step of etching the lower electrode film, CF 4 , C 2 F 6 , C 3 F 6 , C 3 F 8 , C 4 F 6 , C 4 F 8 , C 5 are used. At least one halogen-based gas selected from the group consisting of F 8 , Cl 2 , BCl 3 , SiCl 4 , HBr, HI, and at least one inert gas selected from the group consisting of N 2 , Ne, Ar, Xe Any one of a mixed gas of a gas and the halogen-based gas is used as an etching gas,
A method for processing a laminated electrode, wherein in the step of etching the intermediate layer electrode film, a gas containing at least an oxygen gas is used as an etching gas.
In the processing method of the laminated electrode of Claim 1,
The intermediate electrode film is made of Ru;
In the step of etching the intermediate layer electrode film, oxygen gas, CF 4 , C 2 F 6 , C 3 F 6 , C 3 F 8 , C 4 F 6 , C 4 F 8 , C 5 F 8 , Cl 2 are used. , BCl 3 , SiCl 4 , or a mixed gas of at least one halogen-based gas selected from the group consisting of HBr, and an oxygen gas, the halogen-based gas, and a group consisting of N 2 , Ne, Ar, and Xe A method for processing a laminated electrode, wherein any one of a mixed gas with at least one inert gas is used as an etching gas.
In the processing method of the laminated electrode of Claim 1,
The intermediate layer electrode film is made of Cr,
In the step of etching the intermediate layer electrode film, oxygen gas, CF 4 , C 2 F 6 , C 3 F 6 , C 3 F 8 , C 4 F 6 , C 4 F 8 , C 5 F 8 , Cl 2 are used. , BCl 3 , SiCl 4 and at least one gas selected from the group consisting of oxygen gas, the halogen gas, N 2 , Ne, Ar, and Xe. A method for processing a laminated electrode, wherein any one of a mixed gas with two inert gases is used as an etching gas.
In the processing method of the laminated electrode according to any one of claims 1 to 3,
The step of etching the intermediate layer electrode film ends when a part of the lower layer electrode film is exposed,
The step of etching the lower layer electrode film comprises etching the lower layer electrode film together with a part of the intermediate layer electrode film remaining on the lower layer electrode film.
In the processing method of the laminated electrode according to any one of claims 1 to 4,
A method of processing a laminated electrode, wherein the step of etching the intermediate layer electrode film is performed at a pressure of 0.1 Pa or more and 10 Pa or less.
In the processing method of the laminated electrode according to any one of claims 1 to 5,
The resist covers the entire magnetoresistive element formed on the upper electrode film,
The method for processing a laminated electrode, wherein the laminated electrode is a lower electrode of the magnetoresistive element.
In the processing method of the laminated electrode of Claim 1,
In each step of etching the upper electrode film and etching the lower electrode film, supply of oxygen gas is stopped and CF 4 , C 2 F 6 , C 3 F 6 , C 3 F 8 , C 4 are stopped. Supplying at least one halogen-based gas selected from the group consisting of F 6 , C 4 F 8 , C 5 F 8 , Cl 2 , BCl 3 , SiCl 4 , HBr, HI to the chamber;
The method of processing a laminated electrode, wherein the step of etching the intermediate layer electrode film includes supplying at least oxygen gas to the chamber.
In the processing method of the laminated electrode of Claim 7,
Each of the process of etching the upper electrode film and the process of etching the lower electrode film supplies at least one inert gas selected from the group consisting of N 2 , Ne, Ar, and Xe to the chamber. The processing method of the laminated electrode further including this.
In the processing method of the laminated electrode of Claim 7,
The method for processing a laminated electrode, wherein the etching conditions of the step of etching the upper electrode film and the step of etching the lower electrode film are the same except for the etching time.
In the processing method of the laminated electrode according to claim 9,
The step of etching the upper electrode film is performed for an etching time obtained by adding a time margin to an estimated etching completion time obtained by dividing the thickness of the upper electrode film by the etching rate of the upper electrode film,
The step of etching the intermediate electrode film is performed for the same etching time as the estimated etching completion time obtained by dividing the thickness of the intermediate electrode film by the etching rate of the intermediate electrode film,
The step of etching the lower electrode film is a method for processing a laminated electrode, which is performed for a time longer than an etching time of the upper electrode film.