JP4364669B2 - Dry etching method - Google Patents

Description

  The present invention relates to a dry etching method, and more particularly to etching a conductive member containing a transition metal element as a main constituent element or a non-conductive member such as an oxide containing a transition metal as a main constituent element without generating an etching residue. The present invention relates to a dry etching method characterized by a structure for selectively removing without causing damage.

  In recent years, non-volatile solid-state magnetic memory (MRAM) and the like have been demanded to have a large capacity and high density, and microfabrication technology has become important for the production of such a large capacity and highly integrated memory device. ing.

  The basic structure of the MRAM is a three-layer structure of a ferromagnetic layer / nonmagnetic layer / ferromagnetic layer. This magnetic material is made of a transition metal element such as Fe, Ni, Co or an alloy of them, permalloy ( Fe-Ni alloy), Ni-Fe-Co alloy, Co-Cr alloy, Co-Pt alloy, Co-Ni-Cr alloy, Co-Ni-Pt alloy, Co-Fe alloy, and the like are used.

  In order to prevent the spin states of the two ferromagnetic layers in the three-layer structure constituting the MRAM described above from being fixed and difficult to reverse, one of the ferromagnetic layers includes an Fe—Mn alloy, an Ir—Mn alloy, Pt An antiferromagnetic material such as a -Mn alloy, a Ni-Mn alloy, or a Ru-Mn alloy is provided, and Ru or the like is used as an intermediate nonmagnetic layer.

  On the other hand, in a semiconductor device, the gate through current flowing due to the gate insulating film having a thickness of about 1 nm as a result of miniaturization has become a big problem for power consumption. A high dielectric constant (High-k) film is used as a gate insulating film.

Such a high dielectric constant film contains transition metals such as hafnia (HfO ₂ ), alumina (Al ₂ O ₃ ), zirconia (ZrO ₂ ), silicates (HfSiO), and nitrogen additives (HfSiON). An insulating member is used.

Furthermore, the gate electrode formed on the gate insulating film is not polysilicon but a conductive member containing a transition metal such as W 2, Ta, Ti, silicide (NiSi, CoSi ₂ ) or the like is used.

  In addition, copper is used for interconnect wiring in semiconductor integrated circuit devices and the like, and in order to prevent copper diffusion (migration), a barrier film such as Ta, CoW or the like is formed around the copper interconnect wiring layer. A conductive member containing a transition metal is provided.

  There is a wet etching method using an acid or alkaline solution as a method for fine processing by etching these materials. However, in the wet etching method, the dissolution of the workpiece proceeds isotropically, so that the degree of integration is increased. It is difficult to transfer a pattern to form a fine shape with a high aspect shape.

For this reason, technology for pattern transfer by forming a vertical shape with directionality has become necessary. For such pattern transfer technology, halogen (such as chlorine) system cultivated in the manufacture of semiconductor elements such as silicon There is a reactive ion etching technique using this gas.
In this case, since the reaction product of the transition metal and the halogen cannot be said to have a high vapor pressure at room temperature, a method of etching at a high substrate temperature is known.

  However, when plasma etching is performed using a gas containing halogen, there is a problem of after-corrosion in which halide remains on the surface and the metal material is corroded by moisture absorption due to subsequent exposure to the atmosphere.

  In order to avoid such after-corrosion problems, when a member containing a difficult-to-etch material such as a transition metal is finely processed, it is called an ion milling method or a bias sputter etching method with enhanced physical etching action. Processing techniques have been used.

Among them, in the case of the conventional ion milling method using rare gas ions such as Ar, in order to avoid the fact that deposits are deposited on the vertically processed side wall and the vertical shape cannot be processed. Therefore, it is necessary to use a technique of irradiating ions at an angle of 45 °.
However, still, a short circuit or by the side wall deposits, there is a problem that physical damage to the material by ion bombardment occurs, the point at which the vertical processing is said to be difficult not solved.

On the other hand, with respect to the physical method described above, a carbonyl compound of transition metal (M) using carbon monoxide (CO) for the purpose of chemically and selectively processing a difficult-to-etch material without using halogen. There is known a method of removing volatilization from the surface, that is, dry etching, by forming _x (CO) _y ].

For example, plasma etching using carbon monoxide plasma has been attempted. In this case, carbon monoxide is decomposed into C atom ions and carbon dioxide (CO ₂ ) by a nonuniform reaction in the plasma gas phase. As a result, a problem has been pointed out that the amount of CO in the gas phase becomes small and carbonyl compounds are hardly formed.

Therefore, as a solution, a method of efficiently forming a carbonyl compound by suppressing a decrease in CO in the gas phase by adding a gas of a nitrogen-containing compound such as NH ₃ has been proposed (for example, Patent Documents). 1).

Further, in such plasma etching, since the etching rate is proportional to the plasma density, it has been proposed that a plasma density of 1 × 10 ¹¹ / cm ³ or more is required at a substrate temperature of 150 ° C. (for example, Patent Documents). 2).

However, when permalloy (NiFe) is processed by CO and NH ₃ plasma etching, carbonyl compound plasma etching reduces damage and sidewall deposits, but reports that sufficient magnetic properties cannot be obtained. (For example, refer nonpatent literature 1).

  This is also true for physical sputtering. If the sputtering component becomes strong in addition to damage, the reaction product accumulates on the side wall and the processed shape cannot be transferred vertically, or the side wall is shorted. It is.

  In addition, in the case of plasma etching using CO, handling of CO gas is troublesome because it is a toxic / combustible gas, and in this respect, the method of generating vapor from a low-molecular carboxylic acid liquid has the advantage of being easy to handle. is there.

  Therefore, there has been proposed a plasma etching method in which a carbonyl compound is formed and volatilized and removed using a gas of a compound having a carboxyl group (—COOH) such as acetylacetone, cellosolve acetate, malonic acid, 2,4-dimethylmenthaic acid. (For example, refer to Patent Document 3).

Alternatively, it has been proposed to etch a metal material in an oxidizing atmosphere using a halogen-containing diketone (see, for example, Patent Document 4).
Japanese Patent Laid-Open No. 08-253881 JP 2000-322710 A Japanese Patent Laid-Open No. 09-205078 Japanese Patent Laid-Open No. 07-093289 S. D. Kim, et al. , IEEE Trans. Magnetics, vol. 35, p. 3397, 1999

  However, as long as plasma is used, even if the gas of the compound having a carboxyl group is used, it is decomposed into CO and the surface of the workpiece is also exposed to the plasma, thereby damaging the workpiece material. This problem is also true for β-diketone compounds.

  Further, when a halogen-containing diketone is used, since halogen is contained in the plasma etching atmosphere, the above-described halogen after-corrosion becomes a problem.

  Therefore, an object of the present invention is to suppress physical damage as compared with a physical etching method when a hard-to-etch material containing a transition metal as a main constituent element is finely processed.

FIG. 1 is a diagram illustrating the basic configuration of the present invention. Means for solving the problems in the present invention will be described with reference to FIG.
Reference numeral 2 in the figure is a mask.
See FIG. 1 In order to solve the above-mentioned problem, in the dry etching method of the present invention, the etching target material 1 containing a transition metal element is exposed to a gaseous substance 4 having at least one carboxyl group, and at least the etching target material 1 is formed. A step of converting the exposed surface into the carboxylate 5 and a step of volatilizing and removing the converted carboxylate 5 by irradiating the exposed surface of the material 1 to be etched with oxygen ions at an acceleration energy of 500 eV or less. Features.

As a result of the inventors' diligent research, as for etching of transition metals or their oxides, a compound having a carboxyl group (—COOH) (carboxylic acid) is used to once form diketonate on the surface of the material 1 to be etched. It has been found that it is effective to volatilize and remove the carboxylate 5 such as carboxylate by forming the carboxylate 5 and heating the carboxylate 5 by irradiation with an energy beam 6.
In particular, by irradiating oxygen ions with an acceleration energy of 500 eV or less, which is lower than the acceleration energy in a normal ion milling process or sputter etching process, the oxidation process of the surface of the material to be etched 1 is performed during the evaporation removal process of the carboxylate 5. It can be carried out.

  In this case, since a simple organic acid that is liquid at normal pressure is vaporized from the liquid and used, it is superior in storage and handling compared to CO, and is a gaseous substance 4 having at least one carboxyl group in a non-plasma state. Because of exposure to plasma, no plasma damage occurs.

  Note that “including a transition metal element” means a degree that is always described when the composition of the material to be etched 1 is expressed, and does not mean a case where the composition is included as an impurity or a trace additive.

In this case, it is desirable to oxidize at least the exposed surface of the material to be etched 1 before the material to be etched 1 is exposed to the gaseous substance 4 having at least one carboxyl group. Etching rate is increased because of easy conversion to
In addition, such an oxidation process includes oxidation accompanying a cleaning process or the like that does not mainly perform oxidation.

The material 1 to be etched containing a transition metal element is typically either a transition metal material itself, an alloy material containing a transition metal as a main constituent element, or an oxide material containing a transition metal as a main constituent element. Is.
However, application to oxynitride materials or nitride materials containing transition metals as main constituent elements is not precluded.

  As the gas having at least one carboxyl group, formic acid, acetic acid, propionic acid, n-butyric acid, n-valeric acid, 2-ethylhexanoic acid, or acetylacetone is suitable.

  Alternatively, as the gas having at least one carboxyl group, either fluoroacetic acid, difluoroacetic acid, or trifluoroacetic acid may be used.

  Further, the above-described method for removing the material to be etched 1 may be used for the side wall deposit removal process accompanying physical etching. In this case, the main portion is etched by high-speed physical etching. After that, the removal of the deposit on the side wall, which is smaller than the etching amount, is performed by dry etching with little damage, so that the fine vertical processing without the deposit on the side wall can be performed in a short time.

In the present invention, the first step of forming an organic acid salt (diketonate or carboxylate) on the surface of the workpiece, and the organic acid salt formed in the first step are combined with oxygen ions having an acceleration energy of 500 eV or less . Since it is composed of a second step that volatilizes and removes by irradiation, a hard-to-etch material containing a transition metal element as a main constituent element is finely processed without causing physical damage, after-corrosion, and side wall deposits. It becomes possible.

The present invention relates to an organic acid such as acetic acid (CH ₃ COOH) in which a thin film laminated material containing a transition metal such as Co formed on a substrate is introduced into a reaction furnace through a mask formed on the laminated material. exposed to steam, organic acid salt in the stacked material surface (diketonate or carboxylate) a first step of forming, the organic acid salt formed in the first step, the following acceleration energy 500eV oxygen ions The first step and the second step are repeated at least once until the etching depth reaches the target.

Here, the dry etching method according to the first embodiment of the present invention will be described with reference to FIGS. 2 to 4. First, the dry etching apparatus used in the first embodiment of the present invention will be described with reference to FIG. .
FIG. 2 is a cross-sectional view showing a conceptual configuration of the dry etching apparatus used in Embodiment 1 of the present invention, which includes a discharge chamber 10 for generating plasma 15 and a processing chamber 20 for etching a sample 21 to be processed. Composed.

  The discharge chamber 10 is made of quartz, and a discharge gas 12 is introduced from a gas inlet port 11. For example, a high-frequency power source 14 is connected to both ends of a one-turn copper coil 13 having a diameter of 3 mm provided to surround the discharge chamber 10. For example, the plasma 15 is generated by applying a high frequency voltage of 13.56 MHz.

  Further, a silicon conductive material provided with a large number of holes for separating positive and negative ions 16 of the plasma 15 generated in the discharge chamber 10 at the boundary between the discharge chamber 10 and the processing chamber 20. The shielding plate 17 is provided with a negative voltage from a power source 18 to accelerate the positive ions 16.

  On the other hand, a stage 22 having an electrostatic chuck function for holding and placing a sample 21 to be processed and a temperature control means 23 for controlling the temperature of the stage 22 are provided inside the processing chamber 20. An organic vapor gas 26 is introduced into the processing chamber 20 from an organic acid vapor generating means 25 through a gas introduction pipe 24.

Next, a dry etching process according to the first embodiment of the present invention will be described with reference to FIGS. Refer to FIG. 3. First, a sample 21 to be processed in which a CoFe layer 32 having a thickness of, for example, 200 nm is formed on a silicon substrate 31, and a resist pattern 33 is formed on the CoFe layer 32 by a normal photolithography process. .
Note that a natural oxide film 34 having a thickness of, for example, 10 nm or less is formed on the exposed surface of the CoFe layer 32 by a process accompanying removal of the resist residue.

  Next, the sample 21 to be treated is installed in the processing chamber 20 described above, and at room temperature (20 ° C.), acetic acid vapor 35 vaporized at a saturated vapor pressure (1 kPa) from the organic vapor generating means 25 is introduced at a flow rate of 50 sccm, for example. An acetate layer 36 is formed on the exposed surface of the CoFe layer 32.

In this case, the natural oxide film 34 is more easily converted to acetate by reaction with the acetic acid vapor 35, but CoFe itself is also converted to acetate.
Although acetic acid is physically adsorbed on the resist pattern 33, the resist pattern 33 is not eroded, and the processing chamber 20 is exhausted by a vacuum evacuation device, so that acetic acid molecules adsorbed on the resist pattern 33 are exhausted. Will volatilize.

At this time, oxygen gas is introduced into the discharge chamber 10 at a flow rate of, for example, 50 sccm, and high frequency power is applied to generate plasma. However, since the potential of the shielding plate 17 is grounded, O gas in the plasma is generated. ⁺ Ions hardly come out of the shielding plate 17.

Then, following -500V to shield 17, more preferably -100V or less, for example, the O ⁺ ions 37 by repeating intermittently applying a negative voltage for 10 minutes 10 seconds applied -10 seconds ground of -50V The sample 21 is accelerated and introduced into the processing chamber 20 to irradiate the sample 21 to be processed.

On the exposed surface of the sample 21 to be processed, the acetate layer 36 is desorbed by being heated and evaporated by collision with the O ⁺ ions 37, and the acetate layer 36 is removed.
At this time, a new natural oxide film 38 is formed on the surface of the clean CoFe layer 32 from which the acetate layer 36 has been removed by the action of the O ⁺ ions 37.
The etching rate depends on the intermittent time and duty of the voltage applied to the shielding plate 17 and the negative voltage value, but an etching rate of about 5 nm / min can be obtained.

Refer to FIG. 4 After repeating such an acetate layer forming process-evaporation process by O ⁺ ion irradiation according to the film thickness of the CoFe layer 32, finally, the sample 21 to be processed is 80 to 300 ° C., for example, 200 The dry etching process is completed by removing the acetate layer 36 remaining on the side wall of the recess in the etching process by heating to ° C.

That is, the O ⁺ ions 37 are highly linear and anisotropic etching, and the acetate layer 36 formed on the sidewalls of the recesses is not removed. Therefore, the acetate layer formation process—the evaporation process by O ⁺ ion irradiation is performed several cycles. Etching excellent in perpendicularity can be performed without repeating etching in the lateral direction repeatedly.

  As described above, in the first embodiment of the present invention, plasma damage is generated in the first step because plasma is not involved in the first step of exposing the sample 21 to be processed to the acetic acid vapor 35. There is no.

Further, in the step of irradiating the O ⁺ ions 37, since acceleration is performed at an acceleration voltage lower than about several kV that is an acceleration voltage in conventional ion milling, it is possible to suppress the occurrence of damage due to ion irradiation.
That is, it is not necessary energy for etching such as physical etching such as ion milling, but acceleration energy for obtaining a heating temperature necessary for evaporation of acetate is sufficient, so that the voltage is lower.

  In Example 1 of the present invention, by combining the first step and the second step described above, a difficult-to-etch sample made of a transition metal material such as CoFe can be produced without generating side wall deposits, and Fine processing with excellent anisotropy is possible without causing etching damage.

The first embodiment of the present invention has been described above. However, the present invention is not limited to the conditions and configuration described in the first embodiment , and various modifications can be made. For example, the film described in the first embodiment Numerical values such as thickness, voltage, temperature, and time are not limited to the numerical values described.

In Example 1 above, acetic acid is used as the organic acid. However, the organic acid is not limited to acetic acid and may be any organic acid having at least one carboxyl group as in acetic acid. For example, formic acid, acetic acid , Propionic acid, n-butyric acid, n-valeric acid, 2-ethylhexanoic acid, or acetylacetone, or any of fluoroacetic acid, difluoroacetic acid, or trifluoroacetic acid is preferable, and the lower molecular weight Organic acids are preferred.

In addition, although the CoFe dry etching process is described in the first embodiment , the object to be etched is not limited to CoFe, but nickel, iron, cobalt, manganese, chromium, platinum, iridium, hafnium, zirconium, ruthenium. It is also applicable to transition metals such as tantalum and tungsten, or compounds and alloys containing them.

That is, in the first embodiment, the etching process of the ferromagnetic layer used in the MRAM or GMR element is premised. However, the invention is not limited to the ferromagnetic material, and Ta, W, etc. used as the gate electrode of the MOSFET. The present invention can also be applied to a transition metal etching process, or a transition metal etching process such as Ta or CoW used as an interconnection wiring.

Furthermore, the present invention is not limited to metal materials, but can be applied to oxides, nitrides, oxynitrides, and the like thereof.
In particular, hafnia (HfO ₂ ), zirconia (ZrO ₂ ), or HfSiON is used as a gate insulating film of a MOSFET by utilizing a high dielectric constant characteristic. Therefore, the present invention also covers such a gate insulating film etching process. It is what.

In the first embodiment, the etching process for a thin film provided on a substrate such as a silicon substrate is described. However, the present invention is not limited to the etching process for a thin film, but can be applied to an etching process for a bulk material. Is.

In the first embodiment, positive ions are used among the generated ions, but negative ions may be used. In this case, if a positive voltage is applied as an acceleration voltage to the shielding plate. good.

  In the first embodiment, the shielding plate is made of silicon. However, the shielding plate is not limited to silicon, and Ti or graphite may be used.

Further, in the above embodiment 1, although Evaporation removing step of forming step and an organic acid salt of an organic acid salt in the same processing chamber, Ru der those may be carried out each in a separate chamber.

The detailed features of the present invention will be described again with reference to FIG. 1 again.
1 again (Appendix 1) The material 1 to be etched containing a transition metal element is exposed to a gaseous substance 4 having at least one carboxyl group, and at least the exposed surface of the material 1 to be etched is converted into a carboxylate 5. A dry etching method comprising: a step; and a step of volatilizing and removing the converted carboxylate 5 by irradiating the exposed surface of the material 1 to be etched with oxygen ions at an acceleration energy of 500 eV or less .
(Additional remark 2) Before exposing the said to-be-etched material 1 to the gaseous substance 4 which has at least one said carboxyl group, it has the process of oxidizing at least the exposed surface of the said to-be-etched material 1 characterized by the above-mentioned. Dry etching method.
(Additional remark 3 ) The to-be-etched material 1 containing the transition metal element is either a transition metal material, an alloy material containing a transition metal as a main constituent element, or an oxide material containing a transition metal as a main constituent element. The dry etching method according to claim 1 or 2 , wherein:
(Appendix 4 ) The gaseous substance having at least one carboxyl group is composed of any one of formic acid, acetic acid, propionic acid, n-butyric acid, n-valeric acid, 2-ethylhexanoic acid, or acetylacetone. The dry etching method according to any one of appendices 1 to 3 .
(Additional remark 5 ) The gaseous substance 4 which has at least one said carboxyl group consists of either fluoroacetic acid, difluoroacetic acid, or trifluoroacetic acid, The any one of Additional remark 1 thru | or 3 characterized by the above-mentioned. Dry etching method.
(Additional remark 6 ) The dry etching method of any one of additional remarks 1 thru | or 5 whose removal process of the said to-be-etched material 1 is a removal process of the side wall deposit accompanying physical etching.

  An application example of the present invention is an etching process of a ferromagnetic film used in an MRAM or the like, but is not limited to a ferromagnetic film, and at least a transition metal element such as another transition metal material or its oxide is used. The present invention is also applicable to an etching process of a member as a main constituent element, for example, an etching process of a gate electrode or an etching process of a gate insulating film.

It is explanatory drawing of the fundamental structure of this invention. It is sectional drawing which shows the notional structure of the dry etching apparatus used for Example 1 of this invention. It is explanatory drawing of the process to the middle of the dry etching process of Example 1 of this invention. It is explanatory drawing of the process after FIG. 3 of the dry etching process of Example 1 of this invention .

DESCRIPTION OF SYMBOLS 1 Material to be etched 2 Mask 3 Oxide layer 4 Gaseous substance 5 having at least one carboxyl group 5 Carboxylate 6 Energy beam 10 Discharge chamber 11 Gas inlet 12 Discharge gas 13 Coil 14 High frequency power supply 15 Plasma 16 Positive ion 17 Shielding Plate 18 Power source 20 Processing chamber 21 Sample 22 Stage 23 Temperature control means 24 Gas introduction pipe 25 Organic acid vapor generation means 26 Organic vapor gas 31 Silicon substrate 32 CoFe layer 33 Resist pattern 34 Natural oxide film 35 Acetic acid vapor 36 Acetate layer 37 O ⁺ ions 38 natural oxidation film

Claims (3)

A step of exposing a material to be etched containing a transition metal element to a gaseous substance having at least one carboxyl group, converting at least an exposed surface of the material to be etched into a carboxylate; and oxygen on the exposed surface of the material to be etched And a step of volatile removal of the converted carboxylate by irradiating ions with acceleration energy of 500 eV or less .   2. The dry etching method according to claim 1, further comprising a step of oxidizing at least an exposed surface of the material to be etched before exposing the material to be etched to a gaseous substance having at least one carboxyl group. The material to be etched containing the transition metal element is any one of a transition metal material, an alloy material containing a transition metal as a main constituent element, or an oxide material containing a transition metal as a main constituent element. Item 3. The dry etching method according to Item 1 or Item 2 .

Images