JP2006165032A - Etching method and apparatus thereof - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an etching method capable of positively removing deposits. <P>SOLUTION: A reaction gas is introduced, and plasma is intermittently generated while a bias is continuously applied to a tunnel junction film 10a. (a) When the plasma is not generated, reaction gas molecules 92a are isotropically absorbed by the sidewall of a recess 20 and a volatile compound is formed. (b) When the plasma is generated, reaction gas ions 94 are collided to the sidewall of the recess 20 and a volatile compound can be released into an atmosphere. Thus, the deposits 22 on the sidewall of the recess portion 20 can be positively and effectively removed. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a tunnel junction having a tunnel barrier layer, such as TMR (Tunneling Magneto-Resistive) or MTJ (Metal Tunneling Junction), which is used in an MRAM (Magnetic Random Access Memory) semiconductor device or a magnetic recording head. The present invention relates to an etching method and apparatus suitable for manufacturing an element.

A tunnel junction element having a tunnel barrier layer called TMR or MTJ is used for an MRAM semiconductor device or a magnetic recording head.
FIG. 6 is a side sectional view of the tunnel junction element. The tunnel junction element 10 is formed of a tunnel junction film 10a in which a magnetic layer (fixed layer) 14, a tunnel barrier layer 15, a magnetic layer (free layer) 16 and the like are sequentially stacked. The tunnel barrier layer 15 is made of an electrically insulating material such as alumina. The magnetization direction in the plane of the fixed layer 14 is kept constant, and the magnetization direction in the plane of the free layer 16 can be reversed by the direction of the external magnetic field. Since the resistance value of the tunnel junction element 10 varies depending on whether the magnetization directions of the fixed layer 14 and the free layer 16 are parallel or antiparallel, when a voltage is applied in the thickness direction of the tunnel junction element 10, the tunnel barrier layer 15 Therefore, the magnitude of the current flowing through the TMR is different (TMR effect). Therefore, by detecting this current value, “1” or “0” can be read out. In many cases, the stacking order of the free layer 16 and the fixed layer 14 is reversed.

The tunnel junction element 10 is formed by etching the tunnel junction film 10a to form a recess 20 having a predetermined pattern that penetrates the tunnel barrier layer 15. For the etching, ion milling such as Ar, reactive ion etching (RIE), or the like is employed. In the RIE, a halogen-based gas such as chlorine gas (Cl ₂ ), bromine gas (Br ₂ ), iodine gas (I ₂ ), fluorine gas (F ₂ ), or a compound gas thereof is used as a reaction gas. ing.
International Publication No. WO01 / 084570 Pamphlet

  However, when the recess 20 is formed by etching the tunnel junction film 10 a, the substance mainly composed of the halogen compound of the magnetic element removed by the etching adheres to the sidewall of the recess 20. Since the deposit 22 has conductivity, there is a problem that a short circuit occurs in the tunnel barrier layer 15 made of an electrically insulating material. Note that the current flowing through the tunnel barrier layer 15 described above is very small, and in order to use the TMR effect, it is assumed that a large short-circuit current does not flow between the fixed layer 14 and the free layer 16. Therefore, when the conductive deposit 22 is present, it does not function as the tunnel junction element 10, which is a big problem in the etching process of the tunnel junction element 10.

  In order to remove the deposits 22, various post-etching treatments such as ashing with oxygen gas and pure water cleaning have been attempted as shown in Patent Document 1. However, since the deposit 22 is mainly composed of a halogen compound of a magnetic element that has a low vapor pressure and is hardly soluble in water, the deposit 22 has not necessarily been successfully removed by the above-described method.

In this regard, if the deposit on the sidewall of the recess can be removed by isotropic dry etching following the formation of the recess by anisotropic dry etching, the tunnel junction element can be efficiently manufactured. Therefore, development of an isotropic dry etching method and apparatus capable of reliably removing deposits is desired.
The present invention has been made to solve the above-described problems, and an object of the present invention is to provide an etching method and apparatus capable of reliably removing deposits.

In order to achieve the above object, the etching method of the present invention performs etching of the functional film by introducing a reaction gas and intermittently generating plasma while continuously applying a bias to the functional film. Features.
According to this configuration, when plasma is not generated, the reactive gas molecules are isotropically adsorbed to the functional film, and a volatile compound is formed. Further, when plasma is generated, ions of the reaction gas can collide with the functional film, and volatile compounds can be released. Thus, by intermittently generating plasma, the deposits on the functional film can be reliably and efficiently removed.

Another etching method of the present invention is characterized in that the functional film is etched by intermittently applying a bias to the functional film while introducing a reactive gas and continuously generating plasma. .
According to this configuration, when no bias is applied, the radicals of the reaction gas are isotropically adsorbed on the functional film, and a volatile compound is formed. Further, when a bias is applied, ions of the reaction gas can collide with the functional film to release the volatile compound. In this way, by applying the bias intermittently, the deposits on the functional film can be reliably and efficiently removed.

In addition, the structure may include an anisotropic dry etching step of forming a predetermined pattern of recesses in the functional film and an isotropic dry etching step of removing deposits on the inner surface of the recesses by the etching method described above. Good.
According to this structure, the deposit | attachment to the side wall of a recessed part can be removed reliably and efficiently.

In addition, an anisotropic dry etching process for forming a recess having a predetermined pattern through the tunnel barrier layer of the tunnel junction film, and a method of removing conductive deposits on the sidewall of the recess by the above-described etching method And a dry dry etching process.
According to this configuration, it is possible to reliably and efficiently remove the conductive deposits on the sidewalls of the recesses and prevent a short circuit of the tunnel barrier layer.

On the other hand, an etching apparatus of the present invention includes a chamber in which a substrate to be etched is disposed, a reaction gas supply unit that introduces a reaction gas into the chamber, a bias application unit that can continuously apply a bias to the substrate, And plasma generating means capable of intermittently generating plasma in the chamber.
According to this configuration, deposits on the substrate can be reliably and efficiently removed.

Another etching apparatus of the present invention includes a chamber in which a substrate to be etched is disposed, a reaction gas supply unit that introduces a reaction gas into the chamber, and a plasma generation unit that can continuously generate plasma in the chamber. And a bias applying means capable of intermittently applying a bias to the substrate.
According to this configuration, deposits on the substrate can be reliably and efficiently removed.

  Embodiments of the present invention will be described below with reference to the drawings. In each drawing used for the following description, the scale of each member is appropriately changed to make each member a recognizable size.

(First embodiment)
First, the first embodiment will be described.
2 and 3 are process diagrams of the etching method according to the first embodiment. As shown in FIG. 2C, the etching method according to the first embodiment includes an anisotropic dry etching process in which a recess 20 having a predetermined pattern is formed through the tunnel barrier layer 15 of the tunnel junction film 10a. As shown in FIG. 3 (a) and FIG. 3 (b), plasma is generated intermittently while a reactive gas is introduced and a bias is continuously applied to the tunnel junction film 10a. And an isotropic dry etching process for removing the deposit 22.

(Tunnel junction element, MRAM)
FIG. 1A is a side sectional view of the tunnel junction element. The tunnel junction element 10 includes an antiferromagnetic layer (not shown) made of PtMn, IrMn, or the like, a magnetic layer (fixed layer) 14 made of NiFe, CoFe, or the like, a tunnel barrier layer 15 made of AlO (alumina), etc., and NiFe, A magnetic layer (free layer) 16 made of CoFe or the like is mainly configured. Actually, functional layers other than those described above are laminated to form a multilayer structure of about 15 layers. In addition, the cross section of the tunnel junction element 10 is not limited to the rectangular shape as shown in FIG. Further, if the thickness of the free layer is made thinner than the thickness of the fixed layer, a coercive force difference type tunnel junction element utilizing the film thickness difference can be formed.

  FIG. 1B is a schematic configuration diagram of an MRAM using a tunnel junction element. The MRAM 100 is configured by arranging MOSFETs 110 and tunnel junction elements 10 in a matrix on the substrate 5. The tunnel junction element 10 described above has an upper end connected to the bit line 102 and a lower end connected to the source electrode or drain electrode of the MOSFET 110. The gate electrode of the MOSFET 110 is connected to the read word line 104. On the other hand, a rewrite word line 106 is disposed below the tunnel junction element 10.

In the tunnel junction element 10 shown in FIG. 1, the magnetization direction of the fixed layer 14 is kept constant, and the magnetization direction of the free layer 16 can be reversed. Since the resistance value of the tunnel junction element 10 varies depending on whether the magnetization directions of the fixed layer 14 and the free layer 16 are parallel or antiparallel, when a voltage is applied in the thickness direction of the tunnel junction element 10, the tunnel barrier layer 15 Therefore, the magnitude of the current flowing through the TMR is different (TMR effect). Therefore, by turning on the MOSFET 110 by the read word line 104 and measuring the current value, “1” or “0” can be read out.
Further, if a current is supplied to the rewrite word line 104 to generate a magnetic field around it, the magnetization direction of the free layer 16 can be reversed. As a result, “1” or “0” can be rewritten.

  Note that the difference in resistance value of the tunnel junction element 10 due to the combination of the magnetization directions of the fixed layer 14 and the free layer 16 is generally very small. In order to detect this slight difference in resistance value, it is necessary to reduce the resistance value of the tunnel barrier layer 15 made of an electrically insulating material such as alumina as much as possible. For this reason, the thickness of the tunnel barrier layer 15 is as thin as 8 to 12 angstroms, which is the thickness of the metal aluminum before oxidation.

(Etching method)
Next, a method for forming a tunnel junction element by etching the tunnel junction film will be described with reference to FIGS.

First, as shown in FIG. 2A, a tunnel junction film 10a is formed. The tunnel junction film 10a can be formed by sputtering or the like.
Next, as shown in FIG. 2B, a mask 90 made of SiO ₂ or the like is formed on the surface of the tunnel junction film 10a. Note that a method for forming the mask 90 is omitted.

(Anisotropic etching process)
Next, as shown in FIG. 2C, the tunnel junction film 10 a is anisotropically dry etched through a mask 90 to form a recess 20 having a predetermined pattern that penetrates the tunnel barrier layer 15. This etching is performed in an etching apparatus described below.

  FIG. 4 is a schematic configuration diagram of the etching apparatus. Hereinafter, an inductive coupling plasma (ICP) reactive ion etching (RIE) apparatus will be described as an example. The etching apparatus 60 includes a reactive gas supply unit to the chamber 61 and an internal gas exhaust unit of the chamber 61. An RF antenna 68 is provided above the chamber 61, and a plasma generating RF power source 69 is connected to the RF antenna 68. Further, an electrode 62 for mounting the substrate 5 is provided below the inside of the chamber 61, and a bias applying RF power source 63 is connected to the electrode 62.

  In addition to this, the etching apparatus 60 includes plasma generating means that can intermittently generate plasma in the chamber 61. Specifically, a pulse signal generating means 69 a is connected to the plasma generating RF power source 69 so that high frequency power can be intermittently applied from the RF antenna 68. In addition, the etching apparatus 60 includes a bias application unit that can intermittently apply a high-frequency bias to the substrate 5. Specifically, a pulse signal generating means 63 a is connected to the bias applying RF power source 63 so that a high frequency bias can be intermittently applied from the electrode 62.

Then, the substrate 5 on which the tunnel junction film and the mask are formed as described above is placed on the electrode 62 in the chamber 61 in the etching apparatus 60. Next, a mixed gas of Cl ₂ and Ar is introduced into the chamber 61 as a reaction gas. Then, plasma is generated in the chamber 61 by the RF antenna 68, and etching of the tunnel junction film is started. Typical conditions for the etching process are as follows: the pressure of the reactive gas is 0.1 to 10 Pa, the input power to the RF antenna 68 for generating plasma is 500 to 700 W, and the electrode for applying a high frequency bias to the substrate 5. The input power to 62 is 50 to 100 W. Here, both the pulse signal generating means 69a and 63a are turned off, and the high frequency power is continuously applied from the power sources 69 and 63.

Reaction plasma radicals and ions are generated by the plasma generated in the chamber. When a high frequency bias is applied to the substrate 5 by the electrode 62, the generated ions can be accelerated and collide with the tunnel junction film 10a as shown in FIG. Is done. Under the etching conditions described above, this chemical / physical etching is dominant. That is, etching is performed mainly in the vertical direction of the substrate and is hardly etched in the horizontal direction, so-called anisotropic etching. In the present embodiment, this processing by anisotropic etching is called a main process.
By this main process, as shown in FIG. 2C, a concave portion 20 having a predetermined pattern is formed below the opening of the mask 90. Thereafter, the mask 90 is removed.

(Isotropic etching process)
Deposits 22 are present on the side wall of the recess 20 formed here. The deposit 22 is a by-product of the main process, and is composed of a halogen compound of a magnetic element having a low vapor pressure. Since this compound has conductivity, there is a possibility that a tunnel barrier layer made of an electrically insulating material will be short-circuited and the tunnel junction element will not function.

Therefore, after the main process, a post-treatment process for removing the deposits is performed. In this post-processing process, isotropic dry etching is performed using an etching apparatus 60 shown in FIG. Specifically, the pressure of the reaction gas in the chamber 61 is set to about 10 to 100 Pa by increasing the flow rate of the mixed gas of Cl ₂ and Ar introduced into the chamber 61 and reducing the opening of the conductance valve in the exhaust means. To increase.

  Then, the input power from the bias applying RF power source 63 is lowered while the pulse signal generating means 63a is kept OFF. Thereby, a small bias is continuously applied from the electrode 62 to the substrate 5. On the other hand, the pulse signal generating means 69a is turned on while the input power from the plasma generating RF power source 69 is maintained at 500 to 700W. For example, the frequency of the pulse signal is about 100 to 1000 Hz, and the duty ratio (ON / OFF time ratio) is 1: 1. As a result, high frequency power is intermittently applied from the RF antenna 68 to intermittently generate plasma in the chamber 61.

While the plasma is OFF, the reaction gas is not excited as shown in FIG. 3A, but the chlorine gas molecules 92a are isotropically adsorbed on the inner surface of the recess 20. Then, the adsorbed chlorine gas reacts with a transition metal constituting the deposit 22 and a transition metal chloride is formed.
When the plasma is turned on, as shown in FIG. 3B, the reaction gas is excited to generate radicals, ions, and the like. Since a bias is applied to the substrate, the generated argon ions 94 are accelerated and directly collide with the side wall of the recess 20. In addition, argon ions recoiled at the bottom surface of the recess 20 and neutral argon atoms that have recoiled due to collision with the bottom surface indirectly collide with the sidewall of the recess 20. By these impacts, the transition metal chloride formed on the sidewall of the recess 20 is released into the atmosphere. Thereby, the deposit 22 on the side wall of the recess 20 is removed.

  Then, by intermittently applying plasma, adsorption of chlorine gas to the recesses, formation of chloride, and detachment of chloride due to collision of argon are repeated. Here, since chlorine gas is adsorbed isotropically, this is a so-called isotropic etching process in which the vertical direction and the horizontal direction can be cut at substantially the same etching rate. Thereby, as shown in FIG.3 (c), the deposit | attachment to the side wall of the recessed part 20 can be removed efficiently. In addition, since the thickness of the deposit is extremely thin, such as several nm, there is almost no re-deposition by etching, and the deposit can be removed in a short time. Therefore, there is almost no influence on the processing dimension of the recess 20.

(Pure water rinse process)
After the above-described post-treatment process, normal post-etching treatment such as pure water rinsing for removing residual chlorine adsorbed on the surface of the tunnel junction film 10a is performed. Thus, the tunnel junction element 10 is formed.
In the main process and the post-treatment process described above, Cl ₂ is used as a reaction gas. However, a halogen-based gas such as BCl ₃ , SiCl ₄ , BI ₃ , BBr ₃ , HBr, SiF ₄ or a mixed gas thereof, or etc. these mixed gas obtained by adding O ₂ may be used. If such a halogen-based gas is employed, the vapor pressure of the by-product by the main process becomes relatively high, and the amount of deposition on the side wall of the recess can be reduced.

As described in detail above, in the tunnel junction element etching method of the present embodiment, an anisotropic dry etching step of forming a recess having a predetermined pattern through the tunnel barrier layer of the tunnel junction film and a reaction gas are introduced. And an isotropic dry etching process in which plasma is intermittently generated while a bias is continuously applied to the tunnel junction film to remove deposits on the sidewalls of the recesses.
According to this configuration, when plasma is not generated, the reactive gas molecules are isotropically adsorbed on the side wall of the recess, and a volatile compound is formed. Further, when plasma is generated, ions of the reaction gas can collide with the side wall of the recess to release the volatile compound. In this way, by intermittently generating plasma, the deposits on the side walls of the recess can be reliably and efficiently removed. As a result, a short circuit of the tunnel barrier layer in the tunnel junction element can be prevented.

(Second Embodiment)
Next, an etching method according to the second embodiment will be described with reference to FIGS. The etching method according to the second embodiment is different from the first embodiment in which the plasma is intermittently generated while the bias is continuously applied in that the bias is intermittently applied while the plasma is continuously generated. ing. Note that detailed description of portions having the same configuration as in the first embodiment is omitted.

In the etching method according to the second embodiment, first, the same main process as that of the first embodiment is performed. That is, as shown in FIG. 2A, the tunnel junction film 10a is formed. Next, as shown in FIG. 2B, a mask 90 made of SiO ₂ or the like is formed on the surface of the tunnel junction film 10a. Next, as shown in FIG. 2C, the tunnel junction film 10 a is anisotropically dry-etched through a mask 90 to form a recess 20 having a predetermined pattern that penetrates the tunnel barrier layer 15.

Deposits 22 are present on the side wall of the recess 20 formed here. Therefore, also in the second embodiment, this deposit is removed by isotropic dry etching. Specifically, after the main process, a post-treatment process for removing deposits is performed using an etching apparatus 60 shown in FIG. In this post-treatment process, the pressure of the reaction gas in the chamber 61 is set to 10 to 100 Pa by increasing the flow rate of the mixed gas of Cl ₂ and Ar introduced into the chamber 61 and reducing the opening of the conductance valve in the exhaust means. Increase to a degree.

  Then, plasma is continuously generated in the chamber 61 while the input power from the RF power source 69 for plasma generation is maintained at 500 to 700 W and the pulse signal generating means 69a is kept OFF. On the other hand, the input power from the bias applying RF power source 63 is lowered to turn on the pulse signal generating means 63a. For example, the frequency of the pulse signal is about 100 to 1000 Hz, and the duty ratio (ON / OFF time ratio) is 1: 1. Thereby, a small bias is intermittently applied from the electrode 62 to the substrate 5.

In the second embodiment, since plasma is continuously generated, the reaction gas is continuously excited to generate radicals, ions, and the like.
While the bias is OFF, as shown in FIG. 5A, excited chlorine radicals 92b, chlorine ions 92c and unexcited chlorine gas molecules 92a are isotropically adsorbed on the inner surface of the recess 20. The Then, the adsorbed chlorine gas molecules 92a, radicals 92b, and ions 92c react with the transition metal or the like constituting the deposit 22 to form a transition metal chloride.
When the bias is turned on, as shown in FIG. 5B, the excited argon ions 94 are accelerated and directly collide with the side wall of the recess 20. In addition, argon ions recoiled at the bottom surface of the recess 20 and neutral argon atoms that have recoiled due to collision with the bottom surface indirectly collide with the sidewall of the recess 20. Due to these impacts, the transition metal chloride formed on the side wall of the recess 20 is released into the atmosphere. Thereby, the deposit 22 on the side wall of the recess 20 is removed.

  Then, by intermittently applying a bias, adsorption of chlorine gas or the like to the concave portion, formation of chloride, and detachment of chloride due to collision of argon are repeated. Here, since chlorine gas or the like is adsorbed isotropically, it is a so-called isotropic etching process in which the vertical direction and the horizontal direction can be cut at substantially the same etching rate. Thereby, as shown in FIG.3 (c), the deposit | attachment to the side wall of the recessed part 20 can be removed efficiently. In addition, since the thickness of the deposit is extremely thin, such as several nm, there is almost no re-deposition by etching, and the deposit can be removed in a short time. Therefore, there is almost no influence on the processing dimension of the recess 20.

Thereafter, as in the first embodiment, a normal post-etching process such as pure water rinsing for removing residual chlorine adsorbed on the surface of the tunnel junction film 10a is performed. Thus, the tunnel junction element 10 is formed.
In the main process and the post-treatment process described above, Cl ₂ is used as a reaction gas. However, a halogen-based gas such as BCl ₃ , SiCl ₄ , BI ₃ , BBr ₃ , HBr, SiF ₄ or a mixed gas thereof, or etc. these mixed gas obtained by adding O ₂ may be used.

As described above in detail, in the etching method according to the second embodiment, a reactive gas is introduced and plasma is continuously generated, while a bias is intermittently applied to the tunnel junction film to A configuration having an isotropic dry etching process for removing the deposits was adopted.
According to this configuration, when no bias is applied, molecules, radicals, ions, and the like of the reaction gas are isotropically adsorbed on the side wall of the recess, and a volatile compound is formed. Further, when a bias is applied, volatile compounds can be released by causing ions of the reaction gas to collide with the side wall of the recess. In this way, by applying the bias intermittently, the deposits on the side wall of the recess can be reliably and efficiently removed. As a result, a short circuit of the tunnel barrier layer in the tunnel junction element can be prevented.

  The technical scope of the present invention is not limited to the above-described embodiments, and includes various modifications made to the above-described embodiments without departing from the spirit of the present invention. That is, the specific materials and configurations described in the embodiments are merely examples, and can be changed as appropriate.

  For example, in each of the above embodiments, one of plasma or bias is generated continuously and the other is generated intermittently, but both may be generated intermittently. In each of the above embodiments, the isotropic dry etching process is performed using the same apparatus following the anisotropic dry etching process, but each may be performed using different apparatuses. At that time, by carrying the substrate between the steps under a vacuum, it is possible to prevent corrosion of the substrate due to adsorption of moisture from the atmosphere. In each of the above embodiments, the bias applied in the isotropic dry etching process is made smaller than that in the anisotropic dry etching process, but an equivalent bias may be applied.

It is a schematic block diagram of a tunnel junction element and MRAM. It is explanatory drawing of the etching method of a tunnel junction element. It is explanatory drawing of the etching method which concerns on 1st Embodiment. It is a schematic block diagram of an etching apparatus. It is explanatory drawing of the etching method which concerns on 2nd Embodiment. It is explanatory drawing of the tunnel junction element to which the electroconductive substance adhered.

Explanation of symbols

  10a ... Tunnel junction film 20 ... Recess 22 ... Deposit 92a ... Reactive gas molecule 94 ... Reactive gas ion

Claims (6)

  An etching method, wherein a reactive gas is introduced and a plasma is intermittently generated while a bias is continuously applied to the functional film to etch the functional film.   An etching method comprising etching a functional film by introducing a reactive gas and generating a plasma continuously while applying a bias to the functional film intermittently. An anisotropic dry etching step of forming a predetermined pattern of recesses in the functional film;
An isotropic dry etching step of removing deposits on the inner surface of the recess by the etching method according to claim 1 or 2,
An etching method comprising: An anisotropic dry etching step of forming a predetermined pattern of recesses through the tunnel barrier layer of the tunnel junction film,
An isotropic dry etching process for removing conductive deposits on the sidewalls of the recesses by the etching method according to claim 1 or 2,
An etching method comprising:   A chamber in which a substrate to be etched is placed, a reactive gas supply means for introducing a reactive gas into the chamber, a bias applying means capable of continuously applying a bias to the substrate, and plasma is intermittently generated in the chamber An etching apparatus comprising plasma generating means that can be used.   A chamber in which a substrate to be etched is arranged, a reaction gas supply means for introducing a reaction gas into the chamber, a plasma generation means capable of continuously generating plasma in the chamber, and a bias is intermittently applied to the substrate An etching apparatus comprising: a bias applying unit capable of performing the same.

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