JP2006332138A - Method of etching metal oxide film - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve the problems wherein a metal oxide film is damaged and device characteristics are poorly affected when using physical sputter for etching the metal oxide film. <P>SOLUTION: Reactive gas is activated by plasma, and the activated reactive gas is allowed to hit against a metal oxide film 44, thus etching the metal oxide film 44 and hence dispensing with the irradiation of high-energy ions as before for obtaining the same etch rate. Additionally, the metal oxide film 44 is heated at 100°C or higher for etching. Further, the etch rate is adjusted to 50 nm/min or smaller. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a method for etching a metal oxide film, and more particularly to a method for dry etching a metal oxide film.

  Currently, research and development for the expansion of the multimedia information society and the realization of ubiquitous services are being actively conducted. In particular, an apparatus (hereinafter referred to as “memory”) for recording information mounted on a network device or an information terminal is an important key device. As functions required for the memory installed in ubiquitous terminals, high-speed operation, long-term retention period, environmental resistance, low power consumption, and the function that does not erase recorded information even when the power is turned off, that is, non-volatility is essential. ing.

As a new nonvolatile memory, a ferroelectric memory has attracted attention. As an example, the structure of a stack type FeRAM (Ferroelectric RAM) is shown in FIG.
The stack type FeRAM includes a MOS transistor and a capacitor using the ferroelectric film 111. The MOS transistor includes a source 102 formed on the semiconductor substrate 101, a drain 103, and a gate electrode 105 provided via a gate insulating film 104. The capacitor has a structure in which a ferroelectric film 111 is sandwiched between an upper electrode 112 and a lower electrode 113, and is connected to the source 102 of the MOS transistor via the source electrode 106. An oxide dielectric such as Bi ₄ Ti ₃ O ₁₂ can be used for the ferroelectric film 111. An ammeter 114 is connected to the drain 103 of the MOS transistor via the drain electrode 107.

  In this FeRAM, by detecting the direction of polarization of the ferroelectric film 111 as a current flowing in the channel 108 between the source 102 and the drain 103, it can be extracted as “on” or “off” data. Since the polarization of the ferroelectric film 111 can be maintained even when no voltage is applied, the FeRAM is nonvolatile.

  In order to manufacture a ferroelectric memory such as FeRAM, a process of processing the ferroelectric film 111 into a predetermined pattern is indispensable. In order to process the ferroelectric film 111, since the vapor pressure of the ferroelectric is small, conventionally, the surface of the ferroelectric film 111 is irradiated with high energy ions to repel particles and remove them. Sputtering has been used (see, for example, Patent Document 1).

JP-A-10-223757

However, when physical sputtering is performed on the ferroelectric film 111 as in the prior art, there is a problem in that high energy ions damage the ferroelectric film 111 and adversely affect the characteristics of the ferroelectric memory.
7A and 7B, the ferroelectric particles (etched material) 111A repelled by the high-energy ions 122 are reattached to the pattern sidewalls of the resist 121 and the ferroelectric film 111. To do. For this reason, when the resist 121 is removed, a film 111B as shown in FIG. 7C is formed on the ferroelectric film 111, which adversely affects the characteristics of the ferroelectric memory.
These problems are common problems in etching of the metal oxide film including the ferroelectric film 111.

  The present invention has been made to solve such a problem, and an object of the present invention is to provide a method for etching a metal oxide film having a small influence on device characteristics.

  In order to achieve such an object, the present invention uses a plasma apparatus including a fixing base for fixing a substrate, a container for housing the fixing base, and plasma generation means for generating plasma in the container. And a step of fixing a substrate on which a metal oxide film made of Bi metal, Ti metal and oxygen is formed on a fixed base, introducing a plasma gas into the container, and using a plasma generation means A step of generating a plasma from a gas, a step of introducing a reactive gas into the container, activating the reactive gas with plasma, and applying the activated reactive gas to the metal oxide film to etch the metal oxide film And a step of performing.

Here, as the reactive gas, at least one of CF ₄ , C ₂ F ₆ , C ₄ F ₈ and SF ₆ can be used.
The step of etching the metal oxide film is more preferably performed while heating the substrate to 100 ° C. or higher.
In the step of etching the metal oxide film, it is further preferable that the etch rate of the metal oxide film is at most 50 nm / min.
An example of the metal oxide film to be etched is a metal oxide film made of Bi ₄ Ti ₃ O ₁₂ .
As the plasma device, for example, an inductively coupled plasma device can be used.

As described above, in the present invention, the activated reactive gas is applied to the metal oxide film to etch the metal oxide film. As a result, it is not necessary to irradiate high energy ions as in the prior art in order to obtain the same etch rate, so that damage to the metal oxide film can be reduced.
Further, by etching the metal oxide film at a rate of at most 50 nm / min, reaction products generated during the etching are reduced. For this reason, even if there is a reaction product reattached to the metal oxide film, the probability of being removed by the irradiated ions is increased. As a result, reattachment to the metal oxide film can be suppressed.
Therefore, according to the present invention, it is possible to manufacture a device having desired characteristics using a metal oxide film.

On the other hand, in the present invention, since the reactive gas is activated and applied to the metal oxide film, the etching reaction can be promoted and the etching rate can be increased.
Many of the reaction products generated during the etching of the metal oxide film have a melting point in the range of 100 to 800 ° C. For this reason, by performing etching while heating the substrate to 100 ° C. or higher, the reaction product can be easily vaporized and the etch rate can be further increased.

Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings.
In this embodiment, reactive etching is performed on a metal oxide film using an inductively coupled (IPC) plasma etching apparatus. That is, by generating inductively coupled plasma with plasma gas, activating the reactive gas with this plasma, and reacting the activated reactive gas with the constituent material of the metal oxide film to vaporize the reaction product. Etching the metal oxide film.
In reactive etching, since a chemical reaction on the film surface is used, it is not necessary to irradiate the metal oxide film with high-energy ions as in the prior art. For this reason, the damage given to a metal oxide film can be reduced.
In this embodiment, the metal oxide film to be etched refers to a metal oxide film composed of Bi metal, Ti metal, and oxygen. An example of the metal oxide film is a ferroelectric film made of Bi ₄ Ti ₃ O ₁₂ .

FIG. 1 shows a conventional Ar (argon) etching rate when an inductively coupled plasma is irradiated on a substrate on which a Bi ₄ Ti ₃ O ₁₂ film is formed and an RF (high frequency) bias power applied to the substrate is changed. is a graph comparing the case of plasma was added reactive gas C ₄ F ₈ in the case of a single plasma and Ar. From this graph, it can be seen that a higher etch rate can be obtained with plasma in which C ₄ F ₈ is added to Ar.

The reason why the etch rate for the Bi ₄ Ti ₃ O ₁₂ film is higher when C ₄ F ₈ is added than when Ar alone is considered is as follows. Bi (bismuth) and Ti (titanium) in the Bi ₄ Ti ₃ O ₁₂ film chemically react with active species F and C _x F _y generated from C ₄ F _{8 in} the plasma, and BiF ₅ and TiF ₄ is generated. These reaction products have melting points of about 150 ° C. and 300 ° C., respectively, and have a much higher vapor pressure than Bi ₄ Ti ₃ O ₁₂ having a melting point of over 1200 ° C. For this reason, it is considered that the etching rate is higher when C ₄ F ₈ is added than when Bi ₄ Ti ₃ O ₁₂ is etched with Ar alone. Thus, it is considered that reactive etching occurs in the plasma to which C ₄ F ₈ is added.

  FIG. 1 shows that RF bias power can be reduced with reactive etching to achieve the same etch rate. Therefore, by using reactive etching, it is not necessary to irradiate the metal oxide film with high energy ions as in the prior art. As a result, damage to the metal oxide film and the underlying film can be reduced, and device characteristics are not adversely affected.

  FIG. 1 shows an example in which etching is performed at a substrate temperature of 30 ° C. without heating the substrate. However, it is also possible to perform etching while heating the substrate with a heater embedded in a fixing base for fixing the substrate. By heating the substrate to 100 ° C. or higher, the reaction product approaches the melting point of the reaction product and the reaction product is more easily vaporized, so that the rate of reactive etching is further increased. As a result, the energy of irradiated ions may be further reduced, which is advantageous for reducing damage.

When reactive etching is used, not only is it effective for reducing irradiation damage, but also when the fine pattern is etched, it is possible to reduce the reattachment of the etched material to the pattern side wall, so that the metal oxide film can be etched more accurately. It becomes possible. FIG. 2 (a) shows the behavior of incident ions and reaction products when a 0.5 micron L & S pattern of a Bi ₄ Ti ₃ O ₁₂ film is reactively etched. Although the prior art shown in FIG. 7 etching object 111A that pops out the pattern side wall direction to form a film 111B remains on the side wall, easily volatile reaction products of many etching was reactive etching and BiF ₅ or TiF ₄ Since it is the object 1A, it is easy to be detached again even if it adheres to the side wall, and the film growth on the pattern side wall is suppressed. Furthermore, since the vapor pressure of the reaction product 1A such as BiF ₅ or TiF ₄ is increased by heating the substrate to 100 ° C. or higher, the reaction product 1A is more easily volatilized, and the etched product that protrudes toward the side wall. Can be prevented from adhering to the side wall. As a result, it is possible to realize pattern processing having favorable dimensions and shapes.

Film formation by the reaction product 1A on the pattern side wall can be suppressed not only by a method of increasing the substrate temperature but also by a method of controlling the etch rate. FIG. 3 is a graph showing the relationship between the etch rate of the Bi ₄ Ti ₃ O ₁₂ film and the thickness of the etched material that re-adheres to the etched pattern sidewalls. This graph is obtained when reactive etching is performed on a Bi ₄ Ti ₃ O ₁₂ film having a thickness of 300 nm using a mixed gas of Ar and C ₄ F ₈ . From this graph, it can be seen that the reattachment of the etched product is suppressed by setting the etch rate to 50 nm / min or less. The thickness of the film adhering to the pattern side wall during the etching is determined by the balance between the number of reaction products 1A jumping out from the etching surface in the direction of the side walls and the number of ions 3 from the upper part that repels the reaction products 1A. Therefore, by reducing the etch rate to 50 nm / min or less, the generated reaction product 1A is reduced, so that the probability that the reaction product 1A adhering to the side wall is removed by the ions 3 increases. Conceivable. Therefore, it is desirable that the etching rate of the Bi ₄ Ti ₃ O ₁₂ film is 50 nm / min or less.

  As described above, by controlling the substrate temperature and the etch rate to suppress the re-deposition of the reaction product 1A on the pattern side wall of the metal oxide film 1, as shown in FIG. A pattern of the metal oxide film 1B without 111B can be obtained. In addition, since the damage given to the metal oxide film 1B can be reduced by using reactive etching, according to the present embodiment, a device having desired characteristics can be manufactured using the metal oxide film 1B. Become.

Next, a processing example of a ferroelectric memory using a ferroelectric film made of Bi ₄ Ti ₃ O ₁₂ will be described. An inductively coupled plasma etching apparatus is used for etching. An inductively coupled plasma etching apparatus is an apparatus that generates electrons by accelerating electrons by an induced electric field generated by a high-frequency induction magnetic field and dissociating gas molecules with the accelerated electrons. The configuration of the inductively coupled plasma etching apparatus includes a fixing base for fixing a substrate to be etched, a processing container for housing the fixing base, an exhaust device for exhausting the processing container, and a gas (plasma gas) that becomes plasma in the processing container. ), A reactive gas introduction device for introducing a reactive gas into the processing vessel, an inductively coupled antenna for forming a high frequency induction magnetic field in the processing vessel, and an RF for applying an RF bias to the substrate It consists of a power supply. A heater for heating the substrate may be incorporated in the fixed base. The plasma gas introduction device and the inductively coupled antenna are collectively called plasma generation means.

FIG. 4 is a cross-sectional view showing the main steps in etching the ferroelectric film Bi ₄ Ti ₃ O ₁₂ .
First, a substrate 31 as shown in FIG. 4A is fixed to a fixed base of an inductively coupled plasma etching apparatus. This substrate 31 is formed on an Si (silicon) substrate 41, an insulating film 42 made of SiO ₂ having a thickness of 100 nm, a metal film 43 made of Ru (ruthenium) having a thickness of 10 to 20 nm, and Bi ₄ Ti having a thickness of 40 nm. _A ferroelectric film 44 made of ₃ O ₁₂ and a metal film 45 made of Ti (titanium) or Ta (tantalum) having a thickness of 50 to 100 nm are sequentially laminated, and a resist pattern 46 is formed on the metal film 45 It is. The substrate temperature is about 40 ° C.

After evacuating the processing vessel in this state, 50 sccm about the Ar as the plasma gas into the processing chamber, introducing a CF ₄ at a flow rate of about 5sccm as a reactive gas. At this time, the pressure is controlled to about 3 Pa. “Sccm” is a unit of flow rate, and represents that 1 cm ³ of gas at 0 ° C. and 1 atm flows per minute.
When the pressure is stabilized, high frequency power of 400 W is introduced to generate inductively coupled plasma. Thereby, Ar plasma is generated, and CF ₄ is activated by this plasma. When an RF bias of about 100 W is applied to the substrate 31 and the surface of the substrate 31 is irradiated with ions having a predetermined energy and active species from CF ₄ , the metal film 45 not covered with the resist pattern 46 is formed. The exposed portion is etched, and then the exposed portion of the ferroelectric film 44 is etched.

As described above, by controlling parameters such as pressure and RF bias power, the etch rate can be reduced to about 50 nm / min. Therefore, the reaction product on the pattern sidewalls of the metal film 45 and the ferroelectric film 44 can be reduced. Reattachment is suppressed. As a result, as shown in FIG. 4B, the conventional pattern of the metal film 45A and the ferroelectric film 44A without the film 111B is obtained.
Further, by adding CF ₄ and processing using reactive etching, it becomes unnecessary to irradiate the ferroelectric film 44 with high energy ions as in the prior art, and the metal film 45A, the ferroelectric film 44A and the metal film are eliminated. The damage given to 43 can be reduced.

Thereafter, the resist pattern 46 is removed. Then, SiO ₂ is deposited on the substrate surface using, for example, a plasma CVD apparatus, and an inter-element insulating film 47 as shown in FIG. 4C is formed.
As described above, a large number of ferroelectric memory capacitors including the metal film 43, the ferroelectric film 44A, and the metal film 45A can be formed on the substrate. The metal film 43 and the metal film 45A function as a lower electrode and an upper electrode of the capacitor, respectively.

  As shown in FIG. 5A, the metal film 43 and the ferroelectric film 44 are subsequently etched to form the metal film 45A, the ferroelectric film 44A, and the metal film 43A, and then the resist pattern is formed. 46 may be removed and an inter-element insulating film 48 may be formed as shown in FIG.

In addition, although an example in which CF ₄ is used as a reactive gas has been shown, a ferroelectric substance using any one of C ₂ F ₆ , C ₄ F ₈ , and SF ₆ instead of CF ₄ under the same conditions. The film 44 can also be etched.
Moreover, although the example which uses Ar as plasma gas was shown, other noble gases, such as Kr (krypton) and Xe (xenon), can also be used instead of Ar.

Although an example using inductively coupled plasma has been shown, the ferroelectric film 44 can be etched by using the above-described gas species even when other high-density plasma such as ECR or helicon is used.
Further, in this example, the substrate temperature is set to 40 ° C. However, when the temperature is set to 100 ° C. or higher, further satisfactory processing can be performed.
Further, the above is an example of a method for etching a metal oxide film, and the constituent material and film thickness of the metal oxide film are not limited to those described above.
The present invention applies not only to the case of using an inductively coupled plasma apparatus, but also to a plasma apparatus that generates a plasma by introducing a gas and activates a reactive gas by the plasma. It can be applied and has the same effect.

  The present invention can be used, for example, for manufacturing a nonvolatile memory element.

It is a graph which shows the relationship between RF bias power applied to a board | substrate, and an etching rate. It is a conceptual diagram for demonstrating the reason why the reattachment of the etching thing to a pattern side wall can be reduced by using reactive etching. It is a graph which shows the relationship between an etching rate and the thickness of the etching thing reattached to a pattern side wall. The ferroelectric film Bi ₄ Ti ₃ O ₁₂ is a sectional view showing major steps in etching. The ferroelectric film Bi ₄ Ti ₃ O ₁₂ is a sectional view showing major steps in etching. It is sectional drawing which shows the structure of stack type FeRAM. It is a conceptual diagram for demonstrating the subject of the conventional etching method of a ferroelectric film.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1,1B ... Metal oxide film, 1A ... Reaction product, 2 ... Mask pattern, 3 ... Ion, 31 ... Substrate, 41 ... Si substrate, 42 ... Insulating film, 43, 43A ... Metal film, 44, 44A ... Ferroelectric Body film, 45, 45A ... metal film, 46 ... resist pattern, 47, 48 ... inter-element insulating film.

Claims (6)

In an etching method using a plasma apparatus including a fixing base for fixing a substrate, a container for housing the fixing base, and a plasma generation means for generating plasma in the container,
Fixing the substrate on which the metal oxide film made of Bi metal, Ti metal and oxygen is formed to the fixing table;
Introducing a plasma gas into the vessel and generating plasma from the plasma gas using the plasma generating means;
Introducing a reactive gas into the vessel and activating the reactive gas with the plasma;
Applying the activated reactive gas to the metal oxide film and etching the metal oxide film. A method of etching a metal oxide film, comprising: The method for etching a metal oxide film according to claim 1,
The method of etching a metal oxide film, wherein the reactive gas is at least one of CF ₄ , C ₂ F ₆ , C ₄ F ₈ and SF ₆ . In the etching method of the metal oxide film according to claim 1 or 2,
Etching the metal oxide film is performed while heating the substrate to 100 ° C. or higher. In the etching method of the metal oxide film of any one of Claims 1-3,
The method of etching a metal oxide film comprises etching the metal oxide film at a rate of 50 nm / min at the most. In the etching method of the metal oxide film of any one of Claims 1-4,
The method for etching a metal oxide film, wherein the metal oxide film is made of Bi ₄ Ti ₃ O ₁₂ . In the etching method of the metal oxide film of any one of Claims 1-5,
The method of etching a metal oxide film, wherein the plasma device is an inductively coupled plasma device.

Images