JP5819243B2 - Dry etching method - Google Patents

Description

  The present invention relates to a dry etching method for a semiconductor device, and more particularly to a dry etching method for selectively etching silicon (Si) and silicon germanium (SiGe).

As for selective dry etching of Si and SiGe, a technique in which Si is selectively side-etched using CF ₄ and SiGe is not side-etched, or SiGe is selectively side-etched using CF ₄ / O ₂ / N _2. The technique to do is disclosed (for example, nonpatent literature 1).

Patent Document 1 describes a selective etching method of SiGe using ClF ₃ and XeF ₂ . Further, Patent Document 2 describes a technique for selectively etching SiGe using HF.

Special table 2009-510750 gazette Japanese Patent Laid-Open No. 2003-77888

ECS (The Electrochemical Society) Transactions Vol. 33, No. 6, pages 777-789 (2010) (in particular, page 780, line 13 and page 782, line 1)

  When the above prior art was tested, the selective ratio was sufficiently high when SiGe was selectively etched and Si was not etched, but conversely, the selective ratio was obtained when Si was selectively etched with respect to SiGe. Was found to be inadequate.

  An object of the present invention is to provide a dry etching method capable of etching Si with a sufficiently high selectivity with respect to SiGe by microfabrication of a semiconductor element having a structure in which a Si film and a SiGe film are mixed. The Si film includes a pure Si film, an oxide film, a nitride film, and the like.

  As an embodiment for achieving the above object, in a dry etching method for selectively etching a film to be etched with respect to a silicon germanium film using plasma, germanium is used as an etching gas for etching the film to be etched. A dry etching method is characterized in that the etching target film is etched by adding a contained gas.

  In addition, a step of preparing a substrate to be processed on which a silicon film and a silicon germanium film are formed, and a plasma of a reactive gas in which a gas containing germanium is added to an etching gas for the silicon film are used for the substrate to be processed. And a step of etching the formed silicon film.

  With the above configuration, it is possible to provide a dry etching method capable of etching a film to be etched such as Si with a sufficiently high selectivity with respect to SiGe.

1 is a schematic cross-sectional view showing an example of a dry etching apparatus for carrying out a dry etching method according to a first embodiment of the present invention. It is a schematic sectional drawing of the board | substrate which shows an example of the structure where Si film and SiGe film which are the object of etching are mixed, (a) is the state before an etching, (b) is the state after an etching. GeF ₄ flow rate is a graph showing the number of foreign matters of a relationship between the ratio and 300mm wafers in the total gas flow rate.

As a result of studying a method of etching Si with a sufficiently high selection ratio with respect to SiGe, the inventors have found that it is effective to add a gas containing Ge in addition to a halogen gas which is an etching gas. . By adding a gas containing Ge in addition to halogen, which is an etching gas, it is considered that the etching rate of SiGe is reduced and Si can be selectively etched with respect to SiGe. Note that GeF ₄ , GeF ₂ Cl ₂ , GeCl ₄ , and GeH ₄ can be used as the gas containing Ge.

  Embodiments of the present invention will be described below with reference to the drawings.

  FIG. 1 is a schematic cross-sectional view showing an example of an etching apparatus for performing a dry etching method according to a first embodiment of the present invention, and a microwave plasma etching apparatus using a microwave and a magnetic field as plasma generating means. It is. This apparatus is provided with a chamber 101 capable of evacuating the inside, a sample stage 103 on which a wafer 102 to be processed is placed, a microwave transmitting window 104 such as quartz provided on the upper surface of the chamber 101, and an upper part thereof. A waveguide 105, a magnetron 106, a solenoid coil 107 provided around the chamber 101, an electrostatic adsorption power source 108, and a high frequency power source 109 connected to the sample stage 103 are provided.

The wafer 102 is carried into the chamber 101 from the wafer carry-in port 110 and then electrostatically adsorbed to the sample stage 103 by the electrostatic adsorption power source 108. Next, process gas is introduced into the chamber 101. The inside of the chamber 101 is evacuated by a vacuum pump (not shown) and adjusted to a predetermined pressure (for example, 0.1 Pa to 50 Pa). Next, a microwave having a frequency of 2.45 GHz is oscillated from the magnetron 106 and propagated into the chamber 101 through the waveguide 105. The processing gas is excited by the action of the microwave and the magnetic field generated by the solenoid coil 107, and plasma 111 is formed in the space above the wafer 102. On the other hand, a bias is applied to the sample stage 103 by a high-frequency power source 109, and ions in the plasma 111 are accelerated and incident on the wafer 102 vertically. The surface of the wafer 102 is anisotropically etched by the action of radicals and ions from the plasma 111. In addition, a pulse generator 112 is attached to the magnetron 106 so that the microwave can be pulse-modulated in a pulse shape.







Next, Table 1 shows an example of conditions for etching a wafer with the apparatus of FIG.

Using the conditions in Table 1, as shown in the cross-sectional view of FIG. 2A, the Si film 203 and the SiGe film 202 are alternately mixed as a film to be processed, and a silicon nitride film is used as the mask 201. The wafer (substrate) 204 that was included was etched. The result is shown in FIG. Step 1 in Table 1 is an etching that removes a natural oxide film or the like attached to the sample surface in the initial state and is called breakthrough. This step is not necessary depending on the sample state. Step 2 is a condition for selectively etching the Si film 203 with respect to the SiGe film 202. Since the wafer bias (high frequency bias power) is 0 W, anisotropic etching is not performed, and isotropic etching is performed. As shown in b), the Si film 203 can be side-etched with a sufficiently high selectivity with respect to the SiGe film 202. However, in the structure in which the Si film and the SiGe film are respectively exposed when viewed from above, isotropic etching is not necessarily required. Here, the CH ₄ gas is deposited on the surfaces of the Si film 203 and the SiGe film 202, that is, has a property of suppressing etching. If there are too many fluorine atoms, the SiGe film 202 also undergoes side etching, so the etching rate is increased. It is added for the purpose of adjusting.

  Next, other conditions of this example are shown in Table 2.

Under this condition, H ₂ and CF ₄ are contained instead of CH ₄ , and the same effect can be obtained under this condition.
The reason why the Si film can be selectively plasma-etched with respect to the SiGe film according to this embodiment is considered as follows.

For example, the etching reaction of SiGe with SF ₆ is expressed by (1). Here, when GeF ₄ gas is added to SF ₆ gas, the reaction proceeds in the direction of decreasing GeF ₄ gas due to chemical equilibrium. That is, as the reaction toward the left side of the equation (1) proceeds, a SiGe film is generated. For this reason, when GeF ₄ gas is added to SF ₆ gas, the etching reaction of the SiGe film is suppressed, and the etching rate of SiGe becomes slow.

_{SiGe + 2SF 6 → GeF 4 +} SiF 4 + 2SF 2 - (1)

On the other hand, since the etching reaction of Si by SF ₆ gas is expressed by the equation (2), even if GeF ₄ gas is added to SF ₆ gas, the etching reaction of Si is not affected.

Si + SF ₆ → SiF ₄ + SF ₂ −− (2)

For this reason, the etching rate is Si> SiGe.
Alternatively, a gas containing Ge is obtained the same effect even _{GeF 2 Cl 2, GeCl 4,} GeH 4 is not limited to GeF _4.
In this embodiment, the silicon oxide film (SiO ₂ ) or the silicon nitride film (Si ₃ N ₄ ) can also be selectively etched with respect to the SiGe film. This is considered as follows.
Etching reactions of the silicon oxide film (SiO ₂ ) and the silicon nitride film (Si ₃ N ₄ ) with SF ₆ gas are expressed by the equations (3) and (4), respectively.

SiO ₂ + SF ₆ → SiF ₄ + SF ₂ + O _2- (3)
Si ₃ N ₄ + 3SF ₆ → 3SiF ₄ + 3SF ₂ + 2N ₂ −− (4)

For this reason, even if GeF ₄ gas is added to SF ₆ gas, the etching reaction of the silicon oxide film (SiO ₂ ) and the etching reaction of the silicon nitride film (Si ₃ N ₄ ) are not affected. Therefore, in this embodiment, the silicon oxide film (SiO ₂ ) or the silicon nitride film (Si ₃ N ₄ ) can also be selectively etched with respect to the SiGe film.

  As described above, according to the present embodiment, a dry etching method capable of etching Si with a sufficiently high selectivity with respect to SiGe in microfabrication of a semiconductor element having a structure in which a Si film and a SiGe film are mixed. Can be provided.

  A second embodiment of the present invention will be described with reference to FIG. Note that the matters described in the first embodiment but not described in the present embodiment can be applied to the present embodiment as long as there is no particular circumstance.

In Example 1, when a gas containing Ge such as GeF ₄ was added to the etching gas, a phenomenon that foreign matter was generated during the etching was observed. There is a possibility that the finely processed wiring is disconnected or short-circuited due to the generation of foreign matter. In this embodiment, a highly selective dry etching method capable of reducing the generation of foreign matter will be described. In order to suppress the generation of foreign substances, it seems that a large amount of GeF ₄ gas is not used and a balance with other gases is necessary. FIG. 3 shows the relationship between the ratio of the GeF ₄ gas flow rate to the total gas flow rate and the number of foreign objects on the 300 mm wafer. It can be seen that the amount of foreign matter suddenly increases from the GeF ₄ gas ratio of 15% or more. This is presumably because the Ge reaction product density is increased because GeF ₄ gas is excessively added, and Ge is solidified to become a foreign substance. From the above, the ratio of the gas flow rate containing Ge to the whole is desirably 15% or less, and it may be diluted with Ar or the like so as to be this ratio.

  As described above, according to the present embodiment, the same effect as the embodiment can be obtained. Further, by setting the ratio of the gas flow rate including Ge to 15% or less, it is possible to reduce adhesion of foreign matters to the object to be processed during etching.

DESCRIPTION OF SYMBOLS 101 ... Chamber, 102 ... Wafer, 103 ... Sample stand, 104 ... Microwave transmission window, 105 ... Waveguide, 106 ... Magnetron, 107 ... Solenoid coil, 108 ... Electrostatic adsorption power source, 109 ... High frequency power source, 110 ... Wafer Carry-in port, 111 ... plasma, 112 ... pulse generator, 201 ... mask, 202 ... SiGe film, 203 ... Si film, 204 ... substrate.

Claims (10)

In a dry etching method of selectively plasma etching a silicon- containing film with respect to a silicon germanium film,
A dry etching method, wherein the silicon-containing film is selectively plasma- etched with respect to the silicon germanium film by using plasma generated by a mixed gas of a fluorine-containing gas and a germanium-containing gas. The dry etching method according to claim 1,
A dry etching method, wherein the silicon-containing film is a silicon film , a silicon oxide film, or a silicon nitride film . In the dry etching method according to claim 1 or 2,
Gas, GeF ₄ gas, _GeF 2 Cl ₂ gas, a dry etching method which is a GeCl ₄ gas or GeH ₄ gas containing the germanium. In the dry etching method according to any one of claims 1 to claim 3,
Mixed gas of gas containing gas and germanium containing said fluorine is mixed further Ar gas and CH ₄ gas,
The dry etching method, wherein the fluorine-containing gas is SF ₆ gas. In the dry etching method according to any one of claims 1 to claim 3,
The mixed gas of the gas containing fluorine and the gas containing germanium is further mixed with H ₂ gas ,
The dry etching method, wherein the gas containing fluorine is CF ₄ gas. The dry etching method according to claim 4,
A dry etching method, wherein a ratio of a flow rate of the germanium-containing gas to a total flow rate of the mixed gas of the SF ₆ gas, the germanium-containing gas, the Ar gas, and the CH ₄ gas is 15% or less. The dry etching method according to claim 5,
A dry etching method, wherein a ratio of a flow rate of the germanium-containing gas to a total flow rate of a mixed gas of the CF ₄ gas, the germanium-containing gas, and the H ₂ gas is 15% or less . Preparing a substrate to be processed on which a silicon film that is a pure silicon film, a silicon oxide film, or a silicon nitride film and a silicon germanium film are formed;
Selectively etching the silicon film formed on the substrate to be processed with respect to the silicon germanium film by using plasma of a reaction gas which is a mixed gas of a gas containing fluorine and a gas containing germanium; dry etching method characterized by having a. The dry etching method according to claim 8 ,
The dry etching method characterized in that the etching in the etching step is isotropic etching. In the dry etching method according to claim 8 or 9 ,
The dry etching method according to claim 1, wherein a flow rate of the gas containing germanium is 15% or less with respect to a flow rate of the reaction gas.

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