JP2018133449A - Method for etching silicon germanium layer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for etching a SiGe layer, by which the generation of an etching residue can be suppressed.SOLUTION: A method for etching a SiGe layer 10 according to the present invention comprises the step of deeply etching the SiGe layer by repeatedly performing an etching process for etching a SiGe layer formed on a surface of a substrate S by plasma, and a protection film-forming process for forming, by plasma, a protection film in a concave portion formed by the etching step. In the method according to the present invention, Ogas is involved as a gas to be supplied to generate plasma in the etching step.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a method for etching a SiGe layer. In particular, the present invention relates to a method for etching a SiGe layer that can suppress generation of etching residues.

2. Description of the Related Art Conventionally, a MEMS (Micro Electro Mechanical Systems) acceleration sensor that includes a movable weight that can be displaced according to a given acceleration and measures acceleration based on a change in capacitance according to the displacement of the movable weight is known. (For example, refer to Patent Document 1).
In principle, the sensitivity of the MEMS acceleration sensor increases as the mass of the movable weight increases. In general, Si is often used as a material for forming the movable weight. However, in order to increase the sensitivity of the MEMS acceleration sensor and reduce the size, it is preferable to use a material having a higher density than Si as a material for forming the movable weight. An example of such a material is SiGe (see, for example, Patent Document 2).

As a method of forming a movable weight made of SiGe, there is a method of etching a SiGe layer formed on the surface of the substrate according to a desired shape (for example, comb-tooth shape) and dimensions of the movable weight. The SiGe layer is formed on the surface of the substrate with a thickness of 10 μm or more by, for example, a plasma CVD method (see, for example, Patent Document 3).
Therefore, it is conceivable to apply a so-called Bosch process method as a method that enables a thick SiGe layer to be etched with a high aspect ratio in accordance with the shape and dimensions of the movable weight. In the Bosch process method, an etching process for etching a layer to be etched such as Si using a plasma such as SF ₆ gas, and a protective film is formed using a plasma such as C ₄ F ₈ gas in a recess formed by the etching process. In this method, the layer to be etched is deeply etched by alternately performing the protective film forming process.

  However, when the present inventors examined the application of the Bosch process method as an etching method for the SiGe layer, if the Bosch process method was applied under the same conditions as when the etching target layer was Si, an etching residue was generated. I found out that

JP 2009-276305 A Japanese Patent Laid-Open No. 2006-125849 JP, 2006-197659, A

  The present invention has been made to solve the above-described problems of the prior art, and an object thereof is to provide an SiGe layer etching method capable of suppressing the generation of etching residues.

In order to solve the above problems, the present inventors have conducted intensive studies.
First, although a method for increasing the etching strength by increasing the flow rate of the gas supplied for the etching process of the Bosch process method, etc. was studied, in this method, the etching selectivity is reduced or the side wall of the recess to be formed is formed. There arises a problem that the shape of this becomes a reverse taper shape.
Next, although a method of reducing the protective film formation rate by reducing the flow rate of the gas supplied for the protective film formation process of the Bosch process method was studied, in this method, the shape of the side wall of the recess to be formed is bowing. The problem of becoming a shape occurred.

Therefore, as a result of further intensive studies, the inventors have found that the generation of etching residues can be suppressed by including O ₂ gas in the gas supplied for the etching process of the Bosch process method. The present invention has been completed.
That is, in order to solve the above-described problems, the present invention provides an etching process for etching a SiGe layer formed on the surface of a substrate using plasma, and a protective film is formed using a plasma in a recess formed by the etching process. A step of deeply etching the SiGe layer by alternately performing a protective film forming process to be performed, and the etching process includes O ₂ gas as a gas supplied to generate plasma. A method for etching a SiGe layer is provided.

The SiGe layer etching method according to the present invention is a so-called Bosch process method including a step of deeply etching a SiGe layer by alternately repeating an etching process and a protective film forming process. In the etching process, since O ₂ gas is included as a gas to be supplied to generate plasma, the generation of etching residues can be suppressed as described above by the inventors.

Here, according to the result of the present inventors have studied intensively, if SF ₆ gas contained in the gas supplied to an etching process, the ratio of the flow rate of O ₂ gas to the flow rate of SF ₆ gas supplied 40% From the above, it has been found that the generation of etching residues can be sufficiently suppressed.

Therefore, in the etching process, SF ₆ gas and O ₂ gas are included as the gas supplied to generate plasma, and the ratio of the flow rate of O ₂ gas to the flow rate of the supplied SF ₆ gas is 40% or more. It is preferable.
Incidentally, focusing only on suppressing the generation of etching residue, although O specifically limited not _{two-flow-rate} upper ratio of gas, too increase the ratio of the flow rate of O ₂ gas, the etching rate of the SiGe layer descend. Therefore, also inhibit lowering of the etching rate of the to suppress the generation of etching residue simultaneously SiGe layer, that a ratio of the flow rate of O ₂ gas to the flow rate of SF ₆ gas supplied is less than 60% 40% preferable.

The structure of the substrate to which the SiGe layer etching method according to the present invention is applied is not particularly limited as long as the SiGe layer is formed on the surface, but from the outermost surface, the SiGe layer, the SiO ₂ layer, and The board | substrate laminated | stacked in order of Si layer can be illustrated.

  According to the present invention, it is possible to suppress the generation of etching residues when the SiGe layer is etched.

It is sectional drawing which shows typically the schematic structure of the plasma etching apparatus for performing the etching method of the SiGe layer which concerns on one Embodiment of this invention, and a board | substrate. It is sectional drawing which shows typically the state of the etching residue generate | occur | produced with the conventional etching method. It is a diagram showing the effect of _O 2 / SF ₆ flow rate ratio etching residue of occurrence or non-occurrence and the etching rate of the SiGe layer.

Hereinafter, an embodiment of the present invention will be described with reference to the drawings as appropriate.
For convenience of explanation, the dimensions and scale ratios of the components shown in the drawings may be different from actual ones.

FIG. 1 is a cross-sectional view schematically showing a schematic configuration of a plasma etching apparatus and a substrate for performing a SiGe layer etching method (hereinafter, simply referred to as “etching method” as appropriate) according to an embodiment of the present invention. is there. FIG. 1A is a schematic configuration diagram of a plasma etching apparatus, and FIG. 1B is a schematic configuration diagram of a substrate. FIG. 1B shows a greatly enlarged dimension in the vertical direction for convenience.
As shown in FIG. 1A, the plasma etching apparatus 100 includes a chamber 1, a coil 2, and a mounting table 3. The chamber 1 is provided with a plasma generation space 11 at the top and a processing space 12 at the bottom. The coil 2 is disposed outside the chamber 1 so as to surround the plasma generation space 11. The mounting table 3 is disposed in the processing space 12, and a substrate S to be etched is mounted thereon.

As shown in FIG. 1B, the substrate S of this embodiment is formed by laminating the SiGe layer 10, the SiO ₂ layer 20, and the Si layer 30 in this order from the outermost surface (uppermost surface). When etching the SiGe layer 10 of the substrate S using the plasma etching apparatus 100, a mask M on which a pattern corresponding to a desired shape and size is formed is disposed on the substrate S (on the SiGe layer 10). . The mask M is formed from, for example, a photoresist.

  As shown in FIG. 1A, the plasma etching apparatus 100 includes high-frequency power sources 4 and 5, impedance matching units 6 and 7, a gas supply source 8, and an exhaust device 9. The high frequency power source 4 applies high frequency power to the coil 2 via the impedance matching unit 6. The high frequency power source 5 applies high frequency power to the mounting table 3 via the impedance matching unit 7. The gas supply source 8 supplies a gas for generating plasma to the plasma generation space 11. The exhaust device 9 exhausts the gas in the chamber 1 (plasma generation space 11 and processing space 12) to the outside of the chamber 1.

The etching method according to the present embodiment is executed using the plasma etching apparatus 100 having the above configuration. Hereinafter, the etching method according to the present embodiment will be described.
The etching method according to the present embodiment includes a step of deeply etching the SiGe layer 10 of the substrate S by alternately and repeatedly performing an etching process and a protective film forming process.

In the etching process, first, the substrate S is placed on the mounting table 3, and after the chamber 1 is decompressed by the exhaust device 9, high-frequency power is applied from the high-frequency power sources 4 and 5 to the coil 2 and the mounting table 3, Etching gas (SF ₆ gas and O ₂ gas in this embodiment) is supplied from the gas supply source 8 to the plasma generation space 11. When the high frequency power is applied to the coil 2, an induced electric field is generated in the plasma generation space 11, and the etching process gas is turned into plasma by the induced electric field. On the other hand, when a high frequency power is applied to the mounting table 3, a potential difference is generated between the mounting table 3 and the plasma, and ions in the plasma move toward the mounting table 3 due to the potential difference. The ions in the plasma collide with the SiGe layer 10 of the substrate S through the mask M, so that the SiGe layer 10 is etched. In the etching process after the protective film formation process, the SiGe layer 10 is etched after the protective film previously deposited on the bottom surface of the recess is removed.

Next, in the protective film forming process, high frequency power is applied from the high frequency power source 4 to the coil 2, and a protective film forming process gas (in this embodiment, C ₄ F ₈ is applied to the plasma generation space 11 from the gas supply source _8. Gas). When high frequency power is applied to the coil 2, an induction electric field is generated in the plasma generation space 11, and the protective film forming gas is turned into plasma by the induction electric field. The generated plasma moves toward the mounting table 3 and deposits in the recesses of the SiGe layer 10 formed by the etching process, whereby a protective film is formed in the recesses of the SiGe layer 10.

  Since the etching method according to the present embodiment employs a so-called Bosch process method in which the above-described etching process and the protective film forming process are alternately repeated, the SiGe layer 10 can be etched deeply. is there.

FIG. 2 shows an electron microscope in which the etching gas does not contain O ₂ gas (only SF ₆ gas) and the SiGe layer 10 is etched deeply (etching depth is about 10 μm) using the conventional Bosch process method. It is a figure which shows typically the surface vicinity cross section of the board | substrate S observed. 2A is a schematic cross-sectional view obtained when a wide opening is formed in the SiGe layer 10, and FIG. 2B is a schematic view obtained when a line and space having a narrow opening width is formed in the SiGe layer 10. It is sectional drawing.
As shown in FIG. 2, when the etching gas does not contain O ₂ gas, if the SiGe layer 10 is deeply etched by the Bosch process method, a needle-like etching residue 10a is generated. The generation of the etching residue 10a is a problem because it may adversely affect the mechanical shape and electrical characteristics of the substrate S.

On the other hand, since the etching method according to the present embodiment includes O ₂ gas in the etching processing gas, generation of the etching residue 10a can be suppressed.
Hereinafter, the effect of the etching process gas containing O ₂ gas, and O ₂ preferred flow (preferred flow ratio of O ₂ gas to the flow rate of SF ₆ gas) of the gas on the results of examination will be described.

Using the plasma etching apparatus 100, a test for deep etching (etching depth of about 10 μm) of the SiGe layer 10 was performed for about 3 minutes under the conditions shown in the following (1) to (4).
(1) SF ₆ gas flow rate 250 sccm, O ₂ gas flow rate 0-150 sccm in the etching process
(2) Time of etching process (when removing the protective film deposited on the bottom of the recess of the SiGe layer 10) is 1.5 seconds, the pressure in the chamber 1 is 2 Pa, the applied power to the coil 2 is 1500 W, and the applied power to the mounting table 3 is 150 W.
(3) Time of etching process (during etching of the SiGe layer 10) 1.1 sec, pressure in the chamber 1 2 Pa, applied power 1500 W to the coil 2, applied power 20 W to the mounting table 3
(4) The flow rate of C ₄ F ₈ gas in the protective film forming process is 300 sccm, the protective film forming process time is 1.2 sec, the pressure in the chamber 1 is 3 Pa, the applied power to the coil 2 is 1500 W, and the applied power to the mounting table 3 is 0 W.
Then, for each flow rate of O ₂ gas, the presence or absence of the etching residue after deep etching and the maximum height of the etching residue were observed with an electron microscope, and the etching rate of the SiGe layer 10 was evaluated.

FIG. 3 is a diagram illustrating an example of the test result. The horizontal axis in FIG. 3 represents the ratio of the flow rate of O ₂ gas to the flow rate of SF ₆ gas, and the vertical axis represents the maximum height of etching residue and the etching rate of the SiGe layer 10. In FIG. 3, the data plotted with “□” indicates the maximum height of the etching residue, and the data plotted with “◯” indicates the etching rate.
As shown in FIG. 3, compared with the case where the etching gas does not contain O ₂ gas (ratio of the flow rate of O ₂ gas to the flow rate of SF ₆ gas = 0%), O ₂ gas is used as the etching gas. If even a little is included (the ratio of the flow rate of O ₂ gas to the flow rate of SF ₆ gas ≧ 10%), even if an etching residue is generated, the maximum height is reduced, and the generation of the etching residue can be suppressed. I understood. Furthermore, it has been found that if the ratio of the O ₂ gas flow rate to the SF ₆ gas flow rate is 40% or more, the generation of etching residues can be sufficiently suppressed. Specifically, when the flow rate ratio was 40%, the maximum height of etching residue was 0.2 μm, and when 50% and 60%, no etching residue was generated.

In addition, when the etching gas does not contain O ₂ gas (only SF ₆ gas), a test for deep etching of the Si layer 30 was also performed. Unlike the case of the SiGe layer 10, the etching residue was completely Did not occur.
The etching residue is not generated in the Si layer 30 and the etching residue is generated in the SiGe layer 10 because of the presence of Ge, the CF-based polymer derived from the C ₄ F ₈ gas that is the starting point of the etching residue is likely to remain. It is thought that this is because. Then, when the SiGe layer 10 is deeply etched, the generation of etching residues is suppressed by including O ₂ gas in the etching process gas because the CF caused by the C ₄ F ₈ gas that is the starting point of the etching residues. This may be because the polymer is ashed with O ₂ gas.
The result shown in FIG. 3 is merely an example, and the ratio of the flow rate of O ₂ gas to the flow rate of SF ₆ gas to be supplied even if various conditions such as the flow rate of SF ₆ gas and the applied power to coil 2 are variously changed. If the content is 40% or more, the generation of etching residues can be sufficiently suppressed under any conditions.

Moreover, as shown in FIG. 3, when the ratio of the flow rate of the O ₂ gas is excessively increased, the etching rate of the SiGe layer 10 is decreased. For this reason, in order to sufficiently suppress the generation of etching residues and to suppress the decrease in the etching rate of the SiGe layer 10, the ratio of the flow rate of O ₂ gas to the flow rate of SF ₆ gas to be supplied is set to 40% or more and 60% or less. It is preferable to do.

  The etching method according to the present embodiment described above can be applied as a method for forming a MEMS pressure sensor or an energy harvester (vibration power generation element) in addition to a method for forming a movable weight of a MEMS acceleration sensor. It is.

DESCRIPTION OF SYMBOLS 1 ... Chamber 2 ... Coil 3 ... Mounting stand 10 ... SiGe layer 100 ... Plasma etching apparatus S ... Substrate

Claims (3)

By alternately and repeatedly performing an etching process for etching the SiGe layer formed on the surface of the substrate using plasma and a protective film forming process for forming a protective film using plasma in the recesses formed by the etching process. And deep etching the SiGe layer,
In the etching process, as a gas supplied to generate plasma, O ₂ gas is included.
An SiGe layer etching method characterized by the above. In the etching process, SF ₆ gas and O ₂ gas are included as the gas supplied to generate plasma,
The ratio of the flow rate of O ₂ gas to the flow rate of SF ₆ gas to be supplied is 40% or more.
The method of etching a SiGe layer according to claim 1. The substrate is laminated in the order of the SiGe layer, the SiO ₂ layer, and the Si layer from the outermost surface.
The method for etching a SiGe layer according to claim 1 or 2, wherein:

Images