JP6865727B2 - Etching method of SiGe layer - Google Patents

Description

The present invention relates to an etching method for a SiGe layer. In particular, the present invention relates to an etching method for a SiGe layer capable of suppressing the generation of etching residues.

Conventionally, a MEMS (Micro Electro Mechanical Systems) acceleration sensor is known which has a movable weight that can be displaced according to a given acceleration and measures the acceleration based on a change in capacitance according to the displacement of the movable weight. (See, for example, Patent Document 1).
In principle, the sensitivity of this MEMS accelerometer increases as the mass of the movable weight increases. Generally, Si is often used as the material for forming the movable weight. However, in order to increase the sensitivity of the MEMS acceleration sensor and at the same time reduce the size, it is preferable to use a material having a higher density than Si as the material for forming the movable weight. SiGe can be exemplified as one of such materials (see, for example, Patent Document 2).

Examples of the method for forming the movable weight made of SiGe include a method of etching the SiGe layer formed on the surface of the substrate according to the desired shape (for example, comb-like shape) and size of the movable weight. The SiGe layer is formed on the surface of the substrate with a thick film 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 the so-called Bosch process method as a method that enables etching of a thick SiGe layer with a high aspect ratio according to the shape and dimensions of the movable weight. In the Bosch process method, an etching process is performed in which a layer to be etched such as Si is etched _{using plasma such as SF 6} gas, and a protective film is formed in a recess formed by the etching process _{using plasma such as C 4} F _{8 gas.} This is a method in which the layer to be etched is deeply etched by alternately repeating 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 layer to be etched was Si, an etching residue was generated. I found out that I would do it.

JP-A-2009-276305 Japanese Unexamined Patent Publication No. 2016-125849 Japanese Unexamined Patent Publication No. 2016-197659

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

In order to solve the above problems, the present inventors have conducted diligent studies.
First, a method of increasing the etching strength by increasing the flow rate of the gas supplied for the etching process of the Bosch process method was examined, but in this method, the etching selectivity is lowered or the side wall of the recess formed is formed. There was a problem that the shape of was inverted tapered.
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 treatment of the Bosch process method was examined, in this method, the shape of the side wall of the recess to be formed is Boeing. There was a problem with the shape.

Therefore, as a result of further diligent studies, the present inventors have found that the generation of etching residues can be suppressed by including _{O 2} gas in the gas supplied for the etching treatment of the Bosch process method. .. Further, 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 is supplied more than 10% It was found that the generation of etching residue can be sufficiently suppressed. The present invention has been completed based on the above findings of the present inventors.
That is, in order to solve the above problems, the present invention includes an etching process in which the SiGe layer formed on the surface of the substrate is etched using plasma, and a protective film is formed in the recesses formed by the etching process using plasma. SF ₆ gas and O ₂ gas are used as gases to be supplied to generate plasma in the etching process, which includes a step of deeply digging and etching the SiGe layer by alternately repeating the protective film forming process. only including, a ratio of the flow rate of _{O 2} gas to the flow rate of SF ₆ gas supplied is 10% or more, to provide an etching method of the SiGe layer, characterized in that.

The method for etching the SiGe layer according to the present invention is a so-called Bosch process method including a step of deeply etching the SiGe layer by alternately repeating an etching process and a protective film forming process. Then, in an etching process, as the gas supplied to generate a plasma, viewed contains a SF ₆ gas and O ₂ gas, the ratio of the flow rate of _{O 2} gas to the flow rate of SF ₆ gas supplied is at least 10% Therefore, as the above-mentioned findings of the present inventors, it is possible to sufficiently suppress the generation of etching residue.

Contact Na, 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 Decreases. Therefore, in order to suppress the generation of etching residue and at the same time suppress the decrease in the etching rate of the SiGe layer, the ratio of the flow rate of O _{2 gas to the flow rate of SF 6} gas to be supplied must be 10% or more and 60% or less. preferable.

The structure of the substrate to which the method for etching the SiGe layer 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 like. An example of a substrate in which Si layers are laminated in this order can be illustrated.

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

It is sectional drawing which shows typically the schematic structure of the plasma etching apparatus and the substrate for carrying out the etching method of the SiGe layer which concerns on one Embodiment of this invention. It is sectional drawing which shows typically the state of the etching residue generated by the conventional etching method. It is a figure which shows the influence _{of the O 2} / SF ₆ flow rate ratio on the etching rate, and the presence / absence of the etching residue 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 ratio of each component shown in each figure may differ from the actual ones.

FIG. 1 is a cross-sectional view schematically showing a schematic configuration of a plasma etching apparatus and a substrate for executing an etching method of a SiGe layer according to an embodiment of the present invention (hereinafter, appropriately simply referred to as an “etching method”). 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 the dimensions in the vertical direction with a large enlargement 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 upper portion and a processing space 12 at the lower portion. The coil 2 is arranged outside the chamber 1 so as to surround the plasma generation space 11. The mounting table 3 is arranged in the processing space 12, and the substrate S to be etched is mounted on the mounting table 3.

As shown in FIG. 1B, the substrate S of the present 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 (top surface). When etching the SiGe layer 10 of the substrate S using the plasma etching apparatus 100, a mask M having a pattern corresponding to a desired shape and dimensions is arranged on the substrate S (on the SiGe layer 10). .. The mask M is formed from, for example, a photoresist.

Further, as shown in FIG. 1A, the plasma etching apparatus 100 includes high-frequency power supplies 4 and 5, impedance matching devices 6 and 7, a gas supply source 8, and an exhaust apparatus 9. The high frequency power supply 4 applies high frequency power to the coil 2 via the impedance matching box 6. The high frequency power supply 5 applies high frequency power to the mounting table 3 via the impedance matching device 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 by using the plasma etching apparatus 100 having the above configuration. Hereinafter, the etching method according to this 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 repeating the etching process and the protective film forming process.

In the etching process, the substrate S is first placed on the mounting table 3, the inside of the chamber 1 is depressurized by the exhaust device 9, and then high-frequency power is applied from the high-frequency power supplies 4 and 5 to the coil 2 and the mounting table 3. _{Etching processing 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 high-frequency power is applied to the coil 2, an induced electric field is generated in the plasma generation space 11, and the etching processing gas is turned into plasma by this induced electric field. On the other hand, when high-frequency power is applied to the mounting table 3, a potential difference is generated between the mounting table 3 and the plasma, and the ions in the plasma move toward the mounting table 3 due to this potential difference. The ions in the plasma collide with the SiGe layer 10 of the substrate S via the mask M, so that the SiGe layer 10 is etched. In the etching process after the protective film forming process, the SiGe layer 10 is etched after the protective film deposited on the bottom surface of the recess is removed first.

Then, in the protective film forming process, the high-frequency power supply 4 to the coil 2 applies a high frequency power, with the protective film forming process gas (in this embodiment with respect to the plasma generation space 11 from the gas supply source 8, C ₄ F ₈ Gas) is supplied. When high-frequency power is applied to the coil 2, an induced electric field is generated in the plasma generation space 11, and the gas for the protective film forming process is turned into plasma by this induced electric field. The generated plasma moves toward the mounting table 3 and is deposited in the recesses of the SiGe layer 10 formed by the etching process, so that a protective film is formed in the recesses of the SiGe layer 10.

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

FIG. 2 shows an electron microscope when the SiGe layer 10 is deeply etched (etching depth is about 10 μm) using the conventional Bosch process method without containing _{O 2 gas in the etching treatment gas (SF 6 gas only).} It is a figure which shows typically the surface near surface cross section of the substrate S observed. FIG. 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 obtained when a line and space having a narrow opening width is formed in the SiGe layer 10. It is a cross-sectional view.
As shown in FIG. 2, when the etching treatment gas _{does not contain O 2} gas, when the SiGe layer 10 is deeply etched by the Bosch process method, a needle-shaped etching residue 10a is generated. If the etching residue 10a is generated, it may adversely affect the mechanical shape and electrical characteristics of the substrate S, which is a problem.

On the other hand, in the etching method according to the present embodiment, since the etching treatment gas contains O ₂ gas, it is possible to suppress the generation of the etching residue 10a.
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 was conducted in which the SiGe layer 10 was deeply etched (etching depth of about 10 μm) for about 3 minutes under the conditions shown in (1) to (4) below.
(1) SF ₆ gas flow _{rate 250 sccm, O 2} gas flow rate 0 to 150 sccm in etching process
(2) Etching process (when removing the protective film deposited on the bottom surface of the recess of the SiGe layer 10) time 1.5 sec, pressure inside the chamber 1 2 Pa, power applied to the coil 2 1500 W, power applied to the mounting table 3 150 W
(3) Etching process (during etching of SiGe layer 10) time 1.1 sec, chamber 1 internal pressure 2 Pa, applied power to coil 2 1500 W, applied power to mounting table 3 20 W
(4) _{Flow rate of C 4} F ₈ gas in protective film forming process 300 sccm, time of protective film forming process 1.2 sec, pressure in chamber 1 3 Pa, electric power applied to coil 2 1500 W, electric power applied to mounting table 3 0 W
Then, _{for each flow rate of the O 2} gas, the presence or absence of 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 showing an example of the above test results. The horizontal axis of FIG. 3 shows the ratio of the flow rate of O _{2 gas to the flow rate of SF 6} gas, and the vertical axis shows the maximum height of the 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, as compared with the case in the etching processing gas does not contain O ₂ gas (SF ₆ Ratio = 0% of the flow rate of O ₂ gas to the flow rate of the gas), the O ₂ gas in the etching processing gas If even a small amount is included (the ratio of the flow rate of O _{2 gas to the flow rate of SF 6} gas ≥ 10%), even if etching residue is generated, its maximum height becomes small and the generation of etching residue can be suppressed. I understood. Furthermore, it was found that the generation of etching residue can be sufficiently suppressed by setting the ratio of the flow rate of O _{2 gas to the flow rate of SF 6 gas to 40% or more.} Specifically, when the flow rate ratio was 40%, the maximum height of the etching residue was 0.2 μm, and when it was 50% and 60%, no etching residue was generated.

A test was also conducted in which the Si layer 30 was deeply etched when the etching treatment gas did not contain _{O 2 gas (SF 6} gas only), but unlike the case of the SiGe layer 10, no etching residue was left. It did not occur.
The reason why the etching residue is not generated in the Si layer 30 and the etching residue is generated in the SiGe layer 10 is that the presence of Ge makes it easy for the CF polymer caused by the _{C 4} F _{8 gas, which is the starting point of the etching residue, to remain.} It is thought that it will be. When the SiGe layer 10 is deeply etched, _{the generation of the etching residue is suppressed by including the O 2} gas in the etching treatment gas because the CF caused by the _{C 4} F ₈ gas, which is the starting point of the etching residue, is suppressed. It is considered that this is because the based polymer is _{ashed with O 2 gas.}
The result shown in FIG. 3 is only 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 power applied to the coil 2 are changed. When was set to 40% or more, the generation of etching residue could be sufficiently suppressed under any condition.

Further, as shown in FIG. 3, if _{the ratio of the flow rate of the O 2} gas is excessively increased, the etching rate of the SiGe layer 10 decreases. Therefore, in order to sufficiently suppress the generation of etching residue and at the same time 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 should be 40% or more and 60% or less. It is preferable to do so.

The etching method according to the present embodiment described above can be applied not only as a method for forming a movable weight of a MEMS acceleration sensor, but also as a method for forming a MEMS pressure sensor or an energy harvester (vibration power generation element), for example. Is.

1 ... Chamber 2 ... Coil 3 ... Mounting stand 10 ... SiGe layer 100 ... Plasma etching equipment S ... Substrate

Claims (2)

By alternately repeating the etching process of etching the SiGe layer formed on the surface of the substrate using plasma and the protective film forming process of forming a protective film using plasma in the recesses formed by the etching process. , Including the step of deep etching the SiGe layer.
In the etching process, as the gas supplied to generate a plasma, viewed contains a SF ₆ gas and O ₂ gas,
The ratio of the flow rate of O ₂ gas to the flow rate of SF ₆ gas to be supplied is 10% or more.
A method for etching a SiGe layer. The ratio of the flow rate of O ₂ gas to the flow rate of SF ₆ gas to be supplied is 60% or less.
The method for etching a SiGe layer according to claim 1.

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