JP2016207753A - Plasma etching method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a high selection ratio with a mask material and a high etching rate, by suppressing sub-trench occurring in the bottom face of a trench or the side-etch occurring in the trench sidewall, in the plasma etching method for forming a trench in a silicon carbide substrate.SOLUTION: A plasma etching method for etching a silicon carbide substrate by using plasma has a first etching step and a second etching step. In the first etching step, mixture gas of SFgas, Ogas, and Ar gas is introduced to an etching processing chamber and plasma is generated, and a processed substrate using the silicon carbide substrate as the substrate material is etched. In the second etching step, plasma is generated using the mixture gas, and the processed substrate is etched by applying continuous high frequency power thereto.SELECTED DRAWING: Figure 8

Description

  The present invention relates to a plasma etching method, and particularly to a technique effective for controlling etching processing of a substrate such as a silicon carbide substrate having high hardness.

  In the field of semiconductors, a silicon substrate (Si substrate) is widely used as a substrate material, but in recent years, a silicon carbide substrate (SiC substrate) having better physical properties than this silicon substrate has attracted attention.

  However, since the silicon carbide substrate has a high physical hardness and is chemically stable, it is difficult to control the etching process and it is not easy to obtain a desired etching shape.

  Therefore, as a method for etching a silicon carbide substrate, Patent Document 1 discloses that a deep trench etching exceeding 10000 nm is a highly practical process, and an acute angle that causes an electric field concentration at the bottom of the trench to affect the breakdown voltage characteristics. There has been disclosed a plasma etching method that can be shaped flat without forming an uneven shape having a thickness.

This plasma etching includes a mask forming step of forming a silicon oxide film (SiO ₂ film) having a mask pattern of a predetermined shape on the surface of the silicon carbide substrate, and heating the silicon carbide substrate to 70 to 100 ° C. Using the film as a mask, a first etching step of plasma-etching the silicon carbide substrate with a mixed gas of SF ₆ gas, O ₂ gas and Ar gas, and heating the silicon carbide substrate to 70 to 100 ° C., the silicon oxide film As a mask, a second etching step of performing plasma etching on the silicon carbide substrate with a mixed gas of O ₂ gas and Ar gas is sequentially performed.

  Patent Document 2 discloses a plasma etching method that can suppress the formation of a sub-trench at the bottom of the trench while improving the flatness of the side surface of the trench. This plasma etching method includes a step of forming an etching mask made of a material having an amorphous structure or a polycrystalline structure on a surface of a silicon carbide substrate, and a surface of the silicon carbide substrate on which the etching mask is formed contains HBr gas. An etching gas is supplied.

Further, in Patent Document 3, a silicon carbide substrate is heated to 200 ° C. or more, and a silicon-based gas containing SiF ₄ gas or SiCl ₄ gas and a mixed gas containing O ₂ gas or N ₂ gas are supplied into the processing chamber. There has been disclosed a plasma etching method that suppresses the formation of a bowing shape and a sub-trench while forming a plasma and forming a silicon oxide film or a silicon nitride film as a protective film on the silicon carbide substrate.

Patent Document 4 discloses a method of plasma-etching a silicon carbide substrate on which a mask pattern made of a silicon oxide film is formed using a mixed gas of SF ₆ gas, O ₂ gas, and SiF ₄ gas. ing. In this technique, since the proportion of the added SiF ₄ gas to the total flow rate of SF ₆ gas and O ₂ gas and SiF ₄ gas below 40% 18.9%, to improve the selection ratio of the silicon oxide film Meanwhile, the shape processing accuracy of the silicon carbide substrate is improved.

JP 2008-294210 A JP 2010-3988 A JP 2013-239757 A JP 2014-44975 A

  However, in Patent Document 1, etching is performed in two stages, a first etching process and a second etching process, and a sub-trench is formed at the bottom of the trench only by the first etching process.

For this reason, the bottom of the trench is flattened in the second etching step, but the bottom of the trench is not flattened in any state, and the proportion of O ₂ gas in the mixed gas containing SF ₆ gas and O ₂ gas Depending on the case, the sub-trench at the bottom of the trench may become large, or the trench side wall may be greatly etched, resulting in a bowing shape.

Moreover, in patent document 2 and patent document 3, formation of the sub-trench in the trench bottom is suppressed by supplying an etching gas containing HBr gas. Alternatively, a silicon carbide substrate is heated to 200 ° C. or higher, and a silicon-based gas containing SiF ₄ gas or SiCl ₄ gas and an etching gas containing O ₂ gas or N ₂ gas are supplied to form a bowing shape or a sub-trench. Is suppressed.

  However, the reaction product generated by the HBr gas is likely to adhere to the trench sidewall and cannot be reproduced, or when the silicon carbide substrate is heated to 200 ° C. or higher, side etching progresses to the sidewall in some cases, resulting in a bowing shape. There is a problem that control is difficult.

In Patent Document 4, the trench shape is formed while improving the selectivity with respect to the mask by adding SiF ₄ gas. However, depending on the ratio of SiF ₄ gas, the etching rate of the silicon carbide substrate decreases, and a desired shape is obtained. There is a possibility that it cannot be etched to the depth.

  An object of the present invention is to suppress a side etch generated in a sub-trench and a trench side wall generated in a bottom surface of a trench in a plasma etching method for forming a trench in a silicon carbide substrate, and to provide a high selectivity with a mask material and a high etching rate. It is to provide a technique that can be obtained.

  The above and other objects and novel features of the present invention will be apparent from the description of this specification and the accompanying drawings.

  Of the inventions disclosed in the present application, the outline of typical ones will be briefly described as follows.

That is, a typical plasma etching method includes a first etching step in which a mixed gas of SF ₆ gas, O ₂ gas, and Ar gas is introduced into an etching process chamber to generate plasma and etch a substrate to be processed; A second etching step of generating plasma using the mixed gas and applying continuous high-frequency power to the substrate to be processed to etch the substrate to be processed.

  In the first etching step, pulse-modulated high frequency power is applied to the substrate to be processed. In particular, the substrate material of the substrate to be processed is silicon carbide.

  Among the inventions disclosed in the present application, effects obtained by typical ones will be briefly described as follows.

  Etching processing can be controlled with high accuracy on a substrate to be processed having high hardness.

It is explanatory drawing which shows an example of the structure in the plasma etching apparatus by Embodiment 1. FIG. It is explanatory drawing which shows an example of the structure of the to-be-processed substrate etched by the plasma etching apparatus of FIG. It is sectional drawing of the to-be-processed substrate of FIG. 2 patterned. By plasma etching to the flow rate of O ₂ gas and SF ₆ gas is an explanatory diagram showing an example of a trench shape. It is explanatory drawing which shows an example of the dependence of the trench shape with respect to a duty ratio. It is explanatory drawing which showed an example of the relationship between the etching amount by which a silicon carbide substrate is etched in a 1st etching process, and the processing time which etches a silicon carbide substrate to 2000 nm. It is explanatory drawing which shows an example of the etching shape at the time of implementing the 2nd etching process with respect to the etching amount of a 1st etching process. It is explanatory drawing which shows an example of the etching conditions in the 1st etching process by Embodiment 1, and a 2nd etching process. SiF ₄ is an explanatory diagram showing the relationship between the selectivity of the ratio between the silicon carbide film / silicon oxide film to the total flow rate of the gas. To the total flow rate of SiF ₄ gas is an explanatory diagram showing an example of etching shape. It is explanatory drawing which shows an example of the etching conditions in the 1st etching process by Embodiment 2, and a 2nd etching process.

  In the following embodiments, when it is necessary for the sake of convenience, the description will be divided into a plurality of sections or embodiments. However, unless otherwise specified, they are not irrelevant to each other. There are some or all of the modifications, details, supplementary explanations, and the like.

  Further, in the following embodiments, when referring to the number of elements (including the number, numerical value, quantity, range, etc.), especially when clearly indicated and when clearly limited to a specific number in principle, etc. Except, it is not limited to the specific number, and may be more or less than the specific number.

  Further, in the following embodiments, the constituent elements (including element steps and the like) are not necessarily indispensable unless otherwise specified and apparently essential in principle. Needless to say.

  Similarly, in the following embodiments, when referring to the shape, positional relationship, etc. of components, etc., the shape of the component is substantially the case unless it is clearly specified and the case where it is clearly not apparent in principle. And the like are included. The same applies to the above numerical values and ranges.

  In all the drawings for explaining the embodiments, the same members are denoted by the same reference symbols in principle, and the repeated explanation thereof is omitted.

<Overview>
In a typical plasma etching method according to the present embodiment, plasma is generated using a mixed gas of SF ₆ gas, O ₂ gas and Ar gas, and the temperature of the sample stage installed in the processing chamber is controlled to 40 to 150 ° C. To do. In addition, a first etching step in which an etching amount is set to 150 to 250 nm by applying a high-frequency bias having a duty ratio of 20 to 50% at a temporally modulated intermittent frequency of 1 kHz to 2 MHz, and SF ₆ Plasma is generated using a mixed gas such as gas, O ₂ gas, and Ar gas, and a second etching process is performed in sequence by applying a continuous high-frequency bias to the silicon carbide substrate to obtain a desired etching amount.

  Hereinafter, embodiments will be described in detail.

(Embodiment 1)
<Configuration example of plasma etching equipment>
FIG. 1 is an explanatory diagram showing an example of the configuration of the plasma etching apparatus according to the first embodiment. In this embodiment, as a technique for forming plasma, a microwave etching apparatus using a microwave and a magnetic field is shown.

  As shown in FIG. 1, the plasma etching apparatus has a cylindrical etching chamber 101 made of aluminum or stainless steel, and has a sample stage 109 on which a substrate 110 to be processed is placed.

In the etching chamber 101, SF ₆ (sulfur hexafluoride, hereinafter referred to as SF ₆ ) gas, O ₂ (oxygen, hereinafter referred to as O ₂ ) gas is introduced into the etching chamber 101 through a porous structure, for example, a transmission window 107 made of quartz. An etching gas which is a mixed gas such as a gas, Ar (argon, hereinafter referred to as Ar), and SiF ₄ (silicon tetrafluoride, hereinafter referred to as SiF ₄ ) gas is supplied.

  Further, the microwave oscillated by the microwave generator 102 is transmitted through the matching unit 103 and the waveguide 104, and the microwave is propagated to the etching processing chamber 101 through the microwave introduction window 105, so that the etching processing chamber is used. The etching gas supplied to 101 is turned into plasma.

  The solenoid coil 108 for generating a magnetic field is disposed around the etching processing chamber 101, and an electron cyclotron resonance (ECR) is generated by the interaction between the generated magnetic field and the incident microwave. Generated and has a structure capable of forming high density plasma.

  The etching processing chamber 101 has a sample stage 109. A substrate 110 to be processed is placed on the sample stage 109, and the substrate to be processed is generated by gas plasma generated by a microwave and a magnetic field generated by the solenoid coil 108. 110 is plasma etched.

  A high frequency power source 111 is connected to the sample stage 109 on which the substrate to be processed 110 is placed. The high frequency power supply 111 supplies a high frequency bias power of about 400 kHz to 13.56 MHz to the sample stage 109.

  The high-frequency power source 111 includes a pulse generator (not shown), and applies a TM (Time Moderation) bias that is time-modulated intermittent high-frequency power or a CW (Continuous Wave) bias that is continuous high-frequency power. The sample is selectively supplied to the sample stage 109.

  An electrostatic adsorption force is generated on the surface of the sample table 109 by applying a DC voltage from the electrostatic adsorption power source 112, and the substrate to be processed 110 is adsorbed on the surface of the sample table 109 by the electrostatic adsorption force.

In addition, a groove is formed on the surface of the sample table 109, and a He gas is supplied from the cooling gas supply port 113 to a channel (not shown) formed between the back surface of the substrate 110 to be processed adsorbed on the surface of the sample table 109. (Helium, hereinafter referred to as He) A cooling gas such as gas, Ar gas, or O ₂ gas is supplied to maintain the inside of the flow path at a predetermined pressure.

  The temperature rise on the surface of the substrate to be processed 110 is transferred to the surface of the sample table 109 by gas heat transfer in the flow path and heat conduction from the contact surface, and is maintained at a constant temperature.

  In order to maintain the substrate 110 to be processed at a predetermined temperature, a refrigerant controlled to a predetermined temperature by the chiller unit 114 is circulated in a refrigerant circulation path (not shown) embedded in the sample table 109.

  An insulating cover (not shown) made of ceramics or quartz is disposed around the substrate to be processed 110. Note that the etching gas introduced into the etching chamber 101 is exhausted outside the etching chamber 101 by the exhaust pump 115 and an exhaust pipe (not shown) during the plasma etching process.

  Next, an etching method using the plasma etching apparatus shown in FIG. 1 will be described.

<Example of substrate structure>
First, the structure of the substrate 110 to be processed will be described with reference to FIG.

  FIG. 2 is an explanatory view showing an example of the structure of the substrate to be processed 110 etched by the plasma etching apparatus of FIG.

  As shown in FIG. 2, the substrate 110 to be processed has a silicon oxide film 202 and a photoresist film 201 patterned in advance by a lithography technique or the like formed on a silicon carbide substrate 203.

<Example of hard mask formation>
Next, a method for forming a hard mask will be described. If the silicon carbide substrate 203 is etched using the photoresist film 201 as a mask, the etching cannot be performed to a desired depth due to insufficient selectivity with the mask. Therefore, the silicon carbide substrate 203 is generally etched using a hard mask such as the silicon oxide film 202.

After forming the pattern of the photoresist film 201, the silicon oxide film 202 is dry-etched using the photoresist film 201 as a mask by a plasma etching apparatus. CF ₄ (tetrafluoromethane, hereinafter referred to as CF ₄ ) gas and CHF ₃ (hereinafter referred to as CHF ₃ ) gas are introduced into the etching chamber 101, and microwave power and high frequency power at a predetermined pressure are introduced. Is applied for etching.

The aperture size of the patterned mask is 1000 nm in the present embodiment. After dry etching of the silicon oxide film 202, the remaining photoresist film 201 is removed with plasma O ₂ gas in an ashing chamber, and the silicon patterned on the silicon carbide substrate 203 as shown in FIG. An oxide film 202 is formed. 3 is a cross-sectional view of the patterned substrate 110 of FIG. 2 that has been patterned.

<Example of etching>
Next, an etching method for forming a deep trench shape exceeding 2000 nm with respect to the silicon carbide substrate 203 will be described. In this etching process, plasma etching of the silicon carbide substrate 203 is performed by changing etching conditions in two stages.

First, the silicon carbide substrate 203 patterned with the silicon oxide film 202 is carried into the etching chamber 101 and placed on the sample stage 109. Thereafter, the first etching process and the second etching process are sequentially performed by controlling the supply flow rates of SF ₆ gas, O ₂ gas, and Ar gas supplied into the etching chamber 101.

  The first etching step is an etching step in which there is no sub-trench on the bottom surface of the trench and the etching side wall is perpendicular to the bottom surface and the etching amount is 150 to 250 nm. The second etching step is an etching step in which an etching amount is set to 2000 nm or more, in which a protective film is formed, there is no sub-trench at the bottom of the trench, and the trench side wall is perpendicular to the bottom.

In the first etching step described above, the silicon carbide substrate 203 is controlled to a temperature of about 40 ° C. to 150 ° C., and SF ₆ gas, O ₂ gas, and Ar gas are respectively supplied from the gas introduction unit 106 into the etching processing chamber 101. To do. Then, the inside of the etching chamber 101 is set to a predetermined pressure by the exhaust pump 115, and high frequency bias power is supplied to the sample stage 109 by the high frequency power source 111.

The flow rate of O ₂ gas, the ratio to the total flow rate of the SF ₆ gas, O ₂ gas, Ar gas is 10% or less, the flow rate of SF ₆ gas, SF ₆ gas, O ₂ gas, the total of the Ar gas The ratio to the flow rate is preferably 5% or less.

FIG. 4 is an explanatory view showing an example of a trench shape by plasma etching with respect to the flow rates of O ₂ gas and SF ₆ gas.

For example, when the supply flow rate of O ₂ gas is large, as shown in FIG. In addition, when the supply flow rate of SF ₆ gas is large, it becomes a bowing shape as shown in FIG.

  In addition, since the silicon carbide substrate 203 has a shorter interatomic distance and higher binding energy than a silicon substrate, a large amount of energy must be applied for etching, and a higher high-frequency bias power is required than when etching a silicon substrate. I need it. However, when etching is performed with high high frequency bias power, a sub-trench is generated at the bottom of the trench as shown in FIG.

  The reason why these etching shapes are not preferable is that when an insulating film or an electrode is embedded in the trench in the next step, a nest is generated and the thickness of the sidewall becomes non-uniform, resulting in electric field concentration and stress, This is because the reliability is lowered and all of them lead to product defects.

  Therefore, an intermittent high frequency power obtained by temporally modulating the high frequency bias power, that is, a TM bias that is a pulse-modulated high frequency power is applied to the silicon carbide substrate 203. As a result, ions that are incident with high perpendicularity are generated, the deposition time of the reaction product is controlled by the duty ratio of the TM bias and the period of application, and the sub-trench generated on the bottom surface of the silicon carbide substrate 203 is suppressed. Can do. The duty ratio is a ratio of the application time to the total time, where the total time for applying and stopping the high frequency bias power is 100%.

  FIG. 5 is an explanatory diagram showing an example of the dependency of the trench shape on the duty ratio. FIG. 5 (a) shows a case where the duty ratio is 20%, and FIG. 5 (b) shows a duty ratio of 50%. FIG. 5C shows the case of a duty ratio of 100%, that is, a continuous high frequency power CW bias.

  The power power at this time is all 150 W. FIG. 5D shows a trench shape having a power of 30 W with a CW bias as a comparative example of the application method. This corresponds to the TM bias power of 150 W and the average bias power of 20% duty ratio in FIG.

  From the results shown in FIGS. 5A and 5B, when the duty ratio is 20 to 50%, there is no sub-trench on the bottom surface of the trench, and an etching shape in which the trench side wall is perpendicular to the bottom surface is obtained. Further, from the results of FIG. 5C and FIG. 5D, in the CW bias, a sub-trench was generated on the bottom surface of the trench regardless of the power value.

  The reason why the sub-trench generated on the bottom surface of the trench can be suppressed at the TM bias duty ratio of 20 to 50% is not clear at present, but the following mechanism is assumed.

  The generation of the sub-trench generally causes ions to concentrate and enter the vicinity of the side wall of the bottom surface of the trench due to the reflection of ions on the side wall of the pattern. Therefore, as shown in FIG. Is greater than the central portion of the bottom of the trench.

  Therefore, in the case of intermittent TM bias modulated in time, since the bias application becomes intermittent, when the bias is applied, the same etching proceeds as described above, but when the bias is stopped, the incidence of ions disappears. The concentration of ions near the side wall is also reduced. Furthermore, during this bias stop period, reaction products generated by etching adhere to the bottom surface of the trench and serve as protection for the bottom surface of the trench. Therefore, even if ions are concentrated during bias application, uneven etching can be prevented. . Needless to say, the smaller the duty ratio is, the more the reaction product adheres to the bottom surface of the trench, so the number of sub-trench decreases.

  However, if the power power of the high-frequency bias is constant and the duty ratio is reduced, the application time of the high-frequency bias power is reduced, so that the etching rate of the silicon carbide substrate 203 is slowed down and can be applied to actual semiconductor device production. It was difficult.

  Therefore, it has been found that a method for controlling the high-frequency bias power applied to the sample stage 109 in two or more steps is effective. That is, in the first etching step, in order to suppress the sub-trench, intermittent TM bias modulated with time is applied to etch the silicon carbide substrate 203 to 150 to 250 nm.

  In the second etching step, in order to obtain a fast etching rate, a continuous CW bias is applied and the silicon carbide substrate 203 is etched to 2000 nm or more. Thereby, the silicon carbide substrate 203 applied to productivity can be etched.

  FIG. 6 is an explanatory diagram showing an example of the relationship between the etching amount by which the silicon carbide substrate 203 is etched in the first etching step and the processing time for etching the silicon carbide substrate 203 to 2000 nm.

  In FIG. 6, the silicon carbide substrate 203 is etched in two stages. From this figure, the larger the etching amount in the first etching step, the longer the processing time up to 2000 nm. When the etching amount exceeds 250 nm, the etching rate of the silicon carbide substrate 203 becomes 300 nm / min or less. Therefore, if the amount of etching in the first etching process is too large, the productivity of the device will be hindered.

  FIG. 7 is an explanatory diagram illustrating an example of an etching shape when the second etching process is performed with respect to the etching amount of the first etching process. FIG. 7A shows the case where the etching amount is 50 nm, and FIG. 7B shows the case where the etching amount is 150 nm. FIG. 7C shows the case where the etching amount is 250 nm.

<Etching conditions>
Moreover, FIG. 8 is explanatory drawing which shows an example of the etching conditions in the 1st etching process by this Embodiment 1, and a 2nd etching process.

  When the etching amount was 150 to 250 nm, there was no sub-trench on the bottom surface of the trench, and an etching shape in which the trench side wall was perpendicular to the bottom surface was obtained. Therefore, if a vertical etching shape without a sub-trench is formed at the initial stage of etching, it is possible to suppress sub-trench and bowing even if a continuous CW bias is applied thereafter.

For example, as shown in FIG. 8, in the first etching step, a mixed gas of SF ₆ gas 14 ml / min, O ₂ gas 20 ml / min, and Ar gas 250 ml / min is used, and application of high-frequency bias power is performed. The method is TM, and the silicon carbide substrate 203 is etched to 150 nm under etching conditions of a high frequency bias power of 150 W, a duty ratio of 20%, and a frequency of 2000 Hz. The etching time at this time is calculated by examining the etching rate of the silicon carbide substrate 203 in advance.

Subsequently, in the second etching step, as shown in FIG. 8, a mixed gas of SF ₆ gas 14 ml / min, O ₂ gas 20 ml / min, and Ar gas 250 ml / min is used. The application method of the high frequency bias power is CW, and the silicon carbide substrate 203 is etched to 2000 nm under the etching conditions of the high frequency bias power of 300 W. The etching time at this time is calculated by examining the etching rate of the silicon carbide substrate 203 in advance.

  By such plasma etching, as shown in FIG. 7B, a trench shape having an etching amount of 2000 nm can be obtained in which there is no sub-trench at the bottom of the trench and the trench side wall is perpendicular to the bottom.

  As described above, side etching that occurs on the sidewall of the trench can be suppressed. Moreover, it becomes possible to obtain a high selectivity with the mask material and a high etching rate. Thereby, highly accurate etching processing control can be performed.

(Embodiment 2)
In the second embodiment, another etching method using the plasma etching apparatus shown in FIG. 1 of the first embodiment will be described.

<Example of substrate structure>
First, the structure of the substrate to be processed 110 will be described. The substrate 110 to be processed is the same as in FIG. 2 of the first embodiment, and a silicon oxide film 202 and a photoresist film 201 previously patterned by a lithography technique or the like are formed on a silicon carbide substrate 203. .

  Next, a method for forming a hard mask will be described.

This is the same as in the first embodiment, and after the patterning of the photoresist film 201, the silicon oxide film 202 is dry etched using the photoresist film 201 as a mask by the plasma etching apparatus of FIG. Etching is performed by introducing CF ₄ gas and CHF ₃ gas into the etching chamber 101 and applying microwave power and high frequency power at a predetermined pressure.

The aperture size of the patterned mask is, for example, 1000 nm. After the dry etching of the silicon oxide film 202, the remaining photoresist film 201 is removed from the plasma O ₂ gas in the ashing chamber, and the silicon patterned on the silicon carbide substrate 203 as shown in FIG. An oxide film 202 is formed.

<Example of etching>
Next, an etching method for forming a deep trench shape exceeding 2000 nm with respect to the silicon carbide substrate 203 will be described. Also here, as in the first embodiment, plasma etching of the silicon carbide substrate 203 is characterized in that the etching conditions are changed in two stages.

First, the silicon carbide substrate 203 patterned with the silicon oxide film 202 is carried into the etching chamber 101 and placed on the sample table 109. Thereafter, the first and second etching steps are performed by controlling the supply flow rates of SF ₆ gas, O ₂ gas, and Ar gas supplied into the etching chamber 101.

  The first etching step is a step in which there is no sub-trench on the bottom surface of the trench and the trench side wall is perpendicular to the bottom surface, and the etching amount is 150 to 250 nm. The second etching step is a trench while forming a protective film. This is an etching process in which there is no sub-trench on the bottom surface and the trench sidewall is perpendicular to the bottom surface and the etching amount is 2000 nm or more.

In the first etching step, the silicon carbide substrate 203 is controlled to a temperature of 40 ° C. to 150 ° C., and SF ₆ gas, O ₂ gas, and Ar gas are supplied from the gas introduction unit 106 into the etching processing chamber 101, respectively.

  Further, the inside of the etching processing chamber 101 is set to a predetermined pressure by the exhaust pump 115, and the TM bias, which is an intermittent high frequency bias power temporally modulated by the high frequency power source 111, is supplied at a duty ratio of 20 to 50%. To do.

The flow rate of O ₂ gas, the ratio to the total flow rate of the SF ₆ gas, O ₂ gas, Ar gas is 10% or less, the flow rate of SF ₆ gas, SF ₆ gas, O ₂ gas, the total of the Ar gas The ratio to the flow rate is preferably 5% or less. Thereby, there is no sub-trench at the bottom of the trench, and an etching shape in which the trench side wall is perpendicular to the bottom is possible.

In the second etching step, the silicon carbide substrate 203 is controlled to a temperature of 40 ° C. to 150 ° C., and SF ₆ gas, O ₂ gas, and Ar gas are supplied from the gas introduction unit 106 into the etching processing chamber 101 and exhausted. The etching chamber 101 is set to a predetermined pressure by the pump 115, and a CW bias, which is a continuous high frequency bias power, is supplied to the sample stage 109 by the high frequency power supply 111.

  Note that when high frequency bias power higher than 300 W is applied to the silicon carbide substrate 203 in order to improve productivity, the etching rate of the silicon carbide film is improved, but the remaining film amount of the silicon oxide film 202 is reduced. The mask opening 204 expands. When the mask opening 204 is widened, the silicon carbide substrate 203 is scraped off, which may cause a defective product of the device.

Therefore, in the second embodiment, SiF ₄ gas is added in the second etching step. As a result, while maintaining the dimension of the mask opening 204, there is no sub-trench at the bottom of the trench, the trench sidewall is formed in an etching shape perpendicular to the bottom, and the etching rate of the silicon carbide film is further improved. Is possible.

That is, regarding the gas flow rate in the second etching step, the flow rate of O ₂ gas is 10% or less of the total flow rate of SF ₆ gas, O ₂ gas, Ar gas, and SiF ₄ gas, and the flow rate of SF ₆ gas. Is 5% or less of the total flow rate of SF ₆ gas, O ₂ gas, Ar gas, and SiF ₄ gas. The flow rate of SiF ₄ gas, SF ₆ gas, O ₂ gas, Ar gas, is possible to add a percentage of the total flow rate of SiF ₄ gas in the range of 2-6% preferred.

FIG. 9 is an explanatory diagram showing the relationship between the ratio of the total flow rate of SiF ₄ gas and the silicon carbide film / silicon oxide film selection ratio.

As the ratio of the SiF ₄ gas to the total flow rate increases, the silicon carbide film / silicon oxide film selection ratio increases. However, if it exceeds 6%, the etching rate of the silicon carbide film decreases, and the silicon carbide film / silicon oxide film selection ratio decreases accordingly. This is because the adhesion of silicon contained in the SiF ₄ gas to the silicon carbide film exceeds the etching of the silicon carbide film.

FIG. 10 is an explanatory diagram showing an example of an etching shape with respect to the total flow rate ratio of the SiF ₄ gas. FIG. 10A shows the case where the total flow rate of SiF ₄ gas is 0%. FIG. 10B shows a case where the total flow rate of SiF ₄ gas is 2%. FIG. 10 (c) shows the total flow rate of 6% of SiF ₄ gas, FIG. 10 (d) shows the case of a total flow rate of 8% SiF ₄ gas.

When the total flow rate of the SiF ₄ gas was 2 to 6%, the mask opening size was maintained, and there was no sub-trench on the bottom surface of the trench, and an etching shape in which the trench side wall was perpendicular to the bottom surface was obtained.

  Normally, when the silicon carbide film / silicon oxide film selection ratio is low, the silicon oxide film 202 which is a mask material during etching of the silicon carbide substrate 203 becomes thin, and the etching action in the vicinity of the mask opening 204 becomes active. As a result, the silicon oxide film 202 is easily etched in the lateral direction. Therefore, the mask opening 204 is widened as shown in FIG.

Therefore, by adding the SiF ₄ gas as described above, Si in the SiF ₄ gas reacts with O in the O ₂ gas, and a new SiO ₂ film is generated. Thus, the etching of the silicon oxide film 202 can be suppressed by increasing the number of silicon oxide films which are the same as the mask material.

However, if the amount of SiF ₄ gas added is too large, the deposition of the reaction product exceeds the etching of the silicon carbide substrate 203, so that a tapered shape is formed as shown in FIG.

Therefore, even when a high frequency bias power of 300 W or more is applied, if the total flow rate of the SiF ₄ gas is 2 to 6%, the highly productive silicon carbide substrate 203 can be etched without increasing the mask opening size. Become.

<Example of etching>
FIG. 11 is an explanatory diagram showing an example of etching conditions in the first etching process and the second etching process according to the second embodiment.

For example, as shown in FIG. 11, in the first etching step, a mixed gas of SF ₆ gas 14 ml / min, O ₂ gas 20 ml / min, and Ar gas 250 ml / min as the first mixed gas is used. .

  Then, the silicon carbide substrate 203 is etched to 150 nm under the etching conditions where the high frequency bias power application method is TM, the high frequency bias power is 150 W, the duty ratio is 20%, and the frequency is 2000 Hz. The etching time at this time is calculated by examining the etching rate of the silicon carbide substrate 203 in advance.

Subsequently, in the second etching step, a mixed gas of 14 ml / min of SF ₆ gas, 20 ml / min of O ₂ gas, 250 ml / min of Ar gas, and 10 ml / min of SiF ₄ gas is used as the second mixed gas. Further, the application method of the high frequency bias power is CW, and the silicon carbide substrate 203 is etched to 2000 nm under the etching conditions of the high frequency bias power of 400 W. The etching time at this time is calculated by examining the etching rate of the silicon carbide substrate 203 in advance.

  By such plasma etching, as shown in FIG. 10C, a trench shape with an etching amount of 2000 nm can be obtained in which there is no sub-trench at the bottom of the trench and the trench side wall is perpendicular to the bottom.

  Note that although an ECR microwave plasma etching apparatus using microwaves is used in this embodiment, the plasma etching apparatus is not limited to this, and a helicon wave plasma etching apparatus, inductively coupled plasma, and the like. The present invention can also be applied to an etching apparatus, a capacitively coupled plasma etching apparatus, and the like.

  In addition, the above-described embodiment shows an example. For example, the etching shape changes depending on the apparatus configuration and process conditions such as the sample base structure, power supply frequency, plasma density, etching gas, etc. It is desirable to select an optimum value according to the apparatus and etching gas.

  Also in the above, highly accurate etching processing control can be performed.

  As mentioned above, the invention made by the present inventor has been specifically described based on the embodiment. However, the present invention is not limited to the embodiment, and various modifications can be made without departing from the scope of the invention. Needless to say.

  In addition, this invention is not limited to above-described embodiment, Various modifications are included. For example, the above-described embodiment has been described in detail for easy understanding of the present invention, and is not necessarily limited to one having all the configurations described.

  Further, a part of the configuration of one embodiment can be replaced with the configuration of another embodiment, and the configuration of another embodiment can be added to the configuration of one embodiment. . In addition, it is possible to add, delete, and replace other configurations for a part of the configuration of each embodiment.

DESCRIPTION OF SYMBOLS 101 Etching chamber 102 Microwave generator 103 Matching device 104 Waveguide 105 Microwave introduction window 106 Gas introduction part 107 Transmission window 108 Solenoid coil 109 Sample stage 110 Substrate 111 High frequency power supply 112 Electrostatic adsorption power supply 113 Cooling gas supply Port 114 Chiller unit 115 Exhaust pump 201 Photoresist film 202 Silicon oxide film 203 Silicon carbide substrate 204 Mask opening

Claims (9)

A plasma etching method for etching a substrate to be processed using plasma,
A first etching step of introducing a mixed gas of SF ₆ gas, O ₂ gas, and Ar gas into the etching chamber to generate plasma and etching the substrate to be processed;
Generating a plasma using the mixed gas, applying a continuous high-frequency power to the substrate to be processed, and etching the substrate to be processed;
A plasma etching method comprising: The plasma etching method according to claim 1,
In the plasma etching method, the first etching step applies pulse-modulated high frequency power to the substrate to be processed. The plasma etching method according to claim 1,
The plasma etching method, wherein an etching amount in the first etching step is a depth of 150 nm to 250 nm. The plasma etching method according to claim 1,
A plasma etching method, wherein a substrate material of the substrate to be processed is silicon carbide. A plasma etching method for etching a substrate to be processed using plasma,
A first etching step of introducing a first mixed gas composed of SF ₆ gas, O ₂ gas, and Ar gas into an etching process chamber to generate plasma and etching the substrate to be processed;
A second etching step of generating plasma using a second mixed gas and etching the substrate to be processed;
Have
The plasma etching method, wherein the second mixed gas is a mixed gas obtained by adding SiF ₄ gas to the first mixed gas. The plasma etching method according to claim 5, wherein
In the plasma etching method, the first etching step applies pulse-modulated high frequency power to the substrate to be processed. The plasma etching method according to claim 5, wherein
The second etching step is a plasma etching method in which continuous high-frequency power is applied to the substrate to be processed. The plasma etching method according to claim 5, wherein
The plasma etching method, wherein an etching amount in the first etching step is a depth of 150 nm to 250 nm. The plasma etching method according to claim 5, wherein
A plasma etching method, wherein a substrate material of the substrate to be processed is silicon carbide.

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