JP6295130B2 - Dry etching method - Google Patents

Description

  The present invention relates to a dry etching method.

  As background art of this technical field, there are JP-A-60-115231 (Patent Document 1) and JP-A-2000-340552 (Patent Document 2).

  In Japanese Patent Laid-Open No. 60-115231 (Patent Document 1), the ratio of the area between the electrode on which the object is to be etched and the other electrode is approximately 0.5 to 1, including C, H, and F. A technique for etching silicon nitride using a gas having a H ratio of 2 or less as a reaction gas is described.

  Japanese Patent Laid-Open No. 2000-340552 (Patent Document 2) discloses a silicon oxide and a photoresist using an etchant gas composition containing a polymerization agent, a hydrogen source, an oxidizing agent, and a rare gas diluent. Describes an anisotropic etching method of silicon nitride having a high degree of selectivity.

JP-A-60-115231 JP 2000-340552 A

  Conventionally, wet etching (wet etching) using hot phosphoric acid has been used for etching silicon nitride, but in recent years, dry etching (dry etching) is used instead of this wet etching. For example, a dry etching method for anisotropically etching silicon nitride has already been put into practical use. However, this dry etching method cannot etch silicon nitride with high selectivity and isotropicity with respect to silicon oxide or silicon.

  Therefore, the present invention provides a dry etching method that etches silicon nitride with high selectivity and isotropicity with respect to silicon oxide or silicon.

In order to solve the above-described problems, the present invention provides a dry etching method using plasma on a silicon nitride film formed on a main surface of a wafer after placing the wafer on a sample stage provided in a processing chamber. Etch. The process gas introduced into the processing chamber is a first mixed gas containing CF ₄ gas, H ₂ gas and CO ₂ gas or a _second mixed gas containing C ₂ F ₆ gas, H ₂ gas and CO ₂ gas. The temperature of the sample stage is 40 ° C. or higher and 150 ° C. or lower, and the power of the high frequency bias applied to the sample stage is greater than 0 W and 5 W or less.

  According to the present invention, it is possible to provide a dry etching method for etching silicon nitride with high selectivity and isotropicity with respect to silicon oxide or silicon.

  Problems, configurations, and effects other than those described above will be clarified by the following description of embodiments.

It is the schematic of the electron cyclotron resonance plasma etching apparatus using a microwave and a magnetic field for the plasma production | generation means by Example 1. FIG. It is a graph explaining the relationship between the vertical direction etching rate and horizontal direction etching rate (SiN etching rate) of a silicon nitride film, and the electric power of a high frequency bias. It is a graph explaining the relationship between the selectivity of a silicon nitride film with respect to a polycrystalline silicon film (SiN / polySi selectivity) and the temperature of a sample stage. 4 is a cross-sectional view of a main part of a silicon material for explaining dry etching of a silicon nitride film according to Example 1. FIG. (A) is principal part sectional drawing of the silicon material before carrying out the dry etching of the silicon nitride film by Example 1. FIG. (B) is principal part sectional drawing of the silicon material after carrying out the dry etching of the silicon nitride film by Example 1. FIG. (C) is a cross-sectional view of the main part of the silicon material after dry etching the silicon nitride film in the case of dry etching in which the selectivity of silicon nitride to silicon, which was examined by the present inventor as a comparative example, is lower than 5. . It is a graph explaining the relationship between the selection ratio (SiN / polySi selection ratio) of the silicon nitride film to the polycrystalline silicon film and the duty ratio of the microwave. It is the schematic of the electron cyclotron resonance plasma etching apparatus using a microwave and a magnetic field for the plasma production | generation means by Example 3. FIG.

  In the following embodiments, when 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, and one is the 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) are not necessarily indispensable unless otherwise specified and clearly considered essential in principle. Needless to say.

  In addition, when referring to “consisting of A”, “consisting of A”, “having A”, and “including A”, other elements are excluded unless specifically indicated that only that element is included. It goes without saying that it is not what you do. Similarly, in the following embodiments, when referring to the shapes, positional relationships, etc. of the components, etc., the shapes are substantially the same unless otherwise specified, or otherwise apparent in principle. And the like are included. The same applies to the above numerical values and ranges.

In the following embodiments, when referring to silicon nitride, silicon nitride, silicon nitride or the like, not only Si ₃ N ₄ but also a similar composition (for example, stoichiometry) of silicon nitride is used. Insulating film having a composition deviated from the target composition). In addition, silicon oxide, silicon oxide, and the like include not only SiO ₂ but also an insulating film having a similar composition (for example, a composition deviating from the stoichiometric composition) using silicon oxide. . In the following embodiments, silicon nitride may be described as “SiN”, silicon oxide may be described as “SiO ₂ ”, and polycrystalline silicon may be described as “polySi”.

  Further, in the drawings used in the following embodiments, hatching may be added to make the drawings easy to see even if they are plan views. In all the drawings for explaining the following embodiments, components having the same function are denoted by the same reference numerals in principle, and repeated description thereof is omitted. Hereinafter, the present embodiment will be described in detail with reference to the drawings.

  A plasma etching apparatus according to the first embodiment will be described with reference to FIG. FIG. 1 is a schematic diagram of an electron cyclotron resonance plasma etching apparatus using a microwave and a magnetic field as plasma generating means according to the first embodiment.

  As shown in FIG. 1, the plasma etching apparatus M1 includes a chamber (also referred to as a processing chamber or a plasma processing chamber) 101 that can be evacuated inside. A sample stage 103 on which a wafer 102 as a sample is mounted is provided inside the chamber 101, and a microwave transmission window 104 made of quartz or the like is provided on the upper surface of the chamber 101. Further, a waveguide 105 and a magnetron 106 are provided above the microwave transmission window 104. A solenoid coil 107 and an electrostatic adsorption power source 108 connected to the sample stage 103 are provided around the chamber 101. A high frequency bias power source 109 is provided.

  Next, dry etching using the plasma etching apparatus M1 will be described with reference to FIG.

  First, the wafer 102 is loaded into the chamber 101 from the wafer loading port 110 and then placed on the sample stage 103. The wafer 102 is electrostatically adsorbed on the sample stage 103 by the electrostatic adsorption power source 108. Although illustration is omitted, the temperature of the sample stage 103 can be controlled by the circulating refrigerant installed in the sample stage 103 and the heater heating.

  Next, process gas is introduced into the chamber 101 from the gas inlet 111. Although not shown, the inside of the chamber 101 is evacuated by a vacuum pump and adjusted to a predetermined pressure, for example, about 0.1 Pa to 50 Pa.

  Next, a microwave having a frequency of 2.45 GHz oscillated from the magnetron 106 is supplied into the chamber 101 through the waveguide 105 and the microwave transmission window 104. The process gas is excited by the interaction between the microwave and the magnetic field generated by the solenoid coil 107, and the plasma 112 containing ions or radicals in the space above the wafer 102 is generated. By applying a high frequency bias from the high frequency bias power source 109 to the sample stage 103, ions or radicals are drawn from the plasma 112 to the wafer 102, and the etching target film formed on the main surface of the wafer 102 is dry etched.

  The output of the magnetron 106 and the output of the high frequency bias power supply 109 can be pulse-modulated, and the outputs can be turned on and off in synchronization with the signal from the pulse generator 113.

  Table 1 shows an example of etching conditions for plasma etching according to the first embodiment.

As the process gas, CF ₄ / H ₂ / CO ₂ gas in which CF ₄ gas, H ₂ gas and CO ₂ gas are mixed is used. The microwave power is 600 W, the duty ratio is 100%, the high frequency bias power is 10 W, and the duty ratio is 50%. The temperature of the sample stage is 40 ° C.

  In anisotropic dry etching, high ion energy is required, but in isotropic dry etching, ion energy is reduced as much as possible, and the etching rate in the vertical direction (the thickness direction of the wafer 102) and the horizontal direction (of the wafer 102). It is necessary to make the etching rate substantially equal to the thickness direction).

  FIG. 2 is a graph illustrating the relationship between the vertical etching rate and horizontal etching rate (SiN etching rate) of the silicon nitride film and the power of the high frequency bias.

  The high frequency bias is pulse-modulated with a duty ratio of 50%, and the on period and the off period are alternately repeated. The high-frequency bias power on the horizontal axis in FIG. 2 represents the average power of the pulse-modulated high-frequency bias. Note that the average power of the pulse-modulated high-frequency bias can be obtained from the product of the peak power (power of the high-frequency bias during the on period) and the duty ratio of the high-frequency bias. For example, if the peak power is 20 W and the duty ratio is 50%, the average power is 10 W.

  As shown in FIG. 2, by making the average power of the pulse-modulated high frequency bias greater than 0 W and 5 W or less, the difference between the vertical etching rate and the horizontal etching rate is within 10%, and isotropic. Can be dry etched.

  FIG. 3 is a graph for explaining the relationship between the selection ratio of the silicon nitride film to the polycrystalline silicon film (SiN / polySi selection ratio) and the temperature of the sample stage.

When the temperature of the sample stage was 40 ° C., the etching rate of the silicon nitride film was 22 nm / min, the etching rate of the polycrystalline silicon film was 4.2 nm / min, and the etching rate of the silicon oxide film was 2.0 nm / min. Accordingly, the selection ratio of silicon nitride to polycrystalline silicon (hereinafter referred to as SiN / polySi selection ratio) is 5.2, and the selection ratio of silicon nitride to silicon oxide (hereinafter referred to as SiN / SiO ₂ selection ratio) is 11. Become. Here, since the standard of the selection ratio replaced from wet etching to dry etching is 5 or more, if the temperature of the sample stage is 40 ° C., the target SiN / polySi selection ratio and SiN / SiO ₂ selection ratio are set. Can be obtained.

The SiN / SiO ₂ selection ratio has a small temperature dependency of the sample stage and is always 10 or more. However, as shown in FIG. 3, the SiN / polySi selection ratio increases as the temperature of the sample stage rises, and reaches a maximum at about 80 ° C. The reason why the SiN / polySi selection ratio increases as the temperature of the sample stage increases until the temperature of the sample stage reaches about 80 ° C. is that the CH radical generated in the plasma is N (nitrogen) in the silicon nitride film. It is estimated that this is because the reaction rate of pulling out increases.

When the temperature of the sample stage exceeds about 80 ° C., the SiN / polySi selection ratio decreases as the temperature of the sample stage increases. When the temperature of the sample stage exceeds about 150 ° C., the SiN / polySi selection ratio is 5 It becomes as follows. In the dry etching according to Example 1, CF ₄ / H ₂ / CO ₂ gas in which CF ₄ gas, H ₂ gas and CO ₂ gas are mixed is used as a process gas, and in this gas, CH is a polycrystalline silicon film or The CH deposited on the surface of the silicon oxide film prevents dry etching of the polycrystalline silicon film or the silicon oxide film, and the deposited CH reacts with N (nitrogen) of the silicon nitride film to evaporate. Thereby, it is considered that SiN / polySi selectivity and SiN / SiO ₂ selectivity are developed. However, as the temperature of the sample table increases, the CH adhesion coefficient decreases and the amount of CH deposited on the surface of the polycrystalline silicon film decreases. Therefore, when the temperature of the sample table exceeds about 80 ° C., SiN It is estimated that the / polySi selection ratio decreases as the temperature of the sample stage increases.

A feature of CF ₄ / H ₂ / CO ₂ gas is that the amount of CH radicals generated can be controlled. With the CH ₂ F ₂ gas or CH ₃ F gas described in Patent Document 1, a large amount of CH is deposited on the surface of the film to be etched, so that dry etching does not proceed when the power of the high frequency bias is 5 W or less. That is, isotropic dry etching is difficult. On the other hand, in Example 1, C (carbon) and H (hydrogen) are supplied independently to generate CH radicals in the plasma, so that even if the power of the high frequency bias is 5 W or less, Etching progresses, and SiN / polySi selectivity and SiN / SiO ₂ selectivity can be increased. In addition, if the power of the high frequency bias is small, the etching rate becomes small and is not suitable for practical use. However, in Example 1, the etching rate suitable for practical use is maintained by maintaining the temperature of the sample stage at 40 ° C. or higher and 150 ° C. or lower. Can be obtained.

The flow rate ratio of CF ₄ / H ₂ / CO ₂ gas is basically CF ₄ gas flow rate: H ₂ gas flow rate: CO ₂ gas flow rate = 1: 2: 1, but depending on the situation, each gas flow rate is ± It is preferable to search within the range of 30% for the optimum gas flow rate ratio. Further, C ₂ F ₆ gas may be used instead of CF ₄ gas.

In the case of a gas having a higher C / F element number ratio than C ₂ F ₆ gas, for example, C ₃ F ₈ gas, a large amount of CH is deposited on the surface of the silicon nitride film. Dry etching does not proceed. Even if CO gas is used instead of CO ₂ gas, dry etching does not proceed if the power of the high frequency bias is low.

  FIG. 4 is a cross-sectional view of the principal part of the silicon material for explaining the dry etching of the silicon nitride film according to the first embodiment. FIG. 4A is a main-portion cross-sectional view of the silicon material before dry etching the silicon nitride film according to the first embodiment. FIG. 4B is a cross-sectional view of the main part of the silicon material after the silicon nitride film according to Example 1 is dry etched. FIG. 4C is a cross-sectional view of the main part of the silicon material after dry-etching the silicon nitride film in the case of dry etching in which the selection ratio of silicon nitride to silicon, which was examined by the present inventor as a comparative example, is lower than 5. It is.

  As shown in FIG. 4A, a plurality of grooves 404 having a predetermined depth are formed in the silicon material 401, and a silicon nitride film 402 is deposited on the surface of the silicon material 401 including the side surfaces and the bottom surface of the grooves 404. ing. The thickness of the silicon nitride film 402 is, for example, about 10 nm.

  FIG. 4B shows the result of dry etching the silicon nitride film 402 for about 40 seconds under the etching conditions shown in Table 1 using the plasma etching apparatus M1 shown in FIG. As shown in FIG. 4B, since the progress of dry etching is suppressed on the side surface and bottom surface of the groove 404 and all the silicon nitride films 402 including the side surface and bottom surface of the groove 404 can be removed, a desired shape is obtained. The groove 404 is obtained.

  On the other hand, as shown in FIG. 4C, in the case of dry etching in which the selection ratio of silicon nitride to silicon is lower than 5, all the silicon nitride films 402 including the side surfaces and the bottom surface of the trench 404 are removed. Side etching 403 occurs at the side and bottom surfaces of the groove 404, and the desired shape of the groove 404 cannot be obtained.

Thus, according to the first embodiment, the process gas is a mixed gas containing CF ₄ gas, H ₂ gas, and CO ₂ gas, and the temperature of the sample stage is 40 ° C. or higher and 150 ° C. or lower and applied to the sample stage 103. By using the plasma etching etching conditions in which the power of the high frequency bias is 5 W or less, silicon nitride can be dry-etched with high selectivity and isotropicity with respect to silicon oxide or silicon.

  Isotropic dry etching of the silicon nitride film using plasma etching according to the second embodiment will be described with reference to FIG. FIG. 5 is a graph illustrating the relationship between the selection ratio of silicon nitride to polycrystalline silicon (SiN / polySi selection ratio) and the duty ratio of the microwave. In addition, the plasma etching apparatus M1 described with reference to FIG. 1 of the above-described first embodiment is used to pulse-modulate the microwave in the etching conditions of the plasma etching described in Table 1 of the above-described first embodiment. The duty ratio is changed. The peak power of the microwave is constant at 600W. In this case, for example, if the duty ratio is 50%, the average power is 300 W. When the duty ratio of the microwave is 50% or less, the duty ratio of the high frequency bias is set to be the same as that of the microwave in synchronization with the microwave.

  As shown in FIG. 5, when the microwave duty ratio is 50% or less, the SiN / polySi selection ratio increases as the microwave duty ratio decreases. Although the etching rate of the silicon nitride film and the polycrystalline silicon film is reduced as the microwave power is reduced, CH is deposited on the surface of the polycrystalline silicon film while the plasma is turned off. Since the etching rate is further reduced, the SiN / polySi selectivity increases.

Although the relationship between the SiN / polySi selection ratio and the microwave duty ratio has been described here, the same effect was obtained with respect to the relationship between the SiN / SiO ₂ selection ratio and the microwave duty ratio.

Thus, according to Example 2, in addition to the plasma etching etching conditions of Example 1 described above, the SiN / polySi selectivity and SiN / SiO are further reduced by setting the microwave duty ratio to 50% or less. _{2 The} selection ratio can be increased.

  Isotropic dry etching of the silicon nitride film using plasma etching according to Example 3 will be described with reference to FIG. FIG. 6 is a schematic diagram of an electron cyclotron resonance plasma etching apparatus using a microwave and a magnetic field as plasma generating means according to the third embodiment. The configuration of the plasma etching apparatus according to the third embodiment is substantially the same as the configuration of the plasma etching apparatus shown in FIG.

  As shown in FIG. 6, a member 501 made of the same material as the film to be etched, that is, the silicon nitride film is provided in the chamber 101 provided in the plasma etching apparatus M2. In plasma etching, a phenomenon occurs in which reactive organisms desorbed from the wafer 102 are dissociated in the plasma 112 and reattached to the wafer 102. This redeposition reduces the etching rate of the film to be etched. In general, the amount of reactive organism reattached is larger in the central portion of the wafer 102 away from the exhaust port than in the outer peripheral portion of the wafer 102. For this reason, the etching rate of the film to be etched tends to be lower in the central portion of the wafer 102 than in the outer peripheral portion of the wafer 102.

  In order to improve this, in the plasma etching apparatus M2 according to the third embodiment, a member 501 made of the same material as the film to be etched, that is, the silicon nitride film, is provided inside the chamber 101. As a result, reactive organisms are also generated from the member 501, and the density concentration of the reactive organisms inside the chamber 101 is made uniform, so that the in-wafer distribution of the etching rate of the film to be etched can be improved. .

  If the member 501 made of silicon is provided in the chamber 101, the amount of silicon reactive organisms reattached to the polycrystalline silicon film increases, so that the etching rate of the polycrystalline silicon film decreases and SiN / The polySi selectivity can be further increased.

  The member 501 is disposed inside the chamber 101 so as to surround the outer periphery of the sample stage 103 in a top view. For example, the member 501 may be installed above the sample table 103 so as to surround the outer periphery of the sample table 103 in a ring shape, or may be installed, for example, on the outer periphery of the microwave transmission window 104.

  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.

101 chamber (processing chamber, plasma processing chamber)
DESCRIPTION OF SYMBOLS 102 Wafer 103 Sample stand 104 Microwave transmission window 105 Waveguide 106 Magnetron 107 Solenoid coil 108 Electrostatic adsorption power supply 109 High frequency bias power supply 110 Wafer inlet 111 Gas inlet 112 Plasma 113 Pulse generator 401 Silicon material 402 Silicon nitride film 403 Side etch 404 Groove 501 Member M1, M2 Plasma etching apparatus

Claims (4)

Produced by the interaction between the microwave and the magnetic field, selectively Te dry etching method odor etching silicon nitride films with a plasma generated by high frequency power is pulse-modulated with respect to silicon oxide or silicon,
Etching the pre Symbol silicon nitride film using the mixed gas of CF ₄ gas and H ₂ gas and CO ₂ gas while applying a high frequency bias the sample is pulse-modulated to the sample stage placed with the silicon nitride film And
The temperature of the sample stage is 40 ° C. or higher and 150 ° C. or lower,
The dry etching method according to claim 1, wherein the product of the on-period power of the pulse-modulated high-frequency bias and the duty ratio of the pulse-modulated high-frequency bias is greater than 0 W and not greater than 5 W. The silicon nitride film by using a plasma generated by the pulse-modulated high-frequency power selectively Te dry etching method smell of etching against divorced,
Before Symbol silicon nitride film using a mixed gas of C ₂ F ₆ gas and H ₂ gas and CO ₂ gas while applying a pulse modulated high frequency bias to the sample stage of the sample is placed with the silicon nitride film A dry etching method characterized by etching. In a dry etching method of selectively etching a silicon nitride film with respect to silicon oxide or silicon using plasma generated by the interaction between a microwave and a magnetic field and generated by pulse-modulated high-frequency power,
While applying a pulse-modulated high frequency bias to a sample stage on which the sample having the silicon nitride film is placed, C ₂ F ₆ Gas and H ₂ Gas and CO ₂ Etching the silicon nitride film using a gas mixture with gas,
The temperature of the sample stage is 40 ° C. or higher and 150 ° C. or lower,
The dry etching method according to claim 1, wherein the product of the on-period power of the pulse-modulated high-frequency bias and the duty ratio of the pulse-modulated high-frequency bias is greater than 0 W and not greater than 5 W. The dry etching method according to claim 1,
The flow rate of the CF ₄ gas: the flow rate of the H ₂ gas: the flow rate of the CO ₂ gas = 1: 2: 1, the flow rate of the CF ₄ gas, the flow rate of the H ₂ gas, and the flow rate of the CO ₂ gas, respectively. If you and the CF ₄ first reference flow rate of the gas, the third reference flow rate of the second reference flow rate and the CO ₂ gas of the _{H 2} gas,
The flow rate of CF ₄ gas, the flow rate within a range of ± 30% from the first reference flow rate,
The flow rate of the H ₂ gas is the flow rate in the range of ± 30% from the second reference flow rate,
The flow rate of the CO ₂ gas, a dry etching method, wherein the said third reference flow rate is a flow rate in the range of ± 30%.

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