Plasma treatment method

Abstract

The present invention provides a plasma treatment method for etching a silicon nitride film isotropically and highly selectively relative to a silicon oxide film. This plasma treatment method is for etching a silicon nitride film by using plasma, and comprises an etching step for etching the silicon nitride film with radicals by using a gas mixture of SF6 gas, H2 gas, and CO2 gas. Furthermore, in the etching step, plasma is generated by high-frequency electrical energy, and no high-frequency bias is applied to a sample stage on which a sample comprising the silicon nitride film has been placed.

Description

Plasma treatment method

[0001] The present disclosure relates to plasma processing methods, and more particularly to plasma processing methods for etching silicon nitride.

[0002] As a background art in this technical field, there is Japanese Patent Application Laid-Open No. 2015-207688 (Patent Document 1). In Patent Document 1, the power of a high frequency bias applied to a sample stage is set to be greater than 0 W and equal to or less than 5 W, and carbon tetrafluoride (CF ４ ) gas, hydrogen (H ２ ) gas and carbon dioxide (CO ２ ) gas mixture, or hexafluoroethane (C ２ F ６ ) Gas, H ２ Gas and CO ２ A method for isotropically etching silicon nitride with high selectivity to silicon oxide and polysilicon using a gas mixture containing silicon nitride and polysilicon is described.

[0003] JP 2015-207688 A

[0004] A dry etching method using fluorocarbon gas to etch silicon nitride anisotropically has been established, but this method cannot etch silicon nitride isotropically and with high selectivity relative to silicon oxide or polysilicon.

[0005] The technology described in Patent Document 1 addresses this issue by ４ Gas, H ２ Gas and CO ２ Gas or C ２ F ６ Gas, H ２ Gas and CO ２ The method provides a method for isotropically etching silicon nitride with high selectivity to silicon oxide by using a mixed gas containing CF4 and applying a high frequency bias of 0 W or more to 5 W or less to the sample stage. ４ Gas, H ２ Gas and CO ２ Gas or C ２ F ６ Gas, H２ Gas and CO ２ In the gas, methine groups (CH) are deposited on the surface of the silicon oxide film, forming a silicon oxide film (SiO ２ This prevents dry etching of the silicon nitride film (SiN film), and the deposited CH reacts with nitrogen in the silicon nitride film (SiN film) and evaporates. ２ However, applying a high frequency bias to a large extent can etch the exposed silicon oxide, which can cause damage to the silicon oxide.

[0006] In order to solve the above-mentioned problems, the present disclosure provides a plasma processing method that suppresses damage to silicon oxide and isotropically etches silicon nitride with high selectivity relative to silicon oxide.

[0007] To solve this problem, the present disclosure provides a plasma processing method for selectively and isotropically etching a silicon nitride film relative to a silicon oxide film using plasma, the method comprising: ６ ) gas and hydrogen (H ２ ) gas and carbon dioxide (CO ２ ) gas, and etching the silicon nitride film with radicals.

[0008] More specifically, by performing etching processing with radicals, the influence of ion bombardment by ions in plasma is reduced or eliminated, and sulfur hexafluoride (SF ６ ) gas and hydrogen (H ２ ) gas and carbon dioxide (CO ２ This is achieved by applying microwave power greater than 0 W to the gas and not applying a high frequency bias to the sample stage (high frequency bias is set to 0 W).

[0009] According to the present disclosure, it is possible to provide a plasma processing method that isotropically etches silicon nitride with high selectivity relative to silicon oxide.

[0010] FIG. 1 is a schematic diagram of a plasma processing apparatus according to an embodiment of the present disclosure; FIG. 2 is a diagram showing a film structure of a wafer used in the present disclosure; FIG. 3 is a diagram showing an etching shape when a wafer is etched using an etching technique of a comparative example; FIG. 4 is a diagram showing an etching shape when a wafer is etched using the etching technique of the present disclosure; FIG. 5 is a table showing etching conditions used in the present disclosure; FIG. 6 is a diagram showing the gas dependency of the etching rate of a silicon nitride film; FIG. 7 is a diagram showing the gas dependency of the selectivity of a silicon nitride film to a silicon oxide film; ２ 10 is a graph showing the flow rate dependency of the selectivity of a silicon nitride film to a silicon oxide film. ２ 1 is a graph showing the flow rate dependency of the etching rate of a silicon nitride film. ２ 1 is a graph showing the flow rate dependency of the CO selectivity of a silicon nitride film to a silicon oxide film. ２ 1 is a diagram showing flow rate dependency; 2 is a diagram showing the film structure of a wafer used in the present disclosure; 3 is a diagram showing etching conditions for the oxidation process used in the present disclosure; 4 is a diagram showing the high-frequency bias dependency of the O ratio on a silicon nitride wafer in the oxidation process by XPS; and 5 is a diagram showing the high-frequency bias dependency of the N ratio on a silicon nitride wafer in the oxidation process by XPS.

[0011] Hereinafter, examples will be described with reference to the drawings. However, in the following description, the same components will be assigned the same reference numerals, and repeated explanations may be omitted. Note that the drawings may be more schematic than the actual embodiment in order to clarify the description, but they are merely examples and do not limit the interpretation of the present invention.

[0012] First, a configuration example of a plasma etching apparatus as a plasma processing apparatus for carrying out the plasma processing method of the present disclosure will be described.

[0013] FIG. 1 shows a schematic configuration example of a plasma etching apparatus 1. A vacuum vessel 101, which constitutes the processing chamber of the plasma etching apparatus 1, is a cylindrical vessel made of a conductive material such as aluminum and is electrically grounded. The upper opening of the vacuum vessel 101 is sealed with a top plate 102 made of a material that is electromagnetically transmissive, such as quartz. A device for evacuating the interior of the vacuum vessel 101 to a predetermined pressure, such as a turbomolecular pump 103, and an auxiliary pump, such as a dry pump 104, connected thereto, are connected to the center of the lower part of the vacuum vessel 101. A waveguide 105 covering the top plate 102 is provided above the top plate 102, and a high-frequency power source for generating plasma (hereinafter referred to as a "plasma power source 107") is connected to the top plate 102 via a matching box 106.

[0014] In this example, the plasma power source 107 generates microwaves of 2.45 GHz. The generated microwaves propagate through the waveguide 105 and are introduced into the vacuum vessel 101 via the top plate 102. A solenoid coil 108 for forming a magnetic field within the vacuum vessel 101 is wound around the outside of the vacuum vessel 101. A shower plate 109 is provided above the vacuum vessel 101 below the top plate 102, and a gas supply device 110 is connected between the top plate 102 of the vacuum vessel 101 and the shower plate 109.

[0015] A processing gas is supplied from a gas supply device 110 into the space between the top plate 102 and the shower plate 109, and is then supplied via the shower plate 109 into a processing chamber formed in the vacuum vessel 101. A sample stage 111 is provided in the vacuum vessel 101, and a wafer 2 is loaded through a wafer loading port (not shown) and placed and held on the sample stage 111. A bias high frequency power supply 114 is connected to the sample stage 111 via a bias matching device 113, and the bias high frequency power supply 114 is connected to a control device 115, which controls the output of the bias power supply.

[0016] In the plasma etching apparatus 1 configured as described above, the processing gas supplied into the vacuum chamber 101 is converted into plasma by the interaction (e.g., electron cyclotron resonance (ECR)) between the electric field of the microwave introduced through the top plate 102 and the magnetic field generated by the solenoid coil 108, and the plasma is generated in the space between the shower plate 109 and the sample stage 111. The magnetic field strength at which the plasma is generated is near the 875 Gauss plane, which is called the ECR plane.

[0017] In addition, in the present plasma etching apparatus 1, an ion shielding plate 112 made of a material that is permeable to electromagnetic waves, for example, quartz, divides the inside of the vacuum vessel 101 into an upper region 101-1 of the vacuum vessel 101 and a lower region 101-2 of the vacuum vessel 101. If plasma can be generated in the upper region 101-1 of the vacuum vessel 101, which is above the ion shielding plate 112, ions are shielded by the ion shielding plate 112 in the lower region 101-2, and it becomes possible to etch the wafer 2 as a sample using radicals. In other words, by controlling the solenoid coil 108 so that an ECR plane is formed in the upper region 101-1 of the vacuum vessel 101, plasma is generated in the upper region 101-1, and a processing gas (sulfur hexafluoride (SF ６ ) gas and hydrogen (H ２ ) gas and carbon dioxide (CO ２ ) gas mixture) is turned into plasma. Then, in the lower region 101-2, ions are blocked by the ion shielding plate 112, so radicals are generated in the lower region 101-2. Using these radicals, plasma processing can be performed to dry etch the wafer 2 as a sample placed on the sample stage 111.

[0018] As described above, the position where the plasma is formed can be controlled by the solenoid coil 108. Furthermore, since the ion shielding plate 112 is made of a material that is permeable to electromagnetic waves, dry etching using ordinary plasma can also be performed by controlling the solenoid coil 108 so that an ECR surface is formed in the lower region 101-2 of the vacuum vessel 101.

[0019] When plasma is generated in the lower region 101-2 of the vacuum vessel 101 to perform dry etching, high frequency power is applied to the sample stage 111 from a bias high frequency power supply 114 via a bias matcher 113. The high frequency power applied to the sample stage 111 is controlled independently of the generation of plasma, and generates a bias voltage that causes ions in the plasma to be incident on the wafer 2.

[0020] The plasma power supply 107 and the bias high frequency power supply 114 are electrically connected to a control device 115 , and the outputs of the power supplies 107 and 114 are controlled by the control device 115 .

[0021] Next, the film structure of the wafer 2, which is the object to be processed in this embodiment, and the etching method will be described.

[0022] FIG. 2 is a diagram showing the film structure of the wafer used in this example. FIG. 2 shows an enlarged cross-sectional view of the main surface side of the wafer 2, in which a silicon nitride film 202 is formed around a silicon oxide film 201. Specifically, the silicon nitride film 202 is thinly formed (deposited) so as to cover the surface of the silicon oxide film 201 in which the grooves are formed, the inner walls of the grooves, and the bottom surfaces of the grooves. In other words, the grooves are formed in the silicon oxide film 201, and the silicon nitride film 202 is deposited in the grooves. To etch the silicon nitride film 202 without damaging the silicon oxide film 201, it is necessary to selectively etch the silicon nitride film 202 with respect to the silicon oxide film 201.

[0023] 3A is a diagram showing an etched shape of a wafer 2 when processed by the etching method of a comparative example (Patent Document 1), and FIG. 3B is a diagram showing an etched shape of a wafer 2 when processed by the etching method of this example.

[0024] In Figure 3A, the silicon oxide film 201 is slightly etched by ions in the plasma, causing damage and side etching to the silicon oxide film 201. Therefore, by etching the wafer 2 using radicals in the lower region 101-2 using the plasma etching apparatus 1, the desired shape can be obtained as shown in Figure 3B. In other words, in this embodiment, the silicon oxide film 201 can be obtained in the desired shape without damage or side etching, as shown in Figure 3B.

[0025] An example of processing conditions in the etching method of this embodiment will be described with reference to the diagram in FIG. 4. The process gas is sulfur hexafluoride (SF ６ ) gas, for example, at a flow rate of 40 ml / min, hydrogen (H ２ ) gas, for example, at a flow rate of 180 ml / min, carbon dioxide (CO ２ The microwave power is, for example, 600 W, its duty ratio is, for example, 100%, and no high frequency bias is applied (high frequency bias (high frequency power) is 0 W). The temperature of the sample stage 111 is, for example, 40°C.

[0026] 5 is a graph showing the etching rate and gas dependency of the silicon nitride film 202. FIG. 6 is a graph showing the gas dependency of the selectivity of the silicon nitride film 202 to the silicon oxide film 201. As shown in FIGS. 5 and 6, SF ６ The silicon nitride film 202 can be etched with high selectivity relative to the silicon oxide film 201 by the gas. ６ The reactivity of the gas is reduced, and etching of the silicon oxide film 201 is suppressed. ３ ) gas and carbon tetrafluoride (CF ４ It is estimated that in the SiO 2 nitride gas, dissociated nitrogen (N) and carbon (C) extract oxygen (O) from the silicon oxide film 201, thereby causing the etching of the silicon oxide film 201 to proceed, and the selectivity of the silicon nitride film 202 to the silicon oxide film 201 to decrease relatively.

[0027] FIG. 7 shows the etching rate of the silicon nitride film 202.２ 8 is a graph showing the flow rate dependency of the silicon nitride film 202 with respect to the silicon oxide film 201. ２ 7 is a graph showing the flow rate dependency. ２ The etching rate of the silicon nitride film 202 increases by increasing the flow rate, and reaches a maximum at 140 ml / min. ２ The selectivity improved with an increase in the flow rate, reaching a maximum at 180 ml / min. It is presumed that the etching rate of the silicon nitride film 202 increased because H (hydrogen) extracted N from the silicon nitride film 202.

[0028] FIG. 9 shows the etching rate of the silicon nitride film 202. ２ 10 is a graph showing the flow rate dependency of the CO selectivity of the silicon nitride film 202 to the silicon oxide film 201. ２ 9 is a graph showing the flow rate dependency. ２ As the flow rate increases, CO ２ The etching rate of the silicon nitride film 202 increased up to a flow rate of 60 ml / min, and then gradually decreased thereafter. ２ The C in the silicon nitride film extracts the N from the silicon nitride film, thereby promoting etching of the silicon nitride film 202. ２ When the flow rate is increased, etching is suppressed by the deposition of C, so CO ２ It is estimated that the flow rate gradually decreased after 60 ml / min. ２ At a flow rate of 170 ml / min, etching could be suppressed, and the selectivity of the silicon nitride film 202 to the silicon oxide film 201 became infinite. ２ It is presumed that the etching was suppressed by oxidation due to the

[0029] Thus, according to Example 1, the process gas is SF ６ Gas, H ２ Gas and CO ２A plasma process is performed in which a mixed gas containing a gas is used, plasma is generated in the upper region 101-1 of the plasma etching apparatus 1, radicals are generated in the lower region 101-2, and the radicals are used to etch the silicon nitride film 202 of the wafer 2. Furthermore, a plasma process is performed in which microwave power greater than 0 W is applied from the plasma power source 107, no high frequency bias is applied to the sample stage 111 (high frequency bias is 0 W), and the temperature of the sample stage 111 is set to 40° C. or higher, thereby etching the silicon nitride film 202 with high selectivity to the silicon oxide 201 and isotropic dry etching.

[0030] Next, a second embodiment of the present disclosure will be described with reference to Fig. 11. In the plasma processing method of the first embodiment, a sidewall silicon nitride film (hereinafter referred to as a sidewall film) 203 of a silicon nitride film 202 and a bottom silicon nitride film (hereinafter simply referred to as a bottom film) 204 of the silicon nitride film 202 shown in Fig. 11 are isotropically etched with high selectivity relative to a silicon oxide film 201. According to the plasma processing method for plasma etching of the second embodiment, only the sidewall film 203 of the silicon nitride film 202 can be etched with high selectivity relative to a silicon oxide film 201 using plasma, while the bottom film 204 of the silicon nitride film 202 is maintained (remains).

[0031] 12 shows an example of etching conditions for plasma etching according to Example 2. Processing conditions for the etching method of this example will be described with reference to FIG. 12. In Example 2, an oxidation step for protecting the bottom film 204 of the silicon nitride film 202 is introduced before the etching step of Example 1. The process gas is CO ２A gas with a flow rate of, for example, 200 ml / min is used. In the oxidation process, the high-frequency power of the pulse-modulated microwave is, for example, 500 W with a duty ratio of, for example, 5%, and the high-frequency power of the pulse-modulated high-frequency bias is, for example, 100 W with a duty ratio of, for example, 5%. The temperature of the sample stage 111 is, for example, 40° C. That is, the oxidation process of Example 2 is performed using plasma generated by the pulse-modulated high-frequency power. The oxidation process is performed while supplying pulse-modulated high-frequency power to the sample stage 111 on which the wafer 2, a sample on which the silicon nitride film 202 is formed, is placed. The oxidation process oxidizes the sidewall film 203 of the silicon nitride film 202 by reactive ion etching (RIE).

[0032] Figure 13A shows the high frequency bias dependence of the O ratio on a silicon nitride wafer during the oxidation process, measured by X-ray photoelectron spectroscopy (XPS). Figure 13B shows the high frequency bias dependence of the N ratio on a silicon nitride wafer during the oxidation process, measured by X-ray photoelectron spectroscopy (XPS). In the legend, "ini" indicates the results for the wafer state (silicon nitride wafer) before processing. "CO2" indicates the CO ２ 12. RF100W and RF0W indicate the conditions under which the power of the high frequency bias (high frequency power) is 100W and 0W under the conditions shown in FIG.

[0033] 13A and 13B, an increase in the RF bias power increases the O ratio and decreases the N ratio on wafer 2. This is presumably because the increase in RF bias power increases the perpendicularity of ions and the ion energy, promoting oxidation.

[0034] As described above, according to the second embodiment, the sidewall film 203 of the silicon nitride film 202 can be etched with high selectivity relative to the silicon oxide film 201 while the bottom film 204 of the silicon nitride film 202 is maintained.

[0035] As described above, the present disclosure is not limited to the above-described embodiment, and various modifications are possible without departing from the spirit of the present disclosure.

[0036] 101: vacuum vessel, 102: top plate, 103: turbo molecular pump, 104: dry pump, 105: waveguide, 106: matching box, 107: plasma power supply, 108: solenoid coil, 109: shower plate, 110: gas supply device, 111: sample stage, 112: ion shielding plate, 113: bias matching box, 114: bias high frequency power supply, 115: control device, 201: silicon oxide film, 202: silicon nitride film, 203: side wall silicon nitride film (side wall film of silicon nitride film), 204: bottom silicon nitride film (bottom film of silicon nitride film).

Claims

1. A plasma processing method for selectively plasma etching a silicon nitride film relative to a silicon oxide film, comprising: ６ Gas and H ２ Gas and CO ２ a plasma processing method comprising an etching step of isotropically etching the silicon nitride film using a mixed gas of a gas.

2. A plasma processing method according to claim 1, wherein the etching step is carried out with 0 W of high frequency power supplied to a sample stage on which the sample having the silicon nitride film formed thereon is placed.

3. The plasma processing method according to claim 1, wherein a groove is formed in said silicon oxide film, and said silicon nitride film is formed in said groove.

4. The plasma processing method according to claim 1, further comprising an oxidation step of oxidizing the silicon nitride film using plasma before the etching step.

5. The plasma processing method according to claim 3, further comprising an oxidation step of oxidizing the silicon nitride film using plasma before the etching step.

6. A plasma processing method according to claim 4, wherein the oxidation step is carried out using plasma generated by pulse-modulated high-frequency power.

7. A plasma processing method according to claim 5, wherein the oxidation step is carried out using plasma generated by pulse-modulated high-frequency power.

8. The plasma processing method according to claim 4, wherein the oxidation step oxidizes the silicon nitride film by reactive ion etching (RIE).

9. The plasma processing method according to claim 5, wherein the oxidation step oxidizes the silicon nitride film by reactive ion etching (RIE).

10. A plasma processing method according to claim 8, wherein the oxidation step is carried out while supplying pulse-modulated high-frequency power to a sample stage on which the sample having the silicon nitride film formed thereon is placed.

11. A plasma processing method according to claim 9, wherein the oxidation step is carried out while supplying pulse-modulated high-frequency power to a sample stage on which the sample having the silicon nitride film formed thereon is placed.

Images