Plasma processing method

Abstract

Disclosed is a plasma processing method for plasma etching a film 201 to be etched of a substrate 301 to be processed having the film 201 to be etched and a sacrificial layer 200 that is patterned above the film to be etched. This plasma processing method includes: a first step for depositing an elemental silicon-containing film 204 on the sacrificial layer; a second step for nitriding the elemental silicon-containing film deposited on the sacrificial layer and the elemental silicon-containing film deposited on the film to be etched using plasma that is generated by an elemental nitrogen-containing gas after the first step; and a third step for oxidizing the elemental silicon-containing film using plasma that is generated by an elemental oxygen-containing gas after the second step.

Description

Plasma treatment method

[0001] The present invention relates to a plasma processing method for a semiconductor substrate.

[0002] Currently, due to the difficulty of direct resolution by exposure, pattern reduction techniques using double or quadruple pitches are widely used. These techniques, called self-aligned double patterning (SADP) and self-aligned quadruple patterning (SAQP), are essential technologies in the semiconductor manufacturing process for forming fine patterns.

[0003] For example, Patent Document 1 and Non-Patent Document 1 disclose the SADP process flow. First, the etching target film, sacrificial film, and resist are deposited and coated in this order, and then the resist is developed and patterned. Next, the sacrificial layer is etched using the resist as a mask. After removing the resist, an oxide film or the like is deposited on the sacrificial layer pattern using ALD (Atomic Layer Deposition) or the like. The deposited oxide film or the like is called a spacer. Next, the portions of the spacer deposited on the top of the sacrificial layer pattern and the bottom between the sacrificial layer patterns (i.e., on the etching target film) are selectively removed by etching. Furthermore, by removing the sacrificial layer, a structure is formed in which only the spacers formed on the sidewalls of the sacrificial layer pattern remain on the etching target film. Then, the etching target film is processed using the remaining spacers as a mask. Using this method, a pattern with half the dimensions of the original pitch (double pitch) can be formed.

[0004] JP 2010-114424 A

[0005] T. Shibata et al., “ALD-SiO2 deposition and CD slimming techniques for double patterning and a heater-less batch tool”, 2010 International Symposium on Semiconductor Manufacturing (ISSM)

[0006] In the SADP examples shown in the prior art documents, a silicon oxide film or the like is formed around the sacrificial layer using a technique such as ALD to serve as a mask. However, since the silicon oxide film formation using ALD and the subsequent etching are performed using different equipment, the wafer must be repeatedly transported back and forth between the deposition equipment and the etching equipment. This increases the equipment footprint and increases the time required for transport between the equipment.

[0007] A plasma processing method according to one embodiment of the present invention is a plasma processing method for plasma etching a film to be etched on a substrate to be processed, the substrate having the film to be etched and a sacrificial layer patterned above the film to be etched, the plasma processing method comprising: a first step of depositing the silicon element-containing film on the sacrificial layer using plasma generated by a silicon element-containing gas; a second step of nitriding, after the first step, the silicon element-containing film deposited on the sacrificial layer and the silicon element-containing film deposited on the film to be etched using plasma generated by a nitrogen element-containing gas; a third step of oxidizing, after the second step, the silicon element-containing film using plasma generated by an oxygen element-containing gas; a fourth step of removing, after the third step, the silicon nitride film on the film to be etched or the sacrificial layer; a fifth step of removing the sacrificial layer after the fourth step; and a sixth step of plasma etching the film to be etched using a silicon oxide film formed on the film to be etched as a mask after the fifth step.

[0008] The present invention provides a plasma processing method capable of carrying out the SADP process in a vacuum environment. Other objects and novel features will become apparent from the description of this specification and the accompanying drawings.

[0009] FIG. 1 is a process flow of the present embodiment. FIG. 2 is a diagram schematically showing a processing step using an SADP process as an example. FIG. 3 is a diagram schematically showing a processing step using an SADP process as an example. FIG. 4 is a diagram schematically showing a processing step using an SADP process as an example. FIG. 5 is a diagram schematically showing a processing step using an SADP process as an example. FIG. 6 is a diagram schematically showing a processing step using an SADP process as an example. FIG. 7 is a diagram schematically showing a processing step using an SADP process as an example. FIG. 8 is a schematic configuration diagram of a plasma processing apparatus. FIG. 9 is a diagram schematically showing a mask (silicon oxide film) shape of a comparative example.

[0010] 3 shows an example of a plasma processing apparatus that performs the plasma processing of this embodiment. Here, an example of a plasma processing apparatus that generates electron cyclotron resonance (ECR) excited plasma is shown. In the ECR excited plasma processing apparatus, microwaves are used as an excitation source, and plasma is generated by applying an external magnetic field.

[0011] The plasma processing apparatus includes a sample stage 303 on which a substrate (wafer) 301 to be processed is placed within a vacuum chamber 300, and performs plasma processing on the substrate 301 using plasma generated within the vacuum chamber 300. A substrate bias high-frequency power supply 310 is connected to the sample stage 303. By controlling the applied substrate bias (high-frequency power), the directionality and energy of ions incident on the substrate 301 to be processed can be controlled. An exhaust pipe 307 is connected to the vacuum chamber 300, and a pressure control valve 308 and a pump 309 are connected to the exhaust pipe 307 to adjust the pressure within the vacuum chamber 300. The pump 309 evacuates the inside of the vacuum chamber 300 via the exhaust pipe 307 and the pressure control valve 308, and maintains the vacuum chamber 300 at a low pressure during plasma processing.

[0012] Microwave generation source 321 generates microwaves upon receiving power from microwave power supply (plasma generation power supply) 304. The microwave power generated by microwave generation source 321 is adjusted by microwave matching box 323 and propagated from rectangular waveguide 322 through converter 324 to circular waveguide 325 and cavity 326, and cavity 326 resonates the propagated microwave power.

[0013] The cavity 326 and the vacuum vessel 300 are separated by a partition plate 328. The partition plate 328 is made of a dielectric material that transmits microwave power and maintains the vacuum state inside the vacuum vessel 300. An electromagnet 327 is provided outside the vacuum vessel 300 and the cavity 326 to form a magnetic field inside the cavity 326 and the vacuum vessel 300 and to generate electron cyclotron resonance.

[0014] A shower plate 302 having a large number of holes formed therein for supplying gas into the vacuum chamber 300 is provided, and a gas line 306 for supplying gas is provided between a partition plate 328 and the shower plate 302. The gas has its flow rate adjusted by a mass flow controller (MFC) 305 and is supplied into the vacuum chamber 300 through the gas line 306. To obtain a desired film quality, it is desirable that the MFC 305 be installed in each gas system. The gases supplied by each gas system are, for example, a silicon (Si)-containing gas, a nitrogen (N)-containing gas, an oxygen (O)-containing gas, and an inert gas. The inert gas can be used for gas switching or to improve uniformity; for example, argon can be used.

[0015] The control unit 311 controls the microwave power supply 304 , the electromagnet 327 , the MFC 305 , the pressure control valve 308 , the pump 309 , and the high frequency power supply for substrate bias 310 to perform plasma processing on the substrate 301 to be processed.

[0016] The process flow of this embodiment will be described using FIGS. 1 and 2A-H. FIGS. 2A-H illustrate an example of an SADP process. First, a film to be etched 201 and a sacrificial layer 200 are sequentially formed on a semiconductor substrate 202 (S01). FIG. 2A illustrates the state after step S01 is completed. The sacrificial layer is preferably a silicon nitride (SiN) film or a polysilicon (Poly-Si) film. The semiconductor substrate 202 may be a bare wafer, or a bare wafer with some kind of base film formed on it. Next, a resist 203 is applied to the sacrificial layer 200, and a pattern is formed by exposure and development (S02). FIG. 2B illustrates the state after step S02 is completed. After step S02 is completed, the substrate 301 is introduced into a plasma processing apparatus such as that shown in FIG. 3, where the following processes are performed.

[0017] First, the sacrificial layer 200 is processed (anisotropically etched) using the resist 203 as a mask (S03), and then the resist 203 is removed (S04). FIG. 2C shows the state after step S04 is completed. Next, silicon is deposited on the patterned sacrificial layer 200. A Si-containing gas is supplied from a gas line 306 to deposit a Si-containing film, resulting in the structure shown in FIG. 2D. The silicon film 204 has an amorphous structure and is deposited isotropically. However, shoulders 205 are formed in the portions where the film is deposited on the corners of the sacrificial layer 200. Examples of silicon-containing gases that can be used include tetrachlorosilane, dichlorosilane, trichlorosilane, dimethyldichlorosilane, trimethylchlorosilane, methyltrichlorosilane, monosilane, disilane, and trisilane.

[0018] Next, a nitrogen-containing gas is supplied from the gas line 306, and nitrogen ions generated by nitrogen plasma are irradiated vertically onto the silicon film 204 (S06). Examples of the nitrogen-containing gas include nitrogen and ammonia. A substrate bias is applied from the substrate bias high-frequency power supply 310, and nitrogen ions are irradiated perpendicularly to the sample mounting surface of the sample stage 303. This causes a reaction between silicon and the nitrogen ions to proceed from the top surface of the silicon film 204. As a result, the silicon film 204 above and below the sacrificial layer pattern (i.e., on the film 201 to be etched) is selectively nitrided to form a silicon nitride film 206, while the silicon film 204 deposited on the side surfaces of the sacrificial layer pattern remains intact. This results in the structure shown in FIG. 2E. In FIG. 2E, the plane parallel to the sample mounting surface of the sample stage 303 is indicated as a horizontal plane H.

[0019] 2E, the shoulder portion 205 is also made of silicon nitride film 206. Because the upper surface of the shoulder portion 205 is angled with respect to the horizontal plane H, the proportion of nitrogen ions incident on the silicon film 204 is reduced, and the boundary between the silicon nitride film 206 on the upper surface of the sacrificial layer pattern and the silicon film 204 on the side surface of the sacrificial layer pattern is therefore gentler than at least the upper surface of the shoulder portion 205 (although the boundary is drawn as if it were parallel to the horizontal plane H in FIG. 2E, this does not mean that it is limited to being horizontal).

[0020] Next, an oxygen-containing gas is supplied from the gas line 306, and oxygen radicals generated by the oxygen plasma are irradiated to oxidize the silicon on the sidewall of the sacrificial layer pattern (S07). Examples of the oxygen-containing gas include oxygen, carbon monoxide, carbon dioxide, and oxygen nitride (NO ２ 2F shows a state after step S07 is completed, in which the silicon film 204 remaining after step S06 is completed is oxidized to form a silicon oxide film 207.

[0021] The temperature at which the ion bombardment by plasma of nitrogen-containing gas in step S06 and the sidewall oxidation by plasma of oxygen-containing gas in step S07 can be performed effectively is approximately 100° C. From this perspective, it is preferable to carry out the process flow of this embodiment using an ECR-excited plasma processing apparatus such as that shown in FIG.

[0022] Thereafter, the silicon nitride film 206 above and on the bottom of the sacrificial layer pattern is removed (S08), and the sacrificial layer is further removed (S09). Fig. 2G shows the state after step S09 is completed. Thereafter, the film to be etched 201 is processed (anisotropically etched) using the remaining silicon oxide film 207 as a mask (S10). Fig. 2H shows the state after step S10 is completed.

[0023] 2F, steps S05 to S07 in the process flow may be repeated multiple times, rather than being performed once. This allows a high-density silicon oxide film 207 to be obtained, and the etching resistance of the mask can be improved.

[0024] The effect of the plasma processing of this embodiment will be described below. In a conventional SADP process, shoulder-dropped portions occur during the formation of a silicon oxide film used as a mask. This state is shown in FIG. 4 as a comparative example. FIG. 4 shows an example in which a silicon oxide film 401 used as a mask is formed on a film 201 to be etched by ALD. In this case, gap A is formed where the shoulder-dropped portions of the mask face each other, and gap B is formed where the non-shoulder-dropped portions of the mask face each other. During etching of the film 201 to be etched, the amount of ions incident on gap A is greater than the amount of ions incident on gap B. This results in variations in the processing width of the film 201 to be etched between gap A and gap B. With fine patterns, such variations in processing width cannot be ignored.

[0025] 2G, the sloped shoulders formed during silicon film deposition are removed before forming the silicon oxide film 207 used as a mask. As a result, at least the slope of the top surface of the silicon oxide film 207 relative to the horizontal plane is gentler than that of the sloped shoulders formed during silicon film deposition, and dimensional variations in the pattern of the film 201 to be etched that is finally obtained can be reduced.

[0026] Furthermore, by forming a silicon oxide film as a mask by oxidation with oxygen radicals, the film quality is strengthened, and a highly durable oxide film mask can be formed.

[0027] The present invention is not limited to the above-described embodiments and includes various modifications. For example, the above-described embodiments and modifications have been described in detail to make the present invention easier to understand, and are not necessarily limited to those including all of the described configurations. Furthermore, it is possible to replace part of the configuration of one embodiment or modification with the configuration of another embodiment or modification, and it is also possible to add the configuration of another embodiment or modification to the configuration of one embodiment or modification. Furthermore, it is possible to add, delete, or replace part of the configuration of each embodiment or modification with other configurations.

[0028] 200: sacrificial layer, 201: film to be etched, 202: semiconductor substrate, 203: resist, 204: silicon film, 205: shoulder portion, 206: silicon nitride film, 207: silicon oxide film, 300: vacuum vessel, 301: substrate to be processed, 302: shower plate, 303: sample stage, 304: microwave power supply, 305: mass flow controller, 306: gas line, 307: exhaust pipe, 308: pressure control valve, 309: pump, 310: high frequency power supply for substrate bias, 311: control unit, 321: microwave generation source, 322: rectangular waveguide, 323: microwave matching box, 324: converter, 325: circular waveguide, 326: cavity, 327: electromagnet, 328: partition plate.

Claims

1. A plasma processing method for plasma etching a film to be etched of a substrate to be processed, the substrate having a film to be etched and a sacrificial layer patterned above the film to be etched, comprising: a first step of depositing a silicon element-containing film on the sacrificial layer using plasma generated by a silicon element-containing gas; after the first step, a second step of nitriding the silicon element-containing film deposited on the sacrificial layer and the silicon element-containing film deposited on the film to be etched using plasma generated by a nitrogen element-containing gas; after the second step, a third step of oxidizing the silicon element-containing film using plasma generated by an oxygen element-containing gas; after the third step, a fourth step of removing a silicon nitride film on the film to be etched or the sacrificial layer; after the fourth step, a fifth step of removing the sacrificial layer; and after the fifth step, a sixth step of plasma etching the film to be etched using a silicon oxide film formed on the film to be etched as a mask.

2. The plasma processing method according to claim 1, wherein the sacrificial layer is a silicon nitride film or a polysilicon film.

3. The plasma processing method according to claim 1, wherein the first step, the second step, the third step, and the like are repeated a predetermined number of times.

4. The plasma processing method according to claim 2, wherein the first step, the second step, the third step, and the like are repeated a predetermined number of times.

5. A plasma processing method according to claim 1, wherein the second step is carried out while supplying high frequency power to a sample stage on which the substrate to be processed is placed.

6. A plasma processing method according to claim 2, wherein the second step is carried out while supplying high frequency power to a sample stage on which the substrate to be processed is placed.

7. A plasma processing method according to claim 1, characterized in that the silicon oxide film is a film formed by oxidizing the silicon element-containing film deposited on the side surface of the sacrificial layer in the third step.

8. A plasma processing method according to claim 2, characterized in that the silicon oxide film is a film formed by oxidizing the silicon element-containing film deposited on the side surface of the sacrificial layer in the third step.

9. The plasma processing method according to claim 1, wherein the plasma in the first step to the third step is plasma generated by electron cyclotron resonance.

10. The plasma processing method according to claim 2, wherein the plasma in the first step to the third step is plasma generated by electron cyclotron resonance.

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