JP7524003B2 - Etching method and plasma processing apparatus - Google Patents

Description

This disclosure relates to an etching method and a plasma processing apparatus.

Patent document 1 discloses a technique for etching openings such as holes and trenches with high aspect ratios.

JP 2016-122774 A

This disclosure provides a technique for improving the mask selectivity while suppressing differences in the shapes of the openings formed in the film to be etched.

According to one aspect of the present disclosure, there is provided an etching method comprising: a step (A) of preparing a substrate having a laminated film in which a first film and a second film are alternately laminated, and a mask on the laminated film; and a step (B) of etching the laminated film by plasma of a process gas containing carbon and fluorine-containing gas, wherein the carbon and fluorine-containing gas has an unsaturated bond of C and a _CF3 group.

According to one aspect, it is possible to improve the mask selectivity while suppressing differences in the shapes of the openings formed in the film to be etched.

1 is a schematic cross-sectional view showing an example of a plasma processing apparatus according to an embodiment; 1A to 1C are diagrams showing an example of an etching method according to an embodiment. 3A and 3B are diagrams showing a laminated film, which is a film to be etched, and a mask structure according to the embodiment; FIG. 4 is a diagram showing an example of an opening according to the embodiment. FIG. 13 is a diagram showing an example of a problem with etching. 4A to 4C are diagrams for explaining the mechanism of etching an opening portion. FIG. 13 is a diagram showing an example of the depth that radicals reach in an opening in a film to be etched depending on the sticking coefficient. FIG. 4 is a diagram showing an example of the relationship between gas types and deposit attachment positions on a mask. 4A to 4C are diagrams showing a model of precursor generation and surface reaction on a substrate according to an embodiment. 5A to 5C are diagrams showing structures for each gas type according to the embodiment. 11A and 11B are diagrams showing a mask selectivity and a depth difference between a central portion and a peripheral portion of a pattern according to the embodiment; 11 is a graph showing a mask selectivity and an etching rate of a laminated film according to the embodiment; 1 is a graph showing the etching rate and mask selectivity of a laminated film versus the surface temperature of a substrate according to an embodiment; 1 is a table showing a mask selectivity and an etching rate of a laminated film for each gas type according to an embodiment.

In the etching process, a mask patterned with multiple holes (or lines) is used to etch the film to be etched. The patterned holes (or lines) are formed densely in a certain area, but after etching is completed, there is a difference in the etching depth between the center and periphery of that area (the inner-outer loading phenomenon). This phenomenon is particularly problematic under conditions where the mask selectivity is high, that is, where deposition is high, and can cause circuit defects. For this reason, there is a demand for an etching method that makes the mask opening dimensions the same in the center and periphery of the pattern. The mask selectivity is the ratio of the etching rate of the film to be etched to the etching rate of the mask (mask E/R) in the etching process.

In this embodiment, a plasma is generated from a gas containing a hydrogen-containing gas and a gas containing carbon and fluorine, and a laminated film (ON layer) of a silicon oxide film (SiOx) and a silicon nitride film (SiN) is etched by the generated plasma, and the carbon and fluorine-containing gas includes a polyvalent hydrofluorocarbon gas having a double bond of C and a _CF3 group.

The amount of active species supplied to each of the dense and sparse regions of the mask pattern and the amount of reaction products generated are different, and the critical dimension (CD) of the frontage of the central part and the outer periphery of the pattern area is different. This causes a difference in the shape of the etched film after etching. Therefore, a carbon gas is used that makes the deposition on the mask as uniform and vertical as possible. The radicals generated from hydrofluorocarbon gas have a higher adhesion coefficient than the radicals generated from fluorocarbon gas, and the larger the polymer, the larger it is. The double bond of C contributes to the deposition on the mask, and the CF ₃ group contributes to ensuring the etching rate (ONE E/R) of the ON layer, so a high mask selectivity is obtained.

The etching method according to this embodiment can prevent differences in the shapes of the openings formed in the film to be etched.

Below, a description will be given of a mode for carrying out the present disclosure with reference to the drawings. In each drawing, the same components are given the same reference numerals, and duplicate descriptions may be omitted.

[Plasma Processing Apparatus]
First, an example of a plasma processing apparatus 1 used in the etching method according to the present embodiment will be described with reference to Fig. 1. Fig. 1 is a schematic cross-sectional view showing an example of the plasma processing apparatus 1 according to the embodiment. The plasma processing apparatus 1 shown in Fig. 1 is a capacitively coupled type apparatus.

The plasma processing apparatus 1 has a chamber 10. The chamber 10 provides an internal space 10s therein. The chamber 10 includes a chamber body 12. The chamber body 12 has a substantially cylindrical shape. The internal space 10s is provided inside the chamber body 12. The chamber body 12 is formed of, for example, aluminum. A corrosion-resistant film is provided on the inner wall surface of the chamber body 12. The corrosion-resistant film may be an oxide film formed of ceramics such as alumina (aluminum oxide) or yttrium oxide and anodized.

A passage 12p is formed in the side wall of the chamber body 12. The substrate W passes through the passage 12p when being transported between the internal space 10s and the outside of the chamber 10. The passage 12p can be opened and closed by a gate valve 12g. The gate valve 12g is provided along the side wall of the chamber body 12.

A support 13 is provided on the bottom of the chamber body 12. The support 13 has a generally cylindrical shape and is made of an insulating material. The support 13 extends upward from the bottom of the chamber body 12 in the internal space 10s. An edge ring 25 (also called a focus ring) that surrounds the periphery of the substrate is provided on the support 13. The edge ring 25 has a generally cylindrical shape and may be made of silicon or the like.

The plasma processing apparatus 1 further includes a mounting table 14. The mounting table 14 is supported by a support portion 13. The mounting table 14 is provided in the internal space 10s. The mounting table 14 is configured to support a substrate W within the chamber 10, i.e., the internal space 10s.

The mounting table 14 has a lower electrode 18 and an electrostatic chuck 20 according to one exemplary embodiment. The mounting table 14 may further have an electrode plate 16. The electrode plate 16 is formed of a conductor such as aluminum and has a substantially disk-like shape. The lower electrode 18 is provided on the electrode plate 16. The lower electrode 18 is formed of a conductor such as aluminum and has a substantially disk-like shape. The lower electrode 18 is electrically connected to the electrode plate 16. The outer peripheral surface of the lower electrode 18 and the outer peripheral surface of the electrode plate 16 are surrounded by the support portion 13.

The electrostatic chuck 20 is provided on the lower electrode 18. The electrode of the electrostatic chuck 20 is connected to a DC power supply 20p via a switch 20s. When a voltage from the DC power supply 20p is applied to the electrode, the substrate W is held by the electrostatic chuck 20 by electrostatic attraction. The electrostatic chuck 20 supports the substrate W and the edge ring 25.

A flow path 18f is provided inside the lower electrode 18. A heat exchange medium (e.g., a refrigerant) is supplied to the flow path 18f from a chiller unit provided outside the chamber 10 via a pipe 22a. The heat exchange medium supplied to the flow path 18f is returned to the chiller unit via a pipe 22b. In the plasma processing apparatus 1, the temperature of the substrate W placed on the electrostatic chuck 20 is adjusted by heat exchange between the heat exchange medium and the lower electrode 18.

The plasma processing apparatus 1 is provided with a heat transfer gas supply line 24. The heat transfer gas supply line 24 supplies a heat transfer gas (e.g., He gas) from a heat transfer gas supply mechanism between the upper surface of the electrostatic chuck 20 and the lower surface of the substrate W.

The plasma processing apparatus 1 further includes an upper electrode 30. The upper electrode 30 is disposed above and facing the mounting table 14. The upper electrode 30 is supported on the upper part of the chamber body 12 via a member 32. The member 32 is made of an insulating material. The upper electrode 30 and the member 32 close the upper opening of the chamber body 12.

The upper electrode 30 may include a top plate 34 and a support 36. The bottom surface of the top plate 34 is the bottom surface on the internal space 10s side. The top plate 34 may be formed from a low-resistance conductor or semiconductor that generates little Joule heat. A plurality of gas discharge holes 34a are formed in the top plate 34. The plurality of gas discharge holes 34a penetrate the top plate 34 in the plate thickness direction.

The support 36 supports the top plate 34 in a removable manner. The support 36 is made of a conductive material such as aluminum. A gas diffusion chamber 36a is provided inside the support 36. A plurality of gas holes 36b are formed in the support 36. The plurality of gas holes 36b extend downward from the gas diffusion chamber 36a. The plurality of gas holes 36b are connected to the plurality of gas discharge holes 34a. A gas inlet 36c is formed in the support 36. The gas inlet 36c is connected to the gas diffusion chamber 36a. A gas supply pipe 38 is connected to the gas inlet 36c.

A gas supply section GS including a gas source group 40, a flow rate controller group 44, and a valve group 42 is connected to the gas supply pipe 38. The gas source group 40 is connected to the gas supply pipe 38 via the flow rate controller group 44 and the valve group 42. The gas source group 40 includes a plurality of gas sources. The valve group 42 includes a plurality of opening and closing valves. The flow rate controller group 44 includes a plurality of flow rate controllers. Each of the plurality of flow rate controllers of the flow rate controller group 44 is a mass flow controller or a pressure-controlled flow rate controller. Each of the plurality of gas sources of the gas source group 40 is connected to the gas supply pipe 38 via the corresponding flow rate controller of the flow rate controller group 44 and the corresponding opening and closing valve of the valve group 42. The power supply 70 is connected to the upper electrode 30. The power supply 70 applies a voltage to the upper electrode 30 to draw positive ions present in the internal space 10s to the top plate 34.

In the plasma processing apparatus 1, a shield 46 is detachably provided along the inner wall surface of the chamber body 12. The shield 46 is also provided on the outer periphery of the support portion 13. The shield 46 prevents reaction products such as etching by-products from adhering to the chamber body 12. The shield 46 is formed, for example, by forming a corrosion-resistant film on the surface of a member made of aluminum. The corrosion-resistant film can be an oxide film such as alumina or yttrium oxide.

A baffle plate 48 is provided between the support 13 and the side wall of the chamber body 12. The baffle plate 48 is formed by forming a corrosion-resistant film on the surface of a member made of, for example, aluminum. The corrosion-resistant film can be an oxide film such as alumina or yttrium oxide. A plurality of through holes are formed in the baffle plate 48. An exhaust port 12e is provided below the baffle plate 48 and at the bottom of the chamber body 12. An exhaust device 50 is connected to the exhaust port 12e via an exhaust pipe 52. The exhaust device 50 has a pressure adjustment valve and a vacuum pump such as a turbomolecular pump.

The plasma processing apparatus 1 includes a first high frequency power supply 62 that applies high frequency HF power for plasma excitation. The first high frequency power supply 62 is configured to generate high frequency HF power in order to generate plasma from gas in the chamber 10. The frequency of the high frequency HF is, for example, within a range of 40 MHz to 100 MHz. The high frequency HF may be a pulsed voltage having a rectangular waveform.

The first high frequency power supply 62 is electrically connected to the electrode plate 16 and the lower electrode 18 via a matching box 66. The matching box 66 has a matching circuit. The matching circuit of the matching box 66 is configured to match the impedance of the load side (lower electrode side) of the first high frequency power supply 62 to the output impedance of the first high frequency power supply 62. In another embodiment, the first high frequency power supply 62 may be electrically connected to the upper electrode 30 via the matching box 66.

The plasma processing apparatus 1 may further include a second high frequency power supply 64 that applies high frequency LF power for the bias voltage. The second high frequency power supply 64 is configured to generate high frequency LF power. The high frequency LF has a frequency that is suitable for attracting ions mainly to the substrate W, and is, for example, a frequency within the range of 400 kHz to 3 MHz. The high frequency LF may be a pulsed voltage having a rectangular waveform.

The second high frequency power supply 64 is electrically connected to the electrode plate 16 and the lower electrode 18 via a matching box 68. The matching box 68 has a matching circuit. The matching circuit of the matching box 68 is configured to match the impedance of the load side (lower electrode side) of the second high frequency power supply 64 to the output impedance of the second high frequency power supply 64.

The plasma processing apparatus 1 may further include a control unit 80. The control unit 80 may be a computer including a processor, a storage unit such as a memory, an input device, a display device, a signal input/output interface, and the like. The control unit 80 controls each part of the plasma processing apparatus 1. In the control unit 80, an operator can use the input device to input commands to manage the plasma processing apparatus 1. In addition, the control unit 80 can visualize and display the operating status of the plasma processing apparatus 1 using the display device. Furthermore, a control program and recipe data are stored in the storage unit of the control unit 80. The control program is executed by the processor of the control unit 80 to execute various processes in the plasma processing apparatus 1. The processor of the control unit 80 executes the control program and controls each part of the plasma processing apparatus 1 according to the recipe data, thereby executing various processes, for example, a plasma processing method, in the plasma processing apparatus 1.

The surface temperature of the substrate (e.g., wafer temperature) is adjusted by transferring the temperature of the electrostatic chuck 20, adjusted to a desired temperature by a heat exchange medium supplied from a chiller unit through a pipe 22a, to the substrate W through the surface of the electrostatic chuck 20 and the heat transfer gas. However, the substrate W is exposed to plasma generated by the high frequency HF power for plasma excitation, and ions attracted by light from the plasma and the high frequency LF power for bias voltage are irradiated onto the substrate W. Therefore, the temperature of the substrate W, particularly the surface temperature of the substrate W facing the plasma, becomes higher than the adjusted temperature of the electrostatic chuck 20. The surface temperature of the substrate W may also increase due to radiant heat from the temperature-adjusted counter electrode or the sidewall of the chamber 10. For this reason, if the actual temperature of the substrate W during the etching process can be measured, or if the temperature difference between the adjusted temperature of the electrostatic chuck 20 and the actual surface temperature of the substrate W can be estimated from the process conditions, the setting of the adjusted temperature of the electrostatic chuck 20 may be lowered to adjust the surface temperature of the substrate W within a predetermined temperature range.

[Etching method]
The etching method according to the present embodiment will be described with reference to Fig. 2 and Fig. 3. Fig. 2 is a diagram showing an example of the etching method according to the embodiment. Fig. 3 is a diagram showing a laminated film, which is a film to be etched according to the embodiment, and a mask structure.

As shown in FIG. 2, in the etching method according to this embodiment, a substrate W is prepared (step S1) having a laminated film 100 in which silicon oxide films and silicon nitride films are alternately laminated as shown in FIG. 3(a) and a mask 101 on the laminated film 100. The silicon oxide film is an example of the first film, and the silicon nitride film is an example of the second film.

Next, the film to be etched is etched using the plasma generated by the plasma processing device 1 (step S2). The etching in step S2 is also called the main etching.

Figure 3(a) shows the film structure of the laminated film 100, which is the film to be etched, and the mask 101, in the initial state before etching. The substrate W has the laminated film 100, the mask 101 on the laminated film 100, and the base film 102 below the laminated film 100. The mask 101 is formed of an organic material, and has an opening HL formed therein. The base film 102 is formed of, for example, polysilicon. However, the base film 102 is not limited to polysilicon, and may be formed of amorphous silicon or single crystal silicon.

In the main etching of step S2, as shown in FIG. 3(b), the laminated film 100 is etched according to the pattern of the mask 101 to form a recess, and further etching is continued until the base film 102 is exposed, as shown in FIG. 3(c).

In this way, in the main etching, the laminated film 100 is etched through the opening HL of the mask 101 by the plasma of the gas supplied to the plasma processing apparatus 1, and an etched recess is formed in the laminated film 100. The hole-shaped recess formed in the laminated film 100 is also called the opening HL.

Figure 4 is a diagram showing an example of an opening HL according to an embodiment. As shown in Figure 4 (a), the opening HL has a plurality of first openings HL1 and a plurality of second openings HL2. The second openings HL2 are located so as to surround the outer periphery of the first opening HL1, and the second openings HL2 do not have an opening on their outer periphery. The CD (Critical Dimension) values of the first openings HL1 and the second openings HL2 are the same. The distance between the second opening HL2 in region 2, which is the outermost periphery, and the first opening HL1 in region 1 adjacent to the second opening HL2 is wider than or equal to the distance between adjacent first openings HL1 in region 1.

For such a configuration, the openings HL of this embodiment are defined as having a sparse or dense pattern on the mask 101. That is, when comparing region 1, where a plurality of first openings HL1 are formed, with region 2 (the region outside region 1), where a plurality of second openings HL2 are formed, the pattern of the mask 101 in region 1 is denser than the pattern of the mask 101 in region 2. In other words, the pattern of the mask 101 in region 2 is coarser than the pattern of the mask 101 in region 1.

The recess formed in the laminated film 100 may be line-shaped. In FIG. 4(b), the line-shaped recess is shown as a first opening LN1 and a second opening LN2. The second opening LN2 is positioned so as to surround the outer periphery of the first opening LN1, and the second opening LN2 does not have an opening on its outer periphery.

As shown in FIG. 4B, the pattern of the mask 101 varies between region 1 where the first opening LN1 is formed and region 2 where the second opening LN2 is formed; the pattern of the mask 101 is dense in region 1 and coarse in region 2. In the following, the pattern of the mask 101 is described using the opening HL as an example, but the etching method according to this embodiment can be applied to the mask 101 pattern in which the recesses are line-shaped.

As shown in FIG. 3, a recess is formed in the laminated film 100 by etching, and as the depth of the recess increases, the thickness of the mask 101 decreases. Furthermore, when the laminated film 100 is used, the aspect ratio of the recess increases, and the etching rate of the laminated film 100 decreases due to the depth loading effect. In particular, in etching a shape with a high aspect ratio of 40 or more, there is a risk that the mask 101 will disappear before the base film 102 is exposed, and etching will not be completed. Therefore, etching of the laminated film 100 with a high mask selectivity is required.

Figure 5 shows the mask selectivity ratio and the depth difference between the central and peripheral parts of the pattern. The horizontal axis of Figure 5(a) shows the mask selectivity ratio, and the vertical axis shows the depth difference (ΔON depth = inner - outer) between the first opening HL1 (inner) and the second opening HL2 (outer).

In general, as shown in Fig. 5(a), an etching _{result with a high mask selectivity can be obtained by using a gas having a high C/F ratio, such as C4F8 gas or C4F6 gas, compared to CF4 gas or C3F8 gas , that is} , a gas having a high ratio of carbon (C) to fluorine (F). Also, when the mask selectivity is about 4 or less, the depth difference (ΔON depth) is close to 0 for all gases. In this case, as shown in Fig. 5(b), the depths of the first opening HL1 and the second opening HL2 are almost the same.

However, for these gases, when the mask selectivity ratio is 4 or more, the depth difference increases rapidly for all gases. At this time, as shown in FIG. 5(c), the depth of the first opening HL1 becomes deeper than the depth of the second opening HL2. In other words, a difference occurs in the depth of the first opening HL1 and the second opening HL2 of the etched laminate film 100 depending on the density of the pattern of the mask 101.

Figure 6 is a diagram for explaining the etching mechanism of the first opening HL1 and the second opening HL2. Figure 6 shows the first opening HL1 at the left end shown in Figure 4(a) and the second opening HL2 adjacent to it on the right side. In region 1 where the first opening HL1 is formed, the pattern of the mask 101 is dense, and in region 2 where the second opening HL2 is formed, the pattern of the mask 101 is sparse.

As shown in FIG. 6, the depth of the second opening HL2 in the etched laminate film 100 is shallower than the depth of the first opening HL1 in response to the density of the pattern of the mask 101.

In the initial state when etching is started, the first opening HL1 and the second opening HL2 formed in the laminated film 100 have almost the same depth. However, as etching of the laminated film 100 progresses, O-containing radicals, which are reaction products generated during etching, vaporize and come out of the mask 101 through the first opening HL1 and the second opening HL2. Since the gas used in the main etching does not contain O-radicals, no O-containing radicals are present in the generated plasma. Therefore, it can be seen that the O-containing radicals generated are radicals generated from reaction products generated when SiO ₂ in the laminated film 100 is etched.

On the other hand, since the etching gas contains C radicals and F radicals, C radicals and F radicals are present in the generated plasma. Of these, the F radicals are mainly consumed in etching the laminated film 100, and the C radicals are deposited on the mask 101.

At this time, the first openings HL1 are densely present in region 1, while the second openings HL2 are sparsely present in region 2. Therefore, the number of O-containing radicals coming out of the mask 101 from the second openings HL2 in region 2 is smaller than the number of O-containing radicals coming out of the mask 101 from the first openings HL1 in region 1.

As a result, in region 1, the O-containing radicals react with the C-containing radicals to become _COx and volatilize. In this way, the C radicals are consumed in region 1, so that it is possible to suppress the C radicals from accumulating at the openings of the mask 101 and narrowing the openings of the mask. Therefore, in region 1, the CD dimension of the openings of the mask 101 does not narrow, and sufficient F-containing radicals enter the first openings HL1 from the openings of the mask 101 and reach the bottom, thereby promoting the etching rate.

On the other hand, in region 2, the presence of multiple second openings HL2 is sparse, so the proportion of O-containing radicals generated is lower than in region 1. Therefore, in region 2, fewer C-containing radicals are consumed in reaction with O-containing radicals than in region 1, and more C radicals accumulate in the openings of mask 101 than in region 1. Therefore, in region 2, the CD dimensions of the openings of mask 101 become narrower due to the accumulation of C radicals, and sufficient F-containing radicals are less likely to enter second openings HL2 through the narrowed openings of mask 101, and the etching rate decreases due to the reduction in F-containing radicals reaching the bottom.

As a result, etching is promoted in the first openings HL1 in region 1, but not in the second openings HL2 in region 2, and the depth of the recess in the second openings HL2 is shallower than the depth of the recess in the first openings HL1.

However, regardless of the density of the pattern of the mask 101, a high throughput due to a high etching rate and a high mask selectivity are required. To obtain a high throughput, etching that is unlikely to cause a difference between the depth of the recess of the second opening HL2 and the depth of the recess of the first opening HL1 is desired.

Therefore, in this embodiment, we propose an etching method that achieves high throughput and high mask selectivity when etching the laminated film 100, regardless of the density of the pattern of the mask 101, and enables etching shapes with a high aspect ratio of, for example, 40 or more.

The etching method according to this embodiment achieves high throughput and high mask selectivity by etching. In addition, a gas is selected that is less likely to reduce the CD dimension of the opening of the second opening HL2 when C radicals adhere to the mask 101.

Specifically, the laminated film 100 is etched by plasma of a process gas containing carbon and fluorine. In this embodiment, the carbon and fluorine containing gas has an unsaturated bond of C and a _CF3 group. An example of the carbon and fluorine containing gas is fluorocarbon gas or _{hydrofluorocarbon} gas. The _{hydrofluorocarbon} gas is, for example, _C3H2F4 gas. In this embodiment, the process gas may further contain a hydrogen containing gas, and an example of the hydrogen containing gas is _H2 gas.

This keeps the CD dimensions of the opening of the mask 101 uniform regardless of the density of the pattern of the mask 101, and realizes an etching process in which there is little difference in the etching depth between the first opening HL1 in region 1 and the second opening HL2 in region 2. The etching method according to this embodiment will be described in detail below.

When selecting a gas that is unlikely to reduce the CD dimension of the opening of the second opening HL2 when C radicals adhere to the mask 101, it is preferable that the gas has a low adhesion coefficient (reaction probability). Figure 7 shows an example of the depth to which radicals reach an opening in the film to be etched, depending on the adhesion coefficient.

As shown in Figure 7, when the radical sticking coefficient is low, fewer radicals are adsorbed to the side of the opening midway, and the radicals reach the bottom of the opening or deep parts of the opening. On the other hand, as the sticking coefficient increases, more radicals are adsorbed to the side of the opening midway, and it becomes more difficult for radicals to reach the bottom of the opening or deep parts of the opening.

In other words, the smaller the molecule of the gas, the lower the adhesion coefficient, and the less likely the reaction products are to adhere to the mask 101, so etching proceeds without narrowing the opening of the mask 101. However, in this case, the mask selectivity is lower.

8 is a diagram showing an example of the relationship between gas species and deposition on a mask. FIG. 8(a) shows the state of the opening of the mask 202 when a mixed gas of H ₂ /CF ₄ is supplied. FIG. 8(b) shows the state of the opening of the mask 204 when a mixed gas of H ₂ /CHF ₃ is supplied. FIG. 8(c) shows the state of the opening of the mask 203 when a mixed gas of H ₂ /CH ₂ F ₂ is supplied. FIG. 8(d) shows the state of the opening of the mask 205 when a mixed gas of H ₂ /CH ₃ F is supplied. The masks 202 to 205 may be made of the same organic material as the mask 101.

According to this, hydrofluorocarbon gas (Fig. 8(b)-Fig. 8(d)) has a higher adhesion coefficient and a higher mask selectivity than fluorocarbon gas (Fig. 8(a)), so in Fig. 8(b)-Fig. 8(d), C radicals tend to adhere to the upper part of the mask more easily than in Fig. 8(a), and the mask opening tends not to become narrower. In other words, a gas with a low adhesion coefficient has a high etching rate but a low mask selectivity, and a gas with a high adhesion coefficient has a high mask selectivity but a low etching rate.

In contrast, the etching method according to the present embodiment achieves both an etching rate and a mask selectivity, which are in a trade-off relationship, and achieves etching that is less likely to cause differences in etching depth for openings HL that have a sparse or dense pattern in the mask 101. For this reason, a hydrofluorocarbon gas having an unsaturated bond of C and a _CF3 group is used as the gas used for etching.

9 is a diagram showing the generation of a precursor according to this embodiment and a surface reaction model on a substrate W. In FIG. 9, C ₃ H ₂ F ₄ gas is taken as an example of a hydrofluorocarbon gas having an unsaturated bond of C and a CF ₃ group for etching. In this embodiment, the unsaturated bond of C is a double bond of C as an example, but is not limited thereto and may be a gas having a triple bond or the like.

As shown in FIG. 9, C ₃ H ₂ F ₄ gas contained in the processing gas supplied in the etching method according to this embodiment is supplied to an internal space 10 s of a chamber 10 and dissociated in a plasma 2 .

Fig _. 10 is a diagram showing the structure of each gas type according to the embodiment. _C3H2F4 gas has the structure shown in Fig. 10(f), _and is easily broken at the connection between the _CF3 group and the unsaturated bond of C, and dissociates into a compound having an unsaturated bond of C (here, a double bond of C) and a compound having a _CF3 group in the plasma 2. Hereinafter, the compound having an unsaturated bond of C is called carbon fragment A, and the compound having a _CF3 group is called fluorocarbon fragment B.

FIG. 9 shows a state in which C ₃ H ₂ F ₄ gas (CHF=CH-CF ₃ ) is dissociated into carbon fragment A (CHF=CH) and fluorocarbon fragment B (CF ₃ ) in plasma 2 .

During etching, carbon fragment A (CHF=CH) preferentially adheres to the upper part of the mask 101 in the main etching (see 103 in FIG. 9). This is because carbon fragment A having a double bond of C is unstable and highly reactive, so that it has a high adhesion coefficient and is likely to preferentially adhere to the upper part of the mask 101. On the other hand, fluorocarbon fragment B is transported to the bottom of the opening HL (recess) formed in the laminated film 100 through the mask 101 by the main etching, and further etches the laminated film 100 because it has a large amount of F relative to C. In other words, carbon fragment A having a double bond of C contributes to a high mask selectivity, and fluorocarbon fragment B having a CF ₃ group contributes to a high etching rate. As a result, in the etching method according to this embodiment, by supplying a process gas containing C ₃ H ₂ F ₄ gas, it is possible to achieve both a high throughput due to a high etching rate and a high mask selectivity.

10A, _{it is difficult to obtain a high mask selectivity. Therefore, in etching using C 4 F 8} gas, it is difficult to achieve both a high throughput and a high mask selectivity.

The _C4F6 gas in Fig. 10(b) has two C double bonds but does not have a _CF3 group. Therefore, although a high mask selectivity can be obtained, it is difficult to obtain a high _{etching rate. Therefore, in etching using C4F6 gas ,} it is difficult to achieve both a high throughput and a high mask selectivity.

The C ₃ F ₈ gas in FIG. 10(c) has a CF ₃ group, so a high etching rate can be obtained, but it does not have an unsaturated bond of C, so it is difficult to obtain a high mask selectivity. Therefore, in etching using C ₃ F ₈ gas, it is difficult to achieve both a high throughput and a high mask selectivity. Similarly, the CH ₂ F ₂ gas in FIG. 10(e) does not have an unsaturated bond of C, so it is difficult to achieve both a high throughput and a high mask selectivity. Therefore, in etching using CH ₂ F ₂ gas, it is difficult to achieve both a high throughput and a high mask selectivity.

The C ₃ F ₆ gas in FIG. 10(d) has a CF ₃ group, so that a high etching rate can be obtained. In addition, because it has a double bond of C, a high mask selectivity can be obtained. Therefore, in etching using C ₃ F ₆ gas, it is possible to achieve both a high throughput and a high mask selectivity. However, in the laminated film 100 in which silicon oxide films and silicon nitride films are alternately laminated, hydrogen is required for etching the silicon nitride film. Therefore, in etching using C ₃ F ₆ gas, it is necessary to include C ₃ F ₆ gas and a hydrogen-containing gas in the processing gas.

10(d) and _C3H2F4 gas in _{FIG. 10(f), the hydrofluorocarbon gas C3H2F4 has a higher adhesion coefficient than the fluorocarbon gas C3F6. Therefore, C3H2F4 gas makes it easier for C radicals} to adhere to the upper part of the mask 101 than _C3F6 gas, _and the _mask selectivity can be _further increased.

However, the carbon- and _fluorine -containing gas used in the etching method according to this embodiment is not limited to _C3H2F4 gas and _C3F6 gas. For example, the carbon- and _fluorine -containing gas may be any gas _that dissociates into a compound containing a fragment having an unsaturated bond of C and a fragment having a _CF3 group when dissociated in the plasma 2.

[Experimental Result 1: Difference in Depth Between First Opening and Second Opening Depending on Gas Type]
Next, _{an experiment was conducted to compare the use of C3H2F4 gas in} the etching method according to this embodiment with the use of a number of other gas species, and to measure the difference in depth between the first opening HL1 and the second opening HI2 for each gas species.

The etching conditions in this embodiment are as follows.
<Etching conditions for Experimental Result 1>
Pressure in processing vessel: 20 mT (2.67 Pa)
High frequency HF power: On
High frequency LF power: On
Processing gas: _{C3H2F4 gas} , _C4F8 gas, _C4F6 gas, _CH2F2 gas Additive gas: _Hydrogen ( _H2 ) gas Substrate _surface temperature: _{0 °} C

11 is a diagram showing the mask selectivity and the depth difference between the central portion and the peripheral portion of the pattern according to the embodiment. In Experimental Result 1, etching was performed using the four gases shown in FIG. 11. The horizontal axis of FIG. 11 shows the mask selectivity, and the vertical axis shows the depth difference (ΔON depth=inner-outer) between the first opening HL1 (inner) and the second opening HL2 (outer). The case where C ₄ F ₈ gas and C ₄ F ₆ gas were used is the same as that shown in FIG. 5.

11, in the cases where _{C4F8 gas} and _C4F6 gas were used, when the mask selectivity was about 4 or less, the depth difference (ΔON depth) for each gas was close to 0. In this case, as shown in FIG. 5B _, the depths of the first opening HL1 and the second opening HL2 are almost the same.

However, when the mask selectivity ratio of these gases is 4 or more, the depth difference increases for all gases. In this case, as shown in FIG. 5(c), the depth of the first opening HL1 becomes deeper than the depth of the second opening HL2.

In the case where _CH2F2 gas was used _, when the mask selectivity was about 4.5 or less, the depth difference was close to 0. However, when the mask selectivity was 4.5 or more, the depth difference increased, and the etching reached the state shown in Figure 5(c).

In contrast, in the case where C ₃ H ₂ F ₄ gas was used, when the mask selectivity was about 4.8 to 4.9 or less, the depth difference was close to 0, and etching proceeded in the state shown in FIG. 5(b).

From the above results, when _C3H2F4 gas was used, carbon fragment A having an unsaturated bond of C contributed to a high mask selectivity, _and the mask selectivity was increased compared to the case of using _CH2F2 gas having no _unsaturated bond of C. In addition, since carbon fragment A having an unsaturated bond of C preferentially adheres to the upper part _of the mask 101 and does not easily narrow the opening of the mask 101, no difference occurs in the progress of etching of the first opening HL1 and the second opening HL2, and it was found that recesses of approximately the same depth can be formed.

[Experimental Result 2: Mask Selectivity and Etching Rate of Layered Film]
Next, _an experiment was conducted to obtain the relationship between the mask selectivity and the etching rate of the laminated film 100 when using _C3H2F4 gas and a plurality of other gases. Fig. 12 is a diagram showing _the relationship between the mask selectivity and the etching rate of the laminated film 100 according to the embodiment. The process conditions other than the gas related to the experimental result 2 are as shown in the above <Etching conditions of the experimental result 1>.

According to the experimental result 2 in FIG. 12, _it was _{found that there is a trade-off between the mask selectivity and the etching rate of the laminated film 100 regardless of whether C4F8 gas, C4F6 gas , C3F8 gas , or C3H2F4} gas is used.

When _C4F6 gas was used, the etching rate of the laminated film 100 was lower than _that of other gases, and the throughput was reduced. In addition, when _C4F6 gas was used, the mask selectivity was relatively lower than that of other gases. When _C3F8 gas was used, the etching rate of the laminated film ₁₀₀ was high, but the mask selectivity could not reach 3.4 or more, and it was not possible to achieve both the mask selectivity and _the etching rate.

When _C3H2F4 gas was used _, the trade-off between the mask selectivity and the _etching rate was improved compared to when _C4F8 gas was used _, and a high mask selectivity was obtained while suppressing the decrease in the _etching rate. This is because when _C3H2F4 gas was used, the carbon fragment A having an unsaturated bond of C contributed to a high mask selectivity, and the fluorocarbon fragment B having _{a CF3} group contributed to a high etching rate.

[Experimental Result 3: Etching rate and mask selectivity of laminated film versus substrate surface temperature]
Next, _an experiment was conducted to obtain the relationship between the etching rate of the laminated film and the mask selectivity with respect to the surface temperature of the substrate when _C3H2F4 gas was used. Fig. 13 is a diagram showing _the relationship between the etching rate of the laminated film and the mask selectivity with respect to the surface temperature of the substrate according to the embodiment. The process conditions other than the gas and the surface temperature of the substrate related to the experimental result 3 are as shown in the above <Etching conditions of experimental result 1>.

As shown in FIG. 13(a), lowering the surface temperature of the substrate increases the etching rate of the laminated film 100. Also, as shown in FIG. 13(b), lowering the surface temperature of the substrate increases the mask selectivity. In the gas type comparisons in Experimental Results 1 (FIG. 11) and 2 (FIG. 12), the substrate surface temperature is 0°C, so in order to obtain conditions for a higher mask selectivity, it is desirable to control the substrate surface temperature to 0°C or below.

[Summary of experimental results]
The experimental results are summarized in FIG. 14. FIG. 14 is a table showing the mask selectivity and the etching rate of the laminated film for each gas type according to the embodiment. Among the items in the table, "mask selectivity" indicates the mask selectivity obtained while maintaining the openness of the second opening HL2. "ONE E/R" is the etching rate obtained while maintaining the difference in depth between the first opening HL1 and the second opening HL2 at approximately 0, and indicates the etching rate of the laminated film 100 when the mask selectivity is fixed at 4.

Among the five gas types, the etching rate of the laminated film 100 was good when using a mixed gas of _H2 / _C4F8 , but since it did not have an unsaturated bond of C _, the mask selectivity was low, and it was not possible to achieve both the mask selectivity and the etching rate of the laminated film 100.

In the etching using a mixed gas of H ₂ /CH ₂ F ₂ , the etching rate of the laminated film 100 was good, but since there was no unsaturated bond of C, the improvement in the mask selectivity was small, and it was not possible to achieve both the mask selectivity and the etching rate of the laminated film 100.

In the etching using a mixed gas of H ₂ /C ₃ H ₂ F ₄ , since the gas has an unsaturated bond of C and a CF ₃ group, both the etching rate of the laminated film 100 and the mask selectivity are improved, and both the mask selectivity and the etching rate of the laminated film 100 are achieved.

In etching using a mixed gas of _H2 / _C4F6 , since the mixed _gas does not contain a _CF3 group, the etching rate of the laminated film 100 is low and no improvement in the mask selectivity is obtained, so that it is not possible to achieve both the mask selectivity and the etching rate of the laminated film 100.

In the etching using a mixed gas of H ₂ /C ₃ F ₈ , the mask selectivity could not reach 3.4 or more, and it was not possible to achieve both a good mask selectivity and a good etching rate.

As described above, in the etching method according to this embodiment _{, by using a process gas containing H2 gas and C3H2F4 gas , it} is possible to achieve both a high mask selectivity and a high etching rate for the laminated film 100.

In addition, when etching the laminated film 100 having openings HL that are coarse on the outermost periphery and dense inside, high throughput and high mask selectivity can be achieved regardless of the density of the pattern of the mask 101.

For example, radicals generated from hydrofluorocarbon gas have a larger sticking coefficient than radicals generated from fluorocarbon gas, and the larger the sticking coefficient is, the higher the molecular weight is. The double bond of C is easily deposited on the mask 101, and a high mask selectivity is obtained. In addition, the CF ₃ group contributes to ensuring the etching rate of the laminated film 100. This makes it possible to suppress the occurrence of differences in the depth (shape) of each opening (first opening HL1 and second opening HL2) formed in the laminated film 100, which is the film to be etched.

The etching method according to the disclosed embodiment should be considered in all respects as illustrative and not restrictive. The embodiments may be modified and improved in various ways without departing from the spirit and scope of the appended claims.

The plasma processing apparatus disclosed herein can be applied to any type of apparatus, including Atomic Layer Deposition (ALD) apparatus, Capacitively Coupled Plasma (CCP), Inductively Coupled Plasma (ICP), Radial Line Slot Antenna (RLSA), Electron Cyclotron Resonance Plasma (ECR), and Helicon Wave Plasma (HWP).

REFERENCE SIGNS LIST 1 Plasma processing apparatus 10 Chamber 14 Mounting table 30 Upper electrode 46 Shield 48 Baffle plate 62 First high frequency power supply 64 Second high frequency power supply 80 Control unit 100 Stacked film 101 Mask 102 Undercoat film HL Opening HL1 First opening HL2 Second opening

Claims (9)

A step (A) of preparing a substrate having a laminated film in which silicon oxide films and silicon nitride films are alternately laminated, and a mask having an opening pattern and disposed on the laminated film;
(B) etching the laminated film with plasma of a process gas containing carbon and fluorine to form a recess ;
Including,
The carbon and fluorine-containing gas has an unsaturated bond of C and a _CF3 group ,
the mask has a first region where the pattern of the openings is dense and a second region where the pattern of the openings is sparser than the first region;
The aspect ratio of the recess is 40 or more;
a depth of the recess formed in the first region and a depth of the recess formed in the second region are substantially equal;
Etching method. The carbon and fluorine containing gas is
dissociates in the plasma into carbon fragments having the unsaturated bonds of C and fluorocarbon fragments having the _CF3 groups;
the carbon fragments preferentially adhere to the upper part of the mask in the step (B);
the fluorocarbon fragments are transported to the bottom of the recess and further etch the film stack;
The etching method according to claim 1 . The carbon and fluorine-containing gas is a fluorocarbon gas or a hydrofluorocarbon gas.
The etching method according to claim 1 or 2 . The hydrofluorocarbon gas is C ₃ H ₂ F ₄ gas;
The etching method according to claim 3 . The process gas further comprises a hydrogen-containing gas.
The etching method according to any one of claims 1 to 4 . The hydrogen - containing gas is _H2 ;
The etching method according to claim 5 . the mask has a plurality of first openings formed in the first region and a plurality of second openings formed in the second region ;
The second opening is located so as to surround an outer periphery of the first opening, and no opening is provided on the outer periphery of the second opening .
The etching method according to any one of claims 1 to 6 . In the step (B) of etching the laminated film, the surface temperature of the substrate is controlled to 0° C. or less.
The etching method according to any one of claims 1 to 7 . A plasma processing apparatus having a chamber and a control unit,
The control unit is
A step (A) of preparing a substrate having a laminated film in which silicon oxide films and silicon nitride films are alternately laminated, and a mask having an opening pattern and disposed on the laminated film, in the chamber;
(B) etching the laminated film with plasma of a process gas containing carbon and fluorine-containing gas to form a recess ;
The carbon and fluorine-containing gas supplied into the chamber in the step (B) has an unsaturated bond of C and a _CF3 group ,
the mask has a first region where the pattern of the openings is dense and a second region where the pattern of the openings is sparser than the first region;
The aspect ratio of the recess is 40 or more;
a depth of the recess formed in the first region and a depth of the recess formed in the second region are substantially equal;
Plasma processing equipment.

Images