Plasma treatment method
The plasma processing method adjusts etching conditions based on distance to maintain a consistent selectivity ratio, addressing the challenge of etching mixed layers with varying silicon and silicon oxide compositions, ensuring uniform etching across different depths.
Patent Information
- Authority / Receiving Office
- JP · JP
- Patent Type
- Patents
- Current Assignee / Owner
- PANASONIC INTELLECTUAL PROPERTY MANAGEMENT CO LTD
- Filing Date
- 2023-02-07
- Publication Date
- 2026-07-03
Smart Images
Figure 0007884213000001 
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Abstract
Description
[Technical Field]
[0001] The present invention relates to a plasma processing method, and more particularly to a method for etching a substrate in a plasma environment. [Background technology]
[0002] Semiconductor devices such as integrated circuits are formed by creating a laminate consisting of an oxide film layer, a metal film layer, a resist layer, etc., on a semiconductor substrate, and then etching the laminate using plasma or the like, with the patterned resist layer as a mask.
[0003] Patent Document 1 discloses a method for manufacturing a semiconductor device having a trench structure, comprising the steps of: forming an insulating layer on a silicon substrate; forming a resist layer on the insulating layer; a first etching step of dry etching the insulating layer using a carbon-containing etching gas with the resist layer as a mask; removing the resist layer from the insulating layer; and a second etching step of dry etching the silicon substrate using a carbon-free etching gas with the insulating layer as a mask.
[0004] In Patent Document 1, CF-based gases such as CF4 gas are used for etching the SiO2 layer, which is an insulating layer. For etching the silicon substrate, gases such as SF6 gas are used. [Prior art documents] [Patent Documents]
[0005] [Patent Document 1] Japanese Patent Publication No. 2007-5528 [Overview of the Initiative] [Problems that the invention aims to solve]
[0006] When performing groove processing by plasma etching after forming an opening on the surface of a substrate, it was sometimes difficult to smoothly etch the layer at the bottom of the opening in which silicon and silicon oxide are distributed in the plane (hereinafter also referred to as the "mixed layer"). [Means for solving the problem]
[0007] One aspect of the present disclosure relates to a plasma processing method comprising: an opening forming step of forming an opening in a substrate having a mixed layer in which a first region of silicon and a second region of silicon oxide are distributed in the plane, the opening exposing the first region and the second region; a distance acquisition step of obtaining the distance from the surface-side edge of the substrate in the opening to the mixed layer; a determination step of determining etching conditions for plasma etching the mixed layer based on the distance; and an etching step of etching the first region and the second region exposed in the opening according to the etching conditions, wherein the etching conditions when the distance is a first distance are defined as the first etching conditions, and the etching conditions when the distance is a second distance greater than the first distance are defined as the second etching conditions, the ratio R1 / R2 of the etching rate of Si to the etching rate of SiO2 in the second etching conditions is smaller than the ratio R1 / R2 in the first etching conditions. [Effects of the Invention]
[0008] According to the present invention, a mixed layer containing a first region of silicon and a second region of silicon oxide, exposed at the bottom of the opening, can be smoothly etched. [Brief explanation of the drawing]
[0009] [Figure 1A] This is a cross-sectional view of a substrate structure showing how grooves penetrating the mixed layer are formed by etching using the plasma processing method of this embodiment. [Figure 1B] This is a cross-sectional view of a substrate structure showing how grooves penetrating the mixed layer are formed by etching using the plasma processing method of this embodiment. [Figure 1C] This is a cross-sectional view of a substrate structure showing how grooves penetrating the mixed layer are formed by etching using the plasma processing method of this embodiment. [Figure 1D] This is a cross-sectional view of a substrate structure showing how grooves penetrating the mixed layer are formed by etching using the plasma processing method of this embodiment. [Figure 2] This is an example of a flowchart illustrating the plasma processing method of this embodiment. [Figure 3] This is a schematic cross-sectional diagram showing an example of the configuration of a plasma processing apparatus (etching apparatus) used in the plasma processing method of this embodiment. [Figure 4A] This is a schematic cross-sectional diagram of a substrate showing an example of the mixed layers in this embodiment. [Figure 4B] This is a schematic cross-sectional diagram of a substrate showing an example of the mixed layers in this embodiment. [Figure 4C] This is a schematic cross-sectional diagram of a substrate showing an example of the mixed layers in this embodiment. [Figure 4D] This is a schematic cross-sectional diagram of a substrate showing an example of the mixed layers in this embodiment. [Modes for carrying out the invention]
[0010] The embodiments of this disclosure will be described below with examples, but this disclosure is not limited to the examples described below. In the following description, specific numerical values and materials may be given as examples, but other numerical values and materials may be applied as long as the effects of this disclosure are obtained. In this specification, the description "numerical value A to numerical value B" includes numerical value A and numerical value B, and can be read as "greater than or equal to numerical value A and less than or equal to numerical value B". In the following description, when lower and upper limits of numerical values relating to specific physical properties or conditions are given as examples, either of the given lower limits and either of the given upper limits can be arbitrarily combined, as long as the lower limit is not greater than or equal to the upper limit. When multiple materials are given as examples, one of them may be selected and used alone, or two or more may be used in combination.
[0011] In addition, the present disclosure includes combinations of matters described in two or more claims arbitrarily selected from a plurality of claims described in the appended claims. That is, as long as no technical contradiction occurs, matters described in two or more claims arbitrarily selected from a plurality of claims described in the appended claims can be combined.
[0012] In the following description, the terms "containing" or "including" are expressions that include "containing (or including)", "substantially consisting of", and "consisting of".
[0013] On the other hand, the "first region (or second region) of silicon (or silicon oxide)" is an expression that includes the "first region (or second region) consisting of silicon (or silicon oxide)" and the "first region (or second region) substantially consisting of silicon (or silicon oxide)". Also, "B consisting of A" and "B substantially consisting of A" mean that, for example, 60 to 100% by mass or 90 to 100% by mass of B is composed of A.
[0014] The plasma processing method according to the present invention includes an opening forming step (i) of forming an opening for exposing the first region and the second region in a substrate including a mixed layer in which the first region of silicon and the second region of silicon oxide are distributed in the plane, a distance acquisition step (ii) of acquiring the distance from the end on the surface side of the substrate in the opening to the mixed layer, a determination step (iii) of determining etching conditions for plasma etching the mixed layer based on the distance, and an etching step (iv) of etching the first region and the second region exposed in the opening according to the etching conditions. On the surface of the mixed layer viewed from the opening side, the first region and the second region are distributed in a predetermined pattern or arrangement. At least one of the first region and the second region may be divided into a plurality of parts.
[0015] In the determination step (iii), the etching conditions may be configured to select one from a plurality of pre-registered etching conditions according to the distance. For example, the etching condition when the distance is the first distance is designated as the first etching condition. The etching condition when the distance is the second distance, which is greater than the first distance, is designated as the second etching condition. If we generalize the expression using an integer n, the etching condition when the distance is the nth distance is designated as the nth etching condition, and the etching condition when the distance is the (n+1)th distance, which is greater than the nth distance, is designated as the (n+1)th etching condition. Multiple etching conditions can be rephrased as n etching conditions.
[0016] Let R1 be the etching rate of Si and R2 be the etching rate of SiO2 under each etching condition, and let R1 / R2 be the selectivity ratio of the etching rate of Si R1 to the etching rate of SiO2 R2. Here, the etching rate depends on the depth of the opening, but R1 and R2 are the rates when etching the surface of the substrate (i.e., when the opening depth is zero). In general, when the depth of the opening is d, the etching rate of Si at the bottom of the opening R Si and the etching rate R of SiO2 SiO2 As shown in the following equation, K1 and K2 decrease with increasing d.
[0017] R Si = R1-K1(d) R SiO2 = R2-K2(d)
[0018] The inventors noted that the dependence of the plasma etching rate of Si and SiO2 on depth d is different. Specifically, the etching rate R of Si Si In this case, K1 is relatively small, and the decrease in etching rate is small with increasing aperture depth d. In contrast, in the etching of SiO2, K2 is relatively large, and the etching rate R decreases with increasing aperture depth d. SiO2 The decrease is significant (K2 > K1).
[0019] The reason is presumed as follows. In the case of plasma etching of Si, since reactive products with high vapor pressure are likely to be generated by the reaction between radicals contained in the plasma and Si, the main etching mechanism is considered to be reactive etching by radicals, and the depth dependence is relatively small. On the other hand, in the case of dry etching of SiO2, since the reactivity of SiO2 is low, the contribution of radicals to etching is small, and the main etching mechanism is ionic etching in which Si is sputtered by ion bombardment contained in the plasma, and the depth dependence is considered to be relatively large. Such a difference in the etching mechanisms between Si and SiO2 is considered to be the cause of the difference in the dependence of the etching rate on the depth d of the opening.
[0020] Normally, when the mixed layer is exposed on the outermost surface of the substrate (when d = 0), by using etching conditions where the value of the selectivity ratio R1 / R2 is approximately 1, this mixed layer can be etched smoothly. However, as the depth d of the opening (the distance from the end on the surface side of the substrate in the opening to the mixed layer) increases (d > 0), even when using the conditions (selectivity ratio R1 / R2 ≒ 1) that can smoothly etch the mixed layer exposed on the outermost surface (depth d = 0), as described above, since the degrees of decrease in the etching rates of Si and SiO2 with respect to depth are different, the balance of the etching rates of the two is disrupted, and the etching rate R of SiO2 on the surface of the mixed layer SiO2 becomes slower than the etching rate R of Si Si , and the effective selectivity ratio R Si / R SiO2 increases, and there may be cases where the mixed layer cannot be etched smoothly.
[0021] According to the plasma processing method of the present disclosure, in accordance with the distance from the end on the surface side of the substrate in the opening to the mixed layer, R1 / R2 that can smoothly etch the mixed layer is selected. Thereby, it becomes possible to smoothly etch the mixed layer regardless of the distance to the mixed layer.
[0022] For example, the selectivity ratio R1 / R2 in the second etching condition when the distance to the mixed layer is greater than the first distance is set to be smaller than the selectivity ratio R1 / R2 in the first etching condition when the distance to the mixed layer is the first distance. As described above, the actual selectivity ratio R on the surface of the mixed layer Si / R SiO2 The selectivity ratio R increases as the distance to the mixed layer increases. However, by setting small R1 / R2 etching conditions, the selectivity ratio R remains almost constant regardless of the distance to the mixed layer. Si / R SiO2 This allows the etching process to proceed, making it possible to etch the mixed layers smoothly.
[0023] The etching process (iv) may be carried out with the substrate placed on a stage equipped with electrodes to which high-frequency power can be applied. An example of etching conditions in this case is one in which high-frequency power is applied to the electrodes while supplying a source gas containing SF6 and Ar.
[0024] In this case, to reduce the selectivity ratio R1 / R2, either R1 should be reduced or R2 should be increased. To reduce R1, the proportion of SF6 contained in the raw material gas should be reduced. In determination step (iii), the etching conditions may be determined such that the proportion of SF6 contained in the raw material gas under the second etching conditions is smaller than the proportion of SF6 under the first etching conditions.
[0025] Furthermore, R2 can be increased by increasing the high-frequency power applied to the electrode. The higher the high-frequency power, the greater the energy of the Ar plasma accelerated toward the substrate or mixed layer, and the greater the collision energy upon impact with the mixed layer, making it easier to etch the SiO2. In determination step (iii), the etching conditions may be determined such that the high-frequency power in the second etching condition is greater than the high-frequency power in the first etching condition.
[0026] If the thickness of the mixed layer to be etched is thick, the etching conditions may be changed during the etching process (iv) to reduce the selectivity ratio R1 / R2 in accordance with the progress of etching of the mixed layer.
[0027] The plasma processing method may further include a distance measurement step (v) in the middle of the etching process, which measures the intermediate distance from the edge of the substrate on the surface side of the aperture to the bottom of the aperture, and a step of changing the etching conditions so that the ratio R1 / R2 gradually decreases in accordance with the increase in the measured intermediate distance.
[0028] The plasma treatment method according to an embodiment of the present invention will be described in detail below with reference to the drawings.
[0029] Figures 1A to 1D are cross-sectional views showing the state of the substrate 30 when grooves penetrating the mixed layer are formed by etching using the plasma processing method of this embodiment. Figure 2 is a flowchart illustrating an example of the plasma processing method of this embodiment.
[0030] (preparation process) First, a substrate 30 having a mixed layer is prepared. As shown in Figure 1A, the substrate 30 comprises a lower layer 31, a mixed layer 32 formed on the lower layer 31, and an upper layer 33 formed on the mixed layer.
[0031] The substrate 30 may be a laminate formed by bonding a first substrate and a second substrate together. In this case, the bonding surface between the first substrate and the second substrate may be within the lower layer 31, the interface between the lower layer 31 and the mixed layer 32, within the mixed layer 32, the interface between the mixed layer 32 and the upper layer 33, or within the upper layer 33.
[0032] The lower layer 31 is, for example, a semiconductor layer such as silicon, a wiring layer, or an insulating layer. The lower layer 31 may be a laminate containing multiple layers, such as a semiconductor layer, a wiring layer, or an insulating layer. The upper layer 33 includes, for example, a semiconductor layer such as silicon, a wiring layer, or an insulating film. The upper layer 33 may be a laminate containing multiple layers, such as a semiconductor layer, a wiring layer, or an insulating layer. A mixed layer 32 exists between the lower layer 31 and the upper layer 33. In the mixed layer 32, a first region of silicon and a second region of silicon oxide are distributed in the plane.
[0033] Figures 4A to 4D show examples of patterns for the first region 32a and the second region 32b in the mixed layer, as cross-sectional views of the substrate 30. Possible patterns for the first and second regions in the mixed layer include the case where the first region 32a (Si) and the second region 32b (SiO2) are distributed in a columnar manner (Figure 4A), the case where the first region 32a (Si) is dispersed so as to be surrounded by the second region 32b (SiO2) (Figure 4B), the case where the second region 32b (SiO2) is dispersed so as to be surrounded by the first region 32a (Si) (Figure 4C), and the case where the first region 32a (Si) or the second region 32b (SiO2) is distributed in a layered manner (Figure 4D). The function of the mixed layer 32 may be capacitance control or an insulating layer for insulation in an integrated circuit, or it may be a photonic crystal layer for refractive index control in an optical circuit.
[0034] Next, as shown in Figure 1B, a mask 34 is formed to cover the area of the upper layer 33 of the substrate where grooves are not to be formed, while exposing the upper layer 33 in the area X where grooves are to be formed.
[0035] (Opening formation process) Next, as shown in Figure 1C, the upper layer 33 is etched until the mixed layer 32 is exposed to form an opening 35. The etching conditions at this time are not particularly limited, and known methods can be used depending on the material of the upper layer 33. The opening width of the opening 35 is, for example, 8 μm.
[0036] (Distance acquisition process) Next, the distance d from the surface edge of the substrate at the aperture 35 to the mixed layer is obtained. The distance d is determined by obtaining the thickness of the upper layer 33 by referring to the manufacturing conditions of the substrate (wafer) 30. The distance d to the mixed layer is obtained by adding the thickness of the mask 34 to the thickness of the upper layer 33. However, it is not limited to this method, and the distance d to the mixed layer may also be measured directly using a laser distance meter or the like.
[0037] (Decision process) Next, etching conditions for plasma etching the mixed layer 32 are determined based on the distance d. For example, the etching conditions may be determined such that a first etching condition is selected when the distance d is less than a predetermined threshold, and a second etching condition is selected when the distance d is greater than or equal to a predetermined threshold. The selectivity ratio R1 / R2 in the second etching condition is smaller than the selectivity ratio R1 / R2 in the first etching condition.
[0038] Depending on the distance d, one etching condition may be selected and determined from a set of pre-prepared etching conditions. The etching conditions may be determined according to the distance d such that the larger the distance d, the smaller the selection ratio R1 / R2. For example, the etching conditions according to distance d may be calculated by interpolation calculations from the etching conditions prepared in advance for the first distance d1 and the etching conditions prepared in advance for the second distance d2. Furthermore, the etching conditions may be determined according to the aspect ratio of the aperture 35, which is the ratio of the distance d to the aperture width of the aperture 35. In this case, if the aspect ratio is the same, the same etching conditions can be selected even if the distance d is different. For example, when etching a substrate with a small aperture 35 and when etching a substrate with a large aperture 35, if the aspect ratio of the aperture 35 is the same, the same etching conditions may be selected.
[0039] (Etching process) Next, the first and second regions exposed in the opening 35 are etched according to the etching conditions determined in the determination step.
[0040] An example of a first etching condition selected when the aperture width of aperture 35 is, for example, 8 μm and the distance d is a first distance less than a predetermined threshold (for example, less than 20 μm) (i.e., when converted to an aspect ratio of aperture 35, it is less than 2.5) is shown below. In this case, the etching rate R1 is 0.37 μm / min, the etching rate R2 is 0.37 μm / min, and the selectivity ratio R1 / R2 is 1.0.
[0041] Etching gas: A mixture of Ar, SF6, C4F8, and O2. Ar flow rate: 300sccm SF6 flow rate: 27sccm C4F8 flow rate: 20sccm O2 flow: 10sccm Total pressure: 2.0 Pa Power applied to the ICP coil: 2400W Bias: 500W
[0042] In contrast, an example of a second etching condition selected when the aperture width of the aperture 35 is, for example, 8 μm and the distance d is a second distance greater than or equal to a predetermined threshold (for example, 24 μm or more) (i.e., when converted to an aspect ratio of aperture 35, it is 3.0 or more) is shown below. In the second etching condition below, the SF6 flow rate is reduced compared to the first etching condition. In this case, the etching rate R1 is 0.20 μm / min, the etching rate R2 is 0.37 μm / min, and the selectivity ratio R1 / R2 is 0.54.
[0043] Etching gas: A mixture of Ar, SF6, C4F8, and O2. Ar flow rate: 300sccm SF6 flow rate: 20sccm C4F8 flow rate: 20sccm O2 flow: 10sccm Total pressure: 2.0 Pa Power applied to the ICP coil: 2400W Bias: 500W
[0044] Another example of the second etching conditions is shown below. In the example below, the high-frequency power (bias) applied to the stage is increased from the first etching conditions. In this case, the etching rate R1 is 0.15 μm / min, the etching rate R2 is 0.60 μm / min, and the selectivity ratio R1 / R2 is 0.25. Because the selectivity ratio R1 / R2 in this example is even smaller than that of the conditions described above, it is suitable for smooth etching in regions where the distance d is even deeper (for example, 40 μm or more, which translates to an aspect ratio of 5.0 or more for aperture 35).
[0045] Etching gas: A mixture of Ar, SF6, C4F8, and O2. Ar flow rate: 80sccm SF6 flow rate: 20sccm C4F8 flow rate: 39sccm O2 flow rate: 25sccm Total pressure: 1.0 Pa Power applied to the ICP coil: 4500W Bias: 1000W
[0046] In this way, by using etching conditions with a small selectivity ratio R1 / R2 in accordance with the distance d to the mixed layer, the mixed layer 32 can be etched smoothly.
[0047] Figure 1D shows the state of the substrate 30 after the etching process. After this, the lower layer 31 exposed at the bottom of the opening 35 is etched off to form a groove. The etching conditions at this time are not particularly limited, and known methods can be used depending on the material of the lower layer 31.
[0048] (distance measurement process) The etching conditions may be changed during the etching of the mixed layer. In this case, the intermediate distance from the edge of the substrate surface at the opening to the bottom of the opening should be measured during the etching process. The etching conditions may be changed so that the ratio R1 / R2 gradually decreases as the measured intermediate distance increases. The intermediate distance may be measured with a laser distance meter or the like, or, since there is a correlation between the intermediate distance and the etching time, the etching time may be used instead of the intermediate distance, and the etching conditions may be changed so that the ratio R1 / R2 gradually decreases as the etching processing time increases.
[0049] (Plasma treatment device) Figure 3 shows an example of the configuration of a plasma processing apparatus (etching apparatus) used in the plasma processing method of this embodiment. The plasma processing apparatus 21 shown in Figure 3 is an inductively coupled plasma (ICP) type dry etching apparatus and includes a chamber 23 that provides a space for generating plasma (i.e., a reaction chamber). The chamber 23 includes a gas inlet 23a for introducing process gas (etching gas) into the reaction chamber and an exhaust port 23b for exhausting gas from the reaction chamber. A gas supply source 24 for supplying process gas into the reaction chamber is connected to the gas inlet 23a. A depressurization mechanism 25 including a depressurization pump for depressurizing and exhausting the reaction chamber is connected to the exhaust port 23b.
[0050] The top of the chamber 23 is closed by a dielectric wall 26. An antenna (ICP coil) 27 is positioned above the dielectric wall 26 as the upper electrode. High-frequency power is applied to the antenna 27 from the first high-frequency power supply 28A. A stage 11 is positioned at the bottom of the chamber 23, and a substrate 22 is placed on the stage 11. The stage 11 is positioned on a metal block 12, which is housed in a base portion 13. The metal block 12 is electrically connected to the second high-frequency power supply 28B and, as the lower electrode, can apply the second high-frequency power to the substrate 22 and generate a bias voltage.
[0051] When the depressurization mechanism 25 is activated, the inside of the chamber 23 is depressurized. With the process gas introduced into the depressurized chamber 23, a high-frequency voltage is applied between the dielectric wall 26 and the stage 11 by the first high-frequency power supply 28A, causing the introduced process gas to be converted into plasma. The process gas flow rate and the output of the depressurization mechanism 25 are controlled by the controller 19. The openings of the inlet 23a and exhaust port 23b are also controlled by the controller 19. In addition, the controller 19 controls each element that constitutes the plasma processing apparatus 21.
[0052] Stage 11 includes a cooling device 14 and electrostatic adsorption electrodes 16 for electrostatically adsorbing the substrate 22. The cooling device 14 includes a refrigerant flow path 12a formed within a metal block 12 and a refrigerant circulation device 15 that circulates temperature-controlled refrigerant through the refrigerant flow path 12a. The electrostatic adsorption electrodes 16 are electrically connected to a drive power supply 17. A heat transfer gas supply hole (not shown) is provided at the position on Stage 11 where the substrate 22 is placed, and heat transfer gas is supplied to this supply hole from a heat transfer gas source 18. [Industrial applicability]
[0053] The plasma processing method according to the present invention can be applied to an etching process that forms an opening through a mixed layer comprising a first region made of silicon and a second region made of silicon oxide. [Explanation of Symbols]
[0054] 21: Plasma processing equipment (etching equipment) 11: Stage 12: Metal block 13: Base section 14: Cooling device 15: Refrigerant circulation device 16: Electrodes for electrostatic adsorption 17: Power supply 18: Heat transfer gas source 19: Controller 23a: Inlet 23b: Exhaust port 24: Gas supply source 25: Decompression mechanism 26: Dielectric wall 27: Antenna 28A: 1st high frequency power supply 28B: 2nd high frequency power supply 30: Circuit board 31: Lower layer 32: Mixed layer 32a: 1st region (Si) 32b: Second region (SiO2) 33: Upper layer 34: Mask 35:Aperture
Claims
1. An opening formation step is to form an opening in a substrate having a mixed layer in which a first region of silicon and a second region of silicon oxide are distributed in the plane, thereby exposing the first region and the second region. A distance acquisition step to obtain the distance from the edge of the substrate on the surface side of the opening to the mixed layer, A determination step for determining etching conditions for plasma etching the mixed layer based on the aforementioned distance, The process includes etching the first region and the second region exposed in the opening using the etching conditions described above, When the etching conditions when the distance is the first distance are defined as the first etching conditions, and when the etching conditions when the distance is a second distance greater than the first distance are defined as the second etching conditions, the etching rate of Si R1 of SiO in the second etching conditions is defined as follows: ２ A plasma processing method in which the ratio R1 / R2 to the etching rate R2 is smaller than the ratio R1 / R2 in the first etching condition.
2. The etching process is carried out with the substrate placed on a stage equipped with electrodes to which high-frequency power can be applied. The etching conditions are SF ６ This includes supplying a raw material gas containing Ar while applying high-frequency power to the electrode, SF contained in the raw material gas in the second etching condition ６ The plasma processing method according to claim 1, wherein the ratio is smaller than the ratio in the first etching condition.
3. The etching process is carried out with the substrate placed on a stage equipped with electrodes to which high-frequency power can be applied. The etching conditions are SF ６ This includes supplying a raw material gas containing Ar while applying high-frequency power to the electrode, The plasma processing method according to claim 1, wherein the high-frequency power in the second etching condition is greater than the high-frequency power in the first etching condition.
4. The etching process further includes a distance measurement step in which the intermediate distance from the edge of the substrate on the surface side of the opening to the bottom of the opening is measured. A plasma processing method according to any one of claims 1 to 3, comprising the step of changing the etching conditions such that the ratio R1 / R2 gradually decreases in response to an increase in the measured intermediate distance.