Method of plasma etching

Abstract

A method of plasma etching includes the following operations. A wafer and a nitride layer are received, wherein the nitride layer is disposed on the wafer. An annular pipe is disposed on an edge portion of the nitride layer, wherein the annular pipe has a plurality of holes, and the holes are directed toward the edge portion of the nitride layer. Plasma is sprayed onto an upper surface of the nitride layer. Unsaturated fluorocarbon is sprayed from the holes of the annular pipe to the edge portion of the nitride layer. The disclosure sprays the unsaturated fluorocarbon onto the edge portion of the nitride layer, reduces the increase of the etching rate on the edge portion, and thus obtains uniform etching.

Description

Technical Field

[0001] This disclosure relates to a plasma etching method. Background Technology

[0002] In the etching process of the semiconductor industry, wafers are positioned within an etching chamber and centered on an electrostatic chuck (ESC) using a focusing ring outside the wafer edge. When the wafer is centered on the ESC, the concentration of the etching gas is uniformly distributed across the wafer, ensuring a consistent etching rate and uniform etching of the material. However, as etching time increases, the focusing ring is damaged by the etching gas. When the focusing ring can no longer hold the wafer centered on the ESC, the distribution of the etching gas on the wafer becomes uneven, necessitating the replacement of the focusing ring, resulting in low yield and waste. Due to the discontinuous shape of the wafer edge, the etching non-uniformity at the wafer edge is more pronounced. Therefore, it is necessary to address the problem of uneven etching of the wafer edge material to extend the service life of the focusing ring. Summary of the Invention

[0003] This disclosure relates to a method for plasma etching, in some embodiments of which the method includes the following operations: receiving a wafer and a nitride layer, wherein the nitride layer is disposed on the wafer; providing an annular channel on an edge portion of the nitride layer, wherein the annular channel has a plurality of holes facing the edge portion of the nitride layer; spraying plasma onto an upper surface of the nitride layer; and spraying unsaturated fluorocarbons from the holes of the annular channel onto the edge portion of the nitride layer.

[0004] In some embodiments, the unsaturated fluorocarbon compound is a gas.

[0005] In some embodiments, the unsaturated fluorocarbon compound includes hexafluorobutadiene.

[0006] In some embodiments, the method further includes forming a polymer on the edge portion of the nitride layer, wherein the polymerization of unsaturated fluorocarbons is induced by plasma.

[0007] In some embodiments, spraying unsaturated fluorocarbons from these holes in the annular conduit includes spraying the unsaturated fluorocarbons at a first flow rate, wherein the first flow rate is between 0.1 SCCM and 1.2 SCCM.

[0008] In some implementations, the first flow rate is between 0.2 SCCM and 0.4 SCCM.

[0009] In some embodiments, spraying unsaturated fluorocarbons from these holes in the annular pipe includes spraying the unsaturated fluorocarbons at a first flow rate and then adjusting the first flow rate to a second flow rate after an etching time, wherein the second flow rate is greater than the first flow rate.

[0010] In some implementations, the second flow rate is between 0.8 SCCM and 3.2 SCCM.

[0011] In some implementations, the second flow rate is between 0.9 SCCM and 1.1 SCCM.

[0012] In some implementations, the etching time is between 250 hours and 350 hours.

[0013] In some embodiments, the edge portion of the nitride layer has a width of 3 mm to 5 mm from the edge of the nitride layer.

[0014] In some implementations, these holes surround the edge portion of the nitride layer when viewed from above.

[0015] In some implementations, the unsaturated fluorocarbon compound is sprayed in a direction substantially perpendicular to the upper surface of the nitride layer.

[0016] In some embodiments, the plasma includes tetrafluoromethane, difluoromethane, oxygen, or combinations thereof.

[0017] In some embodiments, the nitride layer comprises silicon nitride. Attached Figure Description

[0018] When reading the accompanying drawings of this disclosure, it is recommended to understand the various aspects of this disclosure from the following description. It should be noted that, according to industry standard practice, the various feature dimensions are not drawn to scale. For clarity of discussion, the various feature dimensions may be increased or decreased as needed.

[0019] Figure 1 A flowchart illustrating a plasma etching method according to some embodiments of this disclosure is provided.

[0020] Figure 2 Cross-sectional views of a plasma etching apparatus, a wafer, and a nitride layer according to some embodiments of this disclosure are shown.

[0021] Figure 3 A top view of a plasma etching apparatus and a nitride layer according to some embodiments of this disclosure is shown.

[0022] Figure 4 A graph showing the thickness of the nitride layer as a function of the radius of the nitride layer according to some embodiments of this disclosure is provided. Detailed Implementation

[0023] The following provides different embodiments to illustrate different features of this disclosure. To simplify the present disclosure, specific examples of elements and configurations will be described below. Of course, these are merely examples and are not intended to be limiting. For example, the description below of a first feature forming over a second feature may include embodiments where the first and second features are in direct contact, or embodiments where other features are formed between the first and second features, so that the first and second features are not in direct contact.

[0024] Furthermore, spatially relative terms, such as below and above, are used to facilitate the description of the relationship between one element or feature and another element or feature in the figures. In addition to the orientations described in the figures, spatially relative terms are intended to cover different orientations of the device during use or operation. The device may be positioned in other ways (rotated 90 degrees or other orientations), and the spatially relative descriptions used herein can be interpreted accordingly. In the discussion herein, unless otherwise stated, the same reference numerals in different figures refer to the same or similar elements formed using the same or similar materials and by the same or similar methods.

[0025] This disclosure provides a plasma etching method comprising the following operations: receiving a wafer and a nitride layer, wherein the nitride layer is disposed on the wafer; providing an annular channel on an edge portion of the nitride layer, wherein the annular channel has a plurality of holes facing the edge portion of the nitride layer; spraying plasma onto an upper surface of the nitride layer; and spraying unsaturated fluorocarbons from the holes of the annular channel onto the edge portion of the nitride layer. This plasma etching method can prevent uneven plasma etching of the nitride layer (particularly the edge portion of the nitride layer). This disclosure is further illustrated below with examples.

[0026] Figure 1 A flowchart illustrating a plasma etching method 100 according to some embodiments of the present disclosure is provided. To better understand the plasma etching method (e.g., ...) of the present disclosure... Figure 1 As shown), in reading Figure 1 Please refer to the following: Figure 2 and Figure 3 . Figure 2 Cross-sectional views of a plasma etching apparatus, a wafer, and a nitride layer according to some embodiments of this disclosure are shown. The plasma etching apparatus includes an annular channel and an inlet, which will be described later. Figure 3 Some embodiments illustrated in this disclosure are shown Figure 2 A top view of the plasma etching apparatus and the nitride layer.

[0027] Please also refer to Figure 1 and Figure 2 In operation 102 of plasma etching method 100 (e.g.) Figure 1(As shown) Receives wafer 201 and nitride layer 203 disposed on wafer 201 (e.g. Figure 2 (As shown). In some embodiments, wafer 201 includes, but is not limited to, silicon wafers, silicon carbide wafers, gallium nitride wafers, etc. In some embodiments, nitride layer 203 includes silicon nitride, such as Si3N4. In some embodiments, nitride layer 203 including silicon nitride is an insulating layer. The nitride layer 203 of this disclosure is applicable in some embodiments to, for example, a functional layer in dynamic random-access memory (DRAM). In some embodiments, the nitride layer 203 is formed by methods including, but not limited to, chemical vapor deposition (CVD), plasma-enhanced chemical vapor deposition (PECVD), or low-pressure chemical vapor deposition (LPCVD). In some embodiments, the formed nitride layer 203 covers the entire upper surface of wafer 201, such as... Figure 2 and Figure 3 As shown.

[0028] Next, as Figure 1 As shown, in operation 104 of plasma etching method 100, a layer is formed on the edge portion 203E of nitride layer 203 as shown in the figure. Figure 2 and Figure 3 The annular pipe 205 is shown. See also... Figure 2 and Figure 3 The annular conduit 205 has a plurality of holes 205H facing the edge portion 203E of the nitride layer 203 and positioned above the edge portion 203E. The annular conduit 205 is used to spray unsaturated fluorocarbon 207, which will be discussed later in operation 108. Specifically, for example, the unsaturated fluorocarbon 207 is injected into the annular conduit 205 from an inlet (not shown) and then sprayed from the holes 205H onto the edge portion 203E of the nitride layer 203. In some embodiments, the edge portion 203E of the nitride layer 203 is a region within a width W1 between 3 mm and 5 mm from the edge of the nitride layer 203. In some embodiments, such as Figure 3 As shown, the edge portion 203E has an annular shape and substantially overlaps with the annular pipe 205 when viewed from above. In... Figure 2 and Figure 3 As shown, in an embodiment where a nitride layer 203 covers the entire upper surface of wafer 201, the edge portion 203E of the nitride layer 203 is... Figure 3 In the top view, it also overlaps with the edge of wafer 201. To spray unsaturated fluorocarbon 207 onto the edge portion 203E of the nitride layer 203, the hole 205H is designed to face the edge portion 203E of the nitride layer 203, and as... Figure 3 The shown image shows the edge portion 203E surrounding the nitride layer 203, and overlaps with the edge portion 203E of the nitride layer 203. It should be noted that... Figure 3 The number of holes 205H is illustrative, and any applicable number is intended to be included in this disclosure.

[0029] Next, as Figure 1 As shown, in operation 106 of plasma etching method 100, plasma 209 is applied as follows: Figure 2 The spray is shown sprayed onto the upper surface 203U of the nitride layer 203. See also... Figure 2 and Figure 3 Inlet 211 is located above the upper surface 203U of the nitride layer 203, for injecting plasma 209 and spraying plasma 209 onto the entire upper surface 203U of the nitride layer 203. It should be noted that... Figure 2 and Figure 3 The shape and size of the inlet 211 are illustrative, and any shape and size of inlet 211 is intended to be covered by this disclosure. For example, in some embodiments, inlet 211 has a shape like a shower head and inlet 211 is larger, for example, covering the entire upper surface 203U of nitride layer 203. In some embodiments, plasma 209 is radio frequency (RF) plasma with a frequency between 1 MHz and 100 MHz, including tetrafluoromethane (CF4), difluoromethane (CH2F2), oxygen (O2), or combinations thereof. In some embodiments, since nitride layer 203 is disposed, for example by a magnet under wafer 201 ( Figure 2 and Figure 3 The center of the magnetic field generated by the plasma 209 (not shown in the image) is the center of the magnetic field. Therefore, when plasma 209 is sprayed onto the upper surface 203U of nitride layer 203, plasma 209 is uniformly dispersed on nitride layer 203, thus resulting in uniform etching of nitride layer 203. In other words, aligning the spray position of plasma 209 on nitride layer 203 can significantly maintain the uniformity of etching. However, alignment may be lost as etching time increases, for example, when the focusing ring of nitride layer 203 at the center of the magnetic field (not shown in the image) is fixed. Figure 2 and Figure 3When the nitride layer 203 is damaged by bombardment with plasma 209 (as shown in the figure), it becomes impossible to keep the nitride layer 203 in the aligned position. In this case, due to the discontinuity at the edges, the etching of the edge portions 203E of the nitride layer 203 exhibits more significant non-uniformity, for example, a faster etching rate on the edge portions 203E of the nitride layer 203. In some embodiments, the plasma 209 is removed from the etching chamber (not shown) by a vacuum pump (not shown).

[0030] Next, as Figure 1 As shown, in operation 108 of plasma etching method 100, unsaturated fluorocarbon compound 207 is applied at a first flow rate as... Figure 2 The image shows the spray applied to the edge portion 203E of the nitride layer 203. In some embodiments, operations 106 and 108 are performed simultaneously. See also... Figure 2 and Figure 3 Unsaturated fluorocarbon 207 is sprayed from the orifice 205H of the annular conduit 205 to the edge portion 203E of the nitride layer 203, as described above. The direction in which the unsaturated fluorocarbon 207 is sprayed from the orifice 205H of the annular conduit 205 to the edge portion 203E of the nitride layer 203 is substantially perpendicular to the upper surface 203U of the nitride layer 203. That is, the angle A1 between the spraying direction 213 and the upper surface 203U of the nitride layer 203 is substantially equal to 90°. In other embodiments, the angle A1 is 85° to 95°. The unsaturated fluorocarbon 207 is a gas, and as described above... Figure 2 and Figure 3 No plasma is formed in the plasma etching apparatus 200. In some embodiments, the unsaturated fluorocarbon 207 comprises hexafluorobutadiene (C4F6). Because the unsaturated fluorocarbon 207 has unsaturated bonds, it can be polymerized to form polymers (in... Figure 2 and Figure 3(Not shown in the diagram), and this polymerization is induced by plasma 209. The polymer is deposited on the edge portion 203E of the nitride layer 203 and, as a protection, reduces the local concentration of plasma 209 on the edge portion 203E. In other words, the polymer formed by the unsaturated fluorocarbon 207 reduces the etching rate of the edge portion 203E of the nitride layer 203. In some embodiments, in order to uniformly etch the nitride layer 203, the unsaturated fluorocarbon 207 is sprayed onto the edge portion 203E of the nitride layer 203 at a first flow rate between 0.1 SCCM and 1.2 SCCM, preferably between 0.2 SCCM and 0.4 SCCM. If the first flow rate is less than 0.1 SCCM, it may result in an undesirable increase in the etching rate on the edge portion 203E of the nitride layer 203, leading to poor uniformity. If the first flow rate is greater than 1.2 SCCM, it may result in an undesirable decrease in the etching rate on the edge portion 203E of the nitride layer 203, also leading to poor uniformity. In some embodiments, unsaturated fluorocarbon 207 is removed from the etching chamber (not shown) by a vacuum pump (not shown).

[0031] Next, as Figure 1 As shown, in operation 110 of the plasma etching method 100, after a certain etching time, the first flow rate is adjusted to a second flow rate greater than the first flow rate. It has been explained above that the non-uniformity of the etched edge portion 203E of the nitride layer 203 increases with increasing etching time. Therefore, it is necessary to increase the flow rate after a certain etching time, for example, by adjusting the first flow rate to a second flow rate with a larger flow rate. The larger second flow rate offsets the increase in the etching rate of the edge portion 203E of the nitride layer 203. In some embodiments, the etching time for adjusting the flow rate is between 250 hours and 350 hours. The second flow rate is between 0.8 SCCM and 3.2 SCCM, preferably between 0.9 SCCM and 1.1 SCCM. If the second flow rate is below 0.8 SCCM, it may result in an increase in the undesirable etching rate on the edge portion 203E of the nitride layer 203, leading to poor uniformity. If the second flow rate is above 3.2 SCCM, it may result in a decrease in the undesirable etching rate on the edge portion 203E of the nitride layer 203, also leading to poor uniformity.

[0032] The foregoing provides an illustrative description of the present disclosure. To fully understand the present disclosure, the following examples are provided to illustrate the details. These examples are intended to cover more aspects of the present disclosure, and not to limit it.

[0033] Experiment 1: Comparison of spraying unsaturated fluorocarbons and not spraying unsaturated fluorocarbons.

[0034] In Example 1 and Comparative Example 1, the etching depth of 12 etch points uniformly distributed on the edge portion 203E of the nitride layer 203 was measured. The definition of the edge portion 203E of the nitride layer 203 is illustrated in [illustration missing]. Figure 2 and Figure 3 For details, please refer to the above text. The 12 etch points essentially divide the edge portion 203E of the nitride layer 203 into 12 regions, and the measured etch depth represents the depth of each local etch. The difference between Example 1 and Comparative Example 1 is that Example 1 uses the plasma etching method 100 disclosed herein, such as... Figure 1 Operations 102 to 108 are shown, but Comparative Example 1 only includes operations 102 and 106. In other words, Comparative Example 1 does not include operations 102 to 106. Figure 2 and Figure 3 The illustration shows the spraying of unsaturated fluorocarbons onto the edge portion 203E of the nitride layer 203, but includes other operations, such as operations 102 and 106. Operations 102 and 106 are substantially the same in Example 1 and Comparative Example 1, for example, the plasma 209 is a combination of tetrafluoromethane and oxygen at a frequency of 13.56 MHz, and the nitride layer 203 is Si3N4. After the same etching time, the 12 etching depths in Comparative Example 1 were 68.6 nm, 69.9 nm, 69.0 nm, 68.6 nm, 68.3 nm, 68.3 nm, 68.2 nm, 68.0 nm, 68.1 nm, 67.9 nm, 67.7 nm, 67.6 nm, 68.3 nm, 68.4 nm, 68.9 nm, 68.7 nm, 68.2 nm, 68.4 nm, 68.6 nm, 68.4 nm, 68.6 nm, 68.6 nm, 68.6 nm, 69.5 nm, 69.8 nm, and 69.3 nm. The 12 etch depths in Example 1 were 55.0 nm, 55.7 nm, 56.1 nm, 55.6 nm, 55.6 nm, 55.6 nm, 55.5 nm, 55.6 nm, 55.2 nm, 55.3 nm, 55.0 nm, 55.5 nm, 55.6 nm, 55.7 nm, 55.2 nm, 54.9 nm, 54.6 nm, 54.7 nm, 54.7 nm, 55.1 nm, 55.8 nm, 56.3 nm, and 55.7 nm. The relatively small etch depths in Example 1 demonstrate that spraying unsaturated fluorocarbons onto the edge portion 203E of the nitride layer 203 results in a lower etch rate. In Example 1, the first flow rate was 0.5 SCCM. Table 1 summarizes the average values ​​of the 12 etch depths in Example 1 and Comparative Example 1.

[0035] Table 1

[0036] Average etch depth (nm) Comparative Example 1 68.5 Example 1 55.4

[0037] Experiment 2: Comparison of different initial flow rates.

[0038] In Examples 2, 3, and 4, as Figure 1 Operations 102 to 108 of the plasma etching method 100 disclosed herein are all employed. The difference between Examples 2, 3, and 4 lies in the first flow rate. In Example 2, the first flow rate is 1 SCCM. In Example 3, the first flow rate is 0.5 SCCM. In Example 4, the first flow rate is 0.3 SCCM. The remaining experimental conditions are substantially the same, for example, the plasma 209 is a combination of tetrafluoromethane and oxygen at a frequency of 13.56 MHz, and the nitride layer 203 is Si3N4. To investigate the uniformity of etching, measurements were taken as follows: Figure 2 and Figure 3 The thickness of the nitride layer 203 is shown, and the results are summarized in Table 2 below. In Table 2, the average thickness represents the average value of the measured thickness; the range is the difference between the maximum and minimum measured thickness; and the standard deviation is the standard deviation of the measured thickness. After etching for 150 hours at first flow rates of 1 SCCM, 0.5 SCCM, and 0.3 SCCM in Examples 2, 3, and 4, respectively, Example 4 exhibits better range and standard deviation. In Example 4, a smaller range and a smaller standard deviation indicate better etching uniformity.

[0039] Table 2

[0040]

[0041] Experiment 3: Comparison of different second flow rates.

[0042] As described above, after etching for a period of time, the first flow rate can be adjusted to a second flow rate greater than the first flow rate to counteract the increase in etching rate on the edge portion 203E of the nitride layer 203, such as... Figure 2 and Figure 3 As shown. In Examples 5 and 6, as Figure 1Operations 102 to 110 of the plasma etching method 100 shown in this disclosure are all employed. The difference between Example 5 and Example 6 lies in the different second flow rates; otherwise, they are substantially the same, for example, the same first flow rate (0.3 SCCM). In Example 5, the second flow rate is 3 SCCM. In Example 6, the second flow rate is 1 SCCM. Comparative Example 2 employs only operations 102 and 106 compared to Examples 5 and 6. Comparative Example 2 does not spray unsaturated fluorocarbons onto the edge portion 203 of the nitride layer 203E; the remaining experimental conditions are substantially the same as in Examples 5 and 6, for example, the plasma 209 is a combination of tetrafluoromethane and oxygen at a frequency of 13.56 MHz, and the nitride layer 203 is Si3N4. Table 3 summarizes the experimental results of Examples 5, 6, and Comparative Example 2. The average thickness is the average of the measured thicknesses of the nitride layer 203. The maximum and minimum thicknesses are the maximum and minimum values ​​among the measured thicknesses. The range is the difference between the maximum and minimum values. The standard deviation is the standard deviation of the measured thickness. After 300 hours of etching, the second flow rates of Examples 5 and 6 were 3 SCCM and 1 SCCM, respectively, with Example 6 exhibiting a better range and standard deviation. In Example 6, the smaller range and smaller standard deviation indicate better etching uniformity. The curve showing the thickness of the nitride layer 203 as a function of the radius of the nitride layer 203 is shown in... Figure 4 Mark it. In Figure 4 In Comparative Example 2, the thickness variation of the nitride layer 203 is shown by curve CE2, which decreases as the radius of the nitride layer 203 increases. That is, the etching rate increases at the edge portion 203E. However, when unsaturated fluorocarbons are sprayed onto the edge portion 203E of the nitride layer 203, the etching rate on the edge portion 203E decreases, as shown in Example 5 (curve E5) and Example 6 (curve E6). In Examples 5 and 6, Example 6 exhibits better etching uniformity because the thickness does not change significantly with increasing radius.

[0043] Table 3

[0044] Example 5 Example 6 Comparative Example 2 Average thickness (nm) 220.2 113.8 99.6 Maximum thickness (nm) 281.4 138.8 125.5 Minimum thickness (nm) 169.7 91.0 31.5 Range (nm) 111.7 47.7 94 Standard deviation (nm) 40.5 16.8 26.4

[0045] By spraying unsaturated fluorocarbon 207 onto the edge portion 203E of the nitride layer 203, the increase in etching rate on the edge portion 203E can be reduced, thus obtaining uniform etching and extending the part replacement cycle (e.g., holding the nitride layer 203 in the focus ring at the center of the etching), eliminating the need for frequent part replacements, reducing waste and increasing etching yield.

[0046] Although this disclosure has been described in considerable detail with reference to some embodiments, other embodiments are possible, and therefore the spirit and scope of the appended claims should not be limited by the description of the embodiments contained herein.

[0047] It will be apparent to those skilled in the art that various modifications and alterations can be made to the structure of this disclosure without departing from its scope or spirit. In view of the foregoing, this disclosure also covers modifications and alterations to this disclosure, provided they fall within the scope of the appended claims.

[0048] [Symbol Explanation]

[0049] 100: Method

[0050] 102: Operation

[0051] 104: Operation

[0052] 106: Operation

[0053] 108: Operation

[0054] 110: Operation

[0055] 201: Wafer

[0056] 203: Nitride layer

[0057] 203E: Edge section

[0058] 203U: Top surface

[0059] 205: Circular Pipeline

[0060] 205H: Hole

[0061] 207: Unsaturated fluorocarbons

[0062] 209: Plasma

[0063] 211: Entrance

[0064] 213: Direction

[0065] A1:Angle

[0066] CE2: Curve

[0067] E5: Curve

[0068] E6: Curve

[0069] W1: Width.

Claims

1. A method of plasma etching, characterized by, include: Receive a wafer and a nitride layer, wherein the nitride layer is disposed on the wafer; An annular conduit is provided on the edge portion of the nitride layer, wherein the annular conduit has a plurality of holes and the plurality of holes face the edge portion of the nitride layer; Plasma is sprayed onto the upper surface of the nitride layer, the plasma comprising tetrafluoromethane, difluoromethane or a combination thereof; Unsaturated fluorocarbons are sprayed from the plurality of holes in the annular pipe to the edge portion of the nitride layer; and The unsaturated fluorocarbon compound is polymerized to form a polymer on the edge portion of the nitride layer, wherein the polymerization of the unsaturated fluorocarbon compound is induced by the plasma.

2. The method according to claim 1, wherein the unsaturated fluorocarbon compound is a gas.

3. The method according to claim 1, wherein the unsaturated fluorocarbon compound comprises hexafluorobutadiene.

4. The method of claim 1, wherein spraying the unsaturated fluorocarbon compound from the plurality of holes in the annular pipe comprises: The unsaturated fluorocarbon compound is sprayed at a first flow rate, wherein the first flow rate is between 0.1 SCCM and 1.2 SCCM.

5. The method of claim 4, wherein the first flow rate is between 0.2 SCCM and 0.4 SCCM.

6. The method of claim 1, wherein spraying the unsaturated fluorocarbon compound from the plurality of holes in the annular pipe comprises: The unsaturated fluorocarbon compound was sprayed at a first flow rate; as well as After etching time, the first flow rate is adjusted to a second flow rate, wherein the second flow rate is greater than the first flow rate.

7. The method of claim 6, wherein the second flow rate is between 0.8 SCCM and 3.2 SCCM.

8. The method of claim 7, wherein the second flow rate is between 0.9 SCCM and 1.1 SCCM.

9. The method of claim 6, wherein the etching time is between 250 hours and 350 hours.

10. The method of claim 1, wherein the edge portion of the nitride layer has a width of 3 mm to 5 mm from the edge of the nitride layer.

11. The method of claim 1, wherein the plurality of holes surround the edge portion of the nitride layer in a top view.

12. The method of claim 1, wherein the direction of spraying the unsaturated fluorocarbon compound is substantially perpendicular to the upper surface of the nitride layer.

13. The method of claim 1, wherein the nitride layer comprises silicon nitride.

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