Dog bone type exhaust slit channel for processing chamber

Abstract

A process chamber is disclosed and includes a chamber body. The chamber body has: a first side; the second side is opposite to the first side; a window assembly; and a substrate. The first and second sides, the window assembly, and the substrate define a heat treatment region. A flow assembly is disposed adjacent the first side and configured to direct a process gas into the heat treatment zone. An exhaust slit assembly is disposed adjacent the second side. The exhaust slit assembly has an opening exposed to the heat treatment region. The opening has a center and an outer edge of the opening. The center of the opening and an edge of the opening are vertically defined between the window assembly and the substrate. Wherein an outer height at the edge of the opening is at least 30% greater in a vertical direction than a center height at the center of the opening.

Description

Technical Field

[0001] Embodiments of the present disclosure relate generally to apparatus for semiconductor device fabrication and, more particularly, to exhaust slit channels for processing chambers. Background Art

[0002] The production of silicon integrated circuits places difficult demands on manufacturing steps to increase the number of devices while reducing the minimum feature size on the chip. In addition, increasing cost pressures on device manufacturers have created a need to increase the throughput of semiconductor manufacturing facilities. Semiconductor substrates are processed for a variety of applications, including the manufacture of integrated devices and microdevices. A method of processing a substrate includes depositing a material, such as a semiconductor material or a conductive material, on an upper surface of a substrate. The deposition, modification or removal of semiconductor materials on a substrate depends largely on the flux of purge and process gases across the substrate surface. During the deposition operation, a process gas and a purge gas (such as an inert gas) flow simultaneously into a processing chamber, such as an epitaxy (EPI) chamber. Therefore, semiconductor manufacturing processes must perform film formation and modification operations in an extremely uniform manner at low and / or high speeds. One such process is the deposition of a film on a semiconductor substrate. In this process, a gas mixture flows into a processing chamber and deposits or modifies the bottom layer of a substrate by incorporating precursors and / or byproducts therein to form a film.

[0003] The profile of the process gas flowing through the process chamber from the leading edge to the trailing edge of the substrate is related to the uniformity and quality of the deposited material layer. The profile shape of the process gas can be selected to achieve better uniformity of the deposited material layer. The demand for smaller and higher density devices requires increased control of the process gas profile shape. Conventional process chambers have difficulty meeting the requirements for improved profile control of the process gas provided across the substrate, and therefore have difficulty obtaining high tolerance, uniform thickness deposition.

[0004] Therefore, there is a need for an improved apparatus for controlling process gases in a semiconductor processing chamber. Summary of the invention

[0005] The processing chamber disclosed herein includes a slit valve channel having a variable gap opening. The processing chamber includes a chamber body. The chamber body has a first side; a second side, the second side opposite to the first side; a window assembly; and a substrate. The first side, the second side, the window assembly, and the substrate define and enclose a heat treatment region. A flow assembly is disposed adjacent to the first side and configured to guide a process gas into the heat treatment region. An exhaust slit assembly is disposed adjacent to the second side. The exhaust slit assembly has an opening that is exposed to the heat treatment region. The opening has a center and an outer edge of the opening. The center of the opening and the edge of the opening are vertically defined between the window assembly and the substrate. Wherein the outer height at the edge of the opening is at least 30% greater than the center height at the center of the opening in the vertical direction.

[0006] In other embodiments, the exhaust slot assembly is disposed adjacent to the second side. The exhaust slot assembly has an elongated opening that is exposed to the heat treatment region. The elongated opening has a center height of the opening disposed at the center of the elongated opening, and an outer height of the opening disposed along an outer edge of the elongated opening. The outer height of the opening is vertically at least 30% greater than the center height of the opening.

[0007] In other embodiments, a method for thermally processing a substrate is provided. The method includes: flowing a process gas into a processing chamber through a first opening and into a processing area containing a substrate. The process gas flows laterally across the substrate from the first opening toward a second opening of the processing chamber. The second opening has a higher conductivity at an outer edge of the second opening relative to a center of the second opening. Heating the substrate in the presence of the process gas; and depositing a layer of material on the heated substrate in the presence of the process gas. BRIEF DESCRIPTION OF THE DRAWINGS

[0008] In order to be able to understand in detail the manner in which the above features of the present disclosure are achieved, a more specific description of the present disclosure briefly summarized above may be obtained by reference to the embodiments, some of which are illustrated in the accompanying drawings. It should be noted, however, that the accompanying drawings illustrate only exemplary embodiments and are therefore not to be considered as limiting the scope thereof, and other equivalent embodiments may be used.

[0009] Figure 1A is a schematic diagram of a processing system according to one or more embodiments described and discussed herein.

[0010] Figure 1B is another schematic diagram of a processing system according to one or more embodiments described and discussed herein.

[0011] Figure 1Cis a schematic top view of a processing system according to one or more embodiments described and discussed herein.

[0012] Figure 2A is a schematic top view of the exhaust slot assembly of FIG. 1 according to one or more embodiments described and discussed herein.

[0013] Figure 2B is another schematic top view of the exhaust slot assembly of FIG. 1 according to one or more embodiments described and discussed herein.

[0014] Figure 3 yes Figure 2A and 2B Two front views of the openings in the exhaust slot assembly are shown in FIG.

[0015] To facilitate understanding, identical reference numerals have been used, where possible, to designate identical elements that are common to the figures. It is contemplated that elements and features of one or more embodiments may be beneficially incorporated in other embodiments. DETAILED DESCRIPTION

[0016] Embodiments of the present disclosure generally relate to semiconductor device manufacturing equipment and methods for processing substrates therein, and specifically to an exhaust assembly for a processing chamber. The exhaust assembly has an opening shaped to provide a processing gas at a uniform velocity across a substrate disposed in the processing chamber. The opening is provided with an opening profile of a dog bone or dumbbell cross section rather than a conventional uniform cross-sectional profile. The opening profile of the dog bone or dumbbell cross section has a smaller opening at the center, i.e., a gap, and the opening increases from the center toward the edge. The smaller area of ​​the opening at the center promotes better flow through the substrate, thereby improving processing uniformity.

[0017] Figure 1A Illustrated is a substrate processing system 199 that includes an epitaxial (EPI) processing chamber 100. The EPI processing chamber 100 is used to grow epitaxial films on a substrate, such as substrate 150. Alternatively, the EPI processing chamber 100 may be configured for etching.

[0018] The EPI processing chamber 100 includes a chamber body 108. The chamber body 108 includes a susceptor assembly 124, a lower window portion 120, an upper window portion 122, and a base plate 114. The upper window portion 122, the base plate 114, and the lower window portion 120 enclose an interior volume 110 of the chamber body 108. The susceptor assembly 124 is disposed in the interior volume 110 of the chamber body 108.

[0019] The EPI processing chamber 100 additionally includes a plurality of lamp modules 101. The lamp modules 101 include an upper lamp module 102 and a lower lamp module 104. The upper lamp module 102 may include a pyrometer passage in which a pyrometer (e.g., a scanning pyrometer) measures the temperature of a substrate 150 or a component of the chamber body 108.

[0020] The upper window portion 122 is an optically transparent window portion that allows the radiant energy generated by the upper lamp module 102 to pass therethrough. In some embodiments, the upper window portion 122 is formed of a quartz or glass material. The upper window portion 122 has a dome shape and is also referred to as an upper dome in some embodiments. The outer edge of the upper window portion 122 forms a peripheral support. The peripheral support is disposed on the top of the base plate 114.

[0021] The base plate 114 may include one or more cooling channels 188. The cooling channels 188 are configured to allow fluid to flow therethrough to maintain the temperature of the base plate 114. The upper window 122 and the base plate 114 may define a processing region 129. The substrate 150 is exposed to the processing gas in the processing region 129 for processing.

[0022] The liner 154 is located inside the opening of the substrate plate 114. The liner 154 has an annular shape. The liner 154 is configured to separate the inner surface of the substrate plate 114 from the interior volume 110. The liner 154 shields the inner surface of the substrate plate 114 from the processing gas within the interior volume 110, and further protects the interior volume 110 from particles or other contaminants released by the substrate plate 114. The liner 154 further serves to reduce heat transfer from the processing volume to the substrate plate 114. The reduced heat transfer improves uniform heating of the substrate 150 and enables more uniform deposition on the substrate 150 during processing.

[0023] The lower window portion 120 is disposed between the base plate 114 and the lower lamp module 104. The lower window portion 120 is optically transparent so that the radiant energy generated by the lower lamp module 104 passes therethrough. In some embodiments, the lower window portion 120 is formed of a quartz or glass material. The lower window portion 120 has a dome shape and is also referred to as a lower dome in some embodiments. The outer edge of the lower window portion 120 forms a peripheral support. The base plate 114 is disposed on the peripheral support of the lower window portion 120.

[0024] The lower lamp module 104 is disposed below the pedestal assembly 124 and is configured to heat the bottom side of the substrate 150 when the substrate is disposed on the pedestal assembly 124. The lower lamp module 104 includes a plurality of lamp holes. Each of the plurality of lamp holes has a lamp 135 disposed therein. Each lamp 135 is electrically coupled to a power source (not shown). The orientation of the lamp 135 is substantially parallel to the vertical centerline of the EPI processing chamber 100. For example, the lamp 135 may be disposed in an orientation substantially perpendicular to the substrate 150. Alternatively, the orientation of the lamp 135 is parallel to the substrate 150.

[0025] The lower lamp module 104 further includes a base shaft passage 195. The base shaft passage 195 is provided to pass through the middle of the lower lamp module 104. The support shaft 132 is provided to pass through the base shaft passage 195 and is coupled to the base assembly 124. The size of the base shaft passage 195 is designed to allow the support shaft of the base assembly 124 to pass through the lower lamp module 104 and supply bottom purge.

[0026] The base assembly 124 is disposed in the interior volume 110 and is configured to support a substrate 150 on a substrate support surface 151. The base assembly 124 is disposed between the upper lamp module 102 and the lower lamp module 104. The lower window portion 120 is disposed between the base assembly 124 and the lower lamp module 104. The upper window portion 122 is disposed between the base assembly 124 and the upper lamp module 102. The upper lamp module 102 is disposed above the base assembly 124 and is configured to heat the substrate 150 disposed on the base assembly 124. The upper lamp module 102 includes a plurality of lamp apertures. Each of the plurality of lamp apertures includes a lamp base or lamp holder in which a single lamp 135 is disposed. The orientation of the lamp 135 is generally defined by an imaginary line extending along the filament of the lamp 135 to the tip of the lamp 135. The orientation of the lamp 135 can be parallel or perpendicular to the chamber centerline.

[0027] The EPI processing chamber 100 will be additionally referred to as Figure 1B The substrate plate 114 includes a substrate transfer passage 116. The substrate transfer passage 116 is disposed through the substrate plate 114 opposite the cross-flow inlet 196. The substrate transfer passage 116 is formed through the substrate plate 114. The substrate transfer passage 116 is configured to allow a substrate 150 to pass through the substrate transfer passage from a transfer chamber of a cluster tool (not shown).

[0028] A purge gas inlet 192 is provided in a base shaft passage 195 into the lower chamber 113 between the base assembly 124 and the surrounding lower lamp module 104 .

[0029] return Figure 1A The chamber exhaust passage 152 is configured to pass through the base plate 114 and is coupled to the exhaust slot assembly (at Figures 2A to 2B1 and 2. The substrate plate 114 includes one or more gas injectors 198 disposed therethrough. The gas injectors 198 are configured to supply process gas to the interior volume 110. The gas injectors 198 are fluidly coupled to one or more process gas supply sources. The lower chamber exhaust passage 152 is disposed opposite the substrate transfer passage 116 and connects the exhaust slot assembly 200 in the lower chamber to an exhaust pump (not shown). The exhaust pump may also be coupled to and in fluid communication with the two upper chamber exhaust passage openings.

[0030] Figure 2A 1 is a simplified schematic top view of a portion of a substrate processing system 199, including an EPI processing chamber 100 and an exhaust slot assembly 200. A precursor initiator 180 (eg, Figure 1C ) is coupled to the EPI processing chamber 100 via a delivery line 190. When the gas reaches the plasma generation region above the substrate 150, the gas is excited to form a plasma. Downstream of the plasma generation region, gas neutral species, gas ions, and gas radicals flow from the plasma generation region toward the exhaust slot assembly 200.

[0031] The flow assembly 125 is disposed in the chamber inlet 175 extending through the base plate 114 of the chamber body 108 to allow process gases to flow from the precursor activator 180 to the process region 129 of the EPI processing chamber 100. The flow assembly 125 is configured to reduce flow restriction or control flow profile of gases flowing to the EPI processing chamber 100.

[0032] The EPI processing chamber 100 has a distributed pumping structure 127 to remove processing gases from the EPI processing chamber 100. The distributed pumping structure 127 includes an exhaust slit assembly 200. The exhaust slit assembly 200 is provided adjacent to the second side of the base plate 114 of the chamber body 108. The shape of the exhaust slit assembly 200 is designed to control the distribution of gas flowing from the flow assembly 125 across the substrate 150 to the pumping port 128.

[0033] Figures 2A to 2B A perspective view of an exhaust slit assembly 200 is shown. The exhaust slit assembly 200 has a body 201. The body 201 has an exhaust opening 210 (i.e., an exhaust passage). The exhaust slit assembly 200 can be made of a material such as quartz or silicon dioxide to reduce interaction with process gases. In embodiments used with nitrogen radicals, the exhaust slit assembly 200 can be made of a nitridation-resistant material, such as silicon nitride.

[0034] Optionally, the exhaust slot assembly 200 may have a blocker plate 126. The blocker plate 126 promotes uniform thickness of the layer formed on the substrate 150. For example, without the blocker plate 126, the layer at the center of the substrate 150 may be significantly thicker than the layer at the edge of the substrate 150. The blocker plate 126 maintains the diffusion of the airflow to substantially cover the edge portion of the substrate to promote thickness uniformity.

[0035] The exhaust opening 210 may be elongated and have a shape similar to a dumbbell or dog bone. The shape of the exhaust opening 210 of the exhaust slit assembly 200 varies the conductivity from the center to the edge of the opening 210, which promotes thickness uniformity of the deposited material layer. In one embodiment, the shape of the exhaust opening 210 varies during processing to adjust the conductivity profile. In another example, the shape of the exhaust opening 210 is fixed to set the conductivity profile of the exhaust slit assembly 200 in the EPI processing chamber 100.

[0036] The shape of the opening 210 (i.e., dog-bone shape) may be in a plane parallel to the sidewall 115 of the chamber body 108. For example, the exhaust opening 210 may be a geometrically flat opening 209. Alternatively, the shape of the exhaust slit assembly 200 may extend from the sidewall 115 to the pumping port 128. Optionally, a small air chamber 238 may exist around the pumping port 128. The dog-bone shape of the exhaust opening 210 may extend vertically from the sidewall 115 to the pumping port 128, or alternatively, to the air chamber 238. In this way, the shape may be more easily formed into the exhaust slit assembly 200 via machining.

[0037] In yet another example, the shape of the opening 210 may be in a curved plane of the interior volume of the chamber body 108, as shown by the curved opening 208. The shape may be provided by the plate such that the dog bone shape is only along the opening 210. Alternatively, the shape may extend from the opening to the pumping port 128, or alternatively, to the plenum 238. In this manner, the exhaust flow through the exhaust slot assembly 200 may be better controlled.

[0038] It has been found that the shape of the opening 210 directly affects the flow of process gases traveling across the process region 129 of the EPI process chamber 100. By configuring the opening 210 of the exhaust slit in a dumbbell or dog bone shape, the conductivity can be controlled from the center to the edge. The conductivity profile of the opening 210 can be fixed or varied during processing. The shape of the opening 210 will be discussed with reference to a front view of the opening 210.

[0039] Figure 3 Picture shows Figure 2A and 2B. The opening 210 has a profile 320. The opening 210 has an outer edge 391 and a center 398 defined along a centerline 399 of the opening 210. The outer edge 391 is provided on both the left and right sides of the center 398 of the opening 210, that is, there are two outer edges 391. The profile 320 of the opening 210 is smaller at the center 398 than the outer edge 391. The profile 320 may be curved (e.g., Figure 2A ) or flat (as shown in the curved opening 208 in FIG. Figure 2B 20 is shown as a flat opening 209 in the opening 210). The profile 320 may be symmetrical about the center line 399. For ease of description, the profile 320 may be divided into four regions. The four regions include a left side 385, a left center 384, a right center 383, and a right side 382. The left center 384 is defined to the left of the center 398 of the opening 210. The right center 383 is defined to the right of the center 398 of the opening 210.

[0040] The left side 385 and the right side 382 may have a rectangular shape. The left side 385 of the profile 320 may or may not be a mirror image of the right side 382. Therefore, the profile 320 may be symmetrical. Alternatively, the profile 320 may be asymmetrical. For example, the left side 385 and the right side 382 of the profile are not equal in size or shape. The left center 384 and the right center 383 may have a truncated bell shape, that is, a trapezoidal shape with an arched or concave waist connecting the two bottoms, that is, a truncated funnel shape. The left center 384 of the profile 320 may or may not be a mirror image of the right center 383, wherein the short sides of the right center 383 and the left center 384 are shared along the center line 399. In general, the combined shape of the left side 385, the left center 384, the right center 383, and the right side 382 forms a dumbbell or dog bone shape.

[0041] The left side 385 may extend between about 25% and about 35%, such as about 30%, of the distance from the outer edge 391 to the center 398. Similarly, the right side 382 may extend between about 25% and about 35%, such as about 30%, of the distance from the outer edge 391 to the center 398. The left center 384 may extend about 70% of the distance from the center 398 of the opening 210 to the outer edge 391. Similarly, the right center 383 may extend about 70% of the distance from the center 398 to the outer edge 391.

[0042] A vertical centerline 399 at the center 398 of the opening 210 defines a center height 386 of the opening 210. An outer edge height 381 of the opening 210 is defined at the outer edges 391 of the opening 210 on either side of the opening. The center height 386 and the outer edge height 381 of the opening 210 have lengths defined vertically relative to the chamber body 108, that is, in the same direction as the centerline 399.

[0043] The center height 386 can vary from about 0.00 mm (where the center height 386 of the opening 210 is blocked or closed) to about 14.00 mm (where the center height 386 is fully open and no longer has a dog bone shape). In one example, the center height 386 of the opening 210 can be between about 3.00 mm and about 9.00 mm. In another example, the center height 386 of the opening 210 can be between about 3.9 mm and about 8.4 mm. The outer edge height 381 of the opening 210 can be between 10.00 mm and about 14.00 mm. However, it has been found that a larger dimension at the outer edge height 381 of the opening 210 than the dimension of the center height 386 of the opening 210 provides the most desirable processing results on the substrate.

[0044] Simulations and tests were performed in which a portion of the opening 210 for the exhaust slit assembly 200 was blocked at the center 398 of the opening 210. Compared with the feather-shaped deposition thickness profile when the blocker plate 126 is not used under the same conditions, the situation where an area of ​​the exhaust slit channel area is blocked by the blocker plate 126 provides a wider rectangular deposition profile. The blocker plate 126 creates a recirculation area above the substrate, especially adjacent to the blocking area in the exhaust. Similarly, simulation tests were performed for various opening ratios between the center height 386 and the outer edge height 381. The test measured the exhaust velocity from the center 398 of the exhaust opening 210 to the outer edge 391. The contour shape of the opening was found to affect the flow rate. The opening ratio changes from 0% (using the blocker plate 126 that is completely closed in the middle) to 100% (where the center height 386 is equal to the outer edge height 381). For example, ratios of 65% open at center height 386, 60% open at center height 386, 50% open at center height 386, down to 30% open at center height 386 were measured and compared to a conventional opening that was 100% open at center height 386. The results are summarized in Table 1 below.

[0045]

[0046] Table 1 illustrates that an opening between about 25% and about 40% of the center will provide a flat flow rate curve. At the same time, an opening between about 50% and about 70% of the center produces a dome-shaped flow rate curve with a smaller change from center to edge. The outer edge height 381 is greater than or equal to the center height 386. The ratio of the center height 386 to the outer edge height 381 (center height 386 / outer edge height 381) can be between about 30% and about 40%. In another example, the ratio of the center height 386 to the outer edge height 381 is between about 50% and about 70%. In yet another example, the ratio of the center height 386 to the outer edge height 381 is between about 50% and about 80%.

[0047] Although the foregoing is directed to embodiments of the present disclosure, other and further embodiments may be devised without departing from the basic scope thereof, and the scope thereof is determined by the following claims. It is apparent from the foregoing general description and specific embodiments that, although forms of the present disclosure have been illustrated and described, various modifications may be made without departing from the spirit and scope of the present disclosure. Accordingly, the present disclosure is not intended to be limited thereby. Likewise, the term "comprising" is considered synonymous with the term "including".

[0048] Certain embodiments and features have been described using a set of numerical upper limits and a set of numerical lower limits. It should be understood that ranges include any combination of two values, such as any combination of a lower limit value with any upper limit value, any combination of two lower limits values, and / or any combination of two upper limits values, unless otherwise indicated. Certain lower limits, upper limits, and ranges appear in one or more claims below.

Claims

1. A processing chamber, comprising: A chamber body, wherein the chamber body comprises: First side; a second side, the second side being opposite to the first side; Window components; and a substrate, wherein the first side, the second side, the window assembly, and the substrate define and enclose a thermal processing region; a flow assembly disposed adjacent to the first side, wherein the flow assembly is configured to direct a process gas into the thermal processing region; and An exhaust slit assembly, the exhaust slit assembly being disposed adjacent to the second side, the exhaust slit assembly comprising: An opening, the opening is exposed to the heat treatment area, the opening has a center and an outer edge of the opening, the center of the opening and the edge of the opening are vertically defined between the window component and the substrate, and wherein the outer height at the edge of the opening is at least 30% greater in the vertical direction than the central height at the center of the opening.

2. The processing chamber of claim 1, wherein the opening comprises: A blocker plate is disposed at the center of the opening.

3. The processing chamber of claim 1, wherein a ratio of the center height of the opening to the outer height of the opening is between about 30% and about 80%.

4. The processing chamber of claim 1, wherein a ratio of the center height of the opening to the outer height of the opening is between about 30% and about 40%.

5. The processing chamber of claim 1, wherein a ratio of the center height to the outer height of the opening is between about 50% and about 70%.

6. The processing chamber of claim 1, wherein the opening further comprises: Left side; left center; right center; and The right side, wherein the left side and the right side have a rectangular shape, and the left center and the right center have a trapezoidal shape with a curved waist between two bases.

7. The processing chamber of claim 6, wherein the left side and the right side each extend between about 25% and about 35% of the distance from the outer edge to the center, and wherein the left center and the right center each extend between about 75% and about 65% of the distance from the center to the outer edge.

8. The processing chamber of claim 6, wherein the left side, the left center, the right center, and the right side form a dog bone shape.

9. An exhaust slit assembly comprising: A body having an elongated opening configured to receive gas, the elongated opening having a dog-bone shape, wherein the elongated opening has a center height of the opening disposed at the center of the elongated opening, and an outer height of the opening disposed along an outer edge of the elongated opening, wherein the outer height of the opening is vertically at least 30% greater than the center height of the opening.

10. The exhaust slot assembly of claim 9, wherein the dog-bone shape of the elongated opening is asymmetrical, wherein a left edge of the opening and a right edge of the opening are not equal.

11. The exhaust slot assembly of claim 9, wherein a ratio of the center height of the opening to the outer height of the opening is between about 30% and about 80%.

12. The exhaust slot assembly of claim 9, wherein a ratio of the center height to the outer height of the opening is between about 30% and about 40%.

13. The exhaust slot assembly of claim 9, wherein a ratio of the center height to the outer height of the opening is between about 50% and about 70%.

14. The exhaust slot assembly of claim 9, wherein a ratio of the center height to the outer height of the opening is approximately 0%.

15. The exhaust slot assembly of claim 9, wherein the elongated opening further comprises: Left side; left center; right center; and The right side, wherein the left side and the right side have a rectangular shape, and the left center and the right center have a trapezoidal shape with a curved waist between two bases.

16. The exhaust slot assembly of claim 15, wherein the left side and the right side each extend approximately 30% of the distance from the outer edge to the center, and wherein the left center and the right center each extend approximately 70% of the distance from the center to the outer edge.

17. A method for thermally treating a substrate, the method comprising: flowing a process gas into the process chamber through the first opening and into a processing region containing the substrate; flowing the process gas laterally across the substrate from the first opening toward a second opening of the process chamber, the second opening having a higher conductivity at an outer edge of the second opening relative to a center of the second opening; heating the substrate in the presence of the process gas; and A layer of material is deposited on the heated substrate in the presence of the process gas.

18. The method according to claim 17, further comprising: The process gas is flowed through a baffle plate disposed in the middle of the second opening.

19. The method of claim 17, wherein the second opening has an outer height and a center height, and wherein a ratio of the center height to the outer height is between about 30% and about 80%.

20. The method of claim 17, further comprising: The conductivity of the second opening is changed by changing the center height of the opening.

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