Trench device terminal structure capable of improving electric field distribution uniformity

Abstract

The utility model discloses a trench device terminal structure capable of improving electric field distribution uniformity, which comprises a substrate, an epitaxial layer is arranged on the substrate, and a plurality of terminal trench rings are nested on the epitaxial layer. The plurality of terminal groove rings comprise an outer terminal ring on the outer side, an inner terminal ring on the inner side and at least one middle terminal ring arranged between the outer terminal ring and the inner terminal ring, and a plurality of conventional grooves are formed in the inner terminal ring at intervals; two ends of each conventional groove are respectively connected with the inner terminal ring through a first narrow groove, and the groove width of the first narrow groove is smaller than that of the conventional groove. According to the utility model, through the arrangement of the first narrow trench, the electric field distribution of each area of the whole trench device is more consistent, the application performance and reliability of harsh working conditions are improved, and an epitaxial process window of the trench device can be enlarged, so that the difficulty of process research, development and debugging can be reduced; the structure is simple and practicability is high.

Description

Technical Field

[0001] The utility model belongs to the field of power semiconductor devices, and in particular relates to a trench device terminal structure capable of improving the uniformity of electric field distribution. Background Art

[0002] like Figure 1 and Figure 2 As shown, there are two common terminal structures of existing trench MOS such as traditional trench MOS and split-gate trench MOS, among which: Figure 1 The terminal structure is common in devices of 30V and below. Figure 2 The terminal structure is common in 30V to 150V devices. However, both terminal structures have some disadvantages that cannot be ignored:

[0003] (1) Figure 1 The terminal structure is only applicable to the condition of high epitaxial concentration (i.e., the doping concentration of the epitaxial layer is 10% or more higher than the reference concentration). If the epitaxial concentration is relatively light (i.e., the doping concentration of the epitaxial layer is 10% or more lower than the reference concentration), under the reverse bias state, the junction electric field of the "T"-shaped region 171 (i.e., the region where the trenches intersect vertically) of the terminal region will drop to a relatively low level compared to the Cell region (i.e., the cell region), while the electric field at the bottom of the trench will rise to a relatively high level. In this way, the avalanche voltage of the "T"-shaped region 171 will be significantly lower than that of the Cell region, which may easily cause application failure and reliability test failure.

[0004] (2) Figure 2 The terminal structure is only suitable for conditions with relatively light epitaxy. If the epitaxial concentration is high, under reverse bias Figure 2 The epitaxial depletion width of the middle "T"-shaped region 172 is significantly smaller than that of the ordinary Mesa region 170 (i.e., ordinary mesa region), the electric field peak is higher, and the withstand voltage is lower, which is also prone to cause application failure and reliability test failure. In order to overcome this weakness, the "T"-shaped region 172 in this type of terminal structure is often made narrower, but its width is limited by the trench process, so there is an upper limit, and it is often not applicable to devices of 30V and below and other medium and low voltage devices with low RSP. In addition, the end of the trench below the "T"-shaped region 172 in this type of terminal structure is an area of ​​concentrated electric field, which is prone to cause reliability problems. Utility Model Content

[0005] In view of the above-mentioned deficiencies in the prior art, the technical problem to be solved by the present invention is to provide a trench device terminal structure capable of improving the uniformity of electric field distribution.

[0006] In order to solve the above technical problems, the utility model provides the following technical solutions:

[0007] A trench device terminal structure capable of improving the uniformity of electric field distribution comprises a substrate, an epitaxial layer is arranged on the substrate, a plurality of terminal trench rings are nested on the epitaxial layer, the plurality of terminal trench rings comprise an outer terminal ring on the outside, an inner terminal ring on the inside and at least one intermediate terminal ring arranged between the outer terminal ring and the inner terminal ring, a plurality of conventional trenches are arranged inside the inner terminal ring at intervals; both ends of each of the conventional trenches are respectively connected to the inner terminal ring through a first narrow trench, and the trench width of the first narrow trench is smaller than the trench width of the conventional trench.

[0008] Furthermore, each of the terminal groove rings includes two parallel first terminal grooves and two parallel second terminal grooves, the two second terminal grooves are arranged between the two first terminal grooves, and the two ends of the second terminal grooves are respectively connected to the first terminal grooves through a second narrow groove; the first narrow grooves connecting the two ends of the conventional groove are respectively connected to the two first terminal grooves of the inner terminal ring.

[0009] Furthermore, the groove width of the first terminal groove is equal to the groove width of the second terminal groove; the groove width of the conventional groove is less than or equal to the groove width of the first terminal groove, and the groove width of the conventional groove is greater than the groove widths of the first narrow groove, the second narrow groove and the third narrow groove.

[0010] Furthermore, the width of the first narrow groove is less than or equal to two-thirds of the width of the first terminal groove.

[0011] Furthermore, the first terminal groove is perpendicular to the second terminal groove, and the conventional grooves are parallel to the second terminal groove.

[0012] Furthermore, both ends of the first terminal grooves of the inner terminal ring and the middle terminal ring are connected to the second terminal grooves of their outer terminal groove rings through a third narrow groove.

[0013] Furthermore, the widths of the second narrow groove and the third narrow groove are both less than or equal to two-thirds of the width of the first terminal groove.

[0014] Furthermore, isolation oxide layers are arranged on the groove walls of the first terminal groove, the second terminal groove and the conventional groove, and in the first narrow groove, the second narrow groove and the third narrow groove. Source polysilicon is also arranged in the first terminal groove, the second terminal groove and the conventional groove. The groove walls of the first terminal groove, the second terminal groove and the conventional groove are isolated from the source polysilicon by the isolation oxide layer. Gate polysilicon is arranged above the corresponding source polysilicon in the conventional groove, a filling oxide layer is arranged between the gate polysilicon and the source polysilicon, and the gate polysilicon is isolated from the groove wall of the conventional groove by the gate oxide layer.

[0015] Furthermore, a body region is formed on the upper portion of the epitaxial layer, and a source region is formed on the upper portion of the body region between each two adjacent conventional trenches.

[0016] Furthermore, a dielectric layer is arranged on the epitaxial layer, and a contact hole is respectively provided between each two adjacent conventional grooves in the dielectric layer, passing through the dielectric layer and the source region and extending into the body region; a metal layer is arranged on the dielectric layer, and the metal layer extends into the contact hole.

[0017] In the present invention, by setting the first narrow groove, the electric field distribution in each area of ​​the entire groove device can be made more consistent, the application performance and reliability under harsh working conditions can be improved, and the epitaxial process window of the groove device can be increased, thereby reducing the difficulty of process development and debugging. By setting the second narrow groove and the third narrow groove, the terminal structure can have a larger epitaxial process window, and it can also make it easier to share a set of masks for devices with a withstand voltage of 25V to 40V, so that the loss of RSP level becomes smaller than that of the prior art. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] The drawings described herein are used to provide a further understanding of the present application and constitute a part of the present application. The illustrative embodiments of the present application and their descriptions are used to explain the present application and do not constitute an improper limitation on the present application. In the drawings:

[0019] Figure 1 The figure is a schematic diagram of a trench device terminal structure in the prior art.

[0020] Figure 2 It is a schematic structural diagram of another trench device terminal structure in the prior art.

[0021] Figure 3 It is a structural schematic diagram of an embodiment of a trench device terminal structure capable of improving the uniformity of electric field distribution according to the utility model.

[0022] Figure 4 for Figure 3 Schematic diagram of the cross section along the AA direction.

[0023] Figure 5 for Figure 3 Schematic diagram of the cross section along the BB direction.

[0024] Figure 6 for Figure 3 Schematic diagram of the cross section along the CC direction.

[0025] The accompanying drawings in the specification are as follows:

[0026] Epitaxial layer-110; body region-120; source region-130; dielectric layer-140; contact hole-150; ohmic contact structure-151; metal layer-160; common Mesa region-170; "T" shaped regions-171, 172, 173;

[0027] Terminal groove ring-200; outer terminal ring-210; middle terminal ring-220; inner terminal ring-230; first terminal grooves-211, 221, 231; second terminal grooves-212, 222, 232;

[0028] Conventional trench 300; isolation oxide layers 201, 301, 311; source polysilicon 202, 302; filling oxide layer 303; gate polysilicon 304; gate oxide layer 305; first narrow trench 310; second narrow trench 320; third narrow trench 330. DETAILED DESCRIPTION

[0029] The following describes the implementation of the present invention through specific examples. The illustrations provided in the following embodiments are only used to schematically illustrate the basic concept of the present invention. The following embodiments and features in the embodiments may be combined with each other without conflict.

[0030] See also Figure 3 , Figure 3 The present invention is a schematic structural diagram of an embodiment of a trench device terminal structure capable of improving the uniformity of electric field distribution. A trench device terminal structure capable of improving the uniformity of electric field distribution in this embodiment includes a substrate (not shown in the figure), an epitaxial layer 110 is arranged on the substrate, and a plurality of terminal trench rings 200 are nested on the epitaxial layer 110. Each of the terminal trench rings 200 includes two parallel first terminal trenches and two parallel second terminal trenches, and the two second terminal trenches are arranged between the two first terminal trenches, and the first terminal trench is generally perpendicular to the second terminal trench. The groove width of the first terminal trench is generally the same as the groove width of the second terminal trench, and the groove depth of the first terminal trench is generally the same as the groove depth of the second terminal trench.

[0031] This embodiment is described by taking an example of setting an intermediate terminal ring 220 between an outer terminal ring 210 and an inner terminal ring 230; wherein the outer terminal ring 210 includes two first terminal grooves 211 and two second terminal grooves 212, the intermediate terminal ring 220 includes two first terminal grooves 221 and two second terminal grooves 222, and the inner terminal ring 230 includes two first terminal grooves 231 and two second terminal grooves 232.

[0032] The plurality of terminal groove rings 200 include an outer terminal ring 210 on the outside, an inner terminal ring 230 on the inside, and at least one intermediate terminal ring 220 disposed between the outer terminal ring 210 and the inner terminal ring 230. The inner terminal ring 230 is provided with a plurality of conventional grooves 300 at intervals therein; the conventional grooves 300 are generally perpendicular to the first terminal groove. The groove width of the conventional groove 300 is generally less than or equal to the groove width of the first terminal groove, and the groove depth of the conventional groove 300 is generally less than or equal to the groove depth of the first terminal groove. In this embodiment, the groove width and groove depth of the conventional groove 300 are the same as those of the first terminal groove. The two ends of each of the conventional grooves 300 are connected to the two first terminal grooves 231 of the inner terminal ring 230 through a first narrow groove 310, respectively, and the groove width of the first narrow groove 310 is less than the groove width of the conventional groove 300.

[0033] The two ends of the second terminal groove of each terminal groove ring 200 are connected to the first terminal groove thereof through a second narrow groove 320, and the two ends of the first terminal groove of the inner terminal ring 230 and the middle terminal ring 220 are connected to the second terminal groove of the outer terminal groove ring 200 through a third narrow groove 330. In this embodiment, the two ends of the first terminal groove 231 of the inner terminal ring 230 are connected to the second terminal groove 222 of the middle terminal ring 220 through a third narrow groove 330; and the two ends of the first terminal groove 221 of the middle terminal ring 220 are connected to the second terminal groove 212 of the outer terminal ring 210 through a third narrow groove 330.

[0034] The structures of the first narrow groove 310, the second narrow groove 320 and the third narrow groove 330 may be the same. The groove widths of the first narrow groove 310, the second narrow groove 320 and the third narrow groove 330 are all smaller than the groove width of the conventional groove 300. Since the first narrow groove 310, the second narrow groove 320 and the third narrow groove 330 are generally formed by etching through a photolithography process, and the groove depth of the groove formed by etching through a photolithography process is proportional to the groove width; therefore, the groove depths of the first narrow groove 310, the second narrow groove 320 and the third narrow groove 330 are also smaller than the groove depth of the conventional groove 300. Generally, the widths of the first narrow groove 310, the second narrow groove 320 and the third narrow groove 330 are all less than or equal to two-thirds of the width of the first terminal groove, and the widths of the first narrow groove 310, the second narrow groove 320 and the third narrow groove 330 are all greater than or equal to one-third of the width of the first terminal groove.

[0035] See also Figure 4 , Figure 5 and Figure 6For conventional trench MOS (i.e. conventional trench metal oxide field effect transistor) and split gate trench MOS (abbreviated as SGT, i.e. split gate trench metal oxide field effect transistor), an isolation oxide layer 201 is provided on the groove wall of the first terminal groove and the second terminal groove, source polysilicon 202 is provided in both the first terminal groove and the second terminal groove, and the groove wall of the first terminal groove and the second terminal groove is isolated from the source polysilicon 202 by the isolation oxide layer 201. An isolation oxide layer 301 is provided on the groove wall of the conventional groove 300, source polysilicon 302 is provided in the conventional groove 300, and the groove wall of the conventional groove 300 is isolated from the source polysilicon 302 by the isolation oxide layer 301. A gate polysilicon 304 is arranged above the corresponding source polysilicon 302 in the conventional trench 300, and a filling oxide layer 303 is arranged between the gate polysilicon 304 and the source polysilicon 302, so as to achieve isolation between the gate polysilicon 304 and the source polysilicon 302; the gate polysilicon 304 is also isolated from the groove wall of the conventional trench 300 by the gate oxide layer 305. The first narrow groove 310, the second narrow groove 320 and the third narrow groove 330 are all provided with an isolation oxide layer 311, and the isolation oxide layer 311 is generally flush with the notch of the narrow groove (i.e., the first narrow groove 310, the second narrow groove 320 and the third narrow groove 330); polysilicon is not provided in the first narrow groove 310, the second narrow groove 320 and the third narrow groove 330 to achieve isolation between the source polysilicon 302 in the conventional groove 300 and the source polysilicon 202 in the first terminal groove 231.

[0036] A body region 120 is formed on the upper part of the epitaxial layer 110, and a source region 130 is formed on the upper part of the body region 120 between each two adjacent conventional trenches 300. A dielectric layer 140 is provided on the epitaxial layer 110, and a contact hole 150 is respectively formed in the dielectric layer 140 and the source region 130 and extends into the body region 120 between each two adjacent conventional trenches 300; an ohmic contact structure 151 is generally formed at the bottom of the contact hole 150. Of course, a source region 130 may also be formed on the upper part of the body region 120 between the second terminal trench of the inner terminal ring 230 and the adjacent conventional trench 300, and a contact hole 150 may also be respectively formed between the second terminal trench 232 of the inner terminal ring 230 and the adjacent conventional trench 300, and the contact hole 150 may also be respectively formed between the second terminal trench 232 of the inner terminal ring 230 and the adjacent conventional trench 300, and the contact hole 150 may be respectively formed between the dielectric layer 140 and the source region 130 and extends into the body region 120. A metal layer 160 is disposed on the dielectric layer 140 , and the metal layer 160 extends into the contact hole 150 .

[0037] In the common terminal structure of existing trench MOS, Figure 1The "T"-shaped region 171 in the circuit has an additional source polysilicon field plate (the source polysilicon in the "T"-shaped region 171 affects the electric field distribution in the vicinity and acts as a field plate), so the RESURF (Surface Electric Field Reduce) Effect (i.e., surface electric field reduction) will be more obvious, so its junction electric field is lower. The electric field at the bottom of the trench is higher. One of the consequences of a lighter epitaxial concentration is a lower junction electric field. In this way, when using Figure 1 The terminal structure will inevitably cause the avalanche voltage of the "T"-shaped area 171 to be significantly lower than that of the cell area, which may easily cause application failure and reliability test failure.

[0038] like Figure 2 As shown, the "T"-shaped region 172 of the terminal structure does not have grooves on both sides like the ordinary Mesa region 170, but has a continuous groove on one side and the grooves on the other side are periodically discontinuous, which results in a smaller capacitance per unit area of ​​the "T"-shaped region 172 at the same groove spacing, and a smaller number of ions that can be formed in the depletion region under the same bias voltage. Thus, compared with the ordinary Mesa region 170, the groove spacing of the "T"-shaped region 172 needs to be reduced. This spacing is estimated from the perspective that impurity atoms need to be ionized into ions when the device is reverse biased, and is generally 50% to 60% of the spacing of the cell region Final Trench (i.e., the grooves on the wafer chip that flow out using the SGT process; to distinguish it from the grooves in the middle of the process). Since the reduction of the groove spacing of the "T"-shaped region 172 is limited by the stress that the semiconductor material of the ordinary Mesa region 170 needs to withstand during the groove etching and oxidation process, it cannot cause cracking or collapse, and cannot cause leakage. The Pitch (i.e., the width of the minimum repeating unit of the cell) of the trench MOS of 30V and below and other medium and low voltage devices with low RSP is relatively small, and it is obviously difficult to meet the above requirements. In addition, one consequence of the reduction of the trench spacing of the "T"-shaped area 172 is that the electric field at the bottom of the trench of the "T"-shaped area 172 (especially the bottom of the periodically discontinuous end trench) is too high, which is easy to cause reliability problems and directly cause the failure of BV (breakdown voltage) and I dss (leakage current in the static off state between the source and the drain) during CP testing (Chip Prober testing, which refers to the test performed on the wafer after the chip is taped out, which is different from the various tests after the chip is packaged), which increases the difficulty of process development.

[0039] Compared to Figure 1In the structure where the conventional trench 300 in the “T”-shaped region 171 is connected to the source polysilicon in the terminal trench ring 200, the source polysilicon 202 in the first terminal trench 231 of the “T”-shaped region 173 is separated from the source polysilicon 302 in the conventional trench 300 by the first narrow trench 310 (without polysilicon), thereby overcoming the problem that Figure 1 Due to the disadvantages of the middle terminal structure, the trench electric field distribution of the "T"-shaped region 173 in this embodiment is closer to the cell region, making the electric field distribution in each region of the entire MOS device more consistent, which can improve the application performance and reliability of the device under harsh working conditions.

[0040] Of course, the above description is only based on the example of trench MOS. The terminal structure of this embodiment is not only applicable to trench MOS, but also applicable to other trench devices such as deep trench diodes and even IGBTs with high reliability trench process.

[0041] In this embodiment, the groove of the "T"-shaped region 173 of the terminal structure is continuous. Figure 2 The trench on one side of the "T"-shaped region 172 of the middle terminal structure is periodically discontinuous. In this embodiment, the spacing between the source polysilicon 302 in the conventional trench 300 and the source polysilicon 202 in the first terminal trench 231 can be made smaller, which can be suitable for trench devices with higher epitaxial concentrations, and can also enable trench devices with lower epitaxial concentrations to have a larger process window. Figure 2 The semiconductor material spacing between the mutually perpendicular grooves in the "T"-shaped region 172 of the terminal structure, in this embodiment, the conventional groove 300 of the "T"-shaped region 173 and the first terminal groove 231 are separated by the first narrow groove 310 (the first narrow groove 310 is an oxide layer, such as SiO2, without polysilicon), so that the electric field at the bottom of the conventional groove 300 of the "T"-shaped region 173 (especially the bottom of the periodically discontinuous terminal groove) is significantly reduced, which can improve the application performance and reliability under harsh working conditions. In addition, compared with Figure 2 In the special area of ​​the arc-shaped groove of the middle terminal groove ring 200, the corner area of ​​the terminal groove ring 200 of this embodiment does not adopt an arc structure, but is connected by the second narrow groove 320 and the third narrow groove 330, and the distribution is more symmetrical and repetitive, and an electric field distribution closer to the cell area can be obtained. Therefore, the device epitaxial process window can be enlarged, the application performance and reliability under harsh working conditions can be improved, and the difficulty of process development and debugging can be reduced.

[0042] In addition, the current silicon-based SGT products, while ensuring reliability and RSP levels, Figure 1 The terminal structure in is only applicable to devices with a withstand voltage of 30V or less. Figure 2The terminal structure in is only applicable to devices with a withstand voltage of 30V or above; it is difficult to share a set of masks (layouts) for devices with a withstand voltage of 25V to 40V. Even if it can be achieved, a certain RSP level must be sacrificed, such as Figure 2 If the terminal structure in the embodiment is applied to devices of 30V and below, it is only suitable for epitaxial wafers with a relatively low concentration. Figure 1 The terminal structure in the embodiment is difficult to achieve a rated voltage of 40V or above. However, the structure of this embodiment has a larger epitaxial process window. After adopting the structure of this embodiment, it becomes easy to share a set of masks for devices with a withstand voltage of 25V to 40V, and the loss of RSP level will become smaller.

[0043] Therefore, by adopting the terminal structure of this embodiment, the electric field distribution of each region of the entire trench device can be made more consistent, the application performance and reliability under harsh working conditions can be improved, and the epitaxial process window of the trench device can be increased, thereby reducing the difficulty of process development and debugging. In addition, because the terminal structure of this embodiment has a larger epitaxial process window, it can also make it easier to share a set of masks for devices with a withstand voltage of 25V to 40V, making the loss of RSP level smaller than that of the prior art.

[0044] The above embodiments only express the preferred implementation of the utility model, and the description is relatively specific and detailed, but it cannot be understood as limiting the scope of the utility model patent. It should be pointed out that for ordinary technicians in this field, several modifications and improvements can be made without departing from the concept of the utility model, which all belong to the protection scope of the utility model. Therefore, the protection scope of the utility model patent shall be based on the attached claims.

Claims

1. A trench device terminal structure capable of improving the uniformity of electric field distribution, characterized in that: The invention comprises a substrate, an epitaxial layer is arranged on the substrate, a plurality of terminal groove rings are nested on the epitaxial layer, the plurality of terminal groove rings include an outer terminal ring on the outside, an inner terminal ring on the inside and at least one intermediate terminal ring arranged between the outer terminal ring and the inner terminal ring, a plurality of conventional grooves are arranged inside the inner terminal ring at intervals; both ends of each of the conventional grooves are connected to the inner terminal ring through a first narrow groove, and the groove width of the first narrow groove is smaller than the groove width of the conventional groove.

2. A trench device terminal structure capable of improving the uniformity of electric field distribution as claimed in claim 1, characterized in that: Each of the terminal groove rings comprises two parallel first terminal grooves and two parallel second terminal grooves, the two second terminal grooves are arranged between the two first terminal grooves, and both ends of the second terminal grooves are connected to the first terminal grooves through a second narrow groove respectively; The first narrow grooves connected at both ends of the conventional groove are respectively connected to the two first terminal grooves of the inner terminal ring.

3. A trench device terminal structure capable of improving the uniformity of electric field distribution as claimed in claim 2, characterized in that: The groove width of the first terminal groove is equal to the groove width of the second terminal groove; the groove width of the conventional groove is less than or equal to the groove width of the first terminal groove, and the groove width of the conventional groove is greater than the groove widths of the first narrow groove, the second narrow groove and the third narrow groove.

4. A trench device terminal structure capable of improving the uniformity of electric field distribution as claimed in claim 3, characterized in that: The groove width of the first narrow groove is less than or equal to two-thirds of the groove width of the first terminal groove.

5. A trench device terminal structure capable of improving the uniformity of electric field distribution as claimed in claim 2, characterized in that: The first terminal groove is perpendicular to the second terminal groove, and the conventional grooves are parallel to the second terminal groove.

6. A trench device terminal structure capable of improving the uniformity of electric field distribution as claimed in claim 5, characterized in that: Both ends of the first terminal grooves of the inner terminal ring and the middle terminal ring are connected to the second terminal grooves of the outer terminal groove rings through a third narrow groove.

7. A trench device terminal structure capable of improving the uniformity of electric field distribution as claimed in claim 6, characterized in that: The widths of the second narrow groove and the third narrow groove are both less than or equal to two-thirds of the width of the first terminal groove.

8. A trench device terminal structure capable of improving the uniformity of electric field distribution as claimed in any one of claims 2 to 7, characterized in that: The first terminal groove, the second terminal groove, the conventional groove, the first narrow groove, the second narrow groove and the third narrow groove are all provided with an isolation oxide layer. The first terminal groove, the second terminal groove and the conventional groove are also provided with source polysilicon. The groove walls of the first terminal groove, the second terminal groove and the conventional groove are isolated from the source polysilicon by the isolation oxide layer. A gate polysilicon is provided above the corresponding source polysilicon in the conventional groove, a filling oxide layer is provided between the gate polysilicon and the source polysilicon, and the gate polysilicon is isolated from the groove wall of the conventional groove by the gate oxide layer.

9. A trench device terminal structure capable of improving the uniformity of electric field distribution as claimed in claim 8, characterized in that: A body region is formed on the upper portion of the epitaxial layer, and a source region is formed on the upper portion of the body region between each two adjacent conventional trenches.

10. A trench device terminal structure capable of improving the uniformity of electric field distribution as claimed in claim 9, characterized in that: A dielectric layer is arranged on the epitaxial layer, and a contact hole is respectively provided between each two adjacent conventional grooves in the dielectric layer, passing through the dielectric layer and the source region and extending into the body region; a metal layer is arranged on the dielectric layer, and the metal layer extends into the contact hole.

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