Method for manufacturing semiconductor structure

The embodiment of the application provides a method of manufacturing a semiconductor structure, which comprises the following steps: forming a target layer, a first mask layer, an isolation layer and an intermediate layer sequentially on a substrate, wherein first trench is disposed in the intermediate layer in the first region and second trench is disposed in the intermediate layer in the second region; forming a fill layer, and the difference in the height between the top surface of the fill layer in the first region and in the second region is less than or equal to a first preset value; removing a portion of the fill layer in the first region until the top surface of the sacrificial layer is exposed; removing the sacrificial layer; and etching a portion of the target layer through the first opening, wherein the remaining target layer forms a target pattern.

TECHNICAL FIELD

The present application relates to the field of semiconductors, and in particular to a method for manufacturing a semiconductor structure.

BACKGROUND

Before subjecting a layer to selective etching, it is generally necessary to form a mask layer with an opening pattern. The mask layer may be either a photoresist layer or a mask layer composed of one or more other materials. The opening pattern may be formed either by exposing and developing photoresist, or by etching particular materials in a composite layer which are generally formed in a particular position in advance and occupy the position of a to-be-formed opening pattern.

However, the etching of a to-be-etched region may be affected by adjacent regions. For example, a particular material is covered and cannot be exposed to the etching agent such that a preset opening pattern cannot be formed, thereby subjecting the target layer to incomplete selective etching.

SUMMARY

The embodiment of the application provides a method of manufacturing a semiconductor structure, where by selective etching can be performed completely to the target layer.

To solve the above problems, the embodiment of the application provides a method of manufacturing a semiconductor structure, which comprises the following steps: providing a substrate, comprising a first region, a second region, and a third region, wherein the second region is disposed between the first region and the third region; forming a target layer, a first mask layer, an isolation layer and an intermediate layer sequentially on the substrate, wherein the intermediate layer in the first region has at least one first trench therein which exposes the isolation layer, and the bottom and the sidewall of the first trench are covered with a sacrificial layer; etching a portion of the intermediate layer in the second region to form at least one second trench which is disposed in the intermediate layer in the second region; forming a fill layer which fills the first trench and the second trench, wherein the top surface of the fill layer is higher than the top surface of the intermediate layer, and the height difference between the top surface of the fill layer in the first region and the top surface of the fill layer in the second region is smaller than or equal to a first preset value in the direction perpendicular to the top surface of the substrate; performing a maskless dry etching process to remove a portion of the fill layer in the first region until the top surface of the sacrificial layer is exposed and the remaining fill layer in the first region fills the first trench; removing the sacrificial layer which covers the sidewall of the first trench to form a first opening in the first region, wherein the first opening exposes the surface of the isolation layer; and etching sequentially a portion of the isolation layer, a portion of the first mask layer and a portion of the target layer in the first region through the first opening, whereby the remaining target layer forms a target pattern.

DESCRIPTION OF EMBODIMENTS

FIGS.1to18are schematic structure diagrams corresponding to each step in a method of manufacturing a semiconductor structure. The method thereof comprises the following steps:

Referring toFIG.1, there is provided a substrate11, comprising a first region111, a second region112and a third region113, wherein the second region112is disposed between the first region111and the third region113; and a target layer121, a protective layer13, an initial mask layer141and an initial intermediate layer15are formed on the substrate11, which are stacked in sequence.

Referring toFIG.2, a first photoresist layer161having a first opening pattern is formed on the initial intermediate layer15; and the initial intermediate layer15is etched with the first opening pattern to form an intermediate trench15awhich exposes the surface of the initial mask layer141.

The arrangement density of the intermediate trenches15ain the first region111is higher than the arrangement density of the intermediate trenches15ain the second region112, and the arrangement density of the intermediate trenches15ain the second region112is higher than the arrangement density of the intermediate trenches15ain the third region113.

Referring toFIG.3, there is formed an initial sacrificial layer171covering the bottom and the sidewall of the intermediate trench15a, and the initial sacrificial layer171also covers the tops of the initial intermediate layers15in the first region111, the second region112and the third region113.

Referring toFIG.4, a deposition process is performed to form an initial fill layer181filling the intermediate trench15a.

In performing a maskless deposition process, the deposition rates and the deposition time in different regions are the same. That is, the total material of the initial fill layer181deposited per unit area in any region is the same. Since the arrangement density of the intermediate trenches15ain the first region111, the second region112and the third region113decreases gradually, the first region111comprises the most number of intermediate trenches15aper unit area and the second region112comprises the second most number of intermediate trenches15aper unit area. The more intermediate trenches15athere are, the more the material of the initial fill layer181can be accommodated, the less redundant material of the initial fill layer181there will be left on the initial intermediate layer15and the lower the top surface of the initial fill layer181will be. Accordingly, the top surface of the initial fill layer181in the first region111, the second region112and the third region113rises gradually.

Referring toFIGS.5and6, the initial fill layer181is etched and the remaining initial fill layer181exposes the top surface of the initial sacrificial layer171which covers the sidewall of the intermediate trench15a; and the initial sacrificial layer171covering the sidewall of the intermediate trench15ais etched to form an initial gap15bwhich exposes the surface of the initial mask layer141.

Herein, since the initial mask layer141in the third region113need not be etched, an initial gap15bneed not be formed in the third region113. Accordingly, there is no intermediate trench15aand initial sacrificial layer171in the initial intermediate layer15in the third region113, and the initial fill layer181in the third region113need not be removed.

Referring toFIGS.6and7, the initial mask layer141is etched through the initial gap15bto form a first mask layer142; and the remaining initial intermediate layer15, the remaining initial sacrificial layer171and the remaining initial fill layer181are removed after the first mask layer142is formed.

The first mask layer142has a plurality of fourth openings142awith the same opening width in a direction parallel to the substrate11, wherein the width of the fourth opening142ais equal to the thickness of the initial sacrificial layer171which covers the sidewall of the intermediate trench15a; in addition, since the arrangement density of the intermediate trenches15ain the first region111, the second region112and the third region113decreases gradually, the arrangement density of the initial gaps15bin the first region111, the second region112and the third region113decreases gradually, and the arrangement density of the fourth openings142ain the first region111, the second region112and the third region113decreases gradually.

Referring toFIG.8, there is formed on the first mask layer142an isolation layer19and an intermediate layer20stacked in sequence.

Since the arrangement density of the fourth openings142ain the first region111, the second region112and the third region113decreases gradually, the top surface of the isolation layer19in the first region111, the second region112, and the third region113gradually rises when the isolation layer19and the intermediate layer20are uniformly deposited in different regions. Accordingly, the top surface of the intermediate layer20in the first region111, the second region112and the third region113gradually rises.

Referring toFIG.9, there is formed in the intermediate layer20in the first region111at least one first trench20a, which exposes the surface of the isolation layer19; and there is formed a first sacrificial layer172which covers the bottom and the sidewall of the first trench20aand the top surface of the intermediate layer20in the first region111, the second region112and the third region113.

Referring toFIG.10, a second photoresist layer162is formed which fills the first trench20aand is disposed on the intermediate layer20in the first region111, the second region112, and the third region113. The second photoresist layer162has a second opening pattern disposed in the third region113.

Referring toFIG.11, the first sacrificial layer172and the intermediate layer20are etched with the second opening pattern to form a third trench20C which is disposed in the intermediate layer20in the third region113; and the second photoresist layer is removed after the third trench20C is formed.

Referring toFIG.12, a fill layer182is formed which fills the first trench20aand the third trench20c, and the upper surface of the fill layer182is higher than the upper surface of the intermediate layer20.

Since the deposition processes have the same deposition rate and deposition time in different regions, the total material of the fill layer182deposited per unit area in any region is the same. The top surface positions of the fill layer182in the different regions depend on two factors: one is the top surface position of the intermediate layer20in a region and the other is the arrangement density and the opening width of the trenches or the openings in the intermediate layer20in a region. The higher the top surface of the intermediate layer20is, the higher the top surface of the fill layer182is. Whereas the higher the arrangement density and the opening width of the trenches or openings in the intermediate layer20is, the lower the top surface of the fill layer182is.

Specifically, the top surface of the intermediate layer20in the first region111is lower than the top surface of the intermediate layer20in the second region112, and the intermediate layer20in the first region111has the first trench20atherein while the intermediate layer20in the second region112does not have a trench or an opening therein. Accordingly, the top surface of the fill layer182in the first region111is lower than the top surface of the fill layer182in the second region112.

When the difference between the height of the top surface of the fill layer182in the first region111and the height of the top surface of the fill layer182in the second region112is bigger than the first preset value, a portion of the fill layer182material at the edge of the second region112may collapse for lack of support and may slide toward a first edge region111ain the first region111, such that the top surface of the fill layer182in the first edge region111ais higher. In other words, the fill layer182on the intermediate layer20in the first edge region111ais thicker, whereas the fill layer182on the intermediate layer20in the first central region111bis thinner.

Further, if the fill layer182is formed using a spin-coating process, the whole structure of the fill layer182will be loose and the strength of the structure will be low, thereby making the layer prone to collapse for lack of support. Accordingly, if the material of the fill layer182is carbon or a carbon-containing organic substance, the fill layer182which will have a softer texture, lower hardness and lower structure strength is also prone to collapse for lack of support.

In addition, although the top surface of the intermediate layer20in the second region112is lower than the top surface of the intermediate layer20in the third region113, the intermediate layer20in the third region113has the third trenches20C therein such that the top surface of the fill layer182in the third region113may be higher or lower than or flush with the top surface of the fill layer182in the second region112as the third trenches20C vary in arrangement density and opening width.

When the top surface of the fill layer182in the third region113is higher than the top surface of the fill layer182in the second region112, a portion of the fill layer182material in the third region113may collapse for lack of support and may slide to the second region112or even the first region111, such that the top surface of the fill layer182in the first edge region111ais higher; and when the top surface of the fill layer182in the third region113is lower than the top surface of the fill layer182in the second region112, a portion of the fill layer182material in the second region112may slide to the third region113, thereby lowering the top surface of the fill layer182in the second region112and reducing the height difference between the top surface of the fill layer182in the first region111and the top surface of the fill layer182in the second region112, which helps prevent a portion of the fill layer182material in the second region112from sliding to the first region111.

Referring toFIG.13, the fill layer182is etched using a maskless dry etching process.

In the process of a maskless dry etching, the to-be-etched fill layers182in different regions have the same thickness. If the fill layer182on the intermediate layer20in the first edge region111ais thicker and the fill layer182on the intermediate layer20in the first central region111bis thinner, the top surface of the first sacrificial layer172in the first edge region111ais still covered by the fill layer182when the top surface of the first sacrificial layer172in the first central region111bis exposed.

Referring toFIGS.14and15, the first sacrificial layer172on the sidewall of the first trench20ais etched to form a first opening20b; the isolation layer19and the first mask layer142are sequentially etched through the first opening20bto form a second mask layer143; and after the second mask layer143is formed, the remaining isolation layer19, the remaining intermediate layer20, the remaining first sacrificial layer172and the remaining fill layer182are removed.

Since the fill layer182is still left on the intermediate layer20in the first edge region111a, the first sacrificial layer172which covers the sidewall of the first trench20ahas not been completely etched. Therefore, the pattern of the first opening20bis incomplete, and the opening pattern of the second mask layer143which is formed by etching through the first opening20bis also incomplete.

Referring toFIG.16, a transfer layer21and a third photoresist layer163are formed which are sequentially stacked, wherein the third photoresist layer163has a third opening pattern disposed in the second region112and the third region113.

Referring toFIGS.17and18, the transfer layer21and the second mask layer143are sequentially etched using the third opening pattern to form a third mask layer144; and after the third mask layer144is formed, the remaining transfer layer21and the third photoresist layer163are removed, and the protective layer13and the target layer121are sequentially etched through the opening pattern of the third mask layer144, wherein the remaining target layer121serves as the target pattern122.

Since the opening pattern of the second mask layer143is incomplete, the opening pattern of the third mask layer144and the ultimately formed target pattern122are incomplete.

In order to further clarify the purpose, technical schemes and advantages of the embodiment of the present application, the embodiment of the present application will be described in detail with reference to the accompanying drawings. However, one of ordinary skill in the art will appreciate that in the embodiment of the present application a plurality of technical details have been presented for readers to better understand this application. However, even without these technical details and various changes and modifications based on the following embodiment the technical schemes claimed herein may be realized.

FIGS.19to35are schematic structure diagrams corresponding to each step of the method of manufacturing a semiconductor structure provided by the embodiment of the present application. The method comprises the following steps:

Referring toFIG.19, there is provided a substrate31, comprising a first region311, a second region312and a third region313, wherein the second region312is disposed between the first region311and the third region313; and there are formed on the substrate31a target layer321, a protective layer33, an initial mask layer341and an initial intermediate layer35which are sequentially stacked.

In the present embodiment, the first region311is an array region, the second region312is a core region, and the third region313is a peripheral region. The array region, the core region and the peripheral region all comprise a bit line structure, and the arrangement density of the bit line structures in the array region is higher than the arrangement density of the bit line structures in the core region and in the peripheral region.

It should be noted that the first region311, the second region312, and the third region313refer to the different regions of the semiconductor structure which are divided with reference to the substrate31, and do not simply refer to the different parts of the substrate31. The first region311comprises a portion of the substrate31and other layers formed on the substrate31.

In the present embodiment, the protective layer33comprises a first protective layer331and a second protective layer332stacked in sequence, wherein the second protective layer332has a higher hardness than the initial mask layer341and can be used as a hard mask layer complementary to the initial mask layer341. Specifically, the material of the initial mask layer341comprises silicon dioxide and the material of the second protective layer332comprises silicon oxynitride. The initial intermediate layer35comprises a first initial intermediate layer351and a second initial intermediate layer352which are sequentially stacked, and the first initial intermediate layer351having the same material as the second protective layer332can be used as a hard mask layer complementary to a subsequently formed photoresist layer on the initial intermediate layer35.

The first protective layer331may have a lower hardness than the second protective layer332in order to shorten the duration of the etching process and to avoid damages to the target layer321; and similarly, the first initial intermediate layer351may have a lower hardness than the second initial intermediate layer352in order to shorten the duration of the etching process and to avoid damages to the initial mask layer341.

Referring toFIG.20, a first photoresist layer361having a first opening pattern is formed on the initial intermediate layer35; and the initial intermediate layer35is etched through the first opening pattern to form an intermediate trench35awhich exposes the surface of the initial mask layer341.

In the embodiment, the arrangement density of the intermediate trenches35aof the first region311is higher than the arrangement density of the intermediate trenches35ain the second region312, and the arrangement density of the intermediate trenches35ain the second region312is higher than the arrangement density of the intermediate trenches35ain the third region313; in addition, the first opening pattern and the intermediate trench35ahave a first extending direction, and specifically the first extending direction may be 120°.

Referring toFIG.21, an initial sacrificial layer371is formed, which covers the bottom and the sidewall of the intermediate trench35aas well as the top surfaces of the initial intermediate layer35in the first region311, the second region312and the third region313.

Before the initial sacrificial layer371is formed, the first photoresist layer361needs to be removed; and the initial sacrificial layer371may have the same material as the initial mask layer341, which helps to lessen the types of materials required for the semiconductor manufacturing process and to reduce the cost and the complexity of the semiconductor manufacturing process.

Referring toFIG.22, a deposition process is performed to form an initial fill layer381filling the intermediate trench35a.

In performing a maskless deposition process, the deposition rates and the deposition time in different regions are the same, that is, the total material of the initial fill layer381deposited per unit area in any region is the same. Since the arrangement density of the intermediate trenches35ain the first region311, the second region312and the third region313decreases gradually, the first region311comprises the most number of intermediate trenches35aper unit area and the second region312comprises the second most number of intermediate trenches35aper unit area. The more intermediate trenches35athere are, the more the material of the initial fill layer381can be accommodated, the less redundant material of the initial fill layer381there will be left on the initial intermediate layer35and the lower the top surface of the initial fill layer381will be. Accordingly, the top surface of the initial fill layer381in the first region311, the second region312and the third region313rises gradually.

Referring toFIGS.23and24, the initial fill layer381is etched and the remaining initial fill layer381exposes the top surface of the initial sacrificial layer371which covers the sidewall of the intermediate trench35a; and the initial sacrificial layer371which covers the sidewall of the intermediate trench35ais etched to form an initial gap35bwhich exposes the surface of the initial mask layer341.

In the present document, since the initial mask layer341in the third region313need not be etched, an initial gap35bneed not be formed in the third region313. Accordingly, there is no intermediate trench35aand no initial sacrificial layer371in the initial intermediate layer35in the third region313, and the initial fill layer381in the third region313need not be removed.

Referring toFIGS.24and25, the initial mask layer341is etched through the initial gap35bto form a first mask layer342; and the remaining initial intermediate layer35, the remaining initial sacrificial layer371and the remaining initial fill layer381are removed after the first mask layer342is formed.

The first mask layer342has a plurality of fourth openings342awith the same opening width in a direction parallel to the substrate31, wherein the width is equal to the thickness of the initial sacrificial layer371which covers the sidewall of the intermediate trench35a; and the fourth opening342awhich has a first extending direction has the same extending direction as the intermediate trench35a, in addition, since the arrangement density of the intermediate trenches35ain the first region311, the second region312and the third region313decreases gradually, the arrangement density of the initial gaps35bin the first region311, the second region312and the third region313decreases gradually, and the arrangement density of the fourth openings342ain the first region311, the second region312and the third region313decreases gradually.

Referring toFIG.26, there is formed on the first mask layer342an isolation layer39and an intermediate layer40stacked in sequence.

Since the arrangement density of the fourth openings342ain the first region311, the second region312and the third region313decreases gradually, the top surface of the isolation layer39in the first region311, the second region312, and the third region313gradually rises when the isolation layer39and the intermediate layer40are uniformly deposited in different regions, and the top surface of the intermediate layer40in the first region311, the second region312and the third region313gradually rises.

In the embodiment, the isolation layer39comprises a first isolation layer391and a second isolation layer392stacked in sequence, wherein the first isolation layer391has a lower hardness than the second isolation layer392but a bigger thickness than the second isolation layer392, which helps shorten the etching duration of the isolation layer39; and the intermediate layer40comprises a first intermediate layer401and a second intermediate layer402stacked in sequence, wherein the first intermediate layer401has a lower hardness than the second intermediate layer402but a bigger thickness than the second intermediate layer402, which helps shorten the etching duration of the intermediate layer40.

The second isolation layer392may have the same material as the first mask layer342, the first intermediate layer401may have the same material as the first isolation layer391, the second intermediate layer402is used as a hard mask layer, and the second intermediate layer402may have the same material as the second protective layer332, which helps lessen the types of materials required for the semiconductor manufacturing process and the types of etching agents and reduce the cost and the complexity of the semiconductor manufacturing process.

Referring toFIG.27, at least one first trench40ais formed in the intermediate layer40in the first region311, wherein the first trench40aexposes the surface of the isolation layer39; and a sacrificial layer372is formed, wherein the sacrificial layer372covers the bottom and the sidewall of the first trench40aas well as the top surface of the intermediate layer40which covers the first region311, the second region312and the third region313.

In the embodiment, the first region311comprises a first edge region311aadjacent to the second region312and a first central region311bremote from the second region312, wherein the first trench40ais at least partially disposed in the first edge region311aand the sacrificial layer372covering the sidewall of the first trench40ais at least partially disposed in the first edge region311a; in addition, the sacrificial layer372may have the same material as the second isolation layer392.

In the embodiment, the first trench40ahas a second extending direction, for example, a direction of 60°. The orthographic projection of the first extending direction is diagonal to the orthographic projection of the second extending direction in a plane parallel to the substrate31.

Referring toFIG.28, a second photoresist layer362is formed, which fills the first trench40aand is disposed on the intermediate layer40in the first region311, the second region312, and the third region313. And the second photoresist layer362has a second opening pattern, through which the intermediate layer40is etched.

In the embodiment, the second opening pattern of the second photoresist layer362is disposed at least in the second region312, and the intermediate layer40is etched with the second opening pattern to form at least one second trench40bin the second region312, which helps the subsequently formed fill layer partially fill into the second trench40b, thereby reducing the difference between the height of the top surface of the fill layer in the first region311and the height of the top surface of the fill layer in the second region312, preventing a portion of the fill layer material in the second region312from sliding to the first region311for lack of support, and ensuring that the thickness of the fill layer on the intermediate layer40in the first edge region311aand the first central region311bof the first region311remains the same.

In the embodiment, the second trench40bhas a smaller opening width than the first trench40ain a direction parallel to the substrate31, thereby avoiding etching through the second isolation layer392due to the etch loading effect, ensuring the isolating effect of the second isolation layer392and avoiding etching the first isolation layer391and the first mask layer342in case the second isolation layer392is etched through; meanwhile, the arrangement density of the second trenches40bis higher than the arrangement density of the first trenches40a, which helps the second trenches40bin the second region312accommodate more fill layer material, so that the height difference between the top surface of the fill layer in the first region311and the top surface of the fill layer in the second region312is small after the fill layer is formed and the fill layer material in the second region312is prevented from sliding to the first region311.

Further, the thickness of the subsequently formed fill layer on the intermediate layer40in the first region311and in the second region312is equaled by adjusting the opening width and the arrangement density of the second trenches40b. Therefore, after the fill layer is formed, the fill layer on the intermediate layer40in the first region311and the second region312can be etched by the same maskless dry etching process to expose the top surface of the sacrificial layer372.

In the embodiment, the second opening pattern of the second photoresist layer362is also disposed in the third region313. In the same process as etching a portion of the intermediate layer40in the second region312through the second opening pattern, a portion of the intermediate layer40in the third region313is etched to form a third trench40c. Therefore, the third trench40cin the third region313can accommodate a portion of the subsequently deposited fill layer material, which helps prevent the fill layer material in the third region313from sliding to the first region311and helps a portion of the fill layer material in the second region312slide to the third region313, thereby further reducing the height difference between the top surface of the fill layer in the first region311and the top surface of the fill layer in the second region312in a direction perpendicular to the top surface of the substrate31.

It should be noted that when the second region312, due to external restrictions, cannot have the second trenches40bformed in high arrangement density, a portion of the fill layer material in the second region312is directed to slide to the third region313, which can ease to some extent the problem of the low arrangement density of the second trenches40bin the second region312, ensure that the height difference between the top surface of the fill layer in the first region311and the top surface of the fill layer in the second region312is smaller than a first preset value, and prevent a portion of the fill layer material in the second region312from sliding to the first region311.

In the embodiment, the opening width of the third trench40cis equal to the opening width of the second trench40band the arrangement density of the third trenches40cis equal to the arrangement density of the second trenches40b. By providing both the second trench40cand the third trench40cwith the same accommodating capacity per unit area, the fill layer on the intermediate layer40in the second region312and the fill layer on the intermediate layer40in the third region313can have same thickness in the process of depositing the fill layer, so that after the fill layer is formed, the fill layer on the intermediate layer40in the first region311, the second region312and the third region313can be etched by the same maskless dry etching process to expose the sacrificial layer372.

Referring toFIG.29, the second photoresist layer is removed, and a fill layer382is formed which fills the first trench40a, the second trench40band the third trench40c, wherein the top surface of the fill layer382in each region is higher than the top surface of the intermediate layer40in the corresponding region.

In the embodiment, the fill layer382is formed by a spin-coating process which has a faster rate in layer formation and helps shorten the manufacturing process; furthermore, the material of the fill layer382comprises carbon or carbon-containing organic substances which are soft in texture and are easy to be etched and removed, thereby further shortening the manufacturing process of the semiconductor structure.

In the embodiment, the height difference between the top surface of the fill layer382in the first region311and the top surface of the fill layer382in the second region312is smaller than or equal to the first preset value, which helps prevent a portion of the fill layer382material in the second region312from sliding to the first region311due to lack of support; furthermore, the height difference between the top surface of the fill layer382in the first region311and the top surface of the fill layer382in the third region313is smaller than or equal to the second preset value which is greater than the first preset value, which helps prevent a portion of the fill layer material of the third region313from sliding to the first region311due to lack of support.

In addition, the thickness of the fill layer382on the intermediate layer40in the first edge region311ais equal to that in the first central region311b, and the fill layers382on the intermediate layers40in the first region311, the second region312, and the third region313have the same thickness.

In the embodiment, the fill layer382has the same material as the first intermediate layer401such that the same etching agent can subsequently be used to etch a mixed layer composed of the first intermediate layer401and the remaining fill layer382at a fast rate to form the second opening and the third opening, thereby avoiding the problem of uneven etching and the further problem of an inaccurate opening pattern, guaranteeing the accurate formation of the second opening and the third opening, and performing accurate etching of the first mask layer342.

Referring toFIG.30, the maskless dry etching process is performed to remove a portion of the fill layer382in the first region311until the top surface of the sacrificial layer372is exposed and until the remaining fill layer382in the first region311fills the first trench40a.

In the embodiment, the fill layer382on the intermediate layer40in the first region311, the second region312, and the third region313is removed in the same step of the process as the top surface of the sacrificial layer372in the first region311, the second region312, and the third region313is exposed.

Since the thickness of the fill layer382on the intermediate layer40in the first edge region311ais equal to that in the first central region311b, the maskless dry etching process can simultaneously expose the top surface of the sacrificial layer371in the first edge region311aand the first central region311bwithout having to over-etch the fill layer382in the first trench40ato expose the top surface of the sacrificial layer371in the first edge region311aafter the top surface of the sacrificial layer371in the first central region311bis exposed. Accordingly, the fill layer382in the first trench40atends to have good integrity, thereby ensuring that the first opening subsequently formed by etching the sacrificial layer372on the sidewall of the first trench40awith the intermediate layer40and the fill layer as a mask meets the requirements of the preset pattern, and avoiding an oversized first opening caused by etching a portion of the fill layer382in the first trench40a.

In addition, since the fill layer382on the intermediate layer40in the second region312and the third region313is removed simultaneously, no separate etching processes need to be performed to selectively remove the remaining fill layer382on the intermediate layer40in the second region312and the third region313before the formation of the second opening and the third opening, which helps shorten the duration of manufacturing the semiconductor structure; further, as the fill layer382in the second trench40band the third trench40cis not over-etched by the maskless dry etching process, there will not be the problem of an oversized opening caused by over-etching, thereby ensuring the accuracy of the patterns of the second opening and the third opening which are formed later by etching a mixed layer composed of the intermediate layer40and the remaining fill layer382.

Referring toFIG.31, a third photoresist layer363is formed, which has a third opening pattern disposed in the second region312and the third region313; a mixed layer composed of the intermediate layer40and the remaining fill layer382is etched through the third opening pattern to form a second opening40ddisposed in the second region312and a third opening40edisposed in the third region313.

In the embodiment, the second opening40dand the third opening40eexpose the top surface of the second isolation layer392such that the second isolation layer392exposed by the second opening40dand the third opening40ecan be etched through in the subsequent process step of forming a first opening, with an additional process step of etching the second isolation layer392omitted and the etching time shortened.

Referring toFIGS.32and33, the third photoresist layer363is removed, and the sacrificial layer372on the sidewall of the first trench40ain the first region311is etched to form a first opening40f.

In the embodiment, the sacrificial layer372may be removed by a maskless dry etching process to etch through the second isolation layer392in the first region311, the second region312and the third region313when forming the first opening40f.

In addition, the first opening40f, which has a second extending direction, has the same extending direction as the first trench40a. When the first mask layer342is etched through the first opening40f, a mask pattern identical to the target pattern may be formed on the first mask layer342. Specifically, the first extending direction is 120°, the second extending direction is 60°, and a diamond-shaped target pattern may be formed on the first mask layer342.

In addition, the second opening40dand the third opening40eare formed before the formation of the first opening40f, which prevents the third photoresist layer363(refer toFIG.31) from falling into the first opening40f, thereby reducing the difficulty in removing the third photoresist layer363and shortening the time of removing the third photoresist layer363.

Referring toFIGS.33and34, the second isolation layer392, the first isolation layer391, and the first mask layer342are sequentially etched through the first opening40f, the second opening40dand the third opening40eto form a second mask layer344, which has the same mask pattern as the target pattern; after the second mask layer344is formed, the remaining isolation layer39, the remaining intermediate layer40, the remaining fill layer382and the remaining sacrificial layer372are removed.

Referring toFIGS.34and35, the protective layer33and the target layer321are sequentially etched using the second mask layer344, wherein the remaining target layer321serves as the target pattern322; after the target pattern322is formed, the second mask layer344and the remaining protective layer33are removed.

In the embodiment, before the formation of the fill layer, the second trench is formed in the second region such that a portion of the fill layer material in the second region falls into the second trench, thereby reducing the height difference between the top surface of the fill layer in the first region and the top surface of the fill layer in the second region, avoiding a collapse of the fill layer in the second region whereby a portion of the material will slide to the top of the first region and exposing all the top surface of the sacrificial layer without over-etching in the subsequent maskless dry etching process. Therefore, a complete first opening is formed and selective etching is performed completely to the target layer.

In addition, before removing the sacrificial layer on the sidewall of the first trench to form the first opening, the second opening and the third opening are formed, which prevents the photoresist layer used to form the second opening and the third opening from filling the first opening, thereby avoiding the trouble in removing the photoresist material which falls into the first opening and ensuring the effective execution of the subsequent etching process.

It will be apparent to one of ordinary skill in the art that the above described embodiments are specific embodiments to implement the present application and that in practical application various revisions in form and detail may be made thereto without departing from the spirit and scope of the present application. Any person skilled in the art may make their own revisions and modifications without departing from the spirit and scope of the present application, so the scope of protection of the present application shall be subject to the scope defined by the claims.