Semiconductor structure and its formation method

Abstract

This application discloses a semiconductor structure and a method for forming the same. The method includes: providing a first material layer; forming a patterned photoresist layer on the surface of the first material layer; pre-treating the photoresist layer such that the top of the patterned sidewalls of the photoresist layer is tilted inwards towards the pattern and has a preset tilt angle; using the pre-treated photoresist layer as a mask, performing a first etching on the first material layer along the preset tilt angle to form an etched pattern, wherein the sidewalls of the etched pattern have a target tilt angle, and the difference between the target tilt angle and the preset tilt angle is less than a set value. The above method for forming a semiconductor structure can control the tilt angle of the etched pattern's sidewalls.

Description

Technical Field

[0001] This application relates to the field of semiconductor technology, specifically to a semiconductor structure and a method for forming the same. Background Technology

[0002] During the formation of semiconductor structures, it is often necessary to deposit a new material layer on the etched pattern formed by the previous layer. The deposition quality of the new material layer is greatly related to the morphology of the etched pattern of the previous layer. When the sidewalls of the etched pattern of the previous layer are vertical or have inverted trapezoidal sidewalls, the new material layer is prone to defects such as voids and gaps at the sidewalls.

[0003] To improve deposition quality, it is usually necessary to tilt the top of the sidewall of the etched pattern of the previous layer toward the inside of the pattern so that the sidewall can fully contact the deposition gas during the deposition process, thereby improving the deposition quality of the material layer on the sidewall surface.

[0004] The tilt angle can be used to represent the degree of tilt of the sidewalls, defined as the angle between the sidewall and the plane containing the material layer. The tilt angle of the sidewalls of the previous layer etching pattern is crucial for improving deposition quality. If the tilt angle is too large, it will not achieve the desired improvement; if the tilt angle is too small, it will affect the linewidth of the pattern; different materials also require different tilt angles.

[0005] Therefore, how to accurately control the tilt angle of the sidewalls of the etched pattern is a problem that needs to be solved. Summary of the Invention

[0006] In view of this, this application provides a semiconductor structure and a method for forming the same, so as to achieve accurate control of the tilt angle of the sidewalls of the etched pattern.

[0007] This application provides a method for forming a semiconductor structure, comprising: providing a first material layer; forming a patterned photoresist layer on the surface of the first material layer; pre-treating the photoresist layer such that the top of the patterned sidewalls of the photoresist layer is inclined inwards towards the pattern, and has a preset tilt angle with the surface of the first material layer; using the pre-treated photoresist layer as a mask, performing a first etching on the first material layer along the preset tilt angle to form an etched pattern, wherein the sidewalls of the etched pattern have a target tilt angle, and the difference between the target tilt angle and the preset tilt angle is less than a set value.

[0008] Optionally, the target tilt angle is equal to the preset tilt angle.

[0009] Optionally, the preprocessing includes: performing thermal reflow on the photoresist layer to give the pattern of the photoresist layer a raised arc-shaped surface; and performing a second etching on the photoresist layer after thermal reflow to give the pattern sidewalls of the photoresist layer an inclined angle.

[0010] Optionally, the heating temperature of the heat reflux treatment is 200℃~300℃, and the time is 3min~5min.

[0011] Optionally, the thickness of the photoresist layer is 1 micrometer to 2 micrometers.

[0012] Optionally, the set value range is 0 to 5°.

[0013] Optionally, the target tilt angle is 25° to 60°.

[0014] Optionally, the second etching selectivity ratio for the photoresist layer and the first material layer is greater than 100.

[0015] Optionally, the etching gas used in the second etching includes at least one of O2, Cl2, Ar, and He.

[0016] Optionally, the etching selectivity ratio of the first etching to the first material layer and the photoresist layer is greater than 100.

[0017] Optionally, in the first etching process, the molar fraction of the etching gas used that can generate polymer is less than 20%.

[0018] Optionally, the first material layer may include a metal layer, an insulating dielectric layer, or a semiconductor layer.

[0019] Optionally, it may also include forming a second material layer covering the sidewalls and top surface of the etched pattern.

[0020] This application also provides a semiconductor structure, including: a substrate; a first material layer located on the surface of the substrate, wherein an etched pattern is formed in the first material layer, and the sidewalls of the etched pattern are inclined inwards towards the etched pattern, with an angle between the sidewalls and the substrate surface ranging from 25° to 60°.

[0021] Optionally, the material of the first material layer may include metal, insulating medium, or semiconductor.

[0022] Optionally, it may also include a second material layer covering the sidewalls and top surface of the etched pattern.

[0023] The semiconductor structure formation method of this application involves pre-processing a photoresist layer to accurately control the sidewall tilt angle of the photoresist layer pattern, and then using the pre-processed photoresist layer as a mask to etch a first material layer to obtain an etched pattern. The difference between the sidewall tilt angle of the etched pattern and the sidewall tilt angle of the photoresist layer pattern is less than a preset value. By pre-processing the photoresist layer to obtain the preset tilt angle, the sidewall tilt angle of the etched pattern in the first material layer can be controlled.

[0024] Furthermore, the preprocessing includes thermal reflow and second etching. Thermal reflow makes the surface of the photoresist layer pattern convex and arc-shaped, and the surface tangent angle at the sidewall position is close to the preset tilt angle. Combined with the second etching to etch the sidewall, the tilt angle of the sidewall of the photoresist layer pattern can be adjusted to the preset tilt angle, thereby achieving more accurate control of the tilt angle of the sidewall of the photoresist layer pattern. Attached Figure Description

[0025] To more clearly illustrate the technical solutions in the embodiments of this application, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0026] Figure 1 This is a schematic flowchart of a method for forming a semiconductor structure according to an embodiment of this application;

[0027] Figures 2 to 8 This is a schematic diagram of the formation process of a semiconductor structure according to an embodiment of this application. Detailed Implementation

[0028] As described in the background section, it is necessary to form an etch pattern with a specific tilt angle on the sidewalls in order to improve the deposition quality of the material layer subsequently deposited on the etch pattern.

[0029] Currently, there are generally two methods for forming sloping sidewalls. One method uses a thicker photoresist layer as a mask. During the etching process, a high proportion of a gas that generates polymers is used. As the layer to be etched is being etched, the generated polymers accumulate on the sidewalls, protecting them. Simultaneously, the photoresist layer is etched back, exposing new layers to be etched, thus forming the sloping sidewalls. Due to the polymer's protection of the sidewalls, the sloping angle of this method is relatively small, typically within the range of 10° to 25°.

[0030] Another method is to reduce the proportion of etching gases that can generate polymers, so that almost no polymers are generated on the sidewalls of the etched pattern during the etching process, and the sidewall angle of the etched pattern can be consistent with the sidewall of the photoresist layer. In this case, the sidewall tilt angle of the final etched pattern is determined by the sidewall tilt angle of the photoresist mask pattern. Therefore, this method has high requirements for the sidewall tilt angle of the photoresist pattern. In existing technologies, controlling the sidewall angle of the photoresist pattern is quite difficult. The sidewall tilt angle of the pattern formed by the photolithography process is usually relatively high, and therefore the sidewall tilt angle of the resulting etched pattern is also relatively large, usually around 60° to 70°.

[0031] The methods described above all suffer from the problem of inaccurate control of the etching angle and a limited adjustable range of the tilt angle. The inventors have discovered that a tilted sidewall of approximately 45° is beneficial for improving the deposition quality of subsequent material layers. However, existing technologies cannot effectively control the tilt angle of the sidewalls of the etched pattern.

[0032] To address the aforementioned issues, this application proposes a novel technical solution that enables the target tilt angle to be achieved over a wider range, with more accurate control over the tilt angle.

[0033] The technical solutions in the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of this application, and not all of them. Based on the embodiments in this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application. In the absence of conflict, the following embodiments and their technical features can be combined with each other.

[0034] Please refer to Figure 1 This is a schematic flowchart illustrating the formation process of a semiconductor structure according to an embodiment of the present invention.

[0035] The process of forming the semiconductor structure includes the following steps:

[0036] Step S101: Provide a first material layer.

[0037] The first material layer is the material layer to be etched, and the first material layer includes any one of the material layers commonly used in semiconductor processes, such as metal layer, insulating dielectric layer or semiconductor layer.

[0038] Step S102: A patterned photoresist layer is formed on the surface of the first material layer.

[0039] Based on the etching pattern to be formed in the first material layer, a patterned photoresist layer is formed on the surface of the first material layer by photolithography to serve as a mask for subsequent etching of the first material layer.

[0040] Step S103: Pre-process the photoresist layer so that the patterned sidewalls of the photoresist layer are inclined inwards and have a preset tilt angle with the surface of the first material layer.

[0041] The preprocessing includes: performing a thermal reflow treatment on the photoresist layer to give the pattern of the photoresist layer a raised arc-shaped surface; and performing a second etching on the photoresist layer after thermal reflow treatment to tilt the sidewalls of the pattern of the photoresist layer and give it a preset tilt angle with the surface of the first material layer.

[0042] Step S104: Using the pre-treated photoresist layer as a mask, perform a first etching on the first material layer to form an etched pattern with tilted sidewalls. The sidewalls of the etched pattern have a target tilt angle, and the difference between the target tilt angle and the preset tilt angle is less than a set value.

[0043] Since the photoresist layer is used as a mask, the first etching etches the surface of the first material layer not covered by the photoresist layer along a preset tilt angle. By adjusting the process parameters of the first etching process, the sidewall tilt angle of the etched pattern can be made to have no or only a slight deviation from the preset tilt angle of the photoresist pattern. The set value range is 0 to 5°. The target tilt angle can be slightly greater than, slightly less than, or equal to the preset tilt angle.

[0044] The above method first pre-processes the photoresist layer, then adjusts the tilt angle of the pattern sidewall of the photoresist layer to a preset tilt angle, and then uses the pre-processed photoresist layer as a mask to perform the first etching on the first material layer. The sidewall tilt angle formed by the first etching is relatively close to the preset tilt angle, thereby enabling more accurate control of the sidewall tilt angle of the etched pattern.

[0045] Please refer to Figures 2 to 7 This is a schematic diagram of the formation process of a semiconductor structure according to a specific embodiment of the present invention.

[0046] Please refer to Figure 2 Provides the first material layer 200.

[0047] The first material layer 200 is the layer to be etched, which can be the substrate itself or a material layer formed on a substrate. In this embodiment, the first material layer 200 is formed on the surface of the substrate 100.

[0048] The first material layer 200 can be any one of a semiconductor layer, a metal layer, or an insulating dielectric layer.

[0049] Please refer to Figure 3 A patterned photoresist layer 300 is formed on the surface of the first material layer 200.

[0050] The method for forming the patterned photoresist layer 300 includes: forming a photoresist layer on the surface of the first material layer 200 by spin coating, and then performing photolithography on the photoresist layer to form a patterned photoresist layer.

[0051] The patterned sidewalls of the photoresist formed by the photolithography process are typically perpendicular or nearly perpendicular to the surface of the first material layer 200, with an inclination angle close to 90°.

[0052] The photoresist layer 300 needs to be pre-processed to adjust the tilt angle of the inner pattern sidewalls of the photoresist layer 300.

[0053] Please refer to Figure 4 For the photoresist layer 300 (please refer to...) Figure 3 The photoresist layer 300a is reflowed to create a raised, curved surface.

[0054] The heat reflow process includes a heating process and a cooling process. During the heating process, the photoresist layer is heated to a certain temperature, at least softening the surface material and making it fluid; then, it is naturally cooled, and the photoresist material solidifies, forming a raised arc-shaped surface under the action of surface tension, with the edge thickness of the cross-section being less than the middle thickness.

[0055] The heating temperature of the reflow process can be appropriately set according to the different photoresist materials. This ensures the photoresist softens while preventing excessive deformation of the photoresist layer pattern, which would render it unusable as a mask layer for subsequent etching. In some embodiments, the heating temperature is 200℃~300℃, and the heating time is 3min~5min. After the heating process is complete, the material is allowed to cool naturally or through nitrogen gas.

[0056] Preferably, the patterned surface of the pretreated photoresist layer 300a is generally arc-shaped, such as... Figure 4 As shown, the tangent angle of the arc surface at the sidewall position is close to the preset tilt angle.

[0057] The pattern morphology of the photoresist layer after thermal reflow is the same as that of the initial photoresist layer 300 (please refer to...). Figure 3 The thickness of the photoresist layer is related to the thickness of the photoresist layer. If the 300mm photoresist layer is too thick, after reflow treatment, only the top surface and the top of the sidewalls will be arc-shaped, while the sidewalls near the bottom will still have a vertical shape. Figure 5After pretreatment, the photoresist layer 3001a cannot have its sidewall tilt angle adjusted to the preset tilt angle through subsequent etching. If the thickness of the photoresist layer 300 is too small, the thickness will further decrease after thermal reflow, failing to meet the thickness requirements for use as an etching mask, and the tilt angle at the sidewall will also be too small to achieve the preset tilt angle. In some embodiments, the thickness of the photoresist layer 300 can be set to 1 micrometer to 2 micrometers. In other embodiments, parameters such as the thickness of the photoresist layer 300, the heating temperature during reflow, and the heating time can be reasonably configured according to actual needs.

[0058] Please refer to Figure 6 The photoresist layer 300a after the thermal reflow treatment is etched a second time, so that the sidewall of the photoresist layer 300b after the second etching is tilted and has a preset tilt angle α.

[0059] The second etching can be performed using a dry etching process, and the photoresist layer 300a (please refer to...) Figure 4 The second etching process exhibits high etching selectivity, while producing little or no etching effect on the first material layer 200. Specifically, the etching gas used in the second etching includes at least one of O2, Cl2, Ar, or He, and the photoresist layer 300a is etched through chemical etching and / or physical etching. In some embodiments, the etching selectivity ratio between the photoresist layer 300a and the first material layer 200 in the second etching process is greater than 100. In this embodiment, the etching gas used in the second etching of the photoresist layer 300a includes Ar, He, and Cl2, wherein the flow rate of Ar is 80 sccm to 120 sccm, the flow rate of He is 20 sccm to 50 sccm, the flow rate of Cl2 is 20 sccm to 80 sccm, the etching process pressure is 5 mTorr to 10 mTorr, and the power is 500 W to 1500 W.

[0060] The sidewalls of the photoresist layer 300a can be etched by adjusting the etching direction to form tilted sidewalls. By controlling the etching rate, etching angle, and etching time, the tilt angle of the sidewalls of the photoresist layer 300b after the second etching can reach the preset tilt angle α.

[0061] Although the second etching will cause a certain linewidth (CD) loss in the photoresist layer 300b compared to the photoresist layer 300a, the linewidth of the pattern in the photoresist layer 300a after thermal reflow is slightly larger than that in the photoresist layer 300 before thermal reflow due to the photoresist melting and flowing to the bottom under the influence of gravity. This makes up for the possible linewidth loss caused by the second etching. Therefore, the influence of the entire preprocessing process on the pattern linewidth of the photoresist layer is negligible.

[0062] Please refer to Figure 7 Using the pre-treated photoresist layer 300b as a mask, the first material layer 200 is etched to form an etched pattern 201 with tilted sidewalls. The sidewalls of the etched pattern have a target tilt angle β with respect to the surface of the substrate 100. The difference between the target tilt angle β and the preset tilt angle α is less than a set value.

[0063] A first etching process is employed to perform anisotropic etching on the first material layer 200. This first etching process exhibits high selectivity for the first material layer 200 and has little or no etching effect on the photoresist layer 300b. Preferably, in the first etching process, the etching selectivity ratio between the first material layer 200 and the photoresist layer 300b is greater than 100.

[0064] In the first etching process, the proportion of polymer-generating gases in the etching gas is relatively low, i.e., a low-polymer etching gas is used. In typical etching processes, some etching gases can polymerize or react with the etching products to form polymers. Polymer-generating gases are typically C or B-containing gases, such as CF4, C2F4, C2F6, C3F8, BCl3, N2, CO, etc. A higher proportion of polymer-generating etching gases results in a smaller sidewall tilt angle. In some embodiments, the molar fraction of polymer-generating gases (e.g., C- and / or B-containing gases) used in the first etching process is less than 20% of the total etching gas, to avoid excessive polymer formation on the sidewalls of the etched pattern 201 during the etching process, which could affect the formation of the target tilt angle. Preferably, the etching gas used in the first etching process does not contain polymer-generating etching gases. The first etching is performed using a low-polymer etching gas, which allows etching of the first material layer 200 (see reference) at a predetermined tilt angle α along the sidewall of the photoresist layer 300b. Figure 6 Etching is performed to ensure that the sidewalls of the etched pattern 201 formed after etching the first material layer 200 maintain the same tilt angle as the sidewalls of the photoresist layer 300b. Even if, due to process errors, the target tilt angle β of the etched pattern 201 cannot be strictly matched with the preset tilt angle α of the pattern sidewall of the photoresist layer 300b, the difference between the target tilt angle β and the preset tilt angle α can be controlled within a set value. The set value can be 0–5°, and the target tilt angle can be 25°–60°, which is beneficial for improving the quality of subsequent material layer deposition.

[0065] In this embodiment, the material of the first material layer 200 is Mo, and the tilt angle α of the sidewall of the photoresist layer 300b is 45°. In order to make the tilt angle of the sidewall of the etched pattern formed after etching the first material layer 200 consistent with the tilt angle of the sidewall of the pattern of the photoresist layer 300b, in this embodiment, the etching gas used for the first etching includes: Ar, He, SF6 and Cl2, wherein the flow rate of Ar is 80sccm to 120sccm, the flow rate of He is 20sccm to 50sccm, the flow rate of SF6 is 20sccm to 80sccm, the flow rate of Cl2 is 20sccm to 80sccm, the etching process pressure is 5mTorr to 10mTorr, and the power is 500W to 1500W. By controlling the etching time, the tilt angle β of the sidewall of the finally formed etched pattern 201 is consistent with the tilt angle α of the sidewall of the pattern of the photoresist layer 300b, where β = α = 45°.

[0066] Please refer to Figure 8 A second material layer 400 is formed covering the sidewalls and top surface of the etched pattern 201.

[0067] Before forming the second material layer 400, the process also includes removing the photoresist layer 300b (see reference). Figure 7 ).

[0068] The material of the second material layer 400 can be any one of a semiconductor layer, a metal layer, or an insulating dielectric layer. It can be the same as or different from the material of the first material layer 200, and there is no limitation. Those skilled in the art can choose according to actual needs.

[0069] The second material layer 400 can be formed by various methods such as chemical vapor deposition, plasma-enhanced chemical vapor deposition, sputtering, and electroplating.

[0070] In this embodiment, the second material layer 400 is made of Mo. Because the sidewall tilt angle of the etched pattern 201 in the previous layer is 45°, the second material layer 400 has high step coverage, resulting in high deposition quality on the sidewall surface of the etched pattern 201. This avoids problems such as gaps and voids, improving the reliability of the semiconductor structure.

[0071] Depending on the different materials of the first material layer 200 and the second material layer 400, the target tilt angle β of the sidewall of the etched pattern 201 can also be set to other values. In response, the preset tilt angle α of the sidewall of the pre-processed photoresist layer 300b is adjusted to meet the deposition requirements of different material layers, thereby improving the deposition quality of the second material layer 400.

[0072] Embodiments of the present invention also provide a semiconductor structure.

[0073] Please refer to the figure, which is a schematic diagram of a semiconductor structure provided in an embodiment of the present invention.

[0074] In this embodiment, the semiconductor structure includes: a substrate 100; a first material layer located on the surface of the substrate 100, the first material layer having an etched pattern 201, the sidewalls of the etched pattern 201 being inclined toward the inside of the pattern, and the included angle between the etched pattern 201 and the substrate 100 being in the range of 25° to 60°.

[0075] The material of the first material layer includes metal, insulating medium or semiconductor.

[0076] In this embodiment, the semiconductor structure further includes a second material layer 400 covering the sidewalls and top surface of the etched pattern 201.

[0077] In this embodiment, the sidewall tilt angle of the etched pattern 201 is beneficial to improving the film quality of the second material layer 400 formed on its surface, especially reducing defects at the interface between the second material layer 400 and the sidewall of the etched pattern 201.

[0078] The above description is merely an embodiment of this application and does not limit the patent scope of this application. Any equivalent structural or procedural transformations made using the content of this application's specification and drawings, such as the combination of technical features between embodiments, or direct or indirect applications in other related technical fields, are similarly included within the patent protection scope of this application.

Claims

1. A method for forming a semiconductor structure, characterized in that, include: Provide a first material layer; A patterned photoresist layer is formed on the surface of the first material layer; The photoresist layer is pre-treated such that the top of the patterned sidewall of the photoresist layer is tilted inward towards the pattern, and there is a preset tilt angle between it and the surface of the first material layer. Using the pre-treated photoresist layer as a mask, the first material layer is etched along the preset tilt angle to form an etched pattern. The sidewall of the etched pattern has a target tilt angle of 45°. The difference between the target tilt angle and the preset tilt angle is less than a set value, which is in the range of 0 to 5°. The pretreatment includes: performing thermal reflow on the photoresist layer, wherein the heating temperature of the thermal reflow is 200℃~300℃ and the time is 3min~5min, so that the pattern of the photoresist layer has a raised arc-shaped surface; performing a second etching on the photoresist layer after thermal reflow, so that the sidewalls of the pattern of the photoresist layer are tilted and have the preset tilt angle, and the linewidth of the pattern of the photoresist layer after thermal reflow is greater than the linewidth of the pattern of the photoresist layer before thermal reflow, wherein the etching selectivity ratio of the first etching to the first material layer and the photoresist layer is greater than 100, the etching selectivity ratio of the second etching to the photoresist layer and the first material layer is greater than 100, and during the first etching process, the molar fraction of the etching gas that can generate polymer is less than 20%.

2. The method for forming a semiconductor structure according to claim 1, characterized in that, The target tilt angle is equal to the preset tilt angle.

3. The method for forming a semiconductor structure according to claim 1, characterized in that, The thickness of the photoresist layer is 1 micrometer to 2 micrometers.

4. The method for forming a semiconductor structure according to claim 1, characterized in that, The etching gas used in the second etching includes at least one of O2, Cl2, Ar, and He.

5. The method for forming a semiconductor structure according to claim 1, characterized in that, The first material layer includes a metal layer, an insulating dielectric layer, or a semiconductor layer.

6. The method for forming a semiconductor structure according to claim 1, characterized in that, Also includes: A second material layer is formed covering the sidewalls and top surface of the etched pattern.

7. A semiconductor structure, obtained by the method for forming a semiconductor structure according to any one of claims 1 to 6, characterized in that, include: Base; A first material layer is located on the surface of the substrate, and an etched pattern is formed in the first material layer. The sidewalls of the etched pattern are inclined inwards towards the etched pattern, and the included angle between the etched pattern and the substrate surface is within the range of 45°. A second material layer covers the sidewalls and top surface of the etched pattern.

8. The semiconductor structure according to claim 7, characterized in that, The material of the first material layer includes metal, insulating medium or semiconductor.

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