A method of forming shallow trench isolation
By adjusting the selectivity ratio of nitrides to oxides during the etching process and using multi-stage etching to remove the nitride mask, the problem of surface depression in shallow trench isolation structures was solved, thus improving the performance of semiconductor devices.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- INST OF MICROELECTRONICS CHINESE ACAD OF SCI LTD
- Filing Date
- 2020-09-21
- Publication Date
- 2026-06-02
AI Technical Summary
In the existing technology, during the cleaning of nitrides, the surface of the shallow trench isolation structure is prone to depressions, which affects the performance of semiconductor devices.
The nitride mask is removed by an etching process of at least two stages. By adjusting the etching temperature and/or the etching solution concentration, the selectivity ratio between nitride and oxide is increased during the etching process to control the depression on the surface of the trench isolation structure.
It effectively improves the surface depression problem of trench isolation structure and enhances the performance of semiconductor devices.
Smart Images
Figure CN114256130B_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of semiconductor technology, and more particularly to a method for forming shallow trench isolation. Background Technology
[0002] In semiconductor technology, shallow trench isolation structures are crucial functional structures in semiconductor devices, enabling the isolation of active regions between them. Current techniques typically involve etching a nitride mask onto a semiconductor substrate to create trenches, filling these trenches with an insulating material, and then cleaning away the nitride. However, this nitride removal process also etches the surface material of the shallow trench isolation structure, resulting in surface depressions that negatively impact semiconductor device performance. Figure 1 The diagram shown is a schematic of a shallow trench isolation structure with surface depressions in the prior art. Summary of the Invention
[0003] This application provides a method for forming shallow trench isolation, which solves the problem of surface depressions that occur during the formation of trench isolation structures in the prior art, improves the surface depressions of trench isolation structures, and ensures the performance of semiconductor devices.
[0004] This specification provides an embodiment of a method for forming shallow trench isolation, the method comprising:
[0005] Provide semiconductor substrates;
[0006] Oxides and nitrides are formed on the semiconductor substrate;
[0007] The nitride is patterned to form a nitride mask, exposing the target area where the trenches are to be formed;
[0008] The target region is etched into the semiconductor substrate to form the trench;
[0009] Fill the trench;
[0010] The nitride mask is removed by etching in at least two stages, wherein the selectivity ratio between the nitride and the oxide increases during the etching process.
[0011] Optionally, the nitride mask etched in at least two stages includes:
[0012] For each of the at least two stages, the nitride mask is removed using the etching parameters corresponding to that stage, wherein the etching parameters are etching temperature and / or etching concentration.
[0013] Optionally, the etching temperature ranges from 140°C to 168°C.
[0014] Optionally, the concentration of the etching solution ranges from 70 wt% to 95 wt%.
[0015] Optionally, removing the nitride mask using the etching parameters corresponding to each of the at least two stages includes:
[0016] For each of the at least two stages, the nitride mask is removed using the etching temperature corresponding to that stage, wherein the etching temperature of the previous stage is higher than the etching temperature of the next stage in the at least two stages.
[0017] Optionally, removing the nitride mask using the etching parameters corresponding to each of the at least two stages includes:
[0018] For each of the at least two stages, the nitride mask is removed using the etching concentration corresponding to that stage, wherein the etching concentration of the previous stage is higher than that of the next stage in the at least two stages.
[0019] Optionally, removing the nitride mask using the etching parameters corresponding to each of the at least two stages includes:
[0020] For each of the at least two stages, the nitride mask is removed using the etching concentration and etching temperature corresponding to that stage, wherein in the at least two stages, the etching temperature of the previous stage is higher than the etching temperature of the next stage, and the etching solution concentration of the previous stage is higher than the etching solution concentration of the next stage.
[0021] Optionally, the at least two stages include a first stage, a second stage, and a third stage, wherein the etching temperature range of the first stage is 162℃ to 168℃, the difference between the etching temperature of the first stage and the etching temperature of the second stage is 0.3℃ to 3℃, and the difference between the etching temperature of the second stage and the etching temperature of the third stage is 0.2℃ to 3.5℃.
[0022] Optionally, the at least two stages include a first stage, a second stage, and a third stage, wherein the etching concentration of the first stage ranges from 88wt% to 95wt%, the difference between the etching concentration of the first stage and the etching concentration of the second stage ranges from 0.2wt% to 1wt%, and the difference between the etching concentration of the second stage and the etching concentration of the third stage ranges from 0.2wt% to 1.5wt%.
[0023] Optionally, the step of patterning the nitride to form a nitride mask includes: forming a photoresist image on the nitride, and forming the nitride mask according to the photoresist pattern;
[0024] The filling of the trench includes filling the trench with an oxide or a nitride.
[0025] One or more technical solutions provided in the embodiments of this specification have at least the following technical effects or advantages:
[0026] In the embodiments of this specification, during the formation of the trench isolation structure, oxides and nitrides are formed on a semiconductor substrate; the nitrides are patterned to form a nitride mask, exposing the target area where the trench is to be formed; the target area is etched down to the semiconductor substrate to form the trench; the trench is filled; and the nitride mask is removed by etching in at least two stages, during which the selectivity ratio between nitrides and oxides increases. In the above embodiment, because the selectivity ratio between nitrides and oxides changes during the nitride etching process, the degree of depression on the trench isolation surface is effectively controlled. Attached Figure Description
[0027] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.
[0028] Figure 1 This is a schematic diagram of a shallow trench isolation structure with surface depressions in the prior art.
[0029] Figure 2-5 This is a cross-sectional schematic diagram of a shallow trench isolation provided in an embodiment of this specification;
[0030] Figure 6 This is a temperature variation curve during the silicon nitride etching process as presented in the embodiments of this specification;
[0031] Figure 7 This is a schematic diagram illustrating the change in the selectivity ratio between silicon nitride and silicon oxide as a function of etching temperature, as shown in the embodiments of this specification.
[0032] Figure 8 This is a schematic diagram illustrating the change in the selectivity ratio between silicon nitride and silicon oxide as a function of the etching solution concentration, as shown in the embodiments of this specification. Detailed Implementation
[0033] Embodiments of the present disclosure will now be described with reference to the accompanying drawings. However, it should be understood that these descriptions are exemplary only and are not intended to limit the scope of the disclosure. Furthermore, descriptions of well-known structures and technologies are omitted in the following description to avoid unnecessarily obscuring the concepts of the present disclosure.
[0034] In the context of this disclosure, when a layer / element is referred to as being "above" another layer / element, the layer / element may be directly above the other layer / element, or there may be an intermediate layer / element between them. Additionally, if a layer / element is "above" another layer / element in one orientation, then when the orientation is reversed, the layer / element may be "below" the other layer / element.
[0035] Example 1
[0036] This specification provides an embodiment of a method for forming shallow trench isolation, such as... Figure 2-5 The diagram shown is a cross-sectional view of a method for forming shallow trench isolation according to an embodiment of this specification. The method includes the following steps:
[0037] Provide semiconductor substrates;
[0038] Oxides and nitrides are formed on the semiconductor substrate;
[0039] The nitride is patterned to form a nitride mask, exposing the target area where the trenches are to be formed;
[0040] The target region is etched into the semiconductor substrate to form the trench;
[0041] Fill the trench;
[0042] The nitride mask is removed by etching in at least two stages, wherein the selectivity ratio between the nitride and the oxide increases during the etching process.
[0043] Please refer to Figure 2 , Figure 2 A semiconductor substrate is provided, on which an oxide, such as silicon oxide, is formed. A nitride layer, such as silicon nitride, is then deposited on the oxide surface. Further, the nitride is patterned to form a nitride mask; specifically, photoresist is coated on the nitride to form a photoresist pattern (not shown), and after exposure and development, the target area where trenches are to be formed is exposed.
[0044] Please refer to Figure 3 The target area is etched to remove nitrides, oxides, and part of the semiconductor substrate, forming trenches.
[0045] Please refer to Figure 4The trench is filled, for example, by filling the trench with silicon oxide, ensuring that the filler completely fills the trench. Specifically, during the filling process, the filler material can cover the nitride surface, and then the filler material is polished to expose the nitride.
[0046] Please refer to Figure 5 The nitride mask is removed by etching, specifically using an etching solution such as phosphoric acid solution. In the embodiments of this specification, the nitride etching is performed in at least two stages. By adjusting the selectivity ratio between nitride and oxide in each stage, the selectivity ratio between nitride and oxide is ensured to increase throughout the nitride etching process. By adjusting the selectivity ratio, depressions can be effectively avoided in the final shallow trench isolation structure.
[0047] In the embodiments of this specification, when etching nitride using at least two stages, N stages (N being an integer greater than 1) for etching silicon nitride can be determined, along with the duration of each stage. For example, the total etching time for silicon nitride can be divided into N equal parts, ensuring that each stage has the same duration. In the embodiments of this specification, the N stages can be determined by: determining the total time required to etch the nitride; and determining the duration of each of the N stages based on a preset ratio between the duration of each stage and the total time.
[0048] Specifically, the preset ratio between the duration of each stage and the total duration can be pre-defined. For example, N is 3, meaning the entire silicon nitride etching process is divided into 3 stages, and the ratio between the duration of each stage and the total duration is pre-defined. For example, the duration of the first stage accounts for 30% of the total duration, the duration of the second stage accounts for 30% of the total duration, and the duration of the third stage accounts for 40% of the total duration. The percentage of the duration of each stage is stored so that the duration of each stage can be directly obtained later, and the duration of each of the N stages can be determined based on the total time consumed by the silicon nitride etching.
[0049] In the embodiments of this specification, for each of the at least two stages, the nitride mask is removed using the etching parameters corresponding to that stage. The etching parameters are etching temperature and / or etching concentration. Of course, the etching parameters can also be other parameters that affect the selectivity ratio between nitride and oxide, which are not limited here. By adjusting the etching parameters of different stages, the selectivity ratio between nitride and oxide can be adjusted, thereby controlling the surface depression of the trench isolation structure.
[0050] In the embodiments of this specification, the etching parameters are etching temperature and / or etching solution concentration as examples. That is, the selection of etching parameters includes three cases: the etching parameter is only the etching temperature; the etching parameter is only the etching solution concentration; and the etching parameters include both etching temperature and etching solution concentration.
[0051] For these three scenarios, the etching of nitrides under each scenario will be explained below:
[0052] The first scenario: The etching parameter is the etching solution temperature. For each of the at least two stages, the nitride mask is removed using the etching temperature corresponding to that stage. In the at least two stages, the etching temperature of the previous stage is higher than the etching temperature of the next stage.
[0053] Specifically, the number of etching stages for nitrides can be set according to actual needs. Taking three stages as an example and silicon nitride as the nitride, the silicon nitride etching process is divided into three stages in chronological order: the first stage precedes the second stage, and the second stage precedes the third stage. As the silicon nitride etching time progresses, the etching temperature of each stage gradually decreases; that is, the etching temperature of the first stage is higher than that of the second stage, and the etching temperature of the second stage is higher than that of the third stage. Figure 6 The figure shows the etching temperature variation curve during the silicon nitride etching process. The etching temperature for each stage ranges from 140℃ to 168℃. In one embodiment, the etching temperature range for the first stage is 162℃ to 168℃, the difference between the etching temperature of the first stage and the second stage is 0.3℃ to 3℃, and the difference between the etching temperature of the second stage and the third stage is 0.2℃ to 3.5℃. For example, the etching temperature for the first stage is 163.5℃, the etching temperature for the second stage is 161℃, and the etching temperature for the third stage is 158℃. Because of the differences in etching temperatures between stages, when adjusting from the etching temperature of the previous stage to the etching temperature of the next stage, the etching temperature can be switched directly from the previous stage to the next stage, or the etching temperature of the previous stage can be gradually transitioned to the next stage.
[0054] The second scenario: The etching parameter is the etching solution concentration. For each of the at least two stages, the nitride mask is removed using the etching concentration corresponding to that stage. In the at least two stages, the etching concentration of the previous stage is higher than that of the next stage.
[0055] Continuing with the example of three stages, when the etching parameter is the etching solution concentration, the etching solution concentration gradually decreases in each stage as the silicon nitride etching time progresses. Specifically, the etching solution concentration in the first stage is greater than that in the second stage, and the concentration in the second stage is greater than that in the third stage. The corresponding value range for the etching solution concentration in each stage is 70wt% to 95wt%. In one embodiment, the etching concentration range for the first stage is 88wt% to 95wt%, the difference between the etching concentrations of the first and second stages is 0.2wt% to 1wt%, and the difference between the etching concentrations of the second and third stages is 0.2wt% to 1.5wt%. For example, the etching solution concentration for the first stage is 89.2wt%, the concentration for the second stage is 88.7wt%, and the concentration for the third stage is 88.2wt%. Since there are differences in the etching solution concentration between each stage, when adjusting the etching solution concentration from the previous stage to the next stage, the etching solution concentration from the previous stage can be gradually transitioned to the etching solution concentration from the next stage.
[0056] The third scenario: The etching parameters are etching temperature and etching solution concentration. For each of the at least two stages, the nitride mask is removed using the etching concentration and etching temperature corresponding to that stage. In the at least two stages, the etching temperature of the previous stage is higher than that of the next stage, and the etching solution concentration of the previous stage is higher than that of the next stage.
[0057] Using the example of three stages mentioned above, when the etching parameters are etching temperature and etching solution concentration, as the silicon nitride etching time progresses, the etching temperature of each stage gradually decreases. That is, the etching temperature of the first stage is higher than that of the second stage, and the etching temperature of the second stage is higher than that of the third stage. Furthermore, as the silicon nitride etching time progresses, the etching solution concentration of each stage gradually decreases. That is, the etching solution concentration of the first stage is greater than that of the second stage, and the etching solution concentration of the second stage is greater than that of the third stage.
[0058] The etching temperature for each stage ranges from 140°C to 168°C, and the etching solution concentration for each stage ranges from 70wt% to 95wt%. In one embodiment, the etching temperature for the first stage is 164.5°C, the etching temperature for the second stage is 163.7°C, and the etching temperature for the third stage is 163.2°C; and the etching solution concentration for the first stage is 89.2wt%, the etching solution concentration for the second stage is 88.7wt%, and the etching solution concentration for the third stage is 88.2wt%.
[0059] When adjusting the etching temperature from the previous stage to the next stage, you can directly switch from the previous stage to the next stage, or you can gradually transition from the previous stage to the next stage. When adjusting the etching solution concentration from the previous stage to the next stage, you can gradually transition from the previous stage to the next stage.
[0060] In this embodiment of the specification, for any two adjacent stages in at least two stages, after the previous stage ends, the etching parameters corresponding to the previous stage are used as the starting etching parameters of the next stage; during the etching of the nitride in the next stage, the starting etching parameters are adjusted to the target etching parameters corresponding to the next stage at a preset rate, and the target etching parameters are kept unchanged until the next stage ends.
[0061] Specifically, when the etching parameter is the etching temperature, if the etching temperature of the previous stage differs from that of the next stage, the etching temperature is adjusted according to a preset rate. This preset rate can be set according to actual needs, such as 0.1℃ / min to 1℃ / min. For example, using the example of three stages, the etching temperature of the first stage is 163.5℃, the second stage is 161℃, and the third stage is 158℃. When the first stage ends and the second stage begins, the etching temperature is gradually reduced from 163.5℃ to 161℃ according to the preset rate and maintained at 161℃ until the second stage ends. When the second stage ends and the third stage begins, the etching temperature is gradually reduced from 161℃ to 158℃ according to the preset rate. In the embodiments of this specification, the etching of the nitride is completed during the above-mentioned etching temperature adjustment process.
[0062] When the etching parameter is the etching solution concentration, if the etching solution concentration of the previous stage differs from that of the next stage, the etching solution concentration is adjusted according to a preset rate. This preset rate can be set according to actual needs, such as 0.1 wt% / min to 1 wt% / min. For example, using the example of three stages, the etching solution concentration in the first stage is 89.2 wt%, in the second stage it is 88.7 wt%, and in the third stage it is 88.2 wt%. When the first stage ends and the second stage begins, the etching solution concentration is gradually reduced from 89.2 wt% to 88.7 wt% at the preset rate and maintained at 88.7 wt% until the second stage ends. When the second stage ends and the third stage begins, the etching solution concentration is gradually reduced from 88.7 wt% to 88.2 wt% at the preset rate. In the embodiments of this specification, the etching of nitrides is completed during the above-mentioned etching solution concentration adjustment process.
[0063] When the etching parameters are etching temperature and etching solution concentration, they are adjusted according to the preset rate of etching temperature and the preset rate of etching solution concentration, respectively. The specific implementation method is the same as the above-mentioned method of adjusting etching temperature and adjusting etching solution concentration, so it will not be repeated here.
[0064] In the embodiments of this specification, the selectivity ratio between nitride and oxide varies with etching temperature and / or etching solution concentration. For example, using silicon nitride as the nitride, silicon oxide as the oxide, and phosphoric acid solution as the etching solution... Figure 7 The figure shows a schematic diagram of the selectivity ratio between silicon nitride and silicon oxide as a function of etching temperature. Figure 8 This is a schematic diagram showing the selectivity ratio between silicon nitride and silicon oxide as a function of etching solution concentration. The scheme in the embodiments of this specification, by adjusting the etching parameters, allows the selectivity ratio to gradually increase over time, avoiding the fixed selectivity ratio found in existing technologies. Adjusting the selectivity ratio improves the surface depression of the trench isolation structure, thereby enhancing the performance of the semiconductor device.
[0065] The above description does not provide detailed explanations of the technical aspects of each layer's patterning, etching, etc. However, those skilled in the art should understand that various technical means can be used to form layers and regions of the desired shape. Furthermore, to form the same structure, those skilled in the art can also design methods that are not entirely identical to those described above. Additionally, although various embodiments have been described above, this does not mean that the measures in the various embodiments cannot be used advantageously in combination.
[0066] Although preferred embodiments of the invention have been described, those skilled in the art, upon learning the basic inventive concept, can make other changes and modifications to these embodiments. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments as well as all changes and modifications falling within the scope of the invention.
[0067] Obviously, those skilled in the art can make various modifications and variations to this invention without departing from its spirit and scope. Therefore, if these modifications and variations fall within the scope of the claims of this invention and their equivalents, this invention also intends to include these modifications and variations.
Claims
1. A method of forming shallow trench isolation, characterized by, The method includes: Provide semiconductor substrates; Oxides and nitrides are formed on the semiconductor substrate; The nitride is patterned to form a nitride mask, exposing the target area where the trenches are to be formed; The target region is etched into the semiconductor substrate to form the trench; Fill the trench; The nitride mask is removed by etching in at least two stages, wherein the selectivity ratio between the nitride and the oxide increases during the etching process; The process of removing the nitride mask using at least two stages of etching includes: For each of the at least two stages, the nitride mask is removed using the etching parameters corresponding to that stage; wherein, the etching parameters are parameters that affect the selectivity ratio between the nitride and the oxide, and by adjusting the etching parameters of different stages, the selectivity ratio between the nitride and the oxide increases during the etching process.
2. The method according to claim 1, characterized in that, The etching parameters are etching temperature and / or etching concentration.
3. The method according to claim 2, characterized in that, The etching temperature range is 140℃~168℃.
4. The method according to claim 2, characterized in that, The etching concentration ranges from 70wt% to 95wt%.
5. The method according to claim 2, characterized in that, The step of removing the nitride mask using the etching parameters corresponding to each of the at least two stages includes: For each of the at least two stages, the nitride mask is removed using the etching temperature corresponding to that stage, wherein the etching temperature of the previous stage is higher than the etching temperature of the next stage in the at least two stages.
6. The method according to claim 2, characterized in that, The step of removing the nitride mask using the etching parameters corresponding to each of the at least two stages includes: For each of the at least two stages, the nitride mask is removed using the etching concentration corresponding to that stage, wherein the etching concentration of the previous stage is higher than that of the next stage in the at least two stages.
7. The method according to claim 2, characterized in that, The step of removing the nitride mask using the etching parameters corresponding to each of the at least two stages includes: For each of the at least two stages, the nitride mask is removed using the etching concentration and etching temperature corresponding to that stage, wherein in the at least two stages, the etching temperature of the previous stage is higher than the etching temperature of the next stage, and the etching concentration of the previous stage is higher than the etching concentration of the next stage.
8. The method according to claim 5, characterized in that, The at least two stages include a first stage, a second stage, and a third stage. The etching temperature range of the first stage is 162℃~168℃. The difference between the etching temperature of the first stage and the etching temperature of the second stage is 0.3℃~3℃. The difference between the etching temperature of the second stage and the etching temperature of the third stage is 0.2℃~3.5℃.
9. The method according to claim 6, characterized in that, The at least two stages include a first stage, a second stage, and a third stage. The etching concentration of the first stage ranges from 88 wt% to 95 wt%. The difference between the etching concentration of the first stage and the etching concentration of the second stage ranges from 0.2 wt% to 1 wt%. The difference between the etching concentration of the second stage and the etching concentration of the third stage ranges from 0.2 wt% to 1.5 wt%.
10. The method according to any one of claims 1 to 9, characterized in that, The step of patterning the nitride to form a nitride mask includes: forming a photoresist pattern on the nitride, and forming the nitride mask according to the photoresist pattern; The filling of the trench includes filling the trench with an oxide or a nitride.