CN117894743A - Shallow trench isolation structure and preparation method thereof - Google Patents
Shallow trench isolation structure and preparation method thereof Download PDFInfo
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- CN117894743A CN117894743A CN202311860190.XA CN202311860190A CN117894743A CN 117894743 A CN117894743 A CN 117894743A CN 202311860190 A CN202311860190 A CN 202311860190A CN 117894743 A CN117894743 A CN 117894743A
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Abstract
The application provides a shallow trench isolation structure and a preparation method thereof, comprising the following steps: forming a hard mask layer which is positioned on the upper surface of the substrate and comprises a first film layer and a second film layer which are sequentially laminated; forming at least one first trench extending from the upper surface of the hard mask layer into the substrate; forming a liner layer positioned on the inner wall of the first groove, and carrying out first thinning treatment on the liner layer positioned at the second film layer, wherein the part of the first groove which is not filled with the liner layer is used as a second groove, and the bottom size of the second groove is smaller than the opening size of the second groove; performing second thinning treatment on the liner layer positioned at the first film layer to enlarge the opening size of the liner layer positioned at the first film layer; smoothing the liner layer on the inner wall of the first groove; a fill layer is formed within the second trench. The shallow trench isolation structure and the preparation method thereof realize void-free filling of the trench in the shallow trench isolation structure and ensure the performance of the shallow trench isolation structure.
Description
Technical Field
The application relates to the technical field of semiconductors, in particular to a shallow trench isolation structure and a preparation method thereof.
Background
The HARP (HIGH ASPECT ratio process) process is currently the main STI (shallow trench isolation ) structure filling means below 65 nm, however, although the conventional HARP process can enable MPW (multiple chip wafers) to obtain void-free filling (void-FREE GAP FILLED), as shown in fig. 1-2, which is an SEM image of multiple chip wafers and a first trench-filled SEM image of multiple chip wafers, including the first trench 03, respectively, but some ntus (single chip wafers) can obtain void filling (void GAP FILLED), as shown in fig. 3-4, which is an SEM image of single chip wafer and a first trench-filled image of single chip wafer, including the first trench 03, because the current HARP process can hardly mitigate the keyhole in U-shaped or reentrant trench morphology by adjusting the O 3/ratio or other parameters adopted in the process, and can form voids in some high AR ratio (8:1) STI deposition.
Furthermore, the filling capability of HARP processes is not only affected by the O 3/TEOS ratio in the deposition, but also by the STI profile. Generally, when the trench is V-shaped, the STI structure can easily obtain a good HARP filling effect, as shown in fig. 5, which is a cross-sectional view of the STI structure, including a substrate 01, a hard mask layer 02, a first film 021, a second film 022, a first trench 03, and a filling layer 04; as shown in fig. 6, another cross-sectional view of the STI structure includes a substrate 01, a hard mask layer 02, a first film 021, a second film 022, a first trench 03, and a filling layer 04, when the trench is U-shaped, the upper corners of the STI trench are blocked before the STI is filled with the HARP film, and a keyhole or a crack is formed inside the trench. There is no single easy way to overcome the filling problem when dealing with U-shaped or reentrant STI features, and it is difficult to mitigate keyhole in U-shaped or reentrant trench features by modifying the HARP process.
In view of the above, there is an urgent need for a method for fabricating a shallow trench isolation structure that can effectively solve the problem of void and keyhole formation during filling of the trench of the shallow trench isolation structure.
Disclosure of Invention
In view of the above-mentioned drawbacks of the prior art, an objective of the present application is to provide a shallow trench isolation structure and a method for manufacturing the same, which are used for solving the problem that voids and buttonholes are easily generated during the process of filling the trench of the shallow trench isolation structure in the prior art.
To achieve the above and other related objects, the present application provides a method for manufacturing a shallow trench isolation structure, comprising the steps of:
Forming a hard mask layer on the upper surface of the substrate, wherein the hard mask layer comprises a first film layer and a second film layer which are sequentially laminated;
forming a first trench extending from an upper surface of the hard mask layer into the substrate;
Forming a liner layer positioned on the inner wall of the first groove and the upper surface of the hard mask layer, and performing first thinning treatment on the liner layer positioned at the second film layer, wherein the part of the first groove which is not filled with the liner layer is used as a second groove, and the bottom size of the second groove is smaller than the opening size of the second groove;
performing second thinning treatment on the liner layer at the first film layer to enlarge the opening size of the liner layer at the first film layer;
smoothing the liner layer on the inner wall of the first groove by adopting a smoothing process;
And forming a filling layer in the second groove.
Optionally, the method of forming the liner layer includes high density plasma chemical vapor deposition.
Optionally, the thickness of the liner layer formed to cover the inner wall of the first trench is in a range of
Optionally, in the process of forming the liner layer, the range of the top radio frequency power of the adopted equipment is 5000-7000W, the range of the side radio frequency power is 5000-7000W, and the range of the bias radio frequency power is 2000-3000W; the reaction source gas used comprises O 2 and SiH 4,O2, the gas flow rate of SiH 4 at the top is in the range of 100-200 sccm, the gas flow rate of SiH 4 at the side is in the range of 10-30 sccm.
Optionally, the method of performing the second thinning treatment on the liner layer located at the first film layer includes wet etching.
Optionally, after the second thinning treatment is performed on the liner layer located at the first film layer, the thickness range of the liner layer is that
Optionally, the smoothing process includes a SiCoNi etching process.
Optionally, the method of forming the filling layer includes a high aspect ratio process.
Optionally, the time for forming the filling layer ranges from 60s to 120s, and the deposition rate of the filling layer ranges from 270A/min to 290A/min.
Optionally, the reaction gas used in the process of forming the filling layer includes TEOS, he, N 2O2O3, the gas flow rate of TEOS is 2500 sccm-3000 sccm, the gas flow rate of he is 1000 sccm-3000 sccm, the gas flow rate of n2 is 25000 sccm-35000 sccm, the gas flow rate of o 2 is 20000 sccm-30000 sccm, and the gas flow rate of o 3 is 25000 sccm-30000 sccm.
As described above, the shallow trench isolation structure and the preparation method thereof have the following beneficial effects: the liner layer is formed on the inner wall of the first groove, radio frequency power and gas flow adopted in the process of forming the liner layer are optimized, the liner layer with a thinner thickness is formed, meanwhile, the first thinning treatment can be carried out on the liner layer at the second film layer, the blocking of the opening of the second groove when the liner layer is formed is avoided, the bottom size of the second groove is smaller than the opening size of the second groove, good filling effect is easier to obtain, and the follow-up filling process is facilitated; the opening size of the second groove is enlarged by carrying out second thinning treatment on the liner layer positioned at the first film layer, so that the opening blockage of the second groove in the subsequent filling process is avoided; the smooth treatment is carried out on the lining layer, so that the subsequent filling process is more facilitated; namely, the liner layer is formed in the first groove, and the first thinning treatment, the second thinning treatment and the smoothing treatment are sequentially carried out on the liner layer, so that the formation process of the filling layer with high deposition rate is carried out, void-free filling of the first groove deep in the shallow groove isolation structure is realized, and the performance of the shallow groove isolation structure is ensured.
Drawings
Fig. 1 is an SEM image of a plurality of chip wafers according to the prior art.
Fig. 2 shows a first trench-filling SEM image of a plurality of chip wafers of the prior art.
Fig. 3 shows an SEM image of a single chip wafer of the prior art.
Fig. 4 shows a first trench-filling SEM image of a single chip wafer of the prior art.
Figure 5 illustrates a cross-sectional view of a prior art STI structure.
Fig. 6 shows another cross-sectional view of a prior art STI structure.
FIG. 7 is a cross-sectional view of an embodiment of the present application after forming a hard mask layer.
Fig. 8 is a cross-sectional view of an embodiment of the present application after forming a first trench.
Figure 9 illustrates a cross-sectional view of a liner layer formed in accordance with an embodiment of the present application.
Fig. 10 is a cross-sectional view of the pad layer according to the embodiment of the present application after the second thinning process.
Fig. 11 is a cross-sectional view of a liner layer according to an embodiment of the present application after being smoothed.
FIG. 12 is a cross-sectional view of a shallow trench isolation structure according to an embodiment of the application.
Fig. 13 is a TEM image of a shallow trench isolation structure according to an embodiment of the present application.
Description of element reference numerals
01. Substrate and method for manufacturing the same
02. Hard mask layer
021. First film layer
022. Second film layer
03. First groove
04. Filling layer
1. Substrate and method for manufacturing the same
2. Hard mask layer
21. First film layer
22. Second film layer
3. First groove
4. Liner layer
5. Second groove
6. Filling layer
Detailed Description
Further advantages and effects of the present application will become apparent to those skilled in the art from the disclosure of the present application, which is described by the following specific examples.
Please refer to fig. 1 to 13. It should be understood that the structures, proportions, sizes, etc. shown in the drawings are for illustration purposes only and should not be construed as limiting the application to the extent that it can be practiced, since modifications, changes in the proportions, or otherwise, used in the practice of the application, are not intended to be critical to the essential characteristics of the application, but are intended to fall within the spirit and scope of the application. Also, the terms such as "upper," "lower," "left," "right," "middle," and "a" and the like recited in the present specification are merely for descriptive purposes and are not intended to limit the scope of the application, but are intended to provide relative positional changes or modifications without materially altering the technical context in which the application may be practiced.
Example 1
Fig. 7 to 12 are sectional views showing stages of a method for manufacturing a shallow trench isolation structure according to the present application. The following describes a method for manufacturing a shallow trench isolation structure according to an embodiment of the present application with reference to fig. 7 to 13.
Fig. 7 is a cross-sectional view of the hard mask layer 2 after formation according to an embodiment of the present application. Referring to fig. 7, a hard mask layer 2 is formed on the upper surface of a substrate 1, and the hard mask layer 2 includes a first film layer 21 and a second film layer 22 sequentially stacked.
In one embodiment, the substrate 1 may be an N-type monocrystalline silicon substrate.
In this step, a first film layer 21 is formed on the upper surface of the substrate 1, and a second film layer 22 is formed on the surface of the first film layer 21.
In one embodiment, the first film layer 21 is formed on the upper surface of the substrate 1 by thermal oxidation or chemical vapor deposition. A second film layer 22 is formed on the upper surface of the first film layer 21 by chemical vapor deposition. Thermal Oxidation includes hydrothermal Oxidation of HTO or selective reactive Oxidation of SRO (SELECTIVE REACTIVE Oxidation), chemical Vapor Deposition (CVD) includes Low Pressure Chemical Vapor Deposition (LPCVD) or sub-atmospheric chemical vapor deposition (SACVD).
In one embodiment, the first film 21 is composed of an oxide, such as silicon oxide. The second film layer 22 is composed of nitride, for example, silicon nitride. The second film 22 serves as a stop layer for the subsequent chemical mechanical polishing, and the first film 21 serves as a buffer layer for the second film 22.
Fig. 8 shows a cross-sectional view of an embodiment of the present application after forming the first trench 3. Referring to fig. 8, a first trench 3 is formed extending from the upper surface of the hard mask layer 2 into the substrate 1.
In this step, for example, a photoresist layer is formed by a deposition process, a first trench position in the photoresist layer is formed by a photolithography process, and the first trench 3 position is transferred onto the hard mask layer 2 by an etching process; removing the photoresist layer; a first trench 3 is etched into the substrate 1 using the first trench location on the hard mask layer 2.
In this step, the first film layer 21 and the second film layer 22 in the hard mask layer 2 are made of different materials and have different etching selectivity, so that the etching surface of the hard mask layer 2 is stepped.
In one embodiment, the etching may be a dry etching, such as a plasma milling etching, a plasma etching, a reactive ion etching, a laser etching, or a wet etching. The photoresist layer may be a photoresist mask in one embodiment.
In one embodiment, the shape of the first groove 3 includes a U-shape, a V-shape, or other suitable shape. In the present embodiment, the first groove 3 is U-shaped in shape.
In one embodiment, the aspect ratio of the first trench 3 is 8:1.
Fig. 9 shows a cross-sectional view of an embodiment of the application after formation of the spacer layer 4. Referring to fig. 9, a liner layer 4 is formed on the inner wall of the first trench 3 and the upper surface of the hard mask layer 2, and a first thinning treatment is performed on the liner layer 4 at the second film layer 22, wherein a portion of the first trench 3 not filled with the liner layer 4 is used as a second trench 5, and the bottom dimension of the second trench 5 is smaller than the opening dimension of the second trench 5.
In one embodiment, the liner layer 4 is formed by a method including high density plasma chemical vapor deposition or other suitable method.
In the step, high-density plasma chemical vapor deposition is to prepare high-density plasma by adopting an Inductive Coupling (ICP) mode to deposit a film, and has the advantages of excellent pore-filling performance, reliable deposition quality and electrical property at a lower temperature, high yield and simple operation property.
In one embodiment, the range of rf power at the top of the device used in forming the liner layer 4 is 5000W to 7000W, the range of rf power at the side is 5000W to 7000W, and the range of rf power at the bias is 2000W to 3000W; the reaction source gas includes O 2 (oxygen) and SiH 4 (silane), the gas flow rate of O 2 is 100 sccm-200 sccm, the gas flow rate of SiH 4 at the top is 10 sccm-30 sccm, and the gas flow rate of SiH 4 at the side is 10 sccm-30 sccm.
In this step, parameters such as top/side/bias rf power and O 2 or top and side gas flow of SiH 4 of the equipment used in the process of forming the liner layer 4 may be adjusted for multiple chip wafers or single chips of different products, so as to achieve the optimal matching effect of each process parameter, and form the liner layer 4 with a thinner thickness in the first trench 3.
In one embodiment, the thickness of the liner layer 4 formed to cover the inner wall of the first trench 3 is in the range of
In this step, the first thinning process may be performed on the liner layer 4 located at the second film layer 22, for example, by increasing the bias rf power during formation of the liner layer 4.
In this step, the opening of the second trench 5 at the second film layer 22 is enlarged by performing the first thinning treatment on the liner layer 4 at the second film layer 22, so that the blocking of the opening of the second trench 5 during the formation of the liner layer 4 is avoided, and the subsequent filling process is facilitated.
In one embodiment, the liner layer 4 may be silicon dioxide or other suitable insulating dielectric material.
In this step, in the case of satisfying the performance of the shallow trench isolation structure, the size of the second trench 55 may be selected according to the actual situation, which is not limited herein.
In one embodiment, the shape of the second trench 5 comprises a V-like shape or other suitable shape.
In this step, the bottom dimension of the formed second trench 5 is smaller than the opening dimension of the second trench 5, i.e. the shape of the second trench 5 is V-like, so that a good filling effect is easier to obtain, and the subsequent filling process is facilitated.
In this step, the top/side/bias rf power and the gas flow of the top and side of O 2 or SiH 4 in the process of forming the liner layer 4 are optimized for each process parameter of the shallow isolation trench structure of a plurality of chip wafers or a single chip product with different aspect ratios, the thickness of the formed liner layer 4 is smaller, the rf power and the gas flow of the matched equipment are mild, damage to the substrate 1 is avoided, and the formed liner layer 4 has no hole; in addition, by properly increasing the bias radio frequency power of the equipment, the first thinning treatment can be performed on the liner layer 4 at the opening of the second groove 5, so that the opening of the second groove 5 is prevented from being blocked, and the subsequent filling process is facilitated.
Fig. 10 is a cross-sectional view of the spacer layer 4 according to the embodiment of the present application after the second thinning process, please refer to fig. 10, in which the spacer layer 4 located at the first film layer 21 is subjected to the second thinning process to enlarge the opening size of the spacer layer 4 located at the first film layer 21.
In one embodiment, the second thinning process of the liner layer 4 located at the first film layer 21 includes wet etching or other suitable method.
In one embodiment, hydrofluoric acid may be used as an etchant to perform a second thinning process on the liner layer 4 at the first film layer 21.
In the step, when the adopted etchant is hydrofluoric acid, the concentration range of the hydrofluoric acid is 45% -55%. In this example, the concentration of hydrofluoric acid was 49%.
In one embodiment, the processing time using the etchant ranges from 15s to 25s. In this embodiment, the processing time using the etchant is 20s.
In this step, after the second thinning treatment is performed on the spacer layer located at the first film layer 21, the spacer layer 4 is thinned in the thickness range of
In this step, the wet etching is adopted to perform the second thinning treatment on the first film layer 21, including the first film layer 21 and the partial liner layer 4 located below the first film layer 21, so that the subsequent filling process is facilitated, and the occurrence of voids in the filling process can be avoided.
Fig. 11 is a cross-sectional view of the liner layer 4 according to the embodiment of the present application after smoothing, and please refer to fig. 11, in which the liner layer 4 on the inner wall of the first trench 13 is smoothed by a smoothing process.
In one embodiment, the smoothing process includes a SiCoNi etching process or other suitable process.
In one embodiment, the liner layer 4 may be smoothed using hydrogen, nitrogen trifluoride, and ammonia as reactive gases in the smoothing process.
In this step, when the performance of the shallow trench isolation structure is satisfied, the reaction temperature, reaction time, chamber pressure, and rf power used for smoothing the liner layer 4 may be selected according to the actual situation, and are not limited herein.
In one embodiment, the smoothing process of the cushion layer 4 further includes an annealing step to decompose the solid residue generated during the smoothing process of the cushion layer 4 into a gaseous residue.
In this step, the annealing temperature and the annealing time used in the case of satisfying the performance of the shallow trench isolation structure may be selected according to the actual situation, and are not limited herein.
In this step, the etched liner layer 4 is smoothed, so that the morphology of the liner layer 4 on the inner wall of the second trench 5 can be modified, which is more favorable for the subsequent filling process.
Fig. 12 is a cross-sectional view of a shallow trench isolation structure according to an embodiment of the application, please refer to fig. 12, in which a filling layer 6 is formed in a second trench 21.
In one embodiment, the method of forming the fill layer 6 includes a high aspect ratio process or other suitable method.
In one embodiment, the time for forming the filling layer 6 is in the range of 60s to 120s, and the deposition rate of the filling layer 6 is in the range of 270A/min to 290A/min. In this example, the deposition rate was 280A/min.
In one embodiment, the reaction gas used in the process of forming the filling layer 6 includes TEOS, he (helium), N 2 (nitrogen) and O 2O3, wherein the gas flow rate of TEOS is 2500 sccm-3000 sccm, the gas flow rate of He is 1000 sccm-3000 sccm, the gas flow rate of N 2 is 25000 sccm-35000 sccm, the gas flow rate of O 2 is 20000 sccm-30000 sccm, and the gas flow rate of O 3 is 25000 sccm-30000 sccm.
In one embodiment, the filling layer 6 may be silicon dioxide or other suitable insulating dielectric material.
1 fig. 13 is a TEM image of a shallow trench isolation structure according to an embodiment of the present application, please refer to fig. 13, in which a spacer layer 4 is formed in a first trench 3, and a first thinning process, a second thinning process and a smoothing process are sequentially performed on the spacer layer 4, so that a filling process with a high deposition rate is performed, void-free filling of a deep first trench 3 in the shallow trench isolation structure is realized, performance of the shallow trench isolation structure is ensured, and the flow rate of TEOS, he, N 2O2O3 in the process of forming a filling layer 6 is adjusted according to different products so as to achieve an optimal void-free filling effect.
Example two
The embodiment provides a shallow trench isolation structure, which is prepared by adopting the preparation method of the shallow trench isolation structure in the first embodiment.
In one embodiment, the shallow trench isolation structure includes a semiconductor layer 1, a hard mask layer 21, a first trench 3, a liner layer 4, a second trench 5 and a filling layer 6, wherein the hard mask layer 2 is located on the upper surface of the substrate 1, and the hard mask layer 2 includes a first film layer 21 and a second film layer 22 sequentially stacked; the first trench 3 extends from the upper surface of the hard mask layer 2 into the substrate 1; a liner layer 4 located on the inner wall of the first trench 13; the portion of the first trench 3 not filled with the liner layer 4 serves as a second trench 5, the bottom dimension of the second trench 5 being smaller than the opening dimension of the second trench 5; and the filling layer 3 is positioned in the second groove 5.
In one embodiment, the liner layer 4 in the first trench 3 and the filling layer 6 in the second trench 5 well fill the first trench 3 and fill without voids.
The shallow trench isolation structure is prepared by adopting the preparation method of the shallow trench isolation structure in the first embodiment, and the filling of the first trench 3 in the obtained shallow trench isolation structure has no gap, so that the performance of the shallow trench isolation structure is ensured.
In summary, according to the shallow trench isolation structure and the preparation method thereof, the liner layer is formed on the inner wall of the first trench, the radio frequency power and the gas flow adopted in the process of forming the liner layer are optimized, the liner layer with a thinner thickness is formed, meanwhile, the first thinning treatment can be carried out on the liner layer at the second film layer, the blocking of the opening of the second trench in the process of forming the liner layer is avoided, the bottom size of the obtained second trench is smaller than the opening size of the second trench, a good filling effect is easier to obtain, and the follow-up filling process is facilitated; the opening size of the second groove is enlarged by carrying out second thinning treatment on the liner layer positioned at the first film layer, so that the opening blockage of the second groove in the subsequent filling process is avoided; the smooth treatment of the liner layer is more beneficial to the subsequent filling process; namely, the liner layer is formed in the first groove, and the first thinning treatment, the second thinning treatment and the smoothing treatment are sequentially carried out on the liner layer, so that the formation process of the filling layer with high deposition rate is carried out, the void-free filling of the deep first groove in the shallow groove isolation structure is realized, and the performance of the shallow groove isolation structure is ensured. Therefore, the application effectively overcomes various defects in the prior art and has high industrial utilization value.
The above embodiments are merely illustrative of the principles of the present application and its effectiveness, and are not intended to limit the application. Modifications and variations may be made to the above-described embodiments by those skilled in the art without departing from the spirit and scope of the application. Accordingly, it is intended that all equivalent modifications and variations of the application be covered by the claims, which are within the ordinary skill of the art, be within the spirit and scope of the present disclosure.
Claims (10)
1. The preparation method of the shallow trench isolation structure is characterized by comprising the following steps of:
Forming a hard mask layer on the upper surface of the substrate, wherein the hard mask layer comprises a first film layer and a second film layer which are sequentially laminated;
forming a first trench extending from an upper surface of the hard mask layer into the substrate;
Forming a liner layer positioned on the inner wall of the first groove and the upper surface of the hard mask layer, and performing first thinning treatment on the liner layer positioned at the second film layer, wherein the part of the first groove which is not filled with the liner layer is used as a second groove, and the bottom size of the second groove is smaller than the opening size of the second groove;
performing second thinning treatment on the liner layer at the first film layer to enlarge the opening size of the liner layer at the first film layer;
smoothing the liner layer on the inner wall of the first groove by adopting a smoothing process;
And forming a filling layer in the second groove.
2. The method for manufacturing a shallow trench isolation structure according to claim 1, wherein: methods of forming the liner layer include high density plasma chemical vapor deposition.
3. The method for manufacturing a shallow trench isolation structure according to claim 1, wherein: the thickness of the liner layer covering the inner wall of the first groove ranges from
4. The method for manufacturing a shallow trench isolation structure according to claim 1, wherein: in the process of forming the lining layer, the range of the radio frequency power at the top end of the adopted equipment is 5000-7000W, the range of the radio frequency power at the side surface is 5000-7000W, and the range of the bias radio frequency power is 2000-3000W; the reaction source gas used comprises O 2 and SiH 4,O2, the gas flow rate of SiH 4 at the top is in the range of 100-200 sccm, the gas flow rate of SiH 4 at the side is in the range of 10-30 sccm.
5. The method for manufacturing a shallow trench isolation structure according to claim 1, wherein: a method of performing a second thinning process on the liner layer at the first film layer includes wet etching.
6. The method for manufacturing a shallow trench isolation structure according to claim 1, wherein: after the second thinning treatment is carried out on the liner layer positioned at the first film layer, the thickness range of the liner layer thinning is that
7. The method for manufacturing a shallow trench isolation structure according to claim 1, wherein: the smoothing process includes a sicomini etching process.
8. The method for manufacturing a shallow trench isolation structure according to claim 1, wherein: the method of forming the fill layer includes a high aspect ratio process.
9. The method for manufacturing a shallow trench isolation structure according to claim 1, wherein: the time for forming the filling layer ranges from 60s to 120s, and the deposition rate of the filling layer ranges from 270A/min to 290A/min.
10. The method for manufacturing a shallow trench isolation structure according to claim 1, wherein: the reaction gas used in the process of forming the filling layer comprises TEOS, he, N 2O2O3, the gas flow rate of TEOS is 2500-3000 sccm, the gas flow rate of He is 1000-3000 sccm, the gas flow rate of N 2 is 25000-35000 sccm, the gas flow rate of O 2 is 20000-30000 sccm, and the gas flow rate of O 3 is 25000-30000 sccm.
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| CN202311860190.XA CN117894743A (en) | 2023-12-29 | 2023-12-29 | Shallow trench isolation structure and preparation method thereof |
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