Etching method of hard mask of back metal grid
Through a two-step etching method, the problems of poor uniformity of grid-type groove morphology and sidewall thickness during silicon oxide hard mask etching were solved, and the uniformity of key dimensions of the metal grid and improvement of pattern transfer were achieved.
Patent Information
- Application Number
- CN202510058412.9
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- Filing Date
- 2025-01-14
- Publication Date
- 2025-09-26
- Estimated Expiration
- 2045-01-14
AI Technical Summary
In BSI products, during the etching process of the silicon oxide hard mask, the morphology and sidewall thickness uniformity of the grid-type trench are poor, resulting in poor uniformity of the critical dimensions of the metal grid, affecting the transfer of the metal grid pattern.
A two-step etching method is adopted, firstly, the first hard mask layer is mainly etched in a carbon-rich environment, and then an auxiliary etching is performed in a fluorine-rich environment to trim the lateral dimensions of the grid-type trench and ensure the etching selectivity and by-product removal.
The morphology and sidewall thickness uniformity of the grid-type trench are improved, the key dimension uniformity of the metal grid is improved, and the influence of the metal hard mask side digging and pattern transfer is avoided.
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Figure CN119947287B_ABST
Abstract
Description
Technical Field
[0001] The present application relates to the field of semiconductor manufacturing technology, and in particular to a method for etching a hard mask of a back metal grid. Background Art
[0002] In BSI (Back Illuminated Image Sensor) products, the metal grid is formed through a two-step etching process. First, a silicon oxide hard mask and a metal hard mask (such as TiN) are formed on the metal material layer. Then, the grid pattern is transferred to the metal hard mask through photolithography and etching processes. The silicon oxide hard mask is then etched through the patterned metal hard mask. Finally, the metal material layer is etched using the patterned metal hard mask as a mask layer to obtain the metal grid. Therefore, there are two requirements for the silicon oxide hard mask used as an intermediate transfer:
[0003] 1) The grid-type trench profile / sidewall in the silicon oxide hard mask (film layer) is required to be straight (the grid-type trench profile / sidewall is vertical from top to bottom) with good uniformity;
[0004] 2) It is required that after etching the silicon oxide hard mask, it can stop on the surface of the metal material layer.
[0005] During the actual etching process of the silicon oxide hard mask, to ensure a high selectivity between the silicon oxide hard mask and the metal hard mask, as well as straight grid-shaped trench profiles and sidewalls, the silicon oxide hard mask is etched using C4F8 gas with a high carbon-to-fluorine ratio in a high plasma concentration environment. In the dense metal grid structure of BSI products, under medium and high frequency conditions, the silicon oxide hard mask rapidly reacts in the center of the wafer, forming reaction byproducts (polymer) that quickly deposit on the sidewalls of the grid-shaped trenches, resulting in poor uniformity in the grid-shaped trench morphology and sidewall thickness. The grid-shaped trench morphology and accumulated reaction byproducts manifest as severe roughness and poor uniformity in the measured image. This, in turn, leads to poor uniformity in the critical dimension (CD) of the metal grid formed by further etching the metal material layer, affecting optical parameters. However, if a low-frequency environment is used during the etching process, the TiN (metal hard mask) / OX (silicon oxide hard mask) selectivity ratio will be reduced, and the etching rate of the metal hard mask will be faster than that of the silicon oxide hard mask, resulting in side digging of the top metal hard mask, affecting the transmission of the metal grid pattern (grid pattern). Summary of the Invention
[0006] The present application provides a method for etching a hard mask of a back metal grid, which can solve at least one of the following problems: the side walls of the grid-type grooves in the hard mask lead to poor uniformity in the morphology and thickness of the grid-type grooves, which in turn leads to poor uniformity in the key dimensions of the metal grid, and the metal hard mask forms side hollows that affect the transfer of the metal grid pattern.
[0007] An embodiment of the present application provides a method for etching a hard mask of a back metal grid, comprising:
[0008] Providing a substrate, wherein a gate oxide layer, a metal material layer, a first hard mask layer, and a second hard mask layer are sequentially formed on the back side of the substrate;
[0009] coating a photoresist layer on the second hard mask layer;
[0010] defining a metal grid pattern on the photoresist layer to obtain a patterned photoresist layer;
[0011] Using the patterned photoresist layer as a mask, etching the second hard mask layer to the surface of the first hard mask layer;
[0012] removing the patterned photoresist layer;
[0013] Using the patterned second hard mask layer as a mask, in a carbon-rich environment, performing a main etching on the first hard mask layer and stopping at the surface of the metal material layer to form a grid-type trench in the first hard mask layer, wherein the lateral dimensions of the grid-type trench gradually decrease from the top to the bottom of the grid-type trench;
[0014] In a fluorine-rich environment, the first hard mask layer is auxiliary-etched to trim the lateral dimensions of the grid-type groove near the bottom end so that the lateral dimensions of the grid-type groove from the top end to the bottom end are equal, wherein the chamber pressure of the auxiliary etching is less than the chamber pressure of the main etching, the frequency of the bias RF power supply of the auxiliary etching is greater than the frequency of the bias RF power supply of the main etching, and the RF power of the auxiliary etching is less than the RF power of the main etching.
[0015] Optionally, in the method for etching the hard mask of the back metal grid, the material of the first hard mask layer is silicon dioxide.
[0016] Optionally, in the etching method of the hard mask of the back metal grid, during the main etching process, the etching gas includes at least: C4F8 and O2, wherein the flow rate of C4F8 is 30sccm~50sccm, and the flow rate of O2 is 10sccm~20sccm; the pressure of the process chamber is 100mtorr~150mtorr; the frequency of the bias RF power supply is 100Hz~200Hz; and the RF power is 700W~1000W.
[0017] Optionally, in the etching method of the hard mask of the back metal grid, during the auxiliary etching process, the etching gas includes at least: C4F8, CF4 and O2, wherein the flow rate of C4F8 is 30sccm~50sccm, the flow rate of CF4 is 30sccm~50sccm, and the flow rate of O2 is 10sccm~20sccm; the pressure of the process chamber is 50mtorr~80mtorr; the frequency of the bias RF power supply is 200Hz~400Hz; and the RF power is 200W~400W.
[0018] Optionally, in the etching method of the hard mask of the back metal grid, the thickness of the first hard mask layer is 4000Å~6000Å.
[0019] Optionally, in the method for etching the hard mask of the back metal grid, the material of the second hard mask layer is titanium nitride.
[0020] Optionally, in the etching method of the hard mask of the back metal grid, the thickness of the second hard mask layer is 700Å~1200Å.
[0021] Optionally, in the etching method of the hard mask of the back metal grid, during the main etching and auxiliary etching of the first hard mask layer, a portion of the thickness of the second hard mask layer will also be etched and consumed.
[0022] Optionally, in the etching method of the hard mask of the back metal grid, after auxiliary etching of the first hard mask layer, the etching method of the hard mask of the back metal grid also includes: etching downward the metal material layer according to the grid-type grooves in the first hard mask layer to obtain a metal grid.
[0023] Optionally, in the etching method of the hard mask of the back metal grid, both the main etching and the auxiliary etching are plasma etching processes.
[0024] The technical solution of this application has at least the following advantages:
[0025] The present application etches the first hard mask layer in two steps. Specifically, to ensure a high etching selectivity (the etching rate of the first hard mask layer is greater than the etching rate of the second hard mask layer), the first hard mask layer is opened by performing a main etching in a carbon-rich environment while reducing the oxygen supply to cause a certain amount of byproducts to accumulate on the sidewalls and bottom walls of the trench. Subsequently, the first hard mask layer is subjected to an auxiliary etching in a fluorine-rich environment to trim the profile of the grid-shaped trench and remove excess byproducts attached to the sidewalls and bottom walls of the trench. This ensures that the lateral dimensions of the grid-shaped trench are consistent from the top to the bottom of the trench, thereby improving the morphology of the grid-shaped trench in the second hard mask layer and the uniformity of the thickness of the grid-shaped trench sidewalls. This further improves the uniformity of the critical dimensions of the metal grid formed by the subsequent etching of the metal material layer. This avoids the situation in which traditional etching methods are forced to choose low-frequency etching, which reduces the TiN / SiO2 selectivity, and thus avoids the situation in which the first hard mask layer etch rate is too fast, resulting in undercutting of the grid-shaped opening and thus affecting pattern transfer. BRIEF DESCRIPTION OF THE DRAWINGS
[0026] In order to more clearly illustrate the specific implementation methods of the present application or the technical solutions in the prior art, the following is a brief introduction to the drawings required for use in the specific implementation methods or the description of the prior art. Obviously, the drawings described below are some implementation methods of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without any creative work.
[0027] Figure 1 is a flow chart of a method for etching a hard mask of a back metal grid according to an embodiment of the present invention;
[0028] Figure 2-Figure 9 Schematic diagram of a semiconductor structure in each process step of etching a back metal grid hard mask according to an embodiment of the present invention;
[0029] The description of the accompanying drawings is as follows:
[0030] 10 - substrate, 11 - front side of substrate, 12 - back side of substrate, 13 - gate oxide layer, 20 - metal material layer, 30 - first hard mask layer, 31 - grid-type groove, 40 - second hard mask layer, 41 - grid-type opening, 50 - photoresist layer, 51 - metal grid pattern. DETAILED DESCRIPTION
[0031] The following is a clear and complete description of the technical solutions in this application in conjunction with the accompanying drawings. Obviously, the embodiments described are part of the embodiments of this application, not all of them. Based on the embodiments in this application, all other embodiments obtained by ordinary technicians in this field without making any creative efforts are within the scope of protection of this application.
[0032] In the description of this application, it should be noted that the terms "center," "upper," "lower," "left," "right," "vertical," "horizontal," "inner," and "outer," etc., indicating orientations or positional relationships, are based on the orientations or positional relationships shown in the accompanying drawings and are intended solely to facilitate the description of this application and simplify the description. They do not indicate or imply that the devices or components referred to must have a specific orientation, be constructed, or operate in a specific orientation. Therefore, they should not be construed as limitations on this application. Furthermore, the terms "first," "second," and "third" are used for descriptive purposes only and should not be construed as indicating or implying relative importance.
[0033] In the description of this application, it should be noted that, unless otherwise expressly specified or limited, the terms "installed," "connected," and "connected" should be understood in a broad sense. For example, they can refer to fixed connections, detachable connections, or integral connections; they can refer to mechanical connections or electrical connections; they can refer to direct connections or indirect connections through an intermediate medium; they can refer to internal connections between two components; they can refer to wireless connections or wired connections. Those skilled in the art will understand the specific meanings of the above terms in this application based on the specific circumstances.
[0034] In addition, the technical features involved in the different embodiments of the present application described below can be combined with each other as long as they do not conflict with each other.
[0035] The embodiment of the present application provides a method for etching a hard mask of a back metal grid, referring to Figure 1 , Figure 1 1 is a flow chart of a method for etching a hard mask of a back metal grid according to an embodiment of the present invention. The method for etching a hard mask of a back metal grid includes:
[0036] Step S1: providing a substrate, wherein a gate oxide layer, a metal material layer, a first hard mask layer, and a second hard mask layer are sequentially formed on the back side of the substrate;
[0037] Step S2: coating a photoresist layer on the second hard mask layer;
[0038] Step S3: defining a metal grid pattern on the photoresist layer to obtain a patterned photoresist layer;
[0039] Step S4: using the patterned photoresist layer as a mask, etching the second hard mask layer to the surface of the first hard mask layer;
[0040] Step S5: removing the patterned photoresist layer;
[0041] Step S6: using the patterned second hard mask layer as a mask, in a carbon-rich environment, performing a main etching on the first hard mask layer and stopping at the surface of the metal material layer to form a grid-type trench in the first hard mask layer, wherein the lateral dimensions of the grid-type trench gradually decrease from the top to the bottom of the grid-type trench;
[0042] Step S7: In a fluorine-rich environment, auxiliary etching is performed on the first hard mask layer to trim the lateral dimension of the grid-type groove near the bottom end so that the lateral dimension of the grid-type groove from the top to the bottom end is equal, wherein the chamber pressure of the auxiliary etching is less than the chamber pressure of the main etching, the frequency of the bias RF power supply of the auxiliary etching is greater than the frequency of the bias RF power supply of the main etching, and the RF power of the auxiliary etching is less than the RF power of the main etching.
[0043] Specifically, refer to Figure 2-Figure 9 , Figure 2-Figure 9 It is a schematic diagram of a semiconductor structure in each process step of etching a back metal grid hard mask according to an embodiment of the present invention.
[0044] First, refer to Figure 2 , Figure 2 This is a schematic diagram of the semiconductor structure after the second hard mask layer is formed in an embodiment of the present application. A substrate 10 is provided, and the substrate 10 has a front side 11 of the substrate and a back side 12 of the substrate. The back side 12 of the substrate is sequentially formed with a gate oxide layer 13, a metal material layer 20, a first hard mask layer 30 and a second hard mask layer 40.
[0045] Preferably, the first hard mask layer 30 is made of silicon dioxide.
[0046] Furthermore, the thickness of the first hard mask layer 30 is 4000Å-6000Å.
[0047] Preferably, the second hard mask layer 40 is made of titanium nitride.
[0048] Furthermore, the thickness of the second hard mask layer 40 is 700Å-1200Å.
[0049] In this embodiment, the metal material layer 20 is made of metal tungsten.
[0050] In another embodiment, a buffer layer may be formed between the metal material layer 20 and the gate oxide layer 13 , and the material of the buffer layer may be TiN.
[0051] Then, refer to Figure 3 , Figure 33 is a schematic diagram of a semiconductor structure after a photoresist layer is coated on the second hard mask layer according to an embodiment of the present application, wherein a photoresist layer 50 is coated on the second hard mask layer 40 .
[0052] Next, refer to Figure 4 , Figure 4 This is a schematic diagram of the semiconductor structure after a metal grid pattern is defined on a photoresist layer according to an embodiment of the present application. Through photolithography processes such as exposure and development, a metal grid pattern 51 is defined on the photoresist layer 50 to obtain the patterned photoresist layer 50.
[0053] For further reference, Figure 5 , Figure 5 This is a schematic cross-sectional view of the semiconductor structure after etching the second hard mask layer to form a grid-type opening in an embodiment of the present application. Using the patterned photoresist layer 50 as a mask, the second hard mask layer 40 is etched to the surface of the first hard mask layer 30 to form a grid-type opening 41 in the second hard mask layer 40.
[0054] Next, refer to Figure 6 , Figure 6 1 is a schematic top view of the semiconductor structure after etching the second hard mask layer to form a grid-type opening and removing the patterned photoresist layer according to an embodiment of the present application, wherein the patterned photoresist layer 50 is removed.
[0055] For further reference, Figure 7 , Figure 7 This is a schematic cross-sectional view of the semiconductor structure after the main etching of the first hard mask layer in an embodiment of the present application. Using the patterned second hard mask layer 40 as a mask, the first hard mask layer 30 is mainly etched in a carbon-rich environment and stopped on the surface of the metal material layer 20 to form a grid-type groove 31 in the first hard mask layer 30, wherein the lateral size of the grid-type groove 31 gradually decreases from the top to the bottom of the grid-type groove 31.
[0056] In this embodiment, the main etching is a plasma etching process.
[0057] Specifically, during the main etching process, the etching gas includes at least: C4F8 and O2, wherein the flow rate of C4F8 is 30sccm~50sccm, and the flow rate of O2 is 10sccm~20sccm; the pressure of the process chamber is 100mtorr~150mtorr; the frequency of the bias RF power supply is 100Hz~200Hz; and the RF power is 700W~1000W.
[0058] In order to ensure a high etching selectivity for the first hard mask layer during the main etching process, the present application adopts a high etching selectivity for the first hard mask layer, that is, the etching rate of the first hard mask layer is greater than the etching rate of the second hard mask layer. The first hard mask layer is mainly etched in a carbon-rich environment to open the first hard mask layer. At the same time, compared with the traditional hard mask etching method (the O2 flow rate in the traditional hard mask etching method is usually greater than 20 sccm), the supply of oxygen (oxygen as a cleaning gas) in the main etching process of the present application is reduced, so that a certain amount of long-chain CF polymer is accumulated on the sidewalls and bottom wall near the bottom of the grid-type groove 31, so that the lateral size of the grid-type groove 31 gradually decreases from the top to the bottom of the grid-type groove 31. At the same time, it avoids the situation where the traditional etching method is forced to choose low-frequency etching and reduce the TiN / SiO2 selectivity, thereby avoiding the situation where the etching rate of the first hard mask layer is too fast, resulting in side hollowing of the grid-type opening and affecting the pattern transfer.
[0059] Finally, reference Figure 8 , Figure 8 This is a schematic cross-sectional view of the semiconductor structure after auxiliary etching of the first hard mask layer in an embodiment of the present application. In a fluorine-rich environment, auxiliary etching is performed on the first hard mask layer 30 to trim the lateral dimension of the grid-type groove 31 near the bottom end so that the lateral dimension of the grid-type groove 31 from the top to the bottom end is equal, wherein the chamber pressure of the auxiliary etching is less than the chamber pressure of the main etching, the frequency of the bias RF power supply of the auxiliary etching is greater than the frequency of the bias RF power supply of the main etching, and the RF power of the auxiliary etching is less than the RF power of the main etching.
[0060] In this embodiment, the auxiliary etching is a plasma etching process.
[0061] Specifically, in the auxiliary etching process, the etching gas includes at least: C4F8, CF4 and O2, wherein the flow rate of C4F8 is 30sccm~50sccm, the flow rate of CF4 is 30sccm~50sccm, and the flow rate of O2 is 10sccm~20sccm; the pressure of the process chamber is 50mtorr~80mtorr; the frequency of the bias RF power supply is 200Hz~400Hz; and the RF power is 200W~400W.
[0062] In the present application, the first hard mask layer is auxiliary-etched in a fluorine-rich environment to trim the profile of the grid-type groove. The fluorine-rich environment promotes the etching and removal of the accumulated excess by-products (mainly long-chain CF polymers), thereby completely removing the accumulated excess by-products (mainly long-chain CF polymers) attached to the side walls and bottom walls of the groove, so that the lateral dimensions of the grid-type groove are consistent from the top of the groove to the bottom of the groove, thereby improving the morphology of the grid-type groove in the second hard mask layer and the uniformity of the thickness of the grid-type groove sidewalls, thereby improving the uniformity of the key dimensions of the metal grid formed by the subsequent etching of the metal material layer.
[0063] It is worth noting that, during the main etching and auxiliary etching process of the first hard mask layer 30 , a portion of the thickness of the second hard mask layer 40 will also be etched and consumed.
[0064] For further reference, Figure 9 , Figure 9 This is a schematic cross-sectional view of a semiconductor structure after etching downward the metal material layer to obtain a metal grid according to the grid-type grooves in the first hard mask layer according to an embodiment of the present application. After auxiliary etching of the first hard mask layer 30, the etching method of the hard mask of the back metal grid may further include: etching downward the metal material layer 20 to obtain a metal grid according to the grid-type grooves 31 in the first hard mask layer 30.
[0065] Obviously, the above embodiments are merely examples for clarity of explanation and are not intended to limit the implementation methods. Those skilled in the art will appreciate that other variations or modifications can be made based on the above description. It is not necessary and impossible to enumerate all implementation methods here. Obvious variations or modifications arising therefrom remain within the scope of protection of this application.
Claims
1. A method for etching a hard mask of a back metal grid, characterized in that: include: Providing a substrate, wherein a gate oxide layer, a metal material layer, a first hard mask layer, and a second hard mask layer are sequentially formed on the back side of the substrate; coating a photoresist layer on the second hard mask layer; defining a metal grid pattern on the photoresist layer to obtain a patterned photoresist layer; Using the patterned photoresist layer as a mask, etching the second hard mask layer to the surface of the first hard mask layer; removing the patterned photoresist layer; Using the patterned second hard mask layer as a mask, in a carbon-rich environment, performing a main etching on the first hard mask layer and stopping at the surface of the metal material layer to form a grid-type trench in the first hard mask layer, wherein the lateral dimensions of the grid-type trench gradually decrease from the top to the bottom of the grid-type trench; In a fluorine-rich environment, the first hard mask layer is auxiliary-etched to trim the lateral dimensions of the grid-type groove near the bottom end so that the lateral dimensions of the grid-type groove from the top end to the bottom end are equal, wherein the chamber pressure of the auxiliary etching is less than the chamber pressure of the main etching, the frequency of the bias RF power supply of the auxiliary etching is greater than the frequency of the bias RF power supply of the main etching, and the RF power of the auxiliary etching is less than the RF power of the main etching.
2. The method for etching the hard mask of the back metal grid according to claim 1, characterized in that: The material of the first hard mask layer is silicon dioxide.
3. The method for etching the hard mask of the back metal grid according to claim 2, characterized in that: During the main etching process, the etching gas includes at least: C4F8 and O2, wherein the flow rate of C4F8 is 30 sccm~50 sccm, and the flow rate of O2 is 10 sccm~20 sccm; the pressure of the process chamber is 100 mtorr~150 mtorr; the frequency of the bias RF power supply is 100 Hz~200 Hz; and the RF power is 700 W~1000 W.
4. The method for etching the hard mask of the back metal grid according to claim 2 or 3, characterized in that: During the auxiliary etching process, the etching gas includes at least: C4F8, CF4 and O2, wherein the flow rate of C4F8 is 30sccm~50sccm, the flow rate of CF4 is 30sccm~50sccm, and the flow rate of O2 is 10sccm~20sccm; the pressure of the process chamber is 50mtorr~80mtorr; the frequency of the bias RF power supply is 200Hz~400Hz; and the RF power is 200W~400W.
5. The method for etching a hard mask of a back metal grid according to claim 1, wherein: The thickness of the first hard mask layer is 4000Å~6000Å.
6. The method for etching a hard mask of a back metal grid according to claim 1, wherein: The second hard mask layer is made of titanium nitride.
7. The method for etching a hard mask of a back metal grid according to claim 1, wherein: The thickness of the second hard mask layer is 700Å~1200Å.
8. The method for etching a hard mask of a back metal grid according to claim 1, wherein: During the main etching and auxiliary etching process on the first hard mask layer, a portion of the thickness of the second hard mask layer will also be etched and consumed.
9. The method for etching a hard mask of a back metal grid according to claim 1, wherein: After auxiliary etching of the first hard mask layer, the method for etching the hard mask of the back metal grid further includes: etching downward the metal material layer according to the grid-type grooves in the first hard mask layer to obtain a metal grid.
10. The method for etching a hard mask of a back metal grid according to claim 1, wherein: Both the main etching and the auxiliary etching are plasma etching processes.
Citation Information
Patent Citations
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