Method of forming a cantilever structure

Abstract

The application discloses a method for forming a suspension beam structure, which is applied to a manufacturing process of a CIS and comprises the following steps: providing a substrate, a hard mask layer is formed on the substrate, a groove is formed in the substrate and the hard mask layer, a ratio of a depth to a width of the groove is greater than 4, the groove has an upper part and a lower part, the width of the upper part is smaller than that of the lower part, and a linear oxidation layer is formed on the exposed surface of the hard mask layer and the upper part of the groove; a first epitaxial layer is formed on the circumferential side of the lower part of the groove; the linear oxidation layer is removed; a second epitaxial layer is formed on the exposed surface of the first epitaxial layer and the groove, and the second epitaxial layer fills the opening of the groove; the hard mask layer is removed; and a third epitaxial layer is formed on the substrate and the second epitaxial layer. The method can form a deep PD by the mode of first forming a first epitaxial layer in a deep groove, then forming a second epitaxial layer, and finally forming a third epitaxial layer, so that the problem of early sealing of a born groove can be improved.

Description

Technical Field

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

[0002] Among image sensors, complementary metal oxide semiconductor image sensors (CIS) are image sensors made using CMOS devices. Due to their advantages such as high integration, low power supply voltage, and low technical threshold, they are widely used in fields such as photography and videography, security systems, smart mobile phones, and medical electronics.

[0003] The photosensitivity of CIS is strongly correlated with the size of the pixel area. Traditional photodiodes (PDs) are formed through photolithography and ion implantation processes, which are limited by the aspect ratio of the photoresist and the depth and concentration of ion implantation. To improve photosensitivity on small pixels, the space of the PD can be extended vertically to circumvent the limitations of the photoresist aspect ratio. Therefore, related technologies have proposed forming a cantilever structure in CIS, where the surface device structure is formed after the deep PD layer, thus avoiding the process limitations of ion implantation and photolithography.

[0004] However, due to the high aspect ratio of the cantilever structure, there is a high probability that the opening of the deep trench will be sealed prematurely when filling it with the doped epitaxial layer. The doped epitaxial layer cannot fill the entire surface of the deep trench, thereby reducing the reliability and yield of the device. Summary of the Invention

[0005] This application provides a method for forming a cantilever structure, which can solve the problem that the cantilever structure forming methods provided in the related art are prone to premature sealing when filling the epitaxial layer. The method includes:

[0006] A substrate is provided, on which a hard mask layer is formed, and trenches are formed in the substrate and the hard mask layer. The ratio of the depth to the width of the trenches is greater than 4. The trenches have an upper part and a lower part, the width of the upper part being smaller than the width of the lower part. A linear oxide layer is formed on the surface of the hard mask layer and the upper part of the trenches that are exposed.

[0007] A first epitaxial layer is formed on the peripheral side of the lower part of the trench;

[0008] Remove the linear oxide layer;

[0009] A second epitaxial layer is formed on the exposed surfaces of the first epitaxial layer and the trench, the second epitaxial layer filling the opening of the trench;

[0010] Remove the hard mask layer;

[0011] A third epitaxial layer is formed on the substrate and the second epitaxial layer.

[0012] In some embodiments, the substrate comprises, from bottom to top, a silicon substrate and an epitaxial layer, wherein the epitaxial layer is doped with a second type of impurity.

[0013] In some embodiments, the hard mask layer includes a silicon nitride layer.

[0014] In some embodiments, the second epitaxial layer is doped with a first type of impurity.

[0015] In some embodiments, removing the hard mask layer includes:

[0016] A first planarization process is performed to ensure that the surface of the second epitaxial layer at the trench opening does not protrude.

[0017] Remove the hard mask layer;

[0018] Perform a second flattening process.

[0019] In some embodiments, removing the linear oxide layer includes:

[0020] The linear oxide layer is removed by a wet etching process.

[0021] In some embodiments, the thickness of the first epitaxial layer is 70 nanometers to 200 nanometers.

[0022] The technical solution of this application has at least the following advantages:

[0023] By forming a deep PD by first forming a first epitaxial layer in the deep trench, then forming a second epitaxial layer, and finally forming a third epitaxial layer, the problem of premature sealing of the trench can be improved. This allows the doped second epitaxial layer to fill the entire deep trench region, improving the morphology of the epitaxial layer and, to a certain extent, improving the reliability and yield of the device. Attached Figure Description

[0024] To more clearly illustrate the technical solutions in the specific embodiments of this application or the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of this application. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0025] Figure 1 This is a flowchart of a method for forming a cantilever structure provided in an exemplary embodiment of this application;

[0026] Figure 2 This is a top view of the substrate after trenches have been formed.

[0027] Figures 3 to 10 This is a schematic cross-sectional view illustrating the formation of a cantilever structure provided in an exemplary embodiment of this application. Detailed Implementation

[0028] The technical solutions of this application will now be clearly and completely described with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of this application. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0029] In the description of this application, it should be noted that the terms "center," "upper," "lower," "left," "right," "vertical," "horizontal," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated 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.

[0030] In the description of this application, it should be noted that, unless otherwise expressly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal connection of two components; and they can refer to a wireless connection or a wired connection. Those skilled in the art can understand the specific meaning of the above terms in this application based on the specific circumstances.

[0031] Furthermore, the technical features involved in the different embodiments of this application described below can be combined with each other as long as they do not conflict with each other.

[0032] refer to Figure 1 It illustrates a flowchart of a method for forming a cantilever structure according to an exemplary embodiment of this application, which can be applied to the manufacturing process of CIS, such as... Figure 1 As shown, the method includes:

[0033] Step S1: A substrate is provided, a hard mask layer is formed on the substrate, and trenches are formed in the substrate and the hard mask layer. The ratio of the depth to the width of the trenches is greater than 4. The trenches have an upper part and a lower part, the width of the upper part is smaller than the width of the lower part, and a linear oxide layer is formed on the exposed surfaces of the hard mask layer and the upper part of the trenches.

[0034] refer to Figure 2 It shows a top view schematic diagram after trenches are formed in the substrate; Reference Figure 3 This shows a cross-sectional schematic diagram after trenches have been formed in the substrate. (See diagram for example.) Figure 2 and Figure 3 As shown, from bottom to top, the structure includes a silicon substrate 210 and an epitaxial layer 220. The epitaxial layer 220 is doped with a second type of impurity. A hard mask (HM) layer 230 is formed on the substrate. Trench 300 (the depth-to-width ratio of trench 300 is greater than 4) is formed in the substrate and the hard mask layer 230. The trench 300 has an upper portion 302 and a lower portion 301. The width of the upper portion 302 is smaller than the width of the lower portion 301. A linear oxide layer 240 is formed on the exposed surfaces of the hard mask layer 230 and the upper portion of the trench 300. The hard mask layer 230 may include a silicon nitride (SiN) layer.

[0035] like Figure 2 As shown, from a top view, the trench 300 is elongated, for example, it can be rectangular, rounded rectangle, ellipse, etc. The width W of the elongated shape is the width of the trench 300 (since the trench 300 is narrower at the top and wider at the bottom, the shape viewed from a top view is the opening shape of the upper part 302 of the trench 300, and the top view shape of the lower part 301 is the same as that of the upper part 302, but the size is larger than that of the upper part 302). The rectangular area surrounded by the four trenches 300 is the active area (AA) of the CIS. Figures 3 to 10 The sectional view is divided into three regions. The first region 201 is along... Figure 2 A cross-sectional view along the AA' direction, the second region 202 is along... Figure 2 A cross-sectional view along the BB' direction, the third region 203 is along... Figure 2 A cross-sectional view along the CC' direction.

[0036] Step S2: A first epitaxial layer is formed on the periphery of the lower part of the trench.

[0037] refer to Figure 4 This illustrates a cross-sectional schematic diagram showing the formation of a first epitaxial layer on the periphery of the lower part of the trench. For example, as shown... Figure 4 As shown, a first epitaxial layer 251 can be formed on the periphery of the lower part 301 of the trench 300 by an epitaxial process. Optionally, the thickness of the first epitaxial layer 252 is 70 nanometers (nm) to 200 nanometers.

[0038] Step S3: Remove the linear oxide layer.

[0039] refer to Figure 5 This illustrates a cross-sectional schematic diagram showing the removal of the linear oxide layer. For example, as shown... Figure 5 As shown, the linear oxide layer 240 can be removed by a wet etching process.

[0040] Step S4: A second epitaxial layer is formed on the surface of the first epitaxial layer and the exposed trench, and the second epitaxial layer fills the opening of the trench.

[0041] refer to Figure 6 This illustrates a cross-sectional schematic diagram showing the formation of a second epitaxial layer on the surface exposed by the trenches in the first epitaxial layer. For example, as shown... Figure 6 As shown, a second epitaxial layer 252 can be formed on the exposed surfaces of the first epitaxial layer 251 and the trench 300 through an epitaxial process, and the second epitaxial layer 252 fills the opening of the trench 300. The second epitaxial layer 252 is doped with a first type of impurity, and the epitaxial layer 220 is doped with a second type of impurity. In this embodiment, if the first type of impurity is a P (positive) type impurity, then the second type of impurity is an N (negative) type impurity; if the first type of impurity is an N type impurity, then the second type of impurity is a P type impurity. Optionally, the epitaxial layer 220 is a silicon thin film layer with a crystal orientation of

[110] and doped with N-type impurities.

[0042] Step S5: Remove the hard mask layer.

[0043] For example, step S5 includes, but is not limited to: performing a first planarization process to make the surface of the second epitaxial layer at the trench opening not protrude; removing the hard mask layer; and performing a second planarization process.

[0044] refer to Figure 7 This shows a cross-sectional view after the first planarization process. For example, as shown... Figure 7 As shown, the first planarization process can be performed by chemical mechanical polishing (CMP) to make the surface of the second epitaxial layer 252 at the opening of the trench 300 not protrude.

[0045] refer to Figure 8 This illustrates a cross-sectional view after the hard mask layer has been removed. For example, as shown... Figure 8 As shown, the hard mask layer 230 can be removed by wet etching or dry etching. After the hard mask layer 230 is removed, the second epitaxial layer 252 protrudes again.

[0046] refer to Figure 9 This shows a cross-sectional view after the second planarization process. For example, as shown... Figure 9 As shown, a second planarization process can be performed using CMP to ensure that the surface of the second epitaxial layer 252 at the opening of the trench 300 does not protrude.

[0047] Step S6: Form a third epitaxial layer on the substrate and the second epitaxial layer.

[0048] refer to Figure 10 This shows a cross-sectional schematic diagram after the formation of the third epitaxial layer. For example, as shown... Figure 10 As shown, a third epitaxial layer 253 can be formed on the epitaxial layer 220 by an epitaxial process.

[0049] In summary, in this embodiment of the application, by forming a first epitaxial layer in the deep trench, then forming a second epitaxial layer, and finally forming a third epitaxial layer, a deep PD can be formed. This can improve the problem of premature sealing of the trench, allowing the doped second epitaxial layer to fill the entire deep trench region, improving the morphology of the epitaxial layer, and to a certain extent improving the reliability and yield of the device.

[0050] Obviously, the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this application.

Claims

1. A method of forming a suspended beam structure, the method comprising: The method is applied to a manufacturing process of a CIS, and the method comprises the following steps: providing a substrate, a hard mask layer is formed on the substrate, a trench is formed in the substrate and the hard mask layer, a ratio of a depth to a width of the trench is greater than 4, the trench has an upper part and a lower part, the width of the upper part is less than the width of the lower part, a linear oxidation layer is formed on the hard mask layer and an exposed surface of the upper part of the trench; forming a first epitaxial layer on a circumferential side of the lower part of the trench; removing the linear oxidation layer; forming a second epitaxial layer on the first epitaxial layer and the exposed surface of the trench, the second epitaxial layer fills an opening of the trench; removing the hard mask layer; forming a third epitaxial layer on the substrate and the second epitaxial layer.

2. The method of claim 1, wherein, The substrate comprises a silicon substrate and an epitaxial layer from bottom to top, and the epitaxial layer is doped with impurities of a second type.

3. The method of claim 2, wherein, The hard mask layer comprises a silicon nitride layer.

4. The method of claim 3, wherein, The second epitaxial layer is doped with impurities of a first type.

5. The method of claim 4, wherein, The removing of the hard mask layer comprises: performing a first planarization treatment, so that a surface of the second epitaxial layer at the opening of the trench is not protruding; removing the hard mask layer; performing a second planarization treatment.

6. The method according to any one of claims 1 to 5, characterized in that, The removing of the linear oxidation layer comprises: removing the linear oxidation layer by a wet etching process.

7. The method of claim 6, wherein, The thickness of the first epitaxial layer is 70 nanometers to 200 nanometers.

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