Method of forming photodiode deep trench physical isolation

Abstract

The application provides a method for forming physical isolation of a photodiode deep trench, comprising the following steps: providing a substrate, forming a photodiode structure on the substrate, forming a first epitaxial layer above the photodiode structure on the substrate, and forming an etching stop layer on the first epitaxial layer; forming a photoresist layer on the etching stop layer, then opening the photoresist layer by photolithography to expose the etching stop layer, then etching the exposed etching stop layer to expose the first epitaxial layer below; etching the exposed first epitaxial layer to form a groove, so that the middle part of the sidewall of the groove is concave inward; forming a sidewall protection layer on the groove, then etching the sidewall protection layer at the bottom of the groove and the first epitaxial layer below by using an anisotropic etching method. The sidewall protection layer between the trenches is less lost after the second etching, the area between the trenches is protected and forms a "bottle-shaped" physical isolation, and the problem of sidewall protection layer loss is solved.

Description

Technical Field

[0001] This invention relates to the field of semiconductor technology, and in particular to a method for forming deep trench physical isolation for photodiodes. Background Technology

[0002] CMOS image sensors integrate analog and digital circuits. They mainly consist of four components: microlenses, color filters, photodiodes (PDs), and pixel design. The photoelectric conversion structure of a CMOS sensor is the photodiode, and its performance plays a crucial role in the entire imaging system. Traditional processes use ion implantation to form photodiodes, but as the pixel size of high-end image sensors shrinks to 0.7µm, the aspect ratio of the photoresist during particle implantation for high-energy photodiodes has reached its limit.

[0003] To create physical isolation in photodiode trenches, a portion of the overlapping trenches near the surface can be preserved during silicon trench etching, while the middle and bottom are hollowed out. A P-type epitaxial layer is then applied to fill this gap, forming a "bottle-shaped" physical isolation structure, thus avoiding the limitations of the photoresist's aspect ratio. After the first trench etching, a sidewall protective layer needs to be deposited to protect the intersecting areas between the trenches. Furthermore, the sidewall protective layer should not be significantly damaged after the second trench etching, ensuring that it is preserved in the intersecting areas after isotropic etching. If the top sidewall protective layer of the intersecting area is completely lost after the second trench etching, subsequent isotropic etching will cause the area where the sidewall protective layer was lost to be directly etched off.

[0004] To address the aforementioned issues, a novel method for forming deep trenches for physical isolation of photodiodes is needed. Summary of the Invention

[0005] In view of the shortcomings of the prior art described above, the purpose of the present invention is to provide a method for forming deep trench physical isolation of photodiodes, which solves the problem in the prior art that during the process of forming deep trench physical isolation of photodiodes, the top sidewall protective layer of the intersecting area is completely lost after the second trench etching, and subsequent isotropic etching will cause the sidewall protective layer to be directly etched off at the point of loss.

[0006] To achieve the above and other related objectives, the present invention provides a method for forming a deep trench physical isolation for a photodiode, comprising:

[0007] Step 1: Provide a substrate on which a photodiode structure is formed, and on which a first epitaxial layer is formed above the photodiode structure, and an etch barrier layer is formed on the first epitaxial layer.

[0008] Step 2: A photoresist layer is formed on the etch barrier layer, and then the photoresist layer is opened by photolithography to expose the etch barrier layer. Then the exposed etch barrier layer is etched to expose the first epitaxial layer underneath it.

[0009] Step 3: Etch the exposed first epitaxial layer to form a groove, so that the middle part of the sidewall of the groove is recessed inward;

[0010] Step 4: Form a sidewall protective layer on the groove, then use an anisotropic etching method to etch the sidewall protective layer at the bottom of the groove and the first epitaxial layer below it, so that the sidewall protective layer on the sidewall of the groove is retained. Then use an isotropic etching method to etch the first epitaxial layer at the bottom of the groove, so that the cross-section of the groove is formed into a bottle shape.

[0011] Step 5: Remove the sidewall protective layer and form a second epitaxial layer on the second groove. The second epitaxial layer located in the groove is an air-isolated structure. The sidewall of the groove is a closed thin-walled space filled with air. Then grind the second epitaxial layer to the top of the etching barrier layer.

[0012] Step 6: Remove the etching barrier layer, then grind the second epitaxial layer over the first epitaxial layer, and then form a third epitaxial layer covering the first and second epitaxial layers.

[0013] Preferably, the substrate in step one is a silicon substrate.

[0014] Preferably, the material of the etching barrier layer in step one is at least one of silicon dioxide, silicon oxynitride, and amorphous carbon.

[0015] Preferably, the thickness of the etching barrier layer in step one is 100 to 800 nanometers.

[0016] Preferably, the substrate in step one is a P-type substrate.

[0017] Preferably, the first epitaxial layer in step one is an N-type epitaxial layer.

[0018] Preferably, the second epitaxial layer in step five is a P-type epitaxial layer.

[0019] Preferably, the middle portion of the groove sidewall in step three is recessed inward, and the angle between the arc surface formed and the vertical direction is 0 to 30 degrees.

[0020] Preferably, the depth of the groove in step three is 0.3 to 0.8 micrometers.

[0021] Preferably, the sidewall protective layer in step four is made of silicon nitride or silicon dioxide. The sidewall protective layer at the bottom of the groove and the first epitaxial layer below it are etched using an anisotropic etching method.

[0022] Preferably, in step four, an anisotropic etching method is used to etch the sidewall protective layer at the bottom of the groove and the first epitaxial layer below it, thereby increasing the depth of the groove by 2.2 to 2.7 micrometers.

[0023] As described above, the method for forming deep trench physical isolation for photodiodes according to the present invention has the following beneficial effects:

[0024] This invention solves the problem of sidewall protection layer loss by etching the groove first, causing the middle part of the groove sidewall to be recessed inward. This results in minimal loss of the sidewall protective layer in the relatively different areas between the grooves after the second etching. The relatively different areas between the grooves are protected and form a "bottle-shaped" physical isolation, thus solving the problem of sidewall protective layer loss. Attached Figure Description

[0025] Figure 1 The diagram shown is a schematic representation of the process flow of the present invention.

[0026] Figure 2 The diagram shows a trench formed on the first epitaxial layer by etching according to the present invention.

[0027] Figure 3 The diagram shown illustrates the opening of the etching barrier layer according to the present invention.

[0028] Figure 4 This is a schematic diagram of the first etching of the trenches in this invention;

[0029] Figure 5 The diagram shows the morphology of the trench sidewall of the present invention.

[0030] Figure 6 The diagram shown illustrates the formation of the sidewall protective layer according to the present invention.

[0031] Figure 7 This is a schematic diagram of the second etching of the trenches in this invention;

[0032] Figure 8 This is a schematic diagram of the third etching of the trenches in this invention;

[0033] Figure 9 The diagram shown illustrates the removal of the sidewall protective layer according to the present invention.

[0034] Figure 10 The diagram shown illustrates the formation of the second epitaxial layer according to the present invention.

[0035] Figure 11The diagram shows the grinding of the second epitaxial layer to the top of the etching barrier layer according to the present invention.

[0036] Figure 12 The diagram shown illustrates the removal of the etching barrier layer according to the present invention.

[0037] Figure 13 The diagram shows the grinding of the second epitaxial layer to above the first epitaxial layer according to the present invention;

[0038] Figure 14 The diagram shown illustrates the formation of the third epitaxial layer according to the present invention. Detailed Implementation

[0039] The following specific examples illustrate the implementation of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and various details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention.

[0040] Please see Figure 1 The present invention provides a method for forming a deep trench physical isolation for a photodiode, comprising:

[0041] Step 1: Provide a substrate 101, on which a photodiode structure is formed, a first epitaxial layer 102 located above the photodiode structure is formed on the substrate 101, and an etch barrier layer 103 is formed on the first epitaxial layer 102.

[0042] Preferably, the substrate 101 in step one is a silicon substrate 101.

[0043] Preferably, the material of the etching barrier layer 103 in step one is at least one of silicon dioxide, silicon oxynitride, and amorphous carbon.

[0044] Preferably, the thickness of the etching barrier layer 103 in step one is 100 to 800 nanometers.

[0045] Preferably, if the substrate 101 in step one is a P-type substrate 101, then the first epitaxial layer 102 in step one is an N-type epitaxial layer.

[0046] Step two: A photoresist layer is formed on the etch stop layer 103. Then, photolithography is used to expose the photoresist layer through exposure, vertical film formation, and baking processes. The exposed etch stop layer 103 is then etched to expose the underlying first epitaxial layer 102, forming a layer as shown below. Figure 3 The structure shown is used to define the location where the groove 109 is formed, and the method of opening the etching barrier layer 103 is either dry etching or wet etching.

[0047] Step 3, please refer to Figure 4 The first epitaxial layer 102 is etched to form a groove 109, as shown in the top view. Figure 2 As shown, this causes the middle part of the sidewall of the groove 109 to be recessed inward, and the etching method is usually dry etching.

[0048] Preferably, please refer to Figure 5 In step three, the middle part of the sidewall of the groove 109 is recessed inward, and the angle (108, 109) between the arc surface formed and the vertical direction is 0 to 30 degrees.

[0049] Preferably, the depth of the groove 109 in step three is 0.3 to 0.8 micrometers.

[0050] Step four, form a sidewall protective layer 104 on the groove 109, forming as shown in the figure. Figure 6 The structure shown is then etched using an anisotropic etching method, etching the sidewall protective layer 104 at the bottom of the groove 109 and the first epitaxial layer 102 below it, so that the sidewall protective layer 104 on the sidewall of the groove 109 is retained, forming a structure as shown. Figure 7 The structure shown is then etched using an isotropic etching method to form the first epitaxial layer 102 at the bottom of the groove 109, resulting in a bottle-shaped cross-section of the groove 109. Figure 8 The structure shown;

[0051] Preferably, the sidewall protective layer 104 in step four is made of silicon nitride or silicon dioxide. The sidewall protective layer 104 at the bottom of the groove 109 and the first epitaxial layer 102 below it are etched using an anisotropic etching method.

[0052] Preferably, in step four, an anisotropic etching method is used to etch the sidewall protective layer 104 at the bottom of the groove 109 and the first epitaxial layer 102 below it, thereby increasing the depth of the groove 109 by 2.2 to 2.7 micrometers.

[0053] Step 5: Remove the sidewall protective layer 104 to form a structure as shown in the image. Figure 9 The structure shown typically involves initial sidewall protective layer 104 being formed by wet etching, followed by the formation of a second epitaxial layer 105 on the second groove 109. The second epitaxial layer 105 located in the trench is an air-isolated structure, with the top of the air structure lower than the upper surface of the first epitaxial layer 102, forming a structure as shown. Figure 10 The structure shown has a trench with sidewalls that are closed, thin-walled spaces filled with air. Then, chemical mechanical planarization (CMP) polishing is used to polish the second epitaxial layer 105 up to the top of the etch barrier layer 103, forming a structure as shown. Figure 11 The structure shown;

[0054] Preferably, if the substrate 101 in step one is a P-type substrate 101, the first epitaxial layer 102 in step one is an N-type epitaxial layer, and the second epitaxial layer 105 in step five is a P-type epitaxial layer.

[0055] Step six, remove the etching barrier layer 103 to form a layer as shown in the figure. Figure 12 The structure shown can be formed by removing the etch barrier layer 103 using a wet etching method, followed by grinding the second epitaxial layer 105 up to the top of the first epitaxial layer 102, to create the structure shown. Figure 13 The structure shown can be ground using chemical mechanical planarization, followed by the formation of a third epitaxial layer 106 covering the first and second epitaxial layers, forming a structure as shown. Figure 14 The structure shown.

[0056] It should be noted that the illustrations provided in this embodiment are only schematic representations of the basic concept of the present invention. Therefore, the drawings only show the components related to the present invention and are not drawn according to the actual number, shape and size of the components in the actual implementation. In the actual implementation, the form, quantity and proportion of each component can be arbitrarily changed, and the layout of the components may also be more complex.

[0057] In summary, this invention, through the first trench etching, causes the middle portion of the groove sidewall to be recessed inward. This minimizes the loss of the protective layer on the sidewalls of the relatively different areas between the trenches after the second etching, protecting these areas and forming a "bottle-shaped" physical barrier, thus solving the problem of sidewall protective layer loss. Therefore, this invention effectively overcomes the various shortcomings of the prior art and has high industrial applicability.

[0058] The above embodiments are merely illustrative of the principles and effects of the present invention and are not intended to limit the invention. Any person skilled in the art can modify or alter the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or alterations made by those skilled in the art without departing from the spirit and technical concept disclosed in the present invention should still be covered by the claims of the present invention.

Claims

1. A method for forming a deep trench for physical isolation of a photodiode, characterized in that, At least including: Step 1: Provide a substrate on which a photodiode structure is formed, and on which a first epitaxial layer is formed above the photodiode structure, and an etch barrier layer is formed on the first epitaxial layer. Step 2: A photoresist layer is formed on the etch barrier layer, and then the photoresist layer is opened by photolithography to expose the etch barrier layer. Then the exposed etch barrier layer is etched to expose the first epitaxial layer underneath it. Step 3: Etch the exposed first epitaxial layer to form a groove, so that the middle part of the sidewall of the groove is recessed inward, and the angle between the arc surface formed and the vertical direction is 0 to 30 degrees. Step 4: Form a sidewall protective layer on the groove, then use an anisotropic etching method to etch the sidewall protective layer at the bottom of the groove and the first epitaxial layer below it, so that the sidewall protective layer on the sidewall of the groove is retained. Then use an isotropic etching method to etch the first epitaxial layer at the bottom of the groove, so that the cross-section of the groove is formed into a bottle shape. Step 5: Remove the sidewall protective layer and form a second epitaxial layer on the groove. The second epitaxial layer located in the groove is an air-isolated structure. The sidewall of the groove is a closed thin-walled space filled with air. Then grind the second epitaxial layer to the top of the etching barrier layer. Step 6: Remove the etching barrier layer, then grind the second epitaxial layer over the first epitaxial layer, and then form a third epitaxial layer covering the first and second epitaxial layers.

2. The method for forming a deep trench physical isolation for a photodiode according to claim 1, characterized in that: The substrate mentioned in step one is a silicon substrate.

3. The method for forming a deep trench physical isolation for a photodiode according to claim 1, characterized in that: The material of the etching barrier layer in step one is at least one of silicon dioxide, silicon oxynitride, and amorphous carbon.

4. The method for forming a deep trench physical isolation for a photodiode according to claim 1, characterized in that: The thickness of the etching barrier layer in step one is 100 to 800 nanometers.

5. The method for forming a deep trench physical isolation for a photodiode according to claim 1, characterized in that: The substrate mentioned in step one is a P-type substrate.

6. The method for forming a deep trench for physical isolation of a photodiode according to claim 5, characterized in that: The first epitaxial layer in step one is an N-type epitaxial layer.

7. The method for forming a deep trench physical isolation for a photodiode according to claim 6, characterized in that: The second epitaxial layer in step five is a P-type epitaxial layer.

8. The method for forming a deep trench physical isolation for a photodiode according to claim 1, characterized in that: The depth of the groove in step three is 0.3 to 0.8 micrometers.

9. The method for forming a deep trench physical isolation for a photodiode according to claim 1, characterized in that: The sidewall protective layer in step four is made of silicon nitride or silicon dioxide. The sidewall protective layer at the bottom of the groove and the first epitaxial layer below it are etched using an anisotropic etching method.

10. The method for forming a deep trench physical isolation for a photodiode according to claim 1, characterized in that: In step four, an anisotropic etching method is used to etch the sidewall protective layer at the bottom of the groove and the first epitaxial layer below it, thereby increasing the depth of the groove by 2.2 to 2.7 micrometers.

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