Method for improving peeling of small size photodiodes

Abstract

The application provides a method for improving peeling of small-size photodiodes, which comprises the following steps: providing a substrate, forming a first epitaxial layer on the substrate, and forming a hard mask layer on the first epitaxial layer; forming a photoresist layer on the hard mask layer, and opening the photoresist layer by lithography to expose the hard mask layer thereunder, so as to define a forming area of the photodiode and a reserved area of the hard mask layer, and the reserved hard mask layer serves as a support structure for connecting adjacent photodiodes; etching the exposed hard mask layer to expose the first epitaxial layer thereunder, and then removing the remaining photoresist layer; etching the exposed first epitaxial layer to form the photodiode; etching and removing the first epitaxial layer under the hard mask layer; forming an intrinsic epitaxial layer on the photodiode, and then removing the remaining hard mask layer; and forming a second epitaxial layer covering the photodiode by epitaxy and polishing. The photodiodes are connected by the hard mask layer, so that the photodiodes can be prevented from peeling.

Description

Technical Field

[0001] This invention relates to the field of semiconductor technology, and in particular to a method for improving the peeling of small-sized photodiodes. Background Technology

[0002] When fabricating small-sized, ultra-deep photodiode devices, high aspect ratio etching is required. Due to the high aspect ratio, the photodiode is prone to peeling during subsequent silicon etching processes, which can also affect nearby photodiodes and cause defects.

[0003] To address the aforementioned issues, a novel method for improving the peeling of small-sized photodiodes is needed. Summary of the Invention

[0004] In view of the shortcomings of the prior art described above, the purpose of this invention is to provide a method to improve the peeling of small-sized photodiodes, which solves the problem that in the prior art, high aspect ratio etching is required when fabricating small-sized ultra-deep photodiode devices. Due to the high aspect ratio, the photodiode is easily peeled off during subsequent silicon etching processes, and this can also affect nearby photodiodes, causing defects.

[0005] To achieve the above and other related objectives, the present invention provides a method for improving peeling of small-sized photodiodes, comprising:

[0006] Step 1: Provide a substrate, form a first epitaxial layer on the substrate, and form a hard mask layer on the first epitaxial layer;

[0007] Step 2: A photoresist layer is formed on the hard mask layer. The photoresist layer is then opened by photolithography to expose the hard mask layer underneath, thereby defining the formation area of ​​the photodiode and the reserved area of ​​the hard mask layer. The reserved hard mask layer serves as a support structure connecting adjacent photodiodes.

[0008] Step 3: Etch the exposed hard mask layer to expose the first epitaxial layer underneath, and then remove the remaining photoresist layer;

[0009] Step 4: Etch the exposed first epitaxial layer to form a photodiode;

[0010] Step 5: Etch away the first epitaxial layer beneath the hard mask layer;

[0011] Step 6: Form an intrinsic epitaxial layer on the photodiode, and then remove the remaining hard mask layer;

[0012] Step 7: Form a second epitaxial layer covering the photodiode using epitaxy and grinding.

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

[0014] Preferably, the first epitaxial layer in step one is an N-type epitaxial layer.

[0015] Preferably, the material of the hard mask layer in step one is at least one of silicon nitride and silicon dioxide.

[0016] Preferably, the thickness of the first epitaxial layer in step one is 3 to 6 micrometers.

[0017] Preferably, the support structure in step two is strip-shaped.

[0018] Preferably, the width of the support structure in step two is smaller than the diameter of the photodiode.

[0019] Preferably, the support structure in step two consists of two supports, which are X-shaped.

[0020] Preferably, the support structure in step two consists of four supports, which are shaped like a mouth.

[0021] Preferably, the etching method in step three is anisotropic dry etching.

[0022] Preferably, the etching method in step four is anisotropic dry etching.

[0023] Preferably, the depth of etching the first epitaxial layer in step four is 3 to 3.6 micrometers.

[0024] Preferably, the etching method in step five is isotropic dry etching.

[0025] Preferably, in step six, the remaining hard mask layer is removed using a wet etching method.

[0026] Preferably, the thickness of the intrinsic epitaxial layer in step six is ​​100 to 120 nanometers.

[0027] Preferably, the method for forming a second epitaxial layer covering the photodiode by epitaxy and grinding in step seven includes: forming a second epitaxial layer covering the photodiode, and then grinding the second epitaxial layer to the required height using a chemical mechanical planarization method.

[0028] Preferably, the second epitaxial layer in step seven is a P-type epitaxial layer.

[0029] Preferably, the method further includes the step of forming a CIS device on a substrate.

[0030] As described above, the method for improving the peeling of small-sized photodiodes according to the present invention has the following beneficial effects:

[0031] This invention utilizes a hard mask layer to connect the photodiode, which can prevent the photodiode from peeling off. Attached Figure Description

[0032] Figure 1 The diagram shown is a schematic representation of the process flow of the present invention.

[0033] Figure 2 The diagram shown is a cross-sectional view of the formation of the first epitaxial layer according to the present invention.

[0034] Figure 3 The diagram shown is a cross-sectional view of the formation of the hard mask layer according to the present invention.

[0035] Figure 4 The diagram shown is a schematic cross-sectional view of the graphic hard mask layer of the present invention.

[0036] Figure 5 The diagram shown is a cross-sectional view of the first epitaxial layer etched during the first etching step of this invention.

[0037] Figure 6 The diagram shown is a cross-sectional view of the first epitaxial layer etched in the second step of this invention.

[0038] Figure 7 The diagram shown is a cross-sectional view of the formation of the intrinsic epitaxial layer according to the present invention.

[0039] Figure 8 The diagram shown is a cross-sectional view of the removal of the hard mask layer according to the present invention.

[0040] Figure 9 The diagram shown is a cross-sectional view of the formation of the second epitaxial layer according to the present invention.

[0041] Figure 10 The diagram shown is a cross-sectional view of the second epitaxial layer of the present invention.

[0042] Figure 11 The diagram shown is a top view of the support structure formed according to the present invention.

[0043] Figure 12 The diagram shown is a top view of the formation of the intrinsic epitaxial layer according to the present invention.

[0044] Figure 13 The diagram shown is a top view of the present invention with the support structure removed.

[0045] Figure 14 The diagram shown is a top view of the formation of the second epitaxial layer according to the present invention.

[0046] Figure 15 The diagram shown is a schematic diagram of the CIS device structure of the present invention. Detailed Implementation

[0047] 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.

[0048] Please see Figure 1 The present invention provides a method for improving peeling of small-sized photodiodes, comprising:

[0049] Step 1: Provide a substrate 101, and form a first epitaxial layer 102 on the substrate 101, forming a cross-section as shown in the figure. Figure 2 The structure shown has a hard mask layer 103 formed on the first epitaxial layer 102, forming a cross-section as shown. Figure 3 The structure shown;

[0050] In an embodiment of the present invention, the substrate 101 in step one is a silicon substrate 101.

[0051] In an embodiment of the present invention, the first epitaxial layer 102 in step one is an N-type epitaxial layer.

[0052] In the embodiments of the present invention, the material of the hard mask layer 103 in step one is silicon nitride, but other known materials that can support the photodiode 106 can also be used, and no specific limitation is made here.

[0053] In an embodiment of the present invention, the thickness of the first epitaxial layer 102 in step one is 3 to 6 micrometers.

[0054] Step 2: A photoresist layer is formed on the hard mask layer 103. Photolithography is used to open the photoresist layer to expose the hard mask layer 103 underneath, thereby defining the formation area of ​​the photodiode 106 and the reserved area of ​​the hard mask layer 103. The reserved hard mask layer 103 serves as a support structure connecting adjacent photodiodes 106. That is, the first epitaxial layer 102 below the exposed area needs to be removed to define the photodiode 106 and the support structure connecting the photodiode 106.

[0055] In an embodiment of the present invention, the support structure in step two is strip-shaped.

[0056] In an embodiment of the present invention, the width of the support structure in step two is smaller than the diameter of the photodiode 106.

[0057] Step 3: Etch the exposed hard mask layer 103 to expose the underlying first epitaxial layer 102. Then remove the remaining photoresist layer to form a cross-section as shown. Figure 4 The structure shown forms a top view as Figure 11 The structure shown;

[0058] Specifically, please refer to Figure 11 It shows four adjacent photodiodes 106. The support structure can be two at 45° (X-type) or four at 90° (U-type). It should be noted that the number and shape of the support structure can be adjusted according to actual production, and no specific limitation is made here.

[0059] In an embodiment of the present invention, the etching method in step three is anisotropic dry etching.

[0060] Step 4: Etch the exposed first epitaxial layer 102 to form the photodiode 106. Since the support structure is retained, a portion of the first epitaxial layer 102 is still retained below the support structure, forming a cross-section as shown in the figure. Figure 5 The structure shown;

[0061] In an embodiment of the present invention, the etching method in step four is anisotropic dry etching.

[0062] In an embodiment of the present invention, the depth of etching the first epitaxial layer 102 in step four is 3 to 3.6 micrometers.

[0063] Step 5: Etch away the first epitaxial layer 102 beneath the hard mask layer 103 to form a cross-section as shown in Figure 103. Figure 6 The structure shown;

[0064] In an embodiment of the present invention, the etching method in step five is isotropic dry etching.

[0065] Step 6: Form an intrinsic epitaxial layer 104 on the photodiode 106, forming a cross-section as shown in Figure 104. Figure 7 The structure shown forms a top view as Figure 12 The structure shown is then processed by removing the remaining hard mask layer 103 to form a cross-section as shown. Figure 8 The structure shown forms a top view as Figure 13 The structure shown indicates that after the intrinsic epitaxial layer 104 is grown, the critical dimensions of the photodiode 106 pillar increase, and the pillar stability is enhanced.

[0066] In an embodiment of the present invention, the remaining hard mask layer 103 is removed in step six using a wet etching method.

[0067] In an embodiment of the present invention, the thickness of the intrinsic epitaxial layer 104 in step six is ​​100 to 120 nanometers.

[0068] Step 7: Use epitaxy and grinding to form a second epitaxial layer 105 covering the photodiode 106.

[0069] In an embodiment of the present invention, the method of forming a second epitaxial layer 105 covering the photodiode 106 by epitaxy and grinding in step seven includes: forming a second epitaxial layer 105 covering the photodiode 106, forming a cross-section as shown in the figure. Figure 9 The structure shown is then processed using chemical mechanical planarization to grind the second epitaxial layer 105 to the desired height. The intrinsic epitaxial layer 104 and the second epitaxial layer 105 serve as an isolation structure, forming a cross-section as shown. Figure 10 The structure shown forms a top view as Figure 14 The structure shown.

[0070] In an embodiment of the present invention, the second epitaxial layer 105 in step seven is a P-type epitaxial layer.

[0071] In embodiments of the present invention, the method further includes the step of forming a CIS device on a substrate 101, forming such a device as shown in the figure. Figure 15 The structure shown.

[0072] 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.

[0073] In summary, this invention utilizes a hard mask layer to connect the photodiode, thus preventing the photodiode from peeling off. Therefore, this invention effectively overcomes the various shortcomings of the prior art and has high industrial application value.

[0074] 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 improving peeling off small-sized photodiodes, characterized in that, At least including: Step 1: Provide a substrate, form a first epitaxial layer on the substrate, the first epitaxial layer is an N-type epitaxial layer, and form a hard mask layer on the first epitaxial layer; Step 2: A photoresist layer is formed on the hard mask layer. The photoresist layer is then opened by photolithography to expose the hard mask layer underneath, thereby defining the formation area of ​​the photodiode and the reserved area of ​​the hard mask layer. The reserved hard mask layer serves as a support structure connecting adjacent photodiodes. The support structure is strip-shaped. Between four adjacent photodiodes, the support structure consists of two X-shaped bars and / or four U-shaped bars. Step 3: Etch the exposed hard mask layer to expose the first epitaxial layer underneath, and then remove the remaining photoresist layer; Step 4: Etch the exposed first epitaxial layer to form a photodiode; Step 5: Etch away the first epitaxial layer beneath the hard mask layer; Step 6: Form an intrinsic epitaxial layer on the photodiode, and then remove the remaining hard mask layer; Step 7: Form a second epitaxial layer covering the photodiode using epitaxy and grinding. The second epitaxial layer is a P-type epitaxial layer.

2. The method for improving peeling of small-sized photodiodes according to claim 1, characterized in that: The substrate mentioned in step one is a silicon substrate.

3. The method for improving peeling of small-sized photodiodes according to claim 1, characterized in that: The thickness of the first epitaxial layer in step one is 3 to 6 micrometers.

4. The method for improving peeling of small-sized photodiodes according to claim 1, characterized in that: The material of the hard mask layer in step one is at least one of silicon nitride and silicon dioxide.

5. The method for improving peeling of small-sized photodiodes according to claim 1, characterized in that: The width of the support structure in step two is smaller than the diameter of the photodiode.

6. The method for improving peeling of small-sized photodiodes according to claim 1, characterized in that: The etching method described in step three is anisotropic dry etching.

7. The method for improving peeling of small-sized photodiodes according to claim 1, characterized in that: The etching method described in step four is anisotropic dry etching.

8. The method for improving peeling of small-sized photodiodes according to claim 3, characterized in that: In step four, the depth of etching the first epitaxial layer is 3 to 3.6 micrometers.

9. The method for improving peeling of small-sized photodiodes according to claim 1, characterized in that: The etching method described in step five is isotropic dry etching.

10. The method for improving peeling of small-sized photodiodes according to claim 1, characterized in that: In step six, the remaining hard mask layer is removed using a wet etching method.

11. The method for improving peeling of small-sized photodiodes according to claim 1, characterized in that: The thickness of the intrinsic epitaxial layer in step six is ​​100 to 120 nanometers.

12. The method for improving peeling of small-sized photodiodes according to claim 1, characterized in that: The method for forming a second epitaxial layer covering the photodiode using epitaxy and grinding in step seven includes: forming a second epitaxial layer covering the photodiode, and then grinding the second epitaxial layer to the required height using a chemical mechanical planarization method.

13. The method for improving peeling of small-sized photodiodes according to claim 1, characterized in that: The method also includes the step of forming a CIS device on a substrate.

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