A photolithography mask and chemical mechanical polishing method for removing dishing defects in STI

Abstract

The application discloses a photolithography mask for STI and a CMP method for eliminating dishing defects. The photolithography mask for STI comprises etching main patterns in the center of the mask and auxiliary alignment patterns in the edge of the mask. The area between the etching main patterns and the auxiliary alignment patterns is opaque. A plurality of STI etching patterns are defined in the etching main patterns. The CMP method firstly forms STI areas in the center of the wafer and auxiliary alignment pattern areas in the edge of the wafer by using the photolithography mask for photolithography. Then, insulating material is deposited, a negative photoresist is coated on the surface of the insulating material, the used photolithography mask is loaded, the auxiliary alignment patterns on the photolithography mask are aligned with the auxiliary alignment areas formed in the edge of the wafer and exposed, the insulating material is etched downwards, the surface of the wafer is formed into steps, and finally, the insulating material is subjected to CMP to eliminate the dishing defects of the STI areas.

Description

Technical Field

[0001] This application belongs to the field of semiconductor technology and relates to the optimization and improvement of semiconductor processes, specifically to a chemical mechanical polishing method for photolithography masks used in STI and for eliminating dish-shaped defects. Background Technology

[0002] Shallow trench isolation (STI) is a widely used process in CMOS integrated circuits. It separates gate circuits by creating trenches less than 1 μm deep, preventing them from conducting to each other. With the continuous development of advanced nodes, the spacing between active transistors is becoming increasingly smaller, placing increasingly higher demands on STI technology. Chemical mechanical polishing (CMP) is a key process in STI fabrication, playing a crucial role in reducing scratches, improving yield, and ensuring device performance.

[0003] STI (Stereomechanical Interchange) typically involves two steps: coarse polishing, which removes a significant amount of the previously deposited silicon dioxide while retaining a certain thickness; and fine polishing, which removes the remaining silicon dioxide and stops at the silicon nitride layer. Because the silicon nitride layer is relatively thin, any over-polishing can cause irreversible damage to the device. Therefore, the fine polishing step usually uses a high-quality polishing slurry to reduce the amount of nitride removed. However, this can lead to dish-shaped depressions in the oxide layer during STI, such as… Figure 1 As shown, dish-shaped defects generate significant sidewalls and high electric fields, leading to a decrease in threshold voltage. Furthermore, the uncontrollable depth of dish-shaped defects generated in each processing step can result in uneven height differences between the shallow trench isolation and the substrate, severely impacting the reliability and yield of the final integrated circuit.

[0004] Traditional methods employ the reverse etching back (RME) technique. After the trenches are filled with oxide, a reverse photomask is used to pre-etch a portion of the oxide above the silicon nitride, creating a formation step difference between the oxide above the trenches and the oxide above the silicon nitride, thus preventing dish-shaped defects during fine grinding. However, this method requires a reverse photomask, which presents alignment issues with the main photomask, and necessitates additional lithography, etching, and cleaning steps, increasing the overall process complexity and cycle time. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention proposes a photomask for STI and a chemical mechanical polishing method for eliminating dish-shaped defects. The proposed photomask has an auxiliary alignment pattern, which enables rapid alignment when the same photomask is used for forward and reverse etching in different steps, thus solving the problem of difficult photomask alignment in the traditional reverse etching method.

[0006] A photolithography mask for STI includes a master etch pattern at the center of the mask and an auxiliary alignment pattern at the edge of the mask. The area between the master etch pattern and the auxiliary alignment pattern is opaque.

[0007] Preferably, the minimum distance between the etched main pattern and the auxiliary alignment pattern is 1500 micrometers or more.

[0008] Preferably, there are four auxiliary alignment patterns, distributed at the four vertices of the mask.

[0009] Preferably, the auxiliary alignment pattern is one or more of the following: cross shape, square shape, rectangle, or L shape.

[0010] Preferably, the auxiliary alignment pattern is cross-shaped, with a line width of 2-5 micrometers and an arm length of 20-60 micrometers.

[0011] Preferably, the main etching pattern defines multiple shallow trench isolation etching patterns, which are rectangular with a critical dimension of 0.085±0.007 micrometers and an arm length of 0.25~0.3 micrometers.

[0012] A chemical mechanical polishing method for eliminating STI (spot-shaped defects) defects, comprising the following specific steps:

[0013] Step 1: Provide a substrate and form a barrier layer on top of the substrate. Cover the surface of the barrier layer with positive photoresist, and use the photomask for STI to photolithographically open the shallow trench isolation region and the auxiliary alignment region.

[0014] Step 2: Remove the positive photoresist, form a thin oxide layer in the shallow trench isolated channel, and then deposit the insulating material.

[0015] Preferably, the thin oxide layer within the shallow trench isolation channel is formed by high-temperature thermal oxidation, with a thickness of 100 Å ± 10 Å. The insulating material above the silicon nitride barrier layer has a thickness of 5400 Å ± 300 Å.

[0016] Step 3: Cover the surface of the insulating material with a reverse photoresist.

[0017] Step 4: Locate the auxiliary alignment area formed in Step 1, then load the photomask used in Step 1, perform preliminary position matching between the auxiliary alignment pattern on the photomask and the formed auxiliary alignment area, calculate the offset between them, calibrate the position, and then perform exposure.

[0018] Step 5: Etch the insulating material downwards to create a step difference on the wafer surface.

[0019] Preferably, the insulating material above the shallow trench isolation area is 500 Å ± 100 Å higher than the insulating material above the silicon nitride barrier layer.

[0020] Step 6: Remove the reverse photoresist and perform chemical mechanical polishing on the deposited insulating material until the silicon nitride barrier layer is exposed to eliminate the dish-shaped defects.

[0021] The present invention has the following beneficial effects:

[0022] 1. A photomask including shallow trench isolation pattern and auxiliary alignment pattern is provided. The same photomask is used in the forward and reverse etching steps, which reduces the cost of illumination. At the same time, the auxiliary alignment pattern provides the photolithography machine with a clearer and higher contrast alignment signal, shortens the photolithography alignment time, and provides more accurate position information for the secondary exposure area.

[0023] 2. Using this photolithography mask for shallow trench isolation fabrication can eliminate dish-shaped defects caused by chemical mechanical polishing, reduce process costs, reduce additional photomasks and steps, and solve the alignment difficulties in the reverse mask etch-back scheme, thereby improving device reliability and yield. Attached Figure Description

[0024] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments consistent with this application and, together with the description, serve to explain the principles of this application, and do not constitute an undue limitation of this application.

[0025] Figure 1 This is a schematic diagram of a dish-shaped defect;

[0026] Figure 2 This is a schematic diagram of the photolithography mask used for STI in the embodiment;

[0027] Figures 3-10 The diagram shows an exemplary structural schematic of each step in the manufacturing method described in Example 2.

[0028] The components are: 1. Substrate; 2. Tunneling oxide layer; 3. Silicon nitride barrier layer; 4. Etched main pattern; 5. Auxiliary alignment pattern; 7. Positive photoresist; 8. Shallow trench isolation; 9. Auxiliary pattern; 10. Oxide layer; 11. Reverse photoresist. Detailed Implementation

[0029] The following description, in conjunction with the accompanying drawings, further explains the chemical mechanical polishing method for STI photolithography masks and for eliminating dish-shaped defects provided by the present invention. It should be noted that the drawings are all in a very simplified form and use non-precise proportions, and are only used to facilitate and clarify the illustration of the embodiments of the present invention.

[0030] The following description of specific examples of elements and configurations is presented in a simplified manner. Of course, these elements and configurations are merely examples and are not intended to be limiting. For example, the formation of an initial feature above or on a second feature in the following description may include embodiments where the initial and second features are formed in direct contact, and may also include embodiments where additional features may be formed between the initial and second features, such that the initial and second features do not need to be in direct contact. Furthermore, it should be noted that, unless specifically stated or indicated, the terms "first" and "second," etc., in the specification are used only to distinguish various components, elements, steps, etc., in the specification, and are not used to indicate logical or sequential relationships between various components, elements, steps, etc.

[0031] When referring to spatially related terms in this invention, such as "height," "thickness," "upper," "lower," "vertical," "horizontal," "top," "bottom," "inner," "outer," and similar terms, the indicated orientation or positional relationship is based on the orientation or positional relationship shown in the accompanying drawings. This is solely for the purpose of facilitating and simplifying the description of the invention, and does 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, and should not be construed as a limitation of the invention. In addition to the orientation shown in the figures, these spatially related terms are also used to describe the possible orientation of the semiconductor device during use and operation. As the orientation of the semiconductor device varies (rotation of 90 degrees or other orientations), the spatially related descriptions used to describe its orientation should also be interpreted in a similar manner.

[0032] It should be understood that the scope of protection of this invention is defined by the claims. Therefore, the content of this invention is not limited to the following embodiments, and other improvements made by conventional technical means skilled in the art are also within the scope of protection of this invention. Furthermore, details omitted in specific embodiments fall within the knowledge scope of those skilled in the art.

[0033] Example 1

[0034] This embodiment provides a photolithography mask for STI, including:

[0035] The main etching pattern 4 is located in the center of the mask. Multiple shallow trench isolation etching patterns are defined in the main etching pattern 4.

[0036] The auxiliary alignment pattern 5 is located at the four vertices of the mask edge. The area between the main etching pattern 4 and the auxiliary alignment pattern 5 is opaque.

[0037] like Figure 2 As shown, the auxiliary alignment pattern 5 is cross-shaped, with a line width of 2-5 micrometers, an arm length of 20-60 micrometers, and a minimum distance of 1500 micrometers from the etched main pattern 4.

[0038] In some embodiments, the auxiliary alignment pattern 5 may also be a square, a rectangle, or an L-shape.

[0039] In some embodiments, the shapes of the auxiliary alignment pattern 5 at different locations may be different.

[0040] Example 2

[0041] This embodiment provides a chemical mechanical polishing method for eliminating STI dish-shaped defects, the specific steps of which are as follows:

[0042] Step 1: Provide a substrate 1, and sequentially form a tunneling oxide layer 2 and a silicon nitride barrier layer 3 on the substrate 1. Cover the surface of the silicon nitride barrier layer 3 with positive photoresist 7, and use the photolithography mask for STI to form the main pattern area and auxiliary alignment area 9 within the positive photoresist 7, such as... Figure 3 As shown. Then, etching is performed within the region to form shallow trench isolation 8 within the substrate 1 in the central region of the wafer, and auxiliary patterns 9 are formed at the edge of the wafer, as shown. Figure 4 As shown. Those skilled in the art will understand that in actual production, multiple shallow trench isolations 8 are arranged between the auxiliary patterns 9 and in the central area of ​​the substrate 1. For the sake of simplification, not all shallow trench isolations 8 formed after etching are shown in the figure.

[0043] In some embodiments, the thickness of the substrate 1 is 700-800 micrometers, the thickness of the tunneling oxide layer 2 is 50-150 Å, the thickness of the silicon nitride barrier layer 3 is 500-2000 Å, and the thickness of the covering positive photoresist 7 is 5000-8000 Å. The etching depth of the shallow trench isolation 8 and the auxiliary pattern 9 is 3800-4200 Å.

[0044] Step 2: Remove the positive photoresist 7 and form a thin oxide layer within the channels of the shallow trench isolation 8. Then fill with oxide to form an oxide layer 10 above the shallow trench isolation 8 and the silicon nitride barrier layer 3, as shown below. Figure 5 As shown.

[0045] In some embodiments, the thin oxide layer within the shallow trench isolation 8 channel is formed by high-temperature thermal oxidation, and has a thickness of 100 Å ± 10 Å. The oxide layer 10 above the silicon nitride barrier layer 3 has a thickness of 5400 Å ± 300 Å.

[0046] Step 3: Cover the oxide layer surface with reverse photoresist 11, such as... Figure 6 As shown.

[0047] Step 4: The lithography machine first locates the auxiliary pattern 9 formed in Step 1 on the wafer, then loads the photomask used in Step 1 onto the lithography machine stage. It performs preliminary position matching between the auxiliary alignment pattern 5 on the photomask and the auxiliary pattern 9 on the wafer surface, calculates the offset between them, calibrates the position, and then performs exposure. Figure 7 As shown.

[0048] Step 5: Etch the oxide downwards to create a step difference between the oxides on the wafer surface; specifically, the oxide above the shallow trench isolation 8 region and the auxiliary pattern 9 is higher than the oxide above the silicon nitride barrier layer 3, such as... Figure 8 As shown.

[0049] In some embodiments, the oxide above the shallow trench isolation 8 region is 500 Å ± 100 Å higher than the oxide above the silicon nitride barrier layer 3.

[0050] Step 6: Remove the reverse photoresist 11, such as... Figure 9 As shown. The filled oxide is chemically and mechanically polished until the silicon nitride barrier layer 3 is exposed. The upper surface of the oxide in the shallow trench isolation 8 is flush with the upper surface of the silicon nitride barrier layer 3, eliminating the dish-shaped defect, as shown. Figure 10 As shown.

[0051] In some embodiments, the chemical mechanical polishing (CMP) uses a polishing pressure of 2.5 psi, a polishing time of 75 s, a polishing fluid flow rate of 250 ml / min, a polishing pad rotation speed of 93 rpm, and a polishing head rotation speed of 87 rpm.

Claims

1. A photolithography mask for STI, characterized in that: It includes a main etching pattern (4) located in the center of the mask and an auxiliary alignment pattern (5) located at the edge of the mask; the area between the main etching pattern (4) and the auxiliary alignment pattern (5) is opaque.

2. The photolithographic mask for STI as described in claim 1, characterized in that: The minimum distance between the main etched pattern (4) and the auxiliary alignment pattern (5) is 1500 micrometers or more.

3. The photolithographic mask for STI as described in claim 1, characterized in that: There are four auxiliary alignment patterns (5), which are distributed at the four vertices of the mask.

4. The photolithographic mask for STI as described in claim 3, characterized in that: The auxiliary alignment pattern (5) is one or more of the following: cross shape, square shape, rectangle or L shape.

5. The photolithographic mask for STI as described in claim 3, characterized in that: The auxiliary alignment pattern (5) is cross-shaped with a line width of 2-5 micrometers and an arm length of 20-60 micrometers.

6. The photolithographic mask for STI as described in claim 1, characterized in that: The etching master pattern (4) defines multiple shallow trench isolation etching patterns, and the shallow trench isolation etching patterns are rectangular.

7. A chemical mechanical polishing method for eliminating STI disc-shaped defects, characterized in that: Using a photomask for STI as described in any one of claims 1 to 6, a shallow trench isolation (8) is formed in the center of the wafer by photolithography, and an auxiliary pattern (9) is formed at the edge of the wafer; After depositing the insulating material, a reverse photoresist (11) is covered on the surface of the insulating material, a used photomask is loaded, the auxiliary alignment pattern (5) on the photomask is aligned with the auxiliary pattern (9) formed at the edge of the wafer, the position is calibrated and then exposure is performed. The insulating material is etched downwards to create a step difference on the wafer surface; Finally, the reverse photoresist (11) is removed, and the insulating material is chemically and mechanically polished to eliminate the butterfly defects of the shallow trench isolation (8).

8. The chemical mechanical polishing method for eliminating STI disc-shaped defects as described in claim 7, characterized in that: The wafer comprises, from bottom to top, a substrate (1), a tunneling oxide layer (2), and a silicon nitride barrier layer (3); a shallow trench isolation (8) and an auxiliary pattern (9) formed by photolithography are located within the substrate (1).

9. The chemical mechanical polishing method for eliminating STI disc-shaped defects as described in claim 7, characterized in that: After the insulating material is etched downwards, the insulating material above the shallow trench isolation (8) and auxiliary pattern (9) is higher than the insulating material above the rest of the positions.

10. The chemical mechanical polishing method for eliminating STI dish-shaped defects as described in claim 9, characterized in that: The insulating material above the shallow trench isolation (8) and auxiliary pattern (9) is 500 Å ± 100 Å higher than the insulating material above the other locations.

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