Method for monitoring wafer backside residue

Abstract

The application provides a wafer backside residue monitoring method, before a process node of generating a residue film layer on a wafer backside, a test wafer and a product wafer are produced under the same process condition, a target film layer which covers the whole backside and has a different refractive index from the residue film layer is formed on the backside of the test wafer, optical detection is carried out on the backside of the test wafer by using the principle of prism effect, and then real-time monitoring of the product wafer backside residue is realized. The application covers the target film layer with different refractive index on the backside of the test wafer, uses the prism effect caused by different film layer stacks to visible light to realize the monitoring of wafer backside residue anomaly, and the method is simple, low investment and high timeliness. Further, since the residue defect on the wafer backside is realized fast and real-time monitoring, the subsequent photolithography process will not be affected by the wafer backside residue, and then the pattern transfer will not be affected, and the yield loss of the product is avoided.

Description

Technical Field

[0001] This invention belongs to the field of integrated circuit manufacturing, and specifically relates to a method for monitoring residues on the back side of a wafer. Background Technology

[0002] In chip manufacturing, defects significantly impact product yield, and photolithography, a crucial process for pattern definition, is highly susceptible to defocusing defects. Research has revealed that besides surface defects causing yield losses, even slight back-side residue can indirectly affect surface exposure defocusing, leading to abnormal pattern transfer and further yield losses. However, monitoring these slight residue anomalies on the wafer backside is extremely difficult, typically only detectable in subsequent processes, resulting in poor timeliness. By the time the problem is discovered, a large number of products on the production line have already been affected. Therefore, timely and efficient detection of back-side residue is critical for process monitoring. Summary of the Invention

[0003] The purpose of this invention is to provide a method for monitoring residues on the back side of a wafer, so as to quickly monitor abnormalities caused by residues on the back side of the wafer and avoid abnormal exposure of the wafer surface in subsequent photolithography processes due to residues on the back side.

[0004] To achieve the above objectives, the present invention provides a method for monitoring residues on the back side of a wafer, comprising:

[0005] The process node where test wafers and product wafers are produced under the same process conditions until a residual film layer is generated on the back side of the wafer;

[0006] A target film layer covering the entire back side of the test wafer is formed on the back side, and the refractive index of the target film layer is different from the refractive index of the residual film layer;

[0007] Optical inspection of the back side of the test wafer is performed using the prism effect principle to monitor the residue on the back side of the product wafer in real time.

[0008] In an optional embodiment of the present invention, the process of generating a residual film layer on the back side of the wafer includes at least:

[0009] The first film layer is formed on the front and back sides of the wafer;

[0010] Patterning of the wafer is performed using the first film layer on the front side of the wafer;

[0011] The first film layer deposited on the front and back sides of the wafer is removed, and the first film layer remaining on the back side of the wafer forms a residual film layer.

[0012] In an optional embodiment of the present invention, the first film layer is a silicon nitride thin film.

[0013] In an optional embodiment of the present invention, the target film is a polycrystalline silicon thin film or a silicon oxide thin film.

[0014] In an optional embodiment of the present invention, a first film layer is formed on the front and back sides of the wafer using a furnace tube process or a CVD process.

[0015] In an alternative embodiment of the present invention, a target film layer is formed on the back side of the test wafer using a furnace tube process or a CVD process.

[0016] In an optional embodiment of the present invention, a wet process is used to pattern the wafer and to remove the first film layer on the front and back sides of the wafer.

[0017] In an optional embodiment of the present invention, a macroscopic inspection machine using a visible light source is used to perform optical inspection on the test wafer.

[0018] In an optional embodiment of the present invention, the method for monitoring residues on the back side of the wafer further includes: feeding back the monitoring results of residues on the back side of the product wafer to the production line control system to control the subsequent process flow of the product wafer.

[0019] In an optional embodiment of the present invention, the subsequent process flow of the product wafer includes at least a photolithography process.

[0020] In summary, this invention provides a method for monitoring residues on the back side of a wafer. Before the process node where a residual film layer is formed on the back side of the wafer, test wafers and product wafers are produced under the same process conditions. A target film layer with a different refractive index than the residual film layer is formed on the back side of the test wafer, covering the entire back side. The back side of the test wafer is then optically inspected using the prism effect principle, thereby achieving real-time monitoring of residues on the back side of the product wafer. This invention monitors abnormalities in back side residues by covering the back side of the test wafer with target film layers of different refractive indices and utilizing the prism effect caused by the stacking of different film layers with visible light. The method is simple, low-cost, and highly efficient.

[0021] Furthermore, since the residual defects on the back of the wafer can be monitored quickly in real time, the subsequent photolithography process will not affect the exposure of the crystal surface due to the residue on the back of the wafer, and thus will not affect the pattern transfer, avoiding the loss of product yield. Attached Figure Description

[0022] Figures 1A to 1C This is a schematic diagram of the structure corresponding to some process steps in a semiconductor device manufacturing method.

[0023] Figure 2 A flowchart illustrating a method for monitoring wafer backside residues according to an embodiment of the present invention;

[0024] Figures 3A to 3CThis is a schematic diagram of the structure corresponding to the relevant steps in the monitoring method for wafer backside residues provided in an embodiment of the present invention;

[0025] Figures 4A to 4B A schematic diagram of the back-side optical inspection of a wafer in a method for monitoring residues on the back side of a wafer;

[0026] Figure 5 This is a framework diagram of a method for monitoring wafer backside residues according to an embodiment of the present invention.

[0027] The attached figures are labeled as follows:

[0028] 10, 100 - Wafer; 11a, 11b - Silicon nitride thin film; 110a, 110b - First film layer; 12 - Polycrystalline silicon layer; 120a, 120b - Target film layer; 200 - Macroscopic inspection equipment. Detailed Implementation

[0029] To make the content of this invention clearer and easier to understand, the following description, in conjunction with the accompanying drawings, further illustrates the invention. Of course, this invention is not limited to this specific embodiment, and common substitutions well-known to those skilled in the art are also covered within the scope of protection of this invention.

[0030] Secondly, the present invention is described in detail using schematic diagrams. When describing the examples of the present invention in detail, for ease of explanation, the schematic diagrams are not enlarged to a certain extent according to the general proportions, and this should not be regarded as a limitation of the present invention.

[0031] For ease of description, some embodiments of the present invention may use spatially relative terms such as “above,” “below,” “top,” and “under” to describe the relationship between one element or component and another (or more) elements or components as shown in the accompanying drawings of the embodiments. It should be understood that, in addition to the orientations described in the drawings, the spatially relative terms are also intended to include different orientations of the device during use or operation. For example, if the device in the drawings is flipped, it is described as an element or component “below” or “under” other elements or components, and will subsequently be positioned “above” or “on” other elements or components. The terms “first,” “second,” etc., used below are used to distinguish between similar elements and are not necessarily used to describe a particular order or temporal sequence.

[0032] Figures 1A to 1C This is a schematic diagram of the structure corresponding to some process steps in a semiconductor device manufacturing method.

[0033] refer to Figure 1AAs shown, silicon nitride films 11a and 11b are formed on the front and back sides of wafer 10, respectively. After patterning wafer 10 using the silicon nitride film 11a on the front side, both silicon nitride films 11a and 11b on the back side need to be removed (SIN RM). Generally, a wet process is used to remove SIN. However, during SIN removal, the process window for backside SIN removal is narrow. Often, due to factors such as acid concentration, temperature, process time, or fluctuations in the front layer of the wafer, insufficient processing occurs, resulting in a small amount of residual silicon nitride film (SIN film) on the back side of the wafer. Figure 1B As shown. However, the SIN RM process site has difficulty monitoring this slight residual anomaly; the color difference can only be monitored after the subsequent polysilicon layer 12 deposition (Poly DEP), such as... Figure 1C As shown, the timeliness of anomaly monitoring is poor. By the time the problem is discovered, a large number of products on the production line have already suffered from defocusing of the crystal surface during the photolithography process (Area A) due to residue on the back of the wafer, resulting in abnormal pattern transfer and loss of product yield.

[0034] Residual crystals on the back can indirectly affect the definition of crystal surface patterns. In existing process monitoring methods, crystal back thickness measurement is used for monitoring, but crystal back thickness measurement is not convenient and cannot macroscopically detect abnormalities in crystal back residues.

[0035] In view of this, the present invention provides a method for monitoring residues on the back side of a wafer. Figure 2 This is a flowchart illustrating a method for monitoring wafer backside residues according to an embodiment of the present invention. (See also...) Figure 2 As shown, the monitoring method for wafer backside residues provided in this embodiment includes:

[0036] Step S01: Produce test wafers and product wafers under the same process conditions until the process node where a residual film layer is generated on the back of the wafer;

[0037] Step S02: Form a target film covering the entire back side of the test wafer, wherein the refractive index of the target film is different from the refractive index of the residual film; and,

[0038] Step S03: Optical inspection of the back side of the test wafer is performed using the prism effect principle to monitor the residue on the back side of the product wafer in real time.

[0039] Figures 3A to 3C This is a schematic diagram of the structure corresponding to the relevant steps in the wafer backside residue monitoring method provided in this embodiment. Figures 4A to 4B This is a schematic diagram illustrating the principle of back-side optical inspection of a wafer in a method for monitoring residues on the back side of a wafer. Figure 5 This is a framework diagram of a method for monitoring residues on the back side of a wafer. The following is combined with... Figure 2 , Figures 3A to 3C , Figures 4A to 4B , Figure 5 This embodiment provides a detailed description of the method for monitoring wafer backside residues.

[0040] First, step S01 is executed, producing test wafers and product wafers under the same process conditions, until the process node where a residual film layer is generated on the back of the wafer.

[0041] The process of generating a residual film layer on the back side of the wafer includes at least the following:

[0042] The first film layer is formed on the front and back sides of the wafer;

[0043] Patterning of the wafer is performed using the first film layer on the front side of the wafer;

[0044] The first film layer deposited on the front and back sides of the wafer is removed, and the first film layer remaining on the back side of the wafer forms a residual film layer.

[0045] Specifically, the first film layer is a hard mask layer, such as a silicon nitride thin film (SIN film), see reference. Figure 5 As shown, the test wafer (No Product Wafer, NPW) and the product wafer (PRODUCT) are produced under the same process conditions until the process node where a residual film layer is generated on the back side of the wafer. Before the process node where a residual film layer is generated on the back side of the wafer, the wafer has undergone at least a SIN deposition process and a wet process.

[0046] refer to Figure 3A As shown, a first film layer 110a and a first film layer 110b are formed on the front and back sides of wafer 100, respectively. For example, furnace tube processing or CVD processing can be used to form the first film layers on the front and back sides of the wafer. Then, the first film layer 110a on the front side of wafer 100 is used to pattern the wafer. Next, a wet process is used to remove the first film layers on the front and back sides of the wafer. Here, the first film layer 110b on the back side of the wafer may remain, forming a residual film layer. Figure 3B As shown. In step S01, the test wafer (NPW) and the product wafer (PRODUCT) are batch-processed in wet etching to monitor the back residue of the product.

[0047] Next, step S02 is performed to form a target film layer covering the entire back side of the test wafer, wherein the refractive index of the target film layer is different from the refractive index of the residual film layer.

[0048] refer to Figure 3CAs shown, a target film layer is formed on the back side of the test wafer. The target film layer 120a and the target film layer 120b can be formed on the front and back sides of the test wafer respectively using furnace tube process or CVD process. The target film layer 120b covers the entire back side of the test wafer. The target film layer 120b and the residual film layer 110b have different refractive indices. For example, the target film layer 120b is a polycrystalline silicon thin film or a silicon oxide thin film.

[0049] Of course, the intelligent drum residue anomaly monitoring method for monitoring wafer backside residues provided by the present invention is not limited to monitoring silicon nitride thin film residues. In other embodiments of the present invention, other target film materials can be selected according to the different processes that generate wafer backside residues and the different materials of the residue film.

[0050] Next, step S03 is performed, which uses the prism effect principle to perform optical inspection on the back side of the test wafer in order to monitor the residue on the back side of the product wafer in real time.

[0051] refer to Figure 4A and Figure 4B As shown, a macroscopic inspection machine 200 using a visible light source performs optical inspection on the test wafer. The single-layer thin first film layer 110b (SIN film) residue cannot effectively achieve light wave separation. However, after the target film layer 120b is covered on the SIN film residue, due to the difference in refractive index between the two, a color difference effect is effectively formed according to the principle of prism refraction. By optically detecting the color difference effect through the macroscopic inspection machine 200, it is determined whether there is residue on the back of the crystal. Based on the optical test results of the test wafer, the residue on the back of the product wafer is monitored in real time, so that the crystal back residue defects that were originally invisible can be quickly discovered. The method is simple, low-cost, and highly efficient.

[0052] Furthermore, the monitoring method for back-side residue of the wafer provided in this embodiment also includes: feeding back the monitoring results of back-side residue of the product wafer to the production line control system to control the subsequent process flow of the product wafer, and the subsequent process flow of the product wafer includes at least a photolithography process, such as... Figure 5 As shown, because residual defects on the back side of the wafer are monitored in real time, subsequent photolithography processes will not be affected by abnormal exposure of the crystal surface due to back-side defects, thus avoiding pattern transfer and preventing product yield loss.

[0053] In summary, this invention provides a method for monitoring wafer backside defects. Before the process node where a residual film layer is formed on the backside of the wafer, test wafers and product wafers are produced under the same process conditions. A target film layer with a different refractive index than the residual film layer is formed on the backside of the test wafer, covering the entire backside. The backside of the test wafer is then optically inspected using the prism effect principle, thereby achieving real-time monitoring of wafer backside defects. This invention monitors wafer backside defects by covering the backside of the test wafer with target films of different refractive indices and utilizing the prism effect caused by the stacking of different films with visible light. The method is simple, low-cost, and highly efficient. Furthermore, because the residual defects on the wafer backside are monitored rapidly in real time, subsequent photolithography processes will not be affected by backside defects, thus avoiding impacts on crystal face exposure and pattern transfer, and preventing product yield loss.

[0054] The above description is merely a description of preferred embodiments of the present invention and is not intended to limit the scope of the present invention in any way. Any changes or modifications made by those skilled in the art based on the above disclosure shall fall within the protection scope of the claims.

Claims

1. A method for monitoring residues on the back side of a wafer, characterized in that, The application relates to a method for monitoring the backside of a product wafer. The method comprises the following steps: a test wafer and a product wafer are produced under the same process condition, and a residual film layer is formed on the backside of the wafer; a target film layer is formed on the backside of the test wafer, and the refractive index of the target film layer is different from that of the residual film layer; 2. The method of claim 1, wherein the step of monitoring the round back surface residue is performed by a camera. the backside of the test wafer is optically detected by using the principle of prism effect, so as to monitor the residual on the backside of the product wafer in real time. The process for forming the residual film layer on the backside of the wafer at least comprises the following steps: a first film layer is formed on the front side and the backside of the wafer; the wafer is patterned by using the first film layer on the front side of the wafer; 3. The method of claim 2, wherein the step of determining the presence of a round back face residue comprises the steps of: determining the presence of a round back face residue when the first and second round back face residues are present. the first film layer deposited on the front side and the backside of the wafer is removed, and the residual first film layer on the backside of the wafer forms the residual film layer.

4. The method of monitoring for round back face surface residuals according to claim 3, wherein, The first film layer is a silicon nitride film.

5. The method of claim 2, wherein the step of monitoring the round back surface residue is performed by a camera. The target film layer is a polysilicon film or a silicon oxide film.

6. The method of claim 3, wherein the step of monitoring the round back surface residue is performed by a camera. The first film layer is formed on the front side and the backside of the wafer by using a furnace tube process or a CVD process.

7. The method of claim 2, wherein the step of monitoring the round back surface residue is performed by a camera. The target film layer is formed on the backside of the test wafer by using a furnace tube process or a CVD process.

8. The method of claim 4, wherein the step of monitoring the round back surface residue is characterized by: The wafer is patterned by using a wet process, and the first film layer on the front side and the backside of the wafer is removed by using a wet process.

9. The method of monitoring for round back face surface residuals according to claim 1, wherein, The test wafer is optically detected by using a macroscopic detection machine table of a visible light source. The application further relates to a method for monitoring the backside of a product wafer.

10. The method of claim 9, wherein the step of monitoring the round back surface residue is characterized by, The monitoring result of the residual on the backside of the product wafer is fed back to a production line control system, and the subsequent process flow of the product wafer is controlled. The subsequent process flow of the product wafer at least comprises a photolithography process.

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