A method for characterizing organic material on a silicon wafer surface

Abstract

This invention provides a method for characterizing organic matter on the surface of a silicon wafer. The method involves carbonizing the organic matter on the surface of the silicon wafer to be characterized by heating it from room temperature to a first temperature at a first preset heating rate. Then, the temperature is further increased to a second temperature at a second preset heating rate less than the first preset rate to induce carbon-silicon nucleation on the silicon wafer surface. Finally, the temperature is increased again at a third preset heating rate less than the second preset rate to form target crystal damage regions with specific damage types on the silicon wafer surface. The silicon wafer surface is then scanned, identified, and located. A scanning electron microscope is used to determine the target crystal damage regions on the silicon wafer surface that contain typical defects formed by carbon atoms intruding into the silicon crystal. The characteristic parameters of the crystal damage regions with typical defects are then characterized, thereby achieving effective characterization of trace organic matter on the silicon wafer surface.

Description

Technical Field

[0001] This invention belongs to the field of semiconductor technology and relates to a method for characterizing organic matter on the surface of silicon wafers. Background Technology

[0002] In the semiconductor chip manufacturing process, organic contamination can significantly affect the yield and reliability. For example, if there are organic residues on the silicon surface before the thermal growth of the gate oxide layer, carbon elements will accumulate at the silicon dioxide / silicon interface, thereby destroying the density and uniformity of the oxide layer structure and reducing the dielectric breakdown voltage. Organic contamination can also cause changes in the silicon surface energy and form an invisible "barrier layer", resulting in poor adhesion of CVD (chemical vapor deposition) or PVD (physical vapor deposition) films (such as polycrystalline silicon, silicon nitride, metals, etc.) and easy peeling. In semiconductor chip manufacturing, organic contaminants mainly originate from photoresist in photolithography. Although subsequent processes such as asher (dry ashing) and WET strip (wet resist removal) remove the photoresist, incomplete removal, insufficient HQDR (High-Quality Dump Rinse) cycles in the WET strip, or other reasons can cause trace amounts of organic matter in the SPM (Sulfuric Peroxide Mixture) solution to remain on the silicon wafer surface, resulting in organic contamination of the silicon wafer. The solid concentration of carbon atoms is 4 × 10⁻⁶. 17 atoms / cm³ (The oxygen content of high-purity single-crystal silicon typically needs to be controlled at 1×10 atoms / cm³) 17 When the carbon concentration in organic contaminants is close to the solid concentration (below atoms / cm³), it may affect the performance of silicon wafers. Currently, during the manufacturing process, the presence of organic contaminants on silicon wafers is typically confirmed using the EDX (Energy Dispersive X-ray Spectroscopy) function of a SEM (Scanning Electron Microscope Review) machine to analyze the presence of carbon. However, the lower limit of detection for carbon analysis using the EDX function of SEM machines is usually 1%wt, and it cannot effectively detect trace elements (the solid concentration of carbon is 4×10⁻⁶). 17 atoms / cm³, the atomic density of Si is 5×10 22 (atoms / cm³, carbon-to-silicon ratio approximately eight parts per million).

[0003] Therefore, there is an urgent need for an effective method to characterize trace organic matter on silicon wafers. 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 for characterizing organic matter on the surface of silicon wafers, so as to solve the problem that the prior art cannot effectively characterize trace carbon elements on silicon wafers.

[0005] To achieve the above and other related objectives, the present invention provides a method for characterizing organic matter on the surface of a silicon wafer, comprising the following steps:

[0006] A silicon wafer to be characterized is provided. Under an inert gas atmosphere, the silicon wafer is heated from room temperature to a first temperature at a first preset heating rate to perform a first heating stage treatment so as to carbonize the organic matter on the surface of the silicon wafer.

[0007] The carbonized silicon wafer is heated from the first temperature to the second temperature at a second preset heating rate to perform a second heating stage treatment, so that carbon-silicon nucleation occurs on the surface of the silicon wafer. The second preset heating rate is less than the first preset heating rate.

[0008] The silicon wafer after carbon-silicon nucleation is heated from the second temperature to the third temperature at a third preset heating rate and held at the third temperature for a preset time for a third heating stage, so that a target crystal damage region with a specific damage type is formed on the surface of the silicon wafer. The third preset heating rate is less than the second preset heating rate.

[0009] The surface of the silicon wafer is scanned, identified, and located to identify crystal damage areas on the surface of the silicon wafer.

[0010] The target crystal damage region with typical defects formed by carbon atom intrusion into the silicon crystal was identified using scanning electron microscopy on the surface of the silicon wafer, and the characteristic parameters of the target crystal damage region were characterized.

[0011] Optionally, the first preset heating rate range is 15 ℃ / min-22 ℃ / min.

[0012] Optionally, the first temperature range is 600 ℃-650 ℃.

[0013] Optionally, the second temperature range is 880 ℃-920 ℃.

[0014] Optionally, the specific damage type includes dislocation loops, dislocation networks, and stacking faults.

[0015] Optionally, the second preset heating rate range is 2.5 ℃ / min-3.5 ℃ / min.

[0016] Optionally, the third temperature range is 1080 ℃-1120 ℃.

[0017] Optionally, the typical defects include butterfly-shaped defects, star-shaped defects, and shallow pits.

[0018] Optionally, the third preset heating rate range is 1 ℃ / min-2 ℃ / min.

[0019] Optionally, the preset time range is 30 min-60 min.

[0020] As described above, the present invention provides a method for characterizing organic matter on the surface of a silicon wafer. This method involves carbonizing the organic matter on the surface of the silicon wafer to be characterized, then further heating to cause carbon-silicon nucleation on the silicon wafer surface, followed by another heating treatment to form target crystal damage regions with specific damage types on the silicon wafer surface. The silicon wafer surface is then scanned, identified, and located. A scanning electron microscope is used to determine the target crystal damage regions on the silicon wafer surface that have typical defects formed by carbon atoms invading the silicon crystal, and the characteristic parameters of the crystal damage regions with typical defects are characterized, thereby achieving effective characterization of trace organic matter on the surface of the silicon wafer. Attached Figure Description

[0021] Figure 1 The diagram shows a flowchart of the method for characterizing organic matter on the surface of a silicon wafer according to the present invention.

[0022] Figure 2 The image shown is a characterization diagram of the carbonization of organic matter on the silicon wafer surface according to the present invention.

[0023] Figure 3 The diagram shows a lattice dislocation.

[0024] Figure 4 The diagram shows the locations of multiple crystal damage zones on the silicon wafer surface according to the present invention.

[0025] Figure 5 The diagram shows a typical defect of the present invention.

[0026] Figure 6 The diagram shows a typical defect of the present invention. Detailed Implementation

[0027] 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.

[0028] Please see Figures 1 to 6It 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.

[0029] This invention provides a method for characterizing organic matter on the surface of a silicon wafer. Please refer to [link / reference]. Figure 1 , Figure 1 This is a schematic flowchart of a method for characterizing organic matter on a silicon wafer surface according to the present invention; wherein the method includes the following steps:

[0030] Step S1: Provide a silicon wafer to be characterized. In an inert gas atmosphere, heat the silicon wafer from room temperature to a first temperature at a first preset heating rate to perform a first heating stage treatment so as to carbonize the organic matter on the surface of the silicon wafer.

[0031] Specifically, the type and flow rate of the inert gas can be selected according to actual needs. Under the premise of carbonizing the organic matter on the silicon wafer surface, the first temperature can be selected according to actual needs. For example, nitrogen is used as the inert gas. During the first heating stage, low-molecular-weight substances such as solvents and moisture contained in the contaminants will evaporate first. The chemical bonds of the organic matter (CH, CC, CO, etc.) begin to break, and a large amount of volatile hydrocarbons, CO, CO2, etc., are generated. These gases may form a localized high-carbon atmosphere on the silicon wafer surface. In an oxygen-deficient environment, the organic matter undergoes a "cross-linking" reaction and carbonizes. Figure 2 As shown, Figure 2 The image shown is a characterization diagram of the carbonization of organic matter on the silicon wafer surface according to the present invention.

[0032] In one exemplary embodiment, the first preset heating rate ranges from 15 ℃ / min to 22 ℃ / min.

[0033] Specifically, the carbonization process and time of organic matter are controlled by controlling the heating rate. The heating rate for the first heating stage can be 15 ℃ / min, 18 ℃ / min, 20 ℃ / min, 22 ℃ / min, or any value within the range of 15 ℃ / min to 22 ℃ / min.

[0034] In one exemplary embodiment, the first temperature range is 600 °C to 650 °C.

[0035] Specifically, the first temperature can be 600 ℃, 610 ℃, 620 ℃, 630 ℃, 640 ℃, 650 ℃, or any value within the range of 600 ℃ to 650 ℃.

[0036] Step S2: The carbonized silicon wafer is heated from the first temperature to the second temperature at a second preset heating rate to perform a second heating stage treatment, so that carbon-silicon nucleation occurs on the surface of the silicon wafer. The second preset heating rate is less than the first preset heating rate.

[0037] Specifically, during the second heating stage, when the temperature reaches the second temperature, carbon atoms begin to diffuse into silicon. When the concentration of carbon atoms entering the silicon exceeds the solid solubility at that temperature in a local area, the carbon atoms begin to aggregate and combine with the surrounding silicon atoms to form tiny β-SiC nuclei. The lattice mismatch between the β-SiC nuclei and the silicon matrix has generated tiny local stresses.

[0038] Specifically, under the premise that the second temperature is higher than the first temperature, carbon atoms can combine with surrounding silicon atoms to form tiny β-SiC crystal nuclei, the value of the second temperature can be selected according to actual needs.

[0039] In one exemplary embodiment, the second temperature range is 880 °C to 920 °C.

[0040] Specifically, the second temperature can be selected as 880 ℃, 890 ℃, 900 ℃, 910 ℃, 920 ℃ or any value within the range of 880 ℃ to 920 ℃.

[0041] Specifically, by controlling the heating rate of the second heating stage to be lower than that of the first heating stage, and lowering the heating rate as the temperature increases, risks such as excessive deformation and warping due to uneven heat distribution on the silicon wafer, and wafer breakage due to uneven local thermal stress are avoided. The slow heating in the second heating stage can make the temperature field more uniform, so as to ensure the uniform growth of β-SiC crystal nuclei on the surface of the silicon wafer.

[0042] In one exemplary embodiment, the second preset heating rate ranges from 2.5 ℃ / min to 3.5 ℃ / min.

[0043] Specifically, the second preset heating rate can be selected as 2.5 ℃ / min, 2.8 ℃ / min, 3.0 ℃ / min, 3.2 ℃ / min, 3.3 ℃ / min, 3.5 ℃ / min, or any value within the range of 2.5 ℃ / min to 3.5 ℃ / min.

[0044] Step S3: The silicon wafer after carbon-silicon nucleation is heated from the second temperature to the third temperature at a third preset heating rate and held at the third temperature for a preset time for a third heating stage, so that a target crystal damage area with a specific damage type is formed on the surface of the silicon wafer. The third preset heating rate is less than the second preset heating rate.

[0045] Specifically, the third heating stage includes the process of heating from the second temperature to the third temperature and maintaining the third temperature for a preset time.

[0046] It is important to emphasize that the inert gas atmosphere is maintained throughout the entire heating process. In other words, not only is the first heating stage conducted in an inert gas atmosphere, but the second and third heating stages are also conducted in an inert gas atmosphere.

[0047] Specifically, the purpose of the third heating stage in the silicon wafer is to reduce the overall interface energy. The system tends to reduce the number of small-sized precipitates. Small SiC nuclei dissolve, and carbon atoms diffuse to larger nuclei, causing the SiC precipitates to coarsen. The lattice mismatch (exemplarily 20%) and difference in thermal expansion coefficients between the SiC precipitates and the silicon matrix generate uncoordinated local stresses. To release these enormous stresses, the silicon lattice generates crystal defects such as dislocation loops, dislocation networks, and stacking faults. Ultimately, the near-surface region of the silicon wafer is filled with SiC precipitates as the core, surrounded by dislocations (such as... Figure 3 As shown, Figure 3 (A schematic diagram of lattice dislocations) and a severely damaged crystal region surrounded by networks of stacking faults, etc. Figure 3 In this context, F represents force, b represents Burgers vector, and T represents shear stress.

[0048] Specifically, in order to ensure the full release of local stress, the third temperature is maintained for a preset time in this embodiment of the application. The preset time can be selected according to actual needs.

[0049] In one exemplary implementation, specific damage types include dislocation loops, dislocation networks, and stacking faults.

[0050] Specifically, the specific damage type refers to the target crystal damage region caused by crystal defects such as dislocation loops, stacking fault networks, and stacking layers in the silicon lattice surrounding the SiC precipitate, which are generated around the SiC precipitate.

[0051] In one exemplary embodiment, the third temperature range is 1080 °C to 1120 °C.

[0052] Specifically, the third temperature can be selected as 1080 ℃, 1000 ℃, 1120 ℃ or any value within the range of 1080 ℃-1120 ℃.

[0053] In one exemplary embodiment, the third preset heating rate is less than the second preset heating rate.

[0054] Specifically, by controlling the heating rate to be lower as the temperature increases, risks such as excessive deformation and warping caused by uneven heat distribution of silicon wafers, and wafer breakage caused by uneven local thermal stress can be avoided.

[0055] In one exemplary embodiment, the third preset heating rate ranges from 1 ℃ / min to 2 ℃ / min.

[0056] Specifically, the third preset heating rate can be selected as 1 ℃ / min, 1.2 ℃ / min, 1.4 ℃ / min, 1.6 ℃ / min, 1.8 ℃ / min, 2 ℃ / min or any value in the range of 1 ℃ / min - 2 ℃ / min.

[0057] In one exemplary implementation, the preset time range is 30 min to 60 min.

[0058] Specifically, to ensure the full release of local stress, after heating to the third temperature, the silicon wafer is further processed at the third temperature for 30 min-60 min. The time for maintaining the third temperature can be selected as 30 min, 40 min, 45 min, 50 min, 55 min, 60 min, or any value within the range of 30 min-60 min.

[0059] In one exemplary embodiment, after the third heating stage of the silicon wafer, the method further includes cooling the silicon wafer.

[0060] Specifically, the cooling rate of the cooling process can be selected according to actual needs. For example, a fixed cooling rate can be removed, allowing the silicon wafer to cool naturally to room temperature for subsequent scanning.

[0061] Step S4: Scan the silicon wafer surface, identify and locate the crystal damage area on the silicon wafer surface.

[0062] Specifically, a defect scanning machine can be used to scan the surface of a silicon wafer to identify all crystal damage areas on the surface. In other words, there are multiple crystal damage areas on the silicon wafer surface. These multiple crystal damage areas are then marked to pinpoint their location. Figure 4 As shown, Figure 4 The diagram shows multiple crystal damage areas on the surface of a silicon wafer, with red markings representing crystal damage areas.

[0063] Step S5: Use scanning electron microscopy to identify the target crystal damage region with typical defects formed by carbon atoms invading the silicon crystal in the crystal damage region on the silicon wafer surface, and characterize the characteristic parameters of the target crystal damage region.

[0064] Specifically, based on location markers, scanning electron microscopy is used to locate each crystal damage region on the silicon wafer surface, and to identify the target crystal damage region containing typical defects formed by carbon atoms intruding into the silicon crystal. It should be noted that the multiple crystal damage regions on the silicon wafer surface include the target crystal damage region; that is, the crystal damage regions on the silicon wafer surface include, but are not limited to, the target crystal damage region, which is one or more of the multiple crystal damage regions.

[0065] In one exemplary embodiment, typical defects formed by carbon atoms intruding into a silicon crystal include butterfly defects, star defects, and shallow etch pits.

[0066] For example, using scanning electron microscopy (SEM) to determine that the defect shape of a certain crystal damage area is a butterfly defect, meaning that the crystal damage area with a butterfly defect is the target crystal damage area formed by carbon atoms invading the silicon crystal; using SEM to determine that the defect shape of a certain crystal damage area is a star defect, meaning that the crystal damage area with a star defect is the target crystal damage area formed by carbon atoms invading the silicon crystal; using SEM to determine that the defect shape of a certain crystal damage area is a shallow etch pit, meaning that the crystal damage area with a shallow etch pit is the target crystal damage area formed by carbon atoms invading the silicon crystal. It should be noted that the typical defects formed by carbon atoms invading the silicon crystal characterize the unique defect morphology features of the crystal damage area formed by carbon atoms invading the silicon crystal. Other contaminants on the silicon wafer surface, after being subjected to the heating treatment by the method of this application, either do not produce crystal damage areas or produce crystal damage areas with defect characteristics different from the typical defects formed by carbon atoms invading the silicon crystal. Figure 5 and 6 As shown, Figure 5 The typical defect morphology shown is a butterfly-shaped defect. Figure 6 The typical defect morphology shown is a butterfly-shaped defect.

[0067] Specifically, the characteristic parameters may include area, quantity, density, or other characteristic parameters. For example, after determining the target crystal damage region formed by carbon atoms invading the silicon crystal, a defect scanning machine can be used to determine the area of ​​the target crystal damage region formed by carbon atoms invading the silicon crystal. For example, the size of the target crystal damage region is approximately 0.1 µm to 1 µm. The characteristic parameters of the target crystal damage region depend on the degree of carbon contamination.

[0068] Specifically, this application first involves heating the silicon wafer in an N2 gas atmosphere from room temperature to 650 °C (the first preset heating rate is 20 °C / min). During this first heating stage, low-molecular-weight substances such as solvents and moisture contained in the organic contaminants will evaporate first. The chemical bonds of the organic matter (CH, CC, CO, etc.) will begin to break, and a large amount of volatile hydrocarbons, CO, CO2, and other gases will be generated. These gases may form a localized high-carbon atmosphere on the surface of the silicon wafer. In an oxygen-deficient environment, the organic matter undergoes a "cross-linking" reaction and carbonizes (e.g., Figure 2 (As shown). Then, a second heating stage is performed (the second preset heating rate is 3 ℃ / min): during the heating from 650 ℃ to 900 ℃, carbon atoms begin to diffuse into the silicon. When the concentration of carbon atoms entering the silicon exceeds the solid solubility at that temperature in a local area, carbon atoms begin to aggregate and combine with surrounding silicon atoms to form tiny β-SiC nuclei. The lattice mismatch between the β-SiC nuclei and the silicon matrix has generated small local stresses. Finally, the silicon wafer undergoes a third heating stage (the second preset heating rate is 1.5 ℃ / min): during the heating from 900 ℃ to 1100 ℃ and holding at 1100 ℃ for 40 min, in order to reduce the overall interface energy, the system tends to reduce the number of small-sized precipitates. Small-sized SiC nuclei dissolve, and carbon atoms diffuse to larger nuclei, leading to coarsening of the SiC precipitates and a huge lattice mismatch between the SiC precipitates and the silicon matrix (lattice mismatch rate can reach 20%). The difference in lattice mismatch rate (a parameter used to quantify the degree of alignment of atoms in two crystals) and thermal expansion coefficients creates uncoordinated local stresses. To release these enormous stresses, the silicon lattice generates crystal defects such as dislocation loops, dislocation networks, and stacking faults. Ultimately, the surface area of ​​the silicon wafer is filled with severely damaged crystal regions, with SiC precipitates at the core and surrounded by networks of dislocations and stacking faults. By scanning the silicon wafer surface with a defect scanning machine, all crystal damage regions on the silicon wafer surface are identified and their locations are marked. Then, a scanning electron microscope is used to observe the defect type of each crystal damage region. Crystal damage regions with typical defects formed by carbon atoms invading the silicon crystal are identified as target crystal damage regions formed by carbon atoms invading the silicon crystal. The area of ​​the target crystal damage region with typical defects is determined using a defect scanning machine. Typical defects include butterfly defects, star defects, and shallow etch pits.

[0069] This invention provides a method for characterizing organic matter on the surface of a silicon wafer. The method involves carbonizing the organic matter on the surface of the silicon wafer, then further heating it to induce carbon-silicon nucleation, followed by another heating process to form crystal damage regions on the surface. The silicon wafer surface is then scanned, identified, and located. Using a scanning electron microscope, a crystal damage region with typical defects formed by carbon atoms intruding into the silicon crystal is identified among all the crystal damage regions on the silicon wafer surface and designated as the target crystal damage region. The characteristic parameters of the target crystal damage region with typical defects are then characterized, thereby achieving effective characterization of trace amounts of carbon elements in trace organic matter on the silicon wafer surface.

[0070] 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 characterizing organic matter on the surface of a silicon wafer, characterized in that, Includes the following steps: A silicon wafer to be characterized is provided. Under an inert gas atmosphere, the silicon wafer is heated from room temperature to a first temperature at a first preset heating rate to perform a first heating stage treatment so as to carbonize the organic matter on the surface of the silicon wafer. The carbonized silicon wafer is heated from the first temperature to the second temperature at a second preset heating rate to perform a second heating stage treatment, so that carbon-silicon nucleation occurs on the surface of the silicon wafer. The second preset heating rate is less than the first preset heating rate. The silicon wafer after carbon-silicon nucleation is heated from the second temperature to the third temperature at a third preset heating rate and held at the third temperature for a preset time for a third heating stage, so that a target crystal damage region with a specific damage type is formed on the surface of the silicon wafer. The third preset heating rate is less than the second preset heating rate. The surface of the silicon wafer is scanned, identified, and located to identify crystal damage areas on the surface of the silicon wafer. The target crystal damage region with typical defects formed by carbon atom intrusion into the silicon crystal was identified using scanning electron microscopy on the surface of the silicon wafer, and the characteristic parameters of the target crystal damage region were characterized.

2. The method for characterizing organic matter on the surface of a silicon wafer according to claim 1, characterized in that: The first preset heating rate range is 15 ℃ / min-22 ℃ / min.

3. The method for characterizing organic matter on the surface of a silicon wafer according to claim 1, characterized in that: The first temperature range is 600 ℃-650 ℃.

4. The method for characterizing organic matter on the surface of a silicon wafer according to claim 1, characterized in that: The second temperature range is 880 ℃-920 ℃.

5. The method for characterizing organic matter on the surface of a silicon wafer according to claim 1, characterized in that: The specific damage types include dislocation loops, dislocation networks, and stacking faults.

6. The method for characterizing organic matter on the surface of a silicon wafer according to claim 1, characterized in that: The second preset heating rate range is 2.5 ℃ / min-3.5 ℃ / min.

7. The method for characterizing organic matter on the surface of a silicon wafer according to claim 1, characterized in that: The third temperature range is 1080 ℃-1120 ℃.

8. The method for characterizing organic matter on the surface of a silicon wafer according to claim 1, characterized in that: The typical defects include butterfly-shaped defects, star-shaped defects, and shallow pits.

9. The method for characterizing organic matter on the surface of a silicon wafer according to claim 1, characterized in that: The third preset heating rate range is 1 ℃ / min-2 ℃ / min.

10. The method for characterizing organic matter on the surface of a silicon wafer according to claim 1, characterized in that: The preset time range is 30 min-60 min.

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