Method for detecting pinhole defects of heavily doped phosphorus arsenic substrate epitaxial wafer

Abstract

The present application relates to a kind of heavy phosphorus arsenic substrate epitaxial wafer pinhole defect detection method, the semiconductor wafer detection technical field, for the high misjudgment rate of existing SPX equipment single optical detection to heavy wafer, small pinhole is prone to missed detection and the problem that destructive detection of chemical corrosion cannot mass detect, after non-destructive cleaning pretreatment to the wafer to be measured, based on the existing SPX equipment platform simultaneously opens dark field scattering, phase difference and polarization optical imaging channel, to shield high carrier background noise and collect multi-channel signal;Subsequently, through multidimensional collaborative feature algorithm screening, when defect area simultaneously satisfies dark field signal mutation, phase difference step change and polarization signal significant attenuation, it is determined as pinhole, only single channel abnormal particle, scratch and other pseudo-defects are removed;Finally, output binary screening result.Non-destructive mass detection is realized, pinhole and pseudo-defect are accurately distinguished, misjudgment and missed detection rate are greatly reduced, and existing hardware is reused, which is low in cost and does not affect production line rhythm.

Description

Technical Field

[0001] This invention relates to the field of semiconductor wafer inspection technology, specifically to a method for detecting pinhole defects in heavily phosphorus-arsenic-doped epitaxial wafers. Background Technology

[0002] Heavily phosphorus-doped (Ph++) and heavily arsenic-doped (As++) epitaxial wafers are core materials for semiconductor power devices and radio frequency devices, playing a crucial role in high-frequency, high-voltage, and high-current operating scenarios. However, during the manufacturing process of these heavily doped wafers, pinhole defects are easily generated due to factors such as epitaxial growth processes and stress distribution. Pinhole defects penetrate the epitaxial layer, directly damaging the vertical electrical structure of the device, leading to device breakdown, a surge in leakage current, or even failure, which has a fatal impact on the yield and reliability of downstream devices. Therefore, accurate screening for pinhole defects before wafers leave the factory is crucial.

[0003] However, existing mass production inspection methods for detecting pinhole defects in heavily doped Ph++ and As++ wafers have significant technical bottlenecks and limitations: I. Conventional optical inspection equipment is severely limited, resulting in both false positives and false negatives: Currently, mainstream SPX optical inspection equipment used in mass production typically employs a single optical imaging mode. For Ph++ and As++ ultra-high doped wafers, the extremely high carrier concentration on their surface generates strong background scattering interference, making it impossible for the equipment to effectively distinguish between true pinhole defects and pseudo-defects such as particles, scratches, surface roughness, and lattice dislocations, leading to an extremely high false positive rate. Furthermore, for micron-sized pinholes, conventional optical methods lack sufficient resolution, making false negatives highly likely.

[0004] Second, chemical corrosion testing is destructive and cannot achieve full inspection: Although traditional chemical corrosion methods can reveal pinholes, they are destructive tests that not only damage the usability of the wafers but also take a long time. They cannot be applied to online full inspection of mass-produced wafers and can only be used as a sampling verification method. They cannot achieve full screening of all wafers and there are blind spots in control.

[0005] Third, there is a lack of signal differentiation methods for heavily doped electrical characteristics: the existing single optical imaging mode fails to shield signals and extract features from the high conductivity of heavily doped wafers. The optical signal characteristics of pinholes and ordinary pseudo-defects are very similar, resulting in extremely low detection efficiency and high control risks in high-speed mass production environments.

[0006] Fourth, lack of dedicated non-destructive inspection solutions: The industry currently lacks a dedicated pinhole inspection solution that is suitable for mass production, non-destructive, and highly discriminative. This results in the inability to accurately screen pinhole defects in mass-produced wafers, posing a significant risk that defective products will flow into subsequent processes.

[0007] In summary, there is an urgent need for a non-destructive detection method that is compatible with Ph++ and As++ mass-produced wafers, can optimize existing SPX equipment, and can efficiently and accurately distinguish pinholes from other pseudo-defects. Summary of the Invention

[0008] This invention addresses the shortcomings of existing technologies by providing a pinhole defect detection method for heavily phosphorus-arsenic-doped epitaxial wafers. It tackles the problems of high false positive rates, easy omission of tiny pinholes, and the inability to perform full-scale inspection in mass production using existing SPX equipment with its single optical inspection. After non-destructive cleaning pretreatment of the wafer, the method simultaneously activates dark-field scattering, phase difference, and polarization optical imaging channels on the existing SPX equipment platform to shield high-carrier background noise and acquire multi-channel signals. Subsequently, a multi-dimensional collaborative feature algorithm is used for screening. When a defect region simultaneously meets the criteria of abrupt dark-field signal change, a step change in phase difference, and significant attenuation of polarization signal, it is identified as a pinhole. False defects such as particles and scratches with only a single channel abnormality are discarded. Finally, a binary screening result is output. This method achieves non-destructive mass production full inspection, accurately distinguishes between pinholes and false defects, significantly reduces false positives and omissions, reuses existing hardware at low cost, and does not affect production line cycle time.

[0009] The above-mentioned technical problems of the present invention are mainly solved by the following technical solutions: A method for detecting pinhole defects in a heavily phosphorus-arsenic-doped epitaxial wafer includes the following steps: Step 1: Non-destructive pretreatment of wafers; Non-destructive cleaning and drying of heavily phosphorus-doped or heavily arsenic-doped epitaxial wafers to be tested in mass production to remove loose particles and water stains on the surface without changing the wafer's structure and electrical properties.

[0010] Step 2: Multi-channel differential signal acquisition of SPX equipment; Based on the hardware platform of SPX detection equipment, the dark field scattering imaging channel, phase difference imaging channel and polarization optical imaging channel are simultaneously activated to scan and acquire the pre-processed wafer surface. At the same time, the carrier background noise of the heavily doped wafer is shielded, and the dark field scattering signal, phase difference signal and polarization reflection signal under the same spatial coordinates on the wafer surface are acquired respectively.

[0011] Step 3: Pinhole-specific feature algorithm screening; Based on the collected multi-channel signals, perform multi-dimensional collaborative feature judgment to extract multi-channel signal features of the defect area. If the defect area simultaneously meets the conditions of "sudden change in dark field signal + step change in phase difference + significant attenuation of polarization signal", it is judged as a pinhole defect; if the defect only has a single channel signal abnormality, it is judged as a pseudo-defect and is removed.

[0012] Step 4: Batch rapid screening output: Scan the entire wafer and output the judgment results based on the pinhole-specific feature algorithm. Wafers with pinhole defects are marked as defective, and wafers without pinhole defects are judged as qualified.

[0013] Preferably, the dark field scattering imaging channel is used to acquire scattering signals of the wafer surface morphology and obtain surface microstructure change characteristics; the phase difference imaging channel is used to acquire optical phase change signals caused by the abrupt change in wafer thickness at the pinhole; and the polarization optical imaging channel is used to acquire polarization light reflection difference signals between the three-dimensional structure of the pinhole and the planar wafer surface.

[0014] Preferably, the pseudo-defects include particles, scratches, surface roughness, and lattice dislocations; the specific logic of the multi-dimensional collaborative feature determination is as follows: construct a multi-channel signal superposition matrix, extract the dark field scattering signal, phase difference signal, and polarization reflection signal under the same spatial coordinates, and determine the pinhole defect only when the signals of the three channels simultaneously exhibit specific abrupt change characteristics at the coordinates, thereby eliminating signal confusion caused by single-channel detection.

[0015] As a preferred option, multi-channel signal acquisition is a synchronous, non-destructive acquisition method that does not involve chemical etching or processing steps that damage the wafer surface. It is suitable for 100% full-volume online detection of heavily phosphorus-doped or heavily arsenic-doped epitaxial wafers.

[0016] As a preferred option, full-screening only outputs qualitative results indicating the presence or absence of pinhole defects, without performing quantitative analysis of defect size, in order to match the existing inspection cycle of the production line's SPX equipment.

[0017] A non-destructive testing system for pinhole defects in heavily phosphorus-arsenic-doped epitaxial wafers, characterized in that it is built on the SPX testing equipment hardware platform and includes: The pretreatment module is used for non-destructive cleaning and drying of heavily phosphorus-doped or heavily arsenic-doped epitaxial wafers.

[0018] The multi-channel signal acquisition module is used to simultaneously activate the dark field scattering imaging channel, the phase difference imaging channel, and the polarization optical imaging channel to acquire dark field scattering signals, phase difference signals, and polarization reflection signals under the same spatial coordinates on the wafer surface, while shielding carrier background noise.

[0019] The algorithm recognition module is used to perform multi-dimensional collaborative feature judgment, identify defects that simultaneously meet the criteria of "abrupt change in dark field signal + step change in phase difference + significant attenuation of polarization signal" as pinhole defects, and eliminate pseudo-defects such as particles and scratches that only have a single channel signal abnormality.

[0020] The result output module is used to output a binary determination result of whether there are pinhole defects on the entire wafer, which is suitable for high-speed mass production inspection.

[0021] Preferably, the multi-channel signal acquisition module reuses the hardware optical components of existing mass-produced SPX equipment and uses software configuration to synchronously trigger dark field, phase difference and polarization channels for image acquisition.

[0022] A computer-readable storage medium having a computer program stored thereon, which, when executed by a processor, implements a method for detecting pinhole defects in a heavily phosphorus- and arsenic-doped epitaxial wafer according to any one of claims 1 to 5.

[0023] The present invention can achieve the following effects: This invention provides a method for detecting pinhole defects in heavily phosphorus-arsenic-doped epitaxial wafers. Compared with existing technologies, this method addresses the pain points of detecting heavily doped Ph++ and As++ wafers in mass production by abandoning destructive methods such as chemical etching. Based on the SPX equipment hardware platform, it performs signal acquisition and multi-dimensional feature algorithm optimization, achieving non-destructive, mass-production-grade, highly efficient, and accurate pinhole detection. It has the following significant advantages: I. Non-destructive mass production full inspection: The entire process involves no chemical corrosion, no mechanical contact or damage, and does not change the wafer's structure or electrical properties. It can be directly used for 100% full online inspection of Ph++ and As++ mass production wafers, completely solving the problem that traditional etching methods can only perform sampling inspections and meeting the requirements of batch production control.

[0024] II. Significantly Reduced Equipment False Positive Rate: By simultaneously activating multi-channel acquisition of dark field scattering, phase difference, and polarization optics, and utilizing the superposition of multi-channel optical signals, the high-carrier background noise of heavily doped wafers is effectively shielded. Simultaneously, based on the "three-channel coordinated anomaly" judgment logic, pinholes are accurately distinguished from interference defects such as particles, scratches, and surface roughness, solving the industry pain point of confusion caused by single dark field detection signals.

[0025] III. Significantly Enhanced Detection Capability of Tiny Pinholes: The introduction of phase difference and polarization channels enables the sensitive capture of thickness abrupt changes and three-dimensional structural polarization reflection differences caused by micron-sized pinholes. Compared to conventional SPX single-dark-field detection, this significantly enhances the ability to capture the unique optical signals of tiny pinholes, thereby significantly reducing the false negative rate.

[0026] IV. Perfectly Matched Detection Efficiency to Production Line Cycle: In the screening output stage, this invention only determines the presence or absence of pinhole defects (binary qualitative output) without performing complex quantitative analysis. This simplified approach significantly improves data processing speed, and the detection speed perfectly matches the mass production cycle of the original SPX equipment, without slowing down production line capacity.

[0027] V. Low hardware reuse cost and easy rapid deployment: This method relies on the optical hardware platform of existing mass-produced SPX equipment, mainly through software configuration for synchronous multi-channel acquisition and algorithm upgrades and optimizations. It requires no new large and expensive testing equipment or complex physical mechanical structure modifications. The deployment cost is extremely low, facilitating rapid promotion and adoption in existing production lines. Detailed Implementation

[0028] The technical solution of the invention will be further described in detail below through examples.

[0029] Example: A method for detecting pinhole defects in a heavily phosphorus-arsenic-doped epitaxial wafer, comprising the following steps: S1: Basic Non-destructive Pre-processing of Wafers. Standard mass-production-grade cleaning and drying are performed on heavily phosphorus-doped or heavily arsenic-doped epitaxial wafers awaiting mass production testing. For example, standard SC-1 / SC-2 chemical solutions are used for cleaning, followed by megasonic-assisted particle removal and drying using Marangoni drying technology. This step aims to remove loose particles, organic matter, and water stains adhering to the wafer surface, while ensuring that the cleaning process does not alter the wafer's bulk structure, surface morphology, or highly doped electrical properties, fully meeting the requirements of mass production online non-destructive testing.

[0030] S2: Multi-channel differential signal acquisition in SPX equipment. The pre-processed wafer is transferred to the existing mass-produced SPX optical inspection equipment. On the SPX equipment hardware platform, the dark field scattering imaging channel, phase difference imaging channel, and polarization optical imaging channel are simultaneously activated via software configuration to scan and acquire data from the entire wafer. Due to the extremely high carrier concentration of heavily phosphorus-doped and heavily arsenic-doped wafers, conventional dark field detection is subject to severe carrier background scattering interference. This embodiment effectively shields background carrier noise through synchronous acquisition and differential processing of multi-channel optical signals. The signal acquisition principle of each channel is as follows: Dark-field scattering imaging channel: Illuminate the wafer surface with oblique light and collect the scattering signal of the surface morphology to capture the dark-field signal abrupt change caused by microstructural abrupt change; Phase difference imaging channel: Pinhole defects are essentially porous structures, causing abrupt changes in the local thickness of the wafer in that area. This channel uses coherent optical interferometry or phase-shifting techniques to acquire the optical phase step change signal caused by the abrupt thickness change; Polarization optical imaging channel: Taking advantage of the physical difference between the three-dimensional hole structure of the pinhole and the flat wafer surface, this channel emits a beam of light with a specific polarization state (such as P-polarization or S-polarization) and collects the signal of the change in polarization light reflection characteristics at the edge and bottom of the hole, which manifests as a significant attenuation or depolarization effect of the polarization signal.

[0031] S3: Pinhole-specific feature filtering algorithm. Based on multi-channel acquired image signals, the system constructs a multi-dimensional signal matrix under the same spatial coordinates and executes multi-dimensional collaborative feature determination logic: Pinhole detection: A chip is identified as a pinhole defect when a certain coordinate region of a wafer simultaneously meets the following three conditions: a sudden change in local scattering signal in the dark field channel; a significant step change in the phase difference channel; and a significant attenuation of the reflected polarization state signal in the polarization channel.

[0032] False defect elimination: False defects such as particles, scratches, surface roughness, or lattice dislocations typically only exhibit signal anomalies in a single channel because they lack the characteristics of penetrating holes. For example, surface particles may produce bright spots in the dark field channel, but show no significant steps or attenuation in the phase difference and polarization channels; scratches often exhibit linear characteristics and lack polarization attenuation due to hole structures. Therefore, signals with only single-channel anomalies are directly rejected by the algorithm and are not classified as pinholes.

[0033] S4: Batch Rapid Screening Output. After scanning and algorithmic identification of the entire wafer, the system performs a binary (Pass / Fail) judgment output. It only outputs the presence or absence of pinhole defects: if a pinhole defect satisfying the S3 judgment logic exists in any area of ​​the entire wafer, the wafer is marked as defective, and the defect coordinates can be recorded for re-inspection; if no pinhole defects are found, it is judged as acceptable. This step abandons complex quantitative analysis of defect dimensions, significantly improving data processing speed and perfectly matching the mass production cycle of the SPX equipment on the production line, achieving 100% full-batch inspection.

[0034] A pinhole defect detection system for heavily phosphorus-arsenic-doped epitaxial wafers is provided. This system is built upon a modified existing SPX inspection equipment hardware platform and includes the following functional modules: 1. Pre-processing module: includes a standard semiconductor cleaning tank and a drying unit, used to perform non-destructive cleaning and drying of the wafer in S1 of Example 1.

[0035] II. Multi-channel signal acquisition module: This module reuses the optical components and sensors of the SPX equipment, and synchronously triggers the dark field light source, phase difference interference component, and polarization optical path component through the control unit. During the scanning process, this module acquires dark field scattering images, phase difference images, and polarization images of the same physical location on the wafer surface in real time, and forms a multi-channel signal set through time synchronization or spatial coordinate alignment technology.

[0036] III. Algorithm Recognition Module: This module incorporates multi-dimensional feature filtering logic and receives data from the multi-channel signal acquisition module. It utilizes feature extraction algorithms (such as edge detection, grayscale gradient calculation, and polarization calculation) to extract abnormal features from each channel and performs an AND logic judgment of "simultaneous abnormality in all three channels = pinhole," effectively filtering out false single-channel misjudgment signals such as particles and scratches.

[0037] IV. Result Output Module: Receives the results from the algorithm recognition module, performs binary classification of wafers, and directly outputs "qualified / unqualified" commands through the front-end interface of the equipment or the production line MES system to control the wafer transfer robot to divert the wafers to the good or defective area.

[0038] A computer-readable storage medium stores a computer program thereon. When executed by the main control processor of an SPX inspection device, the computer program can perform steps S2 to S4: namely, controlling the SPX device hardware to synchronously activate the dark field, phase difference, and polarization channels for image acquisition; retrieving multi-channel image data for feature extraction and AND logic determination; and finally outputting a binary pinhole defect detection result. This storage medium enables existing SPX devices to achieve high-precision, non-destructive pinhole detection capabilities without adding complex physical optical and mechanical structures, simply through program upgrades.

[0039] In summary, this method for detecting pinhole defects in heavily phosphorus-arsenic-doped epitaxial wafers abandons the destructive sampling method of traditional chemical etching. It utilizes existing SPX equipment hardware reuse combined with multi-channel optical acquisition and algorithm optimization to effectively shield against carrier background noise interference from heavily doped wafers. It not only accurately distinguishes pinholes from conventional pseudo-defects (particles / scratches, etc.), solving the industry pain point of extremely high false positive rates in single dark-field detection, but also significantly improves the ability to detect minute pinholes. Furthermore, the detection speed meets production line cycle time, demonstrating extremely high industrial practical value and economic efficiency.

[0040] The above description is only a specific embodiment of the present invention, but the structural features of the present invention are not limited thereto. Any changes or modifications made by those skilled in the art within the scope of the present invention are covered by the patent scope of the present invention.

Claims

1. A method for detecting pinhole defects in epitaxial wafers with heavily phosphorus-arsenic-doped substrates, characterized in that, The following steps are included: Step 1: Non-destructive pretreatment of wafers; Non-destructive cleaning and drying of heavy phosphorus-doped or heavy arsenic-doped epitaxial wafers to be tested in mass production to remove loose particles and water stains from the surface without changing the wafer's structure and electrical properties. Step 2: Acquisition of multi-channel differentiated signals from the SPX device; Based on the SPX inspection equipment hardware platform, the dark field scattering imaging channel, phase difference imaging channel and polarization optical imaging channel are simultaneously activated to scan and acquire the pre-processed wafer surface. At the same time, the carrier background noise of the heavily doped wafer is shielded, and the dark field scattering signal, phase difference signal and polarization reflection signal under the same spatial coordinates on the wafer surface are acquired respectively. Step 3: Pinhole-specific feature filtering; Based on the acquired multi-channel signals, multi-dimensional collaborative feature determination is performed to extract the multi-channel signal features of the defect area. If the defect area simultaneously meets the conditions of "abrupt change in dark field signal + step change in phase difference + significant attenuation of polarization signal", it is determined to be a pinhole defect. If the defect only has a single channel signal abnormality, it is determined to be a false defect and is removed. Step 4: Batch rapid screening output: Scan the entire wafer and output the judgment results based on the pinhole-specific feature algorithm. Wafers with pinhole defects are marked as defective, and wafers without pinhole defects are judged as qualified.

2. The method for detecting pinhole defects in heavily phosphorus-arsenic-doped epitaxial wafers according to claim 1, characterized in that: The dark field scattering imaging channel is used to acquire scattering signals of the wafer surface morphology and obtain surface microstructure change characteristics; the phase difference imaging channel is used to acquire optical phase change signals caused by abrupt changes in wafer thickness at pinholes; the polarization optical imaging channel is used to acquire polarization light reflection difference signals between the three-dimensional structure of the pinholes and the planar wafer surface.

3. The method for detecting pinhole defects in heavily phosphorus-arsenic-doped epitaxial wafers according to claim 1, characterized in that: The pseudo-defects include particles, scratches, surface roughness, and lattice dislocations; the specific logic of the multi-dimensional collaborative feature determination is as follows: construct a multi-channel signal superposition matrix, extract the dark field scattering signal, phase difference signal, and polarization reflection signal under the same spatial coordinates, and determine the pinhole defect only when the signals of the three channels simultaneously exhibit specific abrupt change characteristics at the coordinates, thereby eliminating signal confusion caused by single-channel detection.

4. The method for detecting pinhole defects in heavily phosphorus-arsenic-doped epitaxial wafers according to claim 1, characterized in that: Multi-channel signal acquisition is a synchronous, non-destructive acquisition method that does not involve chemical etching or processing steps that damage the wafer surface. It is suitable for 100% full-volume online detection of heavily phosphorus-doped or heavily arsenic-doped epitaxial wafers.

5. The method for detecting pinhole defects in heavily phosphorus-arsenic-doped epitaxial wafers according to claim 1, characterized in that: The full-screening only outputs qualitative results indicating the presence or absence of pinhole defects, without performing quantitative analysis of defect size, in order to match the existing inspection cycle of the production line's SPX equipment.

6. A non-destructive testing system for pinhole defects in epitaxial wafers with heavily phosphorus-arsenic-doped substrates, characterized in that, Built on the SPX testing equipment hardware platform, including: The pretreatment module is used for non-destructive cleaning and drying of heavily phosphorus-doped or heavily arsenic-doped epitaxial wafers; The multi-channel signal acquisition module is used to simultaneously activate the dark field scattering imaging channel, the phase difference imaging channel, and the polarization optical imaging channel to acquire dark field scattering signals, phase difference signals, and polarization reflection signals under the same spatial coordinates on the wafer surface, while shielding carrier background noise. The algorithm recognition module is used to perform multi-dimensional collaborative feature judgment, identify defects that simultaneously satisfy the conditions of dark field signal abrupt change + phase difference step change + significant attenuation of polarization signal as pinhole defects, and eliminate pseudo-defects such as particles and scratches that only have a single channel signal abnormality. The result output module is used to output a binary determination result of whether there are pinhole defects on the entire wafer, which is suitable for high-speed mass production inspection.

7. The method for detecting pinhole defects in heavily phosphorus-arsenic-doped epitaxial wafers according to claim 6, characterized in that: The multi-channel signal acquisition module reuses the hardware optical components of existing mass-produced SPX equipment and uses software configuration to synchronously trigger dark field, phase difference and polarization channels for image acquisition.

8. A computer-readable storage medium having a computer program stored thereon, characterized in that, When executed by a processor, the computer program implements the method for detecting pinhole defects in a heavily phosphorus-arsenic-doped epitaxial wafer according to any one of claims 1 to 5.