Wafer surface metal impurity collection device, detection system and method

Abstract

The invention relates to wafer production, and particularly provides a wafer surface metal impurity collection device, a detection system and a method, and the collection device comprises an application unit which is used for applying an extracting solution to a designated position of a wafer surface; the moving unit is used for realizing relative movement between the wafer and the light emitting end of the laser, so that exciting light emitted by the laser penetrates through the extracting solution and is incident to the specified position on the surface of the wafer; and the collecting unit is used for collecting the extracting solution on the surface of the wafer. The method has the advantages of accurate detection and the like, and is applied to wafer production.

Description

TECHNICAL FIELD

[0001] The present application relates to wafer production, in particular to a wafer surface metal impurity collection device, a detection system and a method. BACKGROUND

[0002] Wafer metal content is one of the important parameters affecting the performance of semiconductor chips. Wafer metal content refers to the content of metal elements in wafer surface impurity detection. As the feature size of IC devices continues to shrink, advanced processes are very demanding on the control level of ultra-trace metal ions on the wafer surface. Therefore, it is very important to monitor the metal contamination content on the wafer surface.

[0003] Although TXRF (Total Reflection X-ray Fluorescence) and TOF-SIMS (Time of Flight Secondary Ion Mass Spectrometry) can detect the metal content on the wafer surface, based on the advantages of detection limit, detection flux, instrument price, etc., ICP-MS (Inductively Coupled Plasma Mass Spectrometry) is the most widely used. When wafer metal impurity analysis is based on ICP-MS, it is particularly important to efficiently collect wafer surface metal impurities without introducing additional metal contamination in order to obtain objective test conditions.

[0004] Currently, VPD (Vapor Phase Decomposition) technology has gradually become the mainstream wafer surface metal impurity extraction technology. The principle of the technology is to place a silicon wafer in a VPD chamber and expose it to HF vapor to dissolve the natural oxide or thermal oxidation SiO2 surface layer. Then, an extraction liquid drop (usually 2% HF / 2% H2O2) is placed on the wafer, and the liquid drop is rolled on the wafer surface to collect impurity elements. Finally, ICP-MS is used for analysis. In addition, when analyzing metal impurities in epitaxial silicon, polysilicon layers or unoxidized pure silicon substrates, ozone needs to be added to the HF vapor for etching. The extraction liquid can only extract the impurities adhered by the surface process or deposited after HF acid dissolution, and when there is a need to analyze noble metals, the extraction liquid needs to be replaced with 5% aqua regia. In addition, wafer metal contamination may be distributed on the surface (adhesion) and the oxide layer, and also exists in the interface layer and even the wafer substrate. When the contamination is in the interface layer, the extraction liquid cannot extract materials (SiC, GaN, etc.) that cannot be decomposed by hydrofluoric acid vapor. The extraction efficiency of VPD is relatively limited, which may cause false negatives and other results, leading to misjudgment of quality control. In the manual extraction method, the wafer is slowly shaken by using a vacuum suction pen, so that the extraction liquid can slide through all the areas on the surface of the silicon wafer. This method requires a high level of skill for the operator, and has the same limitations as the automatic VPD technology. SUMMARY

[0005] To solve the above problems in the prior art, the present application provides a wafer surface metal impurity collection device.

[0006] The purpose of the present application is achieved by the following technical solutions. A wafer surface metal impurity collection device, comprising: An application unit for applying an extraction liquid to a designated position on the wafer surface; A laser and a moving unit for realizing relative movement between the wafer and the light emitting end of the laser, so that the excitation light emitted by the laser passes through the extraction liquid and is incident on the designated position on the wafer surface; A collection unit for collecting the extraction liquid on the wafer surface.

[0007] The purpose of the present application is also to provide a wafer surface metal impurity detection system, which is achieved by the following technical solutions.

[0008] A wafer surface metal impurity detection system, comprising a detection device; characterized in that the detection system further comprises: The collection device of the present application; The detection device is used to detect the extraction liquid collected by the collection unit to obtain the content of metal impurities.

[0009] The application also aims to provide a wafer surface metal impurity detection method.

[0010] A wafer surface metal impurity detection method comprises the following steps: (A1) A applying unit applies an extracting solution to a designated position on the wafer surface; (A2) A moving unit realizes relative movement between the wafer and the light-emitting end of a laser, and the excitation light output by the laser passes through the extracting solution and is incident on the designated position; (A3) The metal impurities on the wafer surface are ablated and enter the extracting solution; (A4) The extracting solution is collected and sent to a detection device for analysis to obtain the content of the metal impurities.

[0011] Compared with the prior art, the application has the following beneficial effects: 1. High extraction efficiency; Compared with the traditional chemical method, all metal impurities are collected in the form of particles, forming a nanoscale colloidal solution or a micrometer-sized suspension, which eliminates the potential technical risk of low extraction efficiency of the traditional chemical extraction method (such as VPD technology) caused by different occurrence forms of metal impurities, and ensures the objectivity and reliability of the metal impurity collection process; The impurities at different depths (um level) of the wafer are extracted by controlling the energy and repetition frequency of the laser; The ablation behavior of each position on the wafer is consistent, which can eliminate the potential risk of uneven extraction in the VPD extraction process; According to the detection requirements, the amount of extracting solution droplets / liquid layer is flexibly adjusted under the premise of ensuring the collection efficiency of nanometer / micrometer particles; 2. Safe and environmentally friendly; In the wafer surface metal impurity extraction process, pure HF, ozone and other chemicals are not required, which is a more green extraction technology, and reduces the experimental risk; 3. Widely applicable; Different wafer metal impurities can be extracted, such as VPD, which requires pure hydrofluoric acid to dissolve the oxide layer, even needs to obtain the oxide layer first, and the impurity extraction of wafers that cannot be dissolved by HF acid.

[0012] The collection device, transmission device and ICP-MS mass spectrometry technology are combined to realize a fully automatic online work process, which can also be performed manually offline. BRIEF DESCRIPTION OF DRAWINGS

[0013] The disclosure of the present application will become more apparent with reference to the drawings. It is readily understood by the skilled in the art that the drawings are only used to illustrate the technical solutions of the present application, and are not intended to limit the protection scope of the present application. In the drawings: Figure 1 is a structural schematic diagram of a wafer surface metal impurity collecting device according to the present application; Figure 2 is a structural schematic diagram of a wafer surface metal impurity collecting device according to the present application; Figure 3 is a flow schematic diagram of a wafer surface metal impurity detecting method according to the present application. DETAILED DESCRIPTION

[0014] Figures 1-3 The optional embodiments of the present application described in the following description are intended to teach those skilled in the art how to make and use the best mode of the present application. Some of the features of this application, however, can be practiced or carried out in other ways as well without departing from the scope of the present application. It is therefore intended that such variations and replacements be included within the scope of the present application. Those skilled in the art will readily recognize from the disclosure herein, that the features described with respect to one embodiment can be used in other embodiments. It is also intended that the features described with respect to one embodiment can be combined with features described with respect to other embodiments. Thus, the present application is not to be limited to the optional embodiments described in the following description.

[0015] Example 1.

[0016] A wafer surface metal impurity collecting device according to an embodiment of the present application, as shown in Figures 1-2 , comprises: an applying unit for applying an extracting liquid to a designated position on the wafer surface; a laser 11 and a moving unit 31 for realizing relative movement between the wafer 21 and the light emitting end of the laser 11, so that the excitation light emitted by the laser 11 passes through the extracting liquid and is incident on the designated position on the wafer 21 surface; a collecting unit for collecting the extracting liquid on the wafer 21 surface.

[0017] In order to adapt to wafers of different properties, further, the wafer 21 is a hydrophilic wafer 21, as shown in Figure 1 , the extracting liquid covers the wafer 21 surface; Alternatively, the wafer 21 is a hydrophobic wafer 21, as shown in Figure 2 , the collecting device further comprises: An adsorption tube 41, the extraction liquid is between the wafer 21 surface and the bottom end of the adsorption tube 41, and is adsorbed by the adsorption tube 41; the moving unit 31 is used to realize the relative movement between the adsorption tube 41 and the wafer 21, and the excitation light sequentially passes through the adsorption tube 41 and the extraction liquid moving with the adsorption tube 41, and is incident on the specified position.

[0018] For safety and low cost, further, the extraction liquid is ultrapure water.

[0019] The wafer surface metal impurity detection system of the embodiment of the application comprises: The collecting device of the embodiment of the application; The pretreatment device is used for homogenizing, digesting and concentrating the collected extraction liquid.

[0020] The detection device is used for detecting the extraction liquid collected by the collecting unit to obtain the content of the metal impurity.

[0021] The wafer surface metal impurity detection method of the embodiment of the application, that is, the working method of the system of the embodiment of the application, as shown in the figure, comprises the following steps: Figure 3 As shown in the figure, the wafer surface metal impurity detection method of the embodiment of the application, that is, the working method of the system of the embodiment of the application, comprises the following steps: (A1) The application unit applies the extraction liquid to the specified position on the wafer 21 surface; (A2) The moving unit 31 realizes the relative movement between the wafer 21 and the light emitting end of the laser 11, and the excitation light output by the laser 11 passes through the extraction liquid and is incident on the specified position on the wafer 21 surface; (A3) The metal impurity on the wafer 21 surface is ablated and enters the extraction liquid; (A4) The extraction liquid is collected and sent to the detection device for analysis to obtain the content of the metal impurity.

[0022] Embodiment 2.

[0023] According to the application example of the wafer surface metal impurity detection system and method of the embodiment 1 of the application.

[0024] In this application example, as shown in the figure, the wafer 21 surface is hydrophilic, and the extraction liquid completely covers the wafer 21 surface, that is, all the specified positions are covered with the extraction liquid. The extraction liquid adopts ultrapure water. Figure 1 The moving unit 31 is arranged on the lower side of the wafer 21 and is used to realize the two-dimensional movement of the wafer 21 on the horizontal plane. The laser 11 and the focusing lens 12 are fixedly arranged, so that when the wafer 21 moves, the light emitted by the laser 11 passes through the extraction liquid and is focused on the specified position on the wafer 21 surface.

[0025]

[0026] ​The transmission device is used for collecting the extraction liquid and transmitting to the pretreatment device. The pretreatment device includes a homogenization unit, a digestion unit and a concentration unit, which are all prior art in the field. The detection device adopts ICP-MS.

[0027] The working method of the detection system of the wafer surface metal impurity detection method of the embodiment of the present application, as shown in Figure 3 , includes the following steps: (A1) The application unit applies the extraction liquid to the specified position on the surface of the wafer 21, based on the hydrophilic property of the wafer 21 surface, and applies the extraction liquid once to cover the surface of the wafer 21.

[0028] (A2) The moving unit 31 drives the wafer 21 to move two-dimensionally in the horizontal plane, that is, to realize the relative movement between the wafer 21 and the light-emitting end of the laser 11, and the excitation light output by the laser 11 passes through the focusing lens 12 and the extraction liquid in turn and is incident on different specified positions on the surface of the wafer 21; (A3) The metal impurities on the surface of the wafer 21 are ablated to form a plasma 13, and the material ablated by the laser exists in the extraction liquid in the form of nano / micron particles 22; (A4) The collection unit collects the extraction liquid containing metal particles, and after homogenization, digestion and concentration by the pretreatment device, sends the detection device for analysis to obtain the content of metal impurities.

[0029] Embodiment 3.

[0030] Application example of the wafer surface metal impurity detection system and method according to the embodiment 1 of the present application.

[0031] In this application example, as shown in Figure 2 , the surface of the 8-inch SiC wafer 21 is hydrophobic, 1 mL of extraction liquid is adsorbed at the bottom end of the vacuum suction tube 41, and is on the surface of the wafer 21.

[0032] The moving unit 31 is arranged on the lower side of the wafer 21 and is used to realize the two-dimensional movement of the wafer 21 in the horizontal plane. The laser 11 (femtosecond laser with a wavelength of 257 nm, energy of 1.2-7 J / cm, spot diameter of 500 μm, laser frequency of 20 Hz, and scanning speed of 10 mm / s), the focusing lens 12 and the suction tube 41 are fixedly arranged, so that when the wafer 21 moves, the light emitted by the laser 11 passes through the focusing lens 12, the suction tube 41 and the extraction liquid in turn and is focused on the specified position on the surface of the wafer 21.

[0033] The transmission device is used for collecting the extraction liquid and transmitting to the pretreatment device. The pretreatment device includes a homogenization unit, a digestion unit and a concentration unit, which are all prior art in the field. The detection device adopts ICP-MS.

[0034] An embodiment of the present invention provides a method for detecting metallic impurities on a wafer surface, namely, the working method of the detection system of this embodiment, as follows: Figure 3 As shown, it includes the following steps: (A1) The bottom of the pipette 4 adsorbs the extract, and the extract is located on the surface of the wafer 21.

[0035] (A2) The moving unit 31 drives the wafer 21 to move in two dimensions in the horizontal plane, that is, to realize the relative movement between the wafer 21 and the suction tube 41 (and the light output end of the laser 11). The excitation light output by the laser 11 passes through the focusing lens 12, the suction tube 41 and the extraction liquid in sequence and is incident on different designated positions on the surface of the wafer 21. (A3) Metal impurities on the surface of wafer 21 are etched off, forming plasma 13. The material etched off by laser exists in the extraction solution in the form of nano / micro particles 22. (A4) The collection unit collects the extract containing metal particles. After homogenization, digestion and concentration by the pretreatment device, it is sent to the detection device for analysis to obtain the content of metal impurities. The results are as follows.

[0036] .

[0037] Example 4.

[0038] The application example of the wafer surface metal impurity detection system and method according to Embodiment 1 of the present invention differs from Embodiment 3 in that: Pretreatment of the extract is carried out manually.

[0039] Comparative example: Analyzing surface metallic impurities in silicon wafers with SiO2 coatings manufactured by vapor deposition. Two 6-inch silicon wafers with SiO2 coatings manufactured by vapor deposition from the same batch were subjected to surface impurity element content extraction using VPD and the method of this invention, respectively, followed by ICP-MS / MS analysis.

[0040] The VPD method uses pure HF acid to dissolve the SiO2 coating. After evaporation, impurity elements are collected by rolling a 2% HF / 2% H2O2 extraction solution on the wafer surface.

[0041] The method of the application uses 8 mL-12 mL ultrapure water as the main component of the extraction solution to uniformly cover the surface. The silicon wafer is placed smoothly on the three-dimensional moving unit. The instrument conditions are 257 nm femtosecond laser, laser energy is 0.75-3 J / cm2, spot diameter is 500 μm, laser frequency is 10 Hz, and scanning speed is 5 mm / s. After the ablation is completed, the colloidal extraction solution is collected, and after appropriate drying and concentration, ultrasonic treatment is performed for 5 min. The colloidal sample extraction solution is tested by ICP-MS / MS.

[0042] The results of the two methods are compared, and it is found that the detection results of the remaining elements are in good agreement except for platinum group elements. Platinum group elements are not detected (< MDL) in VPD extraction solution, but platinum group elements (5-18 ppt level) are detected in the nanoscale sample solution obtained by the liquid phase laser ablation method of the application.

[0043] There are three potential reasons for the differences in some elements: 1. In the traditional chemical extraction VPD method, platinum group element impurities are in the SiO2 coating layer. After dissolution by HF acid, the platinum group elements are strongly combined with the Si substrate, and the 2% HF / 2% H2O2 extraction solution cannot dissolve them, resulting in distorted results.

[0044] 2. Platinum group element pollutants are in the SiO2 coating layer and Si substrate interface layer, which are not dissolved by HF acid in the traditional chemical extraction VPD method.

[0045] 3. Some elements exist in the form of oxides, nitrides, and silicides. The extraction / solubility efficiency of the extraction solution in the traditional VPD technique is limited, resulting in a distorted sample solution. The above three cases can be completely avoided in the technical solution of the application. Based on the liquid phase laser ablation technology for collecting impurity metals on the wafer surface, all components can be collected in the form of particles, which is no longer limited by the chemical reaction kinetics between the extraction solution and the wafer material, and can significantly improve the bias caused by the different element occurrence states in the traditional method.

Claims

1. A device for collecting metallic impurities on a wafer surface, characterized in that, The collection device includes: An application unit is used to apply the extract to a designated location on the surface of the wafer; A laser and a moving unit, wherein the moving unit is used to realize relative movement between the wafer and the laser emission end, so that the excitation light emitted by the laser passes through the extraction liquid and is incident on the designated position on the surface of the wafer; A collection unit for collecting the extract from the surface of the wafer.

2. The collecting device according to claim 1, characterized in that, The wafer is a hydrophilic wafer, and the extraction solution covers the surface of the wafer; Alternatively, the wafer is a hydrophobic wafer, and the collection device further includes: An adsorption tube is used, wherein the extract is located between the wafer surface and the bottom of the adsorption tube, and is adsorbed by the adsorption tube. The moving unit is used to realize the relative movement between the adsorption tube and the wafer. The excitation light passes through the adsorption tube and the extraction liquid that moves with the adsorption tube in sequence and is incident on the designated position.

3. The collecting device according to claim 1, characterized in that, The extract is ultrapure water.

4. A wafer surface metal impurity detection system, comprising a detection device; characterized in that, The detection system also includes: The collecting device according to any one of claims 1-3; The detection device is used to detect the extract collected by the collection unit to obtain the content of metal impurities.

5. The detection system according to claim 4, characterized in that, The detection system also includes: A pretreatment device for homogenizing, digesting and concentrating the collected extract.

6. The detection system according to claim 4, characterized in that, The detection device used is ICP-MS.

7. A method for detecting metallic impurities on a wafer surface, comprising the following steps: (A1) The application unit applies the extract to a designated location on the wafer surface; (A2) The moving unit realizes the relative movement between the wafer and the laser output end, and the excitation light output by the laser passes through the extraction liquid and is incident on a designated position on the surface of the wafer; (A3) Metal impurities on the wafer surface are etched off and enter the extraction solution; (A4) Collect the extract and send it to a detection device for analysis to obtain the content of metal impurities.

8. The detection method according to claim 7, characterized in that, The wafer is a hydrophilic wafer, and the extraction solution covers the surface of the wafer; Alternatively, the wafer is a hydrophobic wafer, and the extract is located between the surface of the wafer and the bottom of the adsorption tube, and is adsorbed by the adsorption tube; The moving unit drives the adsorption tube to a designated position on the wafer surface, and the excitation light passes through the adsorption tube and the extraction liquid moving with the adsorption tube in sequence, and is incident on the designated position.

9. The detection method according to claim 7, characterized in that, In step (A4), the extract is homogenized, digested and concentrated before being sent to the detection device for analysis.

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