Device and method for characterizing the efficiency of silicon wafer gettering of metal impurities by using minority carrier lifetime

Abstract

An embodiment of the present invention discloses a device and method for characterizing the efficiency of silicon wafers in removing metal impurities by means of minority carrier lifetime. The device includes: a cleaning module, which is configured to prepare a silicon wafer to be tested and clean the silicon wafer; a minority carrier lifetime measurement module, which is configured to measure the minority carrier lifetime of the silicon wafer; a heat treatment module, which is configured to perform heat treatment on the silicon wafer; and a calculator module, which is configured to record and calculate the measurement values ​​of the minority carrier lifetime measurement module, and indirectly calculate the efficiency of the silicon wafer in capturing metal impurities based on the measurement values.

Description

Technical Field

[0001] The embodiments of the present invention relate to a silicon wafer detection method, and more particularly to a device and method for characterizing the efficiency of silicon wafer in removing metal impurities by means of minority carrier lifetime. Background Art

[0002] In addition to using silicon wafers to achieve high integration and miniaturization of semiconductor devices, reducing impurities on silicon wafers that can deteriorate the quality of semiconductor devices is also an important task. Therefore, analyzing and controlling impurities, especially metal impurities, is very important for controlling the quality of silicon wafers. The manufacturing process of silicon wafers or semiconductors includes many processes such as raw material processing, wafer processing, cleaning, pre-cleaning for semiconductor manufacturing, and heat treatment. In such a complicated manufacturing process and in raw materials, no matter what element, it may become a source of contamination of metallic impurities. This metallic impurity can combine with elements such as silicon or oxygen inside the silicon wafer to produce metallic defects. This metallic defect is one of the main reasons for leakage current or various semiconductor defects when manufacturing semiconductors.

[0003] In the silicon wafer and semiconductor manufacturing process, the methods that can control this kind of metallic impurities include: wet-blasting method that causes mechanical damage on the back of the wafer, or polycrystalline silicon thin film method that makes polycrystalline silicon thin film on the back of the wafer, or the widely used method of producing uniform oxygen precipitates or BMD (Bulk Micro Defect) inside the silicon wafer, etc. The above methods all require expensive equipment, and the detection standards are very strict, and it is difficult to show the ability to capture metallic impurities in silicon wafers. Summary of the invention

[0004] In view of this, an embodiment of the present invention hopes to provide a device and method for characterizing the efficiency of metal impurity removal of a silicon wafer by means of minority carrier lifetime; the efficiency of metal impurity removal of a silicon wafer can be characterized by the change in minority carrier lifetime before and after heat treatment of the silicon wafer.

[0005] The technical solution of the embodiment of the present invention is achieved as follows:

[0006] In a first aspect, an embodiment of the present invention provides a device for characterizing the efficiency of a silicon wafer in capturing metal impurities by means of minority carrier lifetime, the device comprising:

[0007] A cleaning module, wherein the cleaning module is configured to prepare a silicon wafer to be tested and clean the silicon wafer; a minority carrier lifetime measurement module, wherein the minority carrier lifetime measurement module is configured to measure the minority carrier lifetime of the silicon wafer; a heat treatment module, wherein the heat treatment module is configured to perform heat treatment on the silicon wafer; and a calculator module, wherein the calculator module is configured to record and calculate the measurement values ​​of the minority carrier lifetime measurement module, and indirectly calculate the metal impurity capture efficiency of the silicon wafer based on the measurement values.

[0008] In a second aspect, an embodiment of the present invention provides a method for characterizing the efficiency of a silicon wafer in capturing metal impurities by using minority carrier lifetime, the method comprising:

[0009] The method comprises the following steps: preparing a silicon wafer to be tested and cleaning the silicon wafer; measuring the minority carrier lifetime Ta of the silicon wafer for the first time; cleaning the silicon wafer again after the first measurement; performing a first-stage heat treatment and a second-stage heat treatment on the silicon wafer so that oxygen precipitates are generated on the silicon wafer; measuring the minority carrier lifetime Tb of the silicon wafer for the second time; calculating the change in the minority carrier lifetime before and after the heat treatment of the silicon wafer by a formula and using the formula to characterize the efficiency of the silicon wafer in capturing metal impurities. The formula is: efficiency % = (Ta - Tb) / Ta × 100%.

[0010] An embodiment of the present invention provides a device and method for characterizing the efficiency of silicon wafers in removing metal impurities by means of minority carrier lifetime; the change value of the minority carrier lifetime of the silicon wafer before and after heat treatment is calculated by a formula, and is used to characterize the intrinsic capture efficiency of metallic impurities. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] Figure 1 A schematic diagram of a device for characterizing the efficiency of metal impurity removal from a silicon wafer by using minority carrier lifetime provided in an embodiment of the present invention;

[0012] Figure 2 A graph showing the relationship between minority carrier lifetime and oxygen concentration in an embodiment of the present invention;

[0013] Figure 3 A flow chart of a method for characterizing the efficiency of metal impurity removal from a silicon wafer by using minority carrier lifetime provided in an embodiment of the present invention. DETAILED DESCRIPTION

[0014] The technical solutions in the embodiments of the present invention will be described clearly and completely below in conjunction with the accompanying drawings in the embodiments of the present invention.

[0015] In the heat treatment process of semiconductor manufacturing, intrinsic gettering is the process of controlling the amount of oxygen inside the silicon wafer within a certain range to produce oxygen precipitates inside the silicon wafer. In the heat treatment process of semiconductor manufacturing, pre-annealing can be used to make the oxygen precipitates uniformly generated. This oxygen precipitate can cause oxygen precipitation defects, which can capture metallic impurities that may cause contamination in the manufacturing process, thereby achieving the intrinsic gettering effect of removing metallic impurities near the surface of the semiconductor.

[0016] In the process of producing single crystal silicon by the Czochralski method (CZ method), the produced single crystal silicon inevitably contains oxygen. Oxygen-containing silicon wafers can generate oxygen precipitates through heat treatment in the semiconductor manufacturing process. As mentioned above, this oxygen precipitate can contribute to the resistance effect of metallic impurities. A direct analysis method to detect the effect of capturing this resistance effect is to make a solution of metal elements such as Fe, Cu, and Ni and drop it on the surface of the silicon wafer, then contaminate it with a spincoater, and heat treat the silicon wafer contaminated with metal elements to generate oxygen precipitates. The heat treatment conditions that can be selected at this time are 800℃ + 1000℃ two-step heat treatment conditions, or the temperature conditions implemented in the semiconductor process or device heat treatment can be used to form a simulated cycle for heat treatment. The amount of metal elements diffused on the back of the wafer after heat treatment can be measured by wafer surface metal element analysis technology (VPD ICP-MS), and the difference between the initial contamination amount and the metal contamination amount detected after heat treatment can be measured and analyzed. The implementation of the wafer surface metal element analysis technology includes four steps: (1) Place the silicon wafer in a VPD chamber and expose it to HF vapor to dissolve the natural oxide or thermally oxidized SiO2 surface layer; (2) Place an extraction droplet (usually 250 μL of 2% HF / 2% H2O2) on the wafer and then tilt it in a carefully controlled manner so that the droplet "sweeps" across the wafer surface; (3) As the extraction droplet moves across the wafer surface, it collects dissolved SiO2 and all contaminant metals; (4) Transfer the extraction droplet from the wafer surface to an ICP-MS or ICP-MS / MS system for analysis. The above steps can measure the metal element content on the wafer surface. For example, the initial contamination Cu content is 1 × 10 11 atoms / cm 2 , 5 × 10 10 atoms / cm 2 , it can be regarded as 5 × 10 10 atoms / cm 2However, the analysis steps of the wafer surface metal element analysis technology are strict, the instruments used are precise and the cost is high.

[0017] Therefore, when heat treatment is performed as described above after metal contamination on the wafer surface, as oxygen precipitates are generated, metallic impurities existing on or near the surface will be captured or deposited by the oxygen precipitates, wherein the degree to which metallic impurities are filtered out by the oxygen precipitates is dependent on the density of oxygen precipitates generated on the silicon wafer, and this oxygen precipitate density is dependent on the oxygen concentration initially contained in the silicon wafer. This embodiment proposes a device 100 for characterizing the efficiency of silicon wafers in capturing metal impurities by means of minority carrier lifetime, see the attached Figure 1 The device 100 includes: a cleaning module 101, a minority carrier lifetime measurement module 102, a heat treatment module 103 and a calculator module 104.

[0018] The cleaning module 101 is used to clean the silicon wafer to be tested. The silicon wafer used for testing samples uses polished silicon wafers with a wafer resistivity of more than 1 ohm-cm and an oxygen concentration of more than 9 ppma, or polished silicon wafers that have been heat-treated in advance to uniformly generate oxygen polymers as evaluation samples. The prepared sample silicon wafers are not limited to polished silicon wafers, and can also be wafers whose surfaces are etched with a mixed acid of nitric acid (HNO3), hydrofluoric acid (HF), and acetic acid (CH3COOH) mixed in a certain proportion. The cleaning module 101 uses a mixed solution of HF, NH4, and HCl in a certain proportion with hydrogen peroxide (H2O2) and ultrapure water (DIW) to clean the silicon wafer.

[0019] The minority carrier lifetime measurement module 102 is used to measure the minority carrier lifetime of the sample silicon wafer. The minority carrier lifetime measurement module 102 includes a microwave photoconductive unit for implementing the microwave photoconductive attenuation method (u-PCD). The microwave photoconductive unit includes a microwave light source, a circulator, an antenna, a detector and a pulse light source. The microwave source passes through the circulator and transmits microwave energy to the surface of the sample silicon wafer through the antenna. The reflected microwave signal is collected by the antenna and reaches the detector through the circulator. The detector is used to reflect the microwave signal. The pulse light source irradiates the surface of the sample silicon wafer, causing the conductivity of the sample silicon wafer to change, thereby affecting the reflected microwave energy, causing the microwave reflected power irradiated on the sample silicon wafer to change. Therefore, the change of microwave reflected power over time can reflect the minority carrier lifetime. See Appendix Figure 2 When the sample silicon wafer is subjected to heat treatment, the minority carrier lifetime of the sample silicon wafer decreases according to the oxygen concentration or oxygen precipitation density before and after the heat treatment. Therefore, the intrinsic gettering efficiency of metal impurities can be indirectly predicted by the reduction of the minority carrier lifetime of the sample silicon wafer.

[0020] The heat treatment module 103 is used to perform heat treatment on the sample silicon wafer. The heat treatment conditions can be to form a simulated cycle of the temperature conditions implemented in the semiconductor process to perform heat treatment so that the sample silicon wafer can produce oxygen precipitates. The heat treatment module 103 is configured to perform a first-stage heat treatment on the silicon wafer between 750-900°C, and then perform a second-stage heat treatment on the silicon wafer between 1000-1100°C. The heat treatment stage and temperature range are not limited to the stages and temperature ranges, and the heat treatment stage and general temperature range that ensure the generation of oxygen precipitates in the silicon wafer can be selected to be between 750°C and 1100°C. Preferably, the temperature conditions of the two stages of heat treatment are 800°C and 1000°C.

[0021] The calculator module 104 is configured to record the minority carrier lifetimes before and after the heat treatment of the silicon wafer, and characterize the metal impurity capture efficiency of the silicon wafer by the calculated value of the formula: (first minority carrier lifetime before heat treatment - second minority carrier lifetime after heat treatment) / first minority carrier lifetime before heat treatment × 100%.

[0022] By attaching Figure 1 The device for characterizing the efficiency of silicon wafers in capturing metal impurities by using minority carrier lifetime shown in the figure can perform a series of measurements on silicon wafers with a certain range of oxygen concentrations, perform a first measurement of minority carrier lifetime, and measure a second minority carrier lifetime after heat treatment of the same silicon wafer for the purpose of producing oxygen precipitates. Using the first minority carrier lifetime and the second minority carrier lifetime, the efficiency of silicon wafers in capturing metal impurities can be indirectly evaluated according to the calculation method provided by the present invention. Referring to FIG. 3, which shows a method for characterizing the efficiency of silicon wafers in capturing metal impurities by using minority carrier lifetime, the method is performed by attaching Figure 1 The device shown is implemented, and the method includes the following steps:

[0023] Prepare the silicon wafer to be tested and clean the silicon wafer. A polished silicon wafer with a wafer resistivity of 1 ohm-cm or more and an oxygen concentration of 9 ppma or a polymer polished silicon wafer that has been heat-treated in advance to uniformly generate oxygen can be used. The silicon wafer prepared as an evaluation sample is not limited to a polished silicon wafer, and can also be a wafer whose surface has been etched with a mixed acid of nitric acid (HNO3), hydrofluoric acid (HF), and acetic acid (CH3COOH) mixed in a certain proportion. The solution used to clean the silicon wafer is a mixed solution of HF, NH4, and HCl solutions in a certain proportion with hydrogen peroxide (H2O2) and ultrapure water (DIW).

[0024] The minority carrier lifetime Ta of the silicon wafer is measured for the first time. The minority carrier lifetime measurement can be a general u-PCD measurement method measured after the wafer is oxidized, a corona charged u-PCD measurement method measured after the wafer surface is covered with an electric charge, an iodine passivation u-PCD measurement method measured after the surface is coated with an iodine solution, etc.

[0025] After the first measurement, the silicon wafer is cleaned again. The method used in this step is the same as the above cleaning method.

[0026] The silicon wafer is subjected to a first-stage heat treatment and a second-stage heat treatment so that oxygen precipitates are generated on the silicon wafer. Generally, the heat treatment can be divided into two stages, the first-stage heat treatment is performed at a temperature range of 750°C to 900°C, and the second-stage heat treatment is performed at a temperature range of 1000°C to 1100°C. Preferably, the first-stage heat treatment is performed at a temperature of 800°C, and the second-stage heat treatment is performed at a temperature of 1000°C.

[0027] The minority carrier lifetime Tb of the silicon wafer is measured for the second time. The method used in this step to determine the minority carrier lifetime is the same as the above-mentioned measurement method.

[0028] The change in minority carrier lifetime before and after the heat treatment of the silicon wafer is calculated by a formula and used to characterize the efficiency of the silicon wafer in capturing metal impurities. The formula is: efficiency % = (Ta - Tb) / Ta × 100%.

[0029] For example, if the minority carrier lifetime Ta measured for the first time is 900us and the minority carrier lifetime Tb measured for the second time is 250us, then (900-250) / 900×100%≈72.2%, which can be regarded as the effect or capture capacity of the silicon wafer in capturing metal impurities is about 72.2%.

[0030] Therefore, the present invention provides a device and method for characterizing the efficiency of silicon wafers in capturing metal impurities by means of minority carrier lifetime, and the efficiency of silicon wafers in capturing metallic impurities is characterized by the change in minority carrier lifetime before and after heat treatment.

[0031] It should be noted that the technical solutions described in the embodiments of the present invention can be combined arbitrarily without conflict.

[0032] The above is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any person skilled in the art can easily think of changes or substitutions within the technical scope disclosed by the present invention, which should be included in the protection scope of the present invention. Therefore, the protection scope of the present invention should be based on the protection scope of the claims.

Claims

1. A device for characterizing the efficiency of silicon wafers in capturing metal impurities by means of minority carrier lifetime, characterized in that: The device comprises: a cleaning module, wherein the cleaning module is configured to prepare a silicon wafer to be tested and clean the silicon wafer; A minority carrier lifetime measurement module, wherein the minority carrier lifetime measurement module is configured to measure the minority carrier lifetime Ta of the silicon wafer for the first time, wherein the cleaning module is further configured to clean the silicon wafer again after the first measurement; A heat treatment module, wherein the heat treatment module is configured to perform a first stage heat treatment and a second stage heat treatment on the silicon wafer so as to generate oxygen precipitates on the silicon wafer, wherein the minority carrier lifetime measurement module is further configured to measure the minority carrier lifetime Tb of the silicon wafer for a second time; A calculator module is configured to calculate the change in minority carrier lifetime before and after the silicon wafer is heat treated by a formula and use it to characterize the efficiency of the silicon wafer in capturing metal impurities. The formula is: efficiency % = (Ta-Tb) / Ta×100%.

2. The device according to claim 1, characterized in that The cleaning module stores a mixed solution of HF, NH4, HCl solutions in a certain proportion with hydrogen peroxide (H2O2) and ultrapure water (DIW) for cleaning the silicon wafer.

3. The device according to claim 1, characterized in that The minority carrier lifetime measurement module includes a microwave photoconductivity measurement unit, and the microwave photoconductivity measurement unit includes a microwave light source, a circulator, an antenna, a detector and a pulse light source.

4. The device according to claim 1, characterized in that The heat treatment module is configured to perform a first stage heat treatment on the silicon wafer at a temperature between 750-900° C., and then perform a second stage heat treatment on the silicon wafer at a temperature between 1000-1100° C.

5. A method for characterizing the efficiency of silicon wafers capturing metal impurities by using minority carrier lifetime, the method being applied to the device for characterizing the efficiency of silicon wafers capturing metal impurities by using minority carrier lifetime according to any one of claims 1 to 4, characterized in that: The method comprises: preparing a silicon wafer to be tested and cleaning the silicon wafer; measuring the minority carrier lifetime Ta of the silicon wafer for the first time; After the first measurement is completed, the silicon wafer is cleaned again; Performing a first-stage heat treatment and a second-stage heat treatment on the silicon wafer so as to generate oxygen precipitates on the silicon wafer; Measuring the minority carrier lifetime Tb of the silicon wafer for the second time; The change in minority carrier lifetime before and after the heat treatment of the silicon wafer is calculated by a formula and used to characterize the efficiency of the silicon wafer in capturing metal impurities. The formula is: efficiency % = (Ta - Tb) / Ta × 100%.

6. The method according to claim 5, characterized in that The silicon wafer is not limited to a polished wafer, and a wafer whose surface has been etched by a mixed acid of nitric acid, hydrofluoric acid, and acetic acid mixed in a certain proportion may also be used.

7. The method according to claim 5, characterized in that The preparation of the silicon wafer to be tested and cleaning the silicon wafer include: placing the silicon wafer in a mixed solution of HF, NH4, HCl solutions in a certain proportion with hydrogen peroxide (H2O2) and ultrapure water (DIW) for cleaning.

8. The method according to claim 5, characterized in that The first measurement of the minority carrier lifetime Ta of the silicon wafer and the second measurement of the minority carrier lifetime Tb of the silicon wafer are both performed by microwave photoconductivity attenuation method.

9. The method according to claim 5, characterized in that The first stage heat treatment is performed at 800°C, and the second stage heat treatment is performed at 1000°C.

Images