TWI844077B - Device and method for characterizing the efficiency of silicon wafer capturing metal impurities by using a few-carrier lifespan - Google Patents

Abstract

The present invention discloses a device and method for characterizing the efficiency of a silicon wafer in capturing metal impurities by means of minority carrier life. The device comprises: a cleaning module, which is configured to prepare a silicon wafer to be tested and clean the silicon wafer; a minority carrier life measurement module, which is configured to measure the minority carrier life of the silicon wafer; a heat treatment module, which is configured to perform heat treatment on the silicon wafer; and a computer module, which is configured to record and calculate the measurement value of the minority carrier life measurement module, and indirectly calculate the efficiency of the silicon wafer in capturing metal impurities based on the measurement value.

Description

Device and method for characterizing the efficiency of silicon wafer capturing metal impurities by using a few-carrier lifespan

The present invention is a device and method for testing silicon wafers, and more particularly, a device and method for characterizing the efficiency of silicon wafers in capturing metal impurities by using a few carrier lifetimes.

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, analysis and control of impurities, especially metal impurities, are very important for controlling the quality of silicon wafers. The manufacturing technology of silicon wafers or semiconductors includes raw material processing, wafer processing, cleaning, pre-cleaning for semiconductor manufacturing, heat treatment and many other technologies. In such a complicated manufacturing process and in raw materials, no matter what kind of element, it may become a source of metallic impurity pollution. This kind of metal impurities can combine with elements such as silicon or oxygen inside the silicon wafer to produce metal defects. This kind of metal defect is one of the main reasons for leakage current or various semiconductor defects when manufacturing semiconductors.

In silicon wafer and semiconductor manufacturing technology, 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 generating uniform oxygen precipitates or bulk micro defects (BMD) inside the silicon wafer. 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.

In view of this, the purpose of the present invention is to provide a device and method for characterizing the efficiency of a silicon wafer in capturing metal impurities by means of a few carrier lifetime; the efficiency of a silicon wafer in capturing metal impurities can be characterized by the change in the few carrier lifetime before and after heat treatment of the silicon wafer.

The technical solution of the present invention is implemented as follows: In a first aspect, the present invention provides a device for characterizing the efficiency of a silicon wafer in capturing metal impurities by means of minority carrier life, the device comprising: a cleaning module, the cleaning module being configured to prepare a silicon wafer to be tested and to clean the silicon wafer; a minority carrier life measurement module, the minority carrier life measurement module being configured to measure the minority carrier life of the silicon wafer; a heat treatment module, the heat treatment module being configured to perform heat treatment on the silicon wafer; a computer module, the computer module being configured to record and calculate the measurement value of the minority carrier life measurement module, and indirectly calculate the efficiency of the silicon wafer in capturing metal impurities based on the measurement value. In the second aspect, the present invention provides a method for characterizing the efficiency of a silicon wafer in capturing metal impurities by means of minority carrier life, the steps of which include: preparing a silicon wafer to be tested and cleaning the silicon wafer; measuring the minority carrier life 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 the silicon wafer generates oxygen precipitates; measuring the minority carrier life Tb of the silicon wafer for the second time; calculating the change in the minority carrier life of the silicon wafer before and after the heat treatment by a formula and using it to characterize the efficiency of the silicon wafer in capturing metal impurities, the formula being: efficiency % = (Ta-Tb)/Ta×100%.

The present invention provides a device and method for characterizing the efficiency of silicon wafers in capturing metal impurities by means of minority carrier life; the change value of the minority carrier life of the silicon wafer before and after heat treatment is calculated by a formula, and is used to characterize the efficiency of capturing endogenous metal impurities.

100: Device for characterizing the efficiency of silicon wafers in capturing metal impurities by using a few-carrier lifespan

101: Cleaning module

102: Minority life span measurement module

103: Heat treatment module

104:Computer module

S01~S06: Method steps

FIG1 is a schematic diagram of a device provided by the present invention for characterizing the efficiency of a silicon wafer capturing metal impurities by means of minority carrier lifetime; FIG2 is a diagram showing the relationship between minority carrier lifetime and oxygen concentration in the present invention; FIG3 is a flow chart of a method provided by the present invention for characterizing the efficiency of a silicon wafer capturing metal impurities by means of minority carrier lifetime.

The following will combine the attached figures in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention.

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, thereby generating oxygen precipitates inside the silicon wafer. In the heat treatment process of semiconductor manufacturing, pre-annealing can be performed to ensure uniform generation of oxygen precipitates. Such oxygen precipitates can cause oxygen precipitation defects, which can capture metal impurities that may cause pollution in the manufacturing technology, thereby achieving the intrinsic gettering effect of removing metal impurities near the surface of the manufactured semiconductor.

In the process of producing single crystal silicon by the Czochralski (CZ) method, the produced single crystal silicon inevitably contains oxygen. In semiconductor manufacturing technology, oxygen-containing silicon wafers can generate oxygen precipitates through heat treatment. As mentioned above, this oxygen precipitate can contribute to the resistance effect of metallic impurities. The direct analysis method to detect the capture effect of this resistance effect is to make a water 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 spin coater, and use heat treatment to cause the silicon wafer contaminated by the metal elements to generate oxygen precipitates. At this time, the heat treatment condition that can be selected is a two-step heat treatment condition of 800℃+1000℃, or the temperature conditions implemented in the semiconductor process or device heat treatment can be used to form an analog cycle for heat treatment. The amount of metal elements diffused on the back of the chip after heat treatment can be measured by wafer surface metal element analysis technology (for example, Vapor Phase Decomposition Inductively Coupled Plasma-Mass Spectrometry (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. Wafer surface metal element analysis technology involves four steps: (1) placing a silicon wafer in a VPD chamber and exposing it to HF vapor to dissolve the native oxide or thermally oxidized silicon dioxide ( _SiO2 ) surface layer; (2) placing an extraction droplet (usually 250μL of 2% _HF /2% _H2O2 ) on the wafer and then tilting 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 any contaminant metals; (4) the extraction droplet is transferred 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, if the initial contamination Cu content is 1×10 ¹¹ atoms per square centimeter (atoms/cm ² ), and 5×10 ¹⁰ atoms/cm ² is detected on the back after heat treatment, it can be regarded as a capture amount of 5×10 ¹⁰ atoms/cm ^2. However, the analysis steps of wafer surface metal element analysis technology are strict, and the instruments used are precise and expensive.

Therefore, when heat treatment is performed as described above after the wafer surface is metal-contaminated, metallic impurities existing on the surface or near the surface are captured or deposited by the oxygen precipitates as the oxide precipitates are generated. The degree to which the metallic impurities are filtered out by the oxide precipitates is dependent on the density of the oxide precipitates generated on the silicon wafer, and this density of the oxide precipitates is dependent on the oxygen concentration initially contained in the silicon wafer. This embodiment proposes a device 100 for characterizing the efficiency of capturing metal impurities in a silicon wafer by using minority carrier life. See Figure 1. The device 100 for characterizing the efficiency of capturing metal impurities in a silicon wafer by using minority carrier life includes: a cleaning module 101, a minority carrier life measurement module 102, a heat treatment module 103 and a computer module 104.

The cleaning module 101 is used to clean the silicon wafer to be tested. The silicon wafer used for testing the sample adopts a polished silicon wafer with a wafer resistivity of more than 1 ohm-cm and an oxygen concentration of more than 9 ppma, or a polished silicon wafer that has been heat-treated in advance to uniformly generate oxygen gas polymers as an evaluation sample. The prepared sample silicon wafer is not limited to a polished silicon wafer, and can also be a wafer whose surface is etched using 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 mixture of HF, ammonium ion (NH ₄ ), and hydrogen chloride (HCl) in a certain ratio with hydrogen peroxide (H ₂ O ₂ ) and ultrapure water (DIW) to clean the silicon wafer.

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 that implements 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 reflection power irradiated on the sample silicon wafer to change. Therefore, the change of microwave reflection power over time can reflect the minority carrier lifetime. See Figure 2, when the sample silicon wafer is heat-treated, 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 reduction of the minority carrier lifetime of the sample silicon wafer can indirectly predict the intrinsic gettering efficiency of metal impurities.

The heat treatment module 103 is used to perform heat treatment on the sample silicon wafer. The heat treatment conditions can be to form an analog 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 stage and temperature range, 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. Optionally, the temperature conditions of the two stages of heat treatment are 800°C and 1000°C.

The computer module 104 is configured to record the few carrier life of the silicon wafer before and after heat treatment, and characterize the metal impurity capture efficiency of the silicon wafer through the calculated value of the formula: (first few carrier life before heat treatment - second few carrier life after heat treatment) / first few carrier life before heat treatment × 100%.

By using a device for characterizing the efficiency of a silicon wafer capturing metal impurities by means of minority carrier life as shown in FIG1, a series of measurements can be performed on silicon wafers with a certain range of oxygen concentrations. The minority carrier life is measured for the first time, and the second minority carrier life is measured after the same silicon wafer is heat treated for the purpose of producing oxygen precipitates. The efficiency of a silicon wafer capturing metal impurities can be indirectly evaluated by using the first minority carrier life and the second minority carrier life according to the calculation method provided by the present invention. See FIG3, which shows a method for characterizing the efficiency of a silicon wafer capturing metal impurities by means of minority carrier life, which is implemented by the device shown in FIG1, and includes the following steps:

S01: Prepare the silicon wafer to be tested and clean it. A polished silicon wafer with a wafer resistivity of 1 ohm-cm or more and an oxygen concentration of 9 ppma or more, or a polymer polished silicon wafer that has been heat-treated in advance to generate oxygen uniformly can be used. The silicon wafer prepared as the evaluation sample is not limited to the polished silicon wafer, and can also be a wafer whose surface has been etched with a mixed acid of nitric acid (HNO ₃ ), hydrofluoric acid (HF), and acetic acid (CH ₃ COOH) mixed in a certain proportion. The solution used to clean the silicon wafer is a mixed solution of HF, NH ₄ , and HCl in a certain proportion with hydrogen peroxide (H ₂ O ₂ ) and ultrapure water (DIW).

S02: Measure the minority carrier life Ta of the silicon wafer for the first time. The minority carrier life 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 charges, an iodine passivation u-PCD measurement method measured after the surface is coated with iodine solution, etc.

S03: After the first measurement, clean the silicon wafer again. The method used in this step is the same as the above cleaning method.

S04: Performing a first-stage heat treatment and a second-stage heat treatment on the silicon wafer to generate oxygen precipitates on the silicon wafer. Generally, 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. Optionally, 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.

S05: Measure the minority carrier lifetime Tb of the silicon wafer for the second time. The method used in this step to measure the minority carrier lifetime is the same as the above measurement method.

S06: The change in minority carrier life before and after 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%.

72.2%，可以看作該矽片捕獲金屬雜質的效果或捕獲能力為72.2%左右。 For example, if the first measured minority carrier lifetime Ta is 900us and the second measured minority carrier lifetime Tb 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%.

Therefore, the present invention provides a device and method for characterizing the efficiency of a silicon wafer in capturing metal impurities by means of minority carrier life, and the efficiency of a silicon wafer in capturing metal impurities is characterized by the change in minority carrier life of the silicon wafer before and after heat treatment.

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

The above is only a specific implementation of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily thought of by a skilled person familiar with the technical field within the technical scope disclosed in the present invention should be covered within the protection scope of the present invention. Therefore, the protection scope of the present invention shall be based on the protection scope of the claims.

100: Device for characterizing the efficiency of silicon wafers in capturing metal impurities by using a few-carrier lifespan

101: Cleaning module

102: Minority life span measurement module

103: Heat treatment module

104:Computer module

Claims (9)

A device for characterizing the efficiency of a silicon wafer in capturing metal impurities by means of minority carrier life, mainly comprising: a cleaning module, the cleaning module being configured to prepare a silicon wafer to be tested and to clean the silicon wafer; a minority carrier life measurement module, the minority carrier life measurement module being configured to measure the minority carrier life of the silicon wafer; a heat treatment module, the heat treatment module being configured to perform heat treatment on the silicon wafer; a computer module, the computer module being configured to record the minority carrier life of the silicon wafer before and after heat treatment, and characterizing the efficiency of a silicon wafer in capturing metal impurities by means of the calculated value of the formula: (first minority carrier life before heat treatment - second minority carrier life after heat treatment) / first minority carrier life before heat treatment × 100%. The device for characterizing the efficiency of silicon wafer capturing metal impurities by means of minority carrier lifetime as described in claim 1, wherein the cleaning module stores a mixed solution of hydrofluoric acid (HF), ammonium ion (NH ₄ ) and hydrogen chloride (HCl) in a certain proportion with hydrogen peroxide (H ₂ O ₂ ) and ultrapure water (DIW) for cleaning the silicon wafer. The device for characterizing the efficiency of capturing metal impurities in a silicon wafer by means of minority carrier lifetime as described in claim 1, wherein 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. The device for characterizing the efficiency of capturing metal impurities of a silicon wafer by using minority carrier lifetime as described in claim 1, wherein the heat treatment module 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. A method for characterizing the efficiency of a silicon wafer in capturing metal impurities by means of a few carrier lifetime is applied to a device for characterizing the efficiency of a silicon wafer in capturing metal impurities by means of a few carrier lifetime as described in any one of claims 1 to 4, and the steps include: preparing a silicon wafer to be tested and cleaning the silicon wafer; measuring the few carrier lifetime Ta of the silicon wafer for the first time; cleaning the silicon wafer again after the first measurement is completed; and The silicon wafer undergoes the first stage heat treatment and the second stage heat treatment to produce oxygen precipitates on the silicon wafer; the minority carrier life Tb of the silicon wafer is measured for the second time; the change in the minority carrier life 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%. As described in claim 5, the method for characterizing the efficiency of a silicon wafer in capturing metal impurities by means of minority carrier lifetime, wherein the silicon wafer is not limited to a polished wafer, but can also be a wafer whose surface has been etched by a mixed acid of nitric acid, hydrofluoric acid, and acetic acid. The method for characterizing the efficiency of a silicon wafer in capturing metal impurities by means of minority carrier lifetime as described in claim 5, wherein the preparation of the silicon wafer to be tested and the cleaning of the silicon wafer include: placing the silicon wafer in a mixed solution of a certain ratio of hydrofluoric acid (HF), ammonium ion (NH ₄ ) and hydrogen chloride (HCl) with hydrogen peroxide (H ₂ O ₂ ) and ultrapure water (DIW) for cleaning. The method for characterizing the efficiency of a silicon wafer in capturing metal impurities by means of minority carrier lifetime as described in claim 5, wherein 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 completed by microwave photoconductivity attenuation method. The method for characterizing the efficiency of a silicon wafer in capturing metal impurities by means of minority carrier lifetime as described in claim 5, wherein the first stage heat treatment is performed at 800°C and the second stage heat treatment is performed at 1000°C.

Images