CN114384051A - Method for distinguishing defects in silicon carbide wafer on carbon surface of wafer - Google Patents

Abstract

A method of identifying defects in a silicon carbide wafer at the carbon side of the wafer is provided, the method comprising placing the silicon carbide wafer in an etching chamber, etching the carbon side of the silicon carbide wafer using a microwave plasma; after etching for a preset time, taking the silicon carbide wafer out of the etching cavity, and ultrasonically cleaning the silicon carbide wafer by using deionized water and alcohol; and determining the defect type according to the appearance and the section of the etching pit on the carbon surface of the silicon carbide wafer. According to the method, the etching pits are formed by etching the C surface, and the micropipes and different types of dislocation can be accurately identified according to the appearance and the section information of the etching pits; meanwhile, the substrate material can be compared with the Si-face dislocation condition, so that the behavior of dislocation in the growth process can be directly observed; the dislocation condition of the epitaxial material can be compared with that of the epitaxial surface, and the increment and the transformation mechanism of the dislocation can be further researched.

Description

A method for identifying defects in silicon carbide wafers on the carbon surface of the wafer

technical field

The present application relates to the field of testing and characterization of semiconductor single crystal materials, and in particular, to a method for identifying defects in silicon carbide wafers on the carbon surface of the wafer.

Background technique

As a representative of the third-generation wide-bandgap semiconductor materials, silicon carbide (SiC) materials have excellent properties such as large forbidden band width, high carrier saturation migration velocity, high critical breakdown field strength, high thermal conductivity, and good chemical stability. Physical and chemical properties, based on these properties, SiC materials are considered as ideal materials for high-frequency, high-power, high-temperature and radiation-resistant electronic devices. Has a wide range of applications.

With the gradual improvement of the quality of SiC single crystals, the density of defects such as small-angle grain boundaries and microtubes gradually decreases. However, there are still more or less microtubes in commercial substrates. In the stress birefringence image of SiC wafers, a single Micropipes exhibit butterfly-spot or comet-like stress images. Micropipes extend to the epitaxial layer during epitaxial growth, which is the most harmful defect in SiC power devices. Micropipes will cause reverse bias failure of the device until breakdown. Although the improvement of epitaxial growth technology can be used to close the micropipes, the closed micropipes will still be transformed into different morphological defects such as dislocations or micro-pits, and the birefringence method for detecting micropipes in the substrate is no longer applicable. epitaxial wafer. Therefore, there is a need to explore a method that can easily observe the extension or expansion of micropipes from the substrate to the epitaxial layer.

In addition, the growth method based on physical vapor transport still has a high dislocation density (~10 ⁴ cm ^-2 ), which greatly reduces its actual electrical properties, thus limiting the application of SiC materials in the field of electronic devices. further application. For example, transistors fabricated on high dislocation density have large leakage current, and different types of dislocations have different effects on device performance. Screw dislocations in the substrate will penetrate into the epitaxial layer or be converted into Frank SFs, and Shockley SFs in the epitaxial layer will form below the transition point of basal plane dislocations into edge dislocations, which will seriously affect the performance of SiC power devices and lead to the degradation of device parameters. Therefore, how to quickly and effectively identify the types of dislocation defects is of great significance to the development of SiC materials and devices.

For silicon carbide single crystal defect detection, common measurement methods include X-ray diffraction, X-ray topography, transmission electron microscopy, wet etching (including traditional solution etching, electrochemical etching and defect-selective chemical etching using molten salts) and many more. Among them, the molten KOH corrosion method, which is simple and convenient for sample preparation, is the most commonly used. The SiC wafer is etched into molten KOH to form preferential etching where dislocations exist. Dislocation types are identified based on the size and shape of the etched pits. The larger size hexagonal corrosion pit corresponds to the screw dislocation (TSD), the smaller size hexagonal corrosion pit corresponds to the edge dislocation (TED), the small size shell-shaped corrosion pit corresponds to the basal plane dislocation (BPD), The shape and size of the etch pits are affected by the corrosion conditions, but the highly doped N-type SiC etch pits are circular after wet etching, and the types of dislocations cannot be identified. In response to this problem, in the prior art, carbon tetrafluoride/argon gas is used as an etching gas to perform plasma etching on SiC, so as to satisfy the dislocation detection of highly doped N-type SiC. However, the dislocations observed by the above methods are all observed from the Si surface, so that the integrity of the Si surface structure of the substrate is destroyed, the sample cannot be used continuously, and needs to be re-polished and polished. When exploring the transformation of dislocations from the substrate to the epitaxial layer, the repetitive process of etching→observing→grinding→polishing is also required, which takes a long time. If dislocations can be observed from the carbon surface, the corresponding relationship between the carbon surface of the substrate and the etch pits on the Si surface of the epitaxial layer can be intuitively seen, so as to study the mechanism of dislocation transformation, which is crucial for exploring the correlation between dislocations and failed devices. important.

Therefore, it is necessary to explore a method that can simultaneously observe micropipes and dislocation defects in SiC single crystals from the carbon surface.

SUMMARY OF THE INVENTION

In order to solve the above problems, the embodiments of the present application provide a method for identifying defects in a silicon carbide wafer on the carbon surface of the wafer.

The method for identifying defects in a silicon carbide wafer on the carbon surface of the wafer provided by the embodiment of the present application mainly includes the following steps:

placing the silicon carbide wafer in an etching chamber, and using microwave plasma to etch the carbon surface of the silicon carbide wafer;

After the etching is completed, the silicon carbide wafer is taken out from the etching chamber, and ultrasonically cleaned with deionized water and alcohol;

According to the morphology and cross section of the etched pit on the carbon surface of the silicon carbide wafer, the defect type is determined.

The method provided by the embodiment of the present application has the following beneficial effects:

1. The present invention forms etching pits by etching the C-surface, and micropipes and different types of dislocations can be accurately identified according to the morphology and cross-sectional information of the etching pits.

2. In the present invention, by etching the C surface to observe the micropipes, the morphology defects on the surface of the epitaxial layer can be compared, and the extension and expansion of the micropipes in the epitaxial process can be explored.

3. The present invention observes dislocations by etching the C-plane. For the substrate material, it can be compared with the dislocation situation of the Si plane, so as to directly observe the behavior of dislocations in the growth process; for epitaxial materials, it can be compared with the epitaxial surface for dislocations. , and then study the mechanism of dislocation increment and transformation.

4. The present invention does not use molten strong alkali as a corrosive agent, and is less harmful to human body.

Description of drawings

The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments consistent with the present embodiments, and together with the description serve to explain the principles of the present embodiments.

In order to more clearly illustrate the technical solutions in this embodiment or the prior art, the accompanying drawings that are required to be used in the description of the embodiment or prior art will be briefly introduced below. It is obvious to those skilled in the art that , on the premise of no creative labor, other drawings can also be obtained from these drawings.

1 is a schematic diagram of a microwave plasma chemical vapor deposition apparatus provided in an embodiment of the present application;

Figure 2 is a graph showing the morphology, cross-section and size of the etch pits formed by three types of dislocations in a non-doped 4H-SiC substrate;

Figure 3 shows the morphology, cross-section and size information of the etch pits formed by three types of dislocations in the N-type 4H-SiC substrate;

FIG. 4 is an etched topography diagram of the microtube provided by the embodiment of the present application.

Detailed ways

Exemplary embodiments will be described in detail herein, examples of which are illustrated in the accompanying drawings. When the following description refers to the drawings, the same numbers in different drawings refer to the same or similar elements unless otherwise indicated. The implementations described in the following exemplary embodiments are not intended to represent all implementations consistent with this example. Rather, they are merely examples of apparatus and methods consistent with some aspects of the present embodiments as recited in the appended claims.

In this embodiment, the etching apparatus used in the embodiment is a microwave plasma chemical vapor deposition (MPCVD) growth furnace. 1 is a schematic diagram of a microwave plasma chemical vapor deposition apparatus provided in an embodiment of the present application. As shown in FIG. 1 , the carbon surface of the silicon carbide wafer 2 is placed on the molybdenum sheet 1 with the carbon surface facing upward, and the formed plasma 3 is covered on Silicon carbide wafer 2 surface. The morphology and cross-section information of the etched pits can be obtained by means of a laser confocal microscope, and of course other equipment is also available. The silicon carbide wafer in this embodiment is grown by the physical vapor transport method, and the crystal form is 4H-SiC. The method for identifying silicon carbide single crystal defects on the carbon surface provided by the embodiments of the present application mainly includes the following steps:

S101: place the silicon carbide wafer in an etching chamber, and use microwave plasma to etch the carbon surface of the silicon carbide wafer.

If the silicon carbide wafer in this embodiment is a substrate wafer, the crystal needs to be processed into a wafer by cutting, grinding, polishing and other processes, and the surface meets the requirements of a mirror surface. The device needs to remove the back metal electrode.

The etching gas in this embodiment is hydrogen plasma or hydrogen-oxygen plasma, the sample is placed on the molybdenum plate with the carbon side up, and the equipment is a microwave plasma chemical vapor deposition growth furnace. Plasma is generated under the surface of the sample, covering the carbon surface of the sample, and the temperature of the plasma is adjusted by setting the microwave power

S102: After the etching is completed, the silicon carbide wafer is taken out from the etching chamber, and ultrasonically cleaned with deionized water and alcohol.

SiC single crystals with different doping types need to explore the best etching conditions. The carbon surface defects of the samples etched under the best conditions have clear shape and moderate size of the corrosion pits, and the defects are completely exposed and there is no overlap.

S103: Determine the defect type according to the morphology and cross section of the etching pit on the carbon surface of the silicon carbide wafer.

Based on the above methods, different types of wafers will be classified and introduced below.

Example 1

Research on carbon surface etching dislocations on non-doped 4H-SiC substrates.

The carbon surface of the 4H-SiC substrate is etched upward, the etching gas can be hydrogen-oxygen plasma, the hydrogen flow rate is 200-400 sccm, the oxygen flow rate is 2-4 sccm, the etching temperature is 1000-1200° C., and the etching time is 1.5-2.5 h.

In this example, the flow rate of hydrogen gas was 300 sccm, the flow rate of oxygen gas was 3 sccm, the etching temperature was 1100 °C, and the etching time was 2 h. After the etching was completed, the morphology, cross-section and size information of the etching pit were observed with a LEXT OLS4000 3D laser confocal microscope. The etching pits are divided into three categories, as shown in Figure 2, combined with the analysis of the etching mechanism and dislocation theory, the size is the largest, the cross-section is pear-shaped, and the bottom sharp etching pits are mixed dislocations (TMD); , the etch pit with a triangular cross-section corresponds to TSD; the smallest size, with an arc-shaped cross-section corresponds to TED.

Example 2

Research on etched dislocations on the carbon surface of N-type 4H-SiC substrates. The etching gas can be hydrogen plasma, the flow rate of hydrogen gas is 200-400 sccm, the flow rate of oxygen gas is 2-4 sccm, the etching temperature is 1000-1200° C., and the etching time is 1.5-2.5 h.

The carbon side of the N-doped 4H-SiC sample was etched upward. In this example, the hydrogen flow rate was set to 300 sccm, the etching temperature was 1100° C., and the etching time was 2 h. After the etching is completed, the morphology, cross-section and size information of the etched pits can be observed with a LEXT OLS4000 3D laser confocal microscope. The etched pits can be divided into three categories, as shown in Figure 3, combining the etching mechanism and dislocation theory Analysis, the morphology is hexagonal, the aspect ratio is the smallest, the cross-section is triangular, and the etching pit is TSD; the morphology is elliptical, the aspect ratio is the largest, and the triangular cross-section is the etching pit corresponding to TED; the morphology and aspect ratio are both. Between the two, the etched pit with a trapezoidal cross-section corresponds to the TMD. It is worth noting that the bottom ends of the three types of etched pits are not in the center, which is caused by the 4° angle of the substrate.

Example 3

Research on Etching Micropipes on Carbon Surface of N-type 4H-SiC Substrate

The etching conditions were the same as those in Example 2. As shown in Figure 4, an etching pit with a size of about 30 μm and a bottomless center can be clearly observed, corresponding to a micropipe. It is illustrated that the etching method of this embodiment can effectively distinguish micropipes and dislocations under suitable conditions.

In this embodiment, etching pits are formed by etching the carbon surface, and micropipes and different types of dislocations can be accurately identified according to the morphology and cross-sectional information of the etching pits. By observing the micropipes by etching the carbon surface, the morphology defects on the surface of the epitaxial layer can be compared, and the extension and expansion of the micropipes during the epitaxy process can be explored. By etching the carbon surface to observe dislocations, the substrate material can be compared with the dislocation situation of the Si surface, so as to directly observe the behavior of dislocations during the growth process; for epitaxial materials, the dislocation situation can be compared with the epitaxial surface, and then the dislocation situation can be studied. wrong value-added and transformation mechanisms. This embodiment does not use molten strong alkali as a corrosive agent, which is less harmful to human body.

The various embodiments in this specification are described in a progressive manner, and the same and similar parts between the various embodiments may be referred to each other, and each embodiment focuses on the differences from other embodiments. Other embodiments of the present application will readily occur to those skilled in the art upon consideration of the specification and practice of the disclosure herein. This application is intended to cover any variations, uses or adaptations of this application that follow the general principles of this application and include common knowledge or conventional techniques in the technical field not disclosed in this application . The specification and examples are to be regarded as exemplary only, with the true scope and spirit of the application being indicated by the following claims.

It is to be understood that the present application is not limited to the precise structures described above and illustrated in the accompanying drawings and that various modifications and changes may be made without departing from the scope thereof. The scope of the application is limited only by the appended claims.

Claims (6)

1. A method for identifying defects in a silicon carbide wafer on a carbon surface of a wafer, wherein the method comprises: placing the silicon carbide wafer in an etching chamber, and using microwave plasma to etch the carbon surface of the silicon carbide wafer; After etching for a preset time, the silicon carbide wafer is taken out from the etching chamber, and ultrasonically cleaned with deionized water and alcohol; Defect types are determined according to the morphology and cross section of the etched pits on the carbon surface of the silicon carbide wafer. 2 . The method for identifying defects in a silicon carbide wafer on a carbon surface of a wafer according to claim 1 , wherein the microwave plasma is microwave hydrogen plasma or microwave hydrogen-oxygen plasma. 3 . 3. The method for identifying defects in a silicon carbide wafer on a carbon surface of a wafer according to claim 1, wherein the preset etching time is clear according to the carbon surface defect after etching, the shape of the corrosion pit is clear, the defects are fully exposed and The condition that no overlap occurs is determined. 4 . The method for identifying defects in silicon carbide wafers on a carbon surface of a wafer according to claim 1 , wherein the silicon carbide wafer is a non-doped 4H-SiC substrate, and wherein the microwave plasma is a hydrogen-oxygen plasma. 5 . body, the hydrogen flow rate is 200-400 sccm, the oxygen flow rate is 2-4 sccm, the etching temperature is 1000-1200 ℃, and the etching time is 1.5-2.5 h. 5. The method for identifying defects in a silicon carbide wafer on a carbon surface of a wafer according to claim 1, wherein the silicon carbide wafer is an N-type 4H-SiC substrate, wherein the microwave plasma is hydrogen plasma body, the hydrogen flow rate is 200-400sccm, the etching temperature is 1000-1200°C, and the etching time is 1.5-2.5h. 6. The method for identifying defects in a silicon carbide wafer on a carbon surface of a wafer according to claim 1, wherein the defect type is determined according to the morphology and the cross section of the etching pit on the carbon surface of the silicon carbide wafer, comprising: Using a 3D laser confocal microscope, observe the morphology and cross-section of the etching pit on the carbon surface of the silicon carbide wafer; According to the morphology and cross section of the etching pit, the defect type is determined.

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