JP3855943B2 - HF defect evaluation method for SOI wafer - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for detecting and evaluating HF defects on a silicon-on-insulator (SOI) layer on the surface of a silicon wafer, and the substrate surface is subjected to HF (hydrofluoric acid) vapor treatment as a pretreatment of the wafer. The present invention relates to an SOI wafer HF defect evaluation method that etches and accurately detects HF defects with less particle contamination on the wafer.
[0002]
[Prior art]
An SOI wafer in which a thin silicon layer isolated on a silicon substrate is formed enables a high speed operation and a low power consumption operation by forming a device on the silicon layer. The main manufacturing method of such an SOI wafer is that a SIMOX (Separation by IMplanted Oxygen) wafer in which a buried oxide film is formed inside a silicon substrate by oxygen ion implantation and high temperature annealing, and two silicon wafers are bonded with a thermal oxide film. There are two types of bonded SOI wafers in which one is thinned after being combined.
[0003]
Of these, the SIMOX wafer is considered to be a wafer that has excellent surface SOI layer thickness uniformity and is suitable for reducing power consumption during LSI operation. An ion implantation process for implanting oxygen into a silicon substrate, and then the wafer is heat-treated. It is manufactured from two processes including a high temperature annealing process.
[0004]
In the high-temperature annealing process, it is known that a defect (silicide) in which silicon and metal are combined due to a metal or the like is generated, and this causes a decrease in device yield at the time of device fabrication. As a method for detecting and evaluating this defect, HF defect evaluation is performed by re-etching the SOI layer on the surface of the evaluation substrate by HF cleaning in order to dissolve the defect (silicide), and then observing the entire defective portion of the wafer with an optical microscope. The method is common.
[0005]
[Problems to be solved by the invention]
It is said that the HF defects that can be found by the above evaluation method cause a decrease in the device yield, and it is necessary to suppress the generation in the high-temperature annealing process as much as possible. It is an important factor in technological development.
[0006]
As an HF defect evaluation method, the SOI layer on the substrate surface is etched by HF cleaning, and then the defective portion of the wafer is observed using an automatic defect counting device such as an optical microscope or a surface inspection device. There is a problem that there is a lot of particle contamination on the wafer.
[0007]
That is, when the wafer is cleaned with HF, a large number of particles adhere to the wafer, and when the entire surface of the wafer is observed by the automatic defect counting device, it takes a lot of time and labor to distinguish between HF defects and particles. There is a problem that HF defect evaluation cannot be performed.
[0008]
The present invention is an SOI wafer HF defect evaluation method capable of evaluating HF defects quickly and accurately during automatic defect counting using an optical microscope or the like, with less particle adhesion during pre-processing of a SIMOX wafer or a bonded SOI wafer. The purpose is to provide.
[0009]
[Means for Solving the Problems]
As a result of intensive studies on a method capable of etching with less particle adhesion when defects (silicide) are dissolved, the inventors can achieve the object by etching the SOI layer by HF (hydrofluoric acid) vapor treatment. As a result, the present invention was completed.
[0010]
That is, the present invention is an SOI wafer HF defect evaluation method characterized by detecting and evaluating an HF defect after performing a pretreatment for etching the surface SOI layer of the SOI wafer with HF vapor.
[0011]
Further, according to the present invention, in the pretreatment having the above-described configuration, a reaction container that stores an SOI wafer, and an HF that generates hydrofluoric acid vapor by bubbling a hydrofluoric acid solution with an inert gas and supplies the hydrofluoric acid vapor into the reaction container. A method for evaluating an HF defect in an SOI wafer, characterized by using a steam generator.
[0012]
DETAILED DESCRIPTION OF THE INVENTION
The etching by the conventional HF cleaning is solution etching, and the wafer surface on which the surface natural oxide film is etched exhibits water repellency and many particles adhere to it. On the other hand, the pretreatment of the present invention is an etching method that uses hydrofluoric acid vapor for etching, and has the advantage that fewer particles adhere to the wafer than fewer particles in the vapor.
[0013]
The pre-processing of the HF defect evaluation method according to the present invention will be described in detail. The etching apparatus shown in FIG. 1 includes a reaction vessel containing an SOI wafer, and hydrofluoric acid solution is bubbled with an inert gas to generate hydrofluoric acid vapor. And an HF vapor generator that is generated and supplied into the reaction vessel.
[0014]
As shown in FIG. 1, for example, the apparatus has an open / close door that allows the SOI wafer w to be processed to be taken in and out of a side surface or an upper surface of a reaction vessel 1 made of a material that is not easily eroded by HF vapor, for example, a fluorine resin. Alternatively, a lid 2 is provided, gas inlets 3 and outlets 4 are provided on both side surfaces of the reaction vessel 1, and a stage 5 for horizontally placing the SOI wafer w is disposed in the reaction vessel 1. A configuration in which a cooler 6 capable of cooling the wafer w is incorporated can be adopted.
[0015]
The HF vapor generator 10 stores a hydrofluoric acid solution in a sealable chemical container 11 and generates hydrofluoric acid vapor by bubbling with an inert gas such as N ₂ gas in a high purity gas pipe 12. By exhausting from the exhaust port 4 of the reaction vessel 1 with an intake pump, the gas can be supplied into the reaction vessel 1 through the gas pipe 13 connected to the gas introduction port 3.
[0016]
The bubbling gas is preferably an inert high-purity gas so that particles are not included in the vapor. For example, nitrogen, argon, or helium gas having a dew point of −110 ° C. or less can be employed.
[0017]
In the present invention, the SOI wafer w is placed on the stage 5 in the reaction vessel 1 and cooled by the cooler 6 because the hydrofluoric acid vapor introduced into the reaction vessel 1 is condensed on the surface of the wafer w. In order to promote etching, the cooling temperature may be appropriately selected according to conditions such as the amount of vapor.
[0018]
In this invention, after completing the pretreatment for etching using hydrofluoric acid vapor, the method for evaluating the HF defect of the wafer can adopt any known method and apparatus, for example, by observing the wafer surface to detect the defect. Automatic defect counting devices such as optical microscopes and surface inspection devices that can count the parts can be used.
[0019]
【Example】
Example 1
An etching apparatus comprising the reaction vessel 1 and the HF vapor generator 10 shown in FIG. 1 was used. The lid 2 of the reaction vessel 1 was opened, the SIMOX wafer was placed on the stage 5, and the cooler 6 was operated to cool the stage and the wafer to 15 ° C. As a chemical solution for etching, 300 ml of 50% hydrofluoric acid solution was placed in the chemical solution container 11, and N ₂ gas was allowed to flow at a flow rate of 1 l / min. Etching was allowed to stand for 5 minutes (min) in this air flow state for 1 hour (hr). Thereafter, only N ₂ gas was allowed to flow in the reaction vessel for 15 minutes (min) to perform N ₂ gas replacement, the lid 2 was opened, and the SIMOX wafer was taken out.
[0020]
When the SIMOx wafer after the treatment was measured for the amount of increase in particles of 0.13 μm or more by the wafer surface inspection apparatus measurement, it was 5 or less in the 5-minute treatment and 30 or less in the 1-hour treatment.
[0021]
For comparison, when the amount of increase in particles was measured when the conventional cleaning treatment of immersing in a 0.5% HF solution was performed for 4 minutes, the number of particles increased by 1300 to 2200 (pieces). The results of this comparative example and Example 1 are shown in the graph of FIG. 2 showing the relationship between etching time and increased particles.
[0022]
Example 2
The SIMOX wafer that had been subjected to the pretreatment for 5 minutes in Example 1 was observed for an HF defect of 5.0 (μm) or more and an increased amount of particles with an optical microscope. The result is shown in the graph of FIG. That is, in the etching with HF vapor, the number of particles increased is 4, but in the case of the conventional 0.5% HF cleaning, it is 46, and in the SIMOX wafer, the pre-treatment according to the present invention is more effective than the HF cleaning. Adhesion was extremely small and good.
[0023]
In addition, it is confirmed that the HF defect observation by the optical microscope of the SIMOX wafer subjected to the pretreatment for 5 minutes and 1 hour is good, and according to the present invention, the HF defect on the surface of the SIMOX wafer can be observed easily and quickly. Became clear.
[0024]
【The invention's effect】
According to the present invention, it becomes possible to perform predetermined etching on the surface of the SOI wafer without particle contamination, and the HF defect can be easily and quickly observed during subsequent observation of the entire surface of the HF defect using an optical microscope. Furthermore, the HF defect of the SIMOX wafer can be automatically and accurately measured by an automatic defect counting apparatus such as a surface inspection apparatus, and the SIMOX wafer can improve the processing capability of HF defect observation.
[Brief description of the drawings]
FIG. 1 is an explanatory view showing a configuration example of an etching apparatus according to the present invention.
FIG. 2 is a graph showing the relationship between etching time and increased particles.
FIG. 3 is a graph showing the relationship between a difference in pretreatment methods and increased particles.
[Explanation of symbols]
w SOI wafer 1 reaction vessel 2 lid 3 gas inlet 4 outlet 5 stage 6 cooler 10 HF vapor generator 11 chemical vessel 12 high-purity gas pipe 13 gas pipe

Claims (2)

An SOI wafer HF defect evaluation method for detecting and evaluating an HF defect after performing a pretreatment for etching the surface SOI layer of the SOI wafer with HF vapor. The pre-treatment uses a reaction vessel containing an SOI wafer and an HF vapor generator for bubbling a hydrofluoric acid solution with an inert gas to generate hydrofluoric acid vapor and supplying the vapor into the reaction vessel. The HF defect evaluation method of SOI wafer as described in 2.

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