JP2008021707A - Method of evaluating semiconductor substrate - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method of evaluating a semiconductor substrate by which it can be judged whether or not there is a conductive layer whose conduction type is different from that of the semiconductor substrate in the surface layer of the semiconductor substrate. <P>SOLUTION: The method uses a MOS structure to evaluate a semiconductor substrate. At least, an oxide film is formed on the semiconductor substrate, and an electrode is formed thereon to manufacture a MOS structure, and then an electric field is applied between the electrode and the semiconductor substrate in the direction of carrier accumulation of the semiconductor substrate, so as to measure an I-V characteristic. Based on an F-N current value at a specified electric field strength in the I-V characteristic, whether or not there is a conductive layer whose conductivity type is different from that of the semiconductor substrate in the surface layer of the semiconductor substrate is judged. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a method for evaluating a semiconductor substrate in which a different conductive type layer is unintentionally formed on the surface layer of the semiconductor substrate. Specifically, the electrical characteristics of the semiconductor substrate on which the different conductive type layer is formed are evaluated. It is about the method.

  In recent years, devices with high speed and low power consumption are further demanded as the speed of the system is increased and integration is increased and the development of portable terminals. Therefore, in manufacturing such a high-precision device, for example, a semiconductor substrate such as a silicon substrate having a low defect is required.

  Such a low-defect semiconductor substrate can be obtained by performing a heat treatment as disclosed in Patent Document 1, for example. By performing such a heat treatment, defects existing in the semiconductor substrate can be effectively eliminated, and a high-quality semiconductor substrate with suppressed defects can be provided to the market.

  However, such an annealed wafer is subject to contamination due to heat treatment. Contamination includes not only heavy metals such as Fe, but also contamination by dopants that are different from the conductivity type of the semiconductor substrate, which changes the resistance of the substrate surface, and in some cases, the conductivity type changes only on the surface layer of the substrate. Sometimes it ends up. When the above-described change in conductivity type occurs in the process of manufacturing a semiconductor substrate, such as annealing, it becomes a factor that the threshold voltage characteristics and the like fluctuate in a device manufactured using the semiconductor substrate. .

  Therefore, an evaluation method capable of appropriately evaluating a semiconductor substrate having a conductivity type layer different from the conductivity type of the substrate on the substrate surface as described above is desired. However, such a conductive type layer different from the conductive type of the substrate is not so thick and is limited to the extreme surface layer, and it is very difficult to detect and evaluate it. Conventionally, there has been no effective method for evaluating such an inverted conductivity type layer.

Japanese Patent Laid-Open No. 10-154713

  The present invention has been made in view of the above problems, and an object of the present invention is to provide a semiconductor substrate evaluation method capable of determining the presence or absence of a conductivity type layer different from the conductivity type of the semiconductor substrate in the semiconductor substrate surface layer. And

  In order to achieve the above object, the present invention is a method for evaluating a semiconductor substrate using a MOS structure, and at least an oxide film is formed on the semiconductor substrate and an electrode is formed on the oxide film to form a MOS. After producing the structure, an electric field is applied between the electrode and the semiconductor substrate so as to be on the accumulation side when viewed from the semiconductor substrate, and the IV characteristics are measured. The semiconductor substrate evaluation method is characterized in that the presence or absence of a conductivity type layer different from the conductivity type of the semiconductor substrate is determined from the FN current value of the semiconductor substrate.

In an ordinary semiconductor substrate that does not have a conductive type layer of a different conductivity type from the semiconductor substrate on the surface layer of the semiconductor substrate, an IV field is applied by applying an electric field between the electrode and the semiconductor substrate so as to be on the storage side as viewed from the semiconductor substrate When an electric field is measured, an electric current hardly flows because of the presence of an oxide film, but when an electric field is applied, an FN current is observed at a certain electric field strength.
On the other hand, when there is a conductivity type layer different from the conductivity type of the semiconductor substrate (a layer in which the conductivity type is inverted: hereinafter, simply referred to as a different conductivity type layer), the different conductivity type layer exists. , Resistance will increase by that much. For this reason, the value of the FN current flowing through the oxide film on the surface of the semiconductor substrate becomes small at the same electric field strength as in the case where the different conductivity type layers are not provided.
That is, it is possible to determine whether or not a different conductivity type layer exists on the surface layer of the semiconductor substrate based on the FN current value at a predetermined electric field strength.

In this way, it is possible to easily detect different conductivity type layers formed unintentionally on the extreme surface layer of the substrate that could not be detected in the past by using the MOS structure.
In addition, the present invention can use the same process as the conventional evaluation of GOI characteristics of a semiconductor substrate, and does not require investment for introduction of new equipment and maintenance of the equipment. Yes, it can be quickly evaluated using existing equipment without costing more than necessary.

At this time, when the FN current value when the predetermined electric field strength is 10 MV / cm is 1 μA or less, it can be determined that the semiconductor substrate has a conductivity type layer different from the conductivity type of the semiconductor substrate. ).
Thus, as a criterion for determining the presence or absence of different conductivity type layers, the FN current value when the predetermined electric field strength is 10 MV / cm is 1 μA or less. If the determination is made based on such a value, it is sufficiently smaller than the FN current value observed at the electric field strength of 10 MV / cm in a normal semiconductor substrate, and differs in the surface layer of the semiconductor substrate. If it has a conductive layer, it can be determined more reliably.

  Further, the present invention is a method for evaluating a semiconductor substrate using a MOS structure, at least after forming an oxide film on the semiconductor substrate and forming an electrode on the oxide film to produce a MOS structure, An I-V characteristic is measured by applying an electric field between the electrode and the semiconductor substrate so as to be on the depletion side when viewed from the semiconductor substrate. In the I-V characteristic, from the current value at a predetermined electric field strength, A semiconductor substrate evaluation method is provided, wherein the presence or absence of a conductivity type layer different from the conductivity type of the semiconductor substrate is determined in the semiconductor substrate surface layer.

For example, in the case of a normal semiconductor substrate, when an IV characteristic is measured by applying an electric field so as to be on the depletion side when viewed from the semiconductor substrate, a depletion layer is formed, and this depletion layer becomes a resistance and current does not easily flow. Become. However, in the case of a semiconductor substrate having different conductivity type layers, when an electric field is applied in the same manner, a current flows more easily than in the case of a normal semiconductor substrate, and a higher current value is exhibited. This is because a depletion layer is naturally formed by applying an electric field as described above, but on the other hand, the surface layer of the semiconductor substrate immediately below the oxide film, that is, a different conductivity type between the oxide film and the depletion layer in the semiconductor substrate. Since layers exist and carriers are accumulated, it is considered that the current flows more easily than in the case of a normal semiconductor substrate.
In this way, in the IV characteristics when an electric field is applied to the depletion side, it is possible to determine whether or not there is a different conductivity type on the surface layer of the semiconductor substrate based on the current value at a predetermined electric field strength. It is.

  Thus, different conductivity type layers formed unintentionally on the extreme surface layer of the semiconductor substrate can be easily detected using the MOS structure, and a process similar to the conventional GOI characteristic evaluation is used. Therefore, it is possible to make a quick evaluation with existing equipment without costing more than necessary.

At this time, when the current value when the predetermined electric field strength is 10 MV / cm is 0.1 μA or more, it can be determined that the semiconductor substrate has a conductivity type layer different from the conductivity type of the semiconductor substrate. .
Thus, as a criterion for the presence or absence of different conductivity type layers, the current value when the predetermined electric field strength is 10 MV / cm can be set to 0.1 μA or more. If the determination is made based on such a value, it is a value sufficiently larger than the current value observed when the electric field strength is 10 MV / cm in the IV characteristic of a normal semiconductor substrate, If the semiconductor substrate surface layer has different conductivity type layers, it can be determined more reliably.

  After measuring the IV characteristics, an electric field is further applied between the electrode and the semiconductor substrate to break down the oxide film, and then a voltage is applied again in the same direction to measure a breakdown voltage. The dopant concentration of a conductivity type layer different from the conductivity type of the semiconductor substrate can be calculated from the voltage.

  As described above, after performing the IV characteristic measurement as described above, an electric field is further applied, and after breakdown of the oxide film, a voltage is applied again in the same direction to measure a breakdown voltage, The dopant concentration of different conductivity type layers can be calculated from this breakdown voltage. With this measurement method, it is possible to easily determine the amount of contamination in the semiconductor substrate using conventional equipment.

A plurality of the MOS structures can be formed in the semiconductor substrate surface.
Thus, if a plurality of MOS structures are formed in the semiconductor substrate surface, it becomes possible to detect the in-plane distribution of different conductivity type layers on the surface layer of the substrate, and the semiconductor substrate can be evaluated with higher accuracy. .

At this time, it is preferable that the electrode is made of polysilicon.
In this way, if the electrode is made of polysilicon, it can be easily processed and formed into a desired shape. Moreover, it is a material often used as an electrode and is easy to procure.

The semiconductor substrate is preferably a silicon substrate.
In this way, if the semiconductor substrate is a silicon substrate, it is a material that is widely used in the manufacture of semiconductor elements, so that it can respond to market demand and provide effective data, and in turn, investigate product quality. Can provide security, etc.

  As described above, according to the present invention, it is possible to easily evaluate the surface layer quality of a semiconductor substrate using a MOS structure. In particular, by using a conventional measurement method for a conductive layer having a conductivity type different from that of the semiconductor substrate in the surface layer of the substrate, the semiconductor substrate can be evaluated by simply detecting it without excessive costs.

Hereinafter, embodiments of the present invention will be described, but the present invention is not limited thereto.
When a conductive type layer different from the conductive type of the semiconductor substrate is unintentionally formed on the semiconductor substrate, the thickness of the different conductive type layer is not so thick and is limited to the extreme surface layer. It is very difficult to detect and evaluate such different conductive type layers limited to the vicinity of the surface layer, and there has been no effective evaluation method in the past.

  Therefore, the present inventors conducted extensive research on these different conductivity type layers. As a result, when a MOS structure was produced on a semiconductor substrate and the IV characteristics were measured using the MOS structure, different conductivity types were observed on the surface layer of the semiconductor substrate. It has been found that there is a difference in IV characteristics depending on whether or not a mold layer is formed.

  Specifically, when measuring the IV characteristics, if a voltage is applied so as to be on the storage side when viewed from the semiconductor substrate, the FN current is sufficiently observed when different conductivity type layers exist. Not. This is because, in such a method of applying an electric field, different conductivity type layers existing on the surface of the semiconductor substrate act as resistances. Therefore, even when a voltage at which the FN current is supposed to flow is applied, the FN current does not flow, and the FN current is reduced by the resistance.

On the other hand, when a voltage is applied from the semiconductor side to the depletion side, the current value at the time of measuring IV characteristics is higher when a different conductivity type layer is present than when a different conductivity type layer is not present. Become. This is an application method of such an electric field, where a depletion layer is formed in the semiconductor substrate and the depletion layer acts as a resistance, but when there are different conductivity types on the surface of the semiconductor substrate, the different conductivity types It is thought that this is because current is more likely to flow because carriers are accumulated in the layer.
The present inventors found these things and completed the present invention.

Hereinafter, although the evaluation method of the semiconductor substrate of this invention is demonstrated in detail, referring drawings, this invention is not limited to this. FIG. 1 is a flowchart showing an example of a semiconductor substrate evaluation method of the present invention.
As shown in the flow chart of FIG. 1, first, a MOS structure is fabricated on a semiconductor substrate to be evaluated, and then the IV characteristics are measured using the MOS structure. Then, from this IV characteristic, it is evaluated whether or not a conductive type layer different from the conductive type of the semiconductor substrate is formed on the surface layer of the semiconductor substrate.

In such an evaluation method of the present invention, as will be described later, it is possible to use conventional equipment for the fabrication of the MOS structure and the measurement of the IV characteristics.
Here, an example of a measuring apparatus that can be used in measuring the IV characteristics in the evaluation method of the present invention will be briefly described with reference to FIG.
The IV characteristic measuring apparatus 4 includes a stage 5, which is also a back electrode and is grounded. The substrate to be evaluated W is placed on the stage 5 during measurement. In addition, a probe 7 that is movably supported is disposed, and this probe 7 is connected to one terminal of a variable power source 6 that can change the magnitude of a voltage to be applied. A voltmeter 8 that measures the applied voltage is connected in parallel to the variable power source 6, and an ammeter 9 is interposed between the probe 7 and the variable power source 6.

Hereinafter, the evaluation method of the present invention using such an IV characteristic measuring device 4 and the like will be specifically described for each stage of the flowchart of FIG.
(Production of MOS structure)
First, a substrate to be evaluated is prepared. Here, description will be made using a silicon substrate. As described above, the silicon substrate is widely used as a semiconductor substrate. By obtaining data using this silicon substrate as an evaluation target, it is possible to provide effective evaluation data corresponding to market demand.
Further, such a semiconductor substrate can be subjected to, for example, an annealing process. This is because it is necessary to evaluate whether or not the semiconductor substrate is contaminated by the annealing process and a different conductive type layer is formed on the substrate surface layer. In addition, a substrate to be evaluated can be appropriately prepared according to the purpose.

Next, oxidation is performed on the silicon substrate as described above to form an oxide film (gate oxide film). The oxide film can be easily formed by, for example, placing a silicon substrate on a boat and placing it in a horizontal heat treatment furnace or a vertical heat treatment furnace and performing a heat treatment in an oxygen atmosphere.
The method for forming this oxide film is not particularly limited, and for example, a conventional heat treatment furnace can be used, and the heat treatment conditions and the like can be determined each time according to the evaluation purpose.

Next, an electrode is formed on the oxide film formed on the silicon substrate. As the material of this electrode, for example, polysilicon can be used. If polysilicon is selected as the electrode material in this way, it is easy to process and procure, and it is easy to form an electrode in the same manner as in the prior art.
The material of this electrode is not particularly limited, and other materials such as Al can naturally be selected. It can be determined appropriately according to the cost or the like.

And an electrode is formed using such polysilicon. The electrode can be formed, for example, as follows, but the method for forming the electrode is not particularly limited.
First, a polysilicon film is grown on the oxide film on the silicon substrate surface. This polysilicon film can be grown, for example, by putting a silicon substrate taken out of a heat treatment furnace into a CVD apparatus and introducing a growth gas such as monosilane into a reaction vessel of the apparatus under reduced pressure or normal pressure. Then, after depositing the polysilicon layer as described above, impurities such as phosphorus are doped into the polysilicon layer using a thermal diffusion method or an ion implantation method to form a polysilicon layer having a low resistivity. Note that a low-resistivity polysilicon layer can also be formed by doping impurities at the same time when the polysilicon layer is deposited (Doped Poly-Si method).

After that, the low resistivity polysilicon layer formed as described above is subjected to a series of photolithography processes such as resist coating, exposure, and development, and then an etching process to obtain a desired position on the oxide film. A polysilicon electrode can be formed.
In this way, a MOS structure (MOS capacitor) in which an oxide film and a polysilicon electrode are formed on a silicon substrate can be manufactured.

  Further, when forming the MOS structure as described above, a plurality of MOS structures may be formed in the silicon substrate surface in accordance with the purpose of evaluation. If the evaluation MOS structure is manufactured at each position in the silicon substrate surface of the substrate to be evaluated in this way and evaluated, how the different conductivity type layers are distributed in the substrate surface. It can be easily grasped. The number of MOS structures to be manufactured is not particularly limited, and a large number of MOS structures can be manufactured if it is desired to perform in-plane evaluation with high accuracy. can do. For example, in the photolithography process described above, an MOS pattern can be formed in a desired number and position by forming electrode patterns in accordance with preset conditions.

(Measurement of IV characteristics)
As described above, after the MOS structure is formed on the silicon substrate, the IV characteristics are measured using the IV characteristics measuring apparatus 4 shown in FIG.
First, an evaluation substrate W having a MOS structure including the electrode 1, the oxide film 2, and the silicon substrate 3 is placed on the stage 5 of the IV characteristic measurement apparatus 4. Then, the probe 7 is brought into contact with the electrode 1 and measurement is performed by applying an electric field between the electrode 1 and the silicon substrate 3 using the variable power source 6.

(Evaluation when an electric field is applied to the storage side)
First, an example will be described in which the IV characteristic is measured by applying an electric field so as to be on the accumulation side when viewed from the silicon substrate side. That is, for example, when the conductivity type of the silicon substrate is P type, a negative voltage is applied to the electrode of the MOS structure of the substrate to be evaluated. Conversely, when the conductivity type of the silicon substrate is N-type, a positive voltage is applied to the electrode. In this way, an electric field is applied so as to be on the accumulation side depending on the conductivity type of the silicon substrate.

  At this time, for example, in the case of a normal substrate in which a different conductivity type layer does not exist on the surface layer of the silicon substrate at the position of the MOS structure, the current hardly flows because the oxide film is an insulator up to about 8 MV / cm in electric field strength. When the electric field is higher than this, an FN current (tunnel current) flows through the oxide film, and an IV characteristic in which the current value increases rapidly as shown in FIG. 3 is obtained. In the example shown in FIG. 3, it can be seen that the FN current is generated when the potential difference between the electrode and the silicon substrate exceeds about 20 V (electric field strength: 8 MV / cm, gate oxide film thickness 25 nm). .

  However, conversely, when different conductivity type layers exist, as shown in FIG. 4, the FN current was generated in the example of FIG. : 10 MV / cm, gate oxide film thickness 25 nm), the current value does not change significantly and is almost constant. Thus, the FN current cannot be seen even in the state where the electric field where the FN current should be observed is applied. This is because, as described above, a conductive type layer different from the conductive type of the silicon substrate on the surface layer of the silicon substrate functions as a resistor.

  Therefore, in the case where there is no different conductivity type layer as shown in FIG. 3, an FN current is observed at the time of 25 V (electric field strength: 10 MV / cm), but different conductivity as shown in FIG. In the case where the mold layer is present, no FN current is seen even when 10 MV / cm is applied.

Thus, in the IV characteristics measured by applying an electric field between the electrode and the silicon substrate so as to be on the accumulation side as seen from the silicon substrate, the silicon nitride can be obtained from the FN current value when a constant electric field strength is applied. It can be easily determined whether or not there are different conductivity type layers on the surface layer of the substrate.
As an example of a criterion for determining the presence or absence of the different conductivity type layers, it is determined that the silicon substrate surface layer has different conductivity type layers when the FN current value when applying 10 MV / cm is 1 μA or less. be able to.

(Evaluation when an electric field is applied to the depletion side)
Next, an example in which the IV characteristic is measured by applying an electric field so as to be on the depletion side when viewed from the silicon substrate side will be described. That is, for example, when the conductivity type of the silicon substrate is P-type, a positive voltage is applied to the electrode of the MOS structure of the substrate to be evaluated. Conversely, when the conductivity type of the silicon substrate is N-type, a negative voltage is applied to the electrode. In this way, an electric field is applied so as to be on the depletion side depending on the conductivity type of the silicon substrate.

  In this case, first, in the case of a normal substrate in which a different conductivity type layer (inversion layer) does not exist on the surface layer of the silicon substrate at the position of the MOS structure, a depletion layer is formed immediately below the gate oxide film, and this depletion layer serves as a resistance. In order to work, the FN current is not observed like the IV characteristic without the inversion layer shown in FIG. 5, and is almost constant at around 10 MV / cm (25 V).

  On the other hand, when different conductivity type layers exist on the surface layer, as shown in the graph with the inversion layer in FIG. 5, the value of the flowing current is larger than that in the case of the normal substrate (without the above inversion layer). growing. This is because a depletion layer is formed by applying an electric field so as to be on the depletion side as usual, but on the surface layer of the silicon substrate between the depletion layer and the oxide film on the silicon substrate surface, Different conductivity type layers exist, and carriers exist in the regions of the different conductivity type layers. It is considered that current flows easily by the amount of carriers accumulated in the different conductivity type layers, and the current value is larger.

Thus, in the IV characteristics measured by applying an electric field between the electrode and the silicon substrate so as to be on the depletion side when viewed from the silicon substrate, whether there is a different conductivity type layer on the surface layer of the silicon substrate from the current value. Whether or not can be easily determined.
As an example of a criterion for determining the presence / absence of this different conductivity type layer, in the IV characteristics, when the current value when the electric field strength is 10 MV / cm is 0.1 μA or more, different conductivity is applied to the surface layer of the silicon substrate. It can be determined that it has a mold layer. If such a current value is used as a criterion for determination, the current value is sufficiently larger than the current value in the IV characteristic in the case of a normal substrate in which different conductivity type layers are not formed on the surface layer. It is possible to determine that this is a case having different conductivity type layers.

In addition, when measuring the dopant concentration of a conductive type layer having a conductivity type different from that of the silicon substrate that is unintentionally formed on the surface layer of the silicon substrate as described above, for example, the following method may be used. it can.
First, after measuring the IV characteristics as described above, an electric field is further applied between the electrode and the silicon substrate to break down the oxide film. An example of the state in which the MOS structure is changed is shown in FIG. As shown in FIG. 6, when there is a different conductivity type layer 10 (inversion layer) on the surface layer, a PN junction is formed on the surface of the silicon substrate. In FIG. 6, the oxide film 2 is broken. The silicon substrate 3 is P-type, the different conductivity type layer 10 is N-type, and the polysilicon electrode 1 is N-type by phosphorous doping.
If the silicon substrate 3 is N-type, a P-type polysilicon electrode 1 may be used.

  Then, an electric field is applied again in the same direction to cause an avalanche breakdown at the PN junction, and a breakdown voltage is measured. From the breakdown voltage measured in this way and the formula described on pages 108-109 of the literature (SM Sze. Semiconductor Devices. 2002. John Wiley & Sons, Inc.), the dopant concentration in different conductivity type layers. Can be calculated, and the amount of contamination on the surface layer of the substrate can be measured.

As described above, an effective evaluation method has not been established in the past with respect to the conductive type layers having different substrate surface layers. However, according to the evaluation method of the present invention, a MOS structure is manufactured and IV characteristics are measured. From the obtained characteristics, the presence / absence of a different conductivity type layer can be determined according to the current value at a predetermined electric field strength in accordance with the direction of application of the electric field, which is really simple. And it does not require new equipment, etc. For example, since the same equipment as that used in the conventional GOI measurement etc. can be used, it does not cost more than necessary. Since the same IV characteristic measurement method can be used, measurement can be performed quickly.
Furthermore, the dopant concentration of the conductivity type layer can be measured, and the amount of contamination on the surface of the semiconductor substrate can be known.

EXAMPLES Hereinafter, although an Example demonstrates this invention further in detail, this invention is not limited to this.
As a sample wafer, first, a P-type silicon substrate having a diameter of 200 mm was prepared. Boron was used as the P-type dopant.
And on this P-type silicon substrate, an N-type layer different from the P-type of the silicon substrate is formed on the surface layer of the central portion in the substrate surface by locally contaminating phosphorus (the central portion in the substrate surface). did.
The evaluation method of the present invention is carried out on this sample wafer.

  This sample wafer was put into an oxidation furnace and thermally oxidized in a dry atmosphere at 900 ° C. to form a 25 nm gate oxide film on the surface of the sample wafer. A polysilicon layer was formed by depositing phosphorus-doped polysilicon on the front oxide film on the front-side oxide film by a CVD method on the sample wafer on which this oxide film was formed. The thickness of the polysilicon layer at this time is about 300 nm, and the phosphorus doping amount is 25 ohm / sq. In sheet resistance. I tried to be about.

A photolithography process was performed on this polysilicon layer, and etching was further performed to fabricate a large number of MOS capacitors on the sample wafer surface. Fluorine nitric acid was used for etching the polysilicon layer after the photolithography process.
Finally, in order to remove the oxide film on the back surface, a resist was applied to the surface, and the back surface treatment was performed by wet etching with dilute hydrofluoric acid.

The IV characteristics of the sample wafer thus fabricated were measured using the same MOS method as in the conventional GOI measurement using each in-plane MOS capacitor. In this measurement, a tester connected to a full auto prober was used. In addition, probers and wiring with noise countermeasures were used.
The measurement conditions at this time were the voltage ramp-up method, the averaging time was 20 msec, the step voltage height was 0.25 MV / cm, and the averaging time after the voltage step was increased was 200 msec. And the negative voltage was applied to the electrode so that it might become the accumulation | storage side with respect to a silicon substrate (P type), and the IV characteristic was measured.

  When the measurement is performed in this manner, the IV characteristics as shown in FIG. 3 are seen in the inner and outer peripheral portions of the substrate surface that are not contaminated by phosphorus (N-type), and it is determined that the substrate is not contaminated. I was able to. At this time, the electric field strength when the FN current flows was 10 MV / cm.

  On the other hand, in the central portion in the substrate surface contaminated with phosphorus, the FN current observed in the outer peripheral portion in the substrate surface cannot be observed in the same measurement range, and the IV characteristic as shown in FIG. Obtained and determined to be contaminated.

  On the contrary, when the evaluation method of the present invention was applied by applying an electric field so as to be on the depletion side, it can be determined that more current flows in the contaminated region as shown in FIG. In addition, it was possible to determine that the current did not flow so much in the uncontaminated region and that it was not contaminated, and it was also confirmed that the evaluation method of the present invention was effective.

  The present invention is not limited to the above embodiment. The above-described embodiment is an exemplification, and the present invention has substantially the same configuration as the technical idea described in the claims of the present invention, and any device that exhibits the same function and effect is the present invention. It is included in the technical scope of the invention.

It is a flowchart which shows an example of the evaluation method of the semiconductor substrate of this invention. It is a schematic block diagram which shows an example of the apparatus which measures the IV characteristic which can be used in the evaluation method of the semiconductor substrate of this invention. It is a graph which shows an example of an IV characteristic when an electric field is applied to the accumulation | storage side with respect to a silicon substrate with the normal silicon substrate in which a different conductivity type layer does not exist in a surface layer. It is a graph which shows an example of an IV characteristic when an electric field is applied to the accumulation | storage side with respect to a silicon substrate with the silicon substrate in which a different conductivity type layer exists in a surface layer. A graph showing an example of IV characteristics when an electric field is applied to the depletion side with respect to a silicon substrate on a normal silicon substrate in which different conductivity type layers (inversion layers) do not exist on the surface layer, and different conductivity type layers are surface layers 5 is a graph showing an example of IV characteristics when an electric field is applied to the silicon substrate on the depletion side with respect to the silicon substrate. It is the schematic which shows an example of the MOS structure by which the oxide film was dielectrically broken down.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Electrode, 2 ... Oxide film, 3 ... Silicon substrate, 4 ... IV characteristic measuring apparatus,
5 ... Stage 6 ... Variable power supply 7 ... Probe 8 ... Voltmeter
9 ... ammeter, 10 ... different conductivity type layers, W ... substrate to be evaluated.

Claims (8)

  A method for evaluating a semiconductor substrate using a MOS structure, wherein at least an oxide film is formed on a semiconductor substrate and an electrode is formed on the oxide film to produce a MOS structure, and then the electrode and the semiconductor substrate An I-V characteristic is measured by applying an electric field so as to be on the accumulation side when viewed from the semiconductor substrate, and the surface layer of the semiconductor substrate is determined from the FN current value at a predetermined electric field strength in the IV characteristic. A method for evaluating a semiconductor substrate, comprising: determining whether or not there is a conductivity type layer different from the conductivity type of the semiconductor substrate.   2. The device according to claim 1, wherein when the predetermined electric field strength is 10 MV / cm, when the FN current value is 1 μA or less, it is determined that the semiconductor substrate has a conductivity type layer different from the conductivity type of the semiconductor substrate. Evaluation method of semiconductor substrate.   A method for evaluating a semiconductor substrate using a MOS structure, wherein at least an oxide film is formed on a semiconductor substrate and an electrode is formed on the oxide film to produce a MOS structure, and then the electrode and the semiconductor substrate In the meantime, an I-V characteristic is measured by applying an electric field so as to be on the depletion side when viewed from the semiconductor substrate. In the I-V characteristic, a current value at a predetermined electric field strength is used to measure the semiconductor A method for evaluating a semiconductor substrate, comprising determining whether or not there is a conductive type layer different from the conductive type of the substrate.   4. The method according to claim 3, wherein when the predetermined electric field strength is 10 MV / cm and the current value is 0.1 μA or more, it is determined that the semiconductor substrate has a conductivity type layer different from the conductivity type. 5. A method for evaluating a semiconductor substrate.   After the IV characteristic measurement, an electric field is further applied between the electrode and the semiconductor substrate to break down the oxide film, and then a voltage is applied again in the same direction to measure a breakdown voltage. From the breakdown voltage, The semiconductor substrate evaluation method according to claim 1, wherein a dopant concentration of a conductivity type layer different from a conductivity type of the semiconductor substrate is calculated.   The semiconductor substrate evaluation method according to claim 1, wherein a plurality of the MOS structures are formed in the surface of the semiconductor substrate.   The method for evaluating a semiconductor substrate according to claim 1, wherein the electrode is made of polysilicon. The semiconductor substrate evaluation method according to claim 1, wherein the semiconductor substrate is a silicon substrate.

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