JP2006013102A - Method for evaluating soi wafer - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an evaluation method that dispenses with a large-scale apparatus and a number of processes, such as a photolithography process, and can quickly, easily, and precisely measure the electrical characteristics of an SOI wafer, and improves the working efficiency of a measuring apparatus for evaluating the SOI wafer efficiently. <P>SOLUTION: In the method for evaluating the SOI wafer using a mercury probe, at least a natural oxide film formed on the surface of the SOI wafer is removed by performing fluoric acid cleaning treatment to the SOI wafer, second cleaning treatment is made to the SOI wafer in which the natural oxide film is removed by using a cleaning solution for forming a silicon oxide film, an oxide film is formed on the surface of the SOI layer in the SOI wafer, and the mercury probe is brought into contact with the SOI wafer in which the oxide film is formed for evaluating the SOI wafer. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an SOI wafer evaluation method for evaluating an SOI layer of an SOI wafer and an interface between the SOI layer and a buried oxide layer using a mercury probe.

  In recent years, SOI wafers having an SOI structure in which an SOI layer (also referred to as a silicon active layer) is formed on an electrically insulating oxide film have been developed to have high speed, low power consumption, high withstand voltage, Due to its excellent environmental properties and the like, it is particularly attracting attention as a high-performance LSI wafer for electronic devices. This is because an SOI wafer has a buried oxide film (hereinafter sometimes referred to as a BOX layer) that is an insulator between the support substrate and the SOI layer, and the electronic device formed in the SOI layer has a withstand voltage. This is because it has a great advantage that it is high and the soft error rate of α rays is low.

  In addition, in a thin film SOI wafer having an SOI layer thickness of 1 μm or less, a MOS (Metal Oxide Semiconductor) type semiconductor device formed on the SOI layer has a source / drain PN junction area when operated in a fully depleted type. Since the capacitance can be reduced, parasitic capacitance can be reduced and device drive speed can be increased. Furthermore, since the capacitance of the BOX layer serving as the insulating layer is in series with the depletion layer capacitance formed immediately below the gate oxide film, the depletion layer capacitance is substantially reduced, and low power consumption can be realized.

  Recently, higher-quality SOI wafers are required for further miniaturization and higher performance of electronic devices. For this reason, the quality of the SOI layer of SOI wafers is actively evaluated. As one method for evaluating the quality of the SOI wafer, a MOS structure is formed on the surface of the SOI layer, and a voltage is applied to the electrode portion to evaluate the quality of the SOI layer.

  However, when a MOS structure is formed on an SOI layer in order to evaluate an SOI wafer, a large-scale apparatus and a large number of processes are required to perform a photolithography process and the like. There were problems such as chipping. Further, this method can evaluate the quality of the surface of the SOI layer, but is incomplete as an evaluation of the interface between the SOI layer and the BOX layer.

  Therefore, an evaluation method has been developed that can more easily evaluate an SOI wafer using a mercury probe without forming a MOS structure on the SOI wafer through a number of conventional processes. As one of them, a Pseudo MOS FET method for evaluating an SOI wafer has been proposed (see, for example, Patent Documents 1 and 2 and Non-Patent Documents 1 and 2). According to this method, the interface state density at the interface between the SOI layer and the BOX layer, the electrical characteristics of the SOI layer, and the like can be measured accurately and simply.

  Here, the Pseudo MOS FET method will be briefly described with reference to the drawings. First, as shown in FIG. 7, a needle probe or a mercury probe is directly contacted as an evaluation electrode on the SOI layer 1 side of the SOI wafer 5 that forms a pseudo MOS structure using the BOX layer 2 as a gate oxide film. Are a source electrode 6 and a drain electrode 7. Then, the back surface of the SOI wafer 5, that is, the surface on the support wafer 3 side of the SOI wafer 5 is vacuum-sucked on a stage that is also used as an electrode to form the gate electrode 4, and a voltage is applied between these electrodes. Various electrical characteristics can be obtained. In this case, the gate electrode 4 can be formed, for example, by bringing a needle into contact with the back surface of the SOI wafer 5.

  Further, in the evaluation of the SOI wafer by such a Pseudo MOS FET method, the natural oxide film formed on the surface of the SOI layer can be removed by washing the SOI wafer with an aqueous solution containing hydrofluoric acid before the evaluation. It becomes possible to evaluate the electrical characteristics of the SOI wafer more accurately by eliminating the influence of the natural oxide film.

  Furthermore, in this evaluation method using the Pseudo MOS FET method, if a mercury probe is used as the source electrode and the drain electrode, a probe contact hole generated when the needle probe is brought into contact with the surface of the SOI layer is not formed. In addition, the measurement near the first measurement point can be performed easily and stably.

Then, after forming a Pseudo MOS structure as described above, the relationship between the gate voltage _{V G} and the drain current _{I D} by applying a gate voltage to the positive side while applying a drain voltage, i.e., the _V G -I _D characteristic By measuring, the electron mobility of the SOI layer and the interface state density at the interface between the SOI layer and the BOX layer can be evaluated. On the other hand, by measuring the V _G -I _D characteristic by applying a gate voltage on the negative side while applying a drain voltage, it is possible to evaluate the charge density of the hole mobility and the BOX layer of the SOI layer.

However, when the SOI wafer is evaluated by applying the gate voltage to the negative side as described above, conventionally, the SOI wafer is washed with an aqueous solution containing hydrofluoric acid to remove the natural oxide film on the surface of the SOI layer. since the V _G -I _D characteristic 10-12 hours and then start the measurements, or measurements to be passed more is not stable in, it was not possible to make accurate measurements of V _G -I _D characteristic . Therefore, a very long evaluation time is required to evaluate the SOI wafer, and there is a problem that the efficiency of the SOI wafer evaluation is hindered by reducing the operating rate of the measuring apparatus.

  In this case, since the SOI wafer must be precisely managed so that impurities do not adhere to the wafer after the natural oxide film is removed and until the measurement is completed, there is a problem that the management burden is large. there were.

JP 2001-60676 A JP 2001-267384 A S. Cristoleveanu et al., "A Review of the Pseudo-MOS Transistor in SOI Wafers: Operation, Parameter Extraction, and Applications" IEEE Trans. Electron Dev, 47 1018 (2000). H.J.Hovel, "Si film electrical characterization in SOI substrates by HgFET technique" Solid-State Electronics, 47, 1311 (2003).

  Accordingly, the present invention has been made in view of the above problems, and the object of the present invention is to eliminate the need for a large-scale apparatus such as a photolithography process or the like and a large number of processes, and to shorten the electrical characteristics of the SOI wafer. An object of the present invention is to provide an evaluation method that can be measured easily and accurately in time, and that can efficiently evaluate an SOI wafer by improving the operating rate of the measuring device.

  In order to achieve the above object, according to the present invention, in a method for evaluating an SOI wafer using a mercury probe, at least the SOI wafer is formed on the surface of the SOI wafer by performing a hydrofluoric acid cleaning treatment. After removing the natural oxide film, the SOI wafer from which the natural oxide film has been removed is subjected to a second cleaning process using a cleaning solution capable of forming a silicon oxide film to form an oxide film on the SOI layer surface of the SOI wafer. An SOI wafer evaluation method is provided, characterized in that an SOI wafer is evaluated by contacting a mercury probe with the SOI wafer on which the oxide film is formed and then contacting the mercury probe.

  Thus, after removing the natural oxide film formed on the SOI wafer by the hydrofluoric acid cleaning process, the second cleaning process is performed using the cleaning solution having a component capable of forming the silicon oxide film on the SOI wafer. By newly forming a silicon oxide film having a uniform film thickness on the surface of the SOI layer, the charge state on the surface of the SOI layer can be quickly stabilized to a steady state. As a result, the time required for measuring the electrical characteristics of the SOI wafer after removing the natural oxide film can be greatly reduced compared to the conventional method, and the evaluation of the SOI wafer can be performed in a very short time. The utilization rate can be improved. In addition, the present invention can effectively stabilize the charge state on the surface of the SOI layer in a short time by forming an oxide film by performing the second cleaning process before measuring the electrical characteristics of the SOI wafer. Therefore, management of the SOI wafer is facilitated, variation in measured values is further reduced, and highly reliable SOI wafer can be stably evaluated.

At this time, the thickness of the oxide film formed on the surface of the SOI layer is preferably 5 nm or less (claim 2).
By making the oxide film formed on the surface of the SOI layer very thin with a thickness of 5 nm or less in this way, when the SOI wafer is evaluated by contacting the mercury probe after the oxide film is formed, the thin silicon film is formed. Due to the tunnel effect of the oxide film, electricity can be reliably passed through the oxide film, so that the electrical characteristics of the SOI wafer can be accurately measured.

  In this case, the cleaning solution capable of forming the silicon oxide film includes ozone water, an aqueous solution containing ammonia and hydrogen peroxide solution, a hydrogen peroxide solution, an aqueous solution containing hydrochloric acid and hydrogen peroxide solution, sulfuric acid and hydrogen peroxide solution. (Claim 3), and particularly preferably, the highly oxidative aqueous solution is electrolytic anode water (Claim 4). .

The aqueous solution shown above contains components that can quickly form a silicon oxide film on the SOI layer surface, such as OH ⁻ ions contained in highly oxidizing aqueous solutions such as ozone, hydrogen peroxide, and electrolytic anode water. By performing the second cleaning process on the SOI wafer using an aqueous solution selected from these, an oxide film having a uniform film thickness can be formed very stably on the surface of the SOI layer.

Furthermore, it is preferable that the temperature of the cleaning solution capable of forming the silicon oxide film is room temperature or higher and 80 ° C. or lower when the second cleaning process is performed.
If the second cleaning process is performed using a cleaning solution having a liquid temperature in such a temperature range, OH ⁻ ions contained in ozone, hydrogen peroxide, electrolytic anode water, etc., and silicon on the surface of the SOI layer can be quickly obtained. By reacting, an oxide film having a uniform film thickness can be easily and reliably formed.

In the present invention also by measuring the V _G -I _D characteristic of the oxide film is brought into contact with the mercury probe SOI wafer to form the positive hole side, the hole mobility of the SOI layer in the SOI wafer and / or It is preferable to evaluate the charge density of the buried oxide film.
As described above, in the present invention, the natural oxide film is removed by the hydrofluoric acid cleaning process, and then the second cleaning process is performed to newly form an oxide film on the SOI layer surface, thereby reducing the charge state on the SOI layer surface. since it is possible to time stabilize, then by measuring the V _G -I _D characteristic of the hole side are brought into contact with the mercury probe SOI wafer, it is possible to significantly reduce the variation in the measured values. Therefore, in the past, the measurement values were likely to vary, and the hole mobility of the SOI layer and the charge density of the buried oxide film, which required a long time for accurate measurement, were evaluated with high accuracy and high reliability in a short time. can do.

Furthermore, in the present invention, after the natural oxide film is removed by performing the hydrofluoric acid cleaning treatment, the mercury probe is brought into contact with the SOI wafer from which the natural oxide film has been removed to measure the V _{G- ID} characteristics on the electron side. It is preferable to evaluate the electron mobility of the SOI layer and / or the interface state density between the SOI layer and the buried oxide film, and then perform the second cleaning treatment on the SOI wafer.

As described above, after removing the natural oxide film by the hydrofluoric acid cleaning process, before the second cleaning process is performed on the SOI wafer, the mercury probe is brought into contact with the SOI wafer to measure the V _{G- ID} characteristics on the electron side. Thus, the electron mobility and interface state density can be evaluated with high accuracy, and the quality of the SOI wafer can be evaluated in more detail.

As described above, according to the present invention, when the SOI wafer is evaluated, the SOI wafer is subjected to the second cleaning process after the native oxide film of the SOI wafer is removed by the hydrofluoric acid cleaning process, and the surface of the SOI layer is newly added. By forming the silicon oxide film, the charge state on the surface of the SOI layer can be quickly stabilized to a steady state. As a result, the time required to measure the electrical characteristics of the SOI wafer after removing the natural oxide film can be greatly reduced compared to the conventional method, and the evaluation of the SOI wafer can be performed in a very short time. It is also possible to improve the operating rate. In the present invention, it is possible to greatly reduce the time required for measuring the electrical characteristics of the SOI wafer after removal of the native oxide film, to be facilitated management of the SOI wafer, further measures V _G -I _D characteristic In this case, the charge state on the surface of the SOI layer is stable, and the thickness of the silicon oxide film formed by the second cleaning process is uniform, so that variations in measured values are reduced and high accuracy and reliability are achieved. A high SOI wafer can be evaluated stably.

Hereinafter, although an embodiment is described about the present invention, the present invention is not limited to these.
Conventionally, when evaluating the hole mobility and BOX layer charge density of an SOI layer in an SOI wafer by the Pseudo MOS FET method, the SOI wafer was washed with an aqueous solution containing hydrofluoric acid to remove the natural oxide film on the surface of the SOI layer. After that, the measured value is not stable unless more than 10 hours elapses. Therefore, there is a problem that a very long time is required for the evaluation of the SOI wafer.

This is for example the case of measuring the V _G -I _D characteristic of the gate voltage, such as evaluation of the hole mobility and BOX layer charge density is applied to the negative side, the positive charge such as H + ions on the SOI layer surface If the surface state is not controlled by adsorbing, the charge on the surface of the SOI layer is not stabilized and accurate measurement cannot be performed. That is, after removing the natural oxide film on the surface of the SOI layer by cleaning with hydrofluoric acid, the electrical state on the surface of the SOI layer is not stable unless 10 hours or more elapses, so that the measurement cannot be performed.

  Accordingly, the present inventors, when evaluating an SOI wafer using a mercury probe, evaluate the SOI wafer by stabilizing the charge state on the surface of the SOI layer in a short time after removing the natural oxide film. We thought that the time could be shortened and repeated diligent experiments and studies. As a result, after performing hydrofluoric acid cleaning on the SOI wafer, a second cleaning process is performed on the SOI wafer using a cleaning solution having a component capable of forming a silicon oxide film to form a uniform silicon oxide film on the surface of the SOI layer. By newly forming this uniform oxide film and stabilizing the charge state on the surface of the SOI layer in a short time, and then evaluating the SOI wafer using a mercury probe, the evaluation of the SOI wafer is improved in a short time. The present invention has been completed by finding that it can be carried out with accuracy.

Hereinafter, an SOI wafer evaluation method of the present invention will be described in detail with reference to the drawings. Here, FIG. 1 is a flowchart showing an example of an SOI wafer evaluation method according to the present invention. The flow chart shown in FIG. 1 shows that after performing a hydrofluoric acid cleaning treatment, the V _{G- ID} characteristics on the electron side of the SOI wafer are measured to evaluate the electron mobility / interface state density, and then the SOI forming an oxide film on the layer surface, by measuring the V _G -I _D characteristic of the positive hole side, the case of evaluating the hole mobility / charge density, the present invention as being limited thereto Instead, as will be described in detail below, the formation of an oxide film by the second cleaning process in Step E is performed between Step B and Step C, or Step C and Step D are omitted. Only the mobility / charge density can be evaluated or appropriately changed depending on the purpose.

  First, as shown in FIG. 1, an SOI wafer to be evaluated is prepared (step A). The SOI wafer to be evaluated in the present invention may have any SOI structure in which, for example, a buried oxide film serving as an insulating layer and an SOI layer are formed on a support wafer, and its manufacturing method is particularly limited. It is not something. For example, as an SOI wafer to be prepared, the polished surfaces of two mirror-polished wafers in which a silicon oxide film is formed on at least one silicon wafer surface are bonded to each other, and after heat treatment, one wafer is ground and thinned by polishing. A thing can be used (bonding method). In addition, hydrogen is ion-implanted into one mirror-polished wafer in advance, and another wafer is polished and bonded to the polished surface, followed by heat treatment to peel off one wafer from the hydrogen-ion-implanted layer. Then, after forming the SOI structure, the surface of the thin film that becomes the SOI layer can be polished (hydrogen ion separation method). Further, a so-called SIMOX (Separated Implanted Oxide) wafer manufactured by performing high-temperature heat treatment after ion implantation of oxygen into one mirror-polished wafer may be used.

  Next, the prepared SOI wafer is subjected to a hydrofluoric acid cleaning process as a first cleaning process using an aqueous solution containing hydrofluoric acid to remove a natural oxide film formed on the surface of the SOI wafer (FIG. 1). Step B). Normally, an SOI wafer has a thin oxide film called a natural oxide film formed on the wafer surface by touching the atmosphere. Since this natural oxide film is not uniformly formed on the surface of the SOI wafer, the thickness of the oxide film varies within the wafer surface. Even if an SOI wafer on which such a natural oxide film is formed is evaluated as it is, an accurate evaluation cannot be performed due to variations in the thickness of the natural oxide film and the influence of impurities contained in the natural oxide film. Therefore, first, a hydrofluoric acid cleaning process (first cleaning process) is performed on the prepared SOI wafer to remove the natural oxide film on the wafer surface.

  At this time, the hydrofluoric acid concentration in the aqueous solution used for the hydrofluoric acid cleaning treatment is not particularly limited as long as the natural oxide film can be removed. For example, if the hydrofluoric acid concentration is too high, the hydrofluoric acid concentration is interposed between the SOI layer and the supporting wafer. There is a possibility that the BOX layer to be etched will also be etched. Accordingly, the hydrofluoric acid concentration is preferably relatively low. For example, it is preferable to use an aqueous solution having a hydrofluoric acid concentration of 0.5% to 5%, particularly about 1%. Further, the cleaning conditions such as the aqueous solution temperature and the cleaning time when performing the hydrofluoric acid cleaning process only need to be such that the natural oxide film can be removed, and can be changed as needed.

  The SOI wafer subjected to the hydrofluoric acid cleaning treatment with the aqueous solution containing hydrofluoric acid in this way is then rinsed with pure water in which dissolved oxygen is reduced as much as possible and dried. By using the pure water in which the dissolved oxygen is reduced as much as possible during the rinsing process, it is possible to suppress the natural oxide film from being formed again on the SOI wafer. As a drying method, for example, dry air with a reduced water concentration may be blown onto an SOI wafer for drying, or may be dried using a device such as a spin dryer. Alternatively, it may be dried using a chemical solution such as IPA (isopropyl alcohol).

SOI wafer to remove a native oxide film by performing hydrofluoric acid cleaning treatment as described above, a measurement of V _G -I _D characteristic of the electron-side with immediate mercury probe apparatus 21 as shown in FIG. 3 ( Step C) in FIG. For example, the SOI wafer W is placed so that the SOI layer faces downward, that is, after the surface on the SOI layer side is placed on a stage (not shown) and stored in the apparatus, the opposite side to the surface placed on the stage The surface of the SOI wafer, that is, the surface on the support wafer side of the SOI wafer is adsorbed by the vacuum chuck 22 from above. The vacuum chuck 22 is made of a conductive material such as metal and also serves as a gate electrode.

  When the surface of the SOI wafer W on the support wafer side is attracted to the vacuum chuck 22, the stage is moved away from the SOI wafer W. Thereafter, the mercury probe 23 is brought close to the surface of the SOI layer of the SOI wafer W, and only the mercury electrode portion is brought into contact with the SOI layer. At this time, the mercury probe 23 has a structure as shown in FIG. 4, and one of the mercury electrode portions 24 and 25 is used as a source electrode, and the other is used as a drain electrode. In this way, for example, a Pseudo-MOS structure as shown in FIG. 7 can be formed.

A constant drain voltage is applied in a state in which the Pseudo-MOS structure is formed, and in this state, the gate voltage is applied to the positive side to change it, and the change in the drain current is monitored, whereby the gate voltage V _G on the electron side is monitored. a relationship between the drain current _{I D,} i.e., it is possible to measure the _V G -I _D characteristic of the electron side. V _G -I _D characteristic of the measured electron side is displayed as shown in FIG. 6, for example.

Then, by using a formula that has a gradient of C portion and D portion, for example, in Non-Patent Document 1 or 2 in the V _G -I _D characteristic of the measured electron side as shown in FIG. 6, the SOI wafer The electron mobility of the SOI layer and / or the interface state density between the SOI layer and the buried oxide film can be obtained and evaluated (step D in FIG. 1). At this time, according to the present invention, the V _{G- ID} characteristics on the electron side can be measured immediately on the SOI wafer after removing the natural oxide film as described above. Thus, immediately after the natural oxide film is removed. In addition, if the V _{G- ID} characteristics on the electron side are measured, the measurement data is relatively stable, so that the electron mobility and / or interface state density can be measured correctly.
The measurement of the V _{G- ID} characteristics on the electron side (step C) and the evaluation of electron mobility / interface state density (step D) can be performed in about 2 hours in total of the two steps. it can.

Subsequently, after evaluating the electron mobility and interface state density of the SOI wafer as described above, a second cleaning process is performed using a cleaning solution having a component capable of forming a silicon oxide film on the SOI wafer. Thus, a silicon oxide film is formed on the SOI layer surface of the SOI wafer (step E in FIG. 1). In this way, by performing the second cleaning process on the SOI wafer to uniformly form a silicon oxide film having a desired film thickness on the surface of the SOI layer, the charge state on the surface of the SOI layer can be quickly stabilized. , also the thickness of the silicon oxide film formed so can be made uniform in the wafer plane, when measuring the V _G -I _D characteristic of contacting the mercury probe as described hole side then it follows In addition, it is possible to measure the electrical characteristics with high accuracy without eliminating the influence of the in-plane variation of the oxide film thickness and causing the variation of the measured value.

At this time, the thickness of the oxide film formed on the SOI layer surface is preferably 5 nm or less. Thus the oxide film formed on the SOI layer surface, by the thickness assumed following very thin 5 nm, when subsequently measuring the V _G -I _D characteristic of the hole side, thin thickness Due to the tunnel effect of the silicon oxide film, electricity can be reliably passed through the oxide film, and the electrical characteristics of the SOI wafer can be accurately measured. On the other hand, the thickness of the oxide film formed on the surface of the SOI layer is preferably 0.1 nm or more, so that the charge state on the surface of the SOI layer can be reliably stabilized.

  The cleaning solution used for the second cleaning treatment is not particularly limited as long as it has a component capable of forming a silicon oxide film, and various aqueous solutions can be used. For example, ozone water, ammonia And aqueous solution containing hydrogen peroxide solution, hydrogen peroxide solution, aqueous solution containing hydrochloric acid and hydrogen peroxide solution, aqueous solution containing sulfuric acid and hydrogen peroxide solution, and highly oxidizing aqueous solution with high oxidation-reduction potential It is preferable to use an electrolytic anode water as a highly oxidizing aqueous solution having a high oxidation-reduction potential.

The aqueous solution shown above contains components that can quickly form a silicon oxide film on the SOI layer surface, such as OH ⁻ ions contained in highly oxidizing aqueous solutions such as ozone, hydrogen peroxide, and electrolytic anode water. By performing the second cleaning process using an aqueous solution selected from these as a cleaning solution, the wafer surface is cleaned, and at the same time, an oxide film having a uniform thickness is formed on the SOI layer surface very stably. Can do. The composition of the cleaning solution used in the second cleaning process may be any composition as long as the silicon oxide film can be uniformly formed on the surface of the SOI layer of the SOI wafer, particularly with a thickness of 5 nm or less.

  For example, by selecting an aqueous solution containing ammonia and hydrogen peroxide water as a cleaning solution and performing a second cleaning process on the SOI wafer, the SOI wafer is SC-1 cleaned, so that it adheres to the surface of the SOI layer. In addition to removing contamination such as particles, a silicon oxide film can be uniformly formed on the surface of the SOI layer with a desired thickness.

  In addition, since the SOI wafer is SC-2 cleaned by selecting the aqueous solution containing hydrochloric acid and hydrogen peroxide water as the cleaning solution and performing the second cleaning process, the metal impurities adhering to the surface of the SOI layer In addition, the silicon oxide film can be uniformly formed with a desired thickness on the surface of the SOI layer.

  In addition, by selecting an aqueous solution containing sulfuric acid and hydrogen peroxide water as the cleaning solution and performing the second cleaning treatment, it is possible to remove organic impurities adhering to the surface of the SOI layer, and a silicon oxide film on the surface of the SOI layer. It can be uniformly formed with a desired thickness.

In addition, when a highly oxidative aqueous solution having a high redox potential, such as electrolytic anodic water, is selected as the cleaning solution, the pH of the anodic water should be adjusted to 2 to 6 and the redox potential adjusted to about +300 to +1200 mV. preferable. By performing a second cleaning process SOI wafer with such anode water, OH in a wash solution ^- because ions are abundant, silicon oxide having a desired film thickness uniform on the SOI layer surface of the wafer A film can be easily formed.

  Further, the cleaning solution used in the second cleaning process is not limited to one type. For example, in the second cleaning process, the SOI wafer is washed with an aqueous solution containing ammonia and hydrogen peroxide solution, and the first second cleaning treatment is performed. Then, the SOI wafer is washed with an aqueous solution containing hydrochloric acid and hydrogen peroxide solution. Further, by performing the second cleaning process after the second cleaning, a very thin and uniform silicon oxide film having a thickness of 5 nm or less can be formed on the surface of the SOI layer of the SOI wafer. In this case, in the composition of each aqueous solution, the ratio of the hydrogen peroxide solution, which is a silicon oxide film forming component, is reduced, or the cleaning time is shortened. A thin and uniform silicon oxide film may be formed on the surface of the SOI layer.

Further, when the second cleaning treatment is performed in this manner, the liquid temperature of the cleaning solution is preferably set to room temperature or higher and 80 ° C. or lower. By setting the temperature of the cleaning solution to 80 ° C. or lower, the silicon oxide film forming components such as ozone, hydrogen peroxide, and OH ⁻ ions contained in the cleaning solution are prevented from volatilizing and uniform silicon oxidation is performed. The film can be formed promptly and reliably. On the other hand, if the temperature of the cleaning solution is to be lowered below room temperature, an additional facility for cooling the cleaning solution is required, which increases costs and the cleaning facility itself. Therefore, it is preferable to use a cleaning solution having a liquid temperature of room temperature or higher because the second cleaning process can be easily performed while reducing the cost burden.

  When performing the second cleaning process using the cleaning solution as described above, for example, the second cleaning process is performed for about 30 minutes or less, particularly about 1 to 10 minutes, so that the surface of the SOI layer is 5 nm or less. The silicon oxide film can be formed uniformly. As a specific example, the wafer surface is cleaned and a silicon oxide film of about 3 nm is formed by performing a second cleaning process on the SOI wafer for about 4 minutes using, for example, ozone water at room temperature in which 10 ppm of ozone is dissolved. It can be formed uniformly on the surface of the SOI layer, and the charge state on the surface of the SOI layer can be stabilized in a much shorter time than before.

Then, the SOI wafer in which the oxide film having a desired film thickness is uniformly formed on the surface of the SOI layer as described above is rinsed with, for example, pure water and dried, and then the mercury probe device 21 shown in FIG. 3 is used. Te measuring the _V G -I _D characteristic of the hole side of the SOI wafer (step F in FIG. 1). For example, after the surface of the SOI wafer W on the support wafer side is adsorbed to the vacuum chuck 22, the mercury probe 23 is brought close to the SOI layer surface of the SOI wafer W, and only the mercury electrode portion is brought into contact with the SOI layer. A Pseudo-MOS structure is formed. Thereafter, a constant drain voltage is applied from the mercury probe 23, and in this state, the gate voltage is applied and changed on the negative side, and the change in the drain current is monitored, for example, on the hole side as shown in FIG. it can be measured V _G -I _D characteristic.

Then, by using the formula shown from the slope of the parts A and B, in Non-Patent Document 1 or 2 in the V _G -I _D characteristic of the measured hole side as shown in FIG. 5, the SOI wafer The hole mobility of the SOI layer and / or the charge density of the BOX layer can be obtained and evaluated (Step G in FIG. 1).

In particular, the present invention, SOI before measuring the V _G -I _D characteristic of the hole side of the SOI wafer as described above, by uniformly forming an oxide film on the SOI layer surface by performing a second cleaning process since short time to stabilize the charge states of the layer surface, can measure the V _G -I _D characteristic of the hole-side stably without causing variations in measurements, the hole of the SOI layer The mobility and the charge density of the BOX layer can be evaluated with high accuracy in a short time.
The measurement of the V _{G- ID} characteristics on the hole side (Step F) and the evaluation of hole mobility / charge density (Step G) can be performed in about 2 hours in total of the two steps. it can.

Further, in the present invention, for example, a silicon oxide film is formed between the hydrofluoric acid cleaning treatment (step B) in the flowchart shown in FIG. 1 and the measurement of the V _{G- ID} characteristics on the electron side (step C). A step of performing a cleaning process using a possible cleaning solution to form an oxide film on the surface of the SOI layer may be further added.

As described above, according to the SOI wafer evaluation method of the present invention, the hydrofluoric acid cleaning process is performed on the SOI wafer to remove the natural oxide film on the SOI wafer surface, and then the second cleaning process is performed on the surface of the SOI layer. For example, by newly forming an oxide film having a thickness of 5 nm or less, the charge state on the surface of the SOI layer can be quickly stabilized to a steady state, and then the charge state on the surface of the SOI layer is stabilized. by measuring the V _G -I _D characteristic by contacting a mercury probe to the SOI wafer, the hole mobility and BOX layer charge density, more electrical characteristics of the SOI wafer, such as electron mobility and the interface state density It can be evaluated with high accuracy. Thereby, without requiring a large-scale equipment and a large number of steps such as a photolithography process, to be able to very easily carry out the evaluation of an SOI wafer by using a mercury probe, also, V _G -I _D characteristic Since the charge state on the SOI layer surface is very stable and the thickness of the silicon oxide film formed by the second cleaning process is uniform in the wafer surface, the measured value varies. A highly reliable SOI wafer can be evaluated stably without causing it.

In particular, when evaluating hole mobility and BOX layer charge density of the SOI wafer before the conventional for measuring the _V G -I _D characteristic due to the mercury probe, charge of the SOI layer surface to be placed over 10-12 hours While the state could not make an accurate measurement of the V _G -I _D characteristic for not stable, according to the present invention, by forming an oxide film on the SOI layer surface in the second cleaning process, approximately 30 minutes In the following, the charge state can be stabilized especially in a very short time of 10 minutes or less. Therefore, the present invention can significantly reduce the evaluation time of SOI wafers compared to the prior art, especially when evaluating hole mobility and BOX layer charge density. The evaluation of the SOI wafer can be performed very efficiently, and the management of the SOI wafer when performing the evaluation is much easier than before.

Note that the SOI wafer evaluation method of the present invention is not limited to the process shown in the flow chart of FIG. 1, and the process can be changed or deleted as appropriate according to the purpose or necessity.
For example, as described above, a cleaning solution capable of forming a silicon oxide film is used between the hydrofluoric acid cleaning process (step B) and the measurement of the V _{G- ID} characteristics on the electron side (step C). In addition, a step of forming an oxide film on the surface of the SOI layer by performing a cleaning process can be further added. For example, as shown in FIG. The SOI wafer can also be evaluated by performing steps C, D, F, and G in order without performing the oxide film formation after the cleaning process (step B). As shown in FIG. 2, by forming an oxide film on the SOI layer surface by performing a second cleaning process immediately after the hydrofluoric acid cleaning process, when measuring the V _G -I _D characteristic of the electron-side and holes when measuring V _G -I _D characteristic of the side, together with the charge state of the SOI layer surface is stable, and surely eliminate the influence of the natural oxide film that may be formed during the measurement, the measured value Thus, it is possible to perform measurement stably without causing variations in the electron mobility, and it is possible to evaluate the electron mobility / interface state density and the hole mobility / charge density with high accuracy.

Furthermore, in the present invention, for example, when only the evaluation of the electron mobility and / or interface state density of the SOI wafer is performed, for example, steps A, B, E, C, and D shown in FIG. At this point, the evaluation of the SOI wafer may be terminated. On the other hand, if only the hole mobility of the SOI wafer and / or the charge density of the BOX layer is to be evaluated, step C in the flow chart shown in FIG. Steps E to G may be performed immediately after Steps A and B are omitted. In this case, V _G -I _D characteristic of the hole side as described above, since the measured value and measured immediately after removal of the native oxide film takes a long time to stabilize, oxidation by the second cleaning step E It is necessary to form a film.

  If necessary, two SOI wafers manufactured under the same conditions in step A are prepared, and steps B, E, C, and D are sequentially performed on one SOI wafer, and electron mobility and / or interface states are prepared. The density may be evaluated, and steps B, E, F, and G may be sequentially performed on the other SOI wafer to evaluate the hole mobility and / or the charge density of the BOX layer. Thus, by preparing two SOI wafers and evaluating each separately, the gate voltage sweeps only on the positive side or the negative side, so that the SOI wafer can be evaluated in a shorter time. In addition, the stress applied to the SOI wafer can be reduced.

  Furthermore, in the present invention, the SOI wafer may be evaluated by replacing the processes C and D and the processes E to G in FIG. That is, after preparing an SOI wafer and performing a hydrofluoric acid cleaning process (steps A and B), a second cleaning process is performed to form an oxide film on the SOI layer surface, thereby quickly changing the charge state on the SOI layer surface. After stabilization, Steps F and G are performed to evaluate hole mobility / BOX layer charge density, and then Steps C and D are performed to evaluate electron mobility / interface state density.

That is, the present invention after the hydrofluoric acid cleaning treatment, V _G -I _D characteristic before measuring, SOI layer surface, especially by performing a second cleaning process before measuring the V _G -I _D characteristic of the hole-side well if a silicon oxide film, thereby, it is possible to stabilize in a short time the charge state of the SOI layer surface, 10 to 12 hours an SOI wafer prior to the measurement of V _G -I _D characteristic as in the prior art There is no need to store the above, and the SOI wafer can be evaluated very efficiently. Therefore, in the present invention, for example, either the measurement of the V _{G- ID} characteristic on the electron side or the measurement of the V _{G- ID} characteristic on the hole side may be performed first.

EXAMPLES Hereinafter, although an Example and a comparative example are shown and this invention is demonstrated more concretely, this invention is not limited to these.
Example 1
By using a silicon wafer having a p-type conductivity, a diameter of 200 mm, and a crystal orientation <100> as a bond wafer for forming a support wafer and an SOI layer, an SOI wafer is manufactured by a hydrogen ion delamination method. An SOI wafer was prepared (step A). Boron was used as a dopant for making the conductivity type of the wafer p-type. Moreover, the thicknesses of the SOI layer and the BOX layer of the manufactured SOI wafer were about 100 nm and 145 nm, respectively.
The prepared SOI wafer was subjected to a hydrofluoric acid cleaning treatment for 1 minute using an aqueous solution containing 1% by weight of hydrofluoric acid (step B). Thereafter, rinsing was performed with pure water in which dissolved oxygen was reduced as much as possible, and then moisture was removed by drying the SOI wafer by blowing dry air, followed by drying.

After drying, it was measured _V G -I _D characteristic of the electron-side sets immediately SOI wafer mercury probe apparatus (Four DIMENSIONS Co. CVmap92) (Step C). The measurement results are shown in FIG. At this time, the measurement of V _G -I _D characteristic of the electron-side can be performed by monitoring the drain current causes the gate voltage is changed while applying a constant drain voltage from the drain electrode. Then, the measurement result of the V _G -I _D characteristic of the electron side shown in FIG. 8, by using the formula shown in Non-Patent Documents 1 and 2, the electron mobility and / or SOI layer of the SOI layer And the interface state density of the buried oxide film can be obtained and evaluated (step D). At this time, from the start of measurement of the V _{G- ID} characteristics on the electron side to the determination of electron mobility and interface state density, it could be performed in about 2 hours.

Subsequently, a second cleaning process was performed on the SOI wafer for 4 minutes using ozone water at room temperature in which 10 ppm of ozone was dissolved in pure water by an ozone generator, and further rinsed with pure water. Then, moisture was removed by drying the SOI wafer by blowing dry air, and the SOI wafer was dried. As a result, a silicon oxide film of about 3 nm was formed on the surface of the SOI layer (step E). Immediately thereafter, the SOI wafer was set in a mercury probe device (CVmap 92 manufactured by Four DIMENSIONS), and the V _{G- ID} characteristics on the hole side were measured (step F). The measurement results are shown in FIG. Then, the measurement result of the V _G -I _D characteristic of the positive hole side shown in FIG. 9, by using the formula shown in Non-Patent Documents 1 and 2, the hole mobility and / or BOX of the SOI layer The charge density of the layer can be determined and evaluated (Step G). At this time, from the start of the measurement of the V _G -I _D characteristic of the hole side to determine the charge density of the hole mobility and the BOX layer of the SOI layer, it could be done in about 2 hours.

(Example 2)
An SOI wafer similar to that in Example 1 is prepared (Step A), and the process from hydrofluoric acid cleaning treatment (Step B) to measurement of V _{G- ID} characteristics on the electron side (Step C) is performed under the same conditions as in Example 1. It was. As a result, to obtain a V _G -I _D characteristic of the electron-side as shown in FIG. 8 similar to the first embodiment. Then, from the measurement results of V _G -I _D characteristic of the electron side shown in FIG. 8, in the same manner as in Example 1, the interface state of the buried oxide film and the electron mobility and / or SOI layer of the SOI layer The density can be determined and evaluated (step D). At this time, from the start of measurement of the V _{G- ID} characteristics on the electron side to the determination of electron mobility and interface state density, it could be performed in about 2 hours.

Subsequently, an aqueous solution in which the weight ratio of ammonia: hydrogen peroxide: pure water is 1: 1: 10 is used as the cleaning solution, and the SOI wafer is placed on the SOI wafer for 4 minutes in the cleaning solution maintained at a liquid temperature of 80 ° C. Two washing treatments were performed, and the SOI wafer was rinsed with pure water, and then dried by blowing dry air. As a result, a silicon oxide film having a thickness of about 3 nm was formed on the surface of the SOI layer (step E). Immediately thereafter, the SOI wafer was set in a mercury probe device (CVmap 92 manufactured by Four DIMENSIONS), and the V _{G- ID} characteristics on the hole side were measured (step F). As a result, to obtain a V _G -I _D characteristic of the positive hole side, as shown in Figure 9 the same manner as in Example 1. Then, from the measurement results of V _G -I _D characteristic of the positive hole side shown in FIG. 9, in the same manner as in Example 1, seeking a charge density of hole mobility and / or BOX layer of the SOI layer It can be evaluated (Step G). At this time, from the start of the measurement of the V _G -I _D characteristic of the hole side to determine the charge density of the hole mobility and the BOX layer of the SOI layer, it could be done in about 2 hours.

Example 3
An SOI wafer similar to that in Example 1 is prepared (Step A), and the process from hydrofluoric acid cleaning treatment (Step B) to measurement of V _{G- ID} characteristics on the electron side (Step C) is performed under the same conditions as in Example 1. It was. As a result, to obtain a V _G -I _D characteristic of the electron-side as shown in FIG. 8 similar to the first embodiment. Then, from the measurement results of V _G -I _D characteristic of the electron side shown in FIG. 8, in the same manner as in Example 1, the interface state of the buried oxide film and the electron mobility and / or SOI layer of the SOI layer The density can be determined and evaluated (step D). At this time, from the start of measurement of the V _{G- ID} characteristics on the electron side to the determination of electron mobility and interface state density, it could be performed in about 2 hours.

Subsequently, an aqueous solution (diluted hydrogen peroxide solution) in which the weight ratio of hydrogen peroxide solution: pure water is 1:10 is used as the cleaning solution, and the SOI wafer is applied to the SOI wafer in the cleaning solution maintained at a liquid temperature of 80 ° C. A second washing treatment for 3 minutes was performed, and the SOI wafer was rinsed with pure water, and then dried by blowing dry air. As a result, a silicon oxide film having a thickness of about 3 nm was formed on the surface of the SOI layer (step E). Thereafter, the V _G -I _D characteristic of the hole-side were measured in the same manner as in Example 1 immediately (step F). As a result, to obtain a V _G -I _D characteristic of the positive hole side, as shown in Figure 9 the same manner as in Example 1. Then, from the measurement results of V _G -I _D characteristic of the positive hole side shown in FIG. 9, to evaluate seeking charge density of the hole mobility and / or BOX layer of the SOI layer in the same manner as above (Step G). At this time, from the start of the measurement of the V _G -I _D characteristic of the hole side to determine the charge density of the hole mobility and the BOX layer of the SOI layer, it could be done in about 2 hours.

Example 4
An SOI wafer similar to that in Example 1 is prepared (Step A), and the process from hydrofluoric acid cleaning treatment (Step B) to measurement of V _{G- ID} characteristics on the electron side (Step C) is performed under the same conditions as in Example 1. It was. As a result, to obtain a V _G -I _D characteristic of the electron-side as shown in FIG. 8 similar to the first embodiment. Then, from the measurement results of V _G -I _D characteristic of the electron side shown in FIG. 8, in the same manner as in Example 1, the interface state of the buried oxide film and the electron mobility and / or SOI layer of the SOI layer The density can be determined and evaluated (step D). At this time, from the start of measurement of the V _{G- ID} characteristics on the electron side to the determination of electron mobility and interface state density, it could be performed in about 2 hours.

Subsequently, an aqueous solution having a weight ratio of hydrochloric acid: hydrogen peroxide: pure water of 1: 1: 20 was used as the cleaning solution, and the SOI wafer was subjected to a 4 minute test in a cleaning solution maintained at a liquid temperature of 80 ° C. Two washing treatments were performed, and the SOI wafer was rinsed with pure water, and then dried by blowing dry air. As a result, a silicon oxide film having a thickness of about 3 nm was formed on the surface of the SOI layer (step E). Thereafter, the V _G -I _D characteristic of the hole-side were measured in the same manner as in Example 1 immediately (step F). As a result, to obtain a V _G -I _D characteristic of the positive hole side, as shown in Figure 9 the same manner as in Example 1. Then, from the measurement results of V _G -I _D characteristic of the positive hole side shown in FIG. 9, to evaluate seeking charge density of the hole mobility and / or BOX layer of the SOI layer in the same manner as above (Step G). At this time, from the start of the measurement of the V _G -I _D characteristic of the hole side to determine the charge density of the hole mobility and the BOX layer of the SOI layer, it could be done in about 2 hours.

(Example 5)
An SOI wafer similar to that in Example 1 is prepared (Step A), and the process from hydrofluoric acid cleaning treatment (Step B) to measurement of V _{G- ID} characteristics on the electron side (Step C) is performed under the same conditions as in Example 1. It was. As a result, to obtain a V _G -I _D characteristic of the electron-side as shown in FIG. 8 similar to the first embodiment. Then, from the measurement results of V _G -I _D characteristic of the electron side shown in FIG. 8, in the same manner as in Example 1, the interface state of the buried oxide film and the electron mobility and / or SOI layer of the SOI layer The density can be determined and evaluated (step D). At this time, from the start of measurement of the V _{G- ID} characteristics on the electron side to the determination of electron mobility and interface state density, it could be performed in about 2 hours.

Subsequently, an aqueous solution in which the weight ratio of sulfuric acid: hydrogen peroxide solution: pure water is 1: 1: 20 is used as the cleaning solution, and the second temperature is kept on the SOI wafer for 4 minutes in the cleaning solution kept at the liquid temperature. Washing was performed, and the SOI wafer was rinsed with pure water, and then dried by blowing dry air. As a result, a silicon oxide film having a thickness of about 3 nm was formed on the surface of the SOI layer (step E). Thereafter, the V _G -I _D characteristic of the hole-side were measured in the same manner as in Example 1 immediately (step F). As a result, to obtain a V _G -I _D characteristic of the positive hole side, as shown in Figure 9 the same manner as in Example 1. Then, from the measurement results of V _G -I _D characteristic of the positive hole side shown in FIG. 9, to evaluate seeking charge density of the hole mobility and / or BOX layer of the SOI layer in the same manner as above (Step G). At this time, from the start of the measurement of the V _G -I _D characteristic of the hole side to determine the charge density of the hole mobility and the BOX layer of the SOI layer, it could be done in about 2 hours.

(Example 6)
An SOI wafer similar to that in Example 1 is prepared (Step A), and the process from hydrofluoric acid cleaning treatment (Step B) to measurement of V _{G- ID} characteristics on the electron side (Step C) is performed under the same conditions as in Example 1. It was. As a result, to obtain a V _G -I _D characteristic of the electron-side as shown in FIG. 8 similar to the first embodiment. Then, from the measurement results of V _G -I _D characteristic of the electron side shown in FIG. 8, in the same manner as in Example 1, the interface state of the buried oxide film and the electron mobility and / or SOI layer of the SOI layer The density can be determined and evaluated (step D). At this time, from the start of measurement of the V _{G- ID} characteristics on the electron side to the determination of electron mobility and interface state density, it could be performed in about 2 hours.

Subsequently, pure water was electrolyzed to produce anodic water containing OH ⁻ ions, and the pH adjusted to 4 and the redox potential adjusted to 700 mV was used as a cleaning solution, and the liquid temperature was kept at room temperature. The SOI wafer was subjected to a second cleaning treatment for 10 minutes in the cleaning solution, rinsed with pure water on the SOI wafer, and then dried by blowing dry air. As a result, a silicon oxide film having a thickness of about 3 nm was formed on the surface of the SOI layer (step E). Thereafter, the V _G -I _D characteristic of the hole-side were measured in the same manner as in Example 1 immediately (step F). As a result, to obtain a V _G -I _D characteristic of the positive hole side, as shown in Figure 9 the same manner as in Example 1. Then, from the measurement results of V _G -I _D characteristic of the positive hole side shown in FIG. 9, to evaluate seeking charge density of the hole mobility and / or BOX layer of the SOI layer in the same manner as above (Step G). At this time, from the start of the measurement of the V _G -I _D characteristic of the hole side to determine the charge density of the hole mobility and the BOX layer of the SOI layer, it could be done in about 2 hours.

(Example 7)
An SOI wafer similar to that in Example 1 is prepared (Step A), and the process from hydrofluoric acid cleaning treatment (Step B) to measurement of V _{G- ID} characteristics on the electron side (Step C) is performed under the same conditions as in Example 1. It was. As a result, to obtain a V _G -I _D characteristic of the electron-side as shown in FIG. 8 similar to the first embodiment. Then, from the measurement results of V _G -I _D characteristic of the electron side shown in FIG. 8, in the same manner as in Example 1, the interface state of the buried oxide film and the electron mobility and / or SOI layer of the SOI layer The density can be determined and evaluated (step D). At this time, from the start of measurement of the V _{G- ID} characteristics on the electron side to the determination of electron mobility and interface state density, it could be performed in about 2 hours.

  Subsequently, the second cleaning process was performed twice on the SOI wafer. First, as the second cleaning treatment for the first time, an aqueous solution in which the weight ratio of ammonia: hydrogen peroxide: pure water is 1: 1: 10 is used as the cleaning solution, and the cleaning temperature is kept at 80 ° C. The SOI wafer was washed for 2 minutes, and rinsed with pure water. Next, as the second cleaning process for the second time, an aqueous solution in which the weight ratio of hydrochloric acid: hydrogen peroxide: pure water is 1: 1: 20 is used as the cleaning solution, and the cleaning temperature is maintained at 80 ° C. The SOI wafer was washed for 2 minutes, rinsed with pure water, and then dried by blowing dry air. As a result, a silicon oxide film having a thickness of about 3 nm was formed on the surface of the SOI layer (step E).

Thereafter, the V _G -I _D characteristic of the hole-side were measured in the same manner as in Example 1 immediately (step F). As a result, to obtain a V _G -I _D characteristic of the positive hole side, as shown in Figure 9 the same manner as in Example 1. Then, from the measurement results of V _G -I _D characteristic of the positive hole side shown in FIG. 9, to evaluate seeking charge density of the hole mobility and / or BOX layer of the SOI layer in the same manner as above (Step G). At this time, from the start of the measurement of the V _G -I _D characteristic of the hole side to determine the charge density of the hole mobility and the BOX layer of the SOI layer, it could be done in about 2 hours.

  As described above, in the evaluation of the SOI wafers performed in Examples 1 to 7, in any case, the electron mobility and the interface are short in about 4 hours after the hydrofluoric acid cleaning process is performed on the SOI wafer. The level density, hole mobility, and BOX layer charge density could be evaluated.

(Comparative Example 1)
As Comparative Example 1, an SOI wafer produced under the same conditions as in Example 1 was prepared, and this SOI wafer was subjected to hydrofluoric acid cleaning treatment for 1 minute with an aqueous solution containing 1 wt% hydrofluoric acid in the same manner as in Example 1. Thereafter, rinsing was performed with pure water, and thereafter, moisture was removed by blowing dry air on the SOI wafer to dry the SOI wafer.

After drying the SOI wafer, without measuring the V _{G- ID} characteristics on the electron side, evaluating the electron mobility / interface state density, and without performing the second cleaning process, the SOI wafer was immediately set the mercury probe device was measured V _G -I _D characteristic of the hole side. The measurement results are shown in FIG. The measurement results shown in FIG. 10, when compared with V _G -I _D characteristic of the hole side of Figure 9 as measured in Example 1 to 7, I _D for V _G is lower overall You can see that Think this, after removing the natural oxide film of the SOI wafer, without stabilizing the charge state of the surface of the SOI layer of the SOI wafer, to be caused to the measured V _G -I _D characteristic of the hole-side immediately It is.

(Comparative Example 2)
As Comparative Example 2, an SOI wafer produced under the same conditions as in Example 1 was prepared, and this SOI wafer was subjected to hydrofluoric acid cleaning treatment for 1 minute with an aqueous solution containing 1 wt% hydrofluoric acid in the same manner as in Example 1. Thereafter, rinsing was performed with pure water, and thereafter, moisture was removed by blowing dry air on the SOI wafer to dry the SOI wafer.

Next, after exposing the SOI wafer during 12 hours air, measuring the V _G -I _D characteristic of the electron-side, without evaluation of electron mobility / interface state density, and further, without performing the second cleaning process Then, it was set in a mercury probe device, and the V _{G- ID} characteristics on the hole side were measured. The measurement results are shown in FIG. Then, the hole mobility of the SOI layer and the charge density of the BOX layer were obtained from the measurement results of FIG. 11 and evaluated. At this time, from the start of the measurement of the V _G -I _D characteristic of the hole side to determine the charge density of the hole mobility and the BOX layer of the SOI layer, it could be performed in about 1 hour.

The measurement results shown in FIG. 11 was found to be approximately the same as the V _G -I _D characteristic of the hole side which is measured in Examples 1-7 (FIG. 9). However, in Comparative Example 2, the evaluation of the electron mobility and the interface state density is not performed, but after the hydrofluoric acid cleaning treatment is performed on the SOI wafer, the hole mobility and the charge density are obtained. It took 13 hours or more, and took about three times the evaluation time of Examples 1-7.

From the above results, when evaluating the SOI wafer, the SOI wafer from which the natural oxide film has been removed is subjected to a second cleaning process to form a new silicon oxide film on the SOI layer surface, thereby obtaining a charge state on the SOI layer surface. it is possible to stabilize in a short time, certainly reduce the time to time according to the evaluation of an SOI wafer, in particular after performing a hydrofluoric acid cleaning process until the measured V _G -I _D characteristic of the hole-side I was able to confirm that I could do it. In addition, there are few disturbance factors such as wafer contamination as in the case where the wafer is exposed for 12 hours or more, and the reliability of the data is high.

  The present invention is not limited to the above embodiment. The above embodiment is merely an example, and the present invention has the same configuration as that of 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 SOI wafer of this invention. It is a flowchart which shows another example of the evaluation method of SOI wafer of this invention. 1 is a schematic configuration diagram of a mercury probe apparatus. It is an electrode top view of the mercury electrode of a mercury probe apparatus. An example of a V _G -I _D characteristic of the hole side which is measured in the evaluation method of an SOI wafer of the present invention is a graph showing. An example of a V _G -I _D characteristic of the electron-side measured in the evaluation method of an SOI wafer of the present invention is a graph showing. It is a schematic diagram which represents typically the Pseudo MOS FET method. It is a graph showing the _V G -I _D characteristic of the electron-side measured in Example 1-7. It is a graph showing the _V G -I _D characteristic of the positive hole side measured in Example 1-7. 6 is a graph showing V _{G- ID} characteristics on the hole side measured in Comparative Example 1. FIG. 6 is a graph showing V _{G- ID} characteristics on the hole side measured in Comparative Example 2. FIG.

Explanation of symbols

1 ... SOI layer, 2 ... BOX layer (buried oxide film),
3 ... support wafer, 4 ... gate electrode, 5 ... SOI wafer,
6 ... Source electrode, 7 ... Drain electrode,
21 ... Mercury probe device, 22 ... Vacuum chuck,
23 ... Mercury probe, 24, 25 ... Mercury electrode,
W ... SOI wafer.

Claims (7)

  In a method of evaluating an SOI wafer using a mercury probe, at least the SOI wafer is subjected to a hydrofluoric acid cleaning treatment to remove a natural oxide film formed on the surface of the SOI wafer, and then the natural oxide film The SOI wafer from which the silicon oxide film has been removed is subjected to a second cleaning process using a cleaning solution capable of forming a silicon oxide film to form an oxide film on the SOI layer surface of the SOI wafer, and then the SOI wafer having the oxide film formed thereon is formed. An SOI wafer evaluation method, comprising: contacting a mercury probe to evaluate an SOI wafer.   2. The method for evaluating an SOI wafer according to claim 1, wherein the thickness of the oxide film formed on the surface of the SOI layer is 5 nm or less.   The cleaning solution capable of forming the silicon oxide film includes ozone water, an aqueous solution containing ammonia and hydrogen peroxide solution, an aqueous solution containing hydrogen peroxide solution, an aqueous solution containing hydrochloric acid and hydrogen peroxide solution, and an aqueous solution containing sulfuric acid and hydrogen peroxide solution. 3. The SOI wafer evaluation method according to claim 1, wherein the method is selected from highly oxidizing aqueous solutions having a high oxidation-reduction potential.   4. The SOI wafer evaluation method according to claim 3, wherein the highly oxidizing aqueous solution is electrolytic anode water.   The liquid temperature of the cleaning solution capable of forming the silicon oxide film is set to room temperature to 80 ° C. when performing the second cleaning process. The evaluation method of SOI wafer of description. A mercury probe is brought into contact with the SOI wafer on which the oxide film is formed, and the V _{G- ID} characteristics on the hole side are measured, whereby the hole mobility of the SOI layer and / or the charge of the buried oxide film in the SOI wafer are measured. 6. The SOI wafer evaluation method according to claim 1, wherein the density is evaluated. After removing the natural oxide film by performing the hydrofluoric acid cleaning process, the mercury probe is brought into contact with the SOI wafer from which the natural oxide film has been removed, and the V _{G- ID} characteristics on the electron side are measured to thereby determine the electrons in the SOI layer. 7. The mobility and / or interface state density between the SOI layer and the buried oxide film are evaluated, and thereafter, the second cleaning process is performed on the SOI wafer. The evaluation method of SOI wafer as described in 1 above.

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