JP5818364B2 - Interface evaluation method between semiconductor substrate and insulating film, and interface evaluation apparatus between semiconductor substrate and insulating film - Google Patents

Description

  The present invention relates to a method for evaluating an interface between a semiconductor substrate and an insulating film provided on the surface thereof based on the lifetime of excess carriers and an interface evaluation apparatus using this method.

  With the recent development of electronics, semiconductor products are used in various fields. Since semiconductor products are generally manufactured from a semiconductor wafer, quality control of the semiconductor wafer is important for improving the performance of the semiconductor product. One of the indexes for evaluating the quality of a semiconductor wafer is a carrier lifetime in the semiconductor.

  As one of methods for measuring the carrier lifetime, a microwave photoconductive decay method (μ-PCD method) described in Patent Document 1 is known. This microwave photoconductive decay method generates excess carriers by irradiating light (measurement light) on a semiconductor wafer (measurement sample) to be measured, and this excess carrier has a carrier lifetime determined by the physical properties of the semiconductor sample. In this method, the process of recombination and extinction is detected by the time change of the reflectance of the microwave or the time change of the transmittance. The generation of excess carriers increases the conductivity of the semiconductor wafer. For this reason, the reflectance or transmittance of the microwave irradiated to the semiconductor portion (part, region) where excess carriers are generated by photoexcitation changes in accordance with the density of excess carriers. This microwave photoconductive decay method measures the carrier lifetime by utilizing this phenomenon.

  Conventionally, a silicon wafer (silicon substrate) is used as a semiconductor wafer (semiconductor substrate). In a semiconductor product using this silicon wafer, such as a MOS (Metal Oxide Semiconductor) device or a solar cell, an insulating film is formed on the surface of the silicon wafer. Since the state of the interface between the silicon wafer and the insulating film is related to the performance of semiconductor products such as MOS devices and solar cells, it is important to evaluate the interface between the silicon wafer and the insulating film.

  When the interface between the silicon wafer and the insulating film is evaluated by the microwave photoconductive decay method, light having a short wavelength (for example, ultraviolet light) is used as measurement light. This is because the longer the wavelength, the larger the penetration length. By using light with a short penetration length as measurement light, excessive carriers are intensively generated on the surface of the silicon wafer (interface with the insulating film). The interface is evaluated from the measured carrier lifetime. The penetration length is a distance (depth) from a surface irradiated with light to a point where the light intensity of the light is 1 / e of the incident intensity. Note that e is the number of Napiers.

JP 2008-249240 A

  In recent years, silicon carbide (SiC) has been used instead of silicon (Si) as a semiconductor in power devices due to demands for reducing energy consumption by reducing loss, reducing size by increasing voltage, and ensuring higher temperature operability. Silicon Carbide) has begun to be adopted.

  However, since the penetration length of the excitation light in this silicon carbide substrate is larger than the penetration length in the silicon substrate if the wavelength is the same, when evaluating the interface between the silicon carbide substrate and the insulating film formed on the surface thereof Excitation emitted by this excitation light irradiation device even when using an excitation light irradiation device such as a short-wavelength laser that is practical (providing sufficient output and stability) in the measurement by the microwave photoconductive decay method The penetration length is too large at the wavelength of light, and the silicon carbide substrate surface (interface between the silicon carbide substrate and the insulating film) cannot be accurately evaluated.

  Therefore, in view of the above problems, the present invention is capable of accurately evaluating the interface between the semiconductor substrate and the insulating film formed on the surface thereof even if a silicon carbide substrate is used as the semiconductor substrate. It is an object to provide an evaluation method and an evaluation apparatus for the interface.

As a result of various studies, the present inventor has found that the above problems can be solved by the following present invention. That is, in the method for evaluating an interface between a semiconductor substrate and an insulating film according to one embodiment of the present invention, the measurement region on the surface of the passivated silicon carbide substrate is irradiated with excitation light and a measurement wave, and the measurement region A first measurement step for obtaining a first carrier lifetime in the silicon carbide substrate based on a reflected measurement wave that is the reflected measurement wave or a transmission measurement wave that is the measurement wave that has passed through the measurement region; and the silicon carbide An insulating film forming step for forming an insulating film on the surface of the substrate; and an area corresponding to the measurement area on the insulating film formed on the surface of the silicon carbide substrate is irradiated with the excitation light and the measurement wave. A second carrier for obtaining a second carrier lifetime in the silicon carbide substrate based on a reflected measurement wave reflected in the region or a transmitted measurement wave transmitted through the region. And A lifetime measurement step, characterized in that it comprises an evaluation step of evaluating the interface between the insulating film and the silicon carbide substrate from said first carrier lifetime and the second carrier lifetime.

In another aspect of the present invention, there is provided an interface evaluation apparatus for evaluating an interface between a silicon carbide substrate and an insulating film formed on the surface thereof, and a predetermined measurement on the surface of the silicon carbide substrate subjected to passivation treatment. An excitation light irradiation unit that irradiates predetermined excitation light to a first measurement region that is a region or a second measurement region corresponding to the first measurement region in the insulating film; and the first measurement region or the second measurement region A measurement wave irradiating unit that irradiates a predetermined measurement wave to the light source, a reflected measurement wave that is the measurement wave reflected by the first measurement region or the second measurement region, or the first measurement region or the second measurement region A measurement wave detection unit that detects a transmission measurement wave that is the measurement wave that has passed through, and the silicon carbide substrate and the front based on the reflection measurement wave or the transmission measurement wave detected by the measurement wave detection unit And a computation unit that evaluates the interface with the insulating film. Then, the arithmetic unit comprises a first carrier lifetime in the silicon carbide substrate obtained from the transmission measurements wave first passes through the reflected measurement wave or the first measuring region and reflected by the measurement area, and the second measurement The interface is evaluated from a second carrier lifetime in the silicon carbide substrate obtained from a reflected measurement wave reflected by a region or a transmitted measurement wave transmitted through the second measurement region.

  According to these configurations, the carrier lifetime (first carrier lifetime) measured on the passivated silicon carbide substrate and the carrier lifetime (second carrier lifetime) measured on the silicon carbide substrate on which the insulating film is formed. From the difference between the first carrier lifetime and the second carrier lifetime, the interface between the silicon carbide substrate and the insulating film formed on the surface can be accurately evaluated.

  That is, the silicon carbide substrate in this state is based on the surface state of the silicon carbide substrate in which excess carriers are not easily eliminated due to dangling bonds at the outermost layer (surface) of the silicon carbide substrate by passivation treatment. The carrier lifetime (first carrier lifetime) was measured, and from the difference between the first carrier lifetime and the second carrier lifetime, the silicon carbide substrate on which the second carrier lifetime was measured and the surface thereof were formed. By evaluating the state of the interface with the insulating film, accurate evaluation can be performed.

  For example, specifically, when the passivation treatment is a treatment using hydrofluoric acid for the silicon carbide substrate, dangling bonds on the surface of the silicon carbide substrate are hydrogen-terminated, so that the surface of the silicon carbide substrate is Since it is covered with hydrogen that terminates the dangling bond, excess carriers are hardly lost due to the dangling bond on the surface of the silicon carbide substrate. Thus, from the first carrier lifetime measured in this state and the second carrier lifetime measured on the silicon carbide substrate on which the insulating film is formed instead of the hydrogen termination, the interface between the silicon carbide substrate and the insulating film is obtained. Can be accurately evaluated.

  In addition, when the surface of the silicon substrate is terminated with hydrogen, when the silicon substrate is exposed to an oxygen atmosphere, hydrogen and oxygen are gradually replaced (that is, a natural oxide film is formed) and the silicon substrate surface is roughened. For this reason, it is difficult to accurately measure the carrier lifetime of a silicon substrate terminated with hydrogen. However, in the silicon carbide substrate, the hydrogen-terminated state is maintained unless heated at a temperature higher than room temperature. Therefore, even if the first carrier lifetime is measured in an oxygen atmosphere after the passivation treatment with hydrofluoric acid, Since it is difficult for excess carriers to disappear due to dangling bonds on the surface of the silicon carbide substrate, it is easier to measure the first carrier lifetime than when measuring the first carrier lifetime on the silicon substrate. It can be carried out.

  Further, in the case of performing a passivation treatment using hydrofluoric acid, the method includes a film removal step of removing the passivation film formed by the passivation treatment from the surface of the silicon carbide substrate, and in the insulating film formation step, the film removal step The insulating film is preferably formed on the silicon carbide substrate from which the passivation film has been removed in the process.

  That is, the surface of the silicon carbide is covered with the passivation film by the passivation treatment (specifically, the surface of the silicon carbide substrate is covered with hydrogen terminating the dangling bonds). By forming an insulating film on the silicon carbide substrate from which (terminated hydrogen) is removed, the second carrier lifetime can be measured with higher accuracy.

  In addition, you may perform the said film removal process and the said insulating film formation process simultaneously by heating the silicon carbide substrate in the state in which the said passivation film was formed.

  Since hydrogen due to hydrogen termination on the surface of the silicon carbide substrate can be easily removed from the surface of the silicon carbide substrate by heating, a passivation film (using a heating when forming an oxide film as an insulating film on the surface of the silicon carbide substrate ( By removing the hydrogen that terminates the dangling bonds on the surface of the silicon carbide substrate, the passivation film and the insulating film (oxide film) can be removed at the same time.

  Further, in the method for evaluating an interface between a semiconductor substrate and an insulating film according to the present invention, the first measurement step includes a passivation treatment step for performing a passivation treatment on the silicon carbide substrate, and the silicon carbide substrate subjected to the passivation treatment. Irradiating the measurement region with the excitation light and the measurement wave, and measuring the first carrier lifetime based on the reflection measurement wave or the transmission measurement wave. May be.

Also, the interface apparatus for evaluating a semiconductor substrate and an insulating film according to the present invention, the computing unit, the carbonized before Symbol transmission measurement wave through the reflection measuring wave or the first measuring region and reflected by the first measurement region A carrier for obtaining a first carrier lifetime in a silicon substrate and obtaining a second carrier lifetime in the silicon carbide substrate from a reflected measurement wave reflected by the second measurement region or a transmission measurement wave transmitted through the second measurement region. A life calculation unit and an evaluation as an index indicating the degree of the interface state between the silicon carbide substrate and the insulating film from the first carrier life and the second carrier life obtained by the carrier life calculation unit It is preferable to have an evaluation value calculation unit for obtaining a value.

  According to such a configuration, since the state of the interface between the silicon carbide substrate and the insulating film is obtained as an evaluation value (numerical value), it becomes easy to evaluate the state of the interface.

  As described above, according to the present invention, even when a silicon carbide substrate is used as the semiconductor substrate, the interface evaluation method capable of accurately evaluating the interface between the semiconductor substrate and the insulating film formed on the surface thereof. And the interface evaluation apparatus can be provided.

It is a schematic block diagram of the interface evaluation apparatus of the semiconductor substrate which concerns on this embodiment, and an insulating film. It is a figure which shows the intensity | strength change of the reflected measurement wave measured by the said interface evaluation apparatus. It is a flowchart which shows an example of the operation | movement which the said interface evaluation apparatus evaluates the interface of a silicon carbide substrate and the insulating film formed in the surface.

  Hereinafter, an embodiment of the present invention will be described with reference to the accompanying drawings.

As shown in FIG. 1, an interface evaluation apparatus (hereinafter also simply referred to as “interface evaluation apparatus”) between a semiconductor substrate and an insulating film according to this embodiment includes a stage S, an excitation light irradiation unit 1, and a measurement. A wave input / output unit 2, a detection unit 3, and a control unit 4, and an insulating film X ₂ is formed on the surface of a semiconductor device such as a MOS device or a silicon carbide (SiC) substrate X ₁ such as a solar cell. the evaluation of the interface (interface state) between the SiC substrate _{X 1} and the insulating film _{X 2} in products. In addition, the interface evaluation apparatus A according to the present embodiment includes a passivation unit 5 and a heating unit 6. In the following, the SiC substrate X ₁ having the insulating film X ₂ or the passivation film X ₃ formed on the surface is also simply referred to as a sample X to be measured.

Stage S is a portion SiC substrate _{X 1} or the measured sample X is installed (mounted). In stage S of the present embodiment, SiC substrate X ₁ is installed such that a horizontal posture.

  The excitation light irradiation unit 1 includes a light source unit 11 and a light guide unit 12 and irradiates the sample to be measured X with excitation light under the control of the control unit 4.

  The light source unit 11 is an apparatus that outputs excitation light. In the present embodiment, the light source unit 11 is a laser light source apparatus that outputs laser light. The light source unit 11 of the present embodiment outputs ultraviolet laser light having a wavelength of 266 nm as excitation light. Specifically, the light source unit 11 outputs a fourth harmonic (wavelength is 266 nm) of a YAG laser (wavelength is 1064 nm).

The excitation light output from the light source unit 11 is not limited to ultraviolet laser light having a wavelength of 266 nm, and may be ultraviolet laser light having a wavelength of 355 nm, for example. However, since the SiC constituting the sample X to be measured has a larger band gap than silicon (Si) (the Si band gap is 1.1 eV, the SiC band gap is 3.25 eV), the wavelength Excess carriers are not generated unless excitation light having a short length (that is, energy larger than the band gap) is irradiated. Therefore, the light source unit 11 outputs short-wavelength excitation light capable of generating excess carriers in SiC. That is, when light having a wavelength in the visible light region or a wavelength in the infrared region is used as the excitation light, excess carriers are not generated in the sample to be measured X (SiC substrate X ₁ ), and thus the SiC substrate X ₁ and the insulating film X ₂ cannot be evaluated.

Also, excess carrier number is generated in the vicinity of the interface as the wavelength of the excitation light is short and the SiC substrate ₁ and the insulating film X _2.

The light source unit 11 generates excess carriers (electrons and holes) in the measured sample X (specifically, the SiC substrate X ₁ ) by irradiating the measured sample X with excitation light. In order to measure the lifetime of the generated excess carriers (carrier lifetime / carrier lifetime), it is preferable that the excitation light shifts from a lighting state to a light-off state in a stepped manner. More specifically, it is a pulse laser beam.

  The light guide unit 12 is an optical system that guides the excitation light output from the light source unit 11 to a predetermined region (measurement region) on the surface of the sample X to be measured. The light guide unit 12 of the present embodiment includes a mirror that bends the optical path of the excitation light output from the light source unit 11 in the horizontal direction by about 90 °.

  The measurement wave input / output unit 2 radiates (irradiates) a predetermined measurement wave to the measurement region of the sample X to be measured, and also reflects a reflected measurement wave (specifically, the measurement wave reflected by the measurement region of the sample X to be measured). A measurement wave that has been subjected to a predetermined interaction with the measurement sample X). The measurement wave input / output unit 2 includes a measurement wave generation unit 21, a circulator 22, a waveguide 23, a waveguide antenna 24, and an EH tuner 25.

The measurement wave generation unit 21 generates a predetermined measurement wave according to the control of the control unit 4. In the interface evaluation apparatus A of the present embodiment, for taking out the change in conductivity of the SiC substrate X ₁ caused by generation annihilation process of excess carriers by intensity variation of the measurement wave, the predetermined measurement wave may be any electromagnetic radiation. The measurement wave of the present embodiment is a microwave, and the measurement wave generator 21 is a microwave oscillator that generates a microwave.

  The measurement wave generation unit 21 is connected to one terminal of the circulator 22, and the measurement wave radiated from the measurement wave generation unit 21 enters the circulator 22.

  The circulator 22 has three or more terminals (ports), and irreversibly outputs the input of one terminal to the other terminals cyclically. The circulator 22 of the present embodiment includes three terminals (first to third terminals), emits a measurement wave incident on the first terminal to the second terminal, and transmits a measurement wave incident on the second terminal. Injection to the third terminal. The first terminal of the circulator 22 is connected to the measurement wave generation unit 21, the second terminal is connected to the waveguide 23, and the third terminal is connected to the measurement wave detection unit 31.

  The waveguide 23 is a member that forms a propagation path for guiding a measurement wave. The second terminal of the circulator 22 is connected to one end of the waveguide 23 and the waveguide antenna 24 is connected to the other end. In the present embodiment, since the measurement wave is a microwave, the waveguide 23 is a microwave waveguide.

  The waveguide antenna 24 radiates the measurement wave propagating through the waveguide 23 toward the measurement region of the sample X to be measured, and also measures the measurement wave (reflection measurement wave) that has interacted with the sample X to be measured. ) To guide to the waveguide 23. The waveguide antenna 24 is disposed along the normal direction of the sample X to be measured, and has one end connected to the waveguide 23 and an opening 24a at the other end. The opening 24 a is an opening for radiating a measurement wave to the measurement region of the sample X to be measured and receiving a measurement wave (reflection measurement wave) that has interacted with the sample X to be measured. Then, at one end of the waveguide antenna 24, an opening 24 b for allowing the excitation light emitted from the excitation light irradiating unit 1 to enter the waveguide antenna 24 is provided. In the present embodiment, since the measurement wave is a microwave, the waveguide antenna 24 is a microwave antenna.

  The E-H tuner 25 is interposed in the waveguide 23 between the circulator 22 and the waveguide antenna 24, and measures the measurement wave (reflection measurement wave) that has been interacted with in the sample X to be measured. The magnetic field and electric field of the measurement wave are adjusted so that the signal can be detected better at 31.

  The detection unit 3 is a device that detects a measurement wave (reflection measurement wave) that has been interacted with in the sample X to be measured. The detection unit 3 is, for example, a measurement wave detection unit 31 that detects the intensity of a measurement wave (reflection measurement wave) that has been interacted with in the sample X to be measured. In the present embodiment, since the measurement wave is a microwave, the measurement wave detector 31 is a microwave detector.

The control unit 4 is a device that controls the entire interface evaluation apparatus A, and includes, for example, a microcomputer having a macro processor, a memory, and the like. Then, the control unit 4, evaluation calculation processing for the interface in the measurement sample X on the basis of the intensity of the detected reflected measurement wave in the measuring wave detection unit 31 (the interface with the SiC substrate X ₁ and the insulating film X ₂₎ A unit 41 and an operation storage unit 42 are provided.

Arithmetic processing unit 41, for example, by executing the interface evaluation program for calculating an evaluation of the interface between the SiC substrate X ₁ and the insulating film X ₂ on the basis of the intensity of the reflected measurement wave detected by the measuring wave detecting section 31 Functionally, a carrier life calculation unit 411 and an evaluation value calculation unit 412 are provided. Further, the arithmetic processing unit 41 forms the carrier life storage area 421 in the arithmetic storage unit 42 by executing the interface evaluation program.

The carrier life calculation unit 411 calculates the carrier life τ based on the output of the measurement wave detection unit 31 (the intensity of the reflected measurement wave). For example, the carrier lifetime calculation unit 411 normalizes the output of the measurement wave detection unit 31 with a peak, and derives the time when this value becomes 1 / e as the carrier lifetime τ (see FIG. 2). In the present embodiment, the sample X to be measured in a state where the passivation film X ₃ is formed on the surface of the SiC substrate X _{1 (} the surface of the SiC substrate X ₁ is covered with hydrogen that terminates dangling bonds). the carrier lifetime tau and the first carrier lifetime tau _a, a carrier lifetime tau in the sample to be measured X state where the insulating film X ₂ is formed on the surface of the SiC substrate X ₁ and the second carrier lifetime tau _b.

Carrier lifetime calculating unit 411, of the carrier lifetime tau, derived, and outputs at least a first carrier lifetime tau _a the carrier lifetime storage area 421.

In FIG. 2, the graph indicated by a thick line is the intensity change of the reflected measurement wave when the measured sample X is what insulating film X ₂ is formed on the surface of the SiC substrate X _1, the graph indicated by the thin line shows the intensity change of the reflected measurement wave when the measured sample X is what passivation film X ₃ is formed on the surface of the SiC substrate X _1. Further, the derivation of the carrier life τ in the carrier life calculation unit 411 is not limited to the above method.

Evaluation value calculation unit 412 performs a first carrier lifetime tau _a, and a second carrier lifetime tau _b, the evaluation of the interface (interface state) between the SiC substrate _{X 1} and the insulating film _{X 2.} Specifically, when the carrier life calculation unit 411 calculates the second carrier life τ _b , the evaluation value calculation unit 412 stores the first carrier life τ _a corresponding to the second carrier life τ _b. drawn from region 421, the degree of the state of the interface from the first carrier lifetime tau _a and the second carrier lifetime tau _b and the following formula with (1), the SiC substrate X ₁ and the insulating film X ₂ An evaluation value C serving as an index indicating

C = 1 / τ _b −1 / τ _a (1)
Note that the smaller the evaluation value C is (that is, the closer the second carrier lifetime τ _b is to the first carrier lifetime τ _a ), the more the interface between the SiC substrate X ₁ and the insulating film X ₂ formed on the surface thereof. The condition is good. That is, in FIG. 2, the closer the graph shown by the thin line to the graph shown by the thick line, the better the state of the interface.

  The arithmetic storage unit 42 stores various predetermined data such as a predetermined program and data necessary for execution of the predetermined program. For example, a ROM (Read Only Memory) which is a nonvolatile storage element And EEPROM (Electrically Erasable Programmable Read Only Memory) which is a rewritable nonvolatile memory element. In the arithmetic storage unit 42, when the arithmetic processing unit 41 executes the interface evaluation program, a carrier life storage area 421 is formed therein (in the storage area).

The carrier life storage area 421 stores (stores) the carrier life τ output from the carrier life calculation unit 411. In the carrier lifetime storage area 421 of the present embodiment, at least the first carrier lifetime τ among the carrier lifetimes (first carrier lifetime τ _a and second carrier lifetime τ _b ) obtained by the carrier lifetime calculation unit 411. _a is stored.

Passivation unit 5 forms passivation film X ₃ on the surface of SiC substrate X ₁ under the control of control unit 4. The passivation portion 5 performs the SiC substrate _{X 1} is placed on a stage S, the SiC substrate _{X 1} is moved, a passivation treatment using hydrofluoric acid (HF passivation).

Specifically, the passivation unit 5 includes a hydrofluoric acid aqueous solution (HF aqueous solution) tank 51 and a pure water tank 52. In the HF aqueous solution tank 51, an HF aqueous solution having a hydrofluoric acid concentration of 5%, for example, is stored at room temperature, and the pure water tank 52 stores pure water. After the passivation unit 5, which the SiC substrate X ₁ is placed on a stage S, the SiC substrate X ₁ is immersed for several minutes in an HF solution is moved to the HF solution tank 51 by the control of the control unit 4, It moves to the pure water tank 52 and is immersed in pure water for several minutes. Thus, almost all the dangling bonds at the surface (the top layer) of the SiC substrate X ₁ is hydrogen-terminated. That is, the surface of the SiC substrate X ₁ is substantially covered state by hydrogen to terminate the dangling bonds (a state where the passivation film X ₃ on the surface of the SiC substrate X ₁ is formed). The passivation portion 5, when the surface of the SiC substrate _{X 1} is hydrogen-terminated, return this SiC substrate _{X 1} on the stage S.

The heating unit 6 removes hydrogen (hydrogen group) terminating the dangling bonds from the surface of the SiC substrate X ₁ by heating the SiC substrate X ₁ whose surface is hydrogen-terminated under the control of the control unit 4. while (in the example of this embodiment oxide film) an insulating film on the surface of the SiC substrate X ₁ to form a X _2.

Specifically, the heating unit 6 has a heating chamber 61, in the heating chamber 61, SiC substrate X ₁ is heated in an oxygen atmosphere. The heating unit 6 moves the sample to be measured X (the SiC substrate X _{1 with the} surface terminated with hydrogen) to the heating chamber 61 after the first carrier lifetime τ _a is measured under the control of the control unit 4. The sample to be measured X is heated at, for example, 700 ° C. or higher in an oxygen atmosphere. Thus, the formation of the insulating film (oxide film) _{X 2} for removal of hydrogen in the hydrogen-terminated SiC substrate _{X 1} surface and the (removal of the passivation film _{X 3} of the SiC substrate _{X 1} surface) to the SiC substrate _{X 1} surface Done at once.

When the insulating film X ₂ is formed on the surface of the SiC substrate X ₁ , the heating unit 6 returns the sample to be measured X (SiC substrate X ₁ on which the insulating film X ₂ is formed) on the stage S.

Interface evaluation device A having such a configuration, the following operation, the evaluation of the interface between the insulating film X ₂ formed on the SiC substrate X ₁ and the surface. Figure 3 is a flow chart showing an example of an operation interface evaluation apparatus A performs the evaluation of the interface between the SiC substrate X ₁ and the insulating film X _2.

When SiC substrate _{X 1} is placed on a stage S, a passivation section 5, a SiC substrate _{X 1} passivating process (step S1). Thus, the state in which the surface of the SiC substrate X ₁ is covered with hydrogen terminating the dangling bonds, i.e., a state in which the surface of the SiC substrate X ₁ is covered with a passivation film X _3.

When the surface of the SiC substrate X ₁ is hydrogen termination passivation portion 5 a (SiC substrate X ₁ passivation film X ₃ is formed on the _surface) Sample X to be measured returned to the stage S, the first carrier lifetime τ _a is measured (step S2). In this case, the surface with hydrogen terminated hydrogen SiC substrate X ₁ (hydrogen group) is not Okikawara with oxygen under normal temperature oxygen (air) atmosphere as hydrogen which is hydrogen-terminated by Si substrate surface (i.e., Since a natural oxide film is not formed), it is not necessary to actively take measures to prevent hydrogen bonded to dangling bonds from being replaced with oxygen as in the case of a Si substrate after HF passivation treatment. That is, in the present embodiment, even if the first carrier lifetime τ _a is measured in an environment where the sample to be measured X (SiC substrate X ₁ with the passivation film X ₃ formed on the surface) is exposed to air at normal temperature. Sufficient lateral accuracy is ensured.

When the first carrier lifetime τa is measured, the heating unit 6, (removal of the passivation film X ₃₎ removal of hydrogen terminating the dangling bonds of the SiC substrate X ₁ surface to the SiC substrate X ₁ surface insulating film performing the formation of (oxide film) _{X 2} (step S3).

In the present embodiment, the heating process by the heating unit 6, and the removal of the hydrogen terminating the dangling bonds of the SiC substrate X ₁ surface, the insulating film to the hydrogen removed SiC substrate X ₁ surface ( the formation of oxide film) X _2, although but have been made at one time (by one step), is not limited thereto and may be performed separately. That is, the step of removing the passivation film X ₃ from the surface of the SiC substrate X ₁ is performed, then, forming an insulating film X ₂ on the surface of the SiC substrate X ₁ may be performed.

When the insulating film X ₂ is formed, the heating unit 6 returns the sample to be measured X (SiC substrate X ₁ in a state where the insulating film X ₂ is formed) onto the stage S, and the second carrier lifetime τ _b is It is measured (step S4).

When the second carrier lifetime τ _b is measured, the evaluation value calculation unit 412 receives the _{first value} in the SiC substrate X1 stored in the carrier lifetime storage region 421 from the carrier lifetime storage region 421 of the calculation storage unit 42. The carrier lifetime τ _a is extracted, and the evaluation value C is calculated from the above equation (1) (step S5). This evaluation value C, evaluation of the interface between the SiC substrate _{X 1} and the insulating film _{X 2} is performed. That is, the smaller the evaluation value C, the better the interface state. This is due to the following reason.

In the SiC substrate _{X 1} is HF passivation state almost all the dangling bonds of the SiC substrate _{X 1} surface is hydrogen-terminated, i.e., the SiC substrate _{X 1} and the passivation film _{X 3} are bonded to each other in the entire the interface State. Such an interface (surface) is in a good state, that is, almost all dangling bonds on the surface of the SiC substrate X ₁ are terminated with hydrogen (hydrogen groups) (the SiC substrate X ₁ and the passivation film X ₃ over the entire interface). SiC When the substrate X ₁ for measuring the carrier lifetime tau _a, excess state disappearance of excess carriers other than recombination does not occur between the electrons and holes in the generation annihilation process of the carrier state) where bets are bonded to each other Can be measured.

On the other hand, in the SiC substrate X ₁ having the oxide film (SiO ₂ film) X ₂ formed on the surface, CO, C ₂ O, or the like enters the interface between the oxide film X ₂ and the SiC substrate X _1, and the entered these CO and _{C 2} O such position, since the SiC substrate _{X 1} and oxide film _{X 2} is not bound, the amount of CO and _{C 2} O or the like from entering the interface is increased, SiC substrate _{X 1} a coupling state between the oxide film X ₂ (i.e., the state of the interface) is deteriorated. When the carrier lifetime τ _b is measured with the SiC substrate X ₁ having such a poor interface state, in the process of generating and annihilating excess carriers, it is excessive due to bonding with CO, C ₂ O, etc. in addition to recombination of electrons and holes. Since carriers disappear, the carrier lifetime τ _b becomes shorter (smaller) than when the interface state is good.

Therefore, based on the carrier lifetime (first carrier lifetime) τ _a measured on the SiC substrate X ₁ having a good interface state, the oxide film X ₂ is formed on the first carrier lifetime τ _a and the surface thereof. were measured carrier lifetime in the SiC substrate _{X 1} (second carrier lifetime) tau _b and by comparing, SiC substrate _{X 1} and the oxide film SiC substrate _{X 1} and the oxide film at the interface state (interface with _{X 2} it is possible to evaluate the bonding state) and X _2. Specifically, the second carrier lifetime τ _b is closer to the first carrier lifetime τ _a measured on the SiC substrate X ₁ having a good interface (surface) state (that is, obtained by the above formula (1)). It is higher the value of C is small), while that can be evaluated with good degree of interface states between the SiC substrate X ₁ second carrier lifetime tau _b was measured as oxide film X ₂ is a second carrier lifetime tau _b There increasing distance from the first carrier lifetime tau _a (i.e., as the value of C obtained by the above formula (1) is large), evaluated with the degree of the state of the interface between the SiC substrate X ₁ and the oxide film X ₂ is poor it can.

According to the above semiconductor substrate between the interface evaluation apparatus A with the insulating film, and a first carrier lifetime tau _a measured in SiC substrate X ₁ which is passivated, SiC substrate X ₁ where the insulating film X ₂ is formed The second carrier lifetime τ _b measured in Step 1 is obtained, and from the difference between the first carrier lifetime τ _a and the second carrier lifetime τ _b , the insulating film formed on the SiC substrate X ₁ and its surface evaluation of the interface (interface state) between the X ₂ can be accurately performed.

That is, in order to make the reference of the surface state of the SiC substrate X _{1 in} which excess carriers disappear due to dangling bonds at the outermost layer (surface) of the SiC substrate X ₁ by the passivation treatment, The first carrier lifetime τ _a of the substrate X ₁ is measured, and from the difference between the first carrier lifetime τ _a and the second carrier lifetime τ _b , the SiC substrate X on which the second carrier lifetime τ _b is measured to assess the status of the interface ₁ and the insulating film X _2, it is possible to perform accurate evaluation.

For example, as in the present embodiment, when the passivation process is a process using fluoric acid on the SiC substrate X ₁ (HF passivation), almost all dangling bonds on the surface of the SiC substrate X ₁ are hydrogen-terminated. the surface of the SiC substrate X ₁ is for substantially covered by hydrogen terminating the dangling bonds, disappearance of excess carriers by dangling bonds at the surface of the SiC substrate X ₁ is a occur hardly state by Rukoto. As a result, the first carrier lifetime τ _a measured in this state is measured on the SiC substrate X ₁ on which the insulating film X ₂ is formed instead of the passivation film X ₃ (hydrogen terminating dangling bonds). and a second carrier lifetime tau _b was the evaluation of the interface between the SiC substrate X ₁ and the insulating film X ₂ can be accurately performed.

Moreover, when the surface of the Si substrate is terminated with hydrogen, when the Si substrate is exposed to an oxygen atmosphere, hydrogen and oxygen are gradually replaced (that is, a natural oxide film is formed) and the surface of the Si substrate is roughened. Therefore, it is difficult to accurately measure the carrier lifetime τ of the Si substrate terminated with hydrogen. However, the SiC substrate X _1, since the state in which the hydrogen-terminated to be heated such as at a temperature higher than the room temperature persists, after passivation treatment with hydrofluoric acid, the first carrier lifetime tau _a is measured in an oxygen atmosphere even, because the difficult to occur state disappearance of excess carriers by dangling bonds in the SiC substrate X ₁ surface persists, compared with the case of measuring the first carrier lifetime tau _a in the Si substrate, the first carrier lifetime it is possible to measure tau _a more easily.

In addition, when the passivation process is performed using hydrofluoric acid, the film removal work of the passivation film X ₃ (that is, the SiC substrate X ₁₎ is performed by heating the SiC substrate X ₁ on which the passivation film X ₃ is formed. a dangling process for removing the hydrogen terminating the bond) as an insulating film X ₂ film forming step (insulating film forming step) may be performed at the same time at the surface.

Since hydrogen due to hydrogen termination on the surface of the SiC substrate X ₁ (specifically, hydrogen terminating dangling bonds on the surface of the SiC substrate X ₁ ) can be easily removed from the surface of the SiC substrate X ₁ by heating. by removing the passivation film X ₃ utilizing heating in the formation of the oxide film _(hydrogen terminating the dangling bonds at the surface of the SiC substrate X ₁₎ on the surface of the substrate X ₁ as an insulating film X ₂ , it is possible to perform the removal of the passivation film X ₃ and the insulating film and the formation of (oxide film) X ₂ at the same time.

Further, according to the interface evaluation apparatus A of the present embodiment, since the interface states between the SiC substrate X ₁ and the insulating film (oxide film) X ₂ is obtained as an evaluation value (numeric) C, the interface state evaluation It becomes easy to do.

  The interface evaluation apparatus between the semiconductor substrate and the insulating film of the present invention is not limited to the above embodiment, and it is needless to say that various changes can be made without departing from the gist of the present invention.

In the above embodiment, the insulating film formed on the surface of the SiC substrate X ₁ is an oxide film is not limited thereto. The insulating film only needs to be insulative and transparent to light and microwave, and may be, for example, a SiN (silicon nitride) film or an AlN (aluminum nitride) film.

Further, the interface evaluation apparatus A of the above embodiments, organic passivation unit 5 for HF passivation SiC substrate, a heating unit 6 for removal and formation of the insulating film X ₂ of the passivation film X ₃ in the SiC substrate surface and However, it is not limited to this configuration. For example, the interface evaluation apparatus may not include the passivation unit 5 and / or the heating unit 6. In this case, SiC substrate X ₁ is taken out from the interface evaluation device, passivated at the interface evaluation device outside and / or heat treatment (passivation film X ₃ of film removal, and the formation of the insulating film X ₂₎ is performed .

  Further, the interface evaluation apparatus A of the above embodiment determines the carrier life τ of the sample X to be measured from the intensity change of the reflection-side constant wave, but is not limited to this configuration, and on the back side of the sample X to be measured. A configuration may be used in which the side constant wave (transmission side constant wave) transmitted through the sample is laterally determined, and the carrier life τ of the sample X to be measured is laterally determined from the intensity change.

  In the interface evaluation apparatus A of the above embodiment, the passivation process is HF passivation using hydrofluoric acid, but is not limited to this, and may be iodine passivation or the like.

DESCRIPTION OF SYMBOLS 1 Excitation light irradiation part 2 Measurement wave input / output part 3 Detection part 4 Control part 5 Passivation part 6 Heating part 11 Light source part 21 Measurement wave generation part 31 Measurement wave detection part 41 Operation processing part 42 Operation storage part 411 Carrier lifetime calculation part 412 Evaluation value calculation unit 421 Carrier lifetime recording region C Evaluation value X Sample X ₁ Silicon carbide substrate X ₂ Insulating film X ₃ Passivation film (hydrogen terminating dangling bonds on the surface of silicon carbide)
τ carrier lifetime τ _a first carrier lifetime τ _b second carrier lifetime

Claims (7)

The measurement region on the surface of the passivated silicon carbide substrate is irradiated with excitation light and a measurement wave, and the reflected measurement wave reflected by the measurement region or the measurement wave transmitted through the measurement region. A first measurement step for obtaining a first carrier lifetime in the silicon carbide substrate based on a transmission measurement wave which is:
An insulating film forming step of forming an insulating film on the surface of the silicon carbide substrate;
A region corresponding to the measurement region on the insulating film formed on the surface of the silicon carbide substrate is irradiated with the excitation light and the measurement wave, and the reflected measurement wave reflected in the region or transmitted through the region. A second carrier lifetime measuring step for obtaining a second carrier lifetime in the silicon carbide substrate based on the transmitted measurement wave;
An evaluation step of evaluating an interface between the silicon carbide substrate and the insulating film from the first carrier lifetime and the second carrier lifetime, and an interface evaluation method between the semiconductor substrate and the insulating film .   2. The method for evaluating an interface between a semiconductor substrate and an insulating film according to claim 1, wherein the passivation process is a process using hydrofluoric acid for the silicon carbide substrate. A film removal step of removing the passivation film formed by the passivation treatment from the surface of the silicon carbide substrate,
3. The method for evaluating an interface between a semiconductor substrate and an insulating film according to claim 2, wherein in the insulating film forming step, the insulating film is formed on the silicon carbide substrate from which the passivation film has been removed in the film removing step.   4. The semiconductor substrate and the insulating film according to claim 3, wherein the film removal step and the insulating film forming step are simultaneously performed by heating the silicon carbide substrate on which the passivation film is formed. 5. Interface evaluation method.   The first measurement step includes a passivation treatment step for performing a passivation treatment on the silicon carbide substrate, and irradiating the excitation light and the measurement wave on the measurement region in the silicon carbide substrate subjected to the passivation treatment. And a first carrier lifetime measuring step of measuring the first carrier lifetime based on the reflected measurement wave or the transmitted measurement wave. A method for evaluating an interface between a semiconductor substrate and an insulating film. An interface evaluation apparatus for evaluating an interface between a silicon carbide substrate and an insulating film formed on a surface thereof,
Excitation light irradiation for irradiating predetermined excitation light to a first measurement region which is a predetermined measurement region on the surface of the silicon carbide substrate subjected to passivation treatment or a second measurement region corresponding to the first measurement region in the insulating film And
A measurement wave irradiation unit that irradiates the first measurement region or the second measurement region with a predetermined measurement wave;
A reflected measurement wave that is the measurement wave reflected by the first measurement region or the second measurement region, or a transmission measurement wave that is the measurement wave that has passed through the first measurement region or the second measurement region is detected. A measurement wave detector;
A calculation unit that evaluates an interface between the silicon carbide substrate and the insulating film based on the reflection measurement wave or the transmission measurement wave detected by the measurement wave detection unit;
The arithmetic unit includes a first carrier lifetime in the silicon carbide substrate obtained from the transmission measurements wave first passes through the reflected measurement wave or the first measuring region and reflected by the measurement regions, and in the second measurement region The interface is evaluated from a second carrier lifetime in the silicon carbide substrate obtained from a reflected measurement wave reflected or a transmission measurement wave transmitted through the second measurement region. Interface evaluation device. The arithmetic unit, before SL obtains a first carrier lifetime in the silicon carbide substrate from transmission measurements waves transmitted through the reflection measurement wave or the first measuring region and reflected by the first measurement region, and the second measuring region A carrier life calculation unit for obtaining a second carrier lifetime in the silicon carbide substrate from a reflected measurement wave reflected by the transmission or a transmission measurement wave transmitted through the second measurement region, and the first carrier life calculation unit obtained by the carrier life calculation unit An evaluation value calculation unit that obtains an evaluation value that serves as an index indicating the degree of the state of the interface between the silicon carbide substrate and the insulating film from the carrier life and the second carrier life. 7. An apparatus for evaluating an interface between a semiconductor substrate and an insulating film according to 6.

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