JP6030929B2 - Evaluation method - Google Patents

Description

The present invention relates to an evaluation method of an oxide semiconductor film. Further, the present invention relates to an oxide semiconductor film evaluation apparatus. The present invention also relates to a sampling inspection method in the manufacturing process of a semiconductor device and an apparatus used for the sampling inspection.

A technique for forming a transistor using a semiconductor thin film formed over a substrate having an insulating surface has attracted attention. The transistor is widely applied to an electronic device such as an integrated circuit (IC) or an image display device (also simply referred to as a display device). A silicon-based semiconductor material is widely known as a semiconductor thin film applicable to a transistor, but an oxide semiconductor has attracted attention as another material.

For example, a technique for manufacturing a transistor using zinc oxide or an In—Ga—Zn-based oxide semiconductor as an oxide semiconductor is disclosed (see Patent Documents 1 and 2).

JP 2007-123861 A JP 2007-96055 A

An electrical property of an oxide semiconductor changes due to entry of impurities such as hydrogen or oxygen vacancies. In particular, the electrical characteristics of the oxide semiconductor change depending on the formation conditions of the oxide semiconductor film, the treatment conditions after the formation of the oxide semiconductor film, and the like.

Therefore, an object of one embodiment of the present invention is to evaluate electrical characteristics of an oxide semiconductor film. Another object of one embodiment of the present invention is to evaluate electrical characteristics of an oxide semiconductor film after any treatment is performed on the oxide semiconductor film.

One embodiment of the present invention includes a first step of measuring a thickness and a sheet resistance of an oxide semiconductor film for a sample having an oxide semiconductor film provided in contact with an insulating surface on an outermost surface; In this evaluation method, the second step of etching a part of the film and the third step of measuring the film thickness and the sheet resistance of the oxide semiconductor film partially etched are performed in this order.

Another embodiment of the present invention is a sample manufacturing process in which an oxide semiconductor film in contact with an insulating surface is formed, a conductive film is formed over the oxide semiconductor film, and the conductive film is removed. A first step of measuring thickness and sheet resistance; a second step of etching part of the oxide semiconductor film; and a third step of measuring film thickness and sheet resistance of the partially etched oxide semiconductor film This is an evaluation method in which the steps are performed in this order.

In the first step and the third step of each evaluation method described above, the order of measurement of the film thickness of the oxide semiconductor film and measurement of the sheet resistance is not limited. In each step, after measuring the film thickness, the sheet resistance may be measured, or after measuring the sheet resistance, the film thickness may be measured. In each of the above evaluation methods, after the third step is performed, the etching of the oxide semiconductor film, the measurement of the thickness of the oxide semiconductor film after the etching, and the measurement of the sheet resistance are repeatedly performed. Also good. That is, the second step and the third step may be repeated.

In the first step of each of the above evaluation methods, it is preferable to measure the thickness of the oxide semiconductor film using a spectroscopic ellipsometry method. In the first step of each of the above evaluation methods, it is preferable to measure the sheet resistance of the oxide semiconductor film using a four-probe method.

In the second step of each of the above evaluation methods, it is preferable to etch the oxide semiconductor film using a wet etching method.

In the third step of each of the above evaluation methods, it is preferable to measure the thickness of the oxide semiconductor film partially etched using a spectroscopic ellipsometry method. In the third step of each of the above evaluation methods, it is preferable to measure the sheet resistance of the oxide semiconductor film partially etched using the four-probe method.

The conductive film is preferably removed using a wet etching method or a dry etching method.

One embodiment of the present invention includes a first processing chamber, a second processing chamber, and a third processing chamber, and each of the first processing chamber, the second processing chamber, and the third processing chamber. The first processing chamber has a device that can measure the film thickness in a non-contact or non-destructive manner with respect to the sample, and the second processing chamber has a sheet resistance measuring device. The third processing chamber is an evaluation apparatus that has a wet etching apparatus, and the third processing chamber is partitioned from the first processing chamber and the second processing chamber.

One embodiment of the present invention includes a connection chamber, a load lock chamber that supplies a sample to the connection chamber, a first processing chamber, a second processing chamber, and a third processing chamber each having an opening connected to the connection chamber. And the connection chamber has a transport mechanism for loading and unloading the sample into and from each of the first processing chamber, the second processing chamber, and the third processing chamber. , Having a device that can measure the film thickness in a non-contact or non-destructive manner with respect to the sample, the second processing chamber has a sheet resistance measuring device, the third processing chamber has a wet etching device, It is an evaluation apparatus which has a gate in the opening part of the 3rd process chamber connected with a connection chamber.

In each of the above evaluation apparatuses, the apparatus (the apparatus capable of measuring the film thickness in a non-contact or non-destructive manner with respect to the sample) included in the first processing chamber is a spectroscopic ellipsometer or an optical interference type film thickness measuring apparatus. Is preferred.

In each of the evaluation apparatuses described above, the sheet resistance measurement apparatus included in the second processing chamber is preferably an apparatus using a four-probe method.

In the evaluation method of one embodiment of the present invention, the conductivity in the thickness direction of the oxide semiconductor film can be evaluated by measuring the film thickness and the sheet resistance before and after the etching of the oxide semiconductor film. In the evaluation device of one embodiment of the present invention, the etching of the oxide semiconductor film, the film thickness measurement, and the sheet resistance measurement can be performed by one unit, and the conductivity in the thickness direction of the oxide semiconductor film can be easily evaluated. be able to.

FIG. 10 illustrates an example of an evaluation method of one embodiment of the present invention. FIG. 10 illustrates an example of an evaluation method of one embodiment of the present invention. FIG. 10 illustrates an example of an evaluation method of one embodiment of the present invention. The figure which shows an example of the evaluation apparatus of 1 aspect of this invention. The figure which shows an example of the process chamber which the evaluation apparatus of 1 aspect of this invention has. FIG. 6 shows evaluation results of oxide semiconductor films in examples. FIG. 6 shows evaluation results of oxide semiconductor films in examples.

Embodiments will be described in detail with reference to the drawings. However, the present invention is not limited to the following description, and it is easily understood by those skilled in the art that modes and details can be variously changed without departing from the spirit and scope of the present invention. Therefore, the present invention should not be construed as being limited to the description of the embodiments below. Note that in structures of the invention described below, the same portions or portions having similar functions are denoted by the same reference numerals in different drawings, and description thereof is not repeated.

(Embodiment 1)
In this embodiment, an evaluation method of one embodiment of the present invention will be described with reference to FIGS.

In the evaluation method of one embodiment of the present invention, the conductivity in the thickness direction of the oxide semiconductor film can be evaluated.

Factors that lower the resistance of an oxide semiconductor include mixing of impurities (such as hydrogen, silicon, nitrogen, carbon, and metal elements other than main components), oxygen vacancies, and the like.

For example, when a transistor is formed using an oxide semiconductor, if there are many oxygen vacancies in the oxide semiconductor film including the channel formation region of the transistor, electrons are generated in the channel formation region, and the transistor is normally on. This is a factor that causes defects in electrical characteristics, such as increase in leakage current, increase in leakage current, and shift in threshold voltage due to stress application.

In the oxide semiconductor film, hydrogen forms donor levels and increases carrier density. Further, silicon forms impurity levels in the oxide semiconductor film, and the impurity levels may serve as a trap, which may deteriorate the electrical characteristics of the transistor.

Therefore, in order to obtain stable electrical characteristics in a semiconductor device including an oxide semiconductor, measures must be taken to reduce oxygen vacancies in the oxide semiconductor film and reduce the concentration of impurities such as hydrogen and silicon. Is required.

In addition, when a conductive material that is easily bonded to oxygen is brought into contact with the oxide semiconductor film, a phenomenon in which oxygen in the oxide semiconductor film diffuses or moves toward the conductive material that is easily bonded to oxygen. Since there are several heating steps in the manufacturing process of the transistor, oxygen vacancies are generated in the vicinity of the oxide semiconductor film in contact with the source electrode and the drain electrode, and the resistance of the region is reduced. To do. The region with reduced resistance can serve as the source or drain of the transistor. However, if the resistance of the channel formation region of the transistor is reduced due to the generation of oxygen vacancies, the transistor has electrical characteristics in which a threshold voltage shift or a gate voltage cannot be turned on / off (conductive state). .

Based on the above, it is possible to evaluate how much the resistance-reduced region is generated in the thickness direction of the oxide semiconductor film depending on the formation conditions of the oxide semiconductor film and the processing conditions after the formation of the oxide semiconductor film. Is preferred.

Thus, in the evaluation method of one embodiment of the present invention, the conductivity in the thickness direction of the oxide semiconductor film is evaluated by measuring the film thickness and the sheet resistance before and after the etching of the oxide semiconductor film.

<< Sample >>
A sample to be evaluated using the evaluation method of one embodiment of the present invention can have any structure or manufacturing method as long as it has an oxide semiconductor film provided in contact with the insulating surface on the outermost surface. For example, a sample in which an oxide semiconductor film is formed in contact with a supporting substrate or a sample in which an oxide semiconductor film is formed through another film on the supporting substrate can be used. There is no particular limitation on the film provided between the supporting substrate and the oxide semiconductor film, and an insulating film, a conductive film, a semiconductor film, or the like can be provided as a single layer or a stacked layer. Alternatively, a sample in which another film is formed after the other film is formed over the oxide semiconductor film can be used. There is no particular limitation on the film provided over the oxide semiconductor film, and an insulating film, a conductive film, a semiconductor film, or the like can be provided as a single layer or a stacked layer.

Further, heat treatment may be performed during the sample manufacturing process. For example, heat treatment may be performed after the oxide semiconductor film is formed or after the conductive film is formed.

Further, oxygen addition treatment may be performed during the sample manufacturing process. For example, oxygen addition treatment may be performed after the oxide semiconductor film is formed or after the conductive film is removed. As the oxygen addition treatment, heat treatment is performed on the oxide semiconductor film in an oxygen atmosphere, oxygen is added to the oxide semiconductor film by an ion implantation method, an ion doping method, or the like.

Note that the formation method and materials of the oxide semiconductor film are described in detail in Embodiment 3.

≪Evaluation method 1≫
The evaluation method flow 100 shown in FIG. 1 includes steps 101 to 104. Each step will be described with reference to FIGS.

<Step 101: Measurement of film thickness and sheet resistance of oxide semiconductor film>
First, the thickness and sheet resistance of the oxide semiconductor film 303 are measured for the sample 300 including the oxide semiconductor film 303 on the outermost surface illustrated in FIG.

The film thickness of the oxide semiconductor film may be measured at least by a method that can be performed in a non-contact or non-destructive manner with respect to the oxide semiconductor film. For example, a spectroscopic ellipsometry method or a reflection method that is an optical film thickness measurement method. It can be measured using rate spectroscopy (also called an optical interference method).

The sheet resistance of the oxide semiconductor film can be measured using, for example, a four-probe method or a four-terminal method.

The order of the measurement of the thickness of the oxide semiconductor film and the measurement of the sheet resistance does not matter. After measuring the film thickness of the oxide semiconductor film, the sheet resistance may be measured, or after measuring the sheet resistance of the oxide semiconductor film, the film thickness may be measured.

<Step 102: Etching of Oxide Semiconductor Film>
Next, the oxide semiconductor film 303 is etched and part thereof is removed, so that the thickness of the oxide semiconductor film 303 is reduced. The oxide semiconductor film can be etched by a dry etching method or a wet etching method. In this embodiment, the oxide semiconductor film 303 is etched by a wet etching method. By using the wet etching method, damage to the oxide semiconductor film can be reduced and generation of oxygen vacancies or the like can be suppressed as compared to the case of using the dry etching method. Depending on the material of the oxide semiconductor film and the like, etching conditions (for wet etching, the type and temperature of a chemical used for etching, an etching time, or the like) are set as appropriate.

<Step 103: Measurement of thickness and sheet resistance of oxide semiconductor film>
Next, the thickness and the sheet resistance of the oxide semiconductor film 304 which is partially etched are measured (FIG. 3D). The measurement can be performed in the same manner as in step 101.

<Step 104: Do you want to end the evaluation? >
When the evaluation is finished, it is finished. Furthermore, when part of the oxide semiconductor film is etched and the sheet resistance of the oxide semiconductor film whose thickness is reduced is measured, the process returns to Step 102. As an example, FIG. 3E illustrates an oxide semiconductor film 305 in which part of the oxide semiconductor film is etched.

≪Evaluation method 2≫
The flow 110 of another evaluation method illustrated in FIG. 2 includes the above-described steps 101 to 104. The flow 110 includes steps 111 to 113 for preparing a sample before step 101. Hereinafter, step 111 to step 113 will be described with reference to FIGS.

<Step 111: Formation of Oxide Semiconductor Film>
First, the oxide semiconductor film 303 is formed over the insulating surface 301 by using a sputtering method, an MBE (Molecular Beam Epitaxy) method, a CVD (Chemical Vapor Deposition) method, a pulse laser deposition method, an ALD (Atomic Layer Deposition) method, or the like. (FIG. 3A).

<Step 112: Formation of conductive film>
Next, a conductive film 307 is formed over the oxide semiconductor film 303 by a sputtering method, a CVD method, an evaporation method, or the like (FIG. 3B). As a material of the conductive film 307, for example, a metal element selected from aluminum, nickel, yttrium, zirconium, silver, chromium, copper, tantalum, titanium, molybdenum, and tungsten, an alloy containing the above metal element as a component, or the above An alloy combining the above metal elements can be used.

<Step 113: Removal of conductive film>
Next, the conductive film 307 over the oxide semiconductor film 303 is removed by a dry etching method, a wet etching method, or the like (FIG. 3C).

After performing Step 113, Steps 101 to 104 described above are performed.

As described above, in the evaluation method of one embodiment of the present invention, the conductivity in the thickness direction of the oxide semiconductor film can be evaluated by measuring the thickness and sheet resistance of the oxide semiconductor film before and after etching. it can.

Note that one embodiment of the present invention can also be applied to a sampling inspection in the manufacturing process of a semiconductor device. For example, in a manufacturing process of a semiconductor device, a sample for evaluation is manufactured over a supporting substrate at the same time as a transistor having an oxide semiconductor film. The thickness of the oxide semiconductor film on the sample surface after the substrate is extracted before and after an arbitrary step after the oxide semiconductor film is formed (for example, a step of etching a conductive film formed over the oxide semiconductor film) Measurement and sheet resistance measurement may be performed. By performing the inspection, it can be evaluated how much the region with reduced resistance is generated in the thickness direction of the oxide semiconductor film by the process.

This embodiment can be implemented in appropriate combination with any of the other embodiments described in this specification.

(Embodiment 2)
In this embodiment, an evaluation device of one embodiment of the present invention will be described with reference to FIGS. In the evaluation device of one embodiment of the present invention, etching of an oxide semiconductor film, film thickness measurement, and sheet resistance measurement can be performed with one unit, and the conductivity in the thickness direction of the oxide semiconductor film can be easily evaluated. it can.

≪Evaluation equipment≫
FIG. 4A illustrates an evaluation device of one embodiment of the present invention. An evaluation apparatus 200 illustrated in FIG. 4A includes a connection chamber 201 having a transfer mechanism 207, a first processing chamber 203, a second processing chamber 204, and a third processing chamber 205 that are connected to the connection chamber 201, respectively. Have A sample can be carried into and out of each processing chamber using the transport mechanism 207.

In the evaluation apparatus of this embodiment, first, the thickness of the oxide semiconductor film is measured in the first treatment chamber 203, and the sheet resistance of the oxide semiconductor film is measured in the second treatment chamber 204. Next, wet etching of the oxide semiconductor film is performed in the third treatment chamber 205. After that, the thickness of the oxide semiconductor film after wet etching (also referred to as a partially etched oxide semiconductor film) is measured in the first treatment chamber, and the wet etching is performed in the second treatment chamber 204. The sheet resistance of the oxide semiconductor film is measured.

In the third treatment chamber 205, the humidity of the chamber increases when wet etching of the oxide semiconductor film is performed. A gate 206 is provided between the third processing chamber 205 and the connection chamber 201 in order to prevent the measurement environment of the first processing chamber 203 and the second processing chamber 204 from being affected. With the gate 206, the third processing chamber 205 can be partitioned from the first processing chamber 203, the second processing chamber 204, and the connection chamber 201. The gate 206 may be provided with a door, a shutter, or the like. In addition, a similar gate may be provided between the first processing chamber 203 and the connection chamber 201 and between the second processing chamber 204 and the connection chamber 201.

FIG. 4B shows an evaluation apparatus according to another aspect of the present invention. The evaluation apparatus 210 shown in FIG. 4B is different from the evaluation apparatus 200 in that it has a load lock chamber 202 connected to the connection chamber 201. In the load lock chamber 202, a cassette containing a sample is taken in and out. Further, a door may be provided between the load lock chamber 202 and the connection chamber 201.

In the evaluation apparatus of one embodiment of the present invention, the substrate is aligned in the apparatus. For example, it is preferable to carry out in a load lock chamber or a connecting chamber.

The configuration of each processing chamber and the processing to be performed will be described.

<First processing chamber>
In the first treatment chamber 203, the thickness of the oxide semiconductor film is measured.

In this embodiment, the processing chamber in which the film thickness can be measured is only the first processing chamber 203, and an example in which only one sample is measured at a time is illustrated. A plurality of similar processing chambers may be provided. Alternatively, the first processing chamber 203 may include a plurality of film thickness measuring devices (also referred to as film thickness measuring devices) so that a plurality of samples can be measured at a time.

The first processing chamber 203 includes a device that can measure the film thickness in a non-contact or non-destructive manner with respect to the sample. Examples of such an apparatus include an ellipsometer (for example, a spectroscopic ellipsometer) and an optical interference type film thickness measuring apparatus.

In this embodiment, the case where the thickness of an oxide semiconductor film is measured in the first treatment chamber 203 using a spectroscopic ellipsometry is described as an example.

In the first treatment chamber 203 illustrated in FIG. 5A, the sample 260 can be placed over the stage 231. The sample 260 is irradiated with light from the light source 232 and the detector 233 detects the reflected light from the sample 260, whereby the thickness of the oxide semiconductor film in the sample 260 is measured.

The first processing chamber 203 preferably has an exhaust duct (not shown) for humidity and temperature management. The temperature of the first treatment chamber 203 may be 25 ° C., for example.

In order to measure the film thickness of a plurality of locations in the oxide semiconductor film, the stage 231 is preferably movable in a direction (XY direction) parallel to the surface of the oxide semiconductor film.

<Second processing chamber>
In the second treatment chamber 204, the sheet resistance of the oxide semiconductor film is measured.

In this embodiment, the processing chamber in which the sheet resistance can be measured is only the second processing chamber 204, and a case where only one sample can be measured at a time is illustrated. A plurality of similar processing chambers may be provided. Further, the second processing chamber 204 may include a plurality of sheet resistance measuring devices and can measure a plurality of samples at a time.

In the second treatment chamber 204, the thickness of the oxide semiconductor film is measured with a sheet resistance measurement device (also referred to as a sheet resistance measurement device) using a four-probe method, a four-terminal method, or the like.

In this embodiment, the case where the sheet resistance measurement of the oxide semiconductor film is performed in the second treatment chamber 204 with a sheet resistance measurement device using a four-point probe method will be described as an example.

In the second treatment chamber 204 illustrated in FIG. 5B, the sample 260 can be placed over the stage 241. Measure the sheet resistance of the oxide semiconductor film by placing the four-probe probe 243 on the sample 260 in a straight line, passing a constant current between the two outer probes, and measuring the potential difference between the two inner probes. To do.

The second processing chamber 204 preferably has an exhaust duct (not shown) for humidity and temperature management. The temperature of the second treatment chamber 204 may be 25 ° C., for example.

The four probe probe 243 is connected to the drive mechanism 242. At least one of the stage 241 and the drive mechanism 242 is movable in the thickness direction (Z direction) of the oxide semiconductor film. In addition, in order to measure the sheet resistance values at a plurality of locations in the oxide semiconductor film, at least one of the stage 241 and the driving mechanism 242 is movable in a direction parallel to the surface of the oxide semiconductor film (also referred to as an XY direction). It is preferable.

<Third processing chamber>
In the third treatment chamber 205, wet etching of the oxide semiconductor film is performed.

The wet etching apparatus included in the third processing chamber 205 may be a single wafer type apparatus or a batch type apparatus. In this embodiment, the case where the third processing chamber 205 is the only processing chamber in which the oxide semiconductor film can be etched and only one sample can be etched at a time is described. However, the evaluation apparatus of one embodiment of the present invention May have a plurality of similar processing chambers. Alternatively, the third processing chamber 205 may have a configuration in which a plurality of samples can be measured at a time, such as a plurality of single-wafer devices or a batch-type device.

For efficient evaluation, in the evaluation apparatus, the number of samples that can measure the film thickness at a time, the number of samples that can measure the sheet resistance at a time, and the number of samples that can perform wet etching at a time are equal. It is preferable.

In this embodiment, the case where wet etching of an oxide semiconductor film is performed in the third treatment chamber 205 using a single-wafer wet etching apparatus will be described as an example.

In the third treatment chamber 205 illustrated in FIGS. 5C1 and 5C2, the sample 260 can be placed over the stage 251. The chemical nozzle 253a and the chemical nozzle 253b are respectively moved in the XY direction by the drive mechanism 256a or the drive mechanism 256b. For example, an etching solution (hydrogen peroxide solution or a mixed aqueous solution of hydrogen peroxide solution and ammonia) may be discharged from the chemical solution nozzle 253a, and a rinse solution (pure water or the like) may be discharged from the chemical solution nozzle 253b.

The stage 251 has a rotation mechanism that can be rotated by designating the number of rotations within a predetermined time. The chemical liquid can be discharged from the chemical liquid nozzle 253a or the chemical liquid nozzle 253b to the sample 260 while rotating the stage 251 (the upper sample 260). A partition 252 is provided so that the chemical discharged from the chemical nozzle 253a or the chemical nozzle 253b does not adhere to the wall surface of the third processing chamber 205 or the like. The partition 252 has a gate shutter (not shown) that can be opened and closed when the sample 260 is disposed on the stage 251.

The third processing chamber 205 has a waste liquid pipe 254 for transporting the discharged chemical liquid to a waste liquid tank (not shown) in a space surrounded by the partition 252.

As the processing in the third processing chamber 205, for example, first, the etching solution is discharged from the chemical solution nozzle 253a or the chemical solution nozzle 253b to the sample 260 while rotating the stage 251 (the upper sample 260) at a constant speed. Thus, the oxide semiconductor film is etched. Next, while the stage 251 (the upper sample 260) is rotated, the rinsing liquid is discharged from the other of the chemical liquid nozzle 253a or the chemical liquid nozzle 253b to the sample 260, thereby washing away the etching liquid. Furthermore, the sample 260 is dried by rotating the stage 251 (the upper sample 260). The sample 260 in which the oxide semiconductor film is etched by the above treatment is carried into the first treatment chamber 203 or the second treatment chamber 204, whereby the oxide semiconductor film having a thickness different from that before the etching is measured. Film thickness measurement and sheet resistance measurement can be performed.

Note that in the case where the third treatment chamber 205 includes a plurality of chemical nozzles that can discharge an etchant, an etchant that can etch the conductive film may be prepared. Accordingly, not only step 102 (etching of the oxide semiconductor film) described in Embodiment 1 but also step 113 (removal of the conductive film) can be performed by the evaluation device of one embodiment of the present invention. Thereby, since an apparatus required for evaluation can be reduced, evaluation can be performed more simply.

Note that in this embodiment mode, the first processing chamber 203 has a film thickness measuring device, the second processing chamber 204 has a sheet resistance measuring device, and the third processing chamber 205 has a wet etching device. Although the apparatus has been described as an example, the arrangement of the processing chambers is not limited. For example, the first processing chamber 203 has a sheet resistance measuring device, and the second processing chamber 204 has a film thickness measuring device. The third treatment chamber 205 may have a wet etching apparatus.

Note that the evaluation apparatus of one embodiment of the present invention can also be applied to sampling inspection in the manufacturing process of a semiconductor device. For example, in a manufacturing process of a semiconductor device, a sample for evaluation is manufactured over a supporting substrate at the same time as a transistor having an oxide semiconductor film. In the evaluation apparatus of one embodiment of the present invention, a sample is extracted before and after an arbitrary step after the oxide semiconductor film is formed (for example, a step of etching a conductive film formed over the oxide semiconductor film). You may perform the film thickness measurement and sheet resistance measurement of the oxide semiconductor film which has on the surface. By performing the inspection, it can be evaluated how much the region with reduced resistance is generated in the thickness direction of the oxide semiconductor film by the process.

This embodiment can be implemented in appropriate combination with any of the other embodiments described in this specification.

(Embodiment 3)
In this embodiment, an example of an oxide semiconductor film that can be evaluated using the evaluation method of one embodiment of the present invention will be described.

An oxide semiconductor has a large energy gap of 3.0 eV or more. In a transistor to which an oxide semiconductor film obtained by processing an oxide semiconductor under appropriate conditions and sufficiently reducing its carrier density is applied, The leakage current (off-state current) between the source and drain in the off state can be made extremely low as compared with a conventional transistor using silicon. Hereinafter, among oxide semiconductor films that can be evaluated using the evaluation method of one embodiment of the present invention, an oxide semiconductor film suitable as a semiconductor film of a transistor is described.

An oxide semiconductor preferably contains at least indium (In) or zinc (Zn). In particular, In and Zn are preferably included. Further, as a stabilizer for reducing variation in electrical characteristics of a transistor using the oxide semiconductor, in addition to them, gallium (Ga), tin (Sn), hafnium (Hf), zirconium (Zr), titanium (Ti) , Scandium (Sc), yttrium (Y), lanthanoids (for example, cerium (Ce), neodymium (Nd), gadolinium (Gd)), or a plurality of them are preferably included.

For example, as an oxide semiconductor, indium oxide, tin oxide, zinc oxide, In—Zn oxide, Sn—Zn oxide, Al—Zn oxide, Zn—Mg oxide, Sn—Mg oxide In-Mg oxide, In-Ga oxide, In-Ga-Zn oxide, In-Al-Zn oxide, In-Sn-Zn oxide, Sn-Ga-Zn oxide Al-Ga-Zn-based oxide, Sn-Al-Zn-based oxide, In-Hf-Zn-based oxide, In-Zr-Zn-based oxide, In-Ti-Zn-based oxide, In-Sc- Zn-based oxide, In-Y-Zn-based oxide, In-La-Zn-based oxide, In-Ce-Zn-based oxide, In-Pr-Zn-based oxide, In-Nd-Zn-based oxide, In-Sm-Zn oxide, In-Eu-Zn oxide, In-Gd-Zn oxide In-Tb-Zn-based oxide, In-Dy-Zn-based oxide, In-Ho-Zn-based oxide, In-Er-Zn-based oxide, In-Tm-Zn-based oxide, In-Yb- Zn-based oxide, In-Lu-Zn-based oxide, In-Sn-Ga-Zn-based oxide, In-Hf-Ga-Zn-based oxide, In-Al-Ga-Zn-based oxide, In-Sn An -Al-Zn-based oxide, an In-Sn-Hf-Zn-based oxide, or an In-Hf-Al-Zn-based oxide can be used.

Here, the In—Ga—Zn-based oxide means an oxide containing In, Ga, and Zn as main components, and there is no limitation on the ratio of In, Ga, and Zn. Moreover, metal elements other than In, Ga, and Zn may be contained.

Alternatively, a material represented by InMO ₃ (ZnO) _m (m> 0 is satisfied, and m is not an integer) may be used as the oxide semiconductor. Note that M represents one metal element or a plurality of metal elements selected from Ga, Fe, Mn, and Co, or the above-described element as a stabilizer. Alternatively, a material represented by In ₂ SnO ₅ (ZnO) _n (n> 0 is satisfied, and n is an integer) may be used as the oxide semiconductor.

For example, In: Ga: Zn = 1: 1: 1, In: Ga: Zn = 1: 3: 2, In: Ga: Zn = 1: 6: 4, In: Ga: Zn = 1: 9: 6, An In—Ga—Zn-based oxide with an atomic ratio of In: Ga: Zn = 3: 1: 2 or In: Ga: Zn = 2: 1: 3 or an oxide in the vicinity of the composition may be used. Further, indium gallium oxide may be used.

When the oxide semiconductor film contains a large amount of hydrogen, the oxide semiconductor film is bonded to the oxide semiconductor, so that part of the hydrogen becomes a donor and an electron which is a carrier is generated. As a result, the threshold voltage of the transistor shifts in the negative direction. Therefore, after the oxide semiconductor film is formed, dehydration treatment (dehydrogenation treatment) is performed to remove hydrogen or moisture from the oxide semiconductor film so that impurities are contained as little as possible. preferable.

Note that oxygen may be reduced from the oxide semiconductor film at the same time due to dehydration treatment (dehydrogenation treatment) of the oxide semiconductor film. Therefore, it is preferable to add oxygen that has been simultaneously reduced by dehydration treatment (dehydrogenation treatment) to the oxide semiconductor film or supply oxygen to fill oxygen vacancies in the oxide semiconductor film. . In this specification and the like, the case where oxygen is supplied to the oxide semiconductor film may be referred to as oxygenation treatment or peroxygenation treatment.

In this manner, the oxide semiconductor film is made i-type (intrinsic) or i-type by removing hydrogen or moisture by dehydration treatment (dehydrogenation treatment) and filling oxygen vacancies by oxygenation treatment. An oxide semiconductor film that is substantially i-type (intrinsic) can be obtained. Note that substantially intrinsic means that the number of carriers derived from a donor in the oxide semiconductor film is extremely small (near zero), and the carrier density is 1 × 10 ¹⁷ / cm ³ or less, 1 × 10 ¹⁶ / cm ³ or less, It means 1 × 10 ¹⁵ / cm ³ or less, 1 × 10 ¹⁴ / cm ³ or less, and 1 × 10 ¹³ / cm ³ or less.

In this manner, a transistor including an i-type or substantially i-type oxide semiconductor film can achieve extremely excellent off-state current characteristics. For example, the drain current when the transistor including an oxide semiconductor film is off is 1 × 10 ⁻¹⁸ A or less, preferably 1 × 10 ⁻²¹ A or less, more preferably 1 at room temperature (about 25 ° C.). × 10 ⁻²⁴ A or less, or 1 × 10 ⁻¹⁵ A or less, preferably 1 × 10 ⁻¹⁸ A or less, more preferably 1 × 10 ⁻²¹ A or less at 85 ° C. Note that an off state of a transistor means a state where a gate voltage is sufficiently lower than a threshold voltage in the case of an n-channel transistor. Specifically, when the gate voltage is 1 V or higher, 2 V or higher, or 3 V or lower than the threshold voltage, the transistor is turned off.

The oxide semiconductor film may be single crystal or non-single crystal. In the latter case, it may be amorphous or polycrystalline. Moreover, the structure which contains the part which has crystallinity in an amorphous may be sufficient, and a non-amorphous may be sufficient.

Preferably, the oxide semiconductor film is a CAAC-OS (C Axis Crystallized Oxide Semiconductor) film.

The CAAC-OS film is not completely single crystal nor completely amorphous. The CAAC-OS film is an oxide semiconductor film with a crystal-amorphous mixed phase structure where crystal parts and amorphous parts are included in an amorphous phase. Note that the crystal part is often large enough to fit in a cube whose one side is less than 100 nm. Further, in the observation image obtained by a transmission electron microscope (TEM), the boundary between the amorphous part and the crystal part included in the CAAC-OS film is not clear. Further, a grain boundary (also referred to as a grain boundary) cannot be confirmed in the CAAC-OS film by TEM. Therefore, in the CAAC-OS film, reduction in electron mobility due to grain boundaries is suppressed.

The crystal part included in the CAAC-OS film is triangular when viewed from the direction perpendicular to the ab plane and the c-axis is aligned in a direction parallel to the normal vector of the formation surface of the CAAC-OS film or the normal vector of the surface. It has a shape or hexagonal atomic arrangement, and metal atoms are arranged in layers or metal atoms and oxygen atoms are arranged in layers as viewed from the direction perpendicular to the c-axis. Note that the directions of the a-axis and the b-axis may be different between different crystal parts. In this specification, a simple term “perpendicular” includes a range from 85 ° to 95 °. In addition, a simple term “parallel” includes a range from −5 ° to 5 °.

Note that the distribution of crystal parts in the CAAC-OS film is not necessarily uniform. For example, in the formation process of the CAAC-OS film, when crystal growth is performed from the surface side of the oxide semiconductor film, the ratio of crystal parts in the vicinity of the surface of the oxide semiconductor film is higher in the vicinity of the surface. In addition, when an impurity is added to the CAAC-OS film, the crystal part in a region to which the impurity is added becomes amorphous in some cases.

Since the c-axis of the crystal part included in the CAAC-OS film is aligned in a direction parallel to the normal vector of the formation surface of the CAAC-OS film or the normal vector of the surface, the shape of the CAAC-OS film (formation surface) Depending on the cross-sectional shape or the cross-sectional shape of the surface). Note that the c-axis direction of the crystal part is parallel to the normal vector of the surface where the CAAC-OS film is formed or the normal vector of the surface. The crystal part is formed by film formation or by performing crystallization treatment such as heat treatment after film formation.

In a transistor using a CAAC-OS film, change in electrical characteristics due to irradiation with visible light or ultraviolet light is small. Therefore, the transistor has high reliability.

The CAAC-OS film can be formed by a sputtering method using a polycrystalline oxide semiconductor sputtering target, for example. When ions collide with the sputtering target, the crystal region included in the sputtering target is cleaved from the ab plane, and may be separated as flat or pellet-like sputtering particles having a plane parallel to the ab plane. is there. In this case, the CAAC-OS film can be formed when the flat or pellet-like sputtered particles reach the film formation surface while maintaining the crystalline state.

The flat sputtered particles have, for example, a circle-equivalent diameter of a plane parallel to the ab plane of 3 nm to 10 nm and a thickness (length in a direction perpendicular to the ab plane) of 0.7 nm to less than 1 nm. . The flat sputtered particles may have a regular triangle or a regular hexagonal plane parallel to the ab plane. Here, the equivalent circle diameter refers to the diameter of a perfect circle that is equal to the surface area.

In order to form the CAAC-OS film, the following conditions are preferably applied.

By increasing the substrate temperature at the time of film formation, migration of the flat sputtered particles reaching the substrate occurs, and the flat surface of the sputtered particles adheres to the substrate. At this time, since the sputtered particles are positively charged and the sputtered particles adhere to the substrate while being repelled, the sputtered particles are not biased and do not overlap unevenly, and a CAAC-OS film having a uniform thickness is formed. Can be membrane. Specifically, it is preferable to form the film at a substrate temperature of 100 ° C to 740 ° C, preferably 200 ° C to 500 ° C.

In addition, by reducing impurity contamination during film formation, the crystal state can be prevented from being broken by impurities. For example, the concentration of impurities (such as hydrogen, water, carbon dioxide, and nitrogen) existing in the deposition chamber may be reduced. Further, the impurity concentration in the deposition gas may be reduced. Specifically, a deposition gas having a dew point of −80 ° C. or lower, preferably −100 ° C. or lower is used.

In addition, it is preferable to reduce plasma damage during film formation by increasing the oxygen ratio in the film formation gas and optimizing electric power. The oxygen ratio in the deposition gas is 30% by volume or more, preferably 100% by volume.

Heat treatment may be performed after the CAAC-OS film is formed. The temperature of the heat treatment is 100 ° C. or higher and 740 ° C. or lower, preferably 200 ° C. or higher and 500 ° C. or lower. The heat treatment time is 1 minute to 24 hours, preferably 6 minutes to 4 hours. Further, the heat treatment may be performed in an inert atmosphere or an oxidizing atmosphere. Preferably, after heat treatment in an inert atmosphere, heat treatment is performed in an oxidizing atmosphere. By the heat treatment in an inert atmosphere, the impurity concentration of the CAAC-OS film can be reduced in a short time. On the other hand, oxygen vacancies may be generated in the CAAC-OS film by heat treatment in an inert atmosphere. In that case, the oxygen vacancies can be reduced by heat treatment in an oxidizing atmosphere. Further, by performing heat treatment, the crystallinity of the CAAC-OS film can be further increased. Note that the heat treatment may be performed under a reduced pressure of 1000 Pa or less, 100 Pa or less, 10 Pa or less, or 1 Pa or less. Under reduced pressure, the impurity concentration of the CAAC-OS film can be reduced in a shorter time.

As an example of the sputtering target, an In—Ga—Zn—O compound target is described below.

In-Ga-Zn- which is polycrystalline by mixing InO _X powder, GaO _Y powder and ZnO _Z powder in a predetermined number of moles, and after heat treatment at a temperature of 1000 ° C. or higher and 1500 ° C. or lower. An O compound target is used. X, Y, and Z are arbitrary positive numbers. Here, the predetermined mole number ratio is, for example, 1: 1: 1, 1: 1: 2, 1: 3: 2, 1: 6: 4, 1 for InO _X powder, GaO _Y powder, and ZnO _Z powder. : 9: 6, 2: 1: 3, 2: 2: 1, 3: 1: 1, 3: 1: 2, 3: 1: 4, 4: 2: 3, 8: 4: 3, or these It can be a nearby value. In addition, what is necessary is just to change suitably the kind of powder, and the mol number ratio to mix with the sputtering target to produce.

The CAAC-OS film may be formed by the following method.

First, the first oxide semiconductor film is formed with a thickness greater than or equal to 1 nm and less than 10 nm. The first oxide semiconductor film is formed by a sputtering method. Specifically, the film formation is performed at a substrate temperature of 100 ° C. or higher and 500 ° C. or lower, preferably 150 ° C. or higher and 450 ° C. or lower, and an oxygen ratio in the film forming gas is 30% by volume or higher, preferably 100% by volume.

Next, heat treatment is performed so that the first oxide semiconductor film becomes a first CAAC-OS film with high crystallinity. The temperature of the heat treatment is 350 ° C to 740 ° C, preferably 450 ° C to 650 ° C. The heat treatment time is 1 minute to 24 hours, preferably 6 minutes to 4 hours. Further, the heat treatment may be performed in an inert atmosphere or an oxidizing atmosphere. Preferably, after heat treatment in an inert atmosphere, heat treatment is performed in an oxidizing atmosphere. By the heat treatment in the inert atmosphere, the impurity concentration of the first oxide semiconductor film can be reduced in a short time. On the other hand, oxygen vacancies may be generated in the first oxide semiconductor film by heat treatment in an inert atmosphere. In that case, the oxygen vacancies can be reduced by heat treatment in an oxidizing atmosphere. Note that the heat treatment may be performed under a reduced pressure of 1000 Pa or less, 100 Pa or less, 10 Pa or less, or 1 Pa or less. Under reduced pressure, the impurity concentration of the first oxide semiconductor film can be further reduced in a short time.

When the thickness of the first oxide semiconductor film is greater than or equal to 1 nm and less than 10 nm, the first oxide semiconductor film can be easily crystallized by heat treatment as compared with the case where the thickness is greater than or equal to 10 nm.

Next, a second oxide semiconductor film having the same composition as the first oxide semiconductor film is formed to a thickness of greater than or equal to 10 nm and less than or equal to 50 nm. The second oxide semiconductor film is formed by a sputtering method. Specifically, the film formation is performed at a substrate temperature of 100 ° C. or higher and 500 ° C. or lower, preferably 150 ° C. or higher and 450 ° C. or lower, and an oxygen ratio in the film forming gas is 30% by volume or higher, preferably 100% by volume.

Next, heat treatment is performed, and the second oxide semiconductor film is solid-phase grown from the first CAAC-OS film, whereby the second CAAC-OS film with high crystallinity is obtained. The temperature of the heat treatment is 350 ° C to 740 ° C, preferably 450 ° C to 650 ° C. The heat treatment time is 1 minute to 24 hours, preferably 6 minutes to 4 hours. Further, the heat treatment may be performed in an inert atmosphere or an oxidizing atmosphere. Preferably, after heat treatment in an inert atmosphere, heat treatment is performed in an oxidizing atmosphere. By the heat treatment in the inert atmosphere, the impurity concentration of the second oxide semiconductor film can be reduced in a short time. On the other hand, oxygen vacancies may be generated in the second oxide semiconductor film by heat treatment in an inert atmosphere. In that case, the oxygen vacancies can be reduced by heat treatment in an oxidizing atmosphere. Note that the heat treatment may be performed under a reduced pressure of 1000 Pa or less, 100 Pa or less, 10 Pa or less, or 1 Pa or less. Under reduced pressure, the impurity concentration of the second oxide semiconductor film can be further reduced in a short time.

As described above, a CAAC-OS film with a total thickness of 10 nm or more can be formed.

The oxide semiconductor film may have a structure in which a plurality of oxide semiconductor films are stacked.

For example, the oxide semiconductor film is formed of an element forming the first layer between the oxide semiconductor film (referred to as the first layer for convenience) and the gate insulating film, and has an electron affinity of 0. A second layer smaller than 2 eV may be provided. At this time, when an electric field is applied from the gate electrode, a channel is formed in the first layer, and no channel is formed in the second layer. Since the first layer has the same constituent elements as the second layer, interface scattering hardly occurs at the interface between the first layer and the second layer. Therefore, by providing the second layer between the first layer and the gate insulating film, the field effect mobility of the transistor can be increased.

Further, in the case where a silicon oxide film, a silicon oxynitride film, a silicon nitride oxide film, or a silicon nitride film is used for the gate insulating film, silicon contained in the gate insulating film may be mixed into the oxide semiconductor film. When silicon is contained in the oxide semiconductor film, crystallinity of the oxide semiconductor film, carrier mobility, and the like are reduced. Therefore, in order to reduce the silicon concentration of the first layer in which the channel is formed, it is preferable to provide the second layer between the first layer and the gate insulating film. For the same reason, it is preferable to provide a third layer made of an element constituting the first layer and having an electron affinity of 0.2 eV or more smaller than that of the first layer, and sandwich the first layer between the second layer and the third layer. .

With such a structure, diffusion of impurities such as silicon into a region where a channel is formed can be reduced and prevented, so that a highly reliable transistor can be obtained.

Note that in order to use the oxide semiconductor film as a CAAC-OS film, the concentration of silicon contained in the oxide semiconductor film is set to 2.5 × 10 ²¹ / cm ³ or less. Preferably, the concentration of silicon contained in the oxide semiconductor film is less than 1.4 × 10 ²¹ / cm ³ , more preferably less than 4 × 10 ¹⁹ / cm ³ , and even more preferably 2.0 × 10 ¹⁸ / cm ^3. Less than. When the concentration of silicon contained in the oxide semiconductor film is 1.4 × 10 ²¹ / cm ³ or more, there is a fear that the field-effect mobility of the transistor may be reduced, and 4.0 × 10 ¹⁹ / cm ³ or more. This is because the oxide semiconductor film may become amorphous at the interface between the oxide semiconductor film and the film in contact with the oxide semiconductor film. In addition, when the silicon concentration in the oxide semiconductor film is less than 2.0 × 10 ¹⁸ / cm ³ , further improvement in the reliability of the transistor and reduction in DOS (density of state) in the oxide semiconductor film are expected. it can. Note that the silicon concentration in the oxide semiconductor film can be measured by secondary ion mass spectrometry (SIMS).

This embodiment can be implemented in appropriate combination with any of the other embodiments described in this specification.

In this example, the results of evaluating the conductivity in the thickness direction of an oxide semiconductor film using the evaluation method of one embodiment of the present invention will be described.

≪Evaluation 1≫
In the evaluation 1, the evaluation was performed according to the flow 110 of the evaluation method shown in FIG.

<Step 111: Formation of Oxide Semiconductor Film>
First, an oxide semiconductor film 303 with a thickness of 100 nm was formed over an insulating surface 301 (here, a glass substrate). The oxide semiconductor film 303 was formed by a DC sputtering method using an oxide target of In: Ga: Zn = 1: 1: 1 (atomic ratio) as a sputtering target. The deposition conditions were a substrate temperature of 300 ° C., a deposition gas Ar: O ₂ = 30 sccm: 15 sccm, a deposition power of 0.5 kW, a deposition pressure of 0.4 Pa, and an electrode-substrate distance of 60 mm.

<Step 112: Formation of conductive film>
Next, a conductive film 307 with a thickness of 100 nm was formed over the oxide semiconductor film 303 (FIG. 3B). Here, a tungsten film is formed as the conductive film 307. The tungsten film was formed by DC sputtering using metallic tungsten as a sputtering target. The film formation conditions were a substrate temperature of 130 ° C., a film formation gas Ar, a film formation power of 1 kW, a film formation pressure of 0.8 Pa, and an electrode-substrate distance of 60 mm.

<Step 113: Removal of conductive film>
After that, the conductive film 307 was removed using a wet etching method or a dry etching method (FIG. 3C). In the sample from which the conductive film 307 was removed by the wet etching method, hydrogen peroxide water was used. A sample from which the conductive film 307 has been removed by a dry etching method uses an ICP (Inductively Coupled Plasma) etching method. The etching conditions are a power source power 3000 W, a bias power 110 W, a pressure 0.67 Pa, and a substrate temperature 40 ° C. Etching gas Cl ₂ : CF ₄ : O ₂ = 45 sccm: 55 sccm: 55 sccm.

<Step 101: Measurement of film thickness and sheet resistance of oxide semiconductor film>
Then, the thickness of the oxide semiconductor film 303 was measured using a spectroscopic ellipsometry method, and the sheet resistance of the oxide semiconductor film 303 was measured using a four-point probe method. Note that the measurement result in step 101 corresponds to the value of the sheet resistance when the film thickness reduction amount is 0 nm in FIG.

<Step 102: Etching of Oxide Semiconductor Film>
Next, the oxide semiconductor film 303 was etched using a wet etching method. A mixed aqueous solution of hydrogen peroxide and ammonia was used for etching the oxide semiconductor film 303.

<Step 103: Measurement of thickness and sheet resistance of oxide semiconductor film>
Then, the thickness and the sheet resistance of the oxide semiconductor film 304 which were partially etched were measured (FIG. 3D). The measurement method is the same as in step 101. The thickness of the oxide semiconductor film measured immediately after removing the conductive film 307 (the measurement result in step 101, the thickness of the oxide semiconductor film 303), and the oxide semiconductor measured after the oxide semiconductor film 303 was etched From the difference from the film thickness (the measurement result in step 103, the film thickness of the oxide semiconductor film 304), the reduction amount of the film thickness was obtained.

<Step 104: Do you want to end the evaluation? >
The evaluation was completed after repeating Step 102 and Step 103 until the value of the sheet resistance reached (or immediately before) the measurement limit.

The evaluation results are shown in FIG. In the sample in which the tungsten film was formed over the oxide semiconductor film, it was confirmed that the resistance of the surface of the oxide semiconductor film was reduced. This is because a mixed layer of a low-resistance oxide semiconductor and tungsten is formed in the vicinity of the surface of the oxide semiconductor film, or oxygen in the oxide semiconductor film is taken into the tungsten film. This suggests that a region with reduced resistance is formed by oxygen deficiency near the surface of the semiconductor film. In particular, in the sample from which the tungsten film was removed by the dry etching method, it was confirmed that the resistance was reduced to a depth of about 5 nm in the thickness direction from the surface, which is lower than that in the sample from which the tungsten film was removed by the wet etching method. I found out that it was resisting. This suggests that plasma damage or the like during dry etching affects the resistance reduction of the oxide semiconductor film.

≪Evaluation 2≫
In the evaluation 2, the evaluation was performed according to the flow 110 of the evaluation method shown in FIG. However, the heat treatment was performed on the sample between Step 112 and Step 113.

<Step 111: Formation of Oxide Semiconductor Film>
First, an oxide semiconductor film 303 with a thickness of 50 nm was formed over an insulating surface 301 (here, a glass substrate) (FIG. 3A). The oxide semiconductor film 303 was formed by a DC sputtering method using an oxide target of In: Ga: Zn = 1: 1: 1 (atomic ratio) as a sputtering target. The deposition conditions were a substrate temperature of 300 ° C., a deposition gas Ar: O ₂ = 30 sccm: 15 sccm, a deposition power of 0.5 kW, a deposition pressure of 0.4 Pa, and an electrode-substrate distance of 60 mm.

<Step 112: Formation of conductive film>
Next, a conductive film 307 with a thickness of 100 nm was formed over the oxide semiconductor film 303 (FIG. 3B). As the conductive film 307, a tungsten film, a tantalum nitride film, or a titanium nitride film was formed. The tungsten film was formed by DC sputtering using tungsten as a sputtering target. The film formation conditions were a substrate temperature of 130 ° C., a film formation gas Ar, a film formation power of 1 kW, a film formation pressure of 0.8 Pa, and an electrode-substrate distance of 60 mm. The tantalum nitride film was formed using tantalum as a sputtering target and a reactive sputtering method (DC sputtering method). The deposition conditions were a substrate temperature of 25 ° C. (room temperature), a deposition gas Ar: N ₂ = 50 sccm: 10 sccm, a deposition power of 1 kW, a deposition pressure of 0.6 Pa, and an electrode-substrate distance of 60 mm. The titanium nitride film was formed by using reactive sputtering (DC sputtering) with titanium as a sputtering target. The film forming conditions were a substrate temperature of 25 ° C. (room temperature), a film forming gas N ₂ , a film forming power of 12 kW, a film forming pressure of 0.2 Pa, and an electrode-substrate distance of 400 mm.

Next, heat treatment was performed. The heat treatment was performed under a nitrogen atmosphere at 400 ° C. for 1 hour.

For comparison, a sample in which the conductive film 307 was not formed over the oxide semiconductor film 303 was also manufactured. This sample was subjected to a heat treatment after step 111, and then subjected to step 101 (steps 112 and 113 relating to formation / removal of the conductive film were not performed).

<Step 113: Removal of conductive film>
After that, the conductive film 307 was removed using a dry etching method (FIG. 3C). The conductive film 307 was etched by an ICP etching method. The etching conditions for removing the tungsten film were as follows: power source power 3000 W, bias power 110 W, pressure 0.67 Pa, substrate temperature 40 ° C., etching gas Cl ₂ : CF ₄ : O ₂ = 45 sccm: 55 sccm: 55 sccm. Etching conditions for removing the tantalum nitride film and the titanium nitride film were a power source power of 2000 W, a bias power of 50 W, a pressure of 0.67 Pa, a substrate temperature of 40 ° C., and an etching gas CF ₄ .

<Step 101: Measurement of film thickness and sheet resistance of oxide semiconductor film>
Then, the thickness of the oxide semiconductor film 303 was measured using a spectroscopic ellipsometry method, and the sheet resistance of the oxide semiconductor film 303 was measured using a four-point probe method. Note that the measurement result in step 101 corresponds to the value of the sheet resistance when the film thickness reduction amount is 0 nm in FIG.

<Step 102: Etching of Oxide Semiconductor Film>
Next, the oxide semiconductor film 303 was etched using a wet etching method. A mixed aqueous solution of hydrogen peroxide and ammonia was used for etching the oxide semiconductor film 303.

<Step 103: Measurement of thickness and sheet resistance of oxide semiconductor film>
Then, the thickness and the sheet resistance of the oxide semiconductor film 304 which were partially etched were measured (FIG. 3D). The measurement method is the same as in step 101. The thickness of the oxide semiconductor film measured immediately after removing the conductive film 307 (the measurement result in step 101, the thickness of the oxide semiconductor film 303), and the oxide semiconductor measured after the oxide semiconductor film 303 was etched From the difference in film thickness (measurement result in step 103, film thickness of the oxide semiconductor film 304), the reduction amount of the film thickness was obtained.

<Step 104: Do you want to end the evaluation? >
The evaluation was completed after repeating Step 102 and Step 103 until the value of the sheet resistance reached the measurement limit (or before the decrease in film thickness exceeded 40 nm).

The evaluation results are shown in FIG. In any of the samples, reduction in resistance of the oxide semiconductor film was confirmed. Here, the resistance of the sample in which the conductive film is formed over the oxide semiconductor film is lower in the vicinity of the surface of the oxide semiconductor film and deeper in the thickness direction than the sample in which the conductive film is not formed. It was confirmed that the resistance was lowered.

As shown in this example, by using the evaluation method of one embodiment of the present invention, the resistance-reduced region is in the thickness direction of the oxide semiconductor film in accordance with the processing conditions after the oxide semiconductor film is formed. It was possible to evaluate how much it will occur. Specifically, by forming a conductive film in contact with the oxide semiconductor film, a region with a reduced resistance in the thickness direction of the oxide semiconductor film is formed, and the method of removing the conductive film reduces the low resistance. It was confirmed that the range in the thickness direction of the resistance region was different.

100 Flow 110 Flow 200 Evaluation device 201 Connection chamber 202 Load lock chamber 203 First processing chamber 204 Second processing chamber 205 Third processing chamber 207 Transfer mechanism 210 Evaluation device 231 Stage 232 Light source 233 Detector 241 Stage 242 Drive mechanism 243 Four-point probe 251 Stage 252 Bulkhead 253a Chemical liquid nozzle 253b Chemical liquid nozzle 254 Waste liquid pipe 256a Drive mechanism 256b Drive mechanism 260 Sample 300 Sample 301 Insulating surface 303 Oxide semiconductor film 304 Oxide semiconductor film 305 Oxide semiconductor film 307 Conductive film

Claims (4)

A sample manufacturing step of forming an oxide semiconductor film in contact with an insulating surface, forming a conductive film over the oxide semiconductor film, and removing the conductive film;
A first step of measuring the thickness and sheet resistance of the oxide semiconductor film;
A second step of etching a part of the oxide semiconductor film;
Perform a third step of the part to measure the film thickness and the sheet resistance of the oxide semiconductor film is etched, in this order,
By comparing the film thickness and sheet resistance of the oxide semiconductor film measured in the first step with the film thickness and sheet resistance of the oxide semiconductor film measured in the third step, An evaluation method for evaluating conductivity in a thickness direction of an oxide semiconductor film. In claim 1 ,
An evaluation method in which the thickness of the oxide semiconductor film in the first step and the third step is measured using a spectroscopic ellipsometry method. In claim 1 or claim 2 ,
An evaluation method in which the sheet resistance of the oxide semiconductor film in the first step and the third step is measured using a four-probe method. In any one of Claims 1 thru | or 3 ,
The etching of the oxide semiconductor film in the second step is an evaluation method using a wet etching method.

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