JP6717218B2 - Semiconductor wafer evaluation method - Google Patents

Description

The disclosure in this specification relates to a semiconductor wafer evaluation method for evaluating damage when a semiconductor wafer is irradiated with ions.

As disclosed in Patent Document 1, oxide film breakdown voltage (GOI) evaluation is known as a method for evaluating the surface quality of a semiconductor wafer.

In the oxide film breakdown voltage evaluation, an oxide film is formed on the surface of a semiconductor wafer by thermal oxidation, and an electrode is formed on the oxide film. Then, an electrical stress is applied to the oxide film which is an insulator, and the surface quality of the semiconductor wafer is evaluated from the insulation degree of the oxide film.

When the semiconductor wafer is subjected to ion irradiation such as dry etching or ion implantation, a defect, that is, damage occurs in the semiconductor wafer having crystallinity. If there is a defect in the surface layer of the semiconductor wafer, it is taken into the oxide film during thermal oxidation and becomes a defect in the film, and the insulating property of the oxide film is reduced. Therefore, the surface quality of the semiconductor wafer can be evaluated by the oxide film withstand voltage evaluation described above.

JP, 2002-158269, A

As described above, conventionally, a semiconductor wafer for evaluation having the same structure and TEG (Test Element Group) as the product is prepared by forming electrodes on the oxide film, and the oxide film breakdown voltage is evaluated. .. For this reason, there is a problem that the process of forming the semiconductor wafer for evaluation is complicated and the evaluation requires a long time.

As a method of evaluating the quality of the thermal oxide film, after forming a pattern of a MIS structure (Metal-Insulator-Semiconductor), a voltage is applied between the electrode and the semiconductor to measure the amount of charge in the film from the capacitance change of the oxide film. CV measurements are also known. However, also in this case, it is necessary to form an electrode on the oxide film. In addition, in this measurement, only the charges near the interface with the semiconductor in the oxide film can be detected, and the charges near the electrode, that is, the charges at positions apart from the interface cannot be detected. Thus, the contact type C-V measurement cannot detect the amount of charges in the film.

The present disclosure has been made in view of such problems, and an object thereof is to provide a semiconductor wafer evaluation method capable of evaluating damage when a semiconductor wafer is irradiated with ions in a short period of time.

The present disclosure employs the following technical means in order to achieve the above object. It should be noted that the reference numerals in parentheses show the correspondence with specific means described in the embodiments described later as one aspect, and do not limit the technical scope.

One evaluation method of the present disclosure is a semiconductor wafer evaluation method for evaluating damage when a semiconductor wafer is irradiated with ions,
The semiconductor wafer (10) is irradiated with ions from one surface side (S11),
By using a predetermined condition that the characteristic of the oxide film when formed on a bare semiconductor wafer without contamination is 1E11 [ions/cm ² ] or less in the film charge, one side of the semiconductor wafer after ion irradiation is used. , An oxide film (15) is formed by thermal oxidation (S15),
With respect to the semiconductor wafer after thermal oxidation, the characteristics of the oxide film were measured by a non-contact type C-V measuring device (S16),
Based on the measurement results, the damage of the semiconductor wafer is evaluated (S17, S17A).

According to this evaluation method, since the measurement is performed using a non-contact type C-V measuring device, unlike the contact type C-V measurement, the electric charge at a position apart from the interface with the semiconductor in the oxide film is also detected. can do. Further, thermal oxidation is performed under predetermined conditions such that the amount of charges in the film is 1E11 [ions/cm ² ] or less in the bare state. Since the oxide film is formed so that the initial amount of charges in the film is reduced, when defects generated by ion irradiation are taken into the oxide film by thermal oxidation, they appear as changes (increases) in the amount of charges in the film. Therefore, the damage of the semiconductor wafer can be evaluated.

Furthermore, since it is not necessary to form an electrode on the oxide film, evaluation can be performed in a short period of time. As described above, damage when the semiconductor wafer is irradiated with ions can be evaluated in a short period of time.

According to another evaluation method of the present disclosure, when the result of the evaluation shows that the damage of the semiconductor wafer is not within the allowable range, the formed oxide film is removed (S18), and then the semiconductor wafer is thermally oxidized again using predetermined conditions. An oxide film is formed on one surface side, and measurement with a non-contact CV measuring device and evaluation of damage to the semiconductor wafer are performed.

According to this evaluation method, since the evaluation is continued until the damage can be tolerated, the thickness of the sacrificial oxidation at the time of manufacturing, that is, the thickness of the damage removal can be determined. Further, since the measurement is performed using a non-contact type C-V measuring device, it is not necessary to form an electrode on the oxide film. Therefore, even if the thermal oxidation is performed again, there is no influence of metal contamination by the electrodes, and therefore damage due to ion irradiation can be evaluated with high accuracy.

3 is a flowchart showing a semiconductor wafer evaluation procedure according to the first embodiment. It is sectional drawing which shows the oxide film formation process before ion irradiation. It is sectional drawing which shows an ion irradiation process. It is sectional drawing which shows the removal process of an etch stopper film. FIG. 6 is a cross-sectional view showing a step of forming a sacrificial oxide film. It is sectional drawing which shows the removal process of a sacrificial oxide film. FIG. 6 is a cross-sectional view showing a step of forming a gate oxide film. It is sectional drawing which shows CV measurement of non-contact. It is a figure for explaining the outline of non-contact CV measurement. Si0 is a diagram showing a charge of an oxide film and the interface in the ₂ -Si structure. It is a figure which shows the relationship between the electric charge amount in a film, and an oxide film variation. It is a figure which shows the relationship between the amount of charges in a film, and the amount of overetching. It is a figure which shows the relationship between a yield and the amount of overetches. 6 is a flowchart showing a semiconductor wafer evaluation procedure according to the second embodiment.

Embodiments will be described with reference to the drawings. In some embodiments, functionally and/or structurally corresponding parts are provided with the same reference numerals.

(First embodiment)
In this embodiment, as an evaluation method for evaluating damage when a semiconductor wafer is irradiated with ions, a polysilicon film is formed on a semiconductor substrate through an etch stopper, the polysilicon is patterned by dry etching, and then sacrificial oxidation is performed. An evaluation method for guaranteeing the quality of a product (semiconductor wafer) obtained by removing a damaged layer by, and then forming a gate oxide film will be described as an example.

A semiconductor wafer evaluation method according to this embodiment will be described with reference to FIGS. 1 to 9.

First, an etch stopper is formed on a semiconductor wafer for evaluation (step S10). As shown in FIG. 2, bare silicon (raw stone) which is not contaminated is prepared as the semiconductor substrate 11, and an oxide film 12 functioning as an etch stopper is formed on one surface side of the semiconductor substrate 11 by thermal oxidation. For example, N-type silicon is adopted as the semiconductor substrate 11, and the (100) plane is one surface. Further, the oxide film 12 having a thickness of, for example, about 50 nm is formed by thermal oxidation. In this way, the semiconductor wafer 10 for evaluation having the oxide film 12 as the etch stopper on the one surface side is prepared.

In the product, the polysilicon in the area where the gate oxide film is formed is completely removed by etching. For this reason, polysilicon is not required to evaluate the damage due to ion irradiation, and in the present embodiment, polysilicon film formation and patterning are not performed. As a result, the evaluation process can be simplified. However, since damage to the semiconductor wafer 10 changes depending on the amount of over-etching when patterning polysilicon, the oxide film 12 is formed according to the manufacturing process of the product in this embodiment.

Next, the semiconductor wafer is irradiated with ions from one surface side (step S11). As shown in FIG. 3, the semiconductor wafer 10 having the oxide film 12 is irradiated with ions from one surface side. In this embodiment, the semiconductor wafer 10 is irradiated with ions by performing dry etching, specifically reactive ion etching (RIE), in accordance with the manufacturing process. The semiconductor substrate 11 having crystallinity produces defects 13 by ion irradiation. This is damage to the semiconductor wafer 10 due to ion irradiation. In this way, by performing ion irradiation in the state where there is no polysilicon, overetching can be simulated, and the state of damage close to an actual product can be reproduced while simplifying the process.

Then, the oxide film functioning as an etching stopper is removed (step S12). After the ion irradiation is completed, the oxide film 12 is removed by a known method such as hydrofluoric acid, as shown in FIG.

Next, sacrificial oxidation is performed to remove damage to the semiconductor wafer 10 (semiconductor substrate 11) (step S13). As shown in FIG. 5, the oxide film 14 is formed on the one surface side of the semiconductor substrate 11 by thermal oxidation. For example, the oxide film 14 having a thickness of about 60 nm is formed. As a result, at least a part of the defects 13 generated in the surface layer of the semiconductor substrate 11 is taken into the oxide film 14.

Next, the oxide film formed in step S13 is removed (step S14). That is, after the sacrificial oxidation, the oxide film 14 is removed by a known method such as hydrofluoric acid, as shown in FIG. As a result, the semiconductor substrate 11 is not considerably damaged and is removed.

Next, gate oxidation is performed (step S15). As shown in FIG. 7, the gate oxide film 15 is formed on the one surface side of the semiconductor substrate 11 by thermal oxidation. For example, the gate oxide film 15 having a thickness of about 60 nm is formed. The gate oxide film 15 is formed under a predetermined condition that the characteristic of the oxide film when formed on bare silicon which is not contaminated is 1E11 [ions/cm ² ] or less in the amount of charges in the film. The step of forming the gate oxide film 15 corresponds to the step of forming an oxide film after ion irradiation.

Next, CV measurement is performed on the semiconductor wafer 10 by the non-contact CV measuring device (step S16). Specifically, as shown in FIG. 8, the measurement electrode 16 of the non-contact CV measuring device is arranged above the gate oxide film 15 with a minute air gap AG therebetween. Then, a voltage is applied between A and B by the measuring device, and the CV characteristic of the semiconductor wafer 10 is measured. In the present embodiment, the in-film charge amount of the gate oxide film 15 is measured as the CV characteristic.

As shown in FIG. 9, the capacitance between A and B is the capacitance Cd of the semiconductor substrate 11, the capacitance Cox of the gate oxide film 15, and the capacitance Cair of the air gap AG connected in series. It can be represented by a shape. Here, if the length of the air gap AG is known, the capacitance Cair of the air gap AG can be obtained. Therefore, if the capacitance Cair is subtracted from the CV measurement result, the capacitance of the semiconductor wafer 10 that does not include the air gap AG can be calculated. Further, because of the structure including the air gap AG, not only the charge in the vicinity of the interface with the semiconductor substrate 11 in the gate oxide film 15 but also the charge at a position distant from the interface, that is, the charge of the surface layer on the side of the measurement electrode 16 are considered. Can also be detected.

Then, the damage of the semiconductor wafer is evaluated based on the measurement result of step S16 (step S17). Specifically, the in-film charge amount measured in step S16 is compared with a preset predetermined value, and when the in-film charge amount is equal to or less than the predetermined value, the film quality of the gate oxide film 15 is good, that is, the semiconductor. It is determined that the damage to the wafer 10 is within an allowable range (the damage is sufficiently reduced). On the other hand, when the amount of charges in the film exceeds the predetermined value, it is determined that the film quality of the gate oxide film 15 is deteriorated, that is, the damage of the semiconductor wafer 10 is not within the allowable range (the damage remains). With the above, a series of evaluations is completed.

Next, the effect of the above-described method for evaluating the semiconductor wafer 10 will be described.

In the present embodiment, the in-film charge amount of the gate oxide film 15 is measured using a non-contact type CV measuring device. Therefore, unlike the contact type C-V measurement, it is possible to detect the electric charge at a position apart from the interface with the semiconductor substrate 11, that is, the electric charge of the surface layer on the air gap AG side. As a result, the amount of charges in the film can be accurately detected.

After performing dry etching (ion irradiation), the gate oxide film 15 is formed by thermal oxidation under a predetermined condition that the amount of charges in the film becomes 1E11 [ions/cm ² ] or less when formed on bare silicon which is not contaminated. To form. As a result, in the gate oxide film 15, the fixed charges Qf and the interface states Qit (interface trap charges) shown in FIG. 10 are regulated to minute amounts. In this way, the gate oxide film 15 is formed so that there is no contamination and the fixed charge Qf is reduced, that is, the amount of charges in the initial film is reduced. Therefore, when the oxide film trap charge Qot increases by incorporating the defect 13 into the gate oxide film 15, it appears as a change (increase) in the in-film charge amount. Thus, the detection sensitivity of the oxide film trap charge Qot, that is, the oxide film defect derived from the defect 13 is high, so that the damage of the semiconductor wafer 10 can be evaluated. Note that Qm shown in FIG. 10 is a movable charge (movable ion).

FIG. 11 shows the measurement result by the present inventor. At that time, bare silicon not contaminated was thermally oxidized at 1000° C. to form a gate oxide film 15 having a film thickness of 60 nm. Then, the in-film charge amount of the gate oxide film 15 was measured by a non-contact type C-V measuring device. Further, five points were measured on the wafer surface, and the difference between the maximum value and the minimum value was defined as the oxide film variation. If defects or metal impurities are taken into the oxide film, the film thickness of the taken-in portion becomes large and the film thickness variation becomes large.

If the conditions for forming the gate oxide film 15 are limited to the condition that the initial amount of charges in the film is 1E11 [ions/cm ² ] or less, the oxide film variation becomes minute as shown in FIG. Therefore, by limiting the conditions for forming the gate oxide film 15 to the above-described predetermined conditions, it is possible to perform an appropriate evaluation excluding the disturbance factors other than the defect 13 due to the ion irradiation.

In order to reduce the initial charge in the film to 1E11 [ions/cm ² ] or less, thermal oxidation may be performed at a temperature of 950° C. or higher when forming the gate oxide film 15, for example. According to this, since the interfacial stress is relieved by viscous flow, the fixed charge Qf can be reduced, that is, the initial amount of charge in the film can be reduced.

Further, the thickness of the gate oxide film 15 for measuring the in-film charge amount may be set to, for example, 20 nm or more. According to this, the distortion of the oxide film is prevented, and thus the pseudo-contamination due to the increase in electric charges due to the distortion is prevented. That is, the amount of charges in the initial film can be reduced.

Further, in the present embodiment, in evaluating the damage, the electrode may not be formed on the gate oxide film 15 in the evaluation semiconductor wafer 10. Therefore, compared with the case where an oxide semiconductor breakdown voltage is evaluated by preparing an evaluation semiconductor wafer having the same structure and TEG (Test Element Group) as the product by forming an electrode on the gate oxide film, It can be shortened.

As described above, according to the evaluation method of this embodiment, it is possible to evaluate the damage when the semiconductor wafer is irradiated with ions in a short period of time.

Further, the present inventor has also confirmed the correlation between the above evaluation and the actual product. FIG. 12 shows the relationship between the in-film charge amount obtained by the measurement in step S16 and the overetch amount in the dry etching performed in step S11 in the semiconductor wafer 10 for evaluation. A square with an overetch amount of 0% shown in FIG. 12 indicates the in-film charge amount of the oxide film 12 after step S10, that is, before the ion irradiation, as the in-film charge amount of the initial oxide film. FIG. 13 shows the relationship between the yield of products obtained through the above manufacturing process and the amount of overetching during product formation. The dry etching conditions were the same for evaluation and product manufacturing. The overetch amount can be replaced with the overetch time.

As shown in FIG. 12, in the semiconductor wafer 10 for evaluation, the in-film charge amount becomes 1E11 [ions/cm ² ] or less when the overetch amount is 15% or less, and the in-film charge amount when the overetch amount is 20% or more. Was 1.4E11 [ions/cm ² ] or more. That is, the in-film charge amount changed significantly between the overetching amount of 15% and 20%. On the other hand, as shown in FIG. 13, in the actual product, the yield greatly changed between the overetch amounts of 15% and 20%. As described above, a large change was observed between the overetching amounts of 15% and 20%. This result confirms that the evaluation method shown in this embodiment is effective as a method for evaluating damage to a semiconductor wafer in an actual product.

(Second embodiment)
This embodiment can refer to the preceding embodiment. Therefore, the description of the portions common to the semiconductor wafer evaluation method shown in the preceding embodiment will be omitted.

In the preceding embodiment, an example is shown in which steps S13 and S14 are performed to remove the damage, the gate oxide film 15 is formed, and then the non-contact CV measurement is performed. On the other hand, in the present embodiment, as shown in FIG. 14, the processes of steps S13 and S14 are not performed, the gate oxide film 15 is formed after the execution of step S12 (step S15), and then the non-contact C- V measurement is performed (step S16).

Then, the in-film charge amount obtained by the non-contact C-V measurement is compared with a preset predetermined value to evaluate damage (step S17A). When the amount of charges in the film is less than or equal to a predetermined value, it is determined that the film quality of the gate oxide film 15 is good, that is, the damage to the semiconductor wafer 10 is within an allowable range (damage is sufficiently reduced), and a series of End the evaluation of.

On the other hand, when the in-film charge amount exceeds a predetermined value, it is determined that the film quality of the gate oxide film 15 is deteriorated, that is, the damage of the semiconductor wafer 10 is not within the allowable range (the damage remains), and the gate is determined. The oxide film 15 is removed with hydrofluoric acid or the like (step S18). Then, the processing from step S15 is repeated again.

As described above, in the present embodiment, with respect to the semiconductor wafer 10 for evaluation, the formation of the gate oxide film 15, the non-contact CV measurement, the damage determination, and the gate oxidation are performed until the damage due to the ion irradiation reaches an allowable level. The removal of the film 15 is repeated. Therefore, it is possible to determine the thickness of sacrificial oxidation at the time of manufacturing a semiconductor wafer as a product, that is, the thickness for removing damage in the semiconductor substrate.

Moreover, since the measurement is performed using a non-contact type C-V measuring device, no electrode is formed on the gate oxide film 15. As a result, even if the thermal oxidation is performed again, there is no influence of metal contamination by the electrodes, and therefore damage due to ion irradiation can be evaluated with high accuracy.

The disclosure of this specification is not limited to the illustrated embodiments. The disclosure encompasses the illustrated embodiments and variations on them based on them. For example, the disclosure is not limited to the combination of elements shown in the embodiments. The disclosure can be implemented in various combinations. The disclosed technical scope is not limited to the description of the embodiments. It is to be understood that some technical scopes disclosed are shown by the description of the claims, and further include meanings equivalent to the description of the claims and all modifications within the scope. ..

The semiconductor wafer evaluation method is not limited to the example shown in the embodiment. As an evaluation method, after irradiating with ions, the gate oxide film 15 was formed by thermal oxidation under a predetermined condition that the initial charge amount in the film was 1E11 [ions/cm ² ] or less, and the non-contact C-V method was used. The characteristics of the gate oxide film 15 may be measured with a measuring instrument, and the damage to the semiconductor wafer 10 may be evaluated based on the measurement result. That is, at least the processes of step S11, step S15, step S16, and steps S17, S17A may be provided.

An example of dry etching is shown as the ion irradiation in step S11, but the ion irradiation is not limited to this. As the ion irradiation, for example, ion implantation for introducing impurities such as P (phosphorus) and boron (B) into the semiconductor substrate 11 can be adopted. In this case, the oxide film 12 formed in step S10 becomes a through film. However, it is preferable to adopt the same ion irradiation method as the product.

Although an example of reactive ion etching is shown as dry etching, the dry etching is not limited to this.

An example of the gate oxide film 15 is shown as an oxide film for measuring the amount of charges in the film, but the oxide film is not limited to this. Any oxide film formed by thermal oxidation may be used.

In the first embodiment, an example is shown in which the gate oxide film 15 is formed after sacrificial oxidation, non-contact CV measurement is performed, and damage is determined from the measurement result. On the other hand, in the second embodiment, the gate oxide film 15 is formed without performing the sacrificial oxidation, and the non-contact CV measurement is performed. When the damage is unacceptable, the gate oxide film 15 is removed. From the above, an example in which the steps after the formation of the gate oxide film 15 are repeated is shown. However, the evaluation method shown in the first embodiment and the evaluation method shown in the second embodiment may be combined.

That is, as shown in the first embodiment (see FIG. 1), after performing the non-contact CV measurement in step S16, the damage evaluation in step S17A shown in the second embodiment (see FIG. 14) is performed. .. When it is determined that the damage remains, the removal of the gate oxide film 15 in step S18 may be performed, and thereafter, the processes of steps S15, S16, and S17A may be performed again.

10... Semiconductor wafer 11... Semiconductor substrate 12... Oxide film 13... Defect 14... Oxide film 15... Gate oxide film 16... Measurement electrode AG... Air gap

Claims (3)

A semiconductor wafer evaluation method for evaluating damage when a semiconductor wafer is irradiated with ions, comprising:
The semiconductor wafer (10) is irradiated with ions from one surface side (S11),
One side of the semiconductor wafer after ion irradiation under the predetermined condition that the characteristic of the oxide film when formed on a bare semiconductor wafer without contamination is 1E11 [ions/cm ² ] or less in the film charge amount. Then, an oxide film (15) is formed by thermal oxidation (S15),
With respect to the semiconductor wafer after thermal oxidation, the characteristics of the oxide film are measured by a non-contact type CV measuring device (S16),
A semiconductor wafer evaluation method for evaluating damage to the semiconductor wafer (S17, S17A) based on a measurement result. As a result of the evaluation, if the damage of the semiconductor wafer is not within the allowable range, the formed oxide film is removed (S18), and then thermal oxidation is performed again using the predetermined condition to remove the oxide film on one surface side of the semiconductor wafer. The method for evaluating a semiconductor wafer according to claim 1, wherein an oxide film is formed, and measurement by the non-contact C-V measuring device and damage evaluation of the semiconductor wafer are performed. The method for evaluating a semiconductor wafer according to claim 1, wherein the thermal oxidation is performed at a temperature of 950° C. or higher.

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