JPH09167789A - Evaluation method for semiconductor device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To realize a highly reliable method for evaluating a semiconductor substrate. SOLUTION: A wafer 110 to be evaluated is mounted on a stage 101 and the position and angle of wafer 110 are adjusted at a control processing section 108. The wafer 110 on the stage 101 is then irradiated sequentially or simultaneously with X-rays, argon laser light and YAG laser light from a light source section 102 and the reflected light or fluorescence is detected by means of a condenser 104 or a light receiving unit 105 in order to perform fluorescent X-ray analysis, locking curve measurement, PL inspection and detect inspection of the wafer 110. Respective characteristics measured through the inspection process are compared with the final pass/fail decision results for a semiconductor laser made of a wafer 110 passed through the inspection process and the evaluation criterion of wafer 10 is determined or corrected.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor substrate evaluation apparatus and evaluation method, and more particularly, to a film thickness, composition, emission characteristics, crystal defects, etc. of a thin film formed on a semiconductor substrate. The present invention relates to an apparatus and method for destructive evaluation.

[0002]

2. Description of the Related Art An example of a conventional method for evaluating a semiconductor substrate will be described by taking the case of evaluating a thin film epitaxially grown on a semiconductor substrate as an example.

With the improvement in performance of devices, for example, in a heterojunction compound semiconductor epitaxial wafer, it is common to stack dozens of ultrathin films having a thickness of several nm to several tens nm by epitaxial growth. In such a thin film, the thickness of each layer, composition, concentration of doping,
It is difficult to maintain the steepness of the interface and the like with good reproducibility, and the characteristics of the thin film vary from growth batch to growth batch.
For this reason, in the semiconductor manufacturing technology, a thin film evaluation step is provided after forming a thin film on a semiconductor substrate to select whether the semiconductor substrate is good or defective and to correct the parameters of the thin film forming apparatus (MBE apparatus or MOCVD apparatus, etc.). There is a need.

FIG. 9 is a flow chart schematically showing the procedure of a conventional evaluation method.

As shown in FIG. 9, in the conventional evaluation method, first, a thin film is epitaxially grown on all the semiconductor wafers in the same batch (S901), and subsequently, the semiconductor wafers for evaluation are selected from these semiconductor wafers. The semiconductor wafers of are selected (S902). Then, the following evaluation tests are sequentially performed on the selected semiconductor wafers.

Then, this semiconductor wafer is set in a film quality evaluation device, and the film quality of the epitaxial growth layer is inspected (S903). With this film quality, after the semiconductor wafer is set on the wafer stage of the oblique light device, the number of particles on the entire surface of the semiconductor wafer is counted using a surface foreign matter inspection device called a particle counter and an optical microscope.

Next, this semiconductor wafer is transported and set on the wafer stage of the X-ray diffraction apparatus, and the rocking curve of the epitaxial growth layer is measured at an arbitrary set position (S904). In this measurement, the epitaxial growth layer is irradiated with X-rays from an X-ray source, and the light intensity of the diffracted light is measured with a scintillation counter. As a result, the composition, film thickness, etc. of the epitaxial growth layer can be specified.

Then, the semiconductor wafer is transferred to a PL
(Photo Luminescence) Set on the wafer stage of the evaluation device, and measure the photoluminescence emission intensity at an arbitrary set position (S905). By measuring the emission intensity, the emission wavelength of the semiconductor laser manufactured using this semiconductor wafer can be specified.

Thereafter, each of these characteristics (S903 to S9)
Based on the result of (05), the quality of the thin film of the semiconductor wafer of the batch is judged (S906). According to the study by the present inventors, it is desirable that this quality evaluation is determined by associating these characteristics with each other, rather than by separately examining the results of the above-described characteristics. For example, even if the characteristic (that is, the number of particles) measured by the oblique light device is “poor”, if the characteristic measured by the X-ray diffractometer or the PL evaluation device is very good, the quality evaluation is “good”. In some cases. If any one of the inspection items is "defective", if the quality evaluation is always judged as "defective", the yield will be reduced more than necessary and it will cause an increase in manufacturing cost. Is. Here, the mutual relevance of each characteristic differs depending on the type, degree of integration, application, etc. of a semiconductor device manufactured using the semiconductor wafer, and the measurement result of each characteristic described above is used as the final pass / fail of the semiconductor device. It is determined empirically by comparing with the judgment result of.

Only when the quality evaluation is cleared, another semiconductor wafer of the batch is put into the next manufacturing process.

[0011]

As described above, in the film quality evaluation of the semiconductor wafer, it is general to perform the evaluation based on the measurement results of a plurality of types of characteristics. When a plurality of types of measurements are performed in this way, conventionally, different evaluation devices have been used for each measurement item, so that it was necessary to transfer the semiconductor wafer for each measurement and set it on the wafer stage. For example, in the case of the evaluation method shown in FIG. 9, it is necessary to transfer the semiconductor wafer in the order of the oblique light device → X-ray diffraction device → PL evaluation device. Therefore, in the conventional evaluation method, in order to inspect a plurality of items on the same portion of the surface of the semiconductor wafer, it is necessary to mark the evaluation portion of the semiconductor wafer with a felt-tip pen or the like.

However, since the marking with the felt-tip pen or the like contaminates the semiconductor wafer (that is, it is not a nondestructive inspection), the marked semiconductor wafer cannot be put into the subsequent manufacturing process. That is, in the conventional method, only the semiconductor wafer that has not undergone the above-described evaluation process is put into the subsequent manufacturing process. Therefore, even if a defective semiconductor device is produced in the subsequent manufacturing process, no measurement result remains for the characteristics of the semiconductor wafer used for manufacturing the defective product.

On the other hand, when marking is not performed,
Problems such as lack of reproducibility in the accuracy of the evaluation position occur.

Therefore, in the conventional evaluation method, the measurement result of the same batch of semiconductor wafers as the semiconductor device judged to be defective is regarded as the characteristic of the semiconductor wafer used for manufacturing this defective product, and It was used to analyze the interrelationship of characteristics. For this reason, it was not possible to strictly analyze the mutual relation of each characteristic, and the reliability of the evaluation of the film quality of the semiconductor wafer was low.

When the reliability of the evaluation of the film quality of the semiconductor wafer is low as described above, not only the semiconductor wafer that can be put into the manufacturing process is sometimes judged to be "defective", but also originally. Since the semiconductor wafers that should be regarded as “defective” are put into the manufacturing process, the yield in the final evaluation of the semiconductor device also lowers. Therefore, when the reliability of the film quality evaluation is low, the manufacturing cost of the semiconductor device becomes very high.

If the semiconductor wafer is transferred and set on the wafer stage for each measurement as in the evaluation method shown in FIG. 9, it takes a long time to transfer the semiconductor wafer and set the evaluation position. Therefore, there is also a drawback that the time required for the evaluation process becomes long.

The present invention has been made in view of the above drawbacks of the prior art, and an object of the present invention is to provide a highly reliable method for evaluating a semiconductor substrate.

[0018]

A method of evaluating a semiconductor substrate according to the present invention is a semiconductor substrate evaluation method, in which a semiconductor substrate for evaluation is mounted on a mounting table, and then the position of the semiconductor substrate mounted on the mounting table and Substrate holding process to adjust the angle in the adjusting unit, a plurality of types of evaluation light used for a plurality of types of evaluation is sequentially or simultaneously irradiated to the semiconductor substrate on the mounting table through the same optical path from a plurality of types of light sources, By detecting reflected light or fluorescence at this time with a plurality of types of photodetectors, respectively, an inspection process for measuring a plurality of types of characteristics of the semiconductor substrate, and the plurality of types of characteristics measured in this inspection process, An evaluation standard for determining or changing the evaluation standard of the semiconductor substrate by comparing with the final judgment result of good / defective for the semiconductor device manufactured from the semiconductor substrate that has undergone this inspection process. Characterized by comprising a constant process, the.

[0019]

BEST MODE FOR CARRYING OUT THE INVENTION An embodiment of the present invention will be described below by taking as an example the case of evaluating a semiconductor wafer used for manufacturing a high frequency transistor.

FIG. 1 is a conceptual diagram showing the configuration of the evaluation device used in this embodiment.

In the figure, the wafer stage 101 is
The semiconductor wafer 110 is held. This wafer stage 1
01 can be moved in the X direction, Y direction and Z direction, and can be driven by θ rotation and φ rotation. Where X direction, Y
The movement in the Z and Z directions can be controlled in steps of 1 μm. Further, θ rotation can be controlled at a pitch of 0.0001 degrees, and φ rotation can be controlled at a pitch of 0.001 degrees.

The light source unit 102 is made of copper or molybdenum X.
It is equipped with a radiation source (either a sealed tube or a rotating anticathode), an argon laser (emission wavelength 488 nm) and a yag laser (emission wavelength 1.06 μm) (none shown). Further, the light source unit 102 is provided with a mirror and a dispersive crystal (both not shown) for guiding the evaluation light (that is, the X-ray and the laser light) emitted from each of these light sources on the same optical axis. There is. In addition, the light source unit 10
Each light source of No. 2 can be driven on the circumference with the wafer stage 101 as the center of rotation under the control of the control calculation unit 108 in steps of an angular error of 0.0001 degrees.

The scintillation counter 103 is used to receive the X-rays emitted from the X-ray source of the light source section 102 and reflected on the surface of the semiconductor wafer 110 to measure the light intensity. Like the light source of the light source unit 102, the scintillation counter 103 is controlled by the control calculation unit 108 so that the circumference around the wafer stage 101 is the center of rotation.
It can be driven in steps with an angular error of 0.0001 degrees.

The condenser 104 is arranged right above the wafer stage 101. The condenser 104 condenses the photoluminescence emitted when the semiconductor laser 110 on the wafer stage 101 is irradiated with the argon laser light of the light source section 102, and also the yag laser light of the light source section 102. It is used to collect scattered light when illuminating.

The light receiver 105, like the light collector 104, is arranged directly above the wafer stage 101. The light receiver 105 is held by a drive system (not shown) so that the light receiver 105 can be moved to the center of the semiconductor wafer 110 on the wafer stage 101 by exchanging positions with the light collector 104. An SSD (Solid State Detector), which is a fluorescent X-ray detector, is used as the light receiver 105, and receives the fluorescent X-ray generated when the semiconductor wafer 110 on the wafer stage 101 is irradiated with the X-ray. .

The spectroscope 106 is connected to the output terminal of the condenser 104 by an optical fiber. Then, using the optical signal input from the condenser 104, the wavelength distribution of the condensing intensity is measured. The measured wavelength distribution is measured by the spectrometer 10.
The signal is output from a signal output terminal 6 (not shown).

The wafer transfer system 107 transfers the semiconductor wafer 110 stored in a cassette (not shown) to the wafer stage 101 for setting.

The control / calculation unit 108 includes the wafer stage 10
1, light source unit 102, scintillation counter 103,
Position control and drive control of the condenser 104 and the light receiver 105 are performed to measure the characteristics of the semiconductor wafer 110 (described later), and drive control of the wafer transfer system 107 is performed. Further, measurement data is generated based on the signals input from the light receiver 105 and the spectroscope 106.

Next, the procedure of the evaluation method according to this embodiment will be described. FIG. 2 is a flowchart schematically showing such a procedure.

First, a thin film is epitaxially grown on all semiconductor wafers 110 of the same batch (S).
201). FIG. 3 shows a cross-sectional view of the thin film structure of the semiconductor wafer 110 used in this embodiment. As described above, this semiconductor wafer 110 is used for manufacturing a high frequency transistor. As shown in the figure, in the present embodiment,
As the semiconductor wafer 110, a semi-insulating GaAs substrate 301 having a thickness of 600 μm is used. And this GaAs
On the surface of the substrate 301, non-doped G having a film thickness of 500 nm
aAs layer 302 and 10-nm-thick non-doped InGa
As layer 303 (In composition ratio is about 0.15) and film thickness 4
AlGaA with an impurity concentration of 3 × 10 ¹⁸ particles / cm ³ at 0 nm
s layer 304 (Al composition ratio is about 0.2) and film thickness 50n
GaAs layer 30 having an impurity concentration of 5 × 10 ¹⁸ / m ³ in m
5 are sequentially stacked.

In the evaluation method according to the present embodiment, the following evaluation is performed on all of the semiconductor wafers 110 on which the thin film is formed, and in this respect, it differs from the conventional evaluation method described above. This is because the evaluation method according to the present embodiment realizes nondestructive inspection.

Next, the semiconductor wafer 11 to be evaluated first
0 is set on the wafer stage 101, and orientation flat alignment is performed (S202). This setting can be automatically performed by using a robot (not shown) of the wafer transfer system 107.

Subsequently, the parallelism of the semiconductor wafer 110 set on the wafer stage 101 is adjusted (S20).
3). In this alignment, the semiconductor wafer 110 is irradiated with X-rays in parallel from the X-ray source of the light source unit 102, and the intensity of the reflected X-rays at this time is monitored by the scintillation counter 103 while adjusting the Z-axis and the θ-axis. . By this adjustment, it is possible to obtain parallelism with an error within 0.001 degree.

Then, as a first inspection of the thin film formed on the semiconductor wafer 110, fluorescent X-ray analysis is performed (S2).
04). As described above, in this fluorescent X-ray analysis, the thin film surface of the semiconductor wafer 110 is irradiated with X-rays from the X-ray source of the light source unit 102, and the fluorescent X-rays generated in the thin film at this time are received by the light receiver 105. This makes it possible to know the pollutants in the thin film. FIG. 4 is a graph showing the characteristics thus obtained. In the figure, the vertical axis represents the relative intensity [cps] of fluorescent X-rays, and the horizontal axis represents energy [ke].
V] is shown. As can be seen from the figure, the semiconductor wafer 110 used in this embodiment contains P, Fe, and Zn as contaminants.

Next, as a second inspection of the thin film, the rocking curve is measured (S205). In this measurement, the X-ray is irradiated from the X-ray source onto the thin film surface of the semiconductor wafer 110 while moving the X-ray source of the light source unit 102 and the scintillation counter 103 at an angle satisfying Bragg's law. Then, the intensity of the diffracted X-ray at this time is measured by the scintillation counter 103. Due to this rocking curve, the InGaAs layer 303 (see FIG. 3)
The composition ratio of In can be known.

FIG. 5 is a graph showing the characteristics thus obtained. In the figure, the vertical axis represents the relative intensity [cps] of the fluorescent X-rays, and the horizontal axis represents the angle [seconds].

In the present embodiment, the PL measurement as the third inspection of the thin film is performed simultaneously with the measurement of the rocking curve (the above process) (S205). In this measurement, the semiconductor laser 110 is irradiated with laser light from the argon laser of the light source unit 102, and the light by photoluminescence at this time is condensed by the condenser 104. The condensed light is sent to the spectroscope 106 by the optical fiber as described above, and is dispersed, and is converted by the photomultiplier tube in the spectroscope 106,
It is sent to the control calculation unit 108. Then, the control calculation unit 10
8, the wavelength distribution of the condensed light intensity is calculated. This PL
From the measurement result, the emission wavelength when a semiconductor laser is manufactured from the semiconductor wafer 110 can be known.

FIG. 6 is a graph showing the characteristics thus obtained. In the figure, the vertical axis represents the relative intensity of the photoluminescence light, and the horizontal axis represents the wavelength [nm] of the photoluminescence light. As a result, InG
It can be seen that the light emission from the quantum well made of aAs is around 965 nm.

Then, as the fourth inspection of the thin film, the scattered light is observed (S206). In this observation, the semiconductor wafer 110 is irradiated with laser light whose beam diameter is narrowed to, for example, 1 μm from the yag laser of the light source unit 102. Then, the scattered light at this time is condensed by the condenser 104. At this time, the irradiation angle of the laser light may be the same as in the case of PL measurement (the above process), but may be another angle. Also,
It is also possible to take a mapping image of scattered light by scanning the wafer stage 101 on the XY plane.

By narrowing the laser light to about 1 μm, the laser light enters the thin film to reach the defect portion and the scattering intensity increases. Further, by performing mapping, it becomes possible to measure the distribution of defects in the thin film.

FIG. 7 is a conceptual diagram showing the defect distribution thus obtained. In the figure, (a) shows the case where the incident angle of the laser beam is 15.1 degrees, and (b) shows the case where the incident angle is 0.2 degrees.

In this embodiment, the angle of the semiconductor wafer is X.
Since it is set with a line (the above-mentioned step), the reproducibility of the irradiation angle of the laser beam can be improved, and thus the low-angle incidence becomes easy. Further, since the accuracy of the angle dependence becomes strict, it becomes possible to know the distribution of defects in the depth direction of the thin film, and therefore only the defects in the thin film can be measured. Since the GaAs substrate 301 (see FIG. 3) contains about 10 ⁴ crystal defects / cm ² , it is very important to separate and evaluate the defects in the substrate and the defects in the thin film. Is.

Thereafter, each of these characteristics (S204-S
Based on the result of (206), the quality of the thin film quality of the semiconductor wafer 110 of the batch is evaluated (S207).
In this quality evaluation, the results of the above-mentioned respective characteristics are not separately examined and judged, but the characteristics are mutually correlated and judged. For example, if the evaluation by some tests is "poor", but the other test results are very good,
In some cases, the final quality evaluation may be “good”.

If necessary, the parameters of the epitaxial growth apparatus are changed according to the result of each characteristic.

After that, only the semiconductor wafer 110 which has passed such quality evaluation is put into the next manufacturing process (S208). Then, when a semiconductor device (here, a high frequency transistor) using the semiconductor wafer 110 is completed, the quality of the semiconductor device is evaluated and a final pass / fail is determined (S208).

Finally, the quality evaluation result of the completed device is compared with the evaluation result of each characteristic of the semiconductor wafer 110, and the evaluation standard of the semiconductor wafer 110 is changed as necessary (S209). Further, if necessary, the parameters of the epitaxial growth apparatus are also changed in accordance with the change of this evaluation standard. As described above, regarding the relationship between each characteristic and the evaluation standard of acceptability, the measurement result of each characteristic described above is used for the semiconductor wafer 10
It is determined empirically by comparing with the final judgment result of good / bad of the semiconductor device manufactured from 1.

FIG. 8 shows an example of the yield transition of the final semiconductor device (here, a high frequency transistor) when the semiconductor wafer 110 is evaluated using this embodiment. In the figure, the vertical axis is the yield (%), and the horizontal axis is the lot number. White circles indicate the case where the evaluation method of this embodiment is used, and black circles indicate the case where the conventional evaluation method (see FIG. 9) is used.

As shown in the figure, according to this embodiment, the yield of the semiconductor device can be reduced by 30% on average, and further, the variation in the yield between lots can be suppressed. This is because the present embodiment realizes nondestructive inspection. That is, according to this embodiment, when a defective semiconductor device is generated in the subsequent manufacturing process, the mutual relation of each characteristic is based on the measurement result of the semiconductor wafer itself used for manufacturing the defective product. Can be analyzed and it is not necessary to substitute the measurement results of other semiconductor wafers 110 in the same batch. For this reason, since it is possible to rigorously analyze the mutual relevance of each characteristic, it is possible to increase the accuracy of the evaluation standard for the film quality of the semiconductor substrate, thereby improving the reliability of the evaluation. It is possible.

Furthermore, according to this embodiment, the semiconductor substrate can be transferred and the evaluation position can be set only once, so that the time required for the evaluation process can be shortened.

[0050]

As described in detail above, according to the present invention, it is possible to provide a highly reliable method for evaluating a semiconductor substrate, which improves the yield of semiconductor devices and shortens the evaluation time. Therefore, it is effective in reducing the manufacturing cost of the semiconductor device.

[Brief description of the drawings]

FIG. 1 is a conceptual diagram showing a configuration of an evaluation device used in an embodiment of the present invention.

FIG. 2 is a flowchart showing a procedure of an evaluation method according to an embodiment of the present invention.

FIG. 3 is a cross-sectional view showing a thin film structure of a semiconductor substrate used in an embodiment of the present invention.

FIG. 4 is a graph showing a fluorescent X-ray analysis result obtained by an evaluation method according to an embodiment of the present invention.

FIG. 5 is a graph showing a rocking curve obtained by the evaluation method according to the embodiment of the present invention.

FIG. 6 is a graph showing measurement results of photoluminescence obtained by an evaluation method according to an embodiment of the present invention.

FIG. 7 is a diagram conceptually showing a defect distribution obtained by an evaluation method according to an embodiment of the present invention, in which (a) is a case where an incident angle of laser light is 15.1 degrees, and (b) is a figure. This is the case where this incident angle is 0.2 degrees.

FIG. 8 is a graph showing an example of the transition of the final yield of semiconductor devices when the evaluation method according to the embodiment of the present invention is performed.

FIG. 9 is a flowchart schematically showing the procedure of a conventional evaluation method.

[Explanation of symbols]

 Reference Signs List 101 wafer stage 102 light source section 103 scintillation counter 104 condenser 105 photodetector 106 spectroscope 107 wafer transfer system 108 control calculation section 110 semiconductor wafer

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI Technical display location G01N 21/64 G01N 21/64 Z 21/88 21/88 E 23/20 23/20 23/223 23/223

Claims (4)

[Claims] 1. A substrate holding process of mounting a semiconductor substrate for evaluation on a mounting table, and then adjusting a position and an angle of the semiconductor substrate mounted on the mounting table by an adjusting section, and a plurality of types of substrate holding steps. Irradiate multiple types of evaluation light used for evaluation from the multiple types of light sources to the semiconductor substrate on the mounting table sequentially or simultaneously, and detect reflected light or fluorescence at this time with multiple types of photodetectors, respectively. The inspection process for measuring a plurality of types of characteristics of the semiconductor substrate, and the final characteristics of the plurality of types of characteristics measured in the inspection process for a semiconductor device manufactured from the semiconductor substrate that has undergone the inspection process. A method of evaluating a semiconductor substrate, comprising: an evaluation criterion determining step of determining or modifying the evaluation criterion of the semiconductor substrate by comparing with a determination result of failure. 2. The light source used in the inspection process,
The semiconductor substrate evaluation method according to claim 1, further comprising at least one of an X-ray source, an argon laser, and a yag laser. 3. The photodetector used in the inspection process is at least one of a scintillation counter for detecting diffracted X-rays, a detector for fluorescent X-rays, or a condenser for laser light and a photomultiplier tube. The method for evaluating a semiconductor substrate according to claim 1, further comprising: 4. The method for evaluating a semiconductor device according to claim 1, wherein the measurement of the plurality of types of characteristics includes any of fluorescent X-ray analysis, rocking curve measurement, photoluminescence measurement, and scattered light observation. .