Defect evaluation method for semiconductor

• US 8,625,085 B2
• Filed: 02/29/2012
• Issued: 01/07/2014
• Est. Priority Date: 03/08/2011
• Status: Active Grant

• Current Assignee: Semiconductor Energy Laboratory Co., Ltd.
• Original Assignee: Semiconductor Energy Laboratory Co., Ltd.
• Inventors: Watanabe, Ryosuke, Tsubuku, Masashi, Inoue, Takayuki
• Primary Examiner(s): Toatley, Gregory J
• Assistant Examiner(s): BOLOGNA, DOMINIC JOSEPH
• Application Number:
  US13/407,943
• Publication Number:
  US 20120229805A1
• Time in Patent Office: 678 Days
• Field of Search: 356 72- 73, 356326-330, 356/225, 324/750.23, 324/754.23, 324/93
• US Class Current: 356/73
• CPC Class Codes: H01L 22/12 for structural parameters, e.g. thickness, line width, refractive index, temperature, warp, bond strength, defects, optical inspection, electrical measurement of structural dimensions, metallurgic measurement of diffusions electrical measurement of diffusions H01L22/14
• CPC Class Codes: H01L 22/14 for electrical parameters, e.g. resistance, deep-levels, CV, diffusions by electrical means

Abstract

Even in the case of a sample exhibiting low photoresponse, such as a wide bandgap semiconductor, a measurement method which enables highly accurate CPM measurement is provided. When CPM measurement is performed, photoexcited carriers which are generated by light irradiation of a sample exhibiting low photoresponse such as a wide bandgap semiconductor are instantly removed by application of positive bias voltage to a third electrode which is provided in the sample in addition to two electrodes used for measurement. When the photoexcited carriers are removed, even in the case of the sample exhibiting low photoresponse, the controllability of a photocurrent value is improved and CPM measurement can be performed accurately.

Claims

1. A defect evaluation method comprising the steps of:

applying direct-current voltage between a first electrode and a second electrode of a sample;

repeating a first step;

the first step comprising;

irradiating the sample with light to generate photoexcited carriers in a semiconductor film of the sample, and detecting a value of current flowing between the first electrode and the second electrode; and

blocking the light, and performing treatment to reduce the photoexcited carriers;

changing an amount of the light so that the value of the current is within a certain range of a given value after the first step;

repeating a second step after the changing step;

the second step comprising;

irradiating the sample with the light to generate photoexcited carriers in the semiconductor film of the sample, and detecting a value of current flowing between the first electrode and the second electrode; and

blocking the light, and performing the treatment to reduce the photoexcited carriers; and

recording a wavelength of the light and the amount of the light after the value of the current is within the certain range of the given value,

wherein the sample includes the first electrode and the second electrode over a semiconductor, an insulating film below the semiconductor, and a third electrode below the insulating film.

2. The defect evaluation method according to claim 1, further comprising the steps of:

changing the wavelength of the light after the recording.

3. The defect evaluation method according to claim 1, further comprising the steps of:

changing the amount of the light so that the value of the current is within the certain range of the given value after the second step.

4. The defect evaluation method according to claim 1, wherein positive bias voltage is applied to the third electrode as the treatment to reduce the photoexcited carriers.

5. The defect evaluation method according to claim 4, wherein the positive bias voltage is applied for a time longer than or equal to 1 μ

sec and shorter than or equal to 1 sec.

6. The defect evaluation method according to claims 1, wherein the semiconductor film comprises an oxide semiconductor.

7. The defect evaluation method according to claims 1, wherein the light is emitted from a xenon lamp.

8. The defect evaluation method according to claims 1, wherein the certain range of the given value is a range of ±

10% of the given value.

9. A measurement apparatus comprising:

a first terminal;

a second terminal;

a third terminal;

a lamp;

a spectroscope;

a filter;

a beam splitter configured to transmit and reflect light emitted from the lamp through the spectroscope and the filter;

a photodiode configured to convert the light entered from the beam splitter into current;

a calculator configured to estimate an amount of the light using a value of the current;

a direct-current power source electrically connected to the first terminal, the second terminal, and a resistor; and

a power source electrically connected to the third terminal, wherein the calculator is configured to feed back a photocurrent value flowing through the resistor to the filter.

10. The measurement apparatus according to claim 9, further comprising:

a first lock-in amplifier electrically connected to the photodiode and the calculator; and

a second lock-in amplifier electrically connected to the resistor and the calculator, wherein the first lock-in amplifier is configured to measure the value of the current, and

wherein the second lock-in amplifier is configured to measure the photocurrent value.

11. The measurement apparatus according to claim 9, wherein the power source is configured to apply positive bias voltage.

12. The measurement apparatus according to claim 11, wherein the power source is configured to apply the positive bias voltage for a time longer than or equal to 1 μ

sec and shorter than or equal to 1 sec.

13. The measurement apparatus according to claims 9, wherein the lamp is a xenon lamp.