阅读说明：本技术 非接触式晶片厚度测定装置 (Non-contact type wafer thickness measuring device ) 是由 宫川千宏 澁谷和孝 青木清仁 于 2020-04-09 设计创作，主要内容包括：具有：单片型波长扫描半导体激光光源(12),其具有激光源(14)、控制激光源(14)的激光控制单元(16)以及处理器(18),该处理器(18)构成为利用激光控制单元(16)来控制激光源(14),以振荡出相对于时间按照设定图谱变化的波长的激光；光学系统(20、22),其将激光引导并照射到晶片(24)；检测部(26),其检测反射光的干涉光信号；A/D转换器(28),其将由检测部(26)检测出的干涉光信号转换成数字信号；以及运算部(30),其通过分析来自所述A/D转换器(28)的数字信号来计算晶片(24)的厚度,其特征在于,处理器(18)使激光控制单元(16)根据时钟信号进行动作,从激光源(14)振荡出相对于时间按照设定图谱进行波长扫描的激光,A/D转换器(28)与所述时钟信号同步地生成采样时钟或将时钟信号直接用作采样时钟,对干涉光信号进行A/D转换。(Comprising: a monolithic wavelength-scanning semiconductor laser light source (12) having a laser light source (14), a laser control unit (16) for controlling the laser light source (14), and a processor (18), wherein the processor (18) is configured to control the laser light source (14) by the laser control unit (16) so as to oscillate laser light of a wavelength that varies with respect to time according to a set pattern; an optical system (20, 22) that guides and irradiates the laser light to the wafer (24); a detection unit (26) that detects an interference light signal of the reflected light; an A/D converter (28) for converting the interference light signal detected by the detection unit (26) into a digital signal; and a calculation unit (30) that calculates the thickness of the wafer (24) by analyzing the digital signal from the A/D converter (28), wherein the processor (18) causes the laser control unit (16) to operate on the basis of a clock signal, and oscillates laser light that is wavelength-scanned from the laser light source (14) with respect to time according to a set pattern, and the A/D converter (28) generates a sampling clock in synchronization with the clock signal or performs A/D conversion on the interference light signal by directly using the clock signal as the sampling clock.)

1. A non-contact type wafer thickness measuring device comprises:

a monolithic wavelength-scanning semiconductor laser light source including a laser light source, a laser control unit for controlling the laser light source, and a processor configured to control the laser light source by the laser control unit so as to oscillate laser light having a wavelength that varies according to a set pattern with respect to time;

an optical system for guiding and irradiating the laser beam to a measurement portion of a wafer whose thickness is to be determined;

a detection unit that detects an interference light signal of the reflected light or the transmitted light obtained from the measurement portion;

an a/D converter that converts the interference light signal detected by the detection unit into a digital signal; and

a calculation unit for calculating the thickness of the wafer by analyzing the digital signal from the A/D converter,

it is characterized in that the preparation method is characterized in that,

the processor causes the laser control unit to operate according to the clock signal generated by the processor, and oscillates laser light from the laser light source, the laser light being wavelength-scanned with respect to time according to a set pattern,

the A/D converter generates a sampling clock in synchronization with the clock signal generated by the processor or performs A/D conversion on the interference light signal using the clock signal directly as the sampling clock.

2. The non-contact wafer thickness measuring device according to claim 1,

the single-chip wavelength-scanning semiconductor laser light source does not have a mechanical operating section.

3. The non-contact wafer thickness measuring device according to claim 1 or 2,

the wavelength scanning frequency is 1 kHz-40 kHz.

4. The non-contact wafer thickness measuring device according to any one of claims 1 to 3,

the wavelength range of scanning is 1200 nm-1400 nm.

5. The non-contact wafer thickness measuring device according to any one of claims 1 to 4,

the frequency of the clock signal is 10 MHz-1 GHz.

6. The non-contact wafer thickness measuring device according to any one of claims 1 to 5,

the thickness of the wafer is measured by continuously detecting the interference light signal while moving the wafer or the probe at a constant speed.

7. The non-contact wafer thickness measuring device according to any one of claims 1 to 6,

the noncontact wafer thickness measuring device is a wafer thickness measuring device for polishing a wafer by a double-side polishing machine or a single-side polishing machine.

8. The non-contact wafer thickness measuring device according to any one of claims 1 to 7,

the monolithic wavelength-scanning semiconductor laser light source is equivalent to SLE-101 manufactured by the american optical solutions company.

9. The non-contact wafer thickness measuring device according to any one of claims 1 to 8,

the noncontact wafer thickness measuring apparatus has a light source monitoring circuit using a reference wafer.

10. The non-contact wafer thickness measuring device according to any one of claims 1 to 8,

the noncontact wafer thickness measuring apparatus has a light source monitoring circuit using an MZI interferometer.

11. The non-contact wafer thickness measuring device according to claim 9 or 10,

the light source monitoring circuit monitors the amount of laser light emitted from the laser light source based on an average value of the voltage output from the detection unit.

12. The non-contact wafer thickness measuring device according to claim 9 or 10,

the light source monitoring circuit monitors the scanning wavelength accuracy, and the scanning wavelength accuracy can be grasped by measuring the average value, the P-P value, or the deviation value of the set number of times with respect to the frequency of the FFT peak of the interference waveform acquired by the detection unit.

Technical Field

The present invention relates to a noncontact wafer thickness measuring apparatus using a single-chip (Monolithic) wavelength scanning semiconductor laser light source.

Background

In a polishing apparatus for a semiconductor wafer such as silicon, double-side polishing or single-side polishing of the wafer is performed to process the wafer to a desired thickness.

Semiconductor wafers are used for semiconductor mechanism elements with higher integration, but in order to make the integration higher and to improve productivity, thickness measurement with higher accuracy is required in the process or in the middle thereof.

Patent document 1 (japanese patent application laid-open No. 7-306018) discloses a semiconductor thickness non-contact measuring apparatus using a wavelength-variable laser.

In the semiconductor thickness non-contact measuring device disclosed in patent document 1, when a light beam transmitted through a semiconductor is irradiated to a target region of a semiconductor of a measurement object, part of the light reflected by a front surface and a bottom surface and interfered with each other is reflected or transmitted. The reflected or transmitted interference light is guided to a detector by an optical unit, and the wavelength of the light beam is changed within a predetermined range. In this case, since the phase (or cycle) of the intensity of the interference light changes depending on the semiconductor thickness, the phase is calculated from the intensity change of the interference light and converted into the absolute value of the semiconductor thickness.

As the wavelength-variable laser, for example, a wavelength-scanning laser light source disclosed in patent document 2 (japanese patent application laid-open No. 2006-80384) is used. Alternatively, a wavelength-scanning laser light source as shown in fig. 6 may be used.

Documents of the prior art

Patent document

Patent document 1: japanese laid-open patent publication No. 7-306018

Patent document 2: japanese patent laid-open No. 2006-80384

Disclosure of Invention

Problems to be solved by the invention

However, in the wavelength-scanning laser light source disclosed in patent document 2, a mechanical operating unit such as a polygon mirror is used to obtain a scanning wavelength. When a mechanical operation portion such as a polygon mirror is used, there is a problem that even a slight deformation of the mirror surface of the reflecting mirror causes a slight deviation in the reflected light, and the wavelength of the scanning light is deviated. Further, the presence of the mechanical operating portion causes variation in the wavelength of scanning even if minute mechanical vibration is generated. Therefore, even if an interference signal of light is acquired to measure the thickness of the same portion, a digital signal is converted, and signal processing is performed by fast fourier transform, the center frequency thereof is shifted, and thus an accidental error occurs in the thickness.

Means for solving the problems

The present invention has been made to solve the above-described problems, and an object thereof is to provide a noncontact wafer thickness measuring apparatus capable of measuring the thickness of a wafer with high accuracy by using a laser beam whose linear scanning wavelength is repeatedly oscillated with high accuracy.

In order to achieve the above object, the present invention has the following configuration.

That is, the noncontact wafer thickness measuring apparatus of the present invention includes: a monolithic wavelength-scanning semiconductor laser light source including a laser light source, a laser control unit for controlling the laser light source, and a processor configured to control the laser light source by the laser control unit so as to oscillate laser light having a wavelength that varies according to a set pattern with respect to time; an optical system for guiding and irradiating the laser beam to a measurement portion of a wafer whose thickness is to be determined; a detection unit that detects an interference light signal of the reflected light or the transmitted light obtained from the measurement portion; an a/D converter that converts the interference light signal detected by the detection unit into a digital signal; and a calculation unit that calculates a thickness of the wafer by analyzing the digital signal from the a/D converter, wherein the processor causes the laser control unit to operate based on a clock signal generated by the processor, and oscillates the laser light from the laser light source that is wavelength-scanned with respect to time according to a set pattern, and the a/D converter generates a sampling clock in synchronization with the clock signal generated by the processor or performs a/D conversion on the interference light signal using the clock signal as it is as the sampling clock.

The noncontact wafer thickness measuring device is characterized in that the single-wafer wavelength scanning semiconductor laser light source does not have a mechanical operating part.

The wavelength scanning frequency can be set to 1kHz to 40 kHz.

The wavelength range of the scanning can be set to 1200nm to 1400 nm.

The frequency of the clock signal can be set to 10MHz to 1 GHz.

The thickness of the wafer can be measured by continuously detecting the interference light signal while moving the wafer or the probe at a constant speed.

The noncontact wafer thickness measuring device can be used as a wafer thickness measuring device when a wafer is polished by a double-side polishing machine or a single-side polishing machine.

As the semiconductor monolithic wavelength scanning laser light source, a light source equivalent to SLE-101 manufactured by American light photonic solutions can be used.

A light source monitoring circuit using a reference wafer can be provided.

Alternatively, a light source monitoring circuit using an MZI interferometer can be provided.

The light source monitoring circuit may monitor the amount of laser light emitted from the laser light source based on an average value of the voltage output from the detection unit.

Alternatively, the light source monitoring circuit may monitor the scanning wavelength accuracy, and the scanning wavelength accuracy may be grasped by measuring an average value, a P-P value, or a deviation value of a set number of times with respect to the frequency of the FFT peak of the interference waveform acquired by the detection unit.

Effects of the invention

According to the present invention, the following advantageous operational effects are achieved.

That is, according to the present invention, a single-chip wavelength scanning semiconductor laser light source is used as a light source, scanning wavelength is repeated at high precision, a clock signal is generated by a processor, an interference signal is obtained by laser light whose wavelength is continuously and linearly scanned based on the clock signal, a sampling clock is generated in synchronization with the clock signal or is directly used as the sampling clock, and a/D conversion is performed on the interference light signal, whereby the interference action of the scanning wavelength on the laser light and the analysis of the interference light signal by fast fourier transform are performed in synchronization, whereby a favorable thickness measurement with less accidental errors of the wafer can be performed.

Drawings

Fig. 1 is a block diagram showing an overall system of a noncontact wafer thickness measuring apparatus according to the present embodiment.

Fig. 2A to 2D show examples of overlapping interference waveforms when the same portion of the wafer is measured 10 times.

Fig. 3A and 3B are graphs (fig. 3A) obtained by superimposing and plotting results obtained by repeating the measurement of the thickness of the wafer 3 times in the radial direction.

Fig. 4 is a block diagram showing an overall system of a noncontact wafer thickness measuring apparatus provided with a light source monitoring circuit using a reference wafer.

Fig. 5 is a block diagram showing an overall system of a noncontact wafer thickness measuring apparatus provided with a light source monitoring circuit using an MZI interferometer.

Fig. 6 is a block diagram of a conventional system having a mechanical operation.

Detailed Description

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.

Fig. 1 is a block diagram showing the entire system of a noncontact wafer thickness measuring apparatus 10 according to the present embodiment.

The system 10 has a single-chip wavelength-scanning semiconductor laser light source (hereinafter sometimes simply referred to as a laser light source) 12.

The monolithic wavelength-scanning semiconductor laser light source 12 includes a semiconductor laser (laser light source) 14 with a wavelength scanning function, a laser control unit 16 that controls the laser light source 14, and a processor 18 that controls the entire system 10.

The laser light source 12 does not have a mechanical operation portion such as a polygon mirror, and is configured as a so-called single-chip wavelength-scanning semiconductor laser light source configured to cause the laser control unit 16 to control the laser light source 14 via the processor 18 so as to oscillate laser light of a wavelength that varies with time according to a set pattern. As such a monolithic wavelength-scanning semiconductor laser light source 12, an SLE-101 light source manufactured by the american optical solutions company can be used.

Specifically, the current value supplied to the semiconductor laser (laser light source) 14 whose wavelength can be changed is changed (tuned), and the wavelength of the laser light oscillated from the laser light source 14 is controlled so as to be changed to a predetermined setting map (preferably, linear). This series of control is shown in, for example, Japanese patent application laid-open No. 2014-522105.

More specifically, the feedback control is performed in the following manner: the current supplied to the laser light source 14 is applied while the supplied current is tuned, and the oscillated laser light is detected by a detector not shown and fed back to the processor 18, whereby the current value supplied to the laser light source 14 is readjusted so that the wavelength of the laser light continuously changes, for example, linearly. This series of feedback control is shown in, for example, japanese patent laying-open No. 2014-522105.

The processor 18 generates a clock signal of, for example, 400MHz (2.5nsec interval), and causes the laser control unit 16 to operate based on the clock signal generated by the processor 18 to tune the current value, thereby oscillating the laser beam of a wavelength that varies with time according to the set pattern from the laser source 14.

As described above, the laser light source 14 emits laser light whose wavelength is continuous and changes in a desired pattern (preferably linearly).

The laser light emitted from the laser light source 14 is irradiated from the circulator 20 and the probe 22 to the measurement site of the wafer 24. The circulator 20 and the probe 22 constitute an optical system.

The laser light (interference light) reflected by the front and back surfaces of the wafer 24 is detected by a photodiode (detection unit) 26 via the probe 22 and the circulator 20, converted into an electrical signal (interference light signal) by the photodiode 26, and amplified by an amplifier.

The laser light reflected by the front surface and the laser light reflected by the back surface of the wafer 24 interfere with each other, and are observed as interference light having a desired phase.

Fig. 2A shows an interference waveform obtained by measuring 10 times and superimposing the same portion of the wafer 24. Fig. 2B is an enlarged waveform of a portion in fig. 2A, fig. 2C is an enlarged waveform of a portion B in fig. 2A, and fig. 2D is an enlarged waveform of a portion C in fig. 2A.

As can be seen from fig. 2, interference waveforms obtained by measuring 10 times at the same point of the wafer 24 and superimposing the measurements substantially match each other from the first to the last. In this way, it is considered that the interference waveforms are substantially uniform because the emission wavelength of the laser light can be stably changed continuously and linearly by using the single-chip wavelength scanning semiconductor laser light source as the light source.

The interference light signal is converted into a digital signal by the a/D converter 28, and is input to the computer (arithmetic unit) 30.

The a/D converter 28 receives the external trigger signal generated by the processor 18 and the clock signal (clock signal for operating the laser control unit 16) and generates a sampling clock in synchronization with the clock signal or directly uses the sampling clock as the sampling clock to perform a/D conversion of the interference optical (electrical) signal.

Further, the interference light of the laser light transmitted through the wafer 24 and the laser light reflected on the back surface of the wafer 24, reflected on the front surface, and transmitted to the back surface side may be observed.

The computer 30 calculates the thickness of the measurement site of the wafer 24 by a known procedure based on the input interference (electrical) signal.

As a known procedure, for example, as shown in the above-mentioned patent document 1 (japanese patent application laid-open No. 7-306018), a phase change of an interference (electric) signal can be detected from a relational expression of interference (including a refractive index of a wafer)Thereby measuring the thickness of the wafer 24.

Further, as shown in patent document 1, it is not necessary to directly obtain a phase changeThe thickness of the wafer can be determined by frequency analysis. That is, when the wavelength of the wavelength-variable laser light is changed by a certain amount Δ λ, the interference signal having the wavelength as the abscissa axis becomes a waveform obtained by applying a minute frequency modulation to the center frequency. The thickness of the wafer can be measured from the relational expression between the center frequency and the refractive index.

Alternatively, the center frequency can be calculated by performing signal processing using fast fourier transform on the interference signal, and the thickness of the wafer 24 can be measured by conversion using a calibration curve obtained in advance and the refractive index of the wafer.

Table 1 shows data obtained by performing signal processing on an interference signal by fast fourier transform to measure the thickness of a measurement site of the wafer 24 when the same site of the wafer 24 is measured 10 times.

As shown in table 1, in the thickness measurement in which signal processing was performed on the interference waveform obtained 10 times at the same position in a wafer having a thickness of approximately 722 μm by fast fourier transform, the standard deviation was 2.99nm, and good measurement with little deviation was possible. In a thickness measurement in which signal processing was performed by fast fourier transform on an interference waveform obtained 10 times at the same position in a wafer having a thickness of about 776 μm, the standard deviation was 3.03nm, and good measurement with little deviation was possible.

On the other hand, as shown in table 1, when a conventional mechanically driven light source was used, the standard deviation was 65.92nm and the deviation was large in the thickness measurement result of signal processing by fast fourier transform on the interference waveform obtained 10 times at the same position in a wafer having a thickness of about 722 μm. In the thickness measurement result of signal processing by fast fourier transform on the interference waveform obtained 10 times at the same position in the wafer having a thickness of about 776 μm, the standard deviation was 96.35nm, and the deviation was large.

FIG. 3A shows a measurement performed three times in the radial direction using a single-chip wavelength scanning semiconductor laser source (SLE-101 light source manufactured by internal photonic solutions of America) shown in FIG. 1The results of the thickness of the wafer of (1) are plotted by superimposing the results three times. The wafer was moved at a speed of 5mm/sec and its thickness was measured over the entire range in the radial direction. As shown in fig. 3, the graphs of the results of the three measurements were completely overlapped without any variation. This shows a case where the repetitive wavelength scanning accuracy of the light source is extremely high.

Fig. 3B shows a thickness measuring device manufactured by seika seiko corporation, which is currently used by the applicant: KURODA NANOMETRO (registered trademark) 300TT-M, to determineThe graphs of the results obtained for the thickness of the wafer in (1) were all the results obtained by the measurement performed by any of the apparatuses shown in fig. 3A and 3B, and the shapes of the convex portions were well matched on the wafer.

Such a favorable thickness measurement can be performed because the scanning wavelength is stabilized every time by using a single-wafer type wavelength scanning semiconductor laser light source as a light source. It is considered that the processor 18 generates a clock signal, obtains an interference signal from the laser light whose wavelength continuously and linearly changes in accordance with the clock signal, generates a sampling clock in synchronization with the clock signal or directly uses the sampling clock as the sampling clock, and performs a/D conversion on the interference optical signal, whereby the interference action of the scanning wavelength on the laser light and analysis such as signal processing by fast fourier transform based on the interference optical signal are performed in synchronization, and there is no variation.

When the thickness of the wafer 24 is measured, the thickness of the wafer 24 can be measured by continuously detecting the interference light signal while moving the wafer 24 or the probe 22 at a constant speed.

When the wafer 24 is polished by a double-side polishing machine or a single-side polishing machine (not shown), the thickness of the wafer 24 can be measured continuously or at regular time intervals during the polishing process using the wafer thickness measuring apparatus 10.

The wavelength scanning frequency of the laser light can be set to 1kHz to 40 kHz.

The wavelength range of the laser light can be 1200nm to 1400nm through the silicon wafer.

The speed of the sampling clock can be varied in wavelength from 10MHz to 1GHz to measure the interference waveform.

The thickness of the wafer can be measured by continuously measuring the interference waveform while moving the wafer 24 or the probe 22 at a constant speed.

Further, it is preferable to measure the polishing rate of the wafer by a double-side polishing machine or a single-side polishing machine for the wafer.

In addition, in order to accurately obtain the amount of wavelength change or the absolute value of the wavelength, it is necessary to use the laser light source 10 with high accuracy, which increases the cost.

Therefore, as shown in patent document 1 (japanese patent application laid-open No. 7-306018), a reference sample having the same composition as the measurement sample and accurately known thickness may be used, and the thickness of the measurement sample may be calculated from a relational expression of the frequency of the interference signal output from the optical system of the measurement sample, the frequency of the interference signal output from the optical system of the reference sample, the thickness of the reference sample, and the thickness of the measurement sample to be obtained.

Fig. 4 is a block diagram illustrating an overall system of another embodiment of the monolithic wavelength-scanning semiconductor laser light source 10.

The same components as those in fig. 1 are denoted by the same reference numerals, and the description thereof is omitted.

In the present embodiment, a light source monitoring circuit 32 using a reference wafer is added.

In the light source monitoring circuit 32, the reference wafer 38 is irradiated with the laser beam emitted from the laser light source 14 and split by the circulator 34 and the probe 36. The laser light (interference light) reflected by the front and back surfaces of the reference wafer 38 is detected by the photodiode 40 via the probe 36 and the circulator 34, converted into a digital signal by the a/D converter 28, and input to the computer 30.

In the computer 30, an average value (average value within a set time) of the voltage output from the photodiode 40 is calculated from the input digital signal value. The voltage value output from the photodiode 40 varies in proportion to an increase or decrease in the amount of laser light emitted from the laser light source 14. The variation of the voltage value is appropriately monitored, and when the average value of the voltages is lower than a predetermined threshold value, it is determined that the voltage is abnormal, and an alarm is issued.

Alternatively, the light source monitoring circuit 32 may be used for monitoring the scanning wavelength accuracy of the single-chip wavelength-scanning semiconductor laser light source 10. Since the thickness (and the distribution thereof) of the reference wafer 38 is constant, when the measured thickness varies, it can be determined that the scanning wavelength accuracy of the single-wafer wavelength-scanning semiconductor laser light source 10 varies, and this can become a standard for grasping the cause of the variation. The scanning wavelength accuracy can be grasped by measuring the average value, P-P value, deviation value, and the like of a set number of times (for example, 1000 times) with respect to the frequency of the FFT peak of the acquired interference waveform.

The timing of monitoring can be set by a program. For example, the thickness of the wafer can be measured immediately before the measurement.

Fig. 5 shows yet another embodiment of the monolithic wavelength-scanning semiconductor laser light source 10. This embodiment is the same as the other embodiments except that an MZI (Mach-Zehnder) interferometer 42 is used as a light source monitoring circuit.

In the present embodiment, as described above, the scanning wavelength accuracy of the single-chip wavelength scanning semiconductor laser light source 10 can be grasped and used for monitoring the light source.

In addition, when the fiber MZI interferometer is used, the refractive index of the fiber quartz glass is about 1.4, and the refractive index of the silicon wafer is less than about 3.5, so that there is an advantage that the change in the optical path length due to the influence of temperature is small.

[ TABLE 1 ]