JPH0685023A - Device for measuring minority carrier lifetime in semiconductor wafer - Google Patents

Abstract

PURPOSE:To provide a lifetime measuring device which can measure the recombination lifetime of minority carrier in the uppermost surface part of a semiconductor wafer, especially in a superficial part made of single crystal silicon layer of an SOI semiconductor wafer. CONSTITUTION:An exciting means A for a lifetime measuring device 1 consists of an irradiating means composed of a heavy hydrogen lamp 10 and a spectroscope 11, and a pulse generating means such as a chopper 20, etc. A concentration measuring means B consists of a microwave oscillator 30, microwave detector 40, etc. The electromagnetic wave lambda1 radiated from the lamp 10 is converted to pulse-like electromagnetic wave lambda2 by the chopper 20, and further it is changed into an electromagnetic wave lambda3 with the wavelength of only 100 to 400nm by the spectroscope 11. The irradiating means and pulse generating means may be composed of a KrF excimer laser that radiates a pulse-like electromagnetic wave lambda6 of 248nm in wavelength and a laser oscillator, respectively.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor single crystal inspection technique and a technique particularly effective when applied to a minority carrier lifetime measurement technique in a semiconductor wafer. For example, a single crystal silicon layer is laminated on an insulating film. The present invention relates to a technique useful for measuring the minority carrier lifetime in a semiconductor wafer having an SOI structure.

[0002]

2. Description of the Related Art In general, a semiconductor wafer is a cutting step for cutting a thin plate from a semiconductor single crystal ingot, a processing deterioration layer removing step for removing a processing deterioration layer generated during the cutting by chemical etching or mechanical polishing, It is made through various processes such as a mirror polishing process for finishing the surface from which the work-affected layer has been removed into a mirror surface state by mechanical or chemical polishing. In various steps such as the above-mentioned steps up to the semiconductor wafer, or an oxidation step of forming an oxide film on the surface of the semiconductor wafer, an impurity introduction step of introducing impurities into the semiconductor wafer, and a heat treatment step of diffusing the impurities The wafer surface may be contaminated or damaged by heavy metals.
In order to evaluate the contamination state of the semiconductor wafer surface in such a manufacturing process, the time until the minority carriers generated in the semiconductor wafer recombine and disappear, that is, the recombination lifetime is measured. .

This lifetime measurement is generally performed by irradiating a semiconductor wafer with an electromagnetic wave (that is, visible light) having a wavelength of 800 nm to 1000 nm to excite minority carriers and measuring the change over time in the concentration of the minority carriers on the semiconductor wafer. It is performed by measuring the reflection intensity of the irradiated microwave. For the measurement of the minority carrier concentration by such a microwave system, for example, "Microwave Techniques" is used.
in Measurement of Lifetime in German "Journa
l of Applied Physics Vol.30 No.7p.p.1054-1
060 (1959).

[0004]

By the way, it is known that when a silicon wafer is irradiated with the above visible light, the visible light reaches the silicon wafer to a depth of about several tens of μm. Therefore, in recent years, its practical application has been strongly desired, and an SOI (Silicon on In) in which a single crystal silicon layer having a thickness of several μm is stacked on an insulating film having a thickness of approximately 1 μm
In the case of a semiconductor wafer having a sulator structure, visible light passes through the single crystal silicon layer and the insulating film to reach the silicon supporting substrate portion under the insulating film, and minority carriers are also excited in the silicon supporting substrate portion. For SOI
With a semiconductor wafer having a structure, the recombination lifetime of minority carriers in the single crystal silicon layer cannot be accurately measured. However, by accurately measuring the recombination lifetime in the single crystal silicon layer, S
Development and practical application cannot be expected unless the contamination state of the surface of the semiconductor wafer having the OI structure is evaluated. Therefore, the urgent development of a measuring device capable of accurately measuring the above-mentioned recombination lifetime is a major issue. It was.

The present invention has been made in view of the above circumstances. Minority carriers are excited only in the outermost surface portion of a semiconductor wafer, particularly in the surface layer portion of a semiconductor wafer having an SOI structure to excite minority carriers. The main object of the present invention is to provide a minority carrier lifetime measuring device that enables the measurement of the minority carrier recombination lifetime in. The above and other objects and novel features of the present invention will be apparent from the description of this specification and the accompanying drawings.

[0006]

The typical ones of the inventions disclosed in the present application will be outlined below. That is, the lifetime measuring device for minority carriers in the semiconductor wafer of the present invention comprises minority carrier excitation means and minority carrier concentration measurement means,
The excitation means is composed of an irradiation means composed of a deuterium lamp and a spectroscope, and a pulse generation means such as a chopper, and the concentration measurement means is composed of a microwave oscillator or a microwave detector. There is. And the chopper etc. emitted from the deuterium lamp 700
Converts electromagnetic waves with wavelengths below nm into pulsed electromagnetic waves,
The spectroscope is configured to convert the electromagnetic wave into an electromagnetic wave having a wavelength of 100 nm to 400 nm. Also,
The irradiation means may be a KrF excimer laser that emits a pulsed electromagnetic wave having a wavelength of 248 nm, and the pulse generation means may be a laser oscillator.

[0007]

According to the above means, in order to excite minority carriers in the semiconductor wafer, the semiconductor wafer is exposed to 400 n
Since the electromagnetic wave having a wavelength of m or less is irradiated, the electromagnetic wave can reach only a depth of about several tens nm to several hundreds nm inside the semiconductor wafer, and minority carriers are excited only at the outermost surface portion of the semiconductor wafer. .

[0008]

【Example】

(First Embodiment) A schematic view of a first embodiment of a minority carrier lifetime measuring apparatus for a semiconductor wafer according to the present invention is shown in FIG. 1 and will be described below. The minority carrier lifetime measuring apparatus 1 (hereinafter, simply referred to as “lifetime measuring apparatus 1”) in the semiconductor wafer is configured to measure the minority carrier recombination lifetime τ ₁ in the semiconductor wafer 2.
And a concentration measuring unit B for measuring the concentration of the excited minority carriers in the semiconductor wafer 2. The excitation unit A includes an irradiation unit including a deuterium lamp 10 (lamp) and a spectroscope 11 (wavelength selection unit), and pulse generation unit made of, for example, a chopper 20. The concentration measuring means B includes a microwave oscillator 30, a microwave detector 40, an amplifier 50, a data processor 60, a processed data display 70, and an oscilloscope 80. Hereinafter, each of the above components will be described in detail along the flow of the measurement procedure.

First, the deuterium lamp 10 is turned on by supplying electric power from the stabilizing power supply 12. This deuterium lamp 10
Is a light source that emits an electromagnetic wave λ ₁ having a wavelength of 700 nm or less, and in particular, the relative intensity of an electromagnetic wave having a wavelength of 200 nm to 300 nm (that is, ultraviolet light) is high.

The electromagnetic wave λ ₁ is converted into a pulsed electromagnetic wave λ ₂ by the chopper 20. Here, chopper 20 is intended to interrupt the transmission of electromagnetic wave lambda _1, the slits 22 (transmission window for transmitting an electromagnetic wave lambda ₁ in a part of the rotary disk 21 (non-transparent plate material) that prevents the transmission of electromagnetic wave lambda ₁ Section) is provided.

The pulse width W of the electromagnetic wave λ ₂ is set by appropriately setting the angular velocity ω of rotation of the rotating disk 21, the opening width a of the slit 22 and the angle b formed by the adjacent slits 22 and 22.
(Time) is made shorter than the minority carrier lifetime τ ₀ (consisting of the occurrence lifetime τ ₂ required for minority carrier generation and the recombination lifetime τ ₁ ) (W <τ ₀ ).
At the same time, the pulse repetition period T (time) of the electromagnetic wave λ ₂ is made longer than the lifetime τ ₀ (T> τ ₀ ). Generally, when the semiconductor wafer 2 is made of single crystal silicon, the lifetime τ ₀ is on the order of μ seconds,
The pulse width W is set to several hundreds of nanoseconds and the repetition period T is 1 m.
It may be set to about a second.

Next, the electromagnetic wave λ ₂ is separated by a spectroscope 11 made of a diffraction grating into an electromagnetic wave λ ₃ (ultraviolet ray) having only a wavelength of 100 nm to 400 nm. Therefore, the semiconductor wafer 2 is irradiated with pulsed ultraviolet rays.

The reason why the wavelength of the electromagnetic wave λ ₃ is limited to the above range is as follows. That is, (1) Since the penetration depth of the electromagnetic wave λ _{3 into} the single crystal silicon is about several tens nm to several hundreds nm, the excitation range of minority carriers is limited to only the outermost surface portion of the semiconductor wafer 2.
(2) In particular, when the semiconductor wafer 2 is a semiconductor wafer having an SOI structure in which a single crystal silicon layer 2B having a thickness of several μm is laminated on an insulating film 2A having a thickness of about 1 μm, 40
Electromagnetic waves (visible light) having a wavelength of 0 nm or more reach the silicon supporting substrate portion 2C below the insulating film 2A, the minority carriers are excited also in the silicon supporting substrate portion 2C, and the minority carriers in the single crystal silicon layer 2B are regenerated. The bond lifetime τ ₁ cannot be measured accurately. (3) Since electromagnetic waves of 100 nm or less are vacuum ultraviolet rays, the path of the excitation means A from the deuterium lamp 10 to the semiconductor wafer 2 must be in a vacuum atmosphere, which leads to an increase in size of the lifetime measuring apparatus 1. .

As described above, the minority carriers are excited only in the outermost surface portion of the semiconductor wafer 2, that is, the single crystal silicon layer 2B, and at the same time, the microwave λ ₀ is made incident on the semiconductor wafer 2 from the microwave oscillator 30. This microwave λ ₀ is reflected with an intensity according to the concentration of minority carriers. This reflected microwave λ ₀ 'is detected by the microwave detector 40.
Is detected and converted into an electric signal S corresponding to the intensity. The electric signal S is amplified by the amplifier 50 into an electric signal S ′, and the data processor 6 such as a computer
In addition to being output to 0, it is output to the oscilloscope 80 and displayed. The electric signal S ′ input to the data processor 60 is converted into numerical data D through a predetermined arithmetic processing and displayed on a processed data display 70 such as a display.

Minority carrier recombination lifetime τ
₁ is obtained from the time from when the intensity of the electric signal S reaches the maximum peak value immediately after irradiation of the electromagnetic wave λ ₃ which is a pulsed ultraviolet ray to 1 / e thereof.

As described above in detail, according to the lifetime measuring apparatus 1 of the first embodiment, the minority carrier excitation region has a maximum depth of several tens nm to several hundreds nm from the surface of the semiconductor wafer 2. Since it can be limited to the surface portion, the recombination lifetime τ ₁ of minority carriers on the outermost surface portion of the semiconductor wafer 2 can be accurately measured. Especially SO
In the case of the semiconductor wafer 2 having the I structure, the minority carriers are excited only in the single crystal silicon layer 2B in the surface layer portion, and the insulating film 2A prevents the minority carriers from diffusing into the silicon supporting substrate portion 2C. , The recombination lifetime τ ₁ of minority carriers in the single crystal silicon layer 2B can be accurately measured. Therefore, it becomes possible to evaluate the contamination state of the surface of the semiconductor wafer 2 having the SOI structure in the manufacturing process, and to evaluate the cause of the deterioration of the characteristics and the cause of the defect.

In the first embodiment, the deuterium lamp 10 is used, but the deuterium lamp 10 is not limited to this. For example, a mercury lamp or a xenon lamp is used, and at least a part or all of 100 nm to 400 nm is used. Any light source may be used as long as it emits ultraviolet light having a wavelength of, and the spectrum may be a continuous spectrum or a line spectrum.

Although the spectroscope 11 is used in the first embodiment, it is needless to say that the spectroscope 11 is not limited to this, and an optical filter, for example, may be used. This filter may be configured by combining a low-pass filter that transmits an electromagnetic wave having a wavelength of 400 nm or less and a high-pass filter that transmits an electromagnetic wave having a wavelength of 100 nm or more, or a band that transmits only an electromagnetic wave having a wavelength of 100 nm to 400 nm. It may be composed of a pass filter.

Further, in the first embodiment, the chopper 20 is provided between the deuterium lamp 10 and the spectroscope 11, but like the lifetime measuring apparatus 1'shown as a modification in FIG. Needless to say, the positions of the spectroscope 11 and the chopper 20 may be exchanged. In this case, the electromagnetic wave λ emitted from the deuterium lamp 10
₁ is first converted into an electromagnetic wave λ ₄ having a wavelength of 100 nm to 400 nm by the spectroscope 11, and then the chopper 20
Is converted into pulsed electromagnetic wave λ ₅ .

(Second Embodiment) A schematic view of a second embodiment of the minority carrier lifetime measuring apparatus for a semiconductor wafer according to the present invention is shown in FIG. 3 and will be described below. For convenience of explanation, the same members and means as those in the first embodiment are designated by the same reference numerals and the description thereof will be omitted. Minority carrier lifetime measuring device 3 in this semiconductor wafer (hereinafter, simply referred to as "lifetime measuring device 3").
However, the difference from the first embodiment is as follows. That is, the irradiation means constituting the excitation means A of the lifetime measuring device 3 is composed of the KrF excimer laser 15 (excimer laser), and the pulse generation means is composed of the laser oscillator 25.

The electromagnetic wave λ ₆ emitted from the KrF excimer laser 15 is a pulsed laser beam in the ultraviolet region having a peak at a wavelength of 248 nm, and its pulse width W is several n.
It is about a second. Therefore, it is not necessary to separate electromagnetic waves having a wavelength in the visible light range or more through a spectroscope or an optical filter. The frequency of the alternating voltage applied to the KrF excimer laser 15 is appropriately set by the laser oscillator 25, and the pulse repetition period T (time) of the electromagnetic wave λ ₆ is set.
Is not particularly limited, but is set to, for example, about several milliseconds to several hundreds of milliseconds.

According to the lifetime measuring apparatus 3 of the second embodiment, in addition to the effect obtained by the lifetime measuring apparatus 1 of the first embodiment described above, a spectroscope, a chopper, etc. are unnecessary, and the apparatus is simplified. To be done.

In the second embodiment, KrF is used.
Although the excimer laser 15 is used, the excimer laser 15 is not limited to this. For example, an XeCl excimer laser having a peak at a wavelength of 308 nm, an ArF excimer laser having a peak at a wavelength of 193 nm, or the like may be used. However, any laser source may be used as long as it emits a laser beam in the ultraviolet range, such as a blue-emitting semiconductor laser.

Although the invention made by the present inventor has been specifically described based on the embodiments, the invention is not limited to the above embodiments, and various modifications can be made without departing from the scope of the invention. Needless to say. For example, the concentration measuring means B is not limited to the means using the microwave,
For example, it may be a means for measuring a change in conductivity of the semiconductor wafer 2, a change in photovoltaic power, or the like by the 4-probe method or the eddy current method.

In the above description, the case where the invention made by the present inventor is mainly applied to a silicon wafer, which is a field of application which is the background of the invention, particularly to a semiconductor wafer having an SOI structure, has been described. However, the present invention is not limited thereto. However, it can also be used for germanium wafers, compound semiconductor wafers, and the like.

[0026]

The effects obtained by the representative one of the inventions disclosed in the present application will be briefly described as follows. That is, when measuring the recombination lifetime of minority carriers in a semiconductor wafer, it is possible to limit the minority carrier excitation region to the outermost surface portion having a depth of about several tens nm to several hundreds nm from the surface of the semiconductor wafer. Therefore, the recombination lifetime of minority carriers on the outermost surface of the semiconductor wafer can be accurately measured. Especially SO
It is effective for measuring the recombination lifetime of minority carriers in the single crystal silicon layer of the surface layer portion of the semiconductor wafer having the I structure.

[Brief description of drawings]

FIG. 1 is a schematic diagram of a lifetime measuring device according to a first embodiment.

FIG. 2 is a schematic view of a modified example of the lifetime measuring device in the first embodiment.

FIG. 3 is a schematic diagram of a lifetime measuring device according to a second embodiment.

[Explanation of symbols]

A excitation means B concentration measurement means 1,3 lifetime measuring device 2 semiconductor wafer 2A insulating film 2B single crystal silicon layer 2C silicon support substrate portion 10 deuterium lamp (lamp) 11 spectroscope (wavelength selection means) 12 stabilizing power supply 15 KrF excimer laser (excimer laser) 20 chopper 21 rotating disk (non-transmissive plate material) 22 slit (transmissive window part) 25 laser oscillator 30, 40 microwave oscillator 50 amplifier 60 data processor 70 processed data display 80 oscilloscope

Claims (3)

[Claims] 1. An apparatus for measuring a minority carrier lifetime in a semiconductor wafer, comprising: excitation means for exciting minority carriers in a semiconductor wafer; and concentration measurement means for measuring the concentration of minority carriers excited by the excitation means. An exciting means for irradiating the semiconductor wafer with an electromagnetic wave having a wavelength of 400 nm or less; and a pulse generation for making the electromagnetic wave into a pulse having a pulse width shorter than the lifetime of minority carriers and a repeating period longer than the lifetime. And a minority carrier lifetime measuring apparatus in a semiconductor wafer. 2. A lamp for radiating an electromagnetic wave having a wavelength of 400 nm or less and a wavelength selecting means for preventing irradiation of an electromagnetic wave having a wavelength of at least 400 nm to the semiconductor wafer among electromagnetic waves radiated from the lamp. And the pulse generating means,
A non-transparent plate member that prevents the transmission of electromagnetic waves is provided with a transmission window portion for transmitting the electromagnetic waves, and is composed of a chopper that interrupts the electromagnetic waves that reach the semiconductor wafer by being rotated at a predetermined angular velocity. A minority carrier lifetime measuring device in a semiconductor wafer according to claim 1. 3. The irradiating means is composed of an excimer laser that emits an electromagnetic wave having a wavelength of 400 nm or less, and the pulse generating means is a laser oscillator that changes the frequency of an AC applied voltage applied to the excimer laser. The lifetime measuring device for minority carriers in a semiconductor wafer according to claim 1, wherein: