JP2021136393A - Silicon wafer surface state diagnostic method and surface modification method - Google Patents

Abstract

To provide a high quality silicon wafer by performing diagnosis of a surface state and recovery effect confirmation while containing a real time processing (during surface modification).SOLUTION: A surface state diagnostic method of a silicon wafer 1, in a surface modification of the silicon wafer 1 using a laser heat treatment, measures a reflectance ratio or an absorption ratio of a surface of the silicon wafer 1, and measures an electrical property. Also, the measurement of the reflectance ratio or the absorption ratio is performed by a laser of which a wavelength is 532 or 785nm. The electrical property arranges an electrode 4 so as to be closed to a surface treatment part of the silicon wafer 1 to measure an electrostatic capacity formed between the silicon wafer 1 and the electrode 4.SELECTED DRAWING: Figure 2

Description

The present invention relates to the repair of surface defects which are processed alteration layers on the surface of a silicon wafer, and particularly regarding the surface modification of a silicon wafer using laser heat treatment, a method for diagnosing the surface condition of a silicon wafer and diagnosing the state of modification of the surface. Regarding the surface modification method.

Semiconductor wafers such as silicon wafers used for manufacturing semiconductor devices and the like are surface-processed by machining processes such as cutting, grinding, lapping, and polling. However, a processed alteration layer is formed on the surface and the inside thereof, and some of the processed alteration layers contain microcracks (microcracks). The removal of internal cracks and the like is mainly performed by chemical and mechanical methods such as etching and chemical mechanical polishing (CMP).

For example, Patent Document 1 describes that a single crystal surface is irradiated with a pulse laser and evaluated by a cross-sectional TEM (transmission electron microscope) observation image of the pulse laser irradiation portion.

Further, Patent Document 2 describes that the warp of a semiconductor wafer is measured, and the depth of the surface alteration layer is obtained based on the measured warp and the grinding depth ground in the grinding step.

Japanese Unexamined Patent Publication No. 2008-147639 Japanese Patent No. 6072166

In the above-mentioned prior art, in the method using a TEM (transmission electron microscope) as described in Patent Document 1, the thickness of the observation sample needs to be about several nm (observable thickness), and therefore the sample. Preparatory work requires great care and takes time. In addition, the sample is measured with destruction when exposed to an electron beam. Electron diffraction for observing an interference pattern by irradiating a sample with electrons and Raman spectroscopic measurement using the interaction between light and a substance are similar and are very expensive devices, and are difficult to introduce.

Further, the method of measuring the warp and evaluating the work-altered layer as described in Patent Document 2 may cause fracture to proceed because a load is applied at the time of measurement. Furthermore, efficient measurement for shapes such as curved surfaces over a wide area such as notches is not known at this time.

An object of the present invention is to solve the above-mentioned problems of the prior art so that it can be mounted on a laser surface modifier. An object of the present invention is to provide a high quality silicon wafer by diagnosing the surface condition and confirming the repair effect, including during real-time processing (during surface modification).

In order to achieve the above object, the present invention is a method for diagnosing a silicon wafer surface condition in silicon wafer surface modification using laser heat treatment, in which the reflectance or absorptivity of the silicon wafer surface is measured and the electrical properties are measured. do.

Further, it is desirable to measure the reflectance or the absorptance with a laser having a wavelength of 532 or 785 nm.

Further, for the electrical characteristics, it is desirable to arrange the electrodes in the vicinity of the surface treatment portion of the silicon wafer and measure the capacitance of the capacitor formed between the silicon wafer and the electrodes.

Further, for the electrical characteristics, it is desirable to arrange the electrodes in the vicinity of the surface treatment portion of the silicon wafer and apply a voltage between the silicon wafer and the electrodes to measure the attractive force between the plates.

Further, it is desirable to measure the attractive force between the plates with a strain gauge.

Further, a ring pole on which the silicon wafer is placed, a thin plate arranged on a ring-shaped electrode plate ring in equal divisions, and a strain gauge attached to the thin plate to form a bridge circuit are provided. It is desirable to arrange the plate ring with a gap from the silicon wafer and apply a voltage between the ring pole and the plate ring to measure the attractive force between the plates.

Further, the present invention is a silicon wafer surface modification method using laser heat treatment, in which step 1 of measuring the reflectance or absorptance of the silicon wafer surface is close to the surface treatment portion of the silicon wafer. Step 2 in which the electrodes are arranged and the capacitance of the capacitor formed between the silicon wafer and the electrodes is measured, and step 1 and step 3 in which the processing conditions for the laser heat treatment are determined based on the steps 1 and 2. Has.

Further, it is desirable to perform the steps 1 and 2 during the processing of the laser heat treatment, and to continue the processing by feedback-controlling the results.

According to the present invention, since the silicon wafer surface state is diagnosed by measuring the reflectance or absorptivity of the silicon wafer surface and measuring the electrical characteristics, it can be mounted on a laser surface modifier. High-quality silicon wafers can be provided by diagnosing the surface condition and confirming the repair effect, including during real-time processing (during surface modification).

A block diagram showing a light reflectance or absorption rate measuring unit according to an embodiment of the present invention. A block diagram showing a unit for measuring capacitance between a silicon wafer and an electrode and an attractive force between plates according to an embodiment. Flowchart of surface modification (processing) and diagnosis according to one embodiment Configuration diagram for measuring the attractive force between the plates according to one embodiment Top view of the electrode ring according to one embodiment Side view of FIG.

FIG. 1 is a block diagram showing a measurement unit for light reflectance or absorption according to one embodiment, and FIG. 2 is a block diagram showing a measurement unit for capacitance between a silicon wafer and an electrode and an attractive force between plates. be. The work-altered layer is mainly an amorphous silicon layer or a polycrystalline state. Although this process-altered layer is extremely thin, it greatly affects the mechanical, electrical, and optical performance.

In this embodiment, the surface state of the surface of the processed alteration layer after grinding or etching is examined by measuring the reflectance (absorption rate) or performing image analysis. Further, regarding the internal state having a depth of about several μm, the reflectance (absorption) is examined by irradiating a measurement laser having a wavelength of 532 nm and near infrared light (785 nm).

Furthermore, by applying a voltage from the outside (charging the surface of the silicon wafer), differences in the electrical characteristics (conductivity, capacitance, attractive force between plates, etc.) of amorphous, polycrystalline silicon, and single crystal silicon are detected. Check the reforming status. That is, the reflectance or absorptivity of the surface of the silicon wafer 1 is measured, and the electrical characteristics are measured.

That is, in this embodiment, in order to diagnose the surface condition of the silicon wafer 1 and confirm the repair effect, it is preferable to comprehensively measure and evaluate by combining the following (1) to (4).
(1) Considering the shape of the measurement surface, the reflectance or absorptivity of a single crystal is obtained by irradiating with polarized near-infrared light (785 nm).
(2) Considering the shape of the measurement surface 1-1 of the silicon wafer 1, polarized visible light or light having a wavelength of 532 nm is applied to obtain amorphous reflectance or absorption. The amorphous silicon layer has strong absorption of light having a wavelength of 532 nm.
(3) Measure the surface shape (including roughness) by an image, contact type, etc.
(4) Obtain differences in the electrical characteristics (electrical conductivity, capacitance, attractive force between plates, etc.) of the object to be processed (silicon wafer) before and after modification and during modification.

In FIG. 1, the measurement light source 2 irradiates the measurement surface 1-1 of the silicon wafer 1 with a measurement laser or visible light as shown by an arrow. The measurement light source (laser heat treatment) 2 is a measurement light source or a laser having a wavelength of 532 or 785 nm, and may be via a polarizer. Then, the reflected light is detected and analyzed by a camera or a detector 3 via a filter, and the reflectance or the absorptivity is evaluated and measured.

In the light reflectance (absorption) evaluation and measurement, the reflectance of silicon during melting is as high as 30% as compared with that of solid, and the surface modification status can be examined by the reflectance measurement during surface modification. .. The light reflectance (absorption rate) is measured by placing the polarizer immediately after the laser emission section in consideration of the influence of the incident angle of the measurement laser irradiated from the measurement light source 2 to the measurement surface 1-1. It is preferable to arrange it.

FIG. 2 shows the measurement of the capacitance 7 between the silicon wafer 1 and the electrode 4 and the attractive force 6 between the plates as the electrical characteristics of (4). In FIG. 2, the electrodes 4 are arranged in close proximity to each other so as to correspond to the surface treatment portion of the silicon wafer 1. Then, the capacitance 7 and the attractive force between the plates 6 are measured by applying a voltage 5 between the silicon wafer 1 and the electrode 4, and are compared before and after the modification.

It is known that the electrical conductivity of molten silicon is 100 times or more higher than that of solid silicon. Therefore, the capacity of the molten silicon can be evaluated by measuring the electrical conductivity of the surface of the silicon wafer 1. The electrical conductivity changes as the capacitance of the capacitor formed between the silicon wafer 1 and the electrode 4 and the attractive force between the plates 6 as the conductivity of the silicon melted during the surface treatment changes. The state of the surface modified portion can be evaluated by observing or measuring the changing phenomenon of the capacitance 7.

FIG. 3 is a flowchart of surface modification (processing) and diagnosis using laser heat treatment. For surface modification (processing) and diagnosis, efficient and effective surface modification is performed by measuring or evaluating the surface condition of the silicon wafer to be modified and irradiating with a laser under the corresponding conditions. First, the reflectance or absorptivity of the surface of the silicon wafer 1 is measured and image analysis is performed before processing by laser irradiation (step 1).
Next, the capacitance 7 is evaluated by the method shown in FIG. 2 (step 2). That is, in steps 1 and 2, the reflectance or absorptivity of the surface of the silicon wafer 1 was measured, and the capacitance 7 as an electrical property was measured. Then, the machining conditions are determined based on the measurements and evaluations of steps 1 and 2 (step 3).

During machining, surface reflectance is measured and capacitance is evaluated (change in electrical conductivity) in the same manner as in steps 1 and 2, and the results are feedback-controlled to continue machining (step 4).

By processing with laser irradiation, oxygen elimination treatment and crystallinity of silicon wafer 1 can be improved, and by irradiating pulse laser, surface defects, which are processing alteration layers on the surface of silicon wafer 1, can be repaired. It is possible.

In particular, after grinding the silicon wafer 1, at least one of the incident angle, the components of s-polarized light and p-polarized light, the energy density, and the number of irradiations per unit area is changed according to the surface shape of the pulse laser. By irradiating, the influence of processing stress can be eliminated and a uniform surface can be modified.

Further, in the processing by pulse laser (nanosecond) irradiation, the amorphous layer of the processing alteration layer is melted at the nanosecond speed. Then, melting by pulse laser (nanosecond) irradiation promotes recrystallization (epitaxial growth) in which the crystal orientations are aligned, and crystal defects generated by machining can be eliminated.

After processing, surface reflectance measurement, image analysis, and capacitance evaluation (steps 5 and 6) are performed in the same manner as in steps 1 and 2, and quality evaluation is performed to determine whether the specifications are OK or NG. Judgment (step 7).
As described above, the silicon wafer 1 can be made of high quality because the surface condition is diagnosed and the repair effect is confirmed even during processing.

FIG. 4 is a configuration diagram for measuring the attractive force 6 between the plates. FIG. 5 is a plan view of the electrode plate ring 10, and FIG. 6 is a side view. The attractive force 6 between the plates shown in FIG. 2 is measured with a strain gauge 10-2. In FIG. 4, the silicon wafer 1 is placed on the ring pole 11. The electrode plate ring 10 corresponds to the electrode 4 shown in FIG. 2, and has a ring-shaped compliance structure (flexible structure).

The thin plate 10-1 is arranged on the upper surface of the electrode plate ring 10 in compliance with an equal division of 120 °. The strain gauges 10-2 are attached near the center of the thin plate 10-1, respectively. Further, the three strain gauges 10-2 form a bridge circuit and detect the stress applied to the thin plate 10-1.

The voltage 5 is applied between the ring pole 11 and the plate ring 10. Since the silicon wafer 1 is placed on the ring pole 11, the voltage 5 is applied between the silicon wafer 1 and the electrode plate ring 10. The ring pole 11 may be mounted on a normal rotary table on which the silicon wafer 1 is placed.

As shown in FIG. 6, the electrode plate ring 10 is provided so that the claw portion 10-3 can rotate. The claw portion 10-3 is rotatable inward of the electrode plate ring 10 as shown by the arrow in FIG. 6 (a), and is fixed at a predetermined position (90 ° in FIG. 6) as shown in FIG. 6 (b). .. Therefore, the silicon wafer 1 and the electrode plate ring 10 are arranged with a gap as shown in FIG. 6B to form the capacitance 7 of FIG.

That is, the electrodes 4 shown in FIG. 2 are configured to sandwich the silicon wafer 1, and the attractive force 6 between the plates is detected by the strain gauge 10-2. The gap between the silicon wafer 1 and the electrode plate ring 10 is set to several hundred μm. Since the conductivity (mobility, resistivity) of the electrode-plate attractive force 6 is significantly different from that of amorphous silicon, polycrystalline silicon, and single crystal silicon, it is possible to determine the surface modification state.

The measurement procedure is as follows.
(1) The silicon wafer 1 is placed on the ring pole 11, and the electrode plate ring 10 is mounted on the silicon wafer 1.
(2) The claw portion 10-3 is rotated inward of the plate ring 10 and a voltage 5 is applied between the ring pole 11 and the plate ring 10.
(3) When the attractive force 6 between the plates is generated, stress is applied to the plate ring 10 and the plate ring 10 is deformed.
(4) Stress is detected by a strain gauge 10-2 attached to a thin plate 10-1 arranged on the upper surface of the electrode plate ring 10 and output as an electric signal.

According to the measurement of the attractive force between the plates described above 6, the difference in the electrical characteristics (electrical conductivity, capacitance, attractive force between the plates, etc.) of the object to be processed (silicon wafer) before and after the modification and during the modification. Can be measured with high sensitivity.

1 ... Silicon wafer 1-1 ... Measurement surface 2 ... Measurement light source 3 ... Detector 4 ... Electrode 5 ... Voltage 6 ... Electrode plate attractive force 7 ... Capacitance 10 ... Electrode plate ring 10-1 ... Thin plate 10-2 ... Gauge 10-3 ... Claw 11 ... Ring pole

Claims (8)

A method for diagnosing a silicon wafer surface condition in silicon wafer surface modification using laser heat treatment.
A method for diagnosing a silicon wafer surface state, which comprises measuring the reflectance or absorptivity of the silicon wafer surface and measuring the electrical characteristics. The silicon wafer surface condition diagnostic method according to claim 1, wherein the reflectance or the absorption rate is measured by a laser having a wavelength of 532 or 785 nm. Claim 1 or 2 is characterized in that an electrode is arranged in the vicinity of a surface treatment portion of the silicon wafer and the capacitance of a capacitor formed between the silicon wafer and the electrode is measured. The method for diagnosing the surface condition of a silicon wafer according to. The electric property is characterized in that an electrode is arranged in the vicinity of the surface treatment portion of the silicon wafer and a voltage is applied between the silicon wafer and the electrode to measure the attractive force between the plates. 2. The method for diagnosing the surface condition of a silicon wafer according to 2. The method for diagnosing the surface state of a silicon wafer according to claim 4, wherein the attractive force between the plates is measured with a strain gauge. A ring pole on which the silicon wafer is placed and
A thin plate arranged evenly on a ring-shaped electrode plate ring,
The strain gauge attached to the thin plate to form a bridge circuit, and
The present invention is characterized in that the plate ring is arranged with a gap from the silicon wafer, and a voltage is applied between the ring pole and the plate ring to measure the attractive force between the plates. Item 5. The method for diagnosing the surface condition of a silicon wafer according to Item 5. A silicon wafer surface modification method using laser heat treatment.
Step 1 of measuring the reflectance or absorptance of the surface of the silicon wafer,
Step 2 of arranging the electrodes close to the surface treatment portion of the silicon wafer and measuring the capacitance of the capacitor formed between the silicon wafer and the electrodes.
Step 1 and step 3 of determining the processing conditions of the laser heat treatment based on the step 2 and
Silicon wafer surface modification method. The silicon wafer surface modification method according to claim 7, wherein during the processing of the laser heat treatment, the steps 1 and 2 are performed, and the results are feedback-controlled to continue the processing.

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