Silicon Wafer Surface State Diagnosis Method and Surface Modification Method

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

Technical Field

[0001] The present invention relates to the repair of surface defects, which are processed and modified layers on the surface of a silicon wafer, and particularly to the surface modification of a silicon wafer using laser heat treatment, and to a method for diagnosing the surface state of a silicon wafer and a method for surface modification for diagnosing the modification status of the surface thereof.

Background Art

[0002] Semiconductor wafers such as silicon wafers used in the production of semiconductor devices and the like are surface-processed by mechanical processing processes such as cutting, grinding, lapping, and polishing. However, a processed and modified layer is formed on the surface and inside thereof, and some of the processed and modified layers contain microcracks (microscopic cracks). The removal of such internal cracks and the like is mainly performed by chemical and mechanical methods such as etching and chemical mechanical polishing (CMP).

[0003] For example, Patent Document 1 describes irradiating a single crystal surface with a pulsed laser and evaluating it by a cross-sectional TEM (transmission electron microscope) image of the pulsed laser irradiation portion.

[0004] Further, Patent Document 2 describes measuring the warp of a semiconductor wafer and obtaining the depth of the surface modified layer based on the measured warp and the grinding depth ground in the grinding process.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0006] In the above prior art, as described in Patent Document 1, the method using a TEM (transmission electron microscope) requires the thickness of the observation sample to be about several nanometers (observable thickness). Therefore, careful attention is required for the sample preparation work, which also takes time. In addition, the sample is measured with destruction by being irradiated with an electron beam. The same applies to electron diffraction for observing an interference pattern by applying electrons to the sample and Raman spectroscopy measurement using the interaction between light and matter, which are very expensive devices and difficult to introduce.

[0007] Also, as described in Patent Document 2, the method of measuring warpage to evaluate the processed modified layer may cause destruction to progress because a load is applied during measurement. Furthermore, efficient measurement for a shape such as a curved surface over a wide area such as a notch part is not known at present.

[0008] An object of the present invention is to solve the problems of the above prior art and enable it to be mounted on a laser surface modification machine. And the present invention aims to provide a high-quality silicon wafer by diagnosing the surface state and confirming the repair effect including during real-time processing (during surface modification).

Means for Solving the Problems

[0009] The configuration of the present invention for achieving the above object is as follows. [1] A method for diagnosing the surface state of a silicon wafer in silicon wafer surface modification using laser heat treatment, characterized by measuring the reflectivity or absorptivity of the surface of the silicon wafer, or measuring the electrical properties. [2] The silicon wafer surface state diagnosis method according to [1], wherein the electrical properties include the attraction force between the electrodes generated between the surface treatment part of the silicon wafer and the electrodes arranged in proximity. [3] The silicon wafer surface state diagnosis method according to [1], wherein the electrical properties include the measured value by a strain gauge of the force generated between the surface treatment part of the silicon wafer and the electrodes arranged in proximity. [4] A method for surface modification of a silicon wafer using laser heat treatment, comprising: measuring the reflectivity or absorptivity of the surface of the silicon wafer, or arranging an electrode in proximity to the surface treatment portion of the silicon wafer and measuring the capacitance of a capacitor formed between the silicon wafer and the electrode; and step B of determining the processing conditions of the laser heat treatment based on step A. A method for surface modification of a silicon wafer having these steps. [5] The method for surface modification of a silicon wafer according to [4], characterized in that during the processing of the laser heat treatment, step A is performed, and the result is feedback-controlled to continue the processing.

[0010] Another configuration of the present invention is a method for diagnosing the surface state of a silicon wafer in surface modification of a silicon wafer using laser heat treatment, which measures the reflectivity or absorptivity of the surface of the silicon wafer and measures the electrical properties.

[0011] Further, it is desirable that the measurement of the reflectivity or the absorptivity is performed with a laser having a wavelength of 532 or 785 nm.

[0012] Furthermore, for the electrical properties, it is desirable to arrange an electrode in proximity to the surface treatment portion of the silicon wafer and measure the capacitance of a capacitor formed between the silicon wafer and the electrode.

[0013] Furthermore, for the electrical properties, it is desirable to arrange an electrode in proximity to the surface treatment portion of the silicon wafer, apply a voltage between the silicon wafer and the electrode, and measure the attractive force between the electrode plates.

[0014] Furthermore, it is desirable that the attractive force between the electrode plates is measured with a strain gauge.

[0015] Furthermore, it is desirable to include a ring pole for placing the silicon wafer, a thin plate equally divided and arranged on a ring-shaped electrode ring, and the strain gauge attached to the thin plate and configured with a bridge circuit, to arrange the electrode ring with a gap from the silicon wafer, and to apply a voltage between the ring pole and the electrode ring to measure the attraction force between the electrodes.

[0016] In addition, the present invention is a method for surface modification of a silicon wafer using laser heat treatment, including: step 1 of measuring the reflectivity or absorptivity of the silicon wafer surface; step 2 of arranging an electrode in proximity to the surface treatment portion of the silicon wafer and measuring the capacitance of a capacitor formed between the silicon wafer and the electrode; and step 3 of determining the processing conditions of the laser heat treatment based on step 1 and step 2.

[0017] Furthermore, during the laser heat treatment process, it is desirable to perform step 1 and step 2, and to perform feedback control on the results to continue the processing.

Advantages of the Invention

[0018] According to the present invention, since the reflectivity or absorptivity of the silicon wafer surface is measured and the electrical properties are measured to diagnose the surface state of the silicon wafer, it can also be mounted on a laser surface modification machine. By diagnosing the surface state and confirming the repair effect, including during real-time processing (during surface modification), high-quality silicon wafers can be provided.

Brief Description of the Drawings

[0019]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Mode for Carrying Out the Invention

[0020] FIG. 1 is a block diagram showing a measuring unit for the reflectance or absorptance of light according to an embodiment, and FIG. 2 is a block diagram showing a measuring unit for the capacitance between a silicon wafer and an electrode and the attraction force between electrode plates. The machined affected layer is mainly in an amorphous silicon layer or a polycrystalline state. Although this machined affected layer is extremely thin, it greatly affects the mechanical, electrical, and optical properties.

[0021] In this embodiment, regarding the surface of the machined affected layer after grinding or etching treatment, the surface state is examined by measuring the reflectance (absorptance) and image analysis. Also, regarding the internal state at a depth of about several micrometers, a measuring laser with wavelengths of 532 nm and near-infrared light (785 nm) is irradiated to examine the reflectance (absorption).

[0022] Furthermore, by applying a voltage from the outside (charging the silicon wafer surface), the differences in the electrical properties (conductivity, capacitance, attraction force between electrode plates, etc.) of amorphous, polycrystalline silicon, and single-crystalline silicon are detected to examine the modification status. That is, the reflectance or absorptance of the surface of the silicon wafer 1 is measured, and the electrical properties are measured.

[0023] That is, in this embodiment, in order to diagnose the surface state 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, irradiate near-infrared light (785 nm) that is polarized or the like to obtain the reflectance or absorptance of the single crystal. (2) Considering the shape of the measurement surface 1-1 of the silicon wafer 1, apply visible light or light with a wavelength of 532 nm that is polarized or the like to obtain the reflectance or absorptance of the amorphous material. Note that the amorphous silicon layer has strong absorption of light with a wavelength of 532 nm. (3) Measure the surface shape (including roughness, etc.) by means of an image, contact, etc. (4) Obtain the differences in the electrical properties (electrical conductivity, capacitance, attraction force between electrodes, etc.) of the object to be processed (silicon wafer) before and after modification and during the modification.

[0024] 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 onto the surface as indicated by the arrow. The measurement light source (laser heat treatment) 2 is a measurement light source or a laser with wavelengths of 532 or 785 nm, and may pass through a polarizer. Then, the reflected light is detected by a camera or a detector 3 through a filter, analyzed, and the reflectance or absorption rate is evaluated and measured.

[0025] In the evaluation and measurement of the light reflectance (absorption), the reflectance of molten silicon is 30% higher than that of the solid, and the surface modification status can be examined by measuring the reflectance during surface modification. Note that in the measurement of the light reflectance (absorption rate), it is preferable to arrange a polarizer immediately after the laser output 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.

[0026] FIG. 2 shows the measurement of the capacitance 7 and the attraction force 6 between the electrodes of the silicon wafer 1 and the electrode 4 as the electrical characteristics in (4). In FIG. 2, the electrode 4 is arranged close to correspond to the surface treatment portion of the silicon wafer 1. Then, the capacitance 7 and the attraction force 6 between the electrodes are measured by applying a voltage 5 between the silicon wafer 1 and the electrode 4 and compared before and after the modification.

[0027] It is known that the electrical conductivity of molten silicon is more than 100 times higher than that of the solid. Therefore, the capacitance of the molten silicon can also be evaluated by measuring the electrical conductivity on the surface of the silicon wafer 1. The electrical conductivity changes as the conductivity of the molten silicon changes during the surface treatment, and changes as the capacitance 7 and the attraction force 6 between the electrodes of the capacitor formed between the silicon wafer 1 and the electrode 4. The status of the surface modification portion can be evaluated by observing or measuring the phenomenon of the change in the capacitance 7.

[0028] Figure 3 is a flowchart of surface modification (processing) and diagnosis using laser heat treatment. Surface modification (processing) and diagnosis efficiently and effectively perform surface modification by measuring or evaluating the surface state of the silicon wafer to be modified and performing laser irradiation under corresponding conditions. First, the reflectance or absorptance of the surface of the silicon wafer 1 and image analysis are measured 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 absorptance of the surface of the silicon wafer 1 is measured, and the capacitance 7 as an electrical property is measured. Then, the processing conditions are determined based on the measurements and evaluations in steps 1 and 2 (step 3).

[0029] During processing, the surface reflectance measurement and capacitance evaluation (change in electrical conductivity) are performed in the same manner as in steps 1 and 2, and the results are feedback-controlled to continue the processing (step 4).

[0030] Note that by processing with laser irradiation, it is possible to remove oxygen from the silicon wafer 1 and improve crystallinity, and by irradiating with a pulsed laser, it is possible to repair surface defects that are the processed modified layer on the surface of the silicon wafer 1.

[0031] In particular, after grinding the silicon wafer 1, by changing 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 corresponding to the surface shape thereof and irradiating with a pulsed laser, the influence of processing stress can be eliminated and the surface can be modified into a uniform one.

[0032] Also, the processing by pulsed laser (nanosecond) irradiation melts the amorphous layer of the processed modified layer at a nanosecond speed. And the melting by pulsed laser (nanosecond) irradiation promotes recrystallization (epitaxial growth) with aligned crystal orientations and can eliminate crystal defects generated by mechanical processing.

[0033] After processing, surface reflectance measurement, image analysis, and capacitance evaluation (Steps 5 and 6) are performed in the same manner as in Step 1 and Step 2, and quality evaluation is carried out to determine whether it is OK or NG with respect to the specifications (Step 7). As described above, since the silicon wafer 1 diagnoses the surface state and confirms the repair effect even during processing, it can be made of high quality.

[0034] FIG. 4 is a configuration diagram for measuring the attraction force 6 between the electrode plates. FIG. 5 is a plan view of the electrode plate ring 10, and FIG. 6 is a side view. The attraction force 6 shown in FIG. 2 is measured by the 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).

[0035] The thin plates 10-1 are arranged on the upper surface of the electrode plate ring 10 with compliance at 120° equal divisions. The strain gauges 10-2 are respectively attached near the centers of the thin plates 10-1. Also, the three strain gauges 10-2 form a bridge circuit to detect the stress applied to the thin plates 10-1.

[0036] The voltage 5 is applied between the ring pole 11 and the electrode 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. Note that the ring pole 11 may be attached to a normal rotating table for placing the silicon wafer 1.

[0037] As shown in FIG. 6, the electrode plate ring 10 is provided with claw portions 10-3 that can rotate. The claw portions 10-3 can rotate inward of the electrode plate ring 10 as shown by the arrow in FIG. 6(a) and are fixed as shown in FIG. 6(b) at a predetermined position (90° in FIG. 6). Therefore, the silicon wafer 1 and the electrode plate ring 10 are arranged with a gap as shown in FIG. 6(b) to form the capacitance 7 in FIG. 2.

[0038] That is, the electrode 4 shown in Fig. 2 is arranged to sandwich the silicon wafer 1, and the attraction force 6 between the electrode 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 micrometers. The attraction force 6 between the electrode plates enables the discrimination of the surface modification status because the conductivity (mobility, specific resistance) varies greatly among amorphous silicon, polycrystalline silicon, and single-crystalline silicon.

[0039] 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 part 10-3 is rotated inside the electrode plate ring 10, and the voltage 5 is applied between the ring pole 11 and the electrode plate ring 10. (3) When the attraction force 6 between the electrode plates is generated, stress is applied to the electrode plate ring 10 and it deforms. (4) The stress is detected by the strain gauge 10-2 attached to the thin plate 10-1 arranged on the upper surface of the electrode plate ring 10 and output as an electrical signal.

[0040] According to the measurement of the attraction force 6 between the electrode plates described above, it is possible to measure with high sensitivity the differences in the electrical properties (electrical conductivity, capacitance, attraction force between electrode plates, etc.) of the object to be processed (silicon wafer) before and after modification and during modification.

Explanation of Reference Numerals

[0041] 1... Silicon wafer 1-1... Measurement surface 2... Light source for measurement 3... Detector 4... Electrode 5... Voltage 6... Attraction force between electrode plates 7... Capacitance 10... Electrode plate ring 10-1... Thin plate 10-2... Gauge 10-3... Claw part 11... Ring pole

Claims

1. A method for diagnosing the surface state of a silicon wafer in the surface modification of a silicon wafer using laser heat treatment, including at least measuring the electrical properties of the surface of the silicon wafer, wherein the electrical properties include the attractive force between the electrodes disposed in proximity to the surface treatment portion of the silicon wafer, and the method for diagnosing the surface state of the silicon wafer.

2. A method for diagnosing the surface state of a silicon wafer in the surface modification of a silicon wafer using laser heat treatment, including at least measuring the electrical properties of the surface of the silicon wafer, wherein the electrical properties include the measured value by a strain gauge of the force generated between the electrodes disposed in proximity to the surface treatment portion of the silicon wafer, and the method for diagnosing the surface state of the silicon wafer.

3. A method for surface modification of a silicon wafer using laser heat treatment, including at least disposing an electrode in proximity to the surface treatment portion of the silicon wafer, and step A of measuring the electrical properties including the attractive force between the electrodes generated between the surface treatment portion of the silicon wafer and the electrode, or the measured value by a strain gauge of the force generated between the electrodes; step B of determining the processing conditions of the laser heat treatment based on step A; and the method for surface modification of a silicon wafer having the above steps.

4. The method for surface modification of a silicon wafer according to claim 3, wherein step A is performed during the laser heat treatment, and the processing is continued by feedback control of the result.

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