JP3727548B2 - Laser processing equipment for silicon substrates - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a laser processing apparatus in which molten silicon does not scatter during laser drilling of a silicon substrate constituting a semiconductor device.
[0002]
[Prior art]
Silicon is used as the most typical substrate material in semiconductor devices, particularly semiconductor integrated circuits (ICs), microelectronic devices, or precision measurement devices. As described above, the silicon substrate is frequently used because an industrially high-purity silicon wafer can be manufactured at a low cost, and furthermore, a chemically extremely stable oxide film (SiO ₂ ) is formed on the silicon substrate. This is because it is possible to easily achieve insulation separation between elements important for manufacturing a highly integrated device.
[0003]
For example, in the manufacture of an IC by a batch system, a large number of devices are simultaneously formed on a single silicon wafer, but the individual devices must be electrically isolated from each other. The insulation separation required for the device characteristics can be achieved by forming an oxide film of about 0.3 to 1.0 μm on the wafer.
[0004]
On the other hand, with the miniaturization of devices, development of micromachining technology is required in the manufacturing process. Correspondingly, a processing method using laser light irradiation has been developed as means for processing a work piece in a non-contact manner with high accuracy and high efficiency, such as cutting, drilling, metal welding or heat treatment.
[0005]
This laser processing apparatus is classified into a solid-state laser, a gas laser, an excimer laser, a metal vapor laser, a dye laser, and the like depending on the light emitting medium. The ruby as a solid laser light source, YAG (yttrium aluminum garnet), glass, alexandrite, _CO 2 as a gas laser source, CO, Ar ions, ArF as excimer laser light source, KrF, XeCl, XeF, metal vapor A Cu ion is known as a laser light source, and a Dye laser is known as a dye laser.
[0006]
Factors that influence the processing characteristics of these lasers include the light collection characteristics, the beam wavelength that affects the beam reflectivity of the workpiece, the output configuration required to optimize the heat input to the workpiece, and the processing There is an average output of the laser that affects the ability of the laser. Therefore, considering the processing characteristics of various lasers, it is necessary to use different lasers according to the material and thickness of the workpiece, the purpose of processing, etc., but in general, a large output can be obtained. Or, CO ₂ lasers are widely used.
[0007]
FIG. 1 is a diagram showing laser output in a temporal mode. Laser oscillation forms include CW (continuous wave) shown in (a) and pulses that are periodically and intermittently irradiated. Further, the pulse oscillation is classified into a normal pulse shown in (b) and a Q-switch pulse having a high peak value but a very short irradiation time as shown in (c).
[0008]
Usually, when there is a possibility of cracking in the workpiece due to rapid heating, such as when cutting or drilling the workpiece, a processing method that repeatedly irradiates pulses is adopted, and metal welding CW processing is suitable for heat treatment and the like.
[0009]
Furthermore, it is necessary to change the energy density with which the surface of the workpiece is irradiated depending on the processing purpose. When cutting or drilling a workpiece, since it is necessary to melt and evaporate the workpiece, a laser having a high energy density is irradiated. For example, when drilling a silicon substrate with a YAG laser (wavelength: 532 μm), it is usually necessary to process with a laser having an energy density of about 110,000 J / m ² .
[0010]
However, when the energy density of the laser irradiated to the workpiece is high, there is a phenomenon that the molten silicon substrate scatters in the portion irradiated with the laser. When such scattering occurs, the isolation between elements, which is the most important element in a semiconductor device, is destroyed, and the insulation characteristics are hindered. This causes a problem of significantly reducing device reliability.
[0011]
An example of a sophisticated device is a ring-type vibration gyro. Conventionally, various improvements have been studied in order to improve the reliability of the vibration gyro, and as a part thereof, a method of adjusting the driving state of the semiconductor vibrator constituting the ring-type vibration gyro has been proposed (Japanese Patent Laid-Open No. 11/1997). -83498). Even in the method proposed here, it is necessary to study a drilling method with excellent processing accuracy in order to ensure insulation characteristics.
[0012]
FIG. 2 is a diagram schematically showing the configuration of the ring-type vibrating gyroscope. As shown in the figure, the ring-type vibrating gyroscope 1 has a suspension having a configuration in which a ring 2 is suspended by a substantially S-shaped beam 3. Further, although not shown, a magnet is installed inside the ring 2, and a magnetic field is generated around the ring 2. On the other hand, a current flows through the ring 2 via the substantially S-shaped beam 3. The ring 2 receives a Lorentz force and generates a vibration mode in the radial direction.
[0013]
The ring-type vibrating gyroscope having such a configuration is processed with high accuracy by applying micromachining technology, but there may be variations in performance as a sensor head. Specifically, this is a case where an angular error (α) in the driving position of the vibration mode or a variation in resonance frequency (F split) in each vibration direction occurs due to unevenness in mass or rigidity in the circumferential direction of the ring. Therefore, in the adjustment method proposed in the above publication, the angular error (α) in the vibration mode and the variation in the resonance frequency of the ring (F split) are detected, and the laser beam is applied to the assumed machining position determined based on the detection result. Irradiation is performed to remove a part of the silicon substrate.
[0014]
FIG. 3 is an enlarged view of the ring formed on the silicon substrate as viewed from above. The ring 2 has a configuration in which a strip electrode 5 having a mark 6 is installed on a silicon substrate 4. Here, the mark 6 is an angle indicating mark that is installed to specify the position when the assumed processing position determined based on the detected angle error or the like is irradiated with the laser. In the adjustment method proposed in the above-mentioned Japanese Patent Application Laid-Open No. 11-83498, by using the position of the angle indicating mark as a guide, a part of the silicon substrate is removed by laser irradiation, and the hole 7 is formed, whereby the ring The balance of the mass in the circumferential direction is adjusted to prevent variation in the driving state of the vibrator.
[0015]
FIG. 4 is an enlarged view of the configuration of the AA cross section in FIG. As shown in the figure, in the silicon substrate 4, an oxide film (SiO ₂ ) 4-2 is formed as an insulating layer on the surface of a silicon wafer 4-1, and a strip electrode 5 is formed on the oxide film. For this reason, since the silicon wafer 4-1 and the strip electrode 5 are separated by the oxide film 4-2, the intended electrical insulation performance is ensured.
[0016]
However, when the silicon substrate 4 is drilled by the above-described laser irradiation with a normal energy density of 110,000 J / m ² or more, a thread-like splatter 8 is generated. A decrease in insulation may occur with the electrode 5 (see the left scattering 8 in the figure), which may reduce the reliability of the vibration gyro.
[0017]
To simply prevent the above-described scattering 8, if a hole is formed by repeatedly irradiating a laser having a low energy density, the scattering can be suppressed to some extent. However, such repeated irradiation with a laser having a low energy density has a large time loss even when processing a shallow hole, and it is difficult to process a deep hole. Further, silicon vaporized by laser irradiation is again deposited (deposited) in the vicinity of the processed hole, and the processed shape is deteriorated.
[0018]
In order to solve such a problem, the present inventors modified the silicon substrate surface by laser beam irradiation and then drilled to prevent the generated molten silicon from scattering and to improve the processing accuracy. An excellent laser processing method was developed (Japanese Patent Application No. 2001-38845 (Japanese Patent Laid-Open No. 2002-239765)).
[0019]
[Problems to be solved by the invention]
The present invention is an apparatus that embodies the above laser processing method, and provides a laser processing apparatus that prevents scattering of molten silicon, has excellent processing accuracy, and can efficiently drill a silicon substrate. The purpose is to do.
[0020]
[Means for Solving the Problems]
The gist of the present invention is the following laser processing apparatus for silicon substrate (1) and (2).
[0021]
(1) A processing device that adjusts the characteristics of a silicon substrate by laser drilling, a characteristic inspection unit that measures the characteristics of the workpiece, and a processing position that determines the assumed processing position based on the measurement data of the characteristic inspection unit Based on the data stored in the determination unit, the assumed processing position and the position of the processed hole, of which processing has already been performed, and the data stored in the processing position storage unit, the presence / absence of processing is determined and the processing is performed. The processing start determination part that transmits the processing start position and the position of the processed hole to be processed first among the assumed processing positions that are not processed, and when there is no processed hole within a radius of 80 μm of the processing start position If a processing pattern to be processed after the modification processing is selected, and there is a processed hole within a radius of 80 μm of the processing start position, the modification processing is not performed. A machining pattern determining unit for selecting a machining pattern to be machined, a machining control unit for adjusting machining conditions so that the machining pattern selected by the machining pattern determining unit can be performed, and a machining unit including at least a laser oscillator and a machining head A laser processing apparatus for a silicon substrate comprising:
[0022]
(2) A processing device that adjusts the ring characteristics of a ring-type vibrating gyroscope by laser drilling, a characteristic inspection unit that measures the vibration characteristics of the ring, and a process that determines the expected processing position based on the measurement data of the characteristic inspection unit Based on the data stored in the position determination unit, the assumed machining position and the position of the machined hole that has already been machined, and the data stored in the machining position storage unit, the presence or absence of machining is determined, and machining is performed. The processing start determination position that transmits the processing start position to be processed first and the position of the processed hole among the assumed processing positions that have not been processed to the processing pattern determination unit, ± 1 ° of the processing start position (center angle of the ring) If there is no machined hole within the range, select the machining pattern to be machined after the modification treatment, and within the range of ± 1 ° (ring center angle) of the machining start position If there is a machined hole, adjust the laser conditions so that drilling is performed with the machining pattern selected by the machining pattern determination unit that selects the machining pattern to be processed without performing the modification process. A laser processing apparatus for a ring-type vibration gyro comprising a processing control unit and a processing unit including at least a laser transmitter and a processing head.
[0023]
In the above (1) and (2), when the modification treatment is performed, it is performed by irradiating a laser whose energy density on the processed surface is 6,500 to 55,000 J / m ² .
[0024]
DETAILED DESCRIPTION OF THE INVENTION
FIG. 5 is a schematic diagram showing an example of the apparatus configuration of the present invention. As shown in the figure, the laser processing apparatus of the present invention is configured so that the workpiece 11 is measured at a measurement position directly below the probe card 13-1 (left side of the arrow in the figure) or a processing position immediately below the processing head 16-3 (in the arrow of the figure XY axis moving table 12 for moving the workpiece 11 to the laser irradiation position at the time of processing, a characteristic inspection unit 13 having a probe card 13-1 and a measuring instrument 13-2, a processing position determination unit 14-1, a machining position storage unit 14-2, a machining process determination unit 14-3 and a machining pattern determination unit 14-4, a machining control unit 15 that adjusts laser conditions such as a Q switch frequency and an irradiation time, In addition, it comprises a processing section 16 comprising a laser oscillator 16-1, an optical fiber 16-2 and a processing head 16-3, and further adjusts the focal position of the laser in conjunction with the Z-axis motor 17 and the CCD camera 18. Auto focusing It is a device with a knit 19.
[0025]
FIG. 6 is a flow chart when laser processing is performed on a workpiece by the laser processing apparatus of the present invention. An embodiment of the present invention will be described with reference to FIG. In the following description, the assumed processing position refers to a position (a plurality of holes) to be drilled on the silicon substrate, and the processed hole position is the actual processing position among the assumed processing positions. The position of the hole that has been processed by the device of the invention means the processing start position, and the processing start position is the position where the drilling processing is first performed among the assumed processing positions that have not been processed by the device of the present invention. And
[0026]
(1) Characteristic Inspection of Work Material The work material 11 is first set at a measurement position immediately below the probe card 13-1 by the XY axis moving table 12, and the characteristic is measured by the characteristic inspection unit 13. The characteristic inspection unit 13 transmits the measurement data to the machining position determination unit 14-1. For example, when the workpiece is a ring-type vibration gyro, the characteristic inspection unit 13 measures the ring characteristic for grasping the variation (F split) and angle error (α) of the resonance frequency of the ring, and obtains the measurement data. The data is transmitted to the machining position determination unit 14-1.
[0027]
As a result of the inspection, the workpiece 11 is sent to the next process when it satisfies a predetermined standard, and does not need to be processed by the laser processing apparatus of the present invention, but does not satisfy the predetermined standard. In this case, the machining position is set at a machining position just below the machining head 16-3 by the XY axis moving table.
[0028]
(2) Determination of the processing assumed position of the workpiece The processing position determination unit 14-1 determines the processing assumed position on the workpiece 11 based on the received measurement data, and processes it in the processing position storage unit 14-2. Transmit data at the assumed position. For example, when the workpiece is a ring-type vibration gyro, the machining position determination unit 14-1 calculates an F split value and an α value based on the received measurement data, and produces the value on the ring based on the F split value. In addition to determining the number of processing holes to be processed, the position of the processing holes to be formed on the ring is determined based on the α value, and the number and positions of the processing holes determined in the processing position storage unit 14-2 (that is, processing assumptions) Position).
[0029]
The holes that have already been processed are transmitted from the processing determination unit 14-3 to the processing position storage unit 14-2 as the positions of the processed holes.
[0030]
(3) Determination of laser processing pattern The processing determination unit 14-3 determines the presence / absence of processing based on data stored in the processing position storage unit 14-2. Specifically, the machining processing determination unit 14-3 stores the position of the machined hole in the machining position storage unit 14-2 after one machining is completed, and further stores the position in the machining position storage unit 14-2. When all of the processing at the assumed processing position is completed, the workpiece 11 is moved to a position directly below the probe card 13-1 by the XY axis movement table 12, and the characteristic inspection unit 13 receives the above (1 ). On the other hand, when there is a position where the machining is not performed among the assumed machining positions stored in the machining position storage unit 14-2, the machining process determination unit 14-3 sets the machining start position in the XY axis movement table 12. The workpiece 11 is moved to the laser irradiation position, and the machining start position and the position of the machined hole are transmitted to the machining pattern determination unit 14-4.
[0031]
The processing pattern determination unit 14-4 selects a processing pattern to be applied to the processing start position based on the received processing assumed position data and processed hole position data, and transmits the determined processing pattern to the processing control unit 15.
[0032]
Specifically, if there is no processed hole within a radius of 80 μm at the processing start position, the processing pattern determination unit 14-4 performs a drilling process after the modification process (hereinafter, processing pattern A). If a processed hole exists within a radius of 80 μm at the processing start position, a processing pattern (hereinafter referred to as processing pattern B) for performing drilling without selecting a modification process is selected.
[0033]
This is because when there is no processed hole within a radius of 80 μm at the processing start position, the molten silicon will be scattered during the drilling process unless it has been subjected to the modification process beforehand. This is because, when there is a processed hole within a radius of 80 μm at the position, the molten silicon does not scatter during the drilling process without performing the modification treatment in advance. Therefore, the processing pattern selection criterion was set to a radius of 80 μm at the processing start position.
[0034]
For example, when the workpiece is a ring-type vibration gyro, the machining pattern determination unit 14-4 determines that the machining pattern is not present when the machining hole is within the range of ± 1 ° (ring central angle) of the machining start position. A is selected, and if there is a machining hole within a range of ± 1 ° (ring central angle) of the machining start position, a machining pattern B is selected.
[0035]
As shown in FIG. 3, the angle indicating marks 6 are provided on the ring of the ring-type vibrating gyroscope, and the interval between the marks is 1 ° (the center angle of the ring). Since the distance is 3 mm, the interval between the marks is 52 μm. Therefore, in the case of a ring-type vibrating gyroscope, if a machining hole already exists within the range of ± 1 ° (ring central angle) of the machining start position, the modification effect by laser irradiation when the hole is produced is Therefore, the processing pattern selection criterion was set to ± 1 ° of the processing start position (the center angle of the ring).
[0036]
In addition, said modification | reformation process is realizable by irradiating with the laser whose energy density in a process surface is 6,500-55,000J / m < ² >. This is because if the energy density on the machined surface is as low as less than 6,500 J / m ² , silicon cannot be modified substantially, and the energy density on the machined surface exceeds 55,000 J / m ^2. Then, the shape of the scattered silicon becomes a thread-like shape, and as shown in FIG. 4, the possibility of a decrease in insulation between the silicon and the electrode portion increases. Therefore, the energy density on the processed surface was set to 6,500-55,000 J / m ² . More desirably, it is 6,500 to 30,000 J / m ² .
[0037]
Hereinafter, an example of a processing pattern selection method in the processing pattern determination unit 14-4 will be described.
[0038]
FIG. 7 is a diagram schematically showing the assumed machining position. It should be noted that the boxes (1) to (5) in the figure have an interval of 80 μm or less, and the interval between the two boxes exceeds 80 μm. In the figure, “●” indicates a processed position, and “◯” indicates a processing start position. As shown in Fig. 7 (a), when drilling the box (3) with the holes already machined in the box (1) and box (5), select the above-mentioned machining pattern A. Drilling must be done. This is because the modification effect by laser irradiation when processing the box (1) or box (5) is applied is up to the box (2) or box (4), and the box (3) is processed. In this case, it is possible to prevent the molten silicon from scattering unless the modification treatment is performed in advance. On the other hand, as shown in FIG. 7 (b), when the hole is to be drilled in the box (3) in the state where the box (2) and the box (5) have the processed holes, the above-mentioned processing pattern B is selected. May be drilled. This is because the modification effect by laser irradiation when processing the box (2) extends to the box (3), so that even if the modification treatment is not performed in advance, the molten silicon splatters. Because there is no.
[0039]
(4) The processing control unit 15 sets laser conditions such as the Q switch frequency and the irradiation time based on the processing pattern determined by the processing pattern determination unit 14-4, and the energy of the laser light emitted from the processing unit 16 Adjust the density. In this way, the workpiece 11 is processed efficiently without the molten silicon being scattered by the processed portion 16.
[0040]
【The invention's effect】
According to the present invention, it is possible to prevent scattering of molten silicon generated when processing a silicon substrate by laser light irradiation, to ensure excellent processing accuracy, and to efficiently drill a hole in the silicon substrate. .
[Brief description of the drawings]
FIG. 1 is a diagram showing laser output in a temporal mode.
FIG. 2 is a diagram schematically showing a configuration of a ring-type vibrating gyroscope.
FIG. 3 is an enlarged view of a ring formed on a silicon substrate as viewed from above.
4 is an enlarged view of the configuration of the AA cross section in FIG. 3; FIG.
FIG. 5 is a schematic diagram showing an example of the apparatus configuration of the present invention.
FIG. 6 is a flow chart when laser processing is performed on a workpiece by the laser processing apparatus of the present invention.
FIG. 7 is a diagram schematically showing an assumed processing position.
[Explanation of symbols]
1. Ring-type vibrating gyroscope, 2. Ring, 3. An approximately S-shaped beam,
4). Silicon substrate, 4-1. Silicon wafer, 4-2. 4. oxide film, Strip electrode,
6). Mark, 7 Hole, 8. Splattered,
11. Work material, 12. XY axis movement table, 13. Characteristic inspection department,
13-1. Probe card, 13-2. Measuring instrument, 14. PC, 14-1. Processing position determination unit,
14-2. Processing position storage unit, 14-3. Machining processing judgment part, 14-4.
15. Processing control unit, 16. Processing part, 16-1. Laser oscillator,
16-2. Optical fiber, 16-3. Processing head, 17. Z-axis motor,
18. CCD camera, 19. Auto focusing unit

Claims (3)

A processing apparatus that adjusts the characteristics of a silicon substrate by laser drilling, a characteristic inspection unit that measures the characteristics of a workpiece, a processing position determination unit that determines a processing assumed position based on measurement data of the characteristic inspection unit, Processing position storage unit that stores the assumed processing position and the position of a processed hole that has already been processed, and whether or not processing is performed based on data stored in the processing position storage unit, and processing that has not been processed A processing determination position that transmits the processing start position to be processed first and the position of the processed hole among the assumed positions to the processing pattern determination unit, and when there is no processed hole within a radius of 80 μm of the processing start position, Select a machining pattern to be machined after the modification process, and if there is a machined hole within a radius of 80μm at the machining start position, add a modification pattern without any modification process. A processing pattern determining unit for selecting a processing pattern to be performed, a processing control unit for adjusting processing conditions so that the processing pattern selected by the processing pattern determining unit can be performed, and a processing unit including at least a laser oscillator and a processing head A laser processing apparatus for a silicon substrate provided. A processing device that adjusts the ring characteristics of a ring-type vibration gyro by laser drilling, a characteristic inspection unit that measures the vibration characteristics of the ring, and a processing position determination unit that determines the expected processing position based on the measurement data of the characteristic inspection unit The processing position storage unit for storing the assumed processing position and the position of the processed hole which has already been processed, the presence or absence of processing is determined based on the data stored in the processing position storage unit, and the processing is not performed A processing determination part that transmits the processing start position and the position of the processed hole to be processed first among the assumed processing positions, to within a range of ± 1 ° (center angle of the ring) of the processing start position If there is no machined hole, select the machining pattern to be machined after the modification process and add it within the range of ± 1 ° (ring center angle) of the machining start position. When there is a finished hole, a machining pattern determination unit that selects a machining pattern to be processed without performing a modification process, and a process that adjusts the laser conditions so that drilling is performed with the machining pattern selected by the machining pattern determination unit A laser processing apparatus for a ring-type vibration gyro, which includes a control unit and a processing unit including at least a laser transmitter and a processing head. 3. The laser processing apparatus for a silicon substrate according to claim 1, wherein the modification treatment is performed by irradiating a laser having an energy density of 6,500 to 55,000 J / m ² on a processing surface.

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