CN218016452U - Ultra-short pulse semiconductor wafer recessive cutting device - Google Patents

Abstract

The utility model relates to an ultrashort pulse semiconductor wafer implicit cutting device. The light source part is arranged before the chirp pulse generating part, and is used to send pulse laser to the chirp pulse generating part; the chirp pulse generating part is arranged between the light source part and the dispersion Between the modulation parts, it is used to widen the ultrashort pulse laser light from the light source part, so that the wide pulse generated by the widened pulse laser is compensated by the dispersion modulation part; the dispersion modulation part sets the focal point inside the semiconductor wafer through the focusing part, so that the focus The dispersion at the point is fully compensated; the wafer cutting platform is set under the focusing part, which is used to place the semiconductor wafer, and the cutting position of the semiconductor wafer can be changed by moving the wafer cutting platform; the trajectory observation and feedback part is used to observe the focus position , and the feedback signal is transmitted to the dispersion modulation part and the focusing part for adjusting the focus position and size. The utility model can stabilize the position of the laser focus, reduce the focus floating caused by nonlinear effects, and improve the precision of laser cutting.

Description

Ultrashort pulse semiconductor wafer implicit cutting device

technical field

The utility model relates to the field of chip processing, in particular to an ultrashort pulse semiconductor wafer implicit cutting device.

Background technique

The core of smart devices is semiconductor chips, high-end manufacturing technologies such as chip processing, hidden cutting, and low-k slotting. Wafer implicit cutting is an essential process in chip processing. The size of high-end chips is at the nanometer scale, so the requirements for the wafer cutting process must be extremely precise. Due to the relatively strong thermal effect of the nanosecond/picosecond light source, it is difficult to achieve high-precision hidden cutting.

In contrast, the femtosecond laser has a small thermal effect and high cutting precision. Therefore, high-end cutting of semiconductor wafers can be achieved with femtosecond lasers. However, during the focusing process of femtosecond pulses, due to the high peak power, the nonlinear effect on the propagation path cannot be ignored. Nonlinear effects lead to spatial self-focusing of the laser pulse, which eventually causes the focal point to move forward in the direction of the laser path during cutting. Spatial self-focusing effect is a typical nonlinear effect of high-order process in light field. When the laser peak power reaches 100MW, it is a physical process that must be considered in the processing process. The degree of spatial self-focusing is proportional to the square of the light intensity, so any disturbance of the laser output energy and the mechanical vibration of the cutting system will be amplified by nonlinear effects, which will eventually lead to the uncertainty of the focus position during the implicit cutting process of the semiconductor wafer.

Many methods are used to reduce the uncertainty in the semiconductor wafer cutting process, such as reducing the laser power, increasing the laser pulse width, and using a focusing objective lens with a large numerical aperture (NA) to focus. However, semiconductor wafer cutting often requires a higher peak power to reach the damage threshold of very semiconductor wafers (such as SiC wafers), so the method of reducing laser power and increasing laser pulse width is not suitable for most semiconductors with high damage threshold wafer. At the same time, increasing the laser pulse width will increase the thermal effect of the cutting process, which greatly reduces the cutting accuracy. Focusing with a focusing objective lens with a high numerical aperture (NA) can reduce the nonlinear effect on the laser focusing path. However, the focal point of the high NA objective lens is too small, so the cutting track is too narrow, which greatly affects the cutting efficiency of the semiconductor wafer. Considering that the current domestic demand for chips is growing, but technological development is still subject to the foreign environment, my country's cutting-edge enterprises are gradually investing funds and personnel for independent research and development. In this form, the accuracy of chip cutting and processing is particularly important. Therefore, there is a need for a semiconductor wafer cutting device that reduces the non-linear effect on the cutting path while ensuring that the peak power of the focus point remains unchanged.

Contents of the invention

The purpose of this utility model is to provide an ultra-short pulse semiconductor wafer implicit cutting device that reduces the nonlinear effect in the cutting process. The device and method can stabilize the position of the laser focus and reduce the focus floating caused by the nonlinear effect. Improve the accuracy of laser cutting.

In order to achieve the above object, the technical solution of the present utility model is: an ultrashort pulse semiconductor wafer implicit cutting device, including a light source unit, a chirped pulse generation unit, a dispersion modulation unit, a focusing unit, a wafer cutting platform, a track observation and The feedback part, the light source part is arranged before the chirped pulse generating part, and is used to send pulsed laser light to the chirped pulse generating part; the said chirped pulse generating part is arranged between the light source part and the dispersion modulation part, and is used for The ultrashort pulse laser of the part is broadened, so that the wide pulse generated by the widened pulse laser is compensated by the dispersion modulation part; the dispersion modulation part sets the focal point inside the semiconductor wafer through the focusing part, so that the dispersion at the focal point is completely compensated; The wafer cutting platform is arranged under the focusing part, and is used to place the semiconductor wafer, and the cutting position of the semiconductor wafer is changed by moving; the track observation and feedback part is arranged above the semiconductor wafer, and is used to observe the focus position, and The feedback signal is transmitted to the dispersion modulation unit and the focusing unit for adjusting the position and size of the focus.

Further, the light source of the light source part is any one of solid, gas, and optical fiber, and the width of the laser pulse output by the light source part is 10 fs-10 ps.

Further, the chirped pulse generator adopts a traditional Martinez grating structure for generating positive chirp, or adopts a pulse propagation medium of a certain length for generating positive chirp when the pulse propagates through the medium; and adopts a traditional Treacy grating structure, It is used to generate negative chirp, or a pulse propagation medium of a certain length is used to generate negative chirp when the pulse propagates through the medium.

Further, the dispersion modulation part is composed of a glass slide, a concave lens, two dichroic mirrors, two gratings, a linear motor, and a Fresnel zone plate; after the widened light beam passes through the slide, it hits two 45° On the reflected dichroic mirror, the beam spot is expanded by a concave lens. The expanded beam spot hits the first grating, and then enters the second grating on the linear motor and then enters the Fresnel zone plate.

Further, the combination of the Fresnel zone plate and the grating is fabricated on the same substrate, the position of the first grating is fixed, the second grating is placed on the linear motor, the first grating and the second grating are the same type of grating, the first grating and the second grating The distance between them is regulated by the feedback signal of the trajectory observation and feedback part.

Further, the focusing part is composed of a concave lens, a focusing objective lens, a linear motor, and a dichroic mirror. The compensated pulsed beam is focused on the dichroic mirror reflected at 45° through the concave lens, and after being reflected to the focusing objective lens, it is focused on the semiconductor inside the wafer.

Further, the focusing objective lens is placed on the linear motor, and the distance between the second focusing objective lens and the semiconductor wafer is regulated by the feedback signal of the trajectory observation and feedback part.

Further, the wafer cutting platform is composed of a marble beam, a marble platform, a θ-axis motor, an X-axis linear motor, and a Y-axis linear motor.

Further, the trajectory observation and feedback part is composed of a position detection sensor and a microscopic objective lens, and the position detection sensor transmits the feedback signal of the trajectory observed through the microscopic objective lens and the focus position to the dispersion modulation part and the focusing part for Control the light intensity at the focal point and the focal point position during the cutting process.

Further, the ultrashort pulse semiconductor wafer implicit cutting device is used for semiconductor wafer cutting, semiconductor wafer surface grooving, chip dicing and low-k chip grooving.

Compared with the prior art, the utility model has the following beneficial effects:

1. The utility model provides a semiconductor wafer cutting method that reduces the nonlinear effect on the cutting path and ensures that the peak power of the focus point remains unchanged. The ultrashort pulse light source is used as the cutting light source. The high peak power of the ultrashort pulse at the focal point can ensure the cutting accuracy, and there are no burrs, blackening, edge collapse and other adverse conditions during the cutting process. At the same time, the weak nonlinear effect (self-focusing effect) on the cutting path controls the translation of the focus position along the laser path within 100nm.

2. Higher cutting speed. Compared with the current mainstream high-NA objective lens focusing and cutting, the diameter of the focal point of our device is adjustable from 1-30 μm. Due to the fact that in the actual wafer cutting process, the width of the dicing line is often 10-30 μm. Compared with the high NA objective lens focusing and cutting that requires multiple scans, our device only needs to adjust the cutting lens group according to the required cutting line width in advance, so that the focal point matches the actual required cutting line width, and only a single scan is required to achieve cutting.

3. Excellent adaptability. Observe the cutting trajectory during the scanning process, adjust the pre-chirp amount, capture the enlarged wafer cutting trajectory on the microscope objective lens by the CCD, and automatically adjust the position of the components on the linear motor to achieve chirp compensation on the cutting path, so that it can adapt to Cutting lanes of various widths.

Description of drawings

Fig. 1 is the structural representation of the ultrashort pulse semiconductor wafer implicit cutting device of the present utility model;

Fig. 2 is the actual optical path diagram of the ultrashort pulse semiconductor wafer implicit cutting device of the present invention;

Fig. 3 is the whole machine integration diagram in the actual process in the utility model.

detailed description

Below in conjunction with accompanying drawing and embodiment the utility model is described in detail, but present embodiment can not be used for limiting the utility model, and every similar method and similar variation thereof that adopts the utility model all should be included in the protection scope of the utility model.

As shown in Figures 1 and 2, the semiconductor wafer implicit cutting device of the present invention includes a light source unit 100, a chirped pulse generation unit 200, a dispersion modulation unit 300, a focusing unit 400, a wafer cutting platform 500, and trajectory observation and feedback. Department 600 etc.

After receiving the light source from the light source unit 100, the chirped pulse generator 200 expands the ultrashort pulse of the light source unit by adding a large amount of chirp, and the generated wide pulse is compensated by the dispersion modulation unit. The dispersion modulation part 300 sets the focal point inside the wafer through the focusing part 400, and the dispersion at the focal point is completely compensated. The semiconductor wafer is placed on the wafer cutting platform 500, and the platform moves to change the cutting position of the semiconductor wafer. The trajectory observation and feedback unit 600 is arranged on the semiconductor wafer for observing the focus position, and the feedback signal is transmitted to the dispersion modulation unit 300 and the focus unit 400 to change the focus position and size.

Preferably, the light source of the light source unit 100 may be a laser system such as solid, gas, or optical fiber, and the light source unit outputs pulsed laser light with a pulse width of 10 fs-10 ps.

Preferably, the chirped pulse generator 200 can generate positive chirp through a traditional Martinez grating structure (or its equivalent structure), or allow the pulse to propagate through a medium of a certain length to generate positive chirp. Negative chirp can be generated by the traditional Treacy grating structure (or its equivalent structure), and negative chirp can also be generated by allowing the pulse to propagate through a medium of a certain length.

Preferably, the dispersion modulator 300 is composed of a concave lens 301 , a first grating 302 , a second grating 303 , a first linear motor 304 , and a Fresnel zone plate 305 . The combination of Fresnel zone plate and grating can be fabricated on the same substrate. The dispersion modulating part ensures that the generated high-order dispersion is conjugate to the chirped pulse generating part, thereby ensuring that the high-order dispersion is compensated during propagation. The position of the first grating 302 is fixed, and the second grating 303 is placed on the first linear motor 304 .

Preferably, the focusing unit 400 is composed of a concave lens 401, a focusing objective lens 402, a linear motor 2 403, and a dichroic mirror 3 404, and focuses the pulse generated by the dispersion modulation unit 300 inside the wafer. The focusing objective lens 2 402 is placed on the linear motor 2 403 , and the distance between it and the semiconductor wafer is regulated by the feedback signal from the trajectory observation and feedback unit 600 .

Preferably, the wafer cutting platform 500 is composed of a marble beam 501 , a marble platform 502 , a θ-axis motor 503 , an X-axis linear motor 504 , and a Y-axis linear motor 505 . The marble beam 501 is rigidly connected to the wafer cutting platform 500 for placing the light source unit 100; the marble platform 502 is used for placing the wafer to be processed; the θ-axis motor 503 is placed in the chassis for controlling the X-axis linear motor 504 and the Y-axis The linear motor 505 ; the X-axis linear motor 504 and the Y-axis linear motor 505 can change the position of the wafer in the directions of the X and Y axes respectively. The semiconductor wafer is placed on the wafer cutting platform 500, and the cutting position can be changed by moving the platform.

Preferably, the trajectory observation and feedback part 600 is composed of a position detection sensor 601 and a microscopic objective lens 602. The position detection sensor 601 observes the trajectory and the focus position through the microscopic objective lens 602, and transmits the feedback signal to the dispersion modulation part and the focusing part. Control the light intensity at the focal point and the focal point position during the cutting process.

Preferably, the semiconductor wafer implicit cutting method and device can be used for semiconductor wafer cutting, and can also be used for semiconductor wafer surface grooving, chip dicing, and low-k chip grooving.

The ultra-short pulse semiconductor wafer implicit cutting method for reducing the nonlinear effect in the cutting process of the utility model reduces the nonlinear effect on the cutting path, and at the same time ensures that the peak power of the focus point remains unchanged. The device is characterized in that an ultrashort pulse is generated by a laser light source component, and the pulse passes through a dispersion compensation element related to a propagation path to compensate chirp during cutting. The pulse dispersion is compensated as completely as possible at the focal point, so the pulse width at the focal point is narrow and the peak power is high, which can be used for cutting. On the laser propagation path, due to the presence of a certain chirp, the pulse width is wide and the nonlinear effect is weak.

In this embodiment: the pulse is output from the light source unit 100. In the actual process, the light source can be a laser system such as solid, gas, or optical fiber. The light source unit outputs pulsed laser with a pulse width of 10fs-10ps. The chirped pulse generator 200 expands the ultrashort pulse of the light source unit 100 by adding a large amount of chirp, and the generated wide pulse is compensated by the dispersion modulation unit 300 . The dispersion modulation part sets the focus point inside the wafer through the focus part 400, and the dispersion at the focus point is completely compensated. The semiconductor wafer is placed on the wafer cutting platform 500, and the platform moves to change the cutting position. The trajectory observation and feedback unit 600 observes the focus position, and the feedback signal is transmitted to the dispersion modulation unit and the focus unit, thereby changing the focus position and size. Pulse dispersion is compensated as fully as possible at the focus point, so that the pulse width is narrow and the peak power is high on the wafer at the focus point. In contrast, on the laser propagation path, due to the existence of certain chirp, the pulse width is wide and the nonlinear effect is weak. Therefore, the device can stabilize the position of the laser focus and reduce the focus floating caused by nonlinear effects, so as to improve the precision of laser cutting.

The ultrashort pulse semiconductor wafer implicit cutting method of this embodiment reduces the nonlinear effect in the cutting process, by reducing the nonlinear effect on the cutting path, while ensuring that the peak power of the focus point remains unchanged. The following introduces the ultrashort pulse semiconductor wafer implicit cutting system combined with the design of the above-mentioned device in the laboratory.

Fig. 2 shows this case as a preferred embodiment of the present invention, which adopts optical fiber + solid-state laser system to implicitly cut semiconductor wafers. The light source unit 100 outputs a pulse width of 300 fs, a single pulse energy of 100 μJ, a repetition frequency of 300 kHz, and a wavelength of 1030 nm. The pulsed laser generates positive chirp through the Martinez grating structure (or its equivalent structure), which broadens the input ultrashort pulse. The broadened light beam passes through a glass slide 201, hits two 45° reflecting dichroic mirrors 1 and 2 202, 203, and then passes through a concave lens 301 to expand the beam spot. The expanded light spot hits the first grating 302 , enters the second grating 303 on the linear motor 304 and then passes through a Fresnel zone plate 305 . The dispersion modulator 300 is used to provide negative dispersion to ensure that the high-order dispersion in the propagation process is compensated. The position of the first grating 302 is fixed, the second grating 303 is placed on the first linear motor 304, and its distance is adjusted by the first linear motor 304, the first linear motor 304 is connected to the trajectory observation and feedback part 600, and is controlled by the trajectory observation and feedback part 600 . As shown in FIG. 2 , the compensated pulse is focused by the concave lens 401 onto the dichroic mirror 3 404 reflecting at 45°, reflected to the focusing objective lens 402 , and then focused inside the semiconductor wafer 700 . Focus point 1-30μm adjustable. The focusing objective lens 402 is placed on the linear motor 2 403, and the linear motor 2 403 is connected to the trajectory observation and feedback unit 600. The distance between the focusing objective lens 402 and the semiconductor wafer 700 is regulated by the feedback signal from the trajectory observation and feedback unit 600.

The reflected light on the semiconductor wafer 700 is captured by the position detection sensor 601 through the microscope objective lens 602 to observe the cutting track in real time and adjust the position of the components on the linear motor.

Fig. 3 is the whole machine integration diagram in the actual process in the utility model. In the actual process, through the mechanical design, a water cooling system is added, and the cutting material at the focusing lens is removed in real time by using a pneumatic device, so as to prevent the splashed wafer fragments from falling on the focusing objective lens, thereby affecting the energy and spot in the actual cutting process model uncertainty. The entire system is integrated on a skeleton made of hollow steel tubes. In this way, the mechanical vibration is effectively prevented. During the experiment, the trajectory uncertainty of the motor scanning can be reduced to below 500nm through the above-mentioned system integration.

In the actual process, the SiC wafer cutting track is realized by the experimental device shown in Figure 3. The cutting track width is about 6.4 μm. The uncertainty of the trajectory of scanning 1mm length is about 120nm. Due to the reduction of the nonlinear effect of the laser on the focusing path during the cutting process, its scanning accuracy is better than that of all semiconductor wafer implicit cutting devices currently commercially available in China.

Claims (9)

1. An ultra-short pulse semiconductor wafer recessing device is used for semiconductor wafer cutting, semiconductor wafer surface grooving, chip cutting and low-k chip grooving, and is characterized in that: the system comprises a light source part, a chirped pulse generating part, a dispersion modulation part, a focusing part, a wafer cutting platform and a track observing and feedback part, wherein the light source part is arranged in front of the chirped pulse generating part and is used for emitting pulse laser to the chirped pulse generating part; the chirp pulse generating part is arranged between the light source part and the dispersion modulation part and is used for widening the ultrashort pulse laser of the light source part and compensating a wide pulse generated by the widened pulse laser by the dispersion modulation part; the dispersion modulation part sets a focusing point in the semiconductor wafer through the focusing part, so that the dispersion at the focusing point is completely compensated; the wafer cutting platform is arranged below the focusing part and used for placing the semiconductor wafer, and the cutting position of the semiconductor wafer is changed by moving the wafer cutting platform; the track observing and feedback part is arranged above the semiconductor wafer and used for observing the focus position, and feeding back signals to the dispersion modulation part and the focusing part and adjusting the focus position and size.

2. The ultrashort pulse semiconductor wafer stealth dicing apparatus of claim 1, wherein: the light source of the light source part is any one of solid, gas and optical fiber, and the width of the laser pulse output by the light source part is 10fs-10ps.

3. The ultrashort pulse semiconductor wafer stealth dicing apparatus of claim 1, wherein: the chirp pulse generating part adopts a traditional Martinez grating structure and is used for generating positive chirp, or adopts a pulse propagation medium with a certain length and is used for generating positive chirp when pulses are propagated through the medium; and a traditional Treacy grating structure is adopted for generating negative chirp, or a pulse propagation medium with a certain length is adopted for generating negative chirp after pulse propagation passes through the medium.

4. The ultrashort pulse semiconductor wafer stealth dicing apparatus of claim 1, wherein: the dispersion modulation part consists of a glass slide, a concave lens, two dichroic mirrors, two gratings, a linear motor and a Fresnel zone plate; after passing through the glass slide, the wide light beams are incident on two 45-degree reflecting dichroic mirrors, then beam-expanded light spots are incident on the first grating and reversely enter the second grating on the linear motor and then enter the Fresnel zone plate through the concave lens.

5. The ultrashort pulse semiconductor wafer stealth dicing apparatus of claim 4, wherein: the Fresnel zone plate and the grating are combined and manufactured on the same substrate, the first grating is fixed in position, the second grating is placed on the linear motor, the first grating and the second grating are the same kind of grating, and the distance between the first grating and the second grating is regulated and controlled by a feedback signal of the track observation and feedback part.

6. The ultrashort pulse semiconductor wafer stealth dicing apparatus of claim 1, wherein: the focusing part consists of a concave lens, a focusing objective lens, a linear motor and a dichroic mirror, and the compensated pulse light beams are focused onto the 45-degree reflecting dichroic mirror through the concave lens, reflected to the focusing objective lens and focused inside the semiconductor wafer.

7. The ultrashort pulse semiconductor wafer stealth device of claim 6, wherein: the focusing objective lens is placed on the linear motor, and the distance between the second focusing objective lens and the semiconductor wafer is regulated and controlled by a feedback signal of the track observation and feedback part.

8. The ultrashort pulse semiconductor wafer stealth dicing apparatus of claim 1, wherein: the wafer cutting platform consists of a marble beam, a marble platform, a theta axis motor, an X axis linear motor and a Y axis linear motor.

9. The ultrashort pulse semiconductor wafer stealth dicing apparatus of claim 1, wherein: the track observing and feedback part consists of a position detection sensor and a microscope objective, and the position detection sensor transmits feedback signals of the track and the focus position observed by the microscope objective to the dispersion modulation part and the focusing part for controlling the light intensity and the focus position at the focus in the cutting process.

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