CO2 laser adaptive fresnel homogenization device and method for wafer annealing

Abstract

The application discloses a CO2 laser self-adaptive Fresnel homogenization device and method for wafer annealing, and belongs to the field of integrated circuit wafer annealing. The device comprises a frequency plate CO2 laser, an optical field sensor, a temperature sensor, a focusing mirror, a reflecting mirror, a diffraction element, a first cylindrical focusing mirror, an adjustable Fresnel prism, a beam splitter, a second cylindrical focusing mirror and a semiconductor laser. The optical field sensor is used for monitoring the uniformity of the light beam after the Fresnel prism homogenization in real time, and the adjustable Fresnel prism is adjusted, so that the uniformity of the laser is improved, the wafer annealing quality is improved, and the success rate of the annealing is increased. The temperature sensor is used for detecting the surface temperature field of the wafer during the wafer annealing, and the information is transmitted to an upper computer. In combination with the optical field distribution, the power of the radio frequency plate CO2 laser is controlled in real time, so that the success rate of the wafer laser annealing is ensured.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of integrated circuit wafer annealing, more particularly, to a CO2 laser beam self-adaptive Fresnel homogenization device for integrated circuit wafer annealing. BACKGROUND

[0002] Wafer annealing is an important step in the manufacture of ultra-large scale integrated circuits. During wafer processing, ions are implanted into silicon wafers to improve the performance of semiconductor materials. This process can cause some lattice defects or damage, and most of the ions cannot be accurately implanted at the corresponding position. The annealing process is to expose the wafer to a certain high temperature for a suitable time to activate the ions to repair defects. In COMS transistors, annealing technology plays a crucial role in the process of activating ultra-shallow junction (USJ) and forming silicide.

[0003] The advantage of laser annealing technology is that it can utilize the energy concentration characteristics of laser beams to irradiate laser beams onto the surface of semiconductor materials, so that the surface and shallow layer of the semiconductor materials can quickly absorb the energy of the laser beams in a very short time and rapidly heat up to the annealing temperature. Since the transmission depth of short-wavelength laser in silicon is shallow, its activation depth is limited, so long-wavelength laser annealing is generally required for the activation of deeper implanted ions. P-polarized CO2 lasers have been used in commercial wafer irradiation systems because, compared with other lower-wavelength laser sources, the absorption of CO2 laser is mainly due to the photoexcitation of thermally active free carriers, and the energy is transferred from the excited carriers to the lattice through electron-phonon scattering (in the time domain), which leads to local heating of the lattice and an exponential increase in the absorption coefficient. CO2 laser incident at Brewster's angle can greatly reduce the "pattern effect" related to reflectivity. Therefore, laser spike annealing uses a long-wavelength CO2 laser to generate a laser beam and shapes it into a line beam, which is irradiated onto the wafer surface at a grazing angle and is scanned back and forth.

[0004] For 28nm USJ activation, RTP spike annealing combined with laser annealing can cause excessive diffusion and short channel effects. The conventional laser annealing step is not long enough to effectively eliminate the end damage caused by ion implantation, which can cause junction leakage. Dual-beam annealing can solve this problem.

[0005] Dual-beam annealing can allow the wafer to stay at the annealing temperature for a longer time and reduce the problem of thermal stress deformation caused by rapid temperature changes. The use of a dual-beam composite light source greatly improves the uniformity of the light spot, making the surface temperature gradient change smaller during laser annealing, the temperature distribution of the annealing area more uniform, and the transient thermal stress caused by excessive temperature difference smaller.

[0006] In the double-beam annealing process, a wider semiconductor laser is used as the front spot, and a CO2 laser is used as the rear spot. Compared with other CO2 lasers, the RF slab CO2 laser has certain advantages, and can be better applied in the field of industrial high-power lasers. It has smaller size, higher photoelectric conversion efficiency and better beam quality.

[0007] Since the RF slab CO2 laser output beam is Gaussian type, the annealing temperature field distribution is not uniform under the Gaussian type distribution of the laser light source, so the beam needs to be shaped. In the beam shaping process of the RF slab CO2 laser, the circular Gaussian beam needs to be cut and rearranged, and finally shaped into a uniform 11mm*75um rectangular beam. However, when the cavity mode changes, the inherent shaping light path system cannot be adjusted in real time, which will cause the beam homogenization quality to decrease, thereby affecting the annealing temperature field distribution on the wafer surface. Therefore, solving the problem of insufficient uniformity of the RF slab CO2 laser after beam shaping is the key to improving the annealing efficiency. SUMMARY

[0008] In view of the defects of the prior art, the purpose of the present application is to provide a CO2 laser beam self-adaptive Fresnel homogenization device for integrated circuit wafer annealing, which aims to solve the problems of insufficient uniformity of the RF slab CO2 laser after beam shaping and the "pattern effect" caused by nodes below 28nm, thereby affecting the annealing success rate.

[0009] To achieve the above-mentioned purpose, the present application provides a CO2 laser beam self-adaptive Fresnel homogenization device for integrated circuit wafer annealing, comprising: a RF slab CO2 laser, an optical field sensor, a temperature sensor, a focusing mirror, a reflecting mirror, a diffraction element, a first cylindrical focusing mirror, an adjustable Fresnel prism, a beam splitter, a second cylindrical focusing mirror, and a semiconductor laser.

[0010] The laser beam generated by the RF slab CO2 laser in accordance with the annealing power is collimated and emitted by the focusing mirror, and then changes the light path direction by the reflecting mirror and is incident to the diffraction element. After diffraction shaping, the circular spot is converted into a rectangular spot, and then collimated and emitted by the first cylindrical focusing mirror. The adjustable Fresnel prism is used to homogenize the line spot. The line spot is divided into two parts by the beam splitter, one of which is received by the optical field sensor for testing the uniformity of the spot, and the sensing signal is transmitted to the upper computer for feedback, so as to adjust the adjustable Fresnel prism in real time and homogenize the laser beam. The other part passes through the second cylindrical focusing mirror to focus the homogenized laser into a narrower first line spot for wafer annealing.

[0011] The second linear light spot generated by the semiconductor laser is incident at the first linear light spot for preheating the wafer; the temperature sensor is used for detecting the wafer surface temperature and transmitting a sensing signal to a feedback upper computer for real-time adjustment of the output power of the radio frequency slab CO2 laser.

[0012] Beneficial effects: the semiconductor linear light spot is incident on the wafer, which plays a role of preheating and slow cooling, so that the wafer can stay at the annealing temperature for a longer time, and the thermal stress deformation problem caused by rapid temperature change is reduced.

[0013] Further, the adjustable Fresnel prism includes a plurality of groups of adjusting rods, a plurality of prism units and a prism support, the same number of prism units with different heights are connected in series on each group of adjusting rods, and the plurality of groups of adjusting rods are distributed side by side on the surface of the prism support. The adjusting rod is used for pushing in the arrangement direction of the prism unit, and the moving distance is fixed each time, so as to adjust the prism height of the incident laser irradiation. The prism angle is changed by rotating the adjusting rod, and finally the laser beam homogenization is realized.

[0014] Preferably, the radio frequency slab CO2 laser is a high-power laser with a rated power of up to 3000W or more, which is used to heat the wafer surface temperature to 1000℃ or more. The semiconductor laser beam has a relatively low power of about 800W, which is used to preheat the annealing part and relieve the thermal stress deformation problem caused by rapid heating.

[0015] Preferably, the transmittance of the beam splitter is 99.5%, which is used to split a small power beam to detect the uniformity, shape and power stability of the laser beam.

[0016] Preferably, the temperature field probe collects the temperature signal of the CO2 laser linear light spot on the wafer surface and transmits it to the temperature sensor for real-time monitoring of the wafer surface temperature.

[0017] Further, the upper computer receives signals from the light field sensor and the temperature sensor, can real-time monitor the power and shape of the light spot, adjusts the adjustable Fresnel prism, and makes the light beam homogenization rate reach more than 98%.

[0018] In one of the embodiments, the whole adaptive adjustment CO2 laser homogenization system working process is as follows: a high-power radio frequency board strip CO2 laser emits a CO2 laser beam with appropriate power, which is a circular spot, the laser beam is reflected by a reflector into a diffraction element, and after diffraction shaping, it becomes a rectangular beam, which is collimated by a cylindrical focusing mirror and converted into an uneven rectangular beam with a size of about 12mm*0.75mm. The rectangular beam enters an adjustable Fresnel prism, which is composed of multiple rows of prisms with different heights and is controlled by a host computer in real time. By pushing the adjusting rod to change the height of the selected prism at the laser beam incidence and rotating the adjusting rod to change the prism angle, the purpose of real-time adjusting the uniformity of the rectangular laser beam is achieved. The adjustable Fresnel prism comprises a prism support for supporting the prism combination, an adjusting rod, the horizontal direction of the prism unit arrangement is defined as the x direction, the adjusting rod arrangement direction is the y direction, the adjusting rod can be pushed in the x direction, and the moving distance is fixed each time, so as to adjust the prism height irradiated by the incident laser, and the prism angle is changed by rotating the adjusting rod, and a prism unit, each prism unit is 1mm long in the x direction and 2mm long in the y direction, and the laser beam homogenization is adjusted by the operating rod according to the laser intensity signals of the rectangular laser beam fed back to the host computer by the optical field sensor.

[0019] After passing through the adjustable Fresnel prism, a rectangular beam with a size of 11mm*0.75mm is obtained, which is incident on a beam splitter, 0.5% of the light is reflected to the optical field sensor as a sampling beam, and the optical field intensity information of the current rectangular laser beam is obtained. In addition, 99.5% of the light is incident on a cylindrical focusing mirror, which is further compressed in the width direction to obtain a 11mm*75um beam, which is output to a wafer and performs laser annealing together with a semiconductor linear spot. The temperature field probe is used to detect the surface temperature field of the wafer during annealing, and the information is transmitted to the host computer, which is combined with the optical field distribution to adjust the adjustable Fresnel prism, so that the beam homogenization rate reaches more than 98%, and the wafer annealing quality is improved.

[0020] The application also provides a CO2 laser adaptive Fresnel homogenization method for wafer annealing, comprising the following steps:

[0021] The collimated laser beam with the annealing power is diffracted and shaped to convert the circular spot with Gaussian distribution into a rectangular spot;

[0022] The Fresnel prism is used to homogenize the linear spot, focus the homogenized laser into a narrower first linear spot, and the linear spot uniformity is detected to adjust the Fresnel prism to homogenize the laser beam in real time; specifically, by adjusting the height of the Fresnel prism irradiated by the incident laser and changing the prism angle, the laser beam homogenization is realized;

[0023] The second linear spot is incident at the first linear spot to preheat the wafer, and the wafer surface temperature is detected to adjust the output power of the laser beam in real time.

[0024] Compared with the prior art, the above technical scheme conceived by the present application can achieve the following

[0025] Advantages:

[0026] 1. The present application monitors the uniformity of the light beam after the homogenization of the Fresnel prism in real time through the light field sensor, feeds back to the upper computer, and can improve the uniformity of the laser through the adjustable Fresnel prism, so that the light beam homogenization rate reaches more than 98%, and the wafer annealing quality is improved to increase the success rate of annealing.

[0027] 2. The present application detects the surface temperature field of the wafer during annealing through the temperature sensor, transmits the information to the upper computer, combines the light field distribution, and adjusts the power of the radio frequency strip CO2 laser in real time to ensure the success rate of wafer laser annealing.

[0028] 3. The adjustable Fresnel lens designed in the present application can solve the problem of non-uniformity after beam shaping caused by laser mode change by adjusting the height and angle of the prism. BRIEF DESCRIPTION OF DRAWINGS

[0029] Figure 1 It is a self-adaptive adjustment CO2 laser homogenization system structure diagram;

[0030] Figure 2 It is a radio frequency strip CO2 laser shaping optical path diagram;

[0031] Figure 3 It is a schematic diagram of the adjustable Fresnel prism structure;

[0032] Figure 4 It is a principle diagram of the homogenization effect of the Fresnel prism on the rectangular laser beam;

[0033] Figure 5 It is a real-time monitoring principle diagram of the rectangular laser beam light field;

[0034] Figure 6 It is a schematic diagram of the radio frequency strip CO2 laser wafer annealing.

[0035] The drawings show that: 1 is an upper computer, 2 is a radio frequency strip CO2 laser, 3 is a refrigeration system, 4 is a power supply, 5 is a light field sensor, 6 is a temperature sensor, 7 is a focusing mirror, 8 is a reflecting mirror, 9 is a diffraction element, 10 is a first cylindrical focusing mirror, 11 is an adjustable Fresnel prism, 12 is a beam splitter, 13 is a second cylindrical focusing mirror, 14 is a temperature field probe, 15 is a wafer, 16 is a semiconductor linear light spot, 17 is an adjusting rod, 18 is a prism unit, 19 is a prism support. DETAILED DESCRIPTION

[0036] In order to make the purpose, technical scheme and advantages of the present application clearer, the present application will be further described in detail below with reference to the drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and do not limit the present application. In addition, the technical features involved in the various embodiments of the present application described below can be combined with each other as long as they do not conflict with each other.

[0037] The purpose of the present application is to provide a CO2 laser adaptive Fresnel homogenization device and method for wafer annealing, which has the advantages of automatically adjusting the laser homogenization effect and monitoring the wafer annealing temperature field distribution, thereby increasing the success rate of annealing.

[0038] In this embodiment, with reference to Figure 1 , the RF strip CO2 laser 2 emits laser beams conforming to the annealing power, the light beams are collimated by the focusing mirror 7, are incident on the mirror 8 to change the light path direction, are converted and collimated by the diffraction element 9 and the first cylindrical focusing mirror 10, are changed from circular light beams to rectangular light beams, and are then homogenized by the adjustable Fresnel prism 11. The homogenized rectangular light beams pass through the beam splitter 12 to make 0.5% of the light beams incident on the light field sensor 5 to check whether the spot uniformity and power meet the requirements, and transmit the signals to the host computer 1 for feedback. The host computer 1 controls the position and angle of the prism unit 18 by adjusting the adjusting rod 17 to homogenize the laser beams. The remaining 99.5% of the light beams are emitted to the second cylindrical focusing mirror 13 to focus in the width direction, focus the homogenized laser beams into narrower rectangular light beams, eliminate spherical aberration, and output to the wafer 15. The double light beams composed of the semiconductor linear spot 16 and the wafer 15 are annealed. The temperature field probe 14 detects the temperature of the CO2 laser beam at the surface of the wafer 15 and transmits the signals to the host computer 1 for feedback to adjust the output power of the RF strip CO2 laser 2.

[0039] In this embodiment, with reference to Figure 2 , the RF strip CO2 laser 2 emits laser beams conforming to the annealing power, the light beams are collimated by the focusing mirror 7, are incident on the mirror 8 to change the light path direction, are converted into rectangular light beams by the diffraction element 9, and are then collimated by the first cylindrical focusing mirror 10 to obtain rectangular light beams with a size of about 12mm x 0.75mm. At this time, the rectangular light beams are not uniform, which shows that there is a dark field.

[0040] In this embodiment, with reference to Figure 3, the rectangular light beam is incident to the adjustable Fresnel lens 11, at this time the spot size is: the length in y direction is 12mm, the length in x direction is 0.75mm, the size of the prism unit 18 is: the length in y direction is 2mm, the length in x direction is 1mm. The working principle is: assuming that the light beam is incident to the second row of prisms, the light beam irradiation prism height can be changed by pushing the adjusting rod, the prism angle can be changed by rotating the adjusting rod, and the homogenization effect is realized in real time by combining the upper computer 1 and the feedback system.

[0041] In the embodiment, referring to Figure 4 , the rectangular light beam with the size of 12mm*0.75mm is incident to the adjustable Fresnel lens 11, and the rectangular light beam with the size of 11mm*0.75mm is obtained, and the light beam homogenization rate of the rectangular light spot can reach more than 98% by the feedback adjustment system.

[0042] In the embodiment, referring to Figure 5 , the rectangular light beam with the size of 11mm*0.75mm is obtained by the adjustable Fresnel lens 11, is incident to the beam splitter 12, 0.5% of the light is incident to the light field sensor 5, the light field distribution and the prism and adjusting rod number corresponding to the light field incident area are obtained, the light field sensor 5 can directly monitor the shape and energy size of the light spot, and feedback to the upper computer 1, and issue an adjusting instruction to adjust the adjustable Fresnel lens 11 in real time, until the homogenization rate reaches 98%, and the stability of the whole system is maintained. The remaining 99.5% is emitted to the second cylindrical focusing mirror 13.

[0043] In the embodiment, referring to Figure 6 , the rectangular light beam after homogenization is compressed in the width direction by the second cylindrical focusing mirror 13 and the spherical aberration is eliminated, and the light beam with the size of 11mm*75um is obtained, and is output to the wafer 15, and is used for laser annealing together with the semiconductor linear light spot 16. The temperature field probe 16 is responsible for the real-time monitoring of the wafer surface temperature at the CO2 linear light spot, and is transmitted to the upper computer 1 through the temperature sensor 6. The temperature detection can adjust the power of the power supply to control the temperature on one hand, and can transmit information to the upper computer 1 on the other hand, and the light field distribution is combined to adjust the adjustable Fresnel lens 11, and the light beam homogenization effect is further strengthened.

[0044] In the embodiment, the power of the radio frequency strip CO2 laser 2 used is 3500W, so as to reach the annealing temperature of the silicon wafer, and the annealing temperature of the silicon wafer is above 1100℃, and the power of the semiconductor laser used is about 800W, which is used for pre-treatment of the wafer.

[0045] Those skilled in the art can easily understand that the above description is only a preferred embodiment of the present application, and is not used to limit the present application, and any modification, equivalent replacement and improvement made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A CO2 laser adaptive Fresnel homogenization device for wafer annealing, characterized in that: include: Radio frequency slab CO2 laser (2), light field sensor (5), temperature sensor (6), focusing mirror (7), reflecting mirror (8), diffraction element (9), first cylindrical focusing mirror (10), adjustable Fresnel prism (11), beam splitter (12), second cylindrical focusing mirror (13), semiconductor laser (16); The laser beam generated by the radio frequency slab CO2 laser (2) and meeting the annealing power is collimated and emitted through a focusing mirror (7), and then changes the direction of the optical path through a reflecting mirror (8) and is incident on a diffraction element (9). After diffraction shaping, the circular light spot is converted into a rectangular light spot, and then collimated and emitted through a first cylindrical focusing mirror (10); the adjustable Fresnel prism (11) is used to homogenize the line light spot; the line light spot is divided into two by a beam splitter (12), one of which is received by a light field sensor (5) for testing the uniformity of the light spot, and the sensor signal is transmitted to the host computer (1) for feedback, and the adjustable Fresnel prism (11) is adjusted in real time to homogenize the laser beam; the other path passes through a second cylindrical focusing mirror (13) and is used to focus the homogenized laser into a narrower first line light spot for annealing the wafer (15); The second line spot generated by the semiconductor laser (16) is incident on the first line spot to preheat the wafer (15); the temperature sensor (6) is used to detect the surface temperature of the wafer (15), transmit the sensing signal to the reflective host computer (1) for feedback, and adjust the output power of the radio frequency slab CO2 laser (2) in real time; The adjustable Fresnel prism (11) comprises a plurality of adjustment rods (17), a plurality of prism units (18) and a prism bracket (19), wherein each group of adjustment rods (17) is connected in series with the same number of prism units (18) of different heights, and the plurality of adjustment rods (17) are arranged side by side on the surface of the prism bracket (19), and the adjustment rods (17) are used to push in the arrangement direction of the prism units (18), and the distance of each movement is fixed to adjust the height of the prism irradiated by the incident laser, and the prism angle is changed by rotating the adjustment rods, thereby finally achieving laser beam homogenization.

2. The device according to claim 1, characterized in that The size of the prism unit in a horizontal cross section is 1 mm×2 mm.

3. The device according to claim 1, characterized in that The size of the first line light spot is 11 mm×75 um.

4. The device according to claim 1, characterized in that The transmittance of the spectroscope (12) is 99.5%.

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