This application claims priority to Taiwan Application Serial Number 96116528, filed May 9, 2007, which is herein incorporated by reference.
1. Field of Invention
The present invention relates to a method for monitoring a manufacturing process of a semiconductor device. More particularly, the present invention relates to a method of real-time monitoring implantation.
2. Description of Related Art
In the semiconductor manufacturing process, implantation is used for modifying electrical properties of silicon wafer by bombarding silicon wafer with some specific ions. Moreover, by changing the conditions of the implantation, such as ion concentration, implantation energy, or implantation angle etc., it can manufacture different kinds of semiconductor devices to satisfy different needs. Therefore, how to control the conditions of implantation in real-time is very important.
In conventional techniques, electrical property analysis, secondary ion mass spectroscopy (SIMS) or four-point probes are used to monitor the conditions of implantation. SIMS is to bombard a surface of a testing sample with a beam of first high energy ions. After that, the energy of the first ion beam will be transferred to the testing sample and the substance in the surface of the testing sample is splattered which becomes ionic second ions. Next, the second ions are detected by instruments to obtain the information about the compositions and atomic distributions of the testing sample in vertical direction.
As regards the four-point probes, it is to insert two outer pins and two inner pins into the substrate and then apply electric currents between the outer pins to measure the voltage between the inner pins. Thus, sheet resistivity of the substrate is obtained. Since the sheet resistivity influenced by several factors, such as implantation concentration, film thickness, or crystal size, implantation information can be obtained by monitoring the sheet resistivity of the substrate.
No matter SIMS or the four-point probes, both of them are destructive methods which damage the surface of the wafer. Moreover, in a real manufacturing process, a standard wafer is implanted first and then detected by SMIS or the four-point probes. In order to reuse the standard wafer, the standard wafer has to be treated with chemical mechanical polishing or etching after finishing detection, and this is time and cost consuming.
In addition, electrical property analysis cannot be performed until the manufacturing process is completed. Therefore, the implantation condition cannot be monitored simultaneously during implantation, and this results in lots of defective products and increased manufacturing costs.
For the foregoing reasons, there is a need to develop a method for real time monitoring implantation and preventing the sample from being destructed. Meanwhile, it is also an important issue to cost down and save time.
The present invention provides a method of real-time monitoring implantation to prevent samples from being destructed and to efficiently control the process.
It is therefore an objective of the present invention to provide a method of real-time monitoring implantation. First, a plurality of standard substrates are provided, wherein the standard substrates are covered with a photoresist. Next, the standard substrates are implanted wherein a implantation condition for each of the standard substrates is changed. After that, photoresist surface roughnesses of the standard substrates are detected to obtain reference intensities of scattering lights. A calibration curve is plotted by using the reference intensities of scattering lights and the implantation conditions corresponding to the reference intensities. A testing substrate is provided wherein the testing substrate is covered with the photoresist. The testing substrate is implanted. A photoresist surface roughness of the testing substrate is detected to obtain a monitoring intensity of scattering light. Finally, the monitoring intensity of scattering light is scaled by using the calibration curve to analyze the implantation condition.
In the foregoing, this method of monitoring implantation not only prevents the sample from being destructed, but also costs down and saves time because the standard substrate can be reused by removing the photoresist on the substrate after finishing detection. In addition, the method above can be performed simultaneously during implantation, which is very efficient.
It is to be understood that both the foregoing general description and the following detailed description are by examples, and are intended to provide further explanation of the invention as claimed.
The accompanying drawings are included to provide a further understanding of the invention, and are incorporated in and constitute a part of this specification. The drawings illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention. In the drawings,
Reference will now be made in detail to the present embodiments of the invention, examples of which are illustrated in the accompanying drawings. Wherever possible, the same reference numbers are used in the drawings and the description to refer to the same or like parts.
In the following embodiment, a method of real-time monitoring implantation is provided. By detecting the photoresist surface roughness before and after implantation, a calibration curve can be plotted and used as a standard for monitoring. To describe each embodiment in detail, it is necessary to introduce the affect of implantation on the photoresist first.
Young's modulus is a measure of material stiffness. The smaller Young's modulus indicates that the substance is easily deformed, which results in greater change of the roughness when the substance is treated with an external force. In general, Young's modulus of photoresists is usually smaller than 5 Gpa. Accordingly, if a substrate is covered with a photoresist, and then implanted, the implantation energy will change the photoresist surface roughness. To prove this assumption, a substrate was covered with a photoresist first, wherein the photoresist used can be I-line photoresist which comprises phenolic resin (Novolac), or deep ultraviolet light (DUV) photoresists, such as DUV photoresist (248 nm) that comprises acetal resin, or DUV photoresist (193 nm) that comprises acryl resin. After that, the photoresist on the substrate was scanned by atomic force microscopy (AFM) to detect the change of photoresist surface roughness. The results are shown as
According to the AMF results obtained by AFM, it demonstrated that the photoresist surface roughness was greatly changed after implantation. Therefore a calibration curve can be plotted on the diagram of implantation conditions versus photoresist surface roughnesses of the photoresist. Moreover, the calibration curve can be used for monitoring implantation. In the following embodiments, the surface roughness was detected by Surfscan by detecting scattering light intensity from the photoresist surface. The stronger intensity of the scattering light indicates less smooth photoresist surface.
Oppositely, weaker scattering light intensity indicates smoother photoresist surface.
According to the principle of energy conservation of, each ion had a particular kinetic energy provided by an implantation machine while doing implantation. However, after the ion left the machine and hit the photoresist, a part of the kinetic energy became work done to the photoresist, which is also called strain energy. Consequently, the surface roughness of the photoresist will be changed. The conversion between kinetic energy (K) and Strain energy (U) is as formula (1):
Wherein V is the ion's velocity after leaving the implantation machine, and M is ion mass, and F is the force that ion applied to the photoresist, and ΔX is the displacement or the change of the surface roughness. According to formula (1), the change of the photoresist surface roughness is proportional to the implantation energy provided by the implantation machine, so a calibration curve can be plotted on the diagram of surface roughness versus implantation energy. The detailed process is described as follows.
Referring to
According to
For example, the scattering light intensity of the photoresist of the testing substrate was detected before and after the implantation to obtain an intensity bias of scattering light. This intensity bias of scattering light is called the testing intensity bias of scattering light. After that, the testing intensity bias of scattering light was corresponded to the calibration curve of the implantation energy to figure out the implantation energy of the testing substrate. If the corresponding energy deviated from the calibration curve, it indicates that the implantation energy provided by the implantation machine is biased. The bias implantation energy will change the photoresist surface roughness of the testing substrate too much or too little. If the deviation is too large, beyond tolerance, it implies that the implantation machine is unstable. However, if the corresponding energy is located on the calibration curve, it implies that the implantation energy provided by the implantation machine is stable.
However, in the manufacturing process, photoresist must be processed by lithography before implantation. To understand the effect of lithography on detecting scattering light intensity mentioned above, therefore the steps of
According to
In addition to the implantation energy, the implantation concentration is also one of important implantation conditions for monitoring. According to formula (2), when the energy provided by the implantation machine is steady, the higher implantation concentration indicates that the sum of the ion mass is larger and the total kinetic energy is larger, too. Therefore, the strain energy applied to the photoresist is increased which resulting in increasing the change of the roughness of the photoresist and the scattering light intensity. Hence, the implantation concentration is also proportional to the intensity bias of scattering light.
Usually, in the manufacturing process, the implantation is increased exponentially. Accordingly, an exponential calibration curve of implantation concentration can be plotted on the diagram of intensity bias of scattering light versus logarithm of the implantation concentration.
In the embodiment of the present invention, 9 standard substrates covered with a photoresist were implanted wherein the implantation energy was 80 Kev and the implantation concentration were 5×1011/cm2, 1×1012/cm2, 2×1012/cm2, 5×1012/cm2, 1×1013/cm2, 2×1013/cm2, 3×1013/cm2, 4×1013/cm2, and 5×1013/cm2. The calibration curve of implantation concentration plotted is shown as
Referring to
In the implantation process, another important implantation condition of for monitoring is tilt angle. Because of the characteristics of silicon lattice arrangement, there are long openings inside silicon wafer. If the moving direction of the ions implanted is parallel to these openings, ions are not able to bombard the silicon atoms completely which decrease the implantation efficiency. This is called tunnel effect. In order to reduce tunnel effect, ion implanting direction has to be tilted while implantation, the angle is called tilt angle. When ion beam incident direction is perpendicular to wafer surface, the tilt angle is 0°. therefore, when ion beam incident direction is parallel to wafer surface, the tilt angle is 90°.
In the embodiment of the present invention, 9 standard substrates covered with a photoresist were implanted wherein the tilt angles were 5°, 15°, 25°, 35°, and 45° respectively. After that, a calibration curve of tilt angle was plotted on the basis of the procedures mentioned above. The relationship between the tilt angles and the scattering light intensities was obtained and used as a monitoring standard. The calibration curve of tilt angle is shown as
Referring to
The method mentioned above is to plot a calibration curve by detecting the surface roughness of a photoresist. However, different types of photoresists will lead to different surface roughness change even if the implantation condition remains the same, because of different compositions or properties of these photoresists.
In the embodiment of the present invention, I-line photoresist (365 nm) and DUV photoresist (248 nm) were used to plot calibration curves of implantation energy on the basis of the procedures mentioned above. The calibration curves were therefore used to understand the effect photoresist composition on surface roughness change. In the embodiment of the present invention, the implantation concentration was 5×1013, and the implantation energies were 80 Kev, 140 Kev, and 200 Kev. The calibration curve is shown as
Referring to
In conclusion, by detecting scattering light intensity and using a calibration curve, the method provided above for monitoring implantation prevents the substrate from being destructed while monitoring. Moreover, this method can simultaneously determine if a implantation condition meets the standard requirement as well as understand if the performance of an implantation machine is deviated from calibrated standard.
It will be apparent to those skilled in the art that various modifications and variations can be made to the structure of the present invention without departing from the scope or spirit of the invention. In view of the foregoing, it is intended that the present invention cover modifications and variations of this invention provided they fall within the scope of the following claims and their equivalents.
Number | Date | Country | Kind |
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96116528 | May 2007 | TW | national |