1.Purpose
A purpose for “minute measurement system for semiconductor surface” is to measure a distribution of film thickness and refractive indices of patterned wafer as two-dimensional image.
This system is based on a principle of ellipsometry detecting changes in a state of polarization of a reflection light, which depends on a thickness and a refractive index of the film.
Differ from the conventional system measuring only one spot of a sample, a variety of systems which we have been developing measures a surface of a sample as a image.
Our company has been engaged in developing new conceptual machine which is applicable to the present production lines in factories with our recognition on the significance of our customers needs. It has been successfully developed that its capability of measurement is about to be accomplished. The following is the detailed explanation of our new method.
2.Mechanisms
This method has its distinctive feature in applying each one of three colors of light sources which are in different conditions of polarization simultaneously. When fixing an azimuthal angle of an analyzer on the reflection side, the intensity of a reflection light from a sample makes a sign-curb as a function of azimuthal angles of a polarizer on the incident side. Therefore, it enables us to perform the ellipsometric measurement with the polarized light of more than three preliminary independent azimuthal angles.
In this method, three primary colors of light are basically used as markings for minimum variable 3 of this azimuthal angle of polarized light. For example, the system applies polarizers with azimuthal angles fixed at -45゜,0゜,45゜respectively as red, green, and blue obliquely to a sample as a common light path (it becomes a white-colored light when the intensities of these three colors are equal) made through a prism. It then films a reflection light which has passed through an analyzer with CCD camera. At this point, the intensity of the red light indicates a reflectivity of the polarized light for -45゜ (same as other two colors of light). If coefficients which are supposed to be multiplied to data of each images are set up at appropriate values, it immediately reckons δ or ψ as a result of addition.
As explained, measuring the intensity of color of reflection light is just same as measuring the reflectivity of sample for incident lights with different azimuthal angles. In this way, it not only eliminates a process of rotating polarizer during measurement and errors due to this process but also reduces time which has been required for the process in the conventional method.
The measurement of ellipsometer is operated through the following three stages: 1. a measurement of reflection luminous intensity as a function of azimuthal angle of analyzer on the reflection side, 2. a calculation (calculation of δ and ψ) of reflecting elliptically polarized light using data in stage 1, 3. a calculation of film thickness and refractive index using data in stage 2 by referring the information relating to a structure of a sample. In the conventional one-spot-typed system, times required for each stages of 1, 2, and 3 are respectively as a time required for the measurement of luminous intensity by rotating analyzer (few minutes), few micro-seconds per 1 spot on a sample, and few 10 mili-seconds per 1 spot on a sample. In this system, these required times are all in proportion to how many spots on a sample its user wants to measure; however, in the conventional two-dimension-typed system, the measurement of luminous intensity of stage 1 can be operated all at once as it measures a sample as a picture. Moreover, in the present system which we have developed, a calculation of reflecting elliptically polarized light in stage 2 is simultaneously operated in the stage 1 so that the calculations of stage 1 and 2 can be done in few seconds all together.
As a different usage of the present system, it measures 630, 580, and 430nm on each wavelength by measuring an analyzer on the reflection side as it rotates any one of three incident light sources. (quasi-spectrum measurement) This system can be effectively utilized for a measurement of multilayers.
Below are the concrete numerical values of this system.
Below are the technical contents for realizing the above values.
It minimizes a distortion of a image in surface at the oblique incidence.
3. Industrial Applicability
Apparently, needs for introducing ellipsometer into semiconductor factories as a detecting system for production lines have been widely recognized. However, because of efficiency problems and enormous time required for measurement in the conventional system produced by other manufacturers, its utilization has been limited.
On the contrary, our two-dimention-typed system has enabled the calculation of δ and ψ on each pixel in a whole image to be done within few seconds. Because a set of δ and ψand a set of film thickness and refractive index has 1 to 1 correspondence, this system can be utilized for quality management on production lines in factories only by using values of δ and ψ (calculation of film thickness and refractive is also possible if necessary).
4. Social and Economical Impact
The present system is beneficial for the following socio-economical effects which systems relating to semiconductor manufacture must all pursue.
It reduces usage of resources and electricity in factories due to yield improvement; as a whole, it contributes to a prevention of global warming.
It contributes to high-accumulation and cost-down in semiconductor market.
It contributes to vertical set-ups for new devices.
The above 2 and 3 contribute to quick collection of investments and profit acquisition.
In addition, fairly high industrial significance can be expected from the present system when utilizing it as the defect detection system. There must be a possibility for technical improvements on the conventional defect detection system as it is clearly stated in estimations such as “technical improvement is expected” or “reform in the fundamental technique is required” made on the conventional defect detection system by various device maker companies. Meanwhile, the present system has successfully developed the method which realized the unprecedented simultaneous classification of particles and defects.
Besides, the present system is also expected in its effectiveness in measuring oxidational level on metalic surface as a detective system for bonding deficiency for packaging such as CSP.
Acknowledgment.
A part of this work was supported by The New Technology Development Foundation.