利用外差干涉術(shù)來(lái)檢驗(yàn)彩色濾光片上遮光層的厚度之新方

1、A new method for inspecting the thickness of the black matrixes on the color filters by using the heterodyne interferometry Shinn-Fwu Wang*, Ming-Jen Wang; Jyh-Shyan Chiu, Lung-Hsiang LeeDepartment of Electronic Engineering, Ching Yun University*Contact Address: No.229, Chien-Hsin Rd., Jhongli City,

2、 Taoyuan, 320, Taiwan, R.O.C., Tel: +886-3-4581196 ext 5113, Fax: +886-3-4588924, E-mail: .twABSTRACTA new method for inspecting the thickness of the black matrixes on the color filters by using the heterodyne interferometry is proposed. In the paper, we can measure the thickness of the

3、 black matrixes on the color filters only by measuring the phase difference instead of the reflectance difference. And the phase difference can be extracted and measured accurately with heterodyne interferometry despite surrounding light and an unstable light source. The method has some merits, e.g.

4、, a simple optical setup, easy operation, real time and rapid measurement etc. Keywords: black matrix, color filter, heterodyne interferometry (HI), surface plasmon resonance (SPR). 摘要利用外差干涉術(shù)來(lái)檢驗(yàn)彩色濾光片上遮光層的厚度之新方法已被提出。在本文中，我們藉由量取相位差的方法(而不採(cǎi)用一般之反射率量測(cè)法)可量測(cè)得到彩色濾光片上遮光層的厚度。此乃利用外差干涉術(shù)不受光強(qiáng)度及外界環(huán)境之干擾的特性，據(jù)以準(zhǔn)確地量得相位

5、差。此方法具有相當(dāng)多的優(yōu)點(diǎn)，例如：光學(xué)架構(gòu)簡(jiǎn)單、易操作、即時(shí)且快速量測(cè)等等的優(yōu)點(diǎn)。關(guān)鍵詞：遮光層，彩色濾光片，外差干涉術(shù)，表面電漿共振。1. INTRODUCTIONOwing to the effects of the color filters on the color chacteristics of the liquid crytal display (LCD), it is important for us to control and inspect the parameters of the color filters during the manufacturing proce

6、ss. And the defects of the black matrixes on the color filters, e.g., particle defects and hole defects, will influence the uniformity of the colors. Traditionally, the method of the refectivity measurement can be used to inspect the defects of the black matrixs. In the paper, we present a new metho

7、d for inspecting the thickness of the black matrixes on the color filters by using the heterodyne interferometry. At this moment, we measure the phase difference instead of the reflectance difference. And the phase difference can be extracted and measured accurately with heterodyne interferometry de

8、spite surrounding light and an unstable light source. In General, researchers are usually devoted to the studies of the small-displacement/small-thichness measurement by using the heterodyne interferometric technique 1-3 based on the Michelson interferometer. Although the method has high resolution,

9、 it is easily influenced by air turbulence and environmental vibration. To overcome the drawbacks, we propose a new method, to our knowledge, for measuring the thickness of the black matrixes on the color filters by use of the attenuated total reflections (ATR) in heterodyne interferometry (HI). For

10、 this method, a common-path heterodyne interferometer is applied to measure the phase differences between s- and p-polarizations at the ATR effect. By measuring the phase differences between s- and p-polarizations, the thickness of the black matrixes can be achieved. The method has some merits, e.g.

11、, a simple optical setup, easy operation, real time and rapid measurement etc. And its feasibility is demonstrated. 2. PRINCIPLES2.1 The principle of the heterodyne interferometryFig.1 shows the basic optical setup of the hetrodyne interferometer. A heterodyne light source 4 is incident on a beamspl

12、itter,BS, and is divided into the reflected and transmitted lights. The reflected light passes through an analyzer ANr, which is at with respect to the x axis, then enters a photodetector Dr. The amplitude detector by Dr is (1), where and are the phase shifts for the x component and the y component,

13、 respectively, of the reflected beam from BS. Hence the intensity of the reflected signal is (2) , where is the phase difference between s- and p- polarizations for the reflected light. In this method, the reflected light is the reference signal. On the other hand, the transmitted light enters the p

14、rism and is totally reflected there, and then it propagates out of the prism. At last, the light passes through an analyzer ANt, which have the transmission axis at 45° with respect to the x axis, and is detected by another photodetector . Here, the signal measured by is the test signal. The am

15、plitude detected by is (3) And its intensity is . (4)From Eq (2) and Eq (4), we can obtain the phase difference, (5) Lock-in AmplifierFig.1 The basic optical setup of the hetrodyne interferometer2.2 The principle of the SPR for three-layer Kretschmanns configuration:For Kretchmanns configuration of

16、a three-layer system as shown in Figure 2, the surface plasmons are excited when equal the resonant angle. From Maxwells equations, the reflection coefficients of p-polarization and s-polarization can be expressed as 5-6 , (6) where , is the thickness of the black matrix, and t = p , s， = ， (7) In E

17、q(7),is the component of the wave vector in medium in thedirection and is given as (8) , where is the refractive index of the glass substrate, is the refractive index of Cr metal, is the refractive index of air and is the wave vector in vacuum. If the amplitude reflection coefficients and are writte

18、n as , (9) , then the phase difference variation between p and s polarization components is. (10)RedGreenBlack Matrix (Cr) n2Glass substrate (n1)The reflected lightThe incident lightAir (n3)Fig. 2 Three-layer Kretschmanns configuration for the black matrixAnalyzerBlack matrixHe-Ne LaserPolarizer (45

19、°)E-ODriverFGLock-in AmpPhotodetectorReference signalTest signalPCGlass substrate Fig.3 The experimental setup3. RESULTS Fig. 3 shows the experimental setup. A heterodyne light source with the wavelength of 632.8nm is incident on the glass substrate at the incident angle . We use the metal chro

20、mium (Cr) as the material of the black matrixes. The permittivities of glass substrate (), the metal Cr film (), and air () are, , and , respectively. Fig.4 shows the plot of the reflectivity of p-polarization versus the incident angle. It is evident from Fig.4 that the reflectivity varies very obvi

21、ously around the resonant angle (). As shown in Fig.5, the phase difference as a function of the incident angle at constant wavelength . Fig.6 shows that the phase difference as a function of the thicknessof the black matrix. Therefore, the thickness of the black matrix can be achieved only by measu

22、ring the phase difference variation.Fig. 4: The plot of the reflectivity of p-polarization versus the incident angleFig. 5: The phase difference as a function of the incident angle Fig. 6: The phase difference as a function of the thicknessof the black matrix.4. DISCUSSION and CONCLUSIONGenernally s

23、perking, the defects of color filters can be divided into two groups,i.e., zero-dimensional point defect and two-dimensional plane defect. Perhaps, there are some defects, e.g., white points, particle defects and hole defects etc., during the manufacturing process. In the paper, we present a new met

24、hod for inspecting the thickness of the black matrix on the color filters by using the heterodyne interferometry. Because there are some drawbacks,e.g., cost highly and environmental pollution, during the process of coating Cr on the glass substrate, the nickel (Ni) has been used as the material of

25、the black matrix instead of Cr recently. However, we still obtain the thickness of the black matrixs only by measuring the phase differences between s- and p-polarizations.The new method for inspecting the thickness of the black matrix on the color filters by using the heterodyne interferometry has

26、some merits, e.g., a simple optical setup, easy operation, real time and rapid measurement etc. And its feasibility is demonstrated.5. ACKNOWLEDGEMENTThis research was partially supported by the National Science Council in Taiwan through Grant 94-2622-E-231-025-CC3.6. REFERENCES1 P. Y. Chien, “Two-frequency disp