JPH02132405A - Spectral filter and spectral measuring sensor - Google Patents

Abstract

PURPOSE:To obtain spectral characteristics which are superior to those obtained by a single filter by superposing a short-wavelength cutoff type interference filter and a long-wavelength cutoff type interference filter one over the other and making the cutoff wavelength of the former shorter than that of the latter. CONSTITUTION:A 1st interference filter F1 which has monotoneously long cutoff wavelength in one direction and transmits light in a longer wavelength range than the cutoff wavelength and a 2nd interference filter which transmits light in a shorter wavelength range than the cutoff wavelength are put one over the other so that their cutoff wavelengths are made coincident with each other. Then, the cutoff wavelength of the filter F1 is made shorter than the cutoff wavelength at the corresponding position of the filter F2. The short-wavelength cutoff characteristics of the spectral characteristics of those filters are determined by the 1st filter F1 about the peak wavelength of spectral transmissivity as a border and the long-wavelength side cutoff characteristics are determined by the 2nd filter F2, so the spectral characteristics which are superior to those obtained by a single filter are easily obtained.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a spectral filter and a spectral measurement sensor using an interference filter, and is used, for example, in a spectrometer or a film thickness monitoring device for a vacuum-deposited film. be.

[Prior Art] A spectrometry sensor has been proposed in which a plurality of light-receiving elements are arranged along the wavelength change direction of a spectral filter whose transmitted wavelength changes continuously along one direction (Tokukō Shō). 58-49807).

In this publication, a wedge-shaped interference filter is used in which the transmission wavelength changes continuously along the direction of change in film thickness by continuously changing the film thickness in one direction. The spectral characteristics of this interference filter are determined by the configuration of the membrane. The quality of spectral characteristics affects the accuracy of spectroscopic measurements, and the narrower the half-width and the smaller the tail, the higher the accuracy of spectroscopic measurements. This is because the spectral outputs of each light-receiving element overlap each other in the wavelength direction, and the smaller the overlap, the higher the wavelength purity of the spectral output of one light-receiving element.

[Problems to be Solved by the Invention] As described above, in order to increase the wavelength purity of a spectral filter, it is necessary to narrow the half-width while suppressing tailing.

To do this, the transmittance must rise sharply at a specific wavelength, and drop sharply when the wavelength deviates from the specific wavelength, but it has been difficult to obtain such characteristics with a single spectral filter. . Furthermore, as mentioned above, the spectral characteristics of a wedge-shaped interference filter are determined by the structure of the film, so once a film is created under certain conditions, its spectral characteristics cannot be changed; for example, it is not possible to change the half-width. The problem was that I couldn't do it.

The present invention has been made in view of these points, and its purpose is to provide a spectral filter and a spectral measurement sensor that have excellent spectral characteristics and can change the spectral characteristics. be.

[Means for Solving the Problems] In order to solve the above problems, in the spectral filter according to the present invention, as shown in FIGS. 1 to 3, the cutoff wavelength is monotonous along one direction. A first interference filter F+ whose cutoff wavelength becomes monotonically longer in one direction and transmits light in a wavelength range longer than the cutoff wavelength, and a first interference filter F+ whose cutoff wavelength becomes monotonically longer in one direction and transmits light in a wavelength range shorter than the cutoff wavelength. 2 interference filters F2 are superimposed so that the monotonically increasing directions of their cutoff wavelengths coincide, and the cutoff wavelength of the first interference filter F1 is shorter than the cutoff wavelength at the corresponding position of the second interference filter F2. It is characterized by:

Here, the first and second interference filters F, F2 are
It is preferable to make the positional relationship of the superposition variable with respect to the direction of change of the cutoff wavelength.

In addition, first and second interference filters F l, F 2
A spectrometry sensor can be obtained by arranging a plurality of light-receiving elements (1) to (4) along the direction of change in the cutoff wavelength.

[Function] In the present invention, a first interference filter F1 of short wavelength cutoff type and a second interference filter F2 of long wavelength cutoff type are overlapped, and the cutoff wavelength of the former is set at a corresponding position of the latter. Since the cutoff wavelength is shorter than the cutoff wavelength, a bandpass type interference filter can be obtained.Moreover, since the monotonically increasing direction of the cutoff wavelength of both is the same, it is possible to obtain spectroscopy in which the transmitted wavelength changes monotonically along one direction. You can get filters. The spectral characteristics of this spectral filter are such that, with the peak wavelength of spectral transmittance as the boundary, the cutoff characteristics on the short wavelength side are determined by the first interference filter F1, and the cutoff characteristics on the long wavelength side are determined by the second interference filter F2. It becomes possible to easily obtain spectral characteristics superior to those obtained with a single interference filter.

Furthermore, as shown in FIGS. 4 and 5, if the positional relationship of the overlapping of the first and second interference filters F, F2 is made variable, the spectral characteristics, especially the half-value width, can be controlled. . At this time, it is necessary to change the positional relationship so that the cutoff wavelength of the first interference filter F1 is shorter than the cutoff wavelength of the second interference filter F2 at the corresponding position. The half-value width immediately before the cutoff wavelengths match becomes extremely narrow, resulting in extremely sharp spectral characteristics.

Note that interference filters whose cutoff wavelength changes monotonically in one direction include wedge-shaped interference filters in which the film thickness increases continuously in one direction, and step-shaped interference filters in which the film thickness increases stepwise. can be used. In particular, when using the former method, by shifting the arrangement direction of the light receiving elements (1) to (4) from the direction of maximum film thickness change, it is possible to narrowly limit the measurement wavelength range and increase the wavelength resolution.

[Example] Examples of the present invention will be described below.

FIG. 1 shows the first interference filter F, FIG. 2 shows the second interference filter F2, and FIG. 3 shows the first and second interference filters F1, F2, respectively.
This figure shows the spectral output characteristics of each of the light-receiving elements (1) to (2) in the state superimposed on the figure and in the same state. In each of the above figures, diagram (a) shows the positional relationship between the light receiving elements (1) to (2) and the interference filter F1 or F2. Also, the minute diagram (b
) represents the output of each of the light receiving elements (1) to (2), and the horizontal axis represents the wavelength λ and the position of each of the light receiving elements (1) to (2). For each curve, only the portions that change are shown, and the portions that do not change much are not shown. The numbers ■～■ attached to each curve correspond to the respective light receiving elements■
It corresponds to the numbers ~■.

Each interference filter Fl, F2 is provided on a separate glass substrate G.
, G2 are deposited with a metal film (for example, Ag+Aj!) or a dielectric film to form a multilayer film, and the film thickness increases along one direction at a predetermined gradient.

In the first interference filter F1, the cutoff wavelength becomes continuously longer in the direction of increase in film thickness, and each portion transmits light in a wavelength range longer than the cutoff wavelength. Second interference filter F
In No. 2, the cutoff wavelength becomes continuously longer along the direction of increase in film thickness, and each part transmits light in a wavelength range shorter than the cutoff wavelength. First and second interference filters F + , F
If the gradients of the film thicknesses of the two films are the same, the amount of change in the cutoff wavelength per unit length will be the same. As shown in FIG. 3(.), the first and second interference filters F l, F 2
are superimposed so that the increasing directions of the cutoff wavelengths match,
If the cutoff wavelength of the first interference filter Fl in each part is made shorter than the cutoff wavelength of the second interference filter F2, each light receiving element
(2) makes it possible to detect the light intensity in each different wavelength range.

Note that the number of light receiving elements (1) to (4) is not limited to the number shown in the drawings, but may be any number. Further, the plurality of light receiving elements may be configured on a semiconductor integrated circuit.

Next, FIGS. 4 and 5 show the principle of controlling the half-width by shifting the positional relationship of the first and second interference filters F, F2 in the direction of film thickness change. however,
For convenience, the spectral characteristics of each of the interference filters F1F2 are illustrated as characteristics that change in a stepwise manner in seven steps. In each of the above figures, the partial diagram (a) shows the position of the first interference filter F1 and the spectral transmittance characteristics of each part, and the partial diagram (b) shows the position of the second interference filter F2 and the spectral transmittance characteristics of each part. , minute diagram (
0) shows the positional relationship of the first and second interference filters F, F2 and the spectral transmittance characteristics of each part.

In the spectral transmittance characteristics, the horizontal direction shows the wavelength λ, the vertical direction shows the transmittance T of the filter for each horizontally long band, and the positional relationship between the bands.

FIG. 4 shows the state in which the first stage of the first interference filter F1 and the second stage of the second interference filter F2 are overlapped, and FIG. The state in which the second stage of the interference filter F2 and the second stage of the interference filter F2 are overlapped so as to coincide with each other is shown. As is clear from the figure, the half-width is wider in the configuration shown in FIG. 5 than in the configuration shown in FIG. 4. In this way, by shifting the positional relationship in which the first and second interference filters F + and F 2 are superimposed in the direction of change of the cutoff wavelength, it is possible to freely change the half-width of the spectral filter obtained by superimposing them. It is.

In this case, the relationship between the amount of physical shift and the amount of change in half-width is determined by the amount of change in cutoff wavelength per unit length in each interference filter Fl+F2. In other words, when using an interference filter with a small amount of change in cutoff wavelength per unit length, the amount of change in half-width relative to the amount of physical shift is small, and conversely, the amount of change in cutoff wavelength per unit length is large. When an interference filter is used, the amount of change in half-width with respect to the amount of physical shift becomes large.

[Effects of the Invention] In the spectral filter of the present invention, the cutoff characteristics on the short wavelength side and the long wavelength side are determined by separate interference filters, with the peak wavelength of spectral transmittance as the boundary, so a single interference filter can be used. There is an effect that spectral characteristics superior to those obtained can be easily obtained.

In addition, if the positional relationship of the superposition of the first and second interference filters is made variable, spectral filters with various half-widths can be obtained by simply creating two spectral filters. This facilitates high-mix, low-volume production.

Further, it is possible to realize a spectral filter or a spectral measurement sensor whose half width can be changed depending on the object to be measured.

[Brief explanation of drawings]

FIG. 1(a) is a sectional view showing the positional relationship between a first interference filter and a light receiving element used in an embodiment of the present invention, and FIG.
) is the same spectral characteristic diagram as above, FIG. Diagram (a)
is a cross-sectional view showing the positional relationship between the first and second interference filters and the light-receiving element used in the above embodiment, FIG. It is a diagram explaining the principle of control. FI+F2 is an interference filter, and ■ to ■ are light receiving elements.

Claims (4)

[Claims] (1) A first interference filter whose cutoff wavelength becomes monotonically longer along one direction and transmits light in a wavelength range longer than the cutoff wavelength; A second interference filter that transmits light in a wavelength range shorter than A spectral filter characterized by having a cutoff wavelength shorter than the cutoff wavelength at the specified position. (2) The spectral filter according to claim 1, wherein the first and second interference filters have a positional relationship in which they are superimposed so as to be variable in a direction in which the cutoff wavelength changes. (3) In the spectral filter according to claim 1 or 2,
A spectrometry sensor comprising a plurality of light-receiving elements that receive light transmitted through first and second interference filters and arranged along a direction in which a cutoff wavelength changes. (4) A spectral filter that includes a wedge-shaped interference filter whose film thickness changes continuously, and whose transmission wavelength changes continuously in the direction of change in film thickness, and a light-receiving element in which multiple light-receiving elements are arranged in a line. A spectroscopic measurement sensor characterized in that the angle between the direction of maximum change in film thickness and the direction in which the light-receiving elements are arranged is variable.