JP2780324B2 - X-ray thickness gauge - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an X-ray film thickness meter for measuring the thickness of a thin film.

[Conventional technology]

Conventionally, this type of X-ray film thickness meter measures the thickness of a metal film using the absorption effect of X-rays. In recent years, this type of X-ray film thickness meter is often used to measure the thickness of a thin film on a semiconductor substrate. I have been.

Although not shown in the drawings, this X-ray film thickness meter includes an X-ray generator that projects X-rays at a predetermined incident angle onto a substrate surface on which a thin film to be measured is formed, and an X-ray generator. And a detector symmetrically arranged obliquely with the detector.

When measuring the thickness of the thin film of the substrate, first, X-rays are irradiated on the surface of the thin film of the substrate, and the X-rays reflected from the elements contained in the thin film and the substrate are measured by a detector, and the intensity difference is measured. Was converted to a film thickness to obtain a film thickness.

[Problems to be solved by the invention]

In the conventional X-ray film thickness meter described above, for example, in the case of a thin film having a thickness of 1 μm or less, when monitoring the intensity of reflected X-rays in the substrate, the density of the elements in the thin film is large and the X-ray mass coefficient is large. If it is large, the absorption in the thin film becomes large, so that the measurement may be possible even with a thin film of 1 μm or less. However, conversely, when the intensity of X-rays reflected by the elements of the substrate is high, the density of the elements in the thin film is small, and the X-ray mass absorption coefficient of the thin film is small, the absorption of X-rays by the thin film is small, and the film thickness is small. There is a problem that measurement cannot be performed.

It is an object of the present invention that a thin film formed on a substrate has a thickness of 1 μm.
It is an object of the present invention to provide an X-ray film thickness meter capable of measuring the film thickness even when the thickness is less than m.

[Means for solving the problem]

The X-ray film thickness meter according to the present invention comprises a film having a critical angle of total reflection θ ₁ on a substrate having a critical angle of total reflection of X-rays θ ₀ and a thin film in which θ ₁ is smaller than the above-mentioned θ _0. in X Senmaku thickness meter for measuring the thickness, a means for setting a take-off angle theta ₂ which detects the X-rays reflected from the incident angle theta _X and the substrate of X-rays to _{θ 1 <θ X = θ 2} <θ 0 Provided and configured.

〔Example〕

 Next, the present invention will be described with reference to the drawings.

FIG. 1 is a schematic sectional view showing the relative positions of an incident and reflected X-ray, a substrate on which a thin film is formed, and a detector for explaining an embodiment of the present invention. In this drawing, the angle of refraction is not shown for convenience of explanation. As shown in FIG. 1, the critical angle of total reflection of the substrate 3 is θ ₀ , the critical angle of total reflection of the thin film 1 is θ ₁ , the incident angle of X-rays is θ _X, and the incident angle of the incident X-rays 2 is theta _X is, when irradiated to the thin film 1 under the condition of _{θ 1 <θ X <θ 0} , the incident X-ray 2 is transmitted through the film 1, to reach the surface of the substrate 3.

It has been found that the source X-ray 5 totally reflected by the substrate 3 can be detected most strongly when the take-out angle θ _{2 of the} detector 4 is θ ₁ <θ ₂ <θ ₀ . Incidentally, take-off angle theta ₂ of the detectors 4 in this case has been set the incident angle of the aforementioned X-ray at an angle equal to theta _X.

Here, for example, when a film of the thin film 1 is d, the incident and source X-ray 2 transmission distance 1/2 becomes 1 = 2d / sin [theta _X. For example, if θ _X = 2 mrad and d = 100 °, 1
= 10 μm. If the thin film 3 is SiO ₂ , the density is 2.3 g / cm ³ and the X-ray mass absorption coefficient is almost
Since it is 100 cm ² / g, the ratio of the intensity X ₀ of the incident X-ray to the intensity X of the source X-ray detected is I / I ₀ = e × p (−100 × 2.3 × 10/10000) = 0.79. Become. Conventionally, when the take-out angle θ _{2 of the} detector 4 is set to about 45 °, the enhancement ratio I / I ₀ becomes 0.996, and the intensity change becomes about an error.
It is difficult to evaluate the film thickness. On the other hand, in the present embodiment using the above-described total reflection, sufficient intensity attenuation for evaluating the thickness of the thin film can be obtained.

Further, the mounting of these X-ray generators and detectors can be easily realized by using known mounting means and allowing the respective angles to be adjusted by remote control from outside the X-ray protection chamber.

〔The invention's effect〕

As described above, the present invention provides a method for measuring the thickness of a thin film having a small thickness, a small density, and a small mass absorption coefficient, at an angle intermediate between the substrate and the X-ray total reflection critical angle of the thin film. By arranging the X-ray generator and detector symmetrically with respect to the irradiation point, a large difference in the intensity between the incident X-ray and the source X-ray can be obtained, so that the X-ray film can accurately measure the film thickness. There is an effect that a thickness gauge can be obtained.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view showing the relative positions of an incident and reflected X-ray, a substrate on which a thin film is formed, and a detector for explaining an embodiment of the present invention. 1 ... thin film, 2 ... incident X-ray, 3 ... substrate, 4 ... detector, 5 ... source X-ray.

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int. Cl. ⁶ , DB name) G01B 15/00-15/06 G01N 23/00-23/227

Claims (1)

(57) [Claims] 1. A The theta ₁ with with a total reflection critical angle theta ₁ on a substrate having a total reflection critical angle theta ₀ of X-ray is the theta
_In an X-ray thickness meter for measuring the thickness of a thin film smaller than ₀ , the incident angle θ _X of X-rays and the extraction angle θ ₂ for detecting X-rays reflected from the substrate are defined as θ ₁ <θ _X =
X provided with means for setting θ ₂ <θ ₀
Wire thickness gauge