JPS6253045B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION In manufacturing MOS integrated circuits, it is important to control the thickness of a glassy thin film (PSG layer) formed on the surface of a silicon substrate and the concentration of phosphorus (P) contained therein. Therefore, in the past, the thickness of the thin film was optically measured and the amount of phosphor attached was measured using a fluorescent X-ray method. The concentration was calculated. As described above, in the past, it was necessary to measure the film thickness optically and to measure the amount of phosphorus deposited using X-rays, and these had to be performed separately, resulting in a drawback that the measurement operation was extremely complicated. As described above, the present invention relates to a PSG formed on a silicon single crystal substrate, for example.
The present invention provides a method and an apparatus for easily measuring the thickness of a thin film using X-ray analysis. Therefore, if necessary, the above-mentioned phosphorus adhesion amount measurement and film thickness measurement using the fluorescent X-ray method can be carried out simultaneously, and the above-mentioned measurements can be carried out efficiently. The present invention will be explained in detail below.

FIG. 1 is a diagram schematically showing a cross section of a MOS integrated circuit, in which silicon oxide layers 2, 3, 4, polycrystalline silicon layers 5, 6, and a glassy (PSG) thin film 7 are formed on a single-crystal silicon wafer 1. , 8 and an aluminum layer 9, etc., and the approximate thickness of each part is as shown in the drawing. As described above, an actual MOS integrated circuit has a complicated structure, and when irradiated with X-rays, the characteristics of the integrated circuit may change. Therefore, when manufacturing a MOS integrated circuit, as shown in FIG. 2, a monitor sample is prepared by using a single-crystal silicon wafer as a base 10 and the PSG thin film 11 is directly deposited thereon, as shown in FIG. Measure the layer thickness and phosphorus coverage. When the surface of such a sample is irradiated with X-rays of an appropriate wavelength, coherent Thomson scattered radiation and incoherent Compton scattered radiation are generated, but in the range where the wavelength of the X-ray is longer than 1.3 Å, the latter is stronger than the former. Since it is extremely weak, by further spectroscopically measuring the Thomson scattered radiation using appropriate means, the latter becomes about 1% of the former, making it possible to ignore the Compton scattered radiation. Further, since the substrate 10 is a single crystal as described above, it generates diffraction lines in a specific direction. Therefore, by arranging the above-mentioned spectroscopic means at a position where the diffraction rays do not enter, only the Thomson scattered rays can be detected.

The intensity of the Thomson scattered rays mentioned above is determined by the atomic scattering factor f
It is proportional to the product of the square of _i (i is the type of element), the electron scattering factor, and the intensity of incident X-rays, but as shown in Figure 2,
Thomson scattered rays 13 and 14 are generated from both the PSG thin film 11 and the substrate 10. As shown in the figure, the incident angle of X-ray 12 is α, and the detected Thomson scattered ray 1
The emission angle of 3,14 is β, the constant is C, the atomic weight of element i is Ai, Avogadro's number is N, the density of PSG thin film is ρ, the concentration ratio of element i is Wi (ΣWi = 1), PSG
The mass absorption coefficient is μ/ρ, the crystal structure factor is F, the Laue diffraction function is G, the number of atoms in the unit cell is n,
When the thickness of the PSG thin film is t, the intensities I ₁ and I ₂ of the scattered rays 13 and 14 are respectively I ₁ =C∫ ^t ₀ ΣρNf〓/AiWi exp{−(μ/ρ)ρt(cosecα+cosecβ)}dt... (1) I ₂ = C | F | ² GN/A _Si・n・e ⁻⁽ 〓 ^/ 〓 ⁾ 〓 ^t(cosec 〓 ^+cosec 〓 ⁾ /(μ/ρ) _Si (
cosecα+cosecβ)...(2) is given. Since G in equation (2) takes a value close to zero when Bragg's diffraction condition is not satisfied, PSG
Assuming that the thickness t of the thin film is 8000 Å and the phosphorus concentration is 8 mol%, the intensity I ₁ of the Thomson scattered ray 13 given by equation (1) is more than 20 times the intensity I ₂ of the scattered ray 14, and the substrate 10 can be ignored. Also, by integrating equation (1), we get is obtained. Therefore, the thickness t of the PSG thin film can be determined by measuring the intensity I ₁ of the Thomson scattered radiation.

Note that PSG is a glassy substance made of silicon oxide (SiO ₂ ) and phosphorus oxide (P ₂ O ₅ ), and there is almost no difference in the scattering and absorption of X-rays by these, and the thickness t is 0 to 0. The concentration of phosphorus (P) is 0 in the range of 8000 Å.
The difference in the amount of PSG deposited between mol% and 8 mol% is 0.3%.
It's just a matter of degree. Furthermore, when measuring the thickness t using equation (3), ρ=1/(W _P2O5 /ρ _P2O5 +1−W _P2
O5 / _ρSiO2 )...(4) is used to correct the density ρ of PSG. And as mentioned above, in order to remove the influence of Compton scattered radiation,
It is necessary to make the wavelength of the line longer than 1.3 Å, and measurement accuracy is improved by increasing the wavelength and increasing μ/ρ in equation (3). But on the other hand
If the wavelength of the radiation is made longer, the scattered radiation will become saturated if the thickness t is large, making measurement impossible, so normally X-rays with a wavelength of 2 to 6 Å are used.

FIG. 3 is a diagram showing the configuration of an apparatus according to an embodiment of the present invention, in which a sample 15 as shown in FIG.
X-rays 17 are irradiated from the sample 15, and the X-rays 13 and the like scattered by the sample 15 are incident on the spectroscopic crystal 18, and the Thomson scattered rays 19 diffracted by the crystal are detected by the X-ray detector 20. In such a device, by using, for example, rhodium (Rh), silver (Ag), or chromium (Cr) as the target of the X-ray tube 16, the unique X-ray Rh-
X-rays containing L, Ag-L, Cr-K, etc. can be made incident on the sample 15. Furthermore, the above-mentioned characteristic X-rays are diffracted by the silicon substrate of sample 15,
By installing the spectroscopic crystal 18 in a position where the diffracted X-rays are not incident, and allowing the characteristic X-rays diffracted by the spectroscopic crystal to enter the detector 20, only the Thomson scattered rays can be spectrally detected. can. Note that the spectroscopic crystal 21 and the X-ray detector 22 are used for the sample 15.
This is to detect the fluorescent X-rays of phosphorus in the PSG thin film and measure the amount of phosphorus attached. In addition, Figure 4 shows the relationship between the relative intensity (I ₁ + I ₂ ) of Rh-La rays (Tososon scattered rays) and film thickness (t) using the above-mentioned apparatus, and the X mark is the theoretical one. The white circles are the actual measured values before density correction, and the black circles are the values after density correction using equation (4). Note that there is only one white circle, but the other P concentration changes are relatively small and are polymerized as shown in the black circles. According to this measurement example, the concentration of phosphorus (P) is 1 to 13 mol%.
It can be confirmed that there is a good correlation between the thickness t and the Thomson scattered radiation intensity within the range of . Note that the scattered radiation intensity I ₂ of the silicon substrate in the logical value corresponds to the case where there is no PSG thin film when the exponential term in equation (2) is 1, so it is calculated based on this actually measured intensity.

As described above, the present invention measures the thickness of an amorphous glassy thin film formed on a single-crystal silicon wafer as a base material, such as a MOS integrated circuit, by irradiating it with X-rays. Then, coherent Thomson scattered rays are generated only in the glassy thin film, and the X-rays that pass through the thin film and enter the substrate are diffracted in specific directions depending on their wavelengths.
Therefore, for X-rays of a single wavelength, the X diffracted by the substrate
Only the Thomson scattered radiation can be detected by arranging the detector at a position where the radiation is not incident. Moreover, the intensity of this Thomson scattered radiation corresponds to the thickness of the glassy film, so the aforementioned film thickness can be measured using this, and by using X-rays with a wavelength of several angstroms, the Compton scattered radiation can be measured. can be ignored and also prevent a decrease in measurement accuracy when the film thickness is large. Furthermore, since the film thickness can be measured using X-rays, it is possible to simultaneously measure the film thickness using fluorescent X-rays if necessary.
By performing line analysis, it is possible to detect the components contained in the thin film or measure their amounts, and therefore the manufacturing process of MOS integrated circuits can be efficiently managed.

[Brief explanation of the drawing]

Fig. 1 is a cross-sectional model of a MOS integrated circuit, Fig. 2 is a cross-sectional view of a monitor sample for measuring the thickness of the glassy thin film shown in Fig. 1, and Fig. 3 is a diagram showing the configuration of an embodiment of the present invention. , FIG. 4 is a curve showing the relationship between film thickness and Thomson scattered radiation intensity. In the figure, 1
5 is a sample 16 is an X-ray tube, 18 and 21 are spectroscopic crystals,
20 and 22 are X-ray detectors.

Claims (1)

[Claims] 1. A sample having a glassy thin film on the surface of a single crystal substrate is irradiated with X-rays, Thomson scattered rays having a single wavelength of several angstroms are detected, and the intensity of the Thomson scattered rays is determined based on the intensity of the Thomson scattered rays. A method for measuring the thickness of a glassy thin film, the method comprising: determining the thickness of the thin film. 2. An X-ray source that irradiates a sample having a glassy thin film on the surface of a single-crystal substrate with X-rays containing characteristic X-rays of several angstroms, and a position where the diffraction rays of the characteristic X-rays from the substrate do not enter. A device for measuring the thickness of a glassy thin film, comprising means for detecting Thomson scattered radiation of the characteristic X-rays by the thin film.