JPS63292045A - Thermal-stress measuring device - Google Patents

Abstract

PURPOSE:To perform measurement simply and accurately, by supporting a reference sample, whose thermal deformation is negligible, and a sample to be measured with the same supporting member together, reading the relative distance between the reflected light beams from both samples, and compensating for the error of fluctuation due to the heat of the supporting member. CONSTITUTION:A sample to be measured 1 and a reference sample 2 are supported with a single supporting member 3 in close proximity and provided in a constant temperature oven 4. A laser light source 5 is arranged so as to face the samples 1 and 2. The fluctuation of the relative distance DELTA between the reflected spots S1 and S2 from the samples 1 and 2 is read with a detecting part 6. Namely, warp is yielded in the sample 1 because of the difference in thermal expansion coefficients of a silicon substrate 7 and a silicon nitride thin film 8. Warp is not yielded in the sample 2 since the sample 2 comprises only a bare silicon substrate 9. Therefore, the thermal fluctuation of the member 3 is automatically compensated by reading the distance DELTA. The thermal stress of the sample 1 can be measured simply and accurately.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a thermal stress measuring device for measuring thermal stress of a thin film on a substrate.

[Summary of the invention]

In a thermal stress measuring device, the present invention arranges a sample to be measured supported by the same support member and a reference sample whose thermal deformation can be ignored in a heating chamber, shines light on both samples, and collects two samples from both samples.
By measuring the relative distances of the two reflected lights, it is possible to compensate for thermal fluctuations in the supporting member and to accurately measure thermal stress on the sample to be measured.

[Conventional technology]

For example, in the field of semiconductor manufacturing, various problems arise due to stress when the temperature rises, such as disappearance of the A1 film deposited on the semiconductor substrate or blistering of the overcoat film. Although it is easy to measure stress at room temperature, it is difficult to determine stress a when the temperature is increased.

Conventionally, there are various methods for measuring stress in thin films.
i) Diffraction method (X-ray diffraction method, electron beam diffraction method), etc.

FIG. 6 is a block diagram of a generally known internal thermal stress measuring device using the optical lever method.

In this device, a substrate (11) is fixed at one end with a support part (12), and light (14) from a light source (13) is transmitted through a prism (
15) and the lens system (16) to the other end of the substrate (11), and the reflected light (14a) is irradiated to the other end of the substrate (11) through the lens system (16).
), the differential photovoltaic cell (18) is illuminated through the prism (15) and lens system (17). When a thin film is deposited on this substrate (11) and the substrate (11) is warped, the irradiation position of the reflected light (14a) on the differential photovoltaic cell shifts, and the differential output from the differential photovoltaic cell causes the inside of the thin film to be distorted. Stress is measured. (19) indicates a micrometer.

[Problem that the invention seeks to solve]

The above-mentioned optical screw method is known as a highly sensitive method, but when heated to measure thermal stress, the supporting portion of the substrate (11) deforms due to thermal expansion, resulting in deformation (warpage) of only the substrate (11). ) cannot be separated. For this reason, thermal stress is generally measured using the Newton-Rig method, but there is ambiguity in measuring the position of interference fringes.
Measurement accuracy does not improve.

In view of the above-mentioned points, the present invention provides a thermal stress measuring device capable of accurately measuring thermal stress of a thin film on a substrate by compensating for errors caused by thermal fluctuations.

[Means for solving problems]

The thermal stress measurement device of the present invention includes a heating chamber (4), a sample to be measured (1) supported by the same support member (3) in the heating chamber (4), and a reference whose thermal deformation can be ignored. sample(
2), a light source (5) that shines light on a part of both samples (11 and (2)), and detects two reflected lights (Sl) and (S2) from both samples (11 and (2)). The detection unit (6) is configured to measure the thermal stress of the sample to be measured (1) by measuring the relative distance Δ between the two reflected lights (Sl) and (S2).

The sample to be measured (1) is a substrate on which a thin film is adhered. The reference sample (2) is a substrate made of a homogeneous material such as Si or glass, which does not warp even when thermally expanded.

[Effect]

Light from the light source is irradiated onto the same height position of the sample to be measured (1) and the reference sample (2), and two reflected spots (Sl) and (S2) of the light are observed by the detection unit (6). be done. Reference sample (2) does not warp even when the temperature is increased. Therefore, when the sample to be measured (1) is not warped, the relative distance Δ between the two reflection spots (Sl) and (S2) is 0. Next, when the temperature is increased, when the sample to be measured (1) warps due to the difference in thermal expansion coefficient between the substrate and the thin film, the position of the reflection spot (Sl) from the sample to be measured (1) is displaced. The amount of displacement of this reflection spot (Sl), that is, both spots (
The relative distance Δ between Sl) and (S2) is measured, and from this relative distance Δ, the amount of warpage δ of the sample to be measured is determined using equation (1) (δ; lΔ/2L), which will be described later. (σ=
Eb2/3 (1-ν)β2 d) allows the sample to be measured (
1) The stress σ is found.

If the support member (3) changes due to heat during temperature rise, the influence of the change in the support member (3) will be
) and (2). Therefore, the double reflection spot (Sl) read by the detection unit (6)
The relative distance Δ between and (S2) is the value after the fluctuation is subtracted, that is, the amount of displacement caused by the warpage of only the sample to be measured (11).Therefore, the relative distance between both reflection spots (Sl) and (S2) is By reading the distance Δ, accurate thermal stress of the thin film of the sample to be measured can be measured.

〔Example〕

Embodiments of the thermal stress measuring device according to the present invention will be described below with reference to the drawings.

In this example, as shown in Figure 1, the sample to be measured (1)
and reference sample (2), and both samples (1) and (2).
One end of each of the samples (1) and (2) is supported by a single support member (3) made of glass, for example, so that the samples (1) and (2) are arranged close to each other. The commonly supported sample to be measured (11) and reference sample (2) are placed in a heating chamber, that is, a constant temperature oven (4).In this example, the sample to be measured (1) is as shown in Figure 3A. Thickness on one side of silicon substrate (7) 1.
A sample on which a 0 μm silicon nitride thin film (8) was deposited by plasma CVD was used, and a bare silicon substrate (9) as shown in FIG. 3B was used as a reference sample (2). In both samples (1) and (2), the silicon substrates (7) and (9) have a thickness of 0.6 mm, a length of 12.5 cm,
The width is 1 cm.

Then, one laser light source (5) for irradiating laser light to both samples (1) and (2) is placed opposite to both samples (11 and (2)) installed in constant temperature M (4). and the reflected spot (S
A detection unit (6) is arranged to detect l) and (S2).

In this case, both samples (1), (21 and laser light source (5)
) is arranged so that the laser spot hits both samples simultaneously. Here, the distance l between the laser irradiation part (10) and the support member (3) in both samples fil and (2) is 8cII
+, distance ML between both samples (11 and (2) and detection part (6)
is 11.8m.

To measure the stress of the thin film (8) when the temperature is increased using this thermal stress measurement device, the following procedure is performed.

Both the sample to be measured (1) and the reference sample (2) supported by a single support member (3) installed in a thermostatic chamber (4) are simultaneously irradiated with laser light from a laser light source (5). Then, the detection unit (6) reads the variation in the relative distance Δ of the respective reflection spots (Sl) and (S2) reflected by the sample to be measured (1) and the reference sample (2). That is, the sample to be measured (1) is a silicon substrate (7) and a silicon nitride thin film (8).
Although warping occurs due to temperature due to the difference in thermal expansion coefficient between the two, since the reference sample (2) uses a bare silicon substrate (9), no warping occurs due to temperature. Also, both samples (11 and (
2) is supported by a common support member (3), so if the support member (3) changes due to heat, both samples (11 and (2)) will be displaced in the same way. Therefore, if the temperature is changed, By reading the relative distance Δ between the reflection spots (Sl) and (S2) of both samples (11 and (2)) when An example of the results of measuring the relative distance Δ of the reflection spot for each measurement temperature is shown in FIG. 4. However, the graph in FIG. 4 is the value obtained by subtracting the relative distance in the initial state (room temperature).

The amount of warpage δ of the sample to be measured (1) can be calculated from this relative distance Δ.

As shown in Figure 5, the angle change of the reflected light corresponding to Δ is θ
This is due to the fact that θ(l). This change is the result of a change in the area irradiated by the laser beam by 6, and therefore, the amount of warpage δ of the sample to be measured (11) can be determined.

Furthermore, the stress σ of the thin film (8) of the sample to be measured (11) is determined by the following equation.

Here, E: Young's modulus of the substrate: Poisson's ratio of the substrate l: Distance between the support member and the laser irradiation part δ: Amount of warp of the two substrates d: Thickness of the thin film Figure 2 shows the invention of the present invention. This is another example of the thermal stress measuring device. In this example, the basic configuration is the same as that in Fig. 1, but two laser light sources (5a) and (5b) whose relative positions are fixed are arranged, and a sample to be measured (1) and a reference sample (2) are arranged. ) is configured to irradiate the respective laser beams.

According to the above-described thermal stress measuring device, the sample to be measured (11) and the reference sample (2), which does not cause warping, are supported by the same support member (3), and both samples (11 and (2) are supported by the detection unit (6). 2) is measuring the relative distance Δ of the reflection spots (Sl) and (S2).

Even if the support member (3) changes in accordance with the temperature rise, the reflection spot relative distance Δ becomes a value obtained by subtracting the amount based on the change, that is, a value corresponding to the amount of warpage of only the sample to be measured (11).

Therefore, thermal fluctuations in the support member (3) are compensated for and the thin film (8
) can be accurately measured.

〔Effect of the invention〕

According to the present invention, a reference sample whose thermal deformation can be ignored is fixed to the same support member together with the sample to be measured, and the relative distance of the reflection spots from both samples is read. Errors caused by fluctuations are compensated for, and the thermal stress of the sample to be measured can be measured easily and accurately.

[Brief explanation of drawings]

1 and 2 are block diagrams showing an example of a thermal stress measuring device according to the present invention, FIG. 3 is a perspective view showing an example of a sample to be measured and a reference sample, and FIG. 4 is a diagram showing measurement temperature and reflection spots. FIG. 5 is a graph showing the relationship between relative distances, FIG. 5 is a diagram for explaining the present invention, and FIG. 6 is a configuration diagram of a conventional internal stress measuring device using the optical lever method. (11 is the sample to be measured, (2) is the reference sample, (3) is the support member, (4) is the thermostat, (5) is the laser light source, (6) is the detection unit, (Sl), (S2) is It is a reflective spot.

Claims (1)

[Scope of Claims] A heating chamber, a sample to be measured and a reference sample whose thermal deformation can be ignored, which are supported by the same support member in the heating chamber, and a light source that irradiates parts of both the samples. A thermal stress measuring device, comprising: a detection unit that detects two reflected lights from both of the samples, and measures a distance between the two reflected lights to measure thermal stress of the sample to be measured.