JPH0621777B2 - Semiconductor crystal surface roughness evaluation method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Outline] In the semiconductor crystal surface roughness evaluation method of the present invention, the composition of the semiconductor crystal to be inspected is confirmed, and the intensity of reflected light from the semiconductor crystal to be inspected and the standard sample surface are used. The ratio of the surface roughness of the semiconductor crystal to the surface of the semiconductor crystal can be optically determined without being affected by the difference in the composition of the semiconductor crystal to be inspected and the variation in the output of the laser light source. In addition, the evaluation is made quantitatively.

[Industrial application field]

 The present invention relates to a semiconductor crystal surface roughness evaluation method.

In an initial step of manufacturing a semiconductor device, a crystal having a desired composition, for example, InGaAsP, is formed on a surface of a semiconductor substrate, for example, InP by epitaxial growth. The roughness of the crystal surface is an important factor that affects the characteristics of the semiconductor device and needs to be accurately evaluated.

[Conventional technology]

Conventionally, the roughness of the semiconductor crystal surface has been evaluated by an inspector by looking at the crystal surface using an optical microscope and comparing it with a standard sample.

[Problems to be solved by the invention]

Therefore, the evaluation is qualitatively performed based on the experience of the inspector, which largely depends on the experience of the inspector, and there is a problem in that the accuracy is insufficient.

The rougher the crystal surface, the lower the reflectance on the crystal surface. Therefore, it is possible to measure the intensity of the reflected light from the semiconductor crystal surface to be inspected and evaluate the surface roughness based on this.

However, the reflectance on the crystal surface changes depending on the refractive index of the crystal itself. The intensity of the reflected light also changes depending on the output of the laser light source that is the light source of the incident light. Therefore, the roughness of the crystal surface cannot be evaluated only from the intensity of the reflected light.

[Means for solving problems]

The semiconductor crystal surface roughness evaluation method of the present invention comprises a step of measuring the wavelength of photoluminescence from a semiconductor crystal to be inspected, and the intensity of light reflected from the surface of the semiconductor crystal to be inspected of light from a light source. Between the step, the step of measuring the intensity of the reflected light on the surface of the standard sample from the light source, the intensity of the reflected light on the surface of the semiconductor crystal to be inspected and the intensity of the reflected light on the surface of the standard sample It comprises a step of obtaining a ratio, and a step of applying the above wavelength and ratio to a crystal surface roughness evaluation criterion obtained for a crystal having a desired surface state to evaluate the surface roughness of the inspected semiconductor crystal.

[Action]

By measuring the wavelength of photoluminescence from the semiconductor crystal to be inspected, the composition of the crystal, that is, the refractive index of the crystal can be known, and the reflectance on the surface of the crystal can be known. Thereby, the roughness of the crystal surface can be evaluated in consideration of the refractive index (reflectance) of the crystal itself.

By evaluating based on the ratio of the intensity of the reflected light on the surface of the semiconductor crystal to be inspected and the intensity of the reflected light on the surface of the standard sample, the roughness of the crystal surface can be obtained without being affected by the variation in the output of the light source. Can be evaluated.

〔Example〕

FIG. 1 shows an evaluation procedure of an embodiment of a semiconductor crystal surface roughness evaluation method according to the present invention.

First, a method of obtaining a crystal surface roughness evaluation criterion necessary for evaluation will be described.

FIG. 2 shows a procedure for obtaining an evaluation judgment standard of crystal surface roughness, FIG. 3 shows an apparatus therefor, and FIG. 4 shows an example of the obtained evaluation judgment standard.

In FIG. 3, 1 is an InP semiconductor substrate and 2 is a semiconductor substrate 1.
Crystal 3 on which InGaAsP is epitaxially grown
It is a semiconductor substrate on which crystals have been formed. The roughness of the evaluation surface of the crystal 3 is the roughness that was inspected by the optical microscope and was accepted.

First, in FIG. 2, in step 4, the wavelength of photoluminescence from the crystal 3 is measured.

For this purpose, the laser light source 10 is oscillated in FIG. As a result, an Ar ⁺ laser beam with a wavelength of 514.5 nm 11
Is circularly polarized by the wave plate 12, and the half mirror 13
The light is reflected by the laser light and illuminates the surface of the crystal 3 through the lens 14. As a result, the crystal 3 is excited, and the crystal 3 emits photoluminescence 15.

The photoluminescence 15 passes through the half mirror 13 together with the reflected light 16, is reflected by the mirror 17, and travels toward the spectroscope 18. The reflected light 16 is cut by the filter 19, and only the photoluminescence 15 is incident on the spectroscope 18, where the wavelength of the photoluminescence 15 is, for example, λ ₁
Can be measured.

The composition of the crystal 3 can be known from the wavelength of the photoluminescence 15, and thus the refractive index of the crystal 3 can be known. The refractive index of the crystal and the wavelength of photoluminescence from the crystal have a corresponding relationship, and in FIG. 4, the horizontal axis represents the wavelength of photoluminescence.

Next, in step 5 in FIG. 2, the intensity of the reflected light 16 from the surface of the crystal 3 is measured.

For this purpose, the mirror 17 is rotated to the position shown by the chain double-dashed line. As a result, the reflected light 16 enters the detector 20 together with the photoluminescence 15, and this output is converted into a voltage by the microvolt meter 21, and the recorder 2
2 is recorded as I _epi . Photoluminescence 15
Is much smaller than the intensity of the reflected light 16 and can be ignored.

Next, in step 6 in FIG. 2, the intensity of the reflected light on the surface of the semiconductor substrate is measured.

To this end, in FIG. 3, the table 23 is moved in the direction of the arrow X, the semiconductor substrate 1 is irradiated with the laser light 11, and the reflected light from this is detected by the detector 20 and the recorder 22.
Record as I _Inp . The surface of the semiconductor substrate 1 is polished, and there is almost no variation in the surface state, and it is suitable as a standard sample, and here it is used as a standard sample.

Next, in FIG. 2, in step 7, the ratio of the intensity I _epi of the reflected light on the crystal 3 to the intensity I _Inp of the reflected light on the semiconductor substrate 1, I
_{Find epi} / I _Inp . It is assumed that this ratio becomes R ₁ . The reason why the ratio of the intensities of the reflected light is obtained here is to eliminate the influence of variations in the output of the laser light source 10.

Next, in step 8 in FIG. 2, a crystal surface roughness evaluation criterion is determined from the wavelength λ ₁ and the intensity ratio R ₁ described above.

Specifically, the point 24 is plotted from the wavelength λ ₁ and the intensity ratio R ₁ , and the steps 4 to 7 are performed by using another crystal-formed semiconductor substrate having a different crystal composition which is acceptable for the surface roughness. Do and plot points 25 and 26. As a result, as shown in FIG. 4, the evaluation judgment base line 27 passing through the points 24, 25, and 26 is drawn in the coordinate system in which the horizontal axis is the wavelength of photoluminescence and the vertical axis is the intensity ratio of reflected light. Be done. The evaluation judgment reference line 27 is stored in the microcomputer 30 shown in FIGS. 5 and 6.

Next, regarding the method of evaluating the semiconductor crystal surface roughness,
This will be described with reference to the drawings and FIG.

FIG. 5 shows an example of a semiconductor crystal surface roughness evaluation apparatus. This device is the same as the device shown in FIG. 3 except that a microcomputer 30 is provided instead of the recorder 22 in FIG. 3, and in FIG. 5 the components corresponding to those shown in FIG. Are denoted by the same reference numerals, and the description thereof will be omitted.

In FIG. 5, reference numeral 40 denotes a semiconductor substrate on which a crystal to be inspected has been formed,
The roughness of the surface of the crystal 41 is evaluated. This semiconductor substrate 4
0 is arranged on the table 23 side by side with the semiconductor substrate 1 as a standard sample.

To evaluate the surface roughness of the crystal 41, first, in FIG.
In step 31, the photoluminescence wavelength is measured from the semiconductor crystal 41 to be inspected.

To this end, Ar ⁺ from the laser light source 10 in FIG.
The crystal 41 is irradiated with the laser light 11, and the photoluminescence 42 from the crystal 41 is received by the spectroscope 18,
The wavelength of photoluminescence 42 is measured.

Next, in step 32 in FIG.
The intensity of the reflected light on the surface of No. 1 is measured. This is performed similarly to the operation of performing step 5 above.

Next, in FIG. 1, in step 33, the intensity of the reflected light on the surface of the semiconductor substrate 1, which is a standard sample, is measured. This is performed in the same manner as the operation of performing step 6 above.

Next, in step 34 in FIG. 1, the ratio of the intensity of the reflected light from the crystal 41 and the intensity of the reflected light from the semiconductor substrate 1 is obtained. This operation is performed in the microcomputer 30 shown in FIG.

Finally, in Fig. 1. In step 35, the wavelengths and ratios are plotted in a diagram in which a crystal surface roughness evaluation reference line 27 is drawn, and the surface roughness of the crystal 41 is evaluated by the position of the plotted points with respect to the evaluation reference line 27. . When the plotted points are on the evaluation judgment reference line 27 or on the upper side thereof, it is evaluated that the surface roughness of the crystal 41 is good and the plotted points are below the evaluation judgment reference line 27. In this case, the surface roughness of the crystal 41 is bad and evaluated as unacceptable. This operation is also performed by the microcomputer 30 in FIG.

As a result, the surface roughness of the crystal 41 takes into account the composition (refractive index) of the crystal 41 itself and the laser light source 10
Accurately and quantitatively evaluated in the state where the influence of the variation of the output of is removed.

If it is evaluated as acceptable, the crystal-formed semiconductor substrate is subjected to the next step, and if it is evaluated as unacceptable, it is skipped here. This makes it possible to stabilize and improve the characteristics of the finished semiconductor device.

FIG. 6 shows another example of a semiconductor crystal surface roughness evaluation apparatus. This device has a configuration in which a fixed mirror 50, a movable mirror 51, and a lens 52 are added to the device shown in FIG. 5, and the same reference numerals are given to the parts corresponding to those shown in FIG. The description is omitted.

By moving the movable mirror 51 stepwise as shown by the arrow, the laser light 11 is irradiated on the surface of the crystal 41 at different positions in order.

According to this apparatus, it is possible to obtain the distribution and average value of roughness over the entire surface of the crystal 41, and further three-dimensional roughness information, and more accurately evaluate the crystal surface roughness based on these. Can be done.

〔The invention's effect〕

According to the present invention, by measuring the wavelength of photoluminescence from the semiconductor crystal to be inspected, the refractive index of the crystal itself is taken into consideration, and the intensity of the reflected light on the surface of the semiconductor crystal to be inspected and the standard sample. By performing the evaluation based on the ratio with the intensity of the reflected light on the surface of, the roughness of the crystal surface can be evaluated accurately and quickly without being affected by the variation in the output of the light source.

[Brief description of drawings]

FIG. 1 is a diagram showing a procedure of an embodiment of a semiconductor crystal surface roughness evaluation method of the present invention, FIG. 2 is a diagram showing a procedure for obtaining a crystal surface roughness evaluation criterion, and FIG. 3 is a crystal surface roughness. The figure which shows the apparatus which calculates | requires an evaluation judgment standard, FIG. 4 is a figure which shows an example of the crystal surface roughness evaluation judgment standard, FIG. 5 is a figure which shows an example of a semiconductor crystal surface roughness evaluation apparatus, FIG. It is a figure which shows another example of a semiconductor crystal surface roughness evaluation apparatus. In the figure, 1 is a semiconductor substrate, 4-8, 31-35 are steps, 10 is a laser light source, 11 is laser light, 15 and 42 are photoluminescence, 16 is reflected light, 18 is a spectroscope, 20 is a detector, 27 is an evaluation judgment reference line, 30 is a microcomputer, 40 is a semiconductor substrate on which a crystal to be inspected is formed, and 41 is a crystal.

Claims (1)

[Claims] 1. A step (31) of measuring a wavelength of photoluminescence (42) from a semiconductor crystal (41) to be inspected, and the semiconductor crystal (41) to be inspected of light (11) from a light source (10). (32) measuring the intensity of the reflected light (16) on the surface of, and measuring the intensity of the reflected light (16) on the surface of the standard sample (1) of the light (11) from the light source (10). Process (33)
And the light reflected by the surface of the semiconductor crystal (41) to be inspected (1
6) and the light reflected by the surface of the standard sample (1) (1
The step (34) of obtaining the ratio to the intensity of 6) and the above wavelength and ratio are applied to the crystal surface roughness evaluation criteria (27) obtained for the crystal having a desired surface state.
A semiconductor crystal surface roughness evaluation method comprising the step (35) of evaluating the surface roughness of the semiconductor crystal (41) to be inspected.