JPH07109849B2 - Semiconductor crystal evaluation method and apparatus - Google Patents

Description

Description: (1) Field of the Invention The present invention relates to GaAs used as a substrate when forming a field effect transistor (FET) which is a basic element of an integrated circuit on a GaAs crystal substrate by an ion implantation method. The present invention relates to a method and a device for nondestructively and efficiently evaluating crystals with good reproducibility.

(2) Conventional Technology and Its Problems In general, an FET using a GaAs crystal as a substrate is manufactured by directly implanting a donor element into the surface of the substrate to form an n-type active layer. Therefore, the performance of the integrated circuit largely depends on the characteristics of the substrate crystal.

Currently, S is used as an implantation element for forming the n-type active layer of GaAs-FET.
i is the most commonly used. Since Si is a group IV element, it acts as an amphoteric element in the GaAs crystal which is a group III-V compound semiconductor. That is, the injected Si is III
Not only is it substituted into the lattice position of Ga, which is a group element, to become a donor, but it is also substituted into the lattice position of As, which is a group V element, to become an acceptor. On the other hand, the group V element has a high vapor pressure and is volatile. For this reason, As, which is a group V element, crystal growth,
During the process of manufacturing the substrate, it was evaporated from the GaAs crystal and
As vacancies are introduced at various concentrations. As a result, even if Si of the same concentration is injected into a GaAs substrate,
The ratio of substitution of Si at the Ga lattice position and that at the As lattice position varies, resulting in non-uniform characteristics of the n-type active layer between the substrates.

As a method of overcoming the non-uniformity of characteristics described above, conventionally, an n-type active layer is formed by ion implantation in advance on a substrate cut out from a position close to a substrate in which a device is actually manufactured and a crystal ingot, and the concentration of the donor is changed. A method has been adopted in which the carrier concentration is calculated by subtracting the acceptor concentration and the Si implantation amount is determined based on the carrier concentration. However, since this method is a destructive inspection, the substrate used for actual device fabrication cannot be directly evaluated, resulting in poor reliability, and since an n-type active layer must be formed, it is complicated and one cycle until the end of evaluation. There was a drawback that it took a long time.

(3) Object of the invention In order to overcome the above-mentioned drawbacks, the present invention directly, non-destructively and efficiently evaluates a crystal substrate used for element fabrication using an optical measuring device at room temperature, that is, with a predetermined Si implantation amount. Provided is a semiconductor crystal evaluation method and device capable of predicting the carrier concentration to be realized.

(4) Structure and Action of the Invention A method and apparatus for evaluating a GaAs crystal substrate according to the present invention will be described below. The measurement is performed using an optical measuring device having the configuration shown in FIG. That is, the crystal substrate to be measured is carried from the unmeasured sample storage cassette 1 to the orientation flat alignment table 2, aligned with a predetermined direction and position, and then transported to the sample table 3. The sample is irradiated with excitation light 5 from the laser light source 4 in this state,
At this time, the luminescence 6 emitted from the sample is analyzed by the spectroscope 7
And the intensity is measured by the detector 8.
After the measurement is completed, the substrate is carried to the measurement-completed sample storage cassette 9 and a series of measurement operations is completed. The mechanism that automatically sets and resets the sample prevents dust accumulation and scratches on the sample during a series of measurement operations, and this device can be used by incorporating it in the actual integrated circuit manufacturing process It is added in order to do so.

FIG. 2 shows a luminescence spectrum from a GaAs crystal substrate measured at room temperature. Normally, the measurement wavelength range 1.0 to
Luminescence is observed only around 2.5 μm. This luminescence is the luminescence related to As substituting at the Ga lattice position, and crystals with strong luminescence indicate that As easily occupies the Ga lattice position, that is, Ga vacancies are in an excessive state. As already mentioned, the carrier concentration of the n-type active layer is
Depends on the proportion of Ga and As lattice positions. This ratio is proportional to the concentration ratio of Ga vacancies and As vacancies in the crystal.
Therefore, the carrier concentration of the n-type active layer can be predicted by the intensity of light emission in the vicinity of 1.75 μm obtained by the above optical measuring device. FIG. 3 shows the results of actually examining these correlations using various GaAs crystal substrates. Here, the n-type active layer is
It was formed by accelerating Si to 60 keV and implanting ions at an area density of 5 × 10 ¹² / cm ² . There is a clear linear relationship between the two. That is, by using the principle of the present invention, the characteristics of the GaAs integrated circuit substrate, that is, the carrier concentration realized by a predetermined Si implantation amount, can be directly predicted nondestructively. Based on this, it is necessary to select a GaAs integrated circuit substrate that can achieve a predetermined carrier concentration with a fixed Si injection amount, or to achieve a desired carrier concentration using a receiving substrate.
It is possible to determine the Si implantation amount.

2 and 3 show the results obtained using a PbS detector generally used in the measurement wavelength range of 1.0 to 2.5 μm. In order to obtain sufficient luminescence output by performing measurements at room temperature on this detector and GaAs crystal, it is necessary to set the laser light output which is the excitation light to 100 mW or more. In this case, the laser irradiation causes oxidation to proceed on the surface of the GaAs substrate, and the luminescence output changes with time as shown in FIG. That is, the luminescence output decreases with the laser light irradiation time and becomes a constant value in about 30 minutes. In both of these, the above-mentioned measurement is performed after 30 minutes or more have passed after laser light irradiation. On the other hand, the sensitivity of the Ge detector sharply decreases when the measurement wavelength exceeds 1.65 μm, but it becomes 3 to 4 orders of magnitude higher than that of the PbS detector in the measurement wavelength range of 1.2 to 1.65 μm. As already mentioned in Fig. 2, the luminescence obtained by measuring the GaAs crystal substrate at room temperature is 1.
In the wavelength range of 0 to 2.5 μm, it is only around 1.75 μm. Further, this light emission is in a wide wavelength range of 1.5 to 2.0 μm. Therefore, the emission intensity of the emission in the vicinity of 1.75 μm can be inferred by measuring the emission intensity in the vicinity of 1.65 μm using a Ge detector. In this case, the Ge detector is 3 to 4 orders of magnitude more sensitive than the PbS detector, and therefore a sufficient measurement output can be obtained even if the output of the excitation laser light is lowered. Therefore, instead of the laser light source, it is possible to use a light source that outputs spectral white light. FIG. 5 shows the correlation between the luminescence output at 0.95 Wm of the sample used in FIG. 3 and the luminescence output at a wavelength of 1.65 μm using a Ge detector, and the correlation with the carrier concentration. is there. The results are completely in agreement with the case of Fig. 3 using the PbS detector. Also, because the laser light output is reduced by two digits, there is no oxidation on the sample surface,
The luminescence output did not change with time as shown in FIG. Based on this, the luminescence measurement shown in FIG. 5 is performed 0.1 seconds after the laser light irradiation. That is, when the Ge detector is used, the measurement time can be significantly shortened, and since oxidation of the sample surface can be avoided, complete nondestructive inspection can be realized. The moving mechanism from the cassette 1 to the cassette 9 in the semiconductor crystal evaluation apparatus shown in FIG. 1 will be further described.

The purpose of this mechanism is to install / remove a sample, such as a 3-inch diameter wafer, on the sample stage for measurement (3 in FIG. 1) with good reproducibility (always at the same place and in the same direction) without any contamination or damage. I am trying. To realize this, dirt can be dealt with in the following item 2.

The vacuum required for wafer adsorption on the stage when the equipment is used in a clean room is realized by a beltless vacuum pump that uses a diaphragm instead of the conventional vacuum pump oil and vacuum pump that uses a belt.

Also, with regard to scratches, paying attention to that most of them are mechanical scratches on the front and back of the wafer with conventional tweezers,
The movement of the wafer can be dealt with by suctioning the back surface of the wafer with vacuum tweezers.

Further, the improvement of the reproducibility of the wafer installation position / direction can be realized by the following procedure using the apparatus configuration shown in FIG. 1 and the orientation flat alignment mechanism shown in FIG.

Wafer Moving Procedure The wafer in the unmeasured sample storage cassette 1 is moved to the orientation flat aligning mechanism (2 in FIG. 1) by using vacuum tweezers (suction on the back surface of the wafer).

The orientation and position of the wafer are set to a fixed state on the orientation flat alignment mechanism.

The wafer is moved from the orientation flat alignment mechanism to the sample table 3 using vacuum tweezers.

The wafer is fixed to the sample table 3 by vacuum suction and measurement is performed.

The wafer is moved from the sample table 3 to the measurement-completed sample storage cassette 9 using the vacuum tweezers.

Wafer Direction / Position Alignment Method Using Orientation Alignment Mechanism Usually, a wafer is provided with a main orientation flat 15a and a sub orientation flat 15b as shown in FIG. 7 in order to clearly indicate the orientation. As shown in FIG. 6, the orientation flat aligning mechanism includes a detecting portion including a light emitting element 11 and a light receiving element 12 for detecting this, a rotary base 13,
It is composed of a sample holder 14 having a tapered groove, and is operated by the following procedure.

The turntable 13 is raised and the wafer 10 sent from the cassette is received on the turntable 13.

The wafer 10 is attracted and the rotary table 13 is rotated to rotate the orientation flat 15
After detecting a and 15b, the turntable 13 is stopped.

The adsorption of the wafer 10 is released, the rotary table 13 is lowered, and the wafer 10 is set on the sample holding table 14.

 Raise the turntable 13 again.

Adsorb the wafer 10, and again, the orientation flat 15a,
Detects 15b.

The wafer 10 is set on the sample holder 14 according to the above item.

The orientation of the wafer 10 is roughly determined in the above section, and the position of the wafer 10 is determined almost accurately in. In wafer 10
The direction of is accurately determined, and the operation is completed. Wafer
When the sample 10 is taken out, it is carried from the sample holder 14 to the next place (sample table 3) with vacuum tweezers. If the positional relationship between the orientation flat aligning mechanism and the sample table 3 is kept constant, the wafer 10 is set in the fixed direction and position of the sample table 3.

(5) Effects of the Invention As described in detail above, according to the present invention, it is possible to directly and non-destructively and efficiently evaluate a GaAs crystal at room temperature, which is particularly effective when applied to the evaluation of substrate performance. Therefore, the effect of improving the performance of the integrated circuit is extremely large.

[Brief description of drawings]

FIG. 1 is a block diagram of an optical measuring device used in the present invention, FIG. 2 is a typical photoluminescence spectrum characteristic diagram of a GaAs crystal substrate measured at room temperature using this optical measuring device, and FIG. 3 is a GaAs crystal. Wavelength calculated for the substrate 1.75 μm
FIG. 4 is a diagram showing the correlation between the emission intensity and the carrier concentration of the n-active layer in FIG. 4, and FIG. 4 is a time change characteristic diagram of luminescence output when measured at room temperature with a pump laser light output of 100 mW.
The figure shows the correlation between the emission intensity at a wavelength of 1.65 μm and the carrier concentration in the n-type active layer, which was obtained by using a Ge detector with a laser light output of 0.9 mW and a Ge detector, and FIG. 6 (a).
(B) is a plan view and a front view showing a configuration example of an orientation flat matching table used in the present invention, and FIG. 7 is a plan view showing an example of the shape of a sample used in the present invention. 1 ... unmeasured sample storage cassette, 2 ... orientation flat alignment table, 3 ... sample table, 4 ... laser light source, 5 ... excitation light,
6 ... Luminescence, 7 ... Spectrometer, 8 ... Detector, 9 ... Measurement end sample storage cassette, 10 ...
... Wafer, 11 ... Light emitting element, 12 ... Light receiving element, 13 ... Rotary table, 14 ... Sample holder, 15a ... Main orientation flat, 15b ... Sub orientation flat.

Claims (2)

[Claims] 1. A wavelength emitted from a GaAs sample after irradiating a GaAs crystal sample with spectral white light or laser light.
1. A semiconductor crystal evaluation method, characterized in that the crystal characteristics of the sample are evaluated by spectroscopically measuring the intensity of light emission in the vicinity of 1.65 μm using a Ge detector. 2. A sample table on which a GaAs crystal sample is mounted for measurement, a light source for irradiating the GaAs crystal sample mounted on the sample table with white light or laser light dispersed, and the laser beam. And a semiconductor crystal evaluation device for spectroscopically measuring the intensity of the light emitted from the GaAs crystal sample near the wavelength of 1.65 μm after the irradiation with a Ge detector for the evaluation of the crystal characteristics of the sample. .