JPS5815943B2 - Annealing processing control device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a control device for a semiconductor annealing process.

In recent years, various new methods and techniques have been introduced in the fabrication process of semiconductor materials and devices.

Ion implantation into semiconductors is one such technique, and is well known to those skilled in the art.

It is known that when ions are implanted into a semiconductor, the structure of the semiconductor in the ion implanted region and the surface region is significantly disturbed.

If the semiconductor is single crystal before ion implantation, the surface region of the semiconductor is amorphous or polycrystalline after ion implantation.

Furthermore, impurity ions implanted into a semiconductor do not move as electrically active carriers such as donors or acceptors if they are simply introduced into the semiconductor.

Therefore, in order to recover from the damage caused by ion implantation and to make the implanted impurities electrically active, so-called annealing is performed.

Semiconductor annealing has traditionally been carried out by applying heat in an electric furnace or the like, but recently a so-called laser annealing method has been developed in which the semiconductor is irradiated with a laser beam.

Annealing methods using electron beams in addition to laser beams have also been developed.

On the other hand, in connection with the development of inexpensive solar cells, research is being actively conducted on forming various amorphous semiconductors such as silicon SiK on various substrates such as metal and glass.

In this case as well, annealing is performed in the same manner as in ion implantation for the purpose of improving the characteristics and crystallizing the amorphous semiconductor.

In these semiconductor annealing processes, it is necessary to apply a certain amount of energy to the semiconductor material in order to recover from damage and activate the implanted impurities, but if too much energy is applied, the crystal structure may be damaged. Not only does this disturb the material, but it is also disadvantageous in terms of the processing of materials or devices.

Therefore, it is extremely important to stop annealing at an appropriate stage.

At this time, if the degree of disorder of the crystal structure of the semiconductor or the activation of impurities, in other words the progress of the annealing, can be monitored simultaneously with the annealing, the annealing can be stopped at an appropriate stage.

However, conventionally, the only way to know the progress of annealing is to measure the carrier concentration using the Hall effect, and it is difficult to check the progress of annealing in a non-contact, non-destructive, and short period of time during the annealing process. was impossible.

Therefore, there has been no conventional control device that can stop annealing at an appropriate stage.

The present invention was made in view of this point, and the Raman scattered light generated when a semiconductor is irradiated with laser light contains information regarding various characteristics such as structural disorder of the semiconductor and carrier concentration in the semiconductor. This is based on the discovery that the intensity, half-width, etc. of Raman scattered light change depending on the degree of progress of annealing.

That is, the inventor used a laser annealing device that also served as a Raman effect monitor as shown in FIG. 1 to investigate changes in the Raman spectrum during the annealing process.

The Raman effect is measured using a commercially available laser Raman spectrophotometer 1 (JR8-400T manufactured by JEOL Ltd.), and the measurement results are displayed on a recorder 2 or a cathode ray tube display 3.

One argon laser oscillator 4 was used for both annealing the semiconductor sample 5 and measuring the Raman effect.

The wavelength of the argon laser can be changed to 5145A and 488OA, and the maximum output is 2W8 degrees.

The beam diameter of the laser can be varied from 50 μm or less to several tens of mm.

Figure 2 shows the Raman spectrum obtained when 100 planes of a GaAs single crystal are irradiated with laser light, with a wave number of approximately 292C.
One peak P1 is observed at m-1.

It is known that this peak is caused by the LO phonon of GaAs, and only the LO phonon is observed as Raman light from the 100 planes of a relatively perfect GaAs single crystal, and its wave number is similar to that of the GaAs single crystal. It is unique to crystals.

Figure 3 shows a relatively small amount of S on the surface of a semi-insulating GaAs single crystal, specifically an ion dose of 2×1O12/cm2.
2 shows the intensity change of the Raman spectrum peak during the process of laser annealing a sample into which i was ion-implanted using the apparatus shown in FIG. 1.

The number of surfaces on which ion implantation and measurement were performed was 100.

Specifically, laser annealing was performed by irradiating the sample with a 4880A laser beam at an output of 2W, and at the same time
Raman band peak P due to LO phonon specific to the surface
Spectrophotometer 1 was fixed at a wave number of 1 and 292 cm-1, and changes in peak intensity were measured.

FIG. 4 shows changes in the band width of the Raman band due to LO phonons during the process of annealing the same sample using the laser annealing apparatus described above.

Specifically, annealing was performed with a laser output of 2 W, and the half-width of peak P1 was measured during the annealing, but during measurement, the laser output was reduced to 500 mW and the annealing was substantially stopped, and the wave number was swept. , the half width was calculated.

From FIGS. 3 and 4, it can be seen that during the T1 period up to about 2 minutes after the start of annealing, the peak intensity increases and the half-width decreases, and the structure of the ion-implanted GaAs approaches a single crystal. In other words, it can be seen that annealing is progressing.

After that, during the period T2 up to about 10 minutes, both the peak intensity and the half-width are approximately constant, indicating that the structure of GaAs has hardly changed.

Then, during the subsequent period T3, the peak intensity decreased and the half-width began to increase, but it was confirmed that this change in T3 was due to the crystal structure starting to be destroyed due to excessive annealing.

Therefore, while annealing the semiconductor, the peak intensity and/or band width of the Raman band due to phonons specific to the semiconductor were monitored, and the peak intensity or band width was saturated with respect to the annealing time.In other words, it became approximately constant. If this is detected, it can be determined that annealing has been completed.

In the examples of FIGS. 3 and 4, annealing for a little over two minutes is sufficient.

Although the above is an example of an ion-implanted sample, the same applies to the annealing of other semiconductors, such as amorphous silicon.

An amorphous silicon layer formed on a metal substrate by high-frequency sputtering or the like was laser annealed using the apparatus shown in Figure 1 in the same manner as described above, and the accompanying changes in the Raman spectrum were investigated. The Raman spectrum peak due to phonons specific to silicon appearing at the position showed changes in peak intensity and band width that were almost the same as in FIGS. 3 and 4.

That is, as the annealing progresses, the peak intensity increases and the band width decreases, and when the annealing is completed, it becomes a substantially constant value, and eventually when the annealing becomes excessive, the peak intensity decreases and the band width begins to increase.

Therefore, even in the case of amorphous silicon, completion of annealing can be known by monitoring the peak intensity and/or band width of the Raman band due to phonons specific to the silicon and detecting that these values have become approximately constant.

By the way, based on the above study, we can monitor the peak intensity or band width of the Raman band due to phonons specific to semiconductors,
It turns out that it is possible to tell when annealing is complete by detecting when these values become approximately constant, but measuring the bandwidth requires sweeping the spectrophotometer, which takes several minutes. Since it takes time, monitoring cannot be performed unless the annealing process is interrupted each time.

On the other hand, the peak intensity can be measured with a fixed spectrophotometer, but since the Raman scattered light is weak, fluctuations due to the influence of noise cannot be removed, and errors are inevitably included.

The present invention takes the above points into consideration and provides a control device with a simple configuration that can accurately know the completion point of annealing and stop the annealing process without interrupting the process.

The present invention will be explained in detail below based on the embodiment shown in FIG.

In FIG. 5, reference numeral 11 denotes an ion-implanted semiconductor wafer placed on a sample stage 12.

The wafer 11 is irradiated with annealing laser light generated from an oscillator 13.

14 is a laser oscillator for Raman observation, and the oscillator 1
The laser beam L2 generated from the laser beam L2 is irradiated to the irradiation point of the laser beam L1, that is, for example, to the center of the area where the annealing process is being performed.

The Raman light R generated by the irradiation of the laser light L2 is transmitted to the mirror 15.
．． The light enters the double monochromator 17 through the slit 16 and is developed as a spectrum according to the shift wave number.

18 is a three-channel weak photodetector arranged on the spectrum expansion plane, and each channel has a photomultiplier tube 19,
20, 21. It consists of amplifiers 22, 23, 24 and photon counters 25, 26, 27.

The output of each channel is sent to a three-channel change stop detection circuit 34 comprising a differentiating circuit 28.degree. 29.30 and discrimination circuits 31, 32, and 33.

35 is an AND circuit that issues a termination signal when discrimination signals are simultaneously generated from each channel of the detection circuit 34;
The termination signal is sent to control circuit 36.

The compensation circuit 36 sends a step signal to the moving mechanism 37 for moving the sample stage 12 based on the end signal, and advances the annealing processing range to the next one.

In the above configuration, a spectrum as shown in FIG. 2 is developed at the output section of the monochromator.

The three detection channels of the detector 18 are arranged within the bandwidth of a Raman band corresponding to phonons specific to the semiconductors making up the wafer.

Specifically, assuming that the spectrum waveform of the Raman band before the start of annealing is shown by A in FIG. 6,
A multiplier tube 20 (channel 2) is placed at the peak center wave number position of the Raman band, and a multiplier tube 20 (channel 2) is placed at the position corresponding to the half-width of A.
A multiplier tube 19 (channel 1) and a multiplier tube 21 (channel 3) are arranged symmetrically with 0 in between.

If the annealing process is started here, the results shown in Figs.
As can be seen from the figure, the peak of the waveform gradually increases and the half-width decreases, changing from A-)B to C in FIG. 6, and the state of C is maintained in the period T2.

Focusing on the output of each channel at this time, since channel 2 is placed at the peak center position, the change is the same as the change from T1 to T2 in FIG. 3.

The incident light to channels 1 and 3 is 31→b,→c1. B2
→ b2 → c2, so that the output approximately corresponds to the change in half width shown in FIG. 4.

One of the features of the invention is that a signal that substantially corresponds to the change in half-width can be obtained without actually sweeping the monochromator.

As mentioned above, if a signal indicating a change in peak intensity and a signal that approximately corresponds to a change in half-width are obtained, these two signals change greatly during the T1 period, then enter the T2 period, stop changing, and remain constant. Completion of annealing can be known by detecting that the value has been reached.

In this embodiment, the rate of change is obtained by differentiating the signal, and it is detected when this rate of change becomes zero.

Figure 1 a and b show the output of each differentiating circuit that differentiates the output of each channel, where a is the differentiating circuit 29 (channel 2),
b is the output of the differentiating circuits 28 and 30 (channels 1 and 3).

The discrimination circuits 31, 32, and 33 monitor whether the output of each differentiating circuit becomes zero (that is, the output has entered the period T2 in FIGS. 3 and 4, and the annealing has been completed sufficiently). At the point in time, a discrimination signal as shown in FIG. 1c and d is generated.

C is the discrimination circuit 32 (channel 2), d is the discrimination circuit 31
(channel 1) and the discrimination signal of the discrimination circuit 33 (channel 3).

Therefore, if the M circuit 35 generates a termination signal as shown in FIG. You can know what you did.

When the end signal is sent, the control circuit 36 issues a step signal and sends it to the moving mechanism, shifts the irradiation position of the laser beam L1 to an adjacent location, and newly starts annealing processing at that location.

In the above embodiment, the case of a GaAs semiconductor was described, but in the case of other semiconductors, T1
It has been found through the experience of the inventors of this invention that it is not sufficient to stop the annealing process when T2 ends and it is better to stop the annealing process when T begins.

Therefore, if such a case is taken into account, the discrimination circuits 31 and 32
．． 33 may have a structure such that it issues a discrimination signal when the outputs of the differentiating circuits 28, 29, and 30 reach predetermined values.

In other words, in the case of a semiconductor such as GaAs where it is better to stop annealing when T1 ends, for other semiconductors it is better to choose zero as the above predetermined value and to stop annealing when T3 ends. In this case, the output of the differentiating circuits 28, 29, and 30 is T2 as the predetermined value.
It is only necessary to select an appropriate threshold level value for determining that after T2 has ended and a change has started to be shown again after T2 has reached zero.

In the above embodiment, a total of 3 channels of detectors were arranged, including one channel at the peak center wave number position and two channels symmetrically sandwiching it, but it is also possible to omit one of the two symmetrically arranged channels. In addition, the position is not necessarily limited to the position corresponding to the half-width of the spectrum before annealing, but may be placed at another position as long as it is within the bandwidth of the Raman band.

Further, in the above embodiments, the present invention is applied to a laser annealing apparatus, but it goes without saying that the present invention is not limited to this and may be applied to other types of annealing apparatuses that do not use a laser.

As detailed above, according to the present invention, by arranging one or more detectors at positions other than the central wavenumber position within the Raman band width corresponding to phonons specific to semiconductors, it is not necessary to sweep the monochromator. In other words, it is possible to extract a signal corresponding to the change in the bandwidth of the Raman band without interrupting the annealing process, and furthermore, it is possible to extract the signal corresponding to the change in the bandwidth of the Raman band without interrupting the annealing process. Since it is determined that annealing is complete based on two signals corresponding to changes in , it is possible to accurately know when annealing is complete even if there are fluctuations in the two signals due to the influence of noise.

Therefore, accurate control of the annealing process can be performed at all times.

[Brief explanation of drawings]

Figure 1 shows the configuration of a laser annealing device that also serves as a Raman effect monitor, Figure 2 shows the Raman spectrum of 100 planes of GaAs single crystal, and Figures 3 and 4 show the intensity of Pl during the annealing process. FIG. 5 is a diagram showing the configuration of an embodiment of the present invention, and FIGS. 6 and 7 are diagrams for explaining the operation of the embodiment. 11: Semiconductor wafer, 12: Sample stage, 13° 14: Laser oscillator, 17: Double monochromator, 18: Weak photodetector, 19, 20. 21: Photomultiplier tube, 28, 29
, 30: Differential circuit, 31° 32. 33: Discrimination circuit, 35
: AND circuit, 36: Control circuit, 37: Movement mechanism.

Claims (1)

[Claims] 1. A laser light source for irradiating laser light onto a semiconductor undergoing annealing treatment, a spectroscope into which Raman light generated by the laser light irradiation is introduced, and a Raman spectrum developed by the spectrometer. A first photodetector placed at a peak center position of a Raman band corresponding to phonons specific to the semiconductor, and a second photodetector placed at a position other than the peak center within the bandwidth of the Raman band. a first detection means for detecting a slope of change in the output of the first photodetector; a second detection means for detecting a slope of change in the output of the second photodetector; a first determining means for determining that the output of the first detecting means has reached a predetermined value; and a second determining means for determining that the output of the second detecting means has reached a predetermined value. An annealing processing control device comprising: means for generating a termination signal for stopping the annealing processing based on the outputs of the first and second determining means. 2. The control device according to claim 1, wherein the first and second determining means generate an output when the outputs of the first and second detecting means become zero.