JPS60240118A - Manufacture of si semiconductor - Google Patents

Abstract

PURPOSE:To obtain an Si semiconductor which has greater electron mobility and the mobility is not reduced even exposed at a high temperature by irradiating pulse light on an Si layer under the conditions that an insulation substrate is cooled or that the insulation substrate is dipped with the Si layer in a refrigerant. CONSTITUTION:An insulation substrate 15 formed with an Si layer 16 is dipped in liquid nitrogen 13 and pulse laser light 10 is irradiated toward the Si layer 16 three times. Since the liquid nitrogen is permeable against ruby laser light, the light arrives at the surface of Si with almost no loss and the Si layer is repeated melting and recrystallization by every irradiation. Consequently, the mobility of a hole in the atmosphere of a room temperature is approx. 1.5 times improved in comparison with the mobility when irradiated by pulse laser light of the same energy density. For example, the mobility even heated at 700 deg.C is not reduced under the value before heating in the case of room temperature irradiation.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Application of the Invention) The present invention relates to a method for manufacturing an St semiconductor having a (100) plane orientation, and particularly relates to a method for manufacturing an 81 semiconductor having a high electron mobility. ) The technique of growing and using Si crystals on an insulating substrate is an important technique for creating radiation-resistant and particle beam-resistant devices, and has been put into practical use for a long time.

For example, SOS crystal (5ilicon on 5ap
phire 1 is formed on the surface of sapphire by thermal decomposition of monosilane (81H4) in a hydrogen atmosphere at 1000°C.

However, the coefficient of thermal expansion of 81 is 4.2 x 10-
'/℃, while that of sapphire is 9.5
10/°C, compressive stress occurs in the 81 layer when the temperature is lowered to room temperature.

In addition, since the lattice constant of the insulating substrate and the lattice constant of the Si crystal are generally different, the crystallinity of the 8i crystal is not good.
, defects often occur in the Si crystal. Such compressive stress and crystal defects in the crystal cause a decrease in carrier mobility in the 8i crystal.

The S1 crystal formed at 1.000° C. is subjected to shrinkage stress. Therefore, when (1001Si crystal is used), the electron mobility (μ) becomes small due to the piezoelectric effect of compressive stress.

Generally, the mobility (μ) when stress is generated in the (100)i9i plane in the plane is expressed by the following equation (1).

Lou μ. /(1+πτ) (1) In this equation, π is the piezo coefficient, which is the stress in the 81 layer.

In a compressed state, the stress τ is negative, and in a tensile state, the stress τ is positive. Note that the piezo coefficient π is -5, Ox i
O-” is a negative value of rl/N.

Therefore, the mobility of electrons in Si under a compressive stress of 8 x 10'N/- as in the previous example is about 70% of the mobility in Si without strain. On the contrary, 8
When a tensile stress of X 10'N/- is generated, the electron mobility in St is improved by about 70% compared to unstrained StI.

Regarding crystallinity, the carrier mobility in polycrystalline Si is about several d/V·8, whereas that in single crystal Si is about t, o o o'ca7 v·B. As can be seen from the above, the crystallinity of the Si crystal has a great effect on the electron mobility.For this reason, conventional methods have been used to improve the crystallinity by annealing the formed sS layer at high temperatures. It has been taken.

It is true that this method improves crystallinity, but it also exposes the substrate to high heat, so after it has cooled to room temperature,
Compressive stress naturally exists, and no significant improvement in electron mobility can be expected.

On the other hand, a short-time pulsed light irradiation method is known as a method to selectively dissolve and recrystallize only the sty on SOS, and is used as a means to improve crystallinity (
(Japanese Patent Publication No. 49-67630, etc.) 0 Furthermore, it is known that the Si layer on an insulating substrate is partially converted into a tensile stress state by pulsed light irradiation (G
,A,5ai-Halasz et al., ,App.
l, Phys.

Lett, 36, 419, 1980).

Therefore, short-term pulsed light irradiation is expected to improve crystallinity, and the presence of tensile stress is expected to improve electron mobility.

However, even if the stress in the Si layer is converted into tensile stress and the electron mobility is increased by pulsed light irradiation,
As shown in curve L1 in Fig. 2, for example, in 80S, 5
It was found that the electron mobility decreased again after heat treatment at 00°C for 40 minutes.

In Fig. 2, the vertical axis represents the electron hole mobility (c
fI/V' a ), and the horizontal axis is the heating cooperation during the heat treatment.

As a result of investigating by X-ray diffraction and laser Raman spectroscopy, it was found that the cause of such a decrease in mobility was not due to the decrease in crystallinity of 81, but due to the internal stress in the tensile state being released and partially in the compressive stress state. As stated above, even if the 81 layer is placed in a tensile stress state by pulsed light irradiation, the MO8 manufacturing process requires a heating process of 500°C or higher. ,M
When O8FFIT is manufactured, the tensile stress in the St layer is converted back to compressive stress.

Therefore, it is not possible to expect a significant improvement in electron mobility in an St semiconductor device by only pulsed light irradiation at room temperature. (Objective of the Invention) The object of the present invention is to An object of the present invention is to provide a method for manufacturing an 81 semiconductor that can dramatically improve the performance and achieve high-speed response. When melting and recrystallizing the 81 semiconductor layer,
Another feature of the present invention is that the insulating substrate is cooled.
When melting and recrystallizing the t-semiconductor layer, not only the insulating substrate but also the 81st layer is cooled, and the molten silicon layer is cooled.
It is characterized by the fact that the crystallinity is improved by rapidly cooling the St. The present invention was made based on the following findings. In order to improve mobility, it is necessary to (a) improve crystallinity, and (f)) create tensile stress in the 81 layer, especially in (100)8i0 (2) Semiconductor In order not to cause a decrease in electron mobility even through the high-temperature process of device manufacturing, it is important to maintain the above ←) condition. When applying pulsed light irradiation to selectively dissolve only the upper 81 layers, it is clear that the following are effective: 0) increasing the cooling effect of the Si layer after irradiation, and ←) utilizing the thermal expansion of the substrate. became.

That is, a substrate with St formed on its surface is placed in a refrigerant with a large cooling effect so that at least the substrate is sufficiently cooled, and pulsed light is irradiated from the 81 side. It has become clear that by melting and recrystallizing the St, an 81 semiconductor can be obtained in which the mobility of electrons in Si is high and the mobility does not decrease even when exposed to high temperatures. Note that the refrigerant here refers to a liquid or gaseous substance.

(Embodiments of the Invention) The present invention will be described in detail below according to Examples.〇 [Example 1] First, a Si layer with a thickness of about 0.5 μm was formed on a 1101-plane sapphire single crystal substrate by thermal decomposition of monosilane. At this time, phosphine is simultaneously thermally decomposed to diffuse phosphorus.The phosphorus concentration is about I x 1016 cyn-'.

The 81 layers thus formed, van der P
The electron mobility by the ILW method is approximately 250 cIL/V
・S, which is very small compared to the value of single crystal S1.

This is due to the poor crystallinity of the S1 layer and the compressive stress ζ, as described above.

Note that the crystallinity and internal stress of the 81 layer can be measured and evaluated by X-ray diffraction and laser Raman spectroscopy.

Next, the insulating substrate 15 with the St layer 16 formed thereon is immersed in liquid nitrogen 13, as shown in FIG.

And energy density 15mJ/mj, pulse width about 2
A 5 ns pulsed laser (flQ switched ruby laser, wavelength 694 nm) 10 is irradiated to the 81 layer 16 side three times (3 pulses).

Since liquid nitrogen is transparent to ruby laser light, the light reaches the St plane with almost no loss.

In this case, the 81 layer 16 repeats melting and recrystallization every time it is irradiated with the pulsed laser beam 10 once (one pulse). In addition, in FIG. 1, 12 is a substrate support jig, and 14 is a liquid nitrogen container.

The substrate on which the St layer was formed by laser irradiation was returned to room temperature, and the hole mobility, crystallinity, and internal stress were measured.

As a result, the Hall mobility was approximately 900 ci/V-s, which is approximately 1.5 times the mobility when irradiated with pulsed laser light of the same energy density in an atmosphere at room temperature. I found that it was improving.

On the other hand, the crystallinity of the 81 layer 16 is almost the same as in the case of room temperature irradiation, and the tensile stress in the St layer by laser Raman spectroscopy is about 12 x 10'N/rr? Therefore, the reason why the electron mobility increased compared to the case of room temperature irradiation can be considered to be that a large tensile stress was generated in the 8i layer 16.

The reason for this increase in tensile stress is due to the efficient etching of the high temperature state due to the rapid cooling of the 81 layer 16 melted by laser irradiation, and the difference in lattice constant between the room temperature and liquid nitrogen temperature of the sapphire substrate. It is thought that it was

According to a simple calculation, when laser irradiated with liquid nitrogen m degrees (78 degrees K) and then returned to room temperature, the S1 layer 16 has a tensile stress of at least about 2XlO'N/-.

It is received from the sapphire substrate 15.

The reason why the tensile stress increased more than this component by irradiation with pulsed laser light in liquid nitrogen is thought to be due to the efficient etching effect of liquid nitrogen.

Next, the sample irradiated with laser in liquid nitrogen as described above was heated in a nitrogen atmosphere for 40 minutes, and then the electron mobility was measured. In this case, as shown by curve L2 in FIG. 2, even when heated to 700° C. m1 degrees, the mobility of the sample does not decrease below the value before heating in the case of chamber width irradiation.

Next, a case where the present invention is applied to the manufacture of MOSFET will be explained.

First, a St.
In order to use the semiconductor as the n-base of a MOSFET, boron is implanted into the portions 31 and 32 that will become the source and drain by ion implantation before the light pulse irradiation, as shown in FIG. 3 (Al).

Next, by the method described above with reference to FIG. 1, at least the insulating substrate 15 is set in liquid nitrogen (not shown), and the laser pulse 10 is irradiated as shown in FIG. 3(B).

Thereafter, an S1 oxide film 5 with a thickness of 500111 or less is formed over the entire surface by plasma CVD. Furthermore, the S1
A polysilicon layer is formed on oxide film 5 at a temperature of 700° C. or lower. Then, the polysilicon layer is etched away, except for the portion 6 that will become the gate electrode and wiring, as shown in FIG. 3(C).

Next, as shown in FIG. 3(D), the si
After forming the oxide film 8, contact windows 21 and 22 are formed by etching in portions corresponding to the source and drain.

Furthermore, by mask vapor deposition from above, (E) in FIG.
Form aluminum electrodes 71 and 72 as shown in MOSFE
Manufacture T.

It has been found that the MOSFET manufactured as described above has a large channel mobility because the n-base layer has a large mobility and this is not degraded by the manufacturing process. Ta.

[Example 2] In order to create an 81 semiconductor having a higher electron mobility than that obtained by laser irradiation in liquid nitrogen, a semiconductor was manufactured in the same manner as in Example 1. An insulating substrate having 81 layers on its surface was placed in liquid helium. Since liquid helium has a boiling point of 4.2 and is easily volatile, the liquid helium container was placed in a liquid nitrogen container.

Next, the 81st layer side is irradiated three times with the same ruby pulse laser as in Example 1. Since liquid helium is transparent to ruby laser light, the light reaches the Si plane with almost no loss.

The sample irradiated with the laser in this way was returned to room temperature, and the hole mobility was measured. Hall mobility is approximately 1.1001
iVV'++, which was found to be increased compared to the case of laser irradiation in liquid nitrogen.

This is thought to be due to the highly efficient cooling effect of liquid helium and the effective difference in lattice constant between the room temperature of the sapphire substrate and the temperature of liquid helium. After heating the sample for 40 minutes in a nitrogen atmosphere, the hole mobility of electrons was measured. As a result, as shown in curve L3 in Figure 2, the sample made by laser irradiation in liquid helium had a Even at a heating temperature of °C, the mobility is the same as that for room temperature irradiation.
It was found that the value did not decrease below the value before heating. As in Example 1, boron was implanted into the Si layer that would become the source and drain of the sample, and after laser irradiation in liquid helium. , a gate oxide film (corresponding to 5 in FIG. 3) was formed at a heating temperature of 750° C. or lower.

Thereafter, MO8FFiT was manufactured in the same manner as in Example 1. As a result, a MOSFET with channel mobility comparable to that of a semiconductor device obtained using bulk 81 single crystal was obtained.
was gotten.

In each of the examples described above, the Si layer was irradiated with the pulsed laser three times, but it is obvious that the number of irradiations - therefore, the number of repetitions of melting and recrystallization of the St layer is not limited to this. .

However, according to the inventor's experiments, an improvement in hole mobility was observed up to 2 irradiation times, almost reached the peak value after 2 to 4 irradiations, and on the contrary, hole mobility decreased after 5 irradiation times. It was observed that

The reason for this is assumed to be approximately as follows.

First, when pulsed laser light is irradiated, the Si layer melts from its surface and recrystallizes.During this recrystallization, the S1 layer is rapidly cooled, so the crystallinity of the recrystallized part is improved, and light transmission in that part The properties are also improved.

Therefore, at the time of the next pulsed laser beam irradiation, the penetration depth of the light into the 81st layer increases; that is, the thickness of the 81st layer melted and recrystallized increases. This □ further improves crystallinity.

However, the thickness of the 81 layers to be melted and recrystallized increases,
When it reaches near the surface of the insulating substrate, the crystallinity of this part is generally poor, so the crystallinity of the 81 layer when recrystallized will actually deteriorate. It is desirable to determine the number of pulsed laser beam irradiations so that the thickness of the crystallized St layer is approximately equal to the thickness of the Si layer.

In each of the above examples, an example was shown in which a sapphire substrate was used as an insulating substrate on which a Si layer was formed, but similar effects were measured with an insulating substrate such as spinel, and the present invention can be applied to any insulating substrate. It was confirmed that it can be applied.

In addition, in each of the above embodiments, 8
Although an example was shown in which one layer was melted, similar effects were measured using flash lamps such as xenon and mercury, and it was found that any light source can be used as long as it uses pulsed light.

Further, in each of the above embodiments, liquid nitrogen and liquid helium were used as the coolant, but any coolant can be used as long as it has good transparency to incident light and has a sufficient cooling effect.

In order to create a St semiconductor with higher electron mobility, it is desirable to use a lower temperature coolant.

However, at present, using liquid helium is more expensive to manufacture than liquid nitrogen.

Further, in each of the above embodiments, an example was shown in which an insulating substrate with 81 layers formed on the surface was cooled by immersing it in a refrigerant.
Even if only the insulating substrate is brought into contact with or immersed in the refrigerant, almost the same effect can be expected. In this case, it is clear that the refrigerant does not need to be optically transparent.

(Effects of the Invention) As is clear from the above description, according to the method of the present invention, the St layer can be irradiated with pulsed light while the insulating substrate is cooled or immersed together with the St layer in a coolant. As a result, it has a higher electron mobility than conventional methods,
Furthermore, it is possible to produce an St semiconductor whose mobility does not decrease even when exposed to high temperatures.

Using the 8i semiconductor manufactured in this way, we have developed an MO with higher channel mobility than conventional ones.
We were able to manufacture SFETs.As is clear, this led to the manufacture of high-speed ICs and high-speed LSIs.In addition, extremely low-temperature processes were adopted in subsequent semiconductor device manufacturing processes. Since there is no need for 0, the manufacturing cost can be reduced without degrading the performance of the semiconductor device.

[Brief explanation of the drawing]

Figure 1 is a cross-sectional view of an SOS crystal exposed to laser irradiation in liquid nitrogen, and Figure 2 is a cross-sectional view of an 80S crystal exposed to high temperatures after laser irradiation at room temperature and in a coolant. FIG. 3 is a graph showing the relationship between mobility and heating temperature, and FIG. 3 is a cross-sectional view showing the process of manufacturing a MOSFET by applying the present invention. 10... Irradiation pulsed light, 12... Substrate support jig, 1
3...Liquid nitrogen, 14...Liquid nitrogen container, 15...
・Insulating substrate, 16...Si layer agent Patent attorney Michi Hiraki Otsu 1 figure 0 year 2 figure (cm/'V fist b) year 3 figure

Claims (6)

[Claims] (1) A method for manufacturing an Si semiconductor comprising an insulating substrate and 81 semiconductor layers with an average plane orientation of (100) laminated on the surface thereof, the method comprising at least the step of cooling the insulating substrate; A method for manufacturing an 81 semiconductor, comprising the step of melting and recrystallizing the St semiconductor layer by irradiating the St semiconductor layer with pulsed light for a short time in a cooled state. (2) Patent method 0 characterized by repeating melting and recrystallization of the St semiconductor layer multiple times by irradiation with short-time pulsed light (3) A method for manufacturing an 81 semiconductor according to claim 1 or 2, characterized in that the insulating substrate is placed in a coolant. (4) A method for manufacturing an 81 semiconductor according to claim 1 or 2, characterized in that the insulating substrate is placed in a coolant together with the 81 semiconductor layer on its surface. (5) St according to any one of claims 1 to 4, characterized in that the refrigerant is liquid oxygen.
Semiconductor manufacturing method. (6) 81 according to any one of claims 1 to 4, wherein the refrigerant is liquid nitrogen.
Semiconductor manufacturing method.