JPS5927757B2 - Vapor phase epitaxial growth method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing a semiconductor device, and particularly to a vapor phase epitaxial growth method.

In the manufacture of semiconductor devices, there is one shown in FIG. 1, for example, which uses epitaxial growth. In FIG. 1, 1 is a silicon single crystal substrate containing a high concentration of impurities that provide conductivity, and 2 is in contact with the substrate 1 and has almost the same crystal structure as the substrate 1 due to its crystallographic connection. The silicon epitaxial layer has an impurity concentration lower than that of the substrate 1, and the epitaxial layer is obtained by epitaxial growth. Another example is shown in FIG.

In Figure 2, 1 is a silicon single crystal substrate containing relatively low concentration of impurities, 2 is an epitaxial layer, and 3 is a buried layer that selectively contains high concentration of impurities, and this buried layer 3 is formed before epitaxial growth. It was introduced selectively. As a method for manufacturing the epitaxial layer 2 shown in FIGS. 1 and 2, there is a conventional epitaxial growth method shown in FIG.

In Figure 3, 1 is a substrate heated to a high temperature, 4 is a substrate 1
5 is a reactor, and this reactor 5
A carrier gas 6, a source gas T for growing an epitaxial layer, and a doping gas 8 for adding impurities to the epitaxial layer are introduced and discharged to an exhaust 9.

The reaction in the reactor 5 includes, for example, a carrier gas 6
As H2. SlH4 was used as the source gas 7, and AsH3 was used as the doping gas 8 at normal pressure (760t0rr).
) and heat a silicon single crystal having a buried layer containing a high concentration of As to 1050° C. as the substrate 1, the following thermal decomposition reaction occurs. As a result of the above reaction, an epitaxial layer of Si grows on the substrate 1, and at the same time As is added as an impurity.

At this time, the growth rate and thickness of the epitaxial layer are controlled by controlling the supply amount and supply time of the source gas 7 per unit time, and the impurity concentration of the epitaxial layer is controlled by controlling the supply amount per unit time of the source gas 7. Controlled by the amount of feed per unit. In the above conventional epitaxial growth method,
Autodoping occurs in which impurities are released into the gas from the surface of the substrate 1 containing high concentration impurities, and the released impurities are incorporated into the growth layer again during epitaxial growth, resulting in a decrease in the impurity concentration of the epitaxial layer 2. This has the disadvantage that control cannot be achieved only by controlling the doping gas. More specifically, the mean free path t of impurities released into the gas is expressed by the following equation.

Here, T is absolute temperature CK), P is pressure (TOrr), and σ
is the molecular collision diameter (?).

When the pressure is 760T0rr, the temperature is 1050℃, and the molecular collision diameter is 10-8CTfL, the mean free path t=3.6X
It is considered to be about 10-4 μm, that is, about 3.6 μm. Therefore, impurity molecules exist at a high concentration in the gas near the substrate 1,
Epitaxial growth will take place in this gas. In order to compensate for the above drawbacks, an epitaxial growth method shown in FIG. 4 has been proposed. In FIG. 4, a vacuum pump 10 is provided between the reactor 5 and the exhaust 9 to maintain the internal pressure of the reactor 5 at a low pressure of 100T0rr or less to perform epitaxial growth. In the epitaxial growth method shown in FIG. 4, the mean free path of impurity molecules released from the substrate 1 is 25 μm or more, and the concentration of impurities in the gas released from the substrate 1 is In addition, if the total amount of gas introduced into the reactor 5 is constant, the gas flow rate inside the reactor 5 increases in inverse proportion to the gas pressure, and the synergistic effect with the elongation of the mean free path increases. This effect has the advantage that the rate at which impurity molecules released from the substrate 1 are discharged from the reactor 5 becomes faster.

On the other hand, in the reactor 5, it is known that the number of molecules that collide with the substrate 1 is inversely proportional to the pressure, and the number of molecules of the source gas 7 that collide with the substrate 1 decreases, for example, the number of molecules that collide with the substrate 1 decreases.
Even if SiH4 is used as the material and the decomposition reaction is accelerated by reducing the pressure, the substantial growth rate of the epitaxial layer 2 will decrease. A decrease in the growth rate leads to a relative extension of the growth time, and even if the rate at which impurities contained inside the substrate 1 move to the surface of the substrate 1 is constant, the total amount of impurities moved, and therefore the amount released into the gas, decreases. , which reduces the advantages of epitaxial growth at low pressures. The present invention was made to eliminate the drawbacks of the conventional growth method as described above, and it is possible to quickly discharge impurities released from the substrate to the outside of the furnace, suppress autodoping, and improve the growth of the epitaxial layer. The object of the present invention is to provide a vapor phase epitaxial growth method that also prevents a decrease in the growth rate of the .

In the present invention, the movement of impurities released from the substrate in the gas and the rate of discharge to the outside of the furnace are greatly affected by the pressure inside the furnace, while the impurities contained inside the substrate move to the surface of the substrate. Speed is the speed of movement in a solid, and the influence of gas pressure is small, which focuses on the difference in the effect of gas pressure on the movement speed of impurities.

Specifically, the pressure of the gas in the furnace is changed periodically, and the impurities released from the substrate at low pressure are moved in the gas, and during the delay in the movement of the impurities contained in the substrate, In this method, epitaxial growth is performed rapidly by changing the gas pressure to

An embodiment of the present invention will be described below with reference to the drawings.

In FIG. 5, 1 is a substrate, 4 is a susceptor, 5 is a reactor,
6 is a carrier gas, 7 is a source gas, 8 is a doping gas, 9 is an exhaust, 10 is a vacuum pump, 11 is a low pressure valve provided between the reactor 5 and the vacuum pump 10, and 12 is provided in parallel with the low pressure valve. This is a high pressure valve.
In the vapor phase epitaxial growth method according to the present invention shown in FIG.
The gas introduced into the reactor 5 and the exhaust from the vacuum pump 10 are the same as in the conventional growth method, but the newly provided low-pressure valve 12 is periodically opened and closed, and the high-pressure valve 1 is opened and closed periodically.
2 keeps it open at all times.

When the low-pressure valve 11 is open, the pressure inside the reactor 5 becomes low, and impurity molecules released from the substrate 1 are accelerated to be discharged from the reactor 5. When the low-pressure valve 11 is closed, the reaction is stopped. The pressure inside the furnace 5 becomes a high pressure state determined by the diameter of the high pressure valve 12 which is always open, and epitaxial growth on the substrate 1 is promoted. As described above, according to the present invention, since the pressure of the gas inside the reactor 5 changes periodically, autodoping can be suppressed and an epitaxial layer that is less affected by impurities contained in the substrate 1 can be obtained. It will be done. In the above example, the high pressure is 760T0r.
r, the low pressure was set to 10T0rr, the low pressure valve 11 was opened and closed at 30 second intervals, and when epitaxial growth was performed by thermal decomposition of SiH4 on a Si single crystal substrate with a buried layer of As, the epitaxial layer was The autodoped layer is 0
．． Good results were obtained with a thickness of 1 μm or less. In addition, in the above example, the change in pressure is 1/7 of the low pressure compared to the high pressure.
6, it was confirmed that the effects of the present invention can be obtained by reducing the low pressure to 1/10 or less of the high pressure. As described above, according to the vapor phase epitaxial growth method of the present invention, impurities emitted from the substrate can be quickly discharged from the furnace, autodoping can be suppressed, and the growth rate of the epitaxial layer can also be reduced. There is an advantage in that it can be effectively prevented.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view showing an example of epitaxial growth, FIG. 2 is a cross-sectional view showing another example of epitaxial growth, FIG. 3 is a schematic diagram showing an example of a conventional epitaxial growth method, and FIG.
This figure is a schematic diagram showing another example of the conventional epitaxial growth method, and FIG. 5 is a schematic diagram showing the vapor phase epitaxial growth method according to the present invention.

Claims (1)

[Claims] 1. A substrate containing high concentration impurities at least on its surface is placed in a reactor, and while heating this substrate to a high temperature, a source gas, a doping gas, and a carrier gas are introduced into the reactor. A vapor phase epitaxial growth method for growing an epitaxial layer on the surface of a substrate containing impurities at a high concentration, the vapor phase epitaxial growth method comprising periodically changing the pressure of the gas in the reactor. 2. A substrate containing high-concentration impurities at least on its surface is placed in a reactor, and the substrate is heated to a high temperature and a source gas, doping gas, and carrier gas are introduced into the reactor. In the vapor phase epitaxial growth method for growing an epitaxial layer on the surface of a substrate containing impurities, the pressure of the gas in the reactor is set at a value of 1/10 or less of the low pressure with respect to the high pressure and is changed periodically. vapor phase epitaxial growth method. 3. A substrate containing highly concentrated impurities at least on its surface is placed in a reaction furnace, and the substrate is heated to a high temperature and a source gas, a doping gas, and a carrier gas are introduced into the reactor. In the vapor phase epitaxial growth method in which an epitaxial layer is grown on the surface of a substrate containing impurities, an exhaust path leading to the reactor is
A vapor phase epitaxial growth method characterized by installing a high-pressure valve and a low-pressure valve in parallel, and changing the gas pressure in the reactor by periodically opening and closing the low-pressure valve.