JPS6136371B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a vacuum epitaxial growth method suitable for growing a particularly thin film of a semiconductor such as silicon with high reproducibility so as to have a highly precise resistivity. Conventionally, to form a silicon film by chemical vapor deposition (CVD), for example, monosilane (SiH ₄ ) or silicon halide (SiCl ₄ ,
Epitaxial growth is achieved by transporting SiH ₂ Cl 3 (SiH 2 Cl ₃ etc.) to the surface of a silicon semiconductor substrate using a carrier gas such as hydrogen (H ₂ ) or an inert gas, and thermally decomposing it there. Therefore, the thickness of the epitaxially grown film largely depends on the flow of the mixed gas of the reaction gas and carrier gas, and the thickness distribution varies depending on the location even within the same wafer or within the same reaction device. In addition, the non-uniformity between lots tends to increase. Moreover, it is difficult to dope impurity atoms such as phosphorus (P ⁺ ) and boron (B ⁺ ) in a thin layer of 10 ¹⁴ to 10 ¹⁷ [cm ^-3 ] with good reproducibility in a silicon epitaxially grown film. It's close to impossible at the moment. This is because it is difficult to obtain a uniform flow of the mixed gas within the reactor, and especially on the silicon semiconductor substrate surface, due to the relationship between intake and exhaust.
The flow becomes laminar in some places and turbulent in others, and the remaining gas components that have undergone thermal decomposition stagnate on the surface of the silicon semiconductor substrate, and new unreacted gases reach the surface. This is to prevent the In addition, in recent years, development of molecular beam epitaxial growth methods apart from the above-mentioned CVD method has been active, but implementing this method requires large-scale equipment. For example, controlling the growth rate requires the use of a deposition crucible. This is done by controlling the temperature, but this requires the use of an electronic computer, and there are many difficulties in controlling it, so it has not yet been able to be applied to mass production processes and has not moved beyond the experimental stage. . The present invention provides an epitaxial growth method that combines the characteristics of the CVD method and the molecular beam epitaxial growth method, and makes it possible to mass-produce semiconductor epitaxially grown films with highly precisely controlled resistivity with good reproducibility. This will be explained in detail below. The figure is a side sectional view of a main part showing an example of a device used to carry out the present invention. In the figure, 1 is a bell jar, 1a is a gas injection port, 2 is a bottom plate, 2a is a gas discharge port, 3 is a susceptor, and 4 is a silicon wafer. An example of implementing the present invention using this device will be described. That is, the wafer 4 is set on the susceptor 3. They can be heated to temperatures of 900 to 1000 degrees Celsius. Inside Bell Jar 1 is 1x
Exhaust to below 10 ^-3 [Torr]. The injection port 1a is formed at a position where it can see all of the wafers 4 set on the susceptor 3, and a fixed amount of the mixed gas is intermittently injected from there. Depending on the case, the mixed gas may be replaced with the reactive gas alone. In this way, a certain amount of gas linearly reaches the wafer 4 from the injection port 1a, decomposes on the surface of the wafer 4, and forms an epitaxially grown film of a certain thickness. By the time the next injection gas arrives, all the previously decomposed gas has been exhausted and the system has completely returned to its original state. If you want to include impurities in the epitaxially grown film, add a dopant to the injection gas.
It is sufficient to mix gases (for example, PCl ₃ , B ₂ H _6, etc.). In the above embodiment, by one gas injection,
The thickness of the epitaxially grown film that can be formed depends on the concentration of the reactant gas in the injection gas,
It is determined by the injection amount, and since it is possible to vary it over a wide range with high precision, it is important to know how many injections are required using a specified gas in order to obtain an epitaxially grown film of the desired thickness. You can know in advance exactly what you need to do, and you can also implement it. Since there is no mutual interference between the intermittently injected gases, epitaxial growth is performed under the same conditions even from a microscopic point of view, and therefore the reproducibility is very good. The same is true when thin impurity doping is desired; the doped gas molecules directly collide with the surface of the silicon wafer 4, and the reaction always occurs with the same probability. Light doped epitaxial with excellent properties.
It is possible to form a dopedepitaxial) growth film. Next, let's explain a concrete example using numerical values. 1 Use a bell jar 1 with a volume of about 50 [] as shown in the figure, keep the inside at 1 × 10 ^-4 [Torr] or less, and add about 4 [ml] (1
[Torr], room temperature) 100 times at 1 [second] intervals
It was injected. At this time, the temperature of the silicon wafer 4 on the susceptor 3 was maintained at 950 [°C].
Since an epitaxially grown film of 50 [Å] was obtained with one injection, the final film thickness was 5000 [Å]. In this case, the film thickness distribution is within the lot (7.5 [cm] φ or 3 [Iwachi] φ
5 [wafers]): 5000 [Å] ± 20 [Å] Between lots (average of 10 [wafers]): 5000 [Å] ±
It was 50 [Å]. 2 Set up the reaction apparatus in the same manner as in 1 above, and add 100% monosilane to 100% as the injection gas.
[ppm] Diborane was mixed uniformly in a ratio of 1:10 ^-3 just before bell jar 1, and the mixed gas was heated at about 10 [℃] to prevent diborane from polymerizing or decomposing on the walls of the equipment. ] The following operations such as cooling were added, and the mixed gas was injected in the same manner as in 1 above to perform epitaxial growth. Accordingly, n ⁺ of specific resistance 0.1 [Ω・cm]
5000〔Å〕±20〔Å〕 on mold silicon wafer
An epitaxially grown film with a p ^- (specific resistance of 10±1 [Ω·cm]) was obtained with good reproducibility. The effects of the present invention explained above are listed below. (b) Compared to the conventional vapor phase epitaxial growth method, the thickness distribution of the epitaxially grown film is extremely small not only within the wafer but also within a lot or between lots; In comparison, the equipment required to carry out the method is significantly simpler; it is possible to add a device for intermittently injecting gas to the equipment used to carry out the vapor phase epitaxial growth method, or to select the position of the gas injection port appropriately. It can be put into practical use just by doing this, and then all you have to do is perform relatively simple control of the device. (b) It is possible to stably grow an epitaxial layer having a desired resistivity by changing impurity doping over a wide range. (c) It is possible to obtain thin epitaxially grown films with high precision and good reproducibility, which cannot be obtained without applying the molecular beam epitaxial growth method. (d) A large number of wafers can be processed simultaneously in a short time, which is completely incomparable to the molecular beam epitaxial growth method. (e) Since epitaxial growth is carried out in a short time and in a dilute gas atmosphere, auto-doping and impurity creep-up from the wafer to the epitaxially grown film are significantly reduced. (F) Compared with conventional vapor phase epitaxial growth methods, a high quality epitaxially grown film with fewer crystal defects, irregularities, etc. can be obtained. As described above, the present invention has various superior effects compared to conventional vapor phase growth methods and molecular beam epitaxial growth methods, but when compared with other characteristics, the following table shows the following. That's right.

【table】

【table】 [Brief explanation of the drawing]

The figure is a side cross-sectional view of essential parts showing an example of an apparatus for carrying out the present invention. In the figure, 1 is a bell jar, 1a is a gas injection port, 2 is a bottom plate, 2a is a gas discharge port, 3 is a susceptor, and 4 is a silicon wafer.

Claims (1)

[Claims] 1. Evacuate the inside of a reaction device in which a semiconductor wafer is placed on a susceptor to maintain a predetermined atmospheric pressure, and then inject a reaction gas from a gas injection port located at a position facing the semiconductor wafer. The reactant gas is injected to directly reach the surface of the semiconductor wafer and thermally decomposed to epitaxially grow a semiconductor film, and then the inside of the reactor is evacuated to maintain the predetermined pressure before the reaction gas is injected. At that point, the reaction gas is injected and the reaction gas is thermally decomposed in the same manner as above to epitaxially grow the semiconductor film, and if necessary, the reaction gas injection and reaction gas thermal decomposition steps are carried out after the evacuation is completed. A vacuum epitaxial growth method characterized in that a semiconductor film of a predetermined thickness is epitaxially grown in multiple steps by repeating the steps.