JPH0488632A - Formation of protective film for heat treatment - Google Patents

Abstract

PURPOSE:To minimize the pinhole formation even if silicon nitride films are thinly formed by a method wherein the silicon nitride films whereon the compression inner stress is imposed are formed by controlling the specific flow rate of monosilane and ammonia as a reaction gas. CONSTITUTION:After the formation of an active layer on the surface of a semiconductor GaAs substrate 1, the surface oxide film is removed. Next, in order to form SiNX films 2 used as protective films for heat treatment, the GaAs substrate 1 is set on a heating base 7 inside the reaction chamber 6 of a plasma CVD device while a gas (alpha) comprising monosilane and ammonia is fed into a plasma CVD device 3 to flow along the surface of the substrate 1 which is supplied with high-frequency output power for depositing the SiNX films 2. Through these procedures, the SiNX films 2 contains the compression inner stress, and the inner stress can be reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a method for forming protection during heat treatment used in the manufacturing process of semiconductor devices.

[Background Art] Various heat treatments are performed in the manufacturing process of the compound semiconductor device 1 and the like. For example, after ion implantation, activation annealing is performed so that the implanted ions function as donors and acceptors.

Activation annealing is also performed in the manufacturing process of compound semiconductor devices such as GaAs devices, AQGaAs devices, [nP devices, etc., but this is done at relatively high temperatures (800 to 900
C), As atoms and P atoms with high vapor pressure fly out, causing decomposition and alteration of the surface of the compound semiconductor substrate, significantly deteriorating device characteristics.

For this reason, conventionally, as shown in FIG. 3(a), Si ions 4 are implanted into the surface of a semi-insulating GaAs substrate 1 to form an ion implantation region 5 on the surface of the GaAs substrate 1. After that, as shown in FIG. 3(b), the ion implantation region 5 is
Sputtering method or CVD method is applied to the surface of GaAs substrate 1 with
t: Yo') Si, N, film 10 from 1000 to 2000
The film had been formed to a thickness comparable to that of a human body.

[Problems to be Solved by the Invention] However, semi-insulating Ga that has been subjected to activation annealing
The crystallinity and electrical characteristics of the As substrate largely depend on the thickness and quality of this 5iaN4 film. For example, if the film thickness is 17
If the thickness of the Si, N4 film is reduced to 1000 Å or more, cracks may occur in the semi-insulating GaAs substrate due to thermal expansion during heat treatment of the 5iJ4 film. The drawback was that many pinholes were generated in the film.

For this reason, S! It is preferable to form a thinner and denser sNn film as possible;
3N, when the film is formed, its tensile internal stress is about L O1
The tensile force is quite large, on the order of "lcfyne/cm".As a result, the tensile internal stress of the 5isN4 film tends to cause crystal defects in the GaAs substrate crystal, which poses a problem in that the reliability of the manufactured semiconductor device decreases. .

The present invention has been made in view of the drawbacks of the conventional examples described above, and its purpose is to prevent pinholes from occurring even when the thickness is reduced, and to prevent crystal defects from forming in the substrate crystal. An object of the present invention is to provide a method for forming protection during heat treatment.

Means for Solving the Problem] Therefore, the method of forming a protection layer during heat treatment of the present invention is a method of forming a silicon nitride film for protection during heat treatment on the surface f of a semiconductor substrate by plasma CVD method, The method is characterized in that a silicon nitride film having compressive internal stress is formed by using monosilane and ammonia as reaction gases and controlling the flow rate ratio of monosilane and ammonia.

[Monosilane (
5LH4) and ammonia (NHs), and the flow rate ratio of monosilane and ammonia was varied (especially, 5tH4) and ammonia (NHs) were used.
As a result, the tensile internal stress of the deposited silicon nitride (SiN) film decreased and finally became compressive internal stress. By controlling the flow rate ratio, a silicon nitride film having compressive internal stress can be formed by plasma CVD.

Since this silicon nitride film has compressive internal stress, pinholes are unlikely to occur even if the film thickness is reduced to, for example, about 100 OA. In addition, the compressive internal stress of a silicon nitride film is extremely small compared to the conventionally used silicon nitride film with tensile internal stress, so it is possible to form a silicon nitride film on the surface of a semiconductor substrate crystal. However, crystal defects are less likely to occur.

[Example code] Embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

After an active layer (ion implantation region 5) is formed on the surface of the semi-insulating QaAs substrate 1 by ion implantation or the like, an oxide film (not shown) on the surface is removed. This oxide film removal process uses a solvent such as trichloroethane or acetone to remove the GaA
After organically cleaning the surface of the s-substrate 1, hydrochloric acid (HCQ)
) to etch the oxide film for several minutes at room temperature.
This cleans and prepares the surface of the GaAs substrate 1. Next, in order to form a SiNx film (silicon nitride film. The GaAs substrate 1 is set on the heating table 7 in the plasma CVD apparatus S, and monosilane (Sit (4
) and ammonia (N)I3) is supplied to the surface of the GaAs substrate 1 at a rate of about 0.2 W/cm.
A high frequency output power of 2 is applied to grow SiN film 2 to a thickness of 1000 nm.

Here, when the temperature T,...l, of the GaAs substrate 1 in the plasma CVD apparatus S is 300°C and 350°C, the gas flow ratio of monosilane and ammonia is changed, and the When the internal stress was measured, the results shown in Figure 2 were obtained.

The horizontal axis of FIG. 2 shows the flow rate ratio of monosilane/ammonia, and the vertical axis shows the internal stress of SiN and the film 2, with the upper part being the compressive internal stress and the lower part being the tensile internal stress. In other words, as the monosilane/ammonia flow rate ratio decreases, the tensile internal stress tends to decrease, and eventually,
When the substrate temperature T a u b is 300°C, the tensile internal stress changes to the compressive internal stress when the monosilane/ammonia flow rate ratio is 0.1'85, and the substrate temperature T,
When ul was 350° C., the tensile internal stress changed to compressive internal stress when the monosilane/ammonia flow rate ratio was about 0.16. Moreover, in the conventional SiNx film 2, the tensile internal stress was approximately 10 gdyne/cm 2 , whereas according to the present invention, the compressive internal stress is approximately uniform, and is approximately 10” dyne/cm 2 . became.

Therefore, when the substrate temperature T, , is 300°C,
The flow rate ratio of gas monosilane:ammonia is approximately 0.1:
1 to 0.185:1, the gas pressure in the reaction chamber 6 was set to 0.8 to 1 torr, the high frequency output power was set to about 0.2 W/am2, and the Si
A N coating film 2 was formed. Alternatively, the substrate temperature T*u
When b is 350°C, the flow rate ratio of monosilane:ammonia as diluent gas is set to approximately 0.1:1~0°1θO:1, and the gas pressure in the reaction chamber is set to 0.8~ttorr1.The high frequency output power is set to approximately 0.2 W/cm'', and the SiNx film 2 was formed to have a film thickness of about 1000 Å.

The SiNx film 2 thus formed has a compressive internal stress, which is as small as about 10 gdyne/cm'', while the tensile internal stress of the conventional SiNx film is about 1011 dyne/cm''. Compared to the previous case, the value was about 1/10 or less, and we were able to significantly reduce internal mental force. The SiN film 2 has compressive stress, so it is not stretched and is as thin as 100 mm (even if it is thin, no pinholes are generated and a high-quality protective film during heat treatment can be obtained. Since it was possible to reduce the value to a small value, crystal defects were less likely to occur in the GaAs substrate crystal on which the SiNx film 2 was formed, and the reliability of the manufactured device could be improved.

Although the above embodiments have been described with reference to the case of a GaAs substrate, it goes without saying that the present invention can also be implemented in other types of semiconductor devices, such as Ⅰ-V group compound semiconductor devices, silicon-based semiconductor devices, and the like.

[Effects of the Invention] According to the present invention, the internal stress of the silicon nitride film used as a protective film for heat treatment can be made into compressive stress. Pinholes will no longer occur. Further, since the thickness of the silicon nitride film can be reduced and the value of internal stress is also reduced, crystal defects are less likely to occur in the substrate crystal under the silicon nitride film. Therefore, a highly reliable semiconductor device (for example, a compound semiconductor device with good ohmic characteristics) can be manufactured.

[Brief explanation of drawings]

Figure 1 is a schematic diagram showing an embodiment of the present invention, Figure 2 is a diagram showing the relationship between the monosilane/ammonia gas flow rate ratio and the internal stress of the silicon nitride film, and Figures 3 (a) and (b) are FIG. 2 is a sectional view illustrating a conventional example. 1...GaAs substrate 2...Silicon nitride film 3...Plasma CVD device α...Reactive gas Patent applicant Murata Manufacturing Co., Ltd. Representative Patent attorney Masafusa Nakano

Claims (1)

[Claims] (1) A method of forming a silicon nitride film for protection during heat treatment on the surface of a semiconductor substrate by plasma CVD method, in which monosilane and ammonia are used as reaction gases, and by controlling the flow rate ratio of monosilane and ammonia, A method for forming a protective film for heat treatment, characterized by forming a silicon nitride film having stress.