JPH03126698A - Formation of protective film for gaas semiconductor - Google Patents

Abstract

PURPOSE:To lessen the generation of the bend and crack of a subject semiconductor and to improve the yield of production by effecting a plasma reaction under specific conditions at the time of forming the protective film of plasma silicon nitride which prevents the dissipation of As in the annealing treatment of a GaAs semiconductor. CONSTITUTION:The annealing treatment of the GaAs semiconductor substrate which is formed with an active layer and is doped with impurity ions is executed by using gaseous SiH4-N2 as the gaseous system for the reaction system of a plasma reaction furnace to form a protective film. The protective film having (0 to 4)X10<7>dyn/cm<2> internal stress (compressive stress), (1 to 1.8)X10<22>cm<-3> hydrogen content, 2000 to 5000Angstrom film thickness, 2.6 to 2.8 density, and 0.8 to 0.9 Si/N atom ratio is formed by setting the pressure for forming the reactive gas at 0.2 to 0.6Torr, the reaction temp. at 250 to 300 deg.C, the flow rate of the reactive gas at 4 to 20sccm to the SiH4, the power source of high frequency for the plasma reaction furnace at 50 to 400kHz or 13.56MHz, and the power source at 100 to 300w.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a method for forming a protective film for a GaAs semiconductor, and more specifically to a method for preventing escape of As during annealing of the semiconductor. Plasma silicon nitride (P-S) for
This relates to the formation of a protective film for iN).

[Prior Art] Conductor elements based on gallium arsenide (GaAs) are widely used in light emitting diodes and the like.

In the manufacturing method of G a A S 'V-conductor, G a
Form an active layer of As, and add impurity ions to it.
, IE is a p- or H-semiconductor, which is then subjected to high-temperature annealing, that is, annealing treatment, to make the atomic arrangement regular and activate it.

However, in the annealing process, A
Since s escapes, a protective film of P-SiN is formed on the p-metal surface to prevent the escape.

FIG. 3 shows part 1 of the GaAs semiconductor manufacturing process described above, in which impurity ions i are implanted into the surface of the GaAs substrate l, and then a protective film 2 is formed on the surface in a plasma CVD reactor. It is then annealed in an inert gas atmosphere at a high temperature of 800°C.

[Problem to be solved] In the above annealing process, the strength of PSIN is 80
Since it cannot withstand a high temperature of 0° C., cracks occur in the protective film 2 and As escapes, so that the protective film does not fully function. Although the cause of the occurrence of such racks is not clear in detail, it is thought to be due to a change in internal stress that occurs during the deposition of the protective film 2. Internal stress depends on many parameters, such as the type and flow rate of the reaction gas system, the generated pressure and temperature, and the frequency and power of the high-frequency power source (hereinafter referred to as plasma 71L) applied to the plasma reactor. Furthermore, depending on these formation conditions, internal stress can be divided into compressive stress and tensile stress. The effect of internal stress will be explained with reference to FIG. 4(b) and (c).

Figure (a) shows the case of compressive stress, in which the substrate 1 and the protective film 2 are curved downward as a unit due to the compressive stress of the protective film 2, and when this is annealed, the compressive stress is reduced and the curve is Almost back to normal. It is said that this stress or change in curvature causes cracks in the protective film 2. Figure (b)
shows an example of the shape and distribution of cracks, and the cracks and cracks, such as round and linear shapes, are randomly distributed.
More As escapes through these. It is thought that one of the other causes of cracks is that the hydrogen contained in the protective film 2 is desorbed due to the high temperature of the annealing process.

Next, FIG. 4(c) shows a case where the forming conditions are set so that the internal stress becomes a tensile force, the substrate 1 is curved upward, and cracks are similarly generated by the annealing process. However, normally, a method is adopted in which the forming conditions are set so as to create compressive stress and the material is curved in the F direction.

Now, as a 1L method for preventing cracks as described above, there is a method of forming a protective film on the front and back surfaces of the substrate 1 to offset the internal stress of both, but in order to form a protective film on the back surface, Configuration of plasma reactor - 1-1 It is necessary to invert the substrate 1 and perform the forming process again, and the inversion operation has disadvantages such as harmful scratches on the surface of the substrate and adhesion of foreign matter. Quality - L Not desirable. In contrast, in this invention, internal stress and hydrogen content are issues, and by forming a small protective film, changes in curvature and hydrogen desorption during annealing treatment are reduced, and cracks are prevented. Defense II-.

The internal stress of the conventional protective film is determined by the method described later, and is determined to be a compressive stress of 8×109 ctyn/Cm2 per unit area of film thickness, and the hydrogen content is 3× It is 1022 cm-3.

Therefore, it is important not only to simply reduce the internal stress and hydrogen content, but also to satisfy the necessary conditions such as film thickness, density, and atomic ratio Si/N to maintain the strength of the protective film.

Here, the known relationship between the internal ratio of the protective film, the force, and the curvature of the substrate will be briefly explained with reference to the fifth drawing. In the figure, it is assumed that the substrate 1 is a circular plate with a flat diameter r, and that a protective film 2 (dotted line) is provided on the -L side. The reference line tangent to the center of the disk (
The surface) is assumed to be S, and the curvature is assumed to be a spherical surface. When the thickness of the protective film 2 is dP, the distance between the disc machining and the standard surface S before it is formed is C0%, and the distance after it is formed is C1, then the thickness of the protective film 2 is The resulting internal stress δ per medium area is δ=k (CI − Go ) / r2 dP --
---...<1), and the coefficient is a positive constant determined by the thickness of the substrate and the mechanical constants (Young's modulus, Poisson's ratio) of the substrate material. According to the equation (2), it can be seen that if the material of the substrate and the dimensions of each part are -. constant, the internal stress δ is proportional to (CIco), that is, the amount of change in the distance between the reference plane S and the edge.

Next, the total internal stress Δ with respect to the film thickness is Δ=dP
δ is expressed as (2), and the size of Δ determines the occurrence of cracks. In addition,
Since Δ is determined in consideration of the dimensions and mechanical constants of the substrate, it is possible to determine the occurrence of cracks regardless of the size and material of the substrate.

The following is a case where the internal stress is a tensile stress, but on the other hand, when the substrate is curved in the opposite direction as shown in Figure 4(a), the internal stress is a compressive stress, and these are In order to differentiate, internal stress δ is given a negative sign IY: depending on the direction of curvature, and self is defined as tensile stress and negative as compressive stress.

In reality, it is difficult to directly measure the internal stress of the protective film, so the internal stress is determined by measuring the curvature of the substrate and using the above formulas, and is given a positive or negative sign depending on the direction of the curvature. Ru.

The present invention solves the above-mentioned problems, and aims to provide a method for forming a P-SiN protective film that has low internal stress and low hydrogen content under appropriate formation conditions, and satisfies requirements such as strength. That is.

[Means for Solving the Problems] The present invention provides 4 P-SiN for annealing a GaAs semiconductor substrate in which an active layer is formed and impurity ions are inhabited.
A method for forming a protective film, in which SiH4-N2 is used as the reactive gas system of a plasma reactor for forming the protective film, and the conditions for forming the protective film include the generation pressure, temperature, flow rate of the reactive gas, and plasma. Set the frequency and power of the voltage to appropriate values, and make sure that the internal stress is compressive stress (0 to 4).
)×109dyn/Cm2, hydrogen content is (1 to 1.8
)010220m-3, film thickness 2000-5000Å,
Density is 2.6 to 2.8, silicon and nitrogen original γ ratio Si
A protective film is formed in which /N is 0.8 to 0.9 (-f).

The embodiment of the protective film formation conditions in the above is the formation F1
The force and temperature are 0.2 to 0.6 Torr and 2, respectively.
50-350°C1 The flow rate of the reaction gas is 4-208 CCM for SiH4, and the frequency of the plasma voltage is 50-350°C.
400kHz or 13°58MHz 1 power is 100
~300W is set.

[Effect] and the internal stress of the protective film formed under the formation conditions from Example 1 are as follows:
(O~4)XIO9 of the above-mentioned conventional one
ayn, /Cm2, so the bay l1tl of the substrate is still half silver, and the hydrogen content is (1~1.8)X
Since it is 60% or more of the conventional value at 1022 cm-3, cracks caused by annealing treatment are reduced or eliminated, and the escape of As is prevented. At the same time, the film thickness, density, and atomic ratio S i required for the strength of the protective film, etc.
/N are all satisfied and are practically perfect.

Hereinafter, the process of determining the forming conditions in the above embodiment will be explained using the measurement data shown in FIGS. 1(a) to 1(e). As for the measurement conditions here, the first thing to consider is the type of reaction gas. Conventionally, to form a P-SiN protective film, a SiH4-N2 system (hereinafter referred to as L-nitrogen system for convenience) and ammonia (NH3) were used. Added S 1H4-NH3
-N2 type (hereinafter referred to as ammonia type) is used, so both will be compared. Also, plasma electric J
-H frequency is the commonly used 50kHz
(hereinafter referred to as low frequency) and 13.5E3MHz (hereinafter referred to as F
We investigated both the high frequency and high frequencies.

Figure 1 (a) shows the internal ratio and force δ with respect to the production pressure, and the solid curve marked with ○ for low frequency in nitrogen-based reactant gases and the +Ib line marked with x for low frequency in ammonia-based reactant gas. ,0
．． Shows δ = (0 to -2)X109dVrl/cm2 within the expected value in the generation pressure range of 2 to 0.8 Torr,
In the ammonia-based high-frequency dashed line marked with Δ, δ exceeds 14×109 regardless of the generation pressure. As a result, the curves marked O and x satisfy the expected values at a generation pressure of 0.2 to 0.8 Torr. However, although the data are not shown in the figure, the characteristics similar to those indicated by the circle mark are also changed in the case of a nitrogen system and a high frequency. Therefore, this combination shall be treated in the same way as the O mark. Next, regarding the generation temperature, a range of 250 to 350°C has been conventionally used in plasma reactors, and it is actually convenient to have a temperature within this range. According to figure (b), this range is generated? Regarding the temperature, only the circle mark almost satisfies the expected value of δ (O~-4)XIO''.

Next, as for the power of the plasma electric F[, as shown in Figure (C), the circle mark satisfies δ in the range of 150 to 300 W, and the flow rate of the reactant gas SiH4 is 30 SCCM as shown in Figure (d).
The following items are marked with ○. However, since SiH4 is diluted to 20% with N2, the flow rate of the mixed gas is five times that of these.

Finally, the hydrogen content measured for the protective film formed under each of the conditions described in 2 is shown in Figure (e). Figure (a) ~
In all of (d), the circle that satisfies δ in each condition indicates that the hydrogen content is (1 to 1°8) XIO22
cm-3, and the other substances have excessive contents and are not compatible.

To summarize, the circle mark indicates that SiH4-N2 based reaction gas is used and the frequency of the plasma voltage is 50kHz.
(including 13.56MHz according to the description in l-), the generation fr force is 0.2 to 0.6Torr r%, and the generation temperature is 25
0~350°Cs SiH4 flow rate 4~208CC
It is clear that both the internal stress δ and the hydrogen content satisfy the expected values when M (20% straight), and the required film thickness, density, and original r ratio S, although the data are omitted.
It has been confirmed that the i/N ratio is also satisfied.

Among the formation conditions described above, the power of the plasma voltage may vary depending on the scale of the plasma reactor or the electrode method, and it needs to be determined for each reactor, but in general, the following is appropriate: It is said that

FIG. 2 shows the structure of a plasma reactor 3 to which the method of forming a protective film for a conductor is applied according to the present invention. An example will be explained. The reaction gas SiH4 introduced into the gas supply device 31 and the nitrogen gas N2 are mixed, and the mixed gas is supplied from the inlet 32 to the shower electrode 34 provided in the casing 33 of the reactor 3. It is injected downward from a large number of small holes 341. The generation pressure and flow rate of the injected mixed gas are determined by the gas supply'& 431
is adjusted to suit the forming conditions. There is an electrode table 35 facing the shower electrode 34, on the surface of which the silicon GaAs substrate 1 to be treated is placed and heated by a heater 38 to a temperature that meets the formation conditions. A plasma voltage with a frequency and power according to the formation conditions is applied between the shower electrode 34 and the electrode table 35 from the high-frequency power source 37, and the reaction gas becomes a plasma state, forming a protective film on the surface of the substrate 1 and completing the reaction. The excess gas is discharged from the outlet 38.

Each of the formation conditions in the above is based on the example above, and the formation pressure is 0.
．． 2~0.6 Tor rlS iH4 flow rate 4~20
8CCM, temperature is 250-350°C, and plasma voltage is at the commonly used frequency of 50-400kHz.
or 13.58 MHz, and its power is 150 to 300 W. In addition, the area of the negative electrode 34 and the electrode table 35 of the plasma reactor 3 in this embodiment is 100 to 1
300 m2, electrode spacing is 15-20 mm.

The protective film formed in the above manner is the above-mentioned (0-4)XI
Compressive stress of O9dyn/cm2 and (1-1.8)01
It has a hydrogen content of 0220 m-3 and a film thickness of 2000 m-3.
5000A1 has a density of 2.6 to 2.8 and an atomic ratio of Si/N of 0.8 to 0.9, which satisfies the relative requirements such as strength, and prevents cracks from occurring during the subsequent annealing process. This eliminates the escape of As.

[Effects of the Invention As is clear from the following explanation, the Ga
In the method for forming a protective film on an As semiconductor, the formation conditions determined by analyzing a large amount of measurement data using the formation conditions as parameters are set in a plasma reactor, and the formation condition is set at 60% with a compressive stress of 50% or more compared to the conventional method. A protective film of P-SiN with a hydrogen content of over 10%, a film thickness, and a density of -14 degrees is formed, and the small internal stress prevents the substrate from bending compared to the conventional method. Coupled with the small hydrogen content, this prevents the occurrence of cracks during annealing, reducing the disadvantage of As escape from the GaAs substrate by υ1.
・There is a great effect on improving the production yield of GaAs 'J' conductors.

[Brief explanation of the drawing]

Figure 1 (a), (b), (c), (
d) and (e) are G a A s according to the present invention.
Figure 2 is a curve diagram showing measurement data for determining the protective film forming conditions in the '14100 protective film forming method. An explanatory diagram of the operation, Fig. 3 is an explanatory diagram of the manufacturing process of GaAs semiconductor, Fig. 4 (a),
(b) and (C) are explanatory diagrams of the curvature of the substrate and cracks generated in the protective film, and FIG. 5 is an explanatory diagram of the relationship between the internal stress of the protective film and the curvature of the substrate. 1...G a As M board, 2... Protective film,
3... Plasma anti-At, furnace, 32... Inlet, 34... Shower electrode, 36... Heater 38... Outlet. 31... Gas supply device, 33... Reactor casing, 35... Electrode table, 37... High frequency power supply,

Claims (2)

[Claims] (1) Ga with active layer formed and impurity ions implanted
In the formation of a P-SiN protective film for annealing treatment of As semiconductor substrates, SiH_4-N_2 is used as the reactive gas system of the plasma reactor in which the protective film is formed, and the conditions for forming the protective film are as follows: By setting the generation pressure, temperature, and flow rate appropriately, and setting the frequency and power of the high-frequency power source applied to the plasma reactor to appropriate values, the internal stress is compressive stress (0 to 4) x 10.
＾9dyn/cm＾2, hydrogen content is (1 to 1.8)×
10^2^2cm^-^3, film thickness 2000-5000
Å, a density of 2.6 to 2.8, and an atomic ratio Si/N of silicon to nitrogen of 0.8 to 0.9. How to form a protective film. (2) The conditions for forming the protective film are as follows: the generation pressure and temperature are 0.2 to 0.6 Torr, respectively, and the flow rate of the reaction gas is 4 to 20 Scc for SiH_4.
2. The GaAs semiconductor protective film according to claim 1, wherein 50 to 400 kHz or 13.56 MHz is used as the frequency of the high frequency power source of the plasma reactor, and the power of the high frequency power source is set to 100 to 300 W. Formation method.