JPS5846053B2 - Semiconductor device and its manufacturing method - Google Patents

Description

[Detailed description of the invention] The present invention relates to a semiconductor device and a method for manufacturing the same.

This invention relates to a method for forming an electrode on a semiconductor substrate having a shallow bonding layer, and it is possible to form an Al electrode that is easier to form than conventional methods and that does not destroy the shallow bonding layer even during post-formation heat treatment. This is the purpose.

In recent years, due to the demand for finer circuit patterns due to higher integration of MO8 type integrated circuits and higher speed of bipolar transistors, it has become necessary to reduce the depth of source, drain, and emitter diffusion layers to make them shallower.

In the conventional method of forming an Al electrode on a diffusion layer with such a shallow junction, Al easily penetrates deeply into the diffusion layer during alloying heat treatment after forming the electrode and destroys the junction. do.

This causes leakage and short circuits between the semiconductor substrate and the electrodes, resulting in a decrease in the yield of semiconductor devices, and there is a strong demand for improvement in this respect.

Therefore, as one of the electrode formation methods for shallow junctions, S
The method of using A7 containing i as an electrode material is well known.

If you use this electrode, since Si is included in Al from the beginning,
Even if heat treatment is applied after electrode formation, the amount of semiconductor atoms in the substrate dissolved into the electrode and the amount of Al atoms penetrating into the substrate are extremely small.

Therefore, bond breakdown that occurs when only pure 7a'Al is used can be greatly reduced.

However, in order to form A7 containing Si in a semiconductor region, a vapor deposition method is used, but at this time, 5i-A#, which serves as a vapor deposition source, is used.
It is technically sophisticated and extremely difficult to form a wiring film with good reproducibility while keeping the Si concentration in the alloy faithful.

This is because there is a large difference in thermal equilibrium vapor pressure between Al and Si at a certain temperature.

FIG. 1 is a diagram showing the thermal equilibrium vapor pressure and temperature. For example, at 1400'C near the melting point of Si, the vapor pressure of AA is
It can be seen that the ratio is 500:1, and there is a considerable difference.

In evaporation methods where the temperature of the evaporation source is relatively low, such as resistance heating evaporation method using a tungsten filament, even if the Si concentration of the evaporation source is several percent, this large difference in vapor pressure causes only A7 atoms to is deposited at a high rate, and almost no Si atoms are contained in the deposited film.

Furthermore, Si that is not vaporized remains in the filament of the deposition source, and during the next deposition, Si in the source alloy remains.
This increases the Si concentration and causes poor Si concentration reproducibility in the deposited film.

This happens because the Si concentration in A7 is the vapor deposition source.
Since the concentration is small compared to the Si concentration, junction leakage occurs after electrode heat treatment, reducing yield, and wiring resistance and contact resistance vary due to variations in Si concentration in the Al film, resulting in unfavorable results in terms of process control.

The present invention was made as a result of studies in view of the current situation, and is intended to form an electrode that improves the above-mentioned drawbacks.

The present invention will be explained in detail below. A feature of the electrode formation of the present invention is that Al containing germanium (Ge) is used as the electrode material.

Ge is a typical semiconductor of the same family as Si, and has many similarities in physical properties such as crystal structure and band structure.

In particular, the Al-Ge binary alloy phase diagram is of the same eutectic reaction type as the AdSi system, and the temperature at which the Al-Ge solid solution phase is formed also ranges from about 200°C to around 600°C.

The temperature range of this is the same as that of the solid solution phase of the Al-8i system. Therefore, if the vapor-deposited Al film for wiring contains Ge from the beginning, the A7 film containing Si will be removed during the subsequent electrode heat treatment. It is expected that the same effect will occur.

In other words, since Ge, which has properties similar to Si, is contained in the A7 film from the beginning, semiconductor atoms are prevented from diffusing into the A7 film from the metal-semiconductor substrate interface, while A7 is also a semiconductor. It is thought that it becomes difficult to penetrate into the board.

Based on this idea, the present inventors conducted an actual experiment and confirmed that the present invention is effective in preventing A7 from entering a semiconductor substrate.

First, the surface of a semiconductor region of an opposite conductivity type formed to a depth of about 17' on a Si substrate of one conductivity type, which will be a contact surface, is
After etching with an etching solution of NH4F:HF=10:1 to remove a thin oxide film on the surface, an A7 alloy containing (1 to 10%) Ge was deposited by resistance heating.

The degree of vacuum was 1×10 −6× to 1×10 −5 Torr.

After that, the A1 alloy deposited without sintering at 420°C in a N2 atmosphere was removed, and the Si surface was examined using an SEM (electron microscope).
I observed it.

FIG. 2a is a SEM image of the sample, and FIG. 2a shows the surface from which Al has been removed after conventional AA has been deposited and sinked.

In this figure, 1 is the SiO2 film on the surface, and 2 is the surface of the diffusion layer.

Haloy pits 3 are seen in conventional Al, and it is extremely likely that penetration into the A7 diffusion layer has occurred.

On the other hand, in the sample in which Al containing Ge was vapor-deposited, only Ge4 precipitated on the surface was visible, and there were no alloy pits, indicating that the intrusion of A7 was prevented.

By the way, at this time, the sink temperature is AA-Ge eutectic temperature 4
It was found that when the temperature is 24°C or higher, interdiffusion between Al and Si occurs rapidly and alloy pits are formed.

Therefore, the sink temperature is preferably 424° C. or lower, which is lower than the eutectic temperature.

In this way, the non-inventors found that if Ad containing Ge is used, A
It was confirmed that this method has the effect of reducing the phenomenon of bond breakdown due to the intrusion of No. 7.

By the way, the melting point of Ge is 940°C, and the melting point of Si is 1.40°C.
It is 0°C.

Therefore, at a certain temperature, the vapor pressure of Ge is considered to be much higher than that of Si.

In fact, as shown in Figure 1, for example, when comparing the case of 1100℃, A#: 1X1O-Torr, Si: 5X10
Torr, Ge: 8X10-5 Torr,
It can be seen that the vapor pressure ratio of Ge to Al is much smaller than that of Si.

It is known that when vapor deposition is performed from a vapor deposition source with an impurity content of wB%, it is expressed by a formula that indicates the content of impurities (FB%) that enters the deposited film.

Here, AA tAB are the activities of Al and impurities, PA , respectively.

PB is the vapor pressure of AA and impurities, MA, respectively.

MB are the molecular weights of A7 and impurities, respectively.

As can be seen from this equation, FB is greatly influenced by the ratio PB/PA of impurity vapor pressure to Al.

The closer PB/PA is to 1, the more the deposition source impurity concentration is reflected in the deposited film.

Therefore, when A7 containing Ge is deposited, the impurity concentration in the deposited film becomes closer to the impurity concentration of the deposition source.

As mentioned above, if Al containing Ge is used as an electrode material,
Since the impurity concentration in the deposited film is closer to the deposition source impurity concentration than in the case of A7 containing Si, it is possible to form an Al electrode containing Ge close to the deposition source impurity concentration even by the resistance heating evaporation method.

Therefore, the amount of the impurities remaining on the filament of the deposition source without being deposited can be reduced, and repeated deposition becomes easy.

Furthermore, Ge in Al has the same effect as Si on electrode heat treatment, prevents junction breakdown due to AA intrusion into the diffusion layer, and can suppress reduction in integrated circuit yield due to junction leakage.

Although the present invention has been described with respect to a method of forming an Al electrode containing only Ge, Si may be mixed with Ge as the main component.

If a small amount of Si is mixed into AA, it becomes difficult for An to penetrate into the 8i substrate even if the sink temperature is set to 424° C. or higher, as can be seen from the conventional method.

Therefore, if Ge is the main component and Si is mixed into A7, G
Since it can be sintered at a higher temperature (424° C. or higher) than when only e is used, it is effective not only in preventing junction breakdown due to Al but also in forming low resistance ohmic contacts.

As described above, by using the A7 electrode containing Ge as an impurity, the present invention can reliably and easily form an electrode in a shallow opposite conductive shadow region formed in a silicon layer, and This greatly contributes to the production of integrated circuits.

[Brief explanation of drawings]

Figure 1 shows the relationship between temperature and thermal equilibrium vapor pressure of Ad, Si, and Ge, and Figure 2a is 5,000 times the surface of the semiconductor substrate from which the electrode was removed by sinking after forming an AA alloy electrode containing Ge. Figure 2 is an SEM image (electron micrograph) of the surface of a conventional substrate with an Al electrode type bottom cut out and sintered to remove A7. 1...S t 02 film, 2... Diffusivity, 4... Ge.

Claims (1)

[Scope of Claims] 1. A semiconductor device characterized in that an aluminum electrode containing germanium is formed in a silicon layer. 2. The semiconductor device according to claim 1, wherein the aluminum electrode contains silicon as a main component and germanium as a main component. 3. A method of manufacturing a semiconductor device, comprising depositing aluminum containing germanium on a silicon layer and heat-treating the silicon layer to form an electrode of the silicon layer. 4. The method for manufacturing a semiconductor device according to claim 3, wherein after the vapor deposition, heat treatment is performed at a temperature below the eutectic temperature. 5. The method of manufacturing a semiconductor device according to claim 3, wherein the aluminum contains germanium as a main component and silicon.