JPS6214941B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method of manufacturing a semiconductor device, and more particularly to a method of manufacturing a semiconductor device having a phosphor glass layer with improved moisture resistance.

2. Description of the Related Art Semiconductor devices, particularly semiconductor integrated circuit devices, are becoming increasingly finer, and the width of metal wiring layers is also becoming significantly narrower. Furthermore, as multi-layer wiring progresses, it is common for very large steps to form in the lower layers where metal wiring crosses, causing wire breaks. To eliminate this level difference, a phosphorus glass layer containing a high concentration of phosphorus is usually formed under the metal wiring, and the fluidity of phosphorus glass is utilized to smooth the step and prevent wire breakage.

However, a drawback of this method is that it has poor moisture resistance. Phosphorus glass has water absorption properties, and reacts with water to form phosphoric acid, which corrodes metal wiring under high temperature and high humidity conditions, causing wire breakage.
Especially when the device is assembled into a plastic package, the waterproofness of the plastic package is much lower than that of ceramics, can cases, etc.
When exposed to a high-temperature, high-humidity atmosphere for a long period of time, moisture easily reaches the surface of the element, reacts with the phosphorous glass layer of the element, produces phosphoric acid, and corrodes the metal wiring. For this reason, it has been extremely difficult to maintain the moisture resistance of a plastic package of an element containing a phosphor glass layer.

Recently, in order to improve the moisture resistance of this type of device, a method has been adopted in which the surface of the device is passivated with a plasma nitride film. It is true that this nitride film has a very large effect on moisture resistance, but it has one major drawback. This causes damage to the device during the growth of the plasma nitride film and increases leakage current. This causes a decrease in yield in products that are sensitive to leakage current (eg, semiconductor memories).

The present invention thus makes it possible to improve moisture resistance without impairing the characteristics of the element.

The present invention involves forming a vapor-phase grown oxide film doped with 1 to 7 mol% of phosphorus (P ₂ O ₅ ) to a thickness of 0.2 to 1.5 μm on a highly concentrated phosphorus glass layer formed on a semiconductor element. This phosphorus-doped oxide film is then heat-treated.
It is characterized in that it is densified and the high-concentration phosphorus glass layer and metal wiring (for example, aluminum wiring) are not brought into direct contact with each other.

The phosphorus-doped vapor-phase grown oxide film prevents water from entering the phosphorus glass layer from the outside and prevents corrosion of the metal wiring due to leaching of phosphoric acid. The vapor-grown oxide film used here is porous and water-permeable after growth, so it cannot be used as it is, but as in the present invention, it is doped with an appropriate amount of phosphorus (P ₂ O ₅ ) and heat-treated. As a result, a dense film similar to a thermal oxide film can be obtained, which has a waterproof effect.

Next, FIG. 1 shows an embodiment in which the present invention is applied to an N-channel silicon gate MOS and LSI. First, the oxide film 2 in the field part, the gate oxide film 3,
and a polysilicon gate electrode 4 (FIG. 1a). Phosphorus then diffuses into the source
After forming the drain region 5, a highly concentrated phosphorus glass layer 6 of 0.5 μm is formed by vapor phase growth (FIG. 1b). Next, after making a contact hole in the phosphorus glass layer 6, a vapor phase growth oxide film 7 doped with 4 mol% of phosphorus (P ₂ O ₅ ) was grown to a thickness of about 0.5 μm, and then heated to a high temperature (900 to 1000°C). The oxide film was densified by heat treatment (FIG. 1c). Next, after drilling a contact hole again, aluminum is deposited and patterned to form a wiring 8, and finally, as a cover, the area other than the bonding pad is covered with a vapor-phase grown film 9 (FIG. 1d).

Note that the heat treatment of the phosphorus-doped vapor-phase grown film can be replaced by other high-temperature heat processes. When the sample made in this way was assembled into a plastic case and subjected to a life test under high pressure and high temperature and humidity, it showed a lifespan more than three times that of the sample without any countermeasures, clearly demonstrating the effectiveness of the present invention. I was disappointed. Figure 2 shows the relationship between the concentration of phosphorus (P ₂ O ₅ ) doped into a vapor-phase grown oxide film and its life time when subjected to a high temperature, high humidity life test under high pressure. It is expressed as a magnification based on time. According to this, it can be seen that an effect can be obtained when the concentration of phosphorus to be doped is 1 to 7 mol%.

[Brief explanation of the drawing]

FIGS. 1a to 1d are cross-sectional views showing an embodiment of the present invention in the order of steps. FIG. 2 is a diagram showing the relationship between the molar concentration of phosphorus doped into a vapor-phase grown oxide film and its lifetime. In the figure, 1... silicon substrate, 2... oxide film, 3... gate oxide film, 4... polysilicon gate electrode, 5... source/drain diffusion region,
6... Phosphorus glass layer, 7... Phosphorus-doped vapor phase grown oxide film, 8... Aluminum wiring, 9... Vapor phase grown oxide film.

Claims (1)

[Claims] 1. A step of forming source and drain regions on a semiconductor substrate provided with a field oxide film, a gate oxide film, and a gate electrode, and then forming the field oxide film, gate electrode, source, and drain regions with a highly concentrated phosphorus glass layer. P 2 O ₅ is coated directly on the high concentration phosphorus glass layer to coat it with P ₂ O 5.
A step of forming an oxide film with a thickness of 0.2 μm to 1.5 μm containing ~7 mol%, a step of densifying the oxide film by heat treatment, and directly depositing on the oxide film and connecting to the source and drain regions. 1. A method for manufacturing a semiconductor device, comprising the steps of: forming an aluminum wiring layer, and covering the entire surface with a vapor-phase growth film.