Method of making a semiconductor device

Details Method of making a semiconductor device Method of making a semiconductor device

2001-09-05

2002-06-04

Chaudhuri, Olik (Department: 2813)

Semiconductor device manufacturing: process

Coating with electrically or thermally conductive material

To form ohmic contact to semiconductive material

C257S382000

Reexamination Certificate

active

06399494

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to processes for producing semiconductor devices and, particularly, to a process for producing semiconductor devices while preventing contamination otherwise produced during low pressure-chemical vapor deposition (LP-CVD).
2. Description of the Related Art
Where semiconductor devices, such as dynamic random access memories (DRAMs), are produced, interconnections on the surface of an n+diffusion layer are made of polysilicon. One way to provide high speed, high-density semiconductor devices is further miniaturization of the devices. For example, a DRAM having a gate length of 0.18 um or less is being developed. To reduce the resistance between the n+diffusion layer and the interconnection in the contact area of a DRAM, tungsten interconnection has been proposed. However, for the 0.18 um or less device, the resistance between the tungsten interconnection and the n+diffusion layer is still too high, and further reduction is demanded. For this reason, cobalt siliside (CoSi2) has been provided between the n+diffusion layer and the tungsten interconnection.
However, after the CoSi2 film is formed on the n+diffusion layer, it is necessary to form an insulation film, such as silicon nitride (SiN) film, on the CoSi2 film. This is made by LP-CVD. The structure or intermediate structure obtained by LP-CVD has a CoSi2 film. Consequently, the back side of the structure can be contaminated by the heavy metal adhering to the carrier used in the heavy metal process wherein the heavy metal or cobalt is used. The inventors have confirmed that the amount of a heavy metal, such as tungsten or titanium, adhering to the back side of the structure is not more than 10 atoms/cm . If such a structure is put into a LP-CVD reaction furnace, the quartz component or dummy wafer in the structure would be contaminated. In addition, where the LP-CVD is batch processed, other devices in the batch process are contaminated. This contamination leads to impairment of the device electrical characteristics.
SUMMARY OF THE INVENTION
Accordingly, it is an object of the invention to provide a process for producing a semiconductor device capable of preventing contamination of the device in the LP-CVD process that is performed after the heavy metal process.
According to the invention there is provided a process for producing a semiconductor device including a heavy metal step wherein a heavy metal is used, comprising the steps of depositing an insulation film on a back side of a structure prior to the heavy metal step; and removing from the insulation film the heavy metal that has adhered to the insulation film in the heavy metal step.
Since the insulation film is formed on the back side of a structure prior to the heavy metal process, the insulation film, to which undesired heavy metal adheres, prevents the heavy metal from diffusing into the structure. The heavy metal is removed from the insulation film prior to the next step so that contamination, by the heavy metal, of the components of a structure is avoided. Also, contamination of the other structures in the same batch is avoided.
It is preferred that the insulation film has a thickness of 10-20 nm. If the film thickness is too large, the formation time is so long that the amount of particles is increased too much to be practical. Thus, it is preferred that the film thickness be no more than 20 nm. To make the insulation even in thickness and high in quality, it is preferred that the film thickness be no less than 10 nm.
Also, it is preferred that the insulation film is an oxide film. An example of the substrate for the structure is a silicon substrate, on the back side of which the oxide film is formed. Then, the structure is subjected to the process with a heavy metal. As a result, the heavy metal adheres to the oxide film. The bonding force between the oxide film and the heavy metal is weaker than that between the silicon substrate and the heavy metal so that the heavy metal can be readily removed with hydrogen fluoride (HF) or the like. Since there is the oxide film between the heavy metal and the substrate, it is possible to suppress diffusion of the heavy metal into the substrate. Where the oxide film is formed by LP-CVD, the oxide film becomes rich with silicon in the first 2-3 nm layer. Consequently, to form a stoichiometric SiO2 film, it is necessary to make the film at least 10 nm thick.
Alternatively, it is preferred that the insulation film is a nitride film. If the substrate is a silicon substrate, the nitride film is formed on the back side of the silicon substrate. Then, the structure is subjected to the process with a heavy metal. As a result, the heavy metal adheres to the nitride film. The chemical bond between silicon and nitrogen of the SiN film is incomplete in comparison with the chemical bond between silicon and oxygen of the SiO2 film so that the heavy metal is bonded with silicon of the nitride film with a strong force. Consequently, there is no danger that the adhered heavy metal diffuses into the silicon substrate from the nitride film. Then, the heavy metal is lifted off together with the nitride surface layer with HF or the like.
Where the insulation film is either oxide or nitride film, it is easy to remove the heavy metal from the surface with HF. More specifically, the structure with the insulation film is immersed in a 0.3% HF solution for 60 seconds to remove the heavy metal.
Then, the insulation film may be removed. This is also achieved by wet etching with HF.


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patent: 6146542 (2000-11-01), Ha et al.
patent: 6207563 (2001-03-01), Wieczorek et al.
patent: 6339245 (2002-01-01), Maa et al.
patent: 9-232253 (1997-09-01), None
patent: 2000-114515 (2000-04-01), None

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