Wet-dry-wet process in wet station

Details Wet-dry-wet process in wet station Wet-dry-wet process in wet station

1999-08-16

2001-04-03

Smith, Matthew (Department: 2825)

Semiconductor device manufacturing: process

Coating with electrically or thermally conductive material

To form ohmic contact to semiconductive material

C438S906000, C438S689000, C134S003000, C134S095200

Reexamination Certificate

active

06211055

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to an improved wet-washing method and apparatus for use in the fabrication of semiconductor devices. More specifically, the present invention relates to an improved but cost-effective post-etching rinsing and cleaning method and apparatus that are adjunct to the process of forming one or more electrically conductive channels through one or more dielectric layers to electrically connect two sandwiching conductive layers. The method and apparatus disclosed in the present invention can eliminate, or at least minimize, the unintended high electric resistance due to the presence of oxide that may be formed on the end face of the channel; they also prevent channel shorting problems when a plurality of channels are being formed in the same etching process. The method and apparatus disclosed in the present invention can also be advantageously utilized in other processes which involve two disparate wet-etching steps and wherein the second wet-etching stage requires a relatively invariant etching strength in order to avoid undesirable side effects.
BACKGROUND OF THE INVENTION
A rinsing and cleaning apparatus (RCA) is a necessary equipment in the fabrication of semiconductor devices. A rinsing and cleaning step is almost always required after the semiconductor wafers have been subjected to an etching process, and typically before they are subjected to other fabrication processes such as diffusion, thermal oxidation, chemical vapor deposition (CVD), etc. The main purpose of rinsing and cleaning is to remove the contamination, particles, organic molecules, metal ions, etc., that maybe left on the wafer surface before subjecting the wafer a subsequent process. Inadequate rinsing and cleaning can lead to poor yield and low product quality problems. However, due to the constant pricing pressure present in the semiconductor industry, semiconductor manufacturers must balance the thoroughness of the rinsing and cleaning procedure relative to the cost thereof. The completeness of rinsing and cleaning, become more critical during the fabrication of ULSI devices where there exists substantially less room for error.
FIG. 1
shows an illustrative schematic diagram of a typical wet washing station in a rinsing and cleaning apparatus. It includes an I/O Station for loading and unloading wafer to be wet washed. A robot
12
transports the wafer into various modules, such as BHF (buffered hydrogen fluoride) module, SC
1
(standard clean
1
) module, SC
2
(standard clean
2
) module. The BHF module is effective in removing oxides, SC
1
(which typically contains a mixture of NH
4
OH, H
2
O
2
, H
2
O) is provided to remove particles, and SC
2
(which typically contains a mixture of HCl, H
2
O
2
, H
2
O) is provided to remove metal impurities. Each of the modules of BHF, SC
1
and SC
2
also contains a QDR (quick dump rinse), which is a water tank for a quick dump rinse of the wafer after going through the each wet wash main module. After the programmed washing steps, the wafer is sent to a dryer, where the wafer is dried, and finally back to the I/O station, where the dried wafer leaves the wet station. The sequence among the various washing modules can be programmed and can be out of order. However, in order to avoid undried wafer leaving the washing station, once the wafer enters the dryer, it cannot return to the washing modules, and must exit the wet washing station after the drying step.
The improved method and apparatus of the present invention were discovered when the co-inventors were investigating a yield problem during the fabrication of semiconductor devices which contain conductive channels (i.e., plugs) that are formed through a dielectric layer to electrically connect two conductive layers sandwiching the dielectric layer. After extensive and careful studies, the co-inventors of the present invention discovered that a native oxide layer can be formed on the surface of the bottom conductive layer, causing a high contact resistance to be present in the plug to be subsequently formed. The native oxide layer was formed due to the use of oxidizer such as hydrogen peroxide in the washing modules which released nascent oxygen atoms. The nascent oxygen atoms would react with the silicon atoms and form the native oxide layer, which is non-conductive.
One possible solution to this problem is to move the BBF module to the end of the wet washing process, making it a BHF-last wet washing station, so as to remove the native oxide. Since the native oxide layer is very thin, the BBF module is typically modified to become a diluted hydrogen fluoride (DHF), so as not to cause other complications. However, another problem arises when a DHF module is used. This occurred because the water-soaked wafer can dilute and adversely affect the strength of the DHF module, rendering it largely ineffective. If a higher strength BHF is used, it can result in different etching rates along the length of the channel, higher etching rate in the top (where etching is not required) and lower etching rate in the bottom (where high etching strength is required). In certain situations, for example, when multiple channels are formed in a relatively close area, short circuiting may occur, resulting in a yield failure.
SUMMARY OF THE INVENTION
The primary object of the present invention is to develop an improved method and apparatus for post-etching rinsing and cleaning operations for semiconductor wafers. More specifically, the primary object of the present invention is to develop an improved method and apparatus which will remove the native oxide layer that may be formed in a conductive channel, while preventing the occurrence of short-circuiting. The method and apparatus of the present invention eliminate the presence of the high contact resistence that often results in poor channel quality, they also avoid the circuit shorting problem which may occur as a result of over-correcting of the first problem. One of the main advantages of the present invention is that it improves both the quality and the yield rate of the channel-containing semiconductor devices in a very cost-effective manner. The method and apparatus of the present invention disclosed in the present invention can also be utilized in other semiconductor fabrication processes which involve two disparate wet washing processes, especially when the strength of the second wet washing process is of critical concern.
In the method disclosed in the present invention, the wet washing process is divided into two parts, the first part comprises at least one washing module which involves the use of an oxidative, agent. And the second part comprises a hydrogen fluoride wash step, which can be a buffered hydrogen fluoride (BHF) step or dilute hydrogen fluoride (DHF) step. A drying step is effectuated in between the two wet wash steps, so as not to dilute the effective strength of the second part wet wash. The method disclosed in the present allows the native oxide layer to be effectively removed, thus preventing the formation of high resistance contact on the conductive substrate. By not diluting the strength of the hydrogen fluoride bath, the method of the present invention eliminates the need for using a high strength solution initially. Thus, the present invention also prevents the over-etching problem that may result in circuit shorting problems when multiple channels are formed in a relatively close area.
Another problem arises when implementing the method discussed above. In order to prevent the un-dried wafer to leave the washing station, all the conventional rinsing and cleaning machines are structured such that the path from the washing modules to the dryer is one-directional. Thus, in order to provide the drying step prior to the second washing step, the wafer must be removed from the wet washing station, then start a new wet washing cycle. This can cause substantial increases in the fabrication time, and thus resulting substantially increased production cost.
In the present invention, the washing station is modified suc

Affiliated with

Also associated with

Rating

Wet-dry-wet process in wet station does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with Wet-dry-wet process in wet station, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Wet-dry-wet process in wet station will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-2465551