Semiconductor device manufacturing: process – Chemical etching – Liquid phase etching
Utility Patent
1999-02-17
2001-01-02
Powell, William (Department: 1765)
Semiconductor device manufacturing: process
Chemical etching
Liquid phase etching
C438S747000
Utility Patent
active
06169038
ABSTRACT:
The invention refers to a method for rough-etching a semiconductor surface.
The manufacture of semiconductors, for example in the form of so-called wafers (circular semiconductor disks based on silicon) requires always special care. This includes also a defined roughness of their surface(s).
As follows from the EP 0 791 953 A2, the wafers may first be polished on both sides (surfaces). Then, the front and the back face are not discernible any longer. This also is true in employing optical sensors, at least as long as both surfaces have the same “surface structure”.
Before the wafer surface is coated with different layers, for example of gold, titanium, copper or polysilicium, the respective surface has to be cleaned and roughened. The aim is a defined roughness being constant throughout the semiconductor surface.
In this context, the EP 0 791 953 A2 proposes to etch a wafer surface by means of a mixture of acids and to polish again the other surface.
The etching time is indicated to be 1 to 3 minutes for a wafer having a diameter of 150 mm. The semiconductor (wafer) is rotated with 10 to 100 rpm during the etching process. The amount of echtant is indicated to be 2-3 liters/min. The roughness of the treated surface was increased from Ra=0.01 &mgr;m to Ra=0.5 to 1.0 &mgr;m (DIN 4766 T1) after etching (corresponding to a roughness of 5,000 to 10.000 Angström).
In this method, disadvantage of an uneven etching treatment remains, especially in highly doped wafers. After etching, the surface is uneven and mostly not reproducible. Dilute etching liquids are not sufficient to obtain the desired roughness.
Absolutely to our surprise, it was found that wafers having a constant reproducible surface roughness can be produced using a rotary etching process, if the etching treatment is carried out on an already wet surface. Particularly constant results can be obtained, if the prewetting of the semiconductor surface is effected on the whole surface, which can be effected in a rotating wafer (for example within an associated chuck) in the fraction of a second, even in a point-like application.
The etching liquid is applied to the semiconductcor surfaces not until after the prewetting.
The etching process is substantially more controllable as compared with the known technologies as described above. Distributing the etching liquid on the wet surface is effected within an extremely short time (within less than 1 second at rotational speeds of the wafers of 200 to 1,000/min) and with an excellent uniformness throughout the whole surface. On the wetted surface, the etching liquid spreads out spontaneously and uniformly. The wetting process is dropped for the etching liquid, if it is applied to an already wet surface.
The uniform, spontaneous distribution of the etching liquid prohibits the formation of local areas having an increased or reduced etchant amount or retention time.
The time for rough-etching may be reduced to less than 30 seconds, partly down to values of 1 to 10 seconds and thus for powers of 10, as compared to the prior art (1 to 3 minutes).
After the etching process the etched semiconductor surface may be washed with a non-etching fluid and/or dried.
The semiconductor is to rotate during all process steps. Here, the handling on a rotating chuck according to EP 316 296 B1 is a good opportunity. In this, the semiconductor may be displaced vertically on the chuck between the process steps, as proposed in the EP 316 296 B1.
According to an embodiment the etching liquid may be applied directly after wetting the semiconductor surface. Both process steps can be carried out within a few seconds.
The wafer may rotate during wetting its surface and/or during applying the etching liquid, rotational speeds of 300 to 500 per minute seem to be sufficient.
According to an embodiment of the process the semiconductor may rotate during wetting of its surface and/or during applying of the etching liquid with mostly constant speed.
After cutting off the feeding of etchant the rotational speed may be increased, in order to throw off laterally a remaining etching liquid in this way.
The rough-etching treatment may be carried out until a desired surface roughness is obtained, for example between 300 and 1,000 Angström.
Acids and mixtures of acids are suitable as the etching liquid, for example hydrofluoric acid, nitric acid, phosphoric acid and/or sulfuric acid.
Afterwards (possibly additionally), the surface may be washed and/or dried.
Deionized water is suitable for washing. Also, the semiconductor surface may be wetted with deionized water before the etching treatment. But a light acid, for example a highly diluted acid, my also be used. On the contrary, a liquid serving for the actual etching is not suitable for wetting. Such etchants result in an increase of the roughness of at least 50 Angström.
Finally it may be provided to dry the semiconductor surface with nitrogen or isopropanol vapor.
REFERENCES:
patent: 4252865 (1981-02-01), Gilbert et al.
patent: 4557785 (1985-12-01), Ohkuma
Kovacs Frederic
Kruwinus Hans-J{umlaut over (u)}rgen
Earley John F. A.
Earley III John F. A.
Harding Earley Follmer & Frailey
Powell William
Sez Semiconductor-Equipment Zubehor fur die Halbleiterfertigung
LandOfFree
Method for rough-etching a semiconductor surface does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Method for rough-etching a semiconductor surface, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method for rough-etching a semiconductor surface will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2548917