半导体晶片的氢氟酸和盐酸蒸汽处理

Disclosed are methods and apparatuses for combined  etching and cleaning of semiconductor wafers and the  like preferably using hydrofluoric acid (HF), hydro  chloric acid (HCl) and water solutions which generate equilibrium vapor mixtures of HF vapor, HCl vapor and water vapor as a homogenous processing gas. The  processing gases do not employ a carrier gas which will  make the vapors nonhomogeneous and reduce etching  rates. The vapors are preferably generated from a liquid  source which is provided within a contained reaction  chamber which holds the wafer. The wafer is prefera bly oriented with the surface being processed directed  downward. The wafer is advantageously positioned  above or in close proximity to the liquid source of the  processing vapor. The wafer is rotated at a rotational  speed in the range of 20-1000 revolutions per minute to provide uniform dispersion of the homogeneous pro  cessing gas across the wafer surface and to facilitate  circulation and transfer from the liquid source into pro cessing gas and onto the processed surface. The liquid  source of the vapor can advantageously be provided in  a bath immediately below the processed surface of the  wafer or in toroidal basin adjacent to the wafer. The  processes provide high speed etching of good unifor  mity and superior particle count performance.

It is common in the processing of silicon wafers to  remove or etch portions of a layer of silicon dioxide  using an etchant. A common etchant is hydrofluoric acid. This is typically done using an immersion process wherein a wafer, or one or more carriers containing a  number of wafers, is immersed in the desired hydroflu oric acid containing processing fluid.

One of the disadvantages of immersion etching pro  cesses is that the wafers typically exhibit an increase in  the numbers of particulates which become adhered to  or imbedded in the wafer. As the feature size of semi  conductor wafers continues to decrease into the sub  micron sizes, now typically in the range of 0.1-0.5 mi  cron, the need for minimizing contamination becomes  more acute. These small feature sizes also create addi  tional problems for immersion processing because sur  face tension effects can reduce etching uniformity and  resulting product quality.

It has previously been recognized that silicon wafers  can be processed by using etchant gases, including gases  which contain hydrofluoric acid (HF). In an article  entitled, "Etching of Thin SiO2 Layers Using Wet HF  Gas' authors P. A. M. van der Heide et al., describe the  etching of silicon dioxide layers by using vapor mix  tures of HF, water and nitrogen. The article describes  using a flow of nitrogen carrier gas through a vessel  containing a 10% hydrofluoric aqueous solution. The  nitrogen carrier produced a flow of etchant gas which  was directed through a nozzle against the surface of a  small silicon wafer being etched. A flow of dry nitrogen  was passed over the opposite side of the wafer to reduce  the effects of ambient atmospheric water which was  present in the essentially open atmospheric process.  Temperatures from 25'-40' C. were indicated for the  HF solution and from 25 C. to about 60' C. for the  wafer. The authors also reported that high temperature  treatment under vacuum conditions foll.

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One deficiency of the process described is the contin  uation of etching after the process exposure has begun. This results in uneven etching rates and problems in the  resulting integrated circuit devices due to variations in  feature sizes across the device. The etching uniformity is also deficient in that the process arrangement may not  provide assurance of equilibrium homogeneous presen tation of the reactant gas to the wafer being processed. Variations in the uptake of the vapors by the incoming carrier gas stream can result in instantaneous variations  in the etchant gas stream which can affect processing. 

A deficiency of both of the above processes is the  relatively poor ability of these techniques in removing  metallic ions or other metallic contaminants which may exist either as impurities in the oxide layer or as particu  late contaminants which have adhered to the surface of  the wafer. It is now common to use a series of cleaning  processes after etching of silicon wafers. Dilute hydro fluoric acid treatment followed by processing in water, hydrogen peroxide and annonium hydroxide is a con  mon cleaning approach. This is typically followed by processing in water, hydrogen peroxide and hydrochlo ric acid to further clean the wafers. These cleaning  processes are in addition to prior HF etching. Such a  series of processing steps is time-consuming and adds to  product cost.

Prior of this invention there has been a long-felt need  in the art for one-step processing which will provide uniform and repeatable etching results while achieving low contamination rates and cleaning of metallic ions  and other metallic impurities and particulates. Other  objectives and advantages of the invention are also  indicated herein.