Classifications

• • H—ELECTRICITY
  • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
  • H10P—GENERIC PROCESSES OR APPARATUS FOR THE MANUFACTURE OR TREATMENT OF DEVICES COVERED BY CLASS H10
  • H10P50/00—Etching of wafers, substrates or parts of devices
  • H10P50/20—Dry etching; Plasma etching; Reactive-ion etching
  • H10P50/24—Dry etching; Plasma etching; Reactive-ion etching of semiconductor materials
  • H10P50/242—Dry etching; Plasma etching; Reactive-ion etching of semiconductor materials of Group IV materials
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
  • Y10S—TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y10S148/00—Metal treatment
  • Y10S148/051—Etching
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
  • Y10S—TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y10S148/00—Metal treatment
  • Y10S148/15—Silicon on sapphire SOS

Definitions

• This invention relates to the vapor phase etching of silicon and more particularly to the etching of silicon with a gaseous mixture containing high purity sulfur hexafluoride.
• gas phase etching is carried out by mounting the semiconductor material in a suitable high temperature reaction chamber and passing a gaseous mixture comprising hydrogen and hydrogen chloride in contact with the heated semiconductor material. While the gas phase etching process involving mixtures of hydrogen and hydrogen chloride has been widely accepted by the semiconductor industry as the predominant etching process, extreme care must be utilized with this corrosive gaseous mixture to avoid corrosion problems.
• a method which comprises passing a gaseous mixture containing sulfur hexafluoride having a low nitrogen concentration and preferably below 200 parts per million by weight of nitrogen and a carrier gas such as hydrogen.
• the temperature of the silicon is between 950 C. and 1250 C. as this gaseous mixture is passed thereover.
• sulfur hexafluoride having a relatively high purity may be used as an effective etchant for silicon.
• Sulfur hexafluoride containing 0 to about 1300 parts per million by weight of nitrogen is diluted with a carrier 3,679,502 Patented July 25, 1972 gas such as hydrogen, argon, or helium to provide an etching mixture which when passed over silicon at a temperature between 950 C. and 1250 C. readily etches the silicon.
• the purity of the sulfur hexafluoride is critical in the practice of the method of this invention.
• Commercially available sulfur hexafluoride containing 98.5 percent SP contains, according to the specification sheets, a maximum of about 3000 to 5000 parts per million of nitrogen by weight.
• Sulfur hexafluoride of this purity (a maximum of 3000 to 5000 parts per million by weight of nitrogen) has been found to be unsuitable as an etchant for silicon except at low etch rate at 1150 C or higher.
• Sulfur hexafluoride of 99 percent purity containing a maximum-of about 1300 parts per million of nitrogen by weight has been found tobe a marginal material to use as an etchant on silicon at temperatures between 950 and 1050 C.
• Sulfur hexafluoride of this purity does, however, yield good results as an etchant in the temperature range of 1050 to Sulfur hexafluoride of 99.98 percent purity containing less than 200 parts per million of nitrogen by weight .
• the minimum detectable nitrogen quanty in SF is a very effective etchant on silicon over the entire temperature range of 950 to 1250 C. It is quiteclear that the efliciency and/or effectiveness of the sulfur hexafluoride as a silicon etchant is directly dependent upon the concentration of the nitrogen in the SF Nitrogen concentrations above 1300 ppm. tend'to render the sulfur hexafluoride ineffective, whereas substantially nitrogen free sulfur hexafluoride provides excellent etching results.
• the SF etchant is used in the etching method described below.
• Silicon wafers are placed on a slab of quartz which serves as a planar support resting on a susceptor of graphite.
• the susceptor is heated by any suitable means, for example, by radio frequency energy from induction coils about the reaction chamber.
• the silicon is heated primarily by conduction from the susceptor although substantial direct heating of the semiconductor by induction does occur in the event substantially elevated temperatures are employed.
• the silicon wafer is then heated to a temperature between 950 and 1250 C.
• Sulfur hexafluoride of high purity containing less than about :1300 parts per million by weight of the nitrogen and preferably below 200 parts by weight nitrogen is mixed with a carrier gas such as hydrogen, argon, or helium, with hydrogen being the preferred gas.
• a carrier gas such as hydrogen, argon, or helium
• the sulfur hexafluoride gas mixture is passed over the heated silicon for a given period of time to etch the silicon surface. When the desired amount of silicon has been etched away, the flow of sulfur hexafluoride is stopped, while the flow of the diluent gas is continued.
• the mole ratio of the sulfur hexafluoride in hydrogen is about 1 10 percent to 1 percent.
• the mole ratio is determined at a given temperature experimentally to obtain the optimum processing conditions, that is, a convenient rate and an adequate surface quality. This will be apparent from the following examples.
• Example 1 A series of silicon wafers were placed on a slab' of quartz on a graphite susceptor. The susceptor was heated by induction coils surrounding the reaction chamber. The susceptor in turn provided suflicient heat to heat the silicon wafers to a temperature of 1000 C. Sulfur hexafluoride containing a maximum of 200 parts per million by weight nitrogen was mixed with hydrogen to form a gaseous mixture containing 21 l0' mole percent SP The sulfur hexafluoride-hydrogen mixture was passed over the heated silicon for about Trm'nutes to etch the silicon micron per minute.” This etching rate is considered "too surface to a depth of four microns.- The how of sulfur slowin most cases at this temperature;
• a borderline surface is a surface which looks good 7 providing a silicon wafer having a mirror-like surface to under room light but which looks hazy when observed v be etched; I i under oblique light from a microscope lamp.
• Table 1 heating said wafer to a temperature lying within the indicates the preferred etching rates at a given temperarange between 950 C. to 1200 C.; ture.
• the etching rate at 1000 C. which is passinga gaseous mixture of hydrogen and sulfur hexapreferred is .59 micron per minute or less since .83 micron fluoride.
• Table 2 lists results 'obtained with sulfur hexafluoride I si+sF H +n,siF+sis containing less than' 1300 parts per million by weight nitrogen. Good surfaces were obtained at temperatures and etchablyremoving portions of said silicon while .of 1050 through 1150" c. with etching rates of from 99 maintaining the mirror-like q ality of said silicon 0.32 micron per minute to 1.62 microns per minute, resurface; and
• said carrier gas being selected from the group consisting of hydrogen, argon and helium;
• said gaseous mixture containing a nitrogen content less than 5000 parts per million by weight, and containing a percentage of sulfur hexafluoride laying within the range between 0.001 and 0.1 mole percent.
• the method for the monopreferential vapor phase etching of a mirror-like silicon surface while maintaining the mirror-like quality of the surface for assuring a suitable silicon surface for semiconductor processing comprising the steps of providing a silicon wafer having a mirror-like surface to be etched;
• said gaseous mixture having a nitrogen content less than 200 parts per million by weight, and containing a percentage of sulfur hexafluoride lying within the range between 0.005 and 0.1 mole percent.

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Cited By (14)

Families Citing this family (2)

• 0
  • BE BE756807D patent/BE756807A/xx unknown
• 1969
  • 1969-09-29 US US862039A patent/US3679502A/en not_active Expired - Lifetime
• 1970
  • 1970-08-25 JP JP45073917A patent/JPS4840810B1/ja active Pending
  • 1970-09-09 GB GB4318470A patent/GB1305625A/en not_active Expired
  • 1970-09-23 DE DE19702046956 patent/DE2046956A1/de active Pending
  • 1970-09-29 FR FR7035244A patent/FR2062802A5/fr not_active Expired

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