Semiconductor device manufacturing: process – With measuring or testing – Optical characteristic sensed
Reexamination Certificate
2000-09-18
2002-08-27
Niebling, John F. (Department: 2812)
Semiconductor device manufacturing: process
With measuring or testing
Optical characteristic sensed
C365S042000, C250S492200
Reexamination Certificate
active
06440760
ABSTRACT:
RELATED APPLICATIONS
This application is related to Korean Application No. 99-40289, filed Sep. 18, 1999 and Korean Application No. 00-41921, filed Jul. 21, 2000, the disclosures of which are hereby incorporated herein by reference.
FIELD OF THE INVENTION
The present invention relates methods for measuring semiconductor wafers, for example, during the manufacture of a semiconductor device, and more particularly, methods for measuring semiconductor wafers which have undergone an over-etching process.
BACKGROUND OF THE INVENTION
When manufacturing semiconductor devices, a dry etching type of contact etching process using over-etching may be applied to form, for example, a direct contact (DC) or a buried contact (BC). Such process may sufficiently etch oxide taking into account the uniformity of the etching process itself. A single crystalline silicon substrate (a wafer) may be over-etched during an etching process, but poly crystalline silicon, not the silicon substrate, is typically over-etched during an etching process for forming a BC, and metal is typically over-etched during a process of forming a metal contact (MC).
After an over-etching process has been performed, the completion of the over-etching process is generally determined based on presence/absence of oxide remaining at an oxide site and the measured thickness of the remaining oxide. Typically, when the film structure of an oxide site is inspected after an over-etching process, it can be seen that oxide is over-etched down to a silicon substrate. Accordingly, the success or failure of over-etching generally can be determined by measuring the thickness of the remaining oxide at an oxide site that has undergone an over-etching process.
However, most conventional measuring equipment has been considered unsuitable for monitoring an over-etching process because an under-etched state of a film typically cannot be exactly discriminated from an over-etched state of a film based on a value measured by the measuring equipment.
FIG. 1
is a graph showing the results of measuring the thickness of remaining oxide (Tox) using an optical measuring apparatus with respect to wafers which are obtained after dry-etching active silicon nitride (SiN) during manufacture of 64-M dynamic random access memory (DRAM) devices. In the process of accumulating measurement data, one wafer is sampled on each day. For example, as shown in
FIG. 1
, the measured values of the thickness of remaining oxide at an oxide site which has undergone dry etching of SiN are uniformly maintained in a range of 0-5 Å (angstroms). Based on the fact that the measured values occupy a very small range, an operator can generally determine whether or not an over-etching process is performed normally and successfully.
FIG. 2
is a graph showing the results of measuring the thickness of remaining oxide with respect to wafers which are obtained after over-etching the oxide for forming a DC during manufacture of 64-M DRAM devices. In the process of accumulating measurement data, five wafers are sampled on each day.
FIG. 2
shows the measured results with respect to wafers on which over-etching has been completed based on actual measurement.
As shown in
FIG. 2
, despite the actual successful over-etching of a wafer during an oxide etching process for forming a DC, the measured results do not always allow an operator to determine that the over-etching is successfully completed. As shown in
FIG. 2
, the measured values of the thickness of remaining oxide on a wafer on which over-etching is actually completed are distributed throughout a range of 0-100 Å. Accordingly, when a measured value is about 90 Å, that is, when it is determined that oxide of a thickness of about 90 Å remains, it is difficult to determine the success or failure of over-etching based on this value.
As the measured results of conventional measuring equipment may be inaccurate, conventionally, the thickness of remaining oxide detected when over-etching is successfully achieved, is set to within a very wide range of 0-400 Å in the case of an over-etching process for forming a DC, and to within an even wider range of 0-1000 Å in the case of an over-etching process for forming a MC. Accordingly, oxide that is not actually etched within this range may not be monitored, thereby potentially causing process failures.
SUMMARY OF THE INVENTION
Embodiments of the present invention include methods for measuring a semiconductor wafer which has been subjected to an etching process. Light is radiated at the semiconductor wafer. Light within a selected wavelength band reflected from the semiconductor wafer is measured to provide an output value. A ratio of the output value and a reference value is determined. The reference value may be based on light within the selected wavelength band reflected from a reference surface, such as a bare silicon reference surface. It is determined that the semiconductor wafer is under-etched if the determined ratio does not meet the reference value. A normalized optical impedance or a polarization ratio may be measured based on light within a selected wave length band reflected from the semiconductor wafer to provide the output value in various embodiments of the present invention. In further aspects of the present invention, a thickness of a remaining oxide layer is determined using an under-etch recipe when it is determined that a semiconductor wafer is under-etched and a thickness of a damaged/polymer layer may be determined using an over-etch recipe when it is determined that the semiconductor wafer is over-etched.
In further embodiments, the present invention provides methods of determining the etched state of a semiconductor wafer. The methods include the steps of radiating light at bare silicon and obtaining a reference value from an electrical signal generated by light within a predetermined wavelength band of the light reflected from the bare silicon, radiating light within the predetermined wavelength band at a target of measurement, i.e., a wafer that has undergone an over-etching process, obtaining an output value corresponding to the reference value from an electrical signal generated by light within the predetermined wavelength band of the light reflected from the wafer, calculating the ratio of the output value to the reference value, and comparing the calculated ratio with a predetermined reference ratio to determine whether or not the wafer is under-etched.
In other embodiments, the present invention provides methods of determining the etched state of a semiconductor wafer. The methods include the steps of radiating light at bare silicon and obtaining a reference value by integrating an electrical signal generated by light within a predetermined wavelength band which is reflected from the bare silicon, radiating light within the predetermined wavelength band at a target of measurement, i.e., a wafer that has undergone an over-etching process, obtaining an output value by integrating an electrical signal of the predetermined wavelength band of light reflected from the wafer, calculating a ratio of the output value to the reference value, and comparing the calculated ratio with a predetermined reference ratio to determine whether or not the wafer is under-etched.
In yet further embodiments, the present invention provides methods of measuring the etched state of a semiconductor wafer. The methods include a first step of radiating light within a predetermined wavelength band at a wafer that has undergone a plasma over-etching process, a second step of obtaining a predetermined output value from an electrical signal corresponding to light reflected from the wafer, a third step of determining whether an optical impedance of the light reflected from the wafer changes based on the output value, a fourth step of determining whether the over-etching process is successfully completed depending on the change in the optical impedance determined in the third step, a fifth step of measuring the thickness of a wafer film according to a recipe employ
Cho Hyung-suk
Choi Sang-bong
Chon Sang-mun
Chun Chung-sam
Kang Min-sub
Myers Bigel & Sibley & Sajovec
Niebling John F.
Stevenson André C
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