Compositions – Etching or brightening compositions
Reexamination Certificate
1999-06-02
2001-08-28
Utech, Benjamin L. (Department: 1765)
Compositions
Etching or brightening compositions
C252S079500, C438S692000, C438S693000
Reexamination Certificate
active
06280652
ABSTRACT:
The present invention relates to a polishing composition suitable for processing the edge surface of semiconductor wafers. More particularly, the present invention relates to an edge polishing composition which provides a high polishing removal rate in the edge surface processing (hereinafter referred to as “edge polishing”) of silicon wafers or semiconductor wafers having an oxide film formed thereon and which is capable of reducing deposition of a dried gel on the wafer surface and at the same time capable of forming an excellent wafer edge surface (hereinafter referred to as “an edge”).
In recent years, high performance semiconductor device chips to be used for high technology products including computers, have been developed for high integration and high capacity, and enlargement of the chip sizes due to high capacity is in progress. Further, in the design rule for semiconductor devices, miniaturization has progressed year after year, and the focal depth in the process for producing devices tends to be shallow, whereby the requirement for precision of the processed surface required for a wafer prior to forming a device has been increasingly strict.
On the other hand, due to the enlargement of chip sizes, decrease in the productivity, increase of production costs and other problems have resulted. To solve such problems, it has been attempted to enlarge the area of a semiconductor wafer from which device chips are produced, thereby to increase the number of chips per unit area, i.e. to enlarge the size of a wafer.
As parameters for the precision of the processed surface, various surface defects may be mentioned, such as deposition of relatively large foreign matters, LPD (Light Point Defects, which will be described hereinafter), scratches, surface roughness, haze levels, SSS (Sub-Surface Scratches, a type of fine scratches which are called also as latent scratches) and other defects.
The relatively large foreign matters which deposit on wafers, may be those attributable to a dry gel formed by drying of a polishing composition, etc. LPD includes defects attributable to fine foreign matters (hereinafter referred to as “particles”) deposited on the surface of a wafer and defects attributable to COP (Crystal Originated Particles).
If such relatively large foreign matters or LPD exists, there will be pattern defects, break down voltage of an insulator, failure in injection of ions or deterioration of other device properties, in the subsequent device-forming step, thus causing a decrease in the yield. Therefore, a study has been made for wafers substantially free from such surface defects or a method for producing such wafers.
A silicon wafer as a typical semiconductor substrate, is prepared by slicing a silicon single crystal ingot to obtain a wafer, which is subjected to rough polishing so-called lapping to shape the contour. Then, the damaged layer formed on the wafer surface by slicing or lapping, is removed by etching. Thereafter, especially in the case of a silicon semiconductor wafer having a large diameter of at least 8 inches, edge polishing is usually applied for the purpose of preventing cracking or chipping of the edge, as described hereinafter, or for the purpose of preventing occurrence of particles. It is common that thereafter, primary polishing so-called stock removal polishing, secondary polishing and final polishing are carried out to polish the wafer surface to a mirror surface, to obtain the final product as a silicon wafer. Depending upon the process, the secondary polishing may be omitted, or an additional polishing step may be added between the secondary polishing and the final polishing.
It is common that when a wafer is taken out of a semiconductor production apparatus and transferred, it is transferred as accommodated in a casing. In the case of a conventional wafer having a relatively small area, for example, with a diameter of up to 6 inches, the weight of the wafer itself is small, and even when the edge may rub against the casing, the impact is small, and cracking or chipping of the edge rarely takes place by such rubbing. However, if the diameter of the wafer becomes at least 8 inches, the weight of the wafer itself becomes large, and the impact of rubbing of the edge against the casing tends to be large, so that cracking or chipping is likely to take place at the edge.
Further, with a wafer not subjected to edge polishing, the edge is not smooth, and there has been a problem that when the edge rubs against the casing or when the edge rubs against an arm or the like of the apparatus during handling in between semiconductor production apparatus, cracking or chipping of the edge as well as abrasion of the casing or the arm or the like, is likely to occur, whereby the material of the wafer itself or wearing down the casing, the arm or the like, are likely to deposit on the wafer surface, thus leading to particle defects.
With respect to such a problem, it has been known that by smoothing edge, it is possible to increase the strength of the edge and to reduce the formation of particles, and it has become common to carry out edge polishing to polish and smooth the edge of a wafer after etching.
Heretofore, in such edge polishing, it has been common to employ an edge polishing composition comprising water and colloidal silica having an average particle size of from 10 to 50 nm, or a primary polishing composition which further contains a basic compound. However, edge polishing by means of such a composition has had a problem that the polishing removal rate is low, and the productivity is poor.
Further, during the processing, the scattered composition is likely to dry on the wafer surface, and silica in the composition may deposit thereon as a dry gel. This dry gel cannot be removed by a cleaning step and thus used to be a factor for causing surface defects. Further, if the dry gel deposited on the wafer surface is subjected to primary polishing in a state not adequately removed in the cleaning step, the dry gel may come off during the polishing to form scratches on the wafer surface. Accordingly, an edge polishing composition has been desired which has a high polishing removal rate and whereby no dry gel will deposit.
On the other hand, the demand for epitaxial wafers is increasing year after year, which are useful for discrete semiconductors, bipolar IC, MOSIC, etc. Such an epitaxial wafer is a wafer having a thin film of a silicon single crystal (hereinafter referred to as “an epitaxial layer”) free from crystal defects grown on the surface of a low resistance wafer containing antimony, arsenic, boron and other dopant in an amount larger than a usual wafer.
In the process for producing such an epitaxial wafer, it may happen that when the epitaxial layer is grown, the dopant contained in the wafer is withdrawn from the back side of the wafer and again taken into the epitaxial layer on the wafer surface, whereby it becomes impossible to obtain a wafer having a prescribed resistance. In order to prevent the dopant from being withdrawn from the back side of the wafer, it has been common to use a semiconductor wafer provided with an oxide film, which is prepared by forming an oxide film on the back side of the wafer after etching, by a chemical or physical method.
Also to such a wafer provided with an oxide film, edge polishing is carried out for the purpose of preventing cracking or chipping of the edge or formation of particles and preventing formation of a crown along the periphery of the wafer. Formation of a crown is a phenomenon in which a silicon single crystal film swells along the periphery of the wafer during the growth of an epitaxial layer, and will be thicker than the center portion of the wafer surface.
Heretofore, as an edge polishing composition for a wafer provided with an oxide film, it has been common to employ an edge polishing composition comprising water and colloidal silica having an average particle size of from 10 to 50 nm, or a primary polishing composition which further contains a basic compound, like in the case of the above-ment
Inoue Yutaka
Kawase Akihiro
Brown Charlotte A.
Fujimi Incorporated
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
Utech Benjamin L.
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