SEMICONDUCTOR MANUFACTURE USING HELIUM-ASSISTED ETCH

Abstract: Semiconductor chip manufacturing is enhanced using a highly selective etching process that enables the formation of structure having near 90 DEG side walls within the chip without degrading the selectivity. According to an example embodiment of the present invention, a plasma generated from an etch gas and an inert gas is used to etch a semiconductor chip having substrate formed over a thin oxide. The chip is etched at an etch pressure and plasma power that, when coupled with the etch gas chemistry, are sufficient to achieve high oxide selectivity. The inert gas supplied concurrently with the etch gas is sufficient to maintain an about vertical side wall profile of the substrate as it is etched without degrading the etch gas selectivity.

Description: SEMICONDUCTOR MANUFACTURE USING HELIUM-ASSISTED ETCH Field of the Invention The present invention relates generally to semiconductor devices and their fabrication and, more particularly, to semiconductor devices and their manufacture involving techniques for etching a semiconductor chip. Background of the Invention The semiconductor industry has recently experienced technological advances that have permitted dramatic increases in circuit density and complexity, and equally dramatic decreases in power consumption and package sizes. Present semiconductor technology now permits single-chip microprocessors with many millions of transistors, operating at speeds of hundreds of millions of instructions per second to be packaged in relatively small, air-cooled semiconductor device packages. Such technological advances are coupled with a heightened complexity of the manufacturing process and increasingly higher performance standards including reliability, speed, and consistency of semiconductor wafers. As the manufacturing processes for semiconductor wafers become more complex, and as product performance standards for such wafers increase, methods for manufacturing these wafers become increasingly important. Not only is it important to ensure that individual chips are functional, it is also important to ensure that batches of chips perform consistently and meet performance standards. In addition, as technology advances, the cost of manufacturing the high tech wafers increases. The increased cost of wafers results in greater losses when the wafers are defective and must be repaired or thrown out. One common method for processing semiconductor wafers includes forming and modifying structure on the wafer using an etch process. One particular etching application involves the formation of structure having a side wall profile, such as a gate electrode. Obtaining profiles near 90° is important for achieving desired performance levels from the chip. However, obtaining such a profile is difficult in many applications, such as in the formation of deep sub-micron gate structures having a thin gate oxide. When etching a deep sub-micron gate structure in a process such as an amorphous Si or poly-Si gate etch process, it is important to avoid etching down to the thin gate oxide. Various methods have been used for improving the gate etch profiles. One such method for etching a deep sub-micron gate structure involves the application of a selective high Si/SiO 2 etch process that does not etch down to the thin gate oxide. The high Si/SiO 2 etch is deficient, however, in that the resulting profile from the etch is often tapered, which can result in a loss in performance of the structure. Another method used in conjunction with the high Si/SiO 2 etch is the application of a high Cl 2 flow for improving the tapering profiles. Although the addition of the high Cl 2 flow can improve the profile, it has drawbacks including the degradation of the Si/SiO 2 etch selectivity. For instance, the addition of the high Cl 2 flow can cause micro- trenching problems as well as severe etch side wall roughness. These and other problems associated with etching semiconductor structure impede the ability to consistently manufacture reliable high-performance semiconductor wafers. Summary of the Invention The present invention is directed to a method for manufacturing a semiconductor device involving the formation of structure, such as a gate electrode, having an about vertical profile without degrading material below the structure. The present invention is exemplified in a number of implementations and applications, some of which are summarized below. According to an example embodiment of the present invention, a semiconductor chip having a substrate formed over a thin oxide is processed. A plasma is generated from an etch gas and an inert gas and is supplied to the chip, wherein the etch gas chemistry, the plasma power, and the pressure at which the plasma is applied are sufficient to maintain a high selectivity to the thin oxide. The inert gas is supplied at a rate that is sufficient to achieve an about vertical side wall profile of the structure while maintaining the high etch selectivity. The semiconductor chip is etched and a structure is formed using the substrate. According to another example embodiment of the present invention, a semiconductor chip includes a structure having at least one side wall that is about vertical and an underlying thin oxide. The structure is formed by patterning a mask over the structure and etching the chip with a highly selective etch gas an in the presence of an inert gas. The inert gas facilitates the formation of about vertical side walls while not degrading the selectivity of the etch gas, thereby inhibiting the etching of the thin oxide. The above summary of the present invention is not intended to describe each illustrated embodiment or every implementation of the present invention. The figures and detailed description which follow more particularly exemplify these embodiments. Brief Description of the Drawings The invention may be more completely understood in consideration of the following detailed description of various embodiments of the invention in connection with the accompanying drawings, in which: FIG. 1 is a semiconductor chip having a substrate formed over a thin oxide, for use in connection with an example embodiment of the present invention; FIG. 2 shows the semiconductor chip of FIG. 1 having an etch gas and inert gas supplied to the substrate, according to an example embodiment of the present invention; FIG. 3 shows the semiconductor chip of FIG. 2, having undergone an etch process, according to another example embodiment of the present invention; and FIG. 4 is a flow diagram for processing a semiconductor chip, according to another example embodiment of the present invention. While the invention is amenable to various modifications and alternative forms, specifics thereof have been shown by way of example in the drawings and will be described in detail. It should be understood, however, that the intention is not to limit the invention to the particular embodiments described. On the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the invention as defined by the appended claims. Detailed Description The present invention is believed to be applicable for a variety of different types of semiconductor devices, and the invention has been found to be particularly suited for devices requiring or benefiting from the formation of structure having about vertical side walls. While the present invention is not necessarily limited to such devices, various aspects of the invention may be appreciated through a discussion of various examples using this context. In connection with an example embodiment of the present invention, it has been discovered that the addition of an inert gas, such as helium, to a conventional etch gas as it is supplied for etching a semiconductor chip substrate can improve the side wall profile of structure formed from the substrate during an etch process. In addition, the inert gas improves the profile while maintaining good etch selectivity to material such as oxide located in the chip. According to an example embodiment of the present invention, a semiconductor chip having substrate formed over a thin oxide is etched. FIG. 1 shows such a chip 100 having a substrate 120 formed over a thin gate oxide layer 110, and a mask 130 formed over a portion 140 of the substrate 120. The substrate may, for example, include gate material such as poly-silicon or amorphous silicon. In one particular implementation, the substrate includes an anti-reflective coating over the substrate 120. FIG. 2 shows the chip 100 of FIG. 1 being etched. A plasma 230 is generated from an etch gas 210 and an inert gas 220, and is then supplied to the substrate 120. The etch gas 220 may, for example, include a plurality of gases. The etch and inert gas supplies, the plasma power, and the etch pressure at which the plasma is supplied are sufficient to achieve about vertical side wall profiles 250 of the masked portion 140 while maintaining the high etch selectivity. In one example implementation, an etch pressure of between about 5 - 100 mTorr, a plasma source power (for controlling the plasma density) of between about 50-400 W, and a plasma bias power (for controlling the energy supplied to the ions) of between about 10-200 W provide conditions adequate for achieving the about vertical side walls. The mask 130 masks the portion 140 of the substrate, and the remaining substrate is etched, as shown in FIG. 3. The resulting structure 340 formed from the masked portion 140 of the substrate has about vertical side walls 350. In one implementation, the selectivity of the etch gas to the thin oxide layer 110, while in the presence of the inert gas, is about infinite. The infinite selectivity permits the formation of the structure 340 without etching the thin oxide layer 110, thereby reducing the harmful effects of problems, such as microtrenching, associated with etch processes that are not as highly selective. In addition, the inert gas can also improve the resulting structure by removing depositions on the side walls. The etch and inert gas supply to the chip can be accomplished in various manners. For instance, in one implementation the chip 100 is placed in an etch chamber, and the gases are supplied to the chip via a supply to the etch chamber. The etch gas 210 may include, for example, a typical etch gas chemistry used in highly selective Si/SiO 2 etch processes. Helium can be supplied as the inert gas and used with the highly selective Si/Si0 2 etch chemistry for etching the chip. In one example implementation, the helium is supplied at a volumetric flow rate of between about 25- 500 seem. In another example implementation, the helium is supplied at a flow rate of at least about 500 seem. In still another example implementation, the inert gas and the etch gas are mixed prior to their introduction to the chip. Referring again to FIG. 3, the side walls 350 of the resulting structure 340 are shown to be close to vertical. In one implementation, the resulting side walls have an included angle θ of at least about 85°, and in another the included angle θ is about 90°. This resulting structure 340 is useful because vertical side walls exhibit improved performance over side walls having a tapered profile. Although FIGs. 1-3 show one structure 340, it should be noted that a plurality of such structures may be formed on the chip. In addition, the chip may be part of a semiconductor wafer having a plurality of chips, some or all of which having a structure formed in a similar manner. The structure formed using the combination of the etch and inert gases as described herein can be used for various applications in semiconductor device manufacture and processing. For example, the structure 340 in FIG. 3 may include a gate used in connection with a transistor. In one example implementation, the thin oxide 110 is a gate oxide, and the chip 100 includes structure such as source and drain regions near the gate. The present invention is particularly advantageous for the formation of deep sub-micron gate structure. For example, in one implementation a gate having a width of less than about 0.20 microns is formed. In another implementation a gate having a width of about 0.15 microns is formed. In still another implementation, a gate having a width of less than about 0.15 microns is formed. FIG. 4 is a flow diagram of an example process for manufacturing a semiconductor chip, according to another example embodiment of the present invention. A thin oxide layer is formed over a semiconductor chip at block 410. After the oxide layer is formed, a substrate, such as gate material including poly- silicon or amorphous silicon, is formed over the oxide at block 420. A mask material is patterned over the substrate at block 430, and the chip is then placed in an etch chamber at block 440. The mask may be patterned, for example, for forming one or more gate structures on the chip. A vacuum is drawn on the chamber at block 450, and an etch gas and an inert gas are supplied to the etch chamber and a plasma is generated at block 460. In one implementation, the etch pressure is held about constant during the addition of the inert gas. The plasma anisotropically etches the unmasked substrate in a manner that forms about vertical side wall profiles on the masked structures that are not etched. The unmasked substrate is etched while etching little or none of the thin oxide layer. After etch is complete, the mask material is removed from the chip at block 470. Optionally, the chip may then be annealed or further processed in other manners. In still another example embodiment of the present invention, a semiconductor chip is manufactured. The chip includes a gate structure having at least one side wall that is about vertical and an underlying thin oxide. The gate structure is formed by patterning a mask over the structure and etching the structure with a highly selective etch gas while in the presence of an inert gas. The inert gas facilitates the formation of about vertical side walls while not degrading the selectivity of the etch gas. In this manner, the resulting gate profile has side walls that are about vertical, and the thin oxide layer is not etched due to the use and maintenance of the highly selective etch process. While the present invention has been described with reference to several particular example embodiments, those skilled in the art will recognize that many changes may be made thereto without departing from the spirit and scope of the present invention, which is set forth in the following claims.

Claims: What is claimed is: 1. A method for processing a semiconductor chip having a substrate formed over a thin oxide, the method comprising: supplying an etch gas including a chemistry sufficient to maintain a high selectivity to the thin oxide; while supplying the etch gas, supplying an amount of inert gas that is sufficient to achieve an about vertical side wall profile of the etched substrate while maintaining the high etch selectivity; and using the etch gas and the inert gas, generating a plasma and etching the semiconductor chip and forming a structure from the substrate. 2. The method of claim 1 , wherein generating a plasma and etching the semiconductor chip includes using a plasma source power, a plasma bias power, and an etch pressure that are sufficient to maintain a high selectivity to the thin oxide when used with the etch gas chemistry. 3. The method of claim 2, wherein the plasma source power is between about 50- 400 Watts; and wherein the plasma bias power is between about 10-200 watts; and wherein the etch pressure is between about 5-100 mTorr. 4. The method of claim 1, wherein the etch gas includes a gas used in a highly selective Si/SiO 2 etch process. 5. The method of claim 1, wherein the inert gas flow rate is sufficient to achieve an at least about 85° side wall profile of the substrate. 6. The method of claim 1 , wherein the plasma does not etch the thin oxide. 7. The method of claim 1, and prior to supplying an etch gas, further comprising: forming a substrate having silicon on the semiconductor chip; patterning a mask material over the substrate; and placing the chip in an etch chamber. 8. The method of claim 1, further comprising drawing a vacuum on the chamber, wherein supplying an inert gas includes keeping the etch pressure about constant. 9. The method of claim 7, wherein the substrate includes amorphous silicon. 10. The method of claim 7, wherein patterning a mask material includes forming a layer of mask material over a gate portion of the substrate. 11. The method of claim 10, wherein etching the semiconductor chip includes forming a gate having side walls extending from an edge of the mask layer and about perpendicular to the layer of mask material. 12. The method of claim 1 , wherein supplying an etch gas and supplying an inert gas include mixing the inert gas with the etch gas. 13. The method of claim 1, further comprising annealing the chip subsequent to etching the chip. 14. The method of claim 1 , further comprising using the inert gas and removing depositions on the side wall.

Inventors: ZHENG TAMMY, ZHENG, TAMMY
Applicants: KONINKL PHILIPS ELECTRONICS NV, PHILIPS SEMICONDUCTORS INC, KONINKLIJKE PHILIPS ELECTRONICS N.V., PHILIPS SEMICONDUCTORS, INC.
Application year: 2000
Main classification: H01L21
IPC codes: H01L21