JP2674038B2 - Silicon trench etching method - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a silicon trench etching method for forming a trench in silicon. In particular, the present invention relates to a silicon trench etching method which is an improved etching gas used for forming a trench in silicon. INDUSTRIAL APPLICABILITY The present invention can be suitably used, for example, in the field of semiconductor device manufacturing, when forming trenches such as grooves and holes in a silicon substrate. SUMMARY OF THE INVENTION The etching method of the present invention is a silicon trench etching method for forming a trench in silicon, which contains silicon chloride, nitrogen and chlorine as an etching gas for silicon, and the amount of chlorine is The etching amount of the silicon, which is the etching material, is set to an amount that does not cause irregularities in the trench etching shape. It is characterized by using an etching gas that is 10% or more and less than 50% of the total volume of the etching gas, which is an amount that maintains the sidewall protection effect of nitride, and this gas is used to protect the silicon substrate or the like. Etching Silicon material is etched by reactive ion etching etc. Desired trench such fine grooves or holes shape control well, and make them can be obtained at a higher etch rate. [Prior Art] Conventionally, it has been performed to etch a silicon material such as a silicon substrate (hereinafter appropriately referred to as a Si substrate) using an etching gas. For example, in the field of semiconductor device manufacturing, the silicon substrate is deeply etched. It is embodied as a so-called silicon trench etching technique for forming grooves and holes.
Such a technique is indispensable for forming a trench capacitor of a dynamic RAM and an application for forming an element isolation of a bipolar element. By the way, in the trench processing for forming trenches such as grooves and holes in such a silicon substrate, it is necessary to secure the capacitance of the capacitor and to perform sufficient isolation between elements.
It is necessary to secure a certain etching depth. In the application fields described above, a depth of 4 μm or more is usually required. However, with the etching rate of the silicon trench etching technique that is currently in practical use, there is a problem that it takes a long time to obtain the required depth. In particular, the etching rate of single crystal silicon at present is about 500 to 800 Å / min at most when using a normal batch type RIE, and it takes about 1 hour to obtain an etching depth of 4 to 5 μm. There is a problem that productivity is very low.
Therefore, development of a silicon etching technique with a high etching rate has been earnestly desired. In particular, there is great demand for etching single crystal silicon. The present inventor has previously made it possible to form fine grooves and holes in silicon with a high aspect ratio, that is, with a large depth relative to the openings and with high precision, and also to engrave the side walls of the grooves and holes and the sub-parts of the bottom. We proposed a gas consisting of silicon tetrachloride and nitrogen as an etching gas for silicon that does not cause trenches and has good shape control (Autumn of Applied Physics, 1986 30a-p
-5). However, this etching gas is not always sufficient in terms of etching rate as in the above case. [Problems to be Solved by the Invention] As described above, in the conventional etching technique, the etching rate for silicon is not sufficient, so that it takes a long time to obtain a necessary etching depth. There is. The present invention is intended to solve the above-mentioned problems, and an object of the present invention is to meet the basic requirement that a hole or groove having a high aspect ratio can be formed with good shape control, while etching silicon (particularly An object of the present invention is to provide a silicon trench etching method capable of improving productivity by solving the drawback that the etching rate is low (for example, during trench etching of single crystal silicon). [Means for Solving the Problems] The etching method of the present invention is: a silicon trench etching method for forming a trench in silicon, wherein the etching gas for silicon contains silicon chloride, nitrogen, and chlorine, and The amount of chlorine is set to an amount that does not cause irregularity in the trench etching shape of the silicon to be etched, and the amount of chlorine is determined by the amount of chlorine in the trench formed in the silicon to be etched due to the progress of etching. An etching gas that is 10% or more and less than 50% of the total volume of the etching gas, which is an amount that maintains the sidewall protection effect of silicon nitride deposited on the sidewall (hereinafter, this may be referred to as the "etching gas of the present invention"). There is) is used. [Operation] According to the silicon trench etching method of the present invention, which performs trench etching on silicon using the etching gas of the present invention, it is possible to form holes and grooves having a high aspect ratio with good shape control, and a high etching rate, You can improve your sex. Although the action of the present invention is not always clear, it is considered that the presence of chlorine in the gas causes a large amount of chlorine radicals Cl ^{* to} be generated, which serves to enhance the etching rate. In trench etching of silicon (for example, single crystal silicon) using an etching gas composed of silicon chloride and nitrogen, for example, Six Ny and Cl ^* are generated in plasma, and Cl ^* is provided while protecting the sidewall by depositing Six Ny ^. Since silicon is etched by the above method, it is considered that an increase in etching rate can be achieved by supplying more Cl ^* here. When the chlorine content is 50% by volume or more of the etching gas, the shape controllability is deteriorated, and the side wall is likely to be carved. The preferred content of chlorine cannot be unequivocally stated because it varies depending on the composition ratio of other gas components, etching conditions, and parameters such as the silicon material to be etched.However, under the conditions of the examples described below, the chlorine content is 10%. It is particularly preferable that the content is ˜40% by volume, and about 33% by volume is more practically preferable. When using a SiCl ₄ as the silicon chloride, chlorine is preferably used in the following the same volume as SiCl _4. [Example] An example of the present invention will be described below. As a matter of course, the present invention is not limited to the embodiments described below. In this embodiment, the etching gas of the present invention is used as an etching gas used for forming fine grooves on a single crystal Si substrate in manufacturing a semiconductor integrated circuit. This example can be embodied as a technique for forming a groove type capacitor or a fine element isolation in a semiconductor device. In this example, SiCl ₄ was used as silicon chloride, and Cl ₂ gas was added to a gas composed of this and N ₂ to obtain an etching gas. That is, when using a SiCl ₄ / N ₂ based gas, first set the etching conditions to obtain an optimum shape without undercut in the groove to be formed, Cl ₂ gas is added to the etching gas under this condition Then, the conditions of the etching rate at that time were investigated. The change in etching rate is shown in the graph of FIG. Note that Si
When setting optimum conditions for Cl ₄ / N ₂ system gas, for example, SiCl
_{When 4} and N ₂ are mixed at a flow ratio of 1: 1 and SiO ₂ is used as a mask and the Si substrate 1 is etched by RIE, the aspect ratio is as shown in FIG. Since the groove 2 having a large ratio can be obtained with good shape controllability, the above experiment can be performed based on this condition. In FIG.
Denoted at 3 is a deposit, which is considered to have a function of protecting the side wall and preventing blistering or the like from occurring on the side wall of the groove. This volume 3 can be easily removed with hydrofluoric acid or the like. In Fig. 1, the horizontal axis is the volume% of Cl ₂ in the etching gas (SiCl ₄ / N ₂ / Cl ₂ mixed gas), and the vertical axis is the etching rate (Å / min). It is shown.
Further, at each measurement point of the graph, the evaluation of the shape controllability of the groove shape formed in the corresponding case is shown, that is, Indicates a particularly good groove shape, ⊚ indicates an extremely good groove shape next, and ∘ indicates a groove shape next to this. X indicates that the scintillation occurred on the side wall of the groove and the groove shape was poor. As is clear from the graph of FIG. 1, it is found that the etching rate of single crystal silicon increases depending on the amount of Cl ₂ gas added. However, when the amount of Cl ₂ gas added increases to 50% by volume, the side wall of the groove is engraved and a good shape cannot be obtained. This is presumably because if the amount of Cl ₂ added is too large, the amount of Cl ^* increases too much and the side wall protection effect becomes insufficient, making it difficult to secure a good anisotropic shape. Therefore, it is necessary to optimize the amount of Cl ₂ added under each set condition. In this example, 33% Cl ₂ was added to the condition where a good shape was obtained under the optimum conditions in the SiCl ₄ / N ₂ system, the shape was not affected, and the etching rate was 90 Å / min to 1400 Å / min
In addition, the effect increased by 50% or more, and the effect of Cl ₂ addition was clear. Of course, this flow rate ratio is not optimal, and it goes without saying that it is necessary to appropriately determine the amount of Cl ₂ added depending on the sample used and the etching apparatus. According to this example, the low etching rate at the time of single crystal silicon trench etching, which has been a problem in the past, could be improved, and the throughput at the time of single crystal silicon etching could be increased. As described above, the present embodiment applies the present invention to the etching of single crystal silicon in which the problem of the etching rate is the most serious, but the present invention is not limited to this, and various silicon materials are used as etching materials. Can be effective. Of course, various other embodiments can be adopted. EFFECTS OF THE INVENTION According to the present invention, the etching rate for silicon is sufficiently high, and thus the productivity can be improved, and the wall is vertical without blistering, and there is no lower sub-trench. You can get various grooves and holes.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a diagram for explaining the present invention, and is a graph showing the relationship between the amount of chlorine added with silicon chloride and nitrogen gas and the etching rate. FIG. 2 is a schematic view showing a groove-shaped cross section formed in one embodiment of the present invention. 1 ... Silicon (Si substrate), 2 ... Groove.

Claims (1)

(57) [Claims] In a silicon trench etching method for forming a trench in silicon, as an etching gas for silicon, silicon chloride, nitrogen and chlorine are contained, and the amount of chlorine is irregular in the trench etching shape of silicon to be etched. The amount of chlorine is set so that it does not occur, and the amount of chlorine is such that the side wall protection effect of silicon nitride deposited on the side walls of the trench formed in the silicon to be etched is maintained as the etching progresses. A method for etching a silicon trench, which comprises using an etching gas that is 10% or more and less than 50% of the total volume of the etching gas.