JP2502536B2 - Pattern formation method - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a pattern forming method for forming an opening such as a groove having a line width of 1 μm or less and having a very good verticality with high density and high accuracy.

2. Description of the Related Art In recent years, semiconductor integrated circuits have been particularly highly densified, and attempts have been made to utilize deep (3 μm or more) grooves formed on the surface of a semiconductor substrate for element isolation and capacitors. These inter-element trench isolations and trench capacitors require an embedding step after the trench etching step. Therefore, if the groove shape becomes an inverse taper, cavities will be created in the trench during the embedding step, and problems such as long-term reliability will arise. .

If the taper is applied in the forward direction too much, the groove depth of the groove having a line width of 1 μm or less is greatly limited. From the above points, the verticality of the side surface is very important for the groove shape, and the point is whether it can be controlled.

Currently, the mainstream of trench etching is RIE (Reactive Ion Etching). However, if the trench formed by RIE has a groove width of 1 μm or less and a groove depth of 3 μm or more, the incident angle of the etchant (ion)
The scattering of ions in the groove, the evaporation of etching products, and the effect of the electric field generated in the groove change between etching when the groove is still shallow and when the groove becomes deeper. Vertical etching becomes very difficult.

For this reason, many attempts have been made to utilize the side deposits in order to obtain a good (vertical) trench shape. These are M.sato and Y.Arita “Energy Dis
tribution and Directionality of Ion in Reactive lo
n Etch "1984 Dry Process Symposium (Dry Proce
ss Symposium) V-4p109〜114.M.Sato et.al “Etched
Shape Control of Single Crystallin Silicon in Reac
tive lon Etching Containing Chlorin "1985 Dry Process Symposium 1V-4p102
~ 107.

Problems to be Solved by the Invention The deposits on the above-mentioned side surface must be allowed to some extent in order to obtain a good shape, but the thickness of the deposits may be the same order as the groove width (for example, a groove of 1 μm). When deposits of 0.1 to 0.2 μm are piled up in a trench having a width), when a trench having a different groove width is formed at the same time, the trench shape becomes completely different. Further, in order to remove these deposits after forming the trench, a wet etching process using O ₂ plasma or a hydrofluoric acid aqueous solution is required. For example, if a wet etching process using a hydrofluoric acid aqueous solution is added,
In many cases, the amount of O ₂ is reduced and the shape is changed, which causes a problem in the ion implantation process and the like, which limits the process.

The reason why this deposit must be used is that, although the optimum etching conditions differ when the groove is shallow and when the groove becomes deeper as described above,
There are cases where etching is attempted under the same conditions.

Means for Solving the Problems In order to obtain a good pattern shape while minimizing the accumulation of deposits, the present invention improves the degree of vacuum or power in RIE etc. as the opening such as a groove deepens. By raising the energy of the ions, the etching is performed under the optimum etching conditions at that time according to the depth of the opening.

Action Generally, when the etching conditions are changed by RIE or the like to increase the energy of ions, the velocity component of ions in the vertical direction with respect to the semiconductor substrate tends to increase in the horizontal direction. When the etching is simply classified into chemical etching and physical etching, the element of physical etching increases as the ion energy increases, and the etching changes to have anisotropy. However, since physical etching accelerates etching by physical impact of ions, the etching selectivity between the etching resistant mask and the semiconductor substrate deteriorates, and as a result, etching generated from the mask (SiO ₂ , resist, etc.) The amount of the substance increases and the rate of redeposition in the opening increases.

As will be described later, if the ion energy is kept small even if the depth of the opening becomes deep, the directionality of the ion is easily affected by the opening (reflection on the side surface of the ion, electric field applied inside the opening, etc.), Further, as the opening becomes deeper, ion energy is consumed due to scattering of ions in the opening, and the phenomenon that the opening expands or warps occurs. Further, if the energy of the ions is increased from the beginning, the distortion of the opening disappears, but the amount of deposits from the etching-resistant mask to the opening increases, and it becomes difficult to remove the deposits or the shape of the opening becomes V. There is a problem that it becomes a glyph.

In the present invention, when the opening is shallow, the energy of the ions is reduced to increase the ratio of chemical etching to suppress the reattachment of etching products, and the energy of the ions is increased to increase the physical energy as the depth of the opening becomes deeper. By increasing the ratio of selective etching and optimizing the side wall deposits and ion energy itself according to the depth of the opening, a good shape is obtained.

Embodiment FIG. 1 shows the shape (cross-sectional view) of an embodiment of trench etching according to an embodiment of the present invention, and FIG. 2 shows the etching conditions under which the etching of FIG. 1 was performed. It shows the groove shape when etching is performed without changing the conditions.

Here, a P-type silicon substrate 2 having a specific resistance of 5 to 10 Ω · cm is used as a semiconductor substrate, and a silicon oxide film 1 having a thickness of 1 μm is used as an etching resistant mask, and etching is performed by reactive ion etching (RIE) to form a Si groove 3. did. As the etching condition, a mixed gas of SiCl ₄ , Cl ₂ , and SF ₆ , which is known as one of the typical gas conditions for forming the Si groove, was used.

There is a relationship that the average energy of ions in RIE increases as V _DC increases.
When the composition ratio / flow rate) is fixed, _VDC is increased by increasing the vacuum degree or increasing the RF power, and therefore the ion energy also tends to be increased. Figure 2 (a), (b), the conditions of performing the etching of (c), respectively _{(a) SiCl 4: 20sccm,} Cl 2: 10sccm, SF
₆ : 12sccm 9Pa 550W, (b) SiCl ₄ : 20sccm, Cl ₂ : 10sccm, SF
₆ : 12sccm 6Pa, 550W, (c) SiCl ₄ : 20sccm, Cl ₂ : 10sccm, SF
₆ : 12sccm, 6Pa, 600W. Gas conditions are (a),
(B) and (c) are set the same, but the condition (b) is a condition that the degree of vacuum is higher and the energy of the ions is larger than the condition (a), and the condition (c) is RF than the condition (b). This is a condition where the power is large and the energy of the ions is large.
By the way, although the ion energy is not measured,
Regarding V _DC , 50, 60, and 80 V are obtained under the conditions (a), (b), and (c), respectively. The reason that V _DC is relatively low is that this is the data obtained by the RIE device using the magnetron, and normally, under the conditions (a), (b), and (c)
_DC is about 250,300,350V. As shown in FIG. 2, as the ion energy increases, the number of side wall deposits 4 (shown in FIG. 2c) increases, and the groove becomes narrower. Further, in (b) where the ion energy is intermediate among these three conditions, the inclination of the groove side wall is different between the upper part of the groove and the lower part of the groove, and the etching state is different between the upper part and the lower part of the groove. I understand.

These phenomena are caused by the change of the ion energy itself or the deposit material corresponding to the ion energy. In the present invention, as shown in FIG. 1, first, the ion energy is small (a) for a fixed time (30 seconds). ) Etching, then continue etching for a certain period of time (120 seconds) under the condition (b), and continue for 150 seconds under the condition that the ion energy is large (c). Optimization of etching conditions corresponding to the groove depth As a result, a good shape was obtained. Of course, it is possible to change the ion energy by changing the gas conditions, but in the case of mass production, changing the gas species means complicated gas piping to the equipment and low reliability of etching due to changes in the gas atmosphere.・ It is desirable to use the same gas conditions because there are problems such as a decrease in throughput due to switching gas conditions.

In addition, although one embodiment in which the present invention is applied to RIE has been described here, the same can be said for plasma etching using ECR (electron cycloton resonance).

EFFECTS OF THE INVENTION The invention described above makes it possible to easily control the shape of a groove having a groove width of 1 μm or less. As semiconductor integrated circuits become more and more dense in the future, they will be of extremely high industrial value as groove formation technology used for various applications such as element isolation and trench capacitors.

[Brief description of drawings]

FIG. 1 is a sectional view of a groove formed by a method of one embodiment of the present invention, and FIG. 2 is a sectional view of a groove formed when etching conditions in the groove forming technique are changed. 1 ... Silicon oxide film, 2 ... Silicon substrate, 3 ...
groove.

Claims (4)

(57) [Claims] 1. A first dry etching step performed under a first etching condition, and a second etching condition performed after the first dry etching step and having a higher ion energy than the first etching condition. 2. A pattern forming method, wherein an opening having a width of 1 μm or less and a desired depth is formed by a plurality of dry etching steps including two dry etching steps, wherein the first etching condition depends on the etching condition. When the area of the upper part of the opening is smaller than the area of the lower part of the opening when the opening is formed, and the second etching condition is that the opening is formed according to the etching condition. Since the deposited film is formed on the side wall of the opening, the area of the upper part of the opening is larger than the area of the lower part of the opening. Pattern forming method characterized in that also a larger etching conditions. 2. The pattern forming method according to claim 1, wherein in the second dry etching step, the ion energy is increased by increasing the degree of vacuum or increasing the RF power. . 3. The pattern forming method according to claim 1, wherein reactive ion etching is used as the dry etching, and the cathode energy drop is increased to increase the ion energy. 4. The pattern forming method according to claim 1, wherein the gas composition ratio and the gas flow rate are constant in the first and second dry etching steps.