JPH05267247A - Dry etching method - Google Patents

Abstract

PURPOSE:To make it possible to etch a layer of a silicon oxide material highly selectively by using a thiocarbonyl compound containing fluorine atoms but not oxygen atoms as an etching gas. CONSTITUTION:A material layer (silicon oxide layer insulating film) 3 of a silicon oxide material is etched by using an etching gas containing a thiocarbonyl compound in molecules. In this case, the silicon oxide layer insulating film 3 is etched (just etched) to a depth which does not exceed the film thickness essentially. Then, in condition that the wafer temperature is made lower than that of the just etching process, the remaining part 3a of the silicon oxide layer insulating film 3 is etched (over etched) by use of the same etching gas. In this way, the silicon oxide layer insulating film 3 can be etched highly selectively without causing any damage due to H<+> to the base layer of a silicon material (impurity diffusion area) 2.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a dry etching method applied in the field of manufacturing semiconductor devices, etc., and particularly etching of a silicon oxide material layer causes damage to the underlying silicon material layer due to H ^+. Without high selectivity.

[0002]

2. Description of the Related Art As semiconductor devices have become more highly integrated and have higher performance as seen in VLSI, ULSI, etc. in recent years, technical requirements for dry etching methods for silicon oxide based material layers have become more and more strict. It has become to. First of all, the area of device / chip is increasing due to high integration, the diameter of the wafer is increasing, the pattern to be formed is highly miniaturized, and uniform processing within the wafer surface is required. As described above, the mainstream of the dry etching apparatus is shifting from the conventional batch type to the single-wafer type because of the demand for high-mix low-volume production. At this time, in order to maintain the same productivity as the conventional one, it is essential to greatly improve the etching rate.

Further, in a situation where the junction depth of the impurity diffusion region is shallow and various material layers are thin in order to increase the speed and miniaturization of the device, the selectivity to the underlayer is more excellent than before. Etching technology with less damage is required. For example, a PM used as an impurity diffusion region formed in a semiconductor substrate or a resistance load element of SRAM.
An example is etching of a SiO ₂ interlayer insulating film performed with a silicon substrate or a polycrystalline silicon layer as a base when a contact is to be formed in a source / drain region of an OS transistor.

However, the characteristics such as high speed, high selectivity, and low damage are in a relation of selection, and it is extremely difficult to establish an etching process that can satisfy all of them.

Conventionally, CHF ₃ , CF ₄ / H ₂ mixed system, CF ₄ / O ₂ mixed system, C, etc. have been used for dry etching a SiO ₂ based material layer while maintaining a high selection ratio with respect to a Si based material layer. _{A 2} F ₆ / CHF ₃ mixed gas or the like has typically been used as an etching gas. All of these are mainly composed of fluorocarbon-based gas having an intramolecular C / F ratio (ratio of the number of carbon atoms and the number of fluorine atoms) of 0.25 or more. These gas systems are used because (a) C contained in the fluorocarbon gas is C- at the surface of the SiO ₂ layer.
(B) CF _x ⁺ , which is the main etching species of the SiO ₂ layer, can be generated, and (c) relatively in plasma. Since a state rich in carbon is created, oxygen in SiO ₂ is removed in the form of CO _x , while carbon-based polymer is present on the surface of the silicon-based material layer due to the contribution of C, H, F, etc. contained in the gas system. Are deposited, the etching rate is reduced, and a high selection ratio with respect to the silicon-based material layer can be obtained.

Here, in the above-mentioned etching gas, a compound such as CHF ₃ having hydrogen as a constituent element in the molecule is used, or H ₂ is used as an additive gas in some form. Many contain hydrogen. This is because H ^* generated in the plasma is in excess of F ^*.
For capturing and removing it in the form of HF (hydrogen fluoride) to the outside of the etching reaction system. This increases the apparent C / F ratio of the etching reaction system and promotes the production of the carbon-based polymer. However, this carbon-based polymer is
On the O ₂ -based material layer, a combustion reaction occurs due to the O atoms supplied from the O ₂ -based material layer, so that the O ₂ -based material layer is not deposited, but is exclusively deposited on the Si-based material layer and contributes to high selectivity. C / F above
For the concept of ratio and the mechanism by which high selectivity is achieved, see J.
Vac. Sci. Tech. 16 (2), p. 391
(1979).

[0007]

As described above, in the conventional etching of the silicon oxide type material layer, in order to obtain a practically sufficient selection ratio, the fluorocarbon type gas having hydrogen in the molecule as a constituent element is used. Or H ₂
It was necessary to add a hydrocarbon gas to the gas system. However, with the miniaturization of design rules, the influence of hydrogen contained in these etching gas systems cannot be ignored.

For example, Applied Physic
s Letters 1988 Vol. 53 No. 18, 17
The induction of defects in single crystal silicon by hydrogen plasma is reported on pages 35 to 1737. That is, since H ⁺ generated in hydrogen plasma has an extremely small ionic radius and mass, it penetrates with a large range when injected into a silicon substrate and acts as a nucleus for inducing crystal defects in the subsequent process.

In the field of manufacturing semiconductor devices, single-wafer processing is becoming mainstream as described above, and even as a dry etching apparatus, while generating high-density plasma by utilizing magnetron discharge or ECR (electron cyclotron resonance) discharge. A high-speed etching type device has been widely used. When a wafer is placed in such a high-density plasma, it is sufficiently predicted that H ⁺ generated by discharge dissociation from a hydrocarbon-based gas will seriously damage the silicon substrate.

Even if crystal defects are not reached, H
It is feared that the crystal strain caused by ⁺ implantation will increase the contact resistance.

Therefore, in a normal process, light etching is performed from the surface layer of the silicon substrate to a depth of several tens nm to remove the damaged layer. However, under the present circumstances where the junction depth of the impurity diffusion region is becoming shallower, the amount of silicon substrate removed by such post-treatment is reaching a level that cannot be neglected. Therefore, it is desired to carry out etching with a gas system that does not generate H ⁺ in plasma.

In view of this point, the applicant of the present invention has previously proposed a process using a saturated or unsaturated cyclic fluorocarbon compound in Japanese Patent Application No. 3-40966. Since the compound has a high C / F ratio due to its own skeleton structure, a relatively high underlayer selectivity can be achieved without the presence of hydrogen in the etching reaction system. However, since the above compound is a cyclic compound, it has at least 3 carbon atoms, and the number of fluorine atoms is considerably large depending on the number of carbon atoms. Therefore, when an etching apparatus of the type that generates high-density plasma is used, the dissociation of compounds may be promoted and a large amount of F ^* may be generated. However, further process improvement is needed.

Therefore, an object of the present invention is to provide a method for etching a silicon oxide material layer having excellent selectivity without causing damage to the underlying Si substrate.

[0014]

The dry etching method of the present invention is proposed to achieve the above-mentioned object, and contains a thiocarbonyl compound having at least a thiocarbonyl group and a fluorine atom in the molecule. It is characterized in that the silicon oxide based material layer is etched using an etching gas.

Further, the present invention further comprises a just etching step of etching the silicon oxide based material layer to a depth that does not substantially exceed the layer thickness, and an over etching step of etching the remaining portion of the silicon oxide based material layer. It is characterized in that it is divided into an etching process and the wafer temperature is relatively lowered in the latter over-etching process.

[0016]

In the present invention, a thiocarbonyl compound having at least a thiocarbonyl group (> C = S) and a fluorine atom in the molecule is used as the main component of the etching gas.
This thiocarbonyl compound produces CF _x ⁺ , CS ⁺ , SF _x ⁺ , F ^*, etc., which are the main etching species of the SiO ₂ -based material layer, under discharge dissociation conditions, and also liberates from the carbon-based polymer as a deposition substance. Can produce S (sulfur). In the conventional process, the depositing substance that contributes to the improvement of the selectivity and the securing of the anisotropy was mainly the carbon-based polymer, but in the present invention, S is added to this. Therefore, the amount of carbon-based polymer deposited can be relatively reduced, and the risk of particle contamination is reduced accordingly. Since S is a sublimable substance, it can be easily removed by heating the wafer to approximately 90 ° C. or higher after completion of etching, and does not itself become a source of particle contamination.

Further, the thiocarbonyl compound as described above has a limited number of fluorine atoms contained in one molecule unless a compound having a particularly complicated structure is assumed, and thus the above-mentioned cyclic fluorocarbon compound is generally used. It does not release a large amount of F ^* into the plasma. Therefore, it is possible to keep the C / F ratio at a practically sufficiently high value without particularly involving hydrogen in the etching reaction system as in the conventional case. Thus, the fact that low damage and low contamination can be achieved while achieving high selectivity is a great advantage of the present invention.

Further, in the present invention, in order to further improve the selectivity with respect to the underlying Si-based material layer, etching is performed in two steps, a just etching step and an overetching step, and the wafer temperature is relatively lowered in the overetching step. I also suggest that. In the over-etching step, the silicon oxide material layer to be etched is reduced, and the underlying material layer such as the Si substrate is exposed in at least a part of the area on the wafer. Therefore, if the wafer temperature in the over-etching step is set lower than that in the just-etching step, the deposition of carbon-based polymer or S is promoted in the over-etching step, and the exposed surface of the underlying material layer is effectively protected from etching. Can be done.

[0019]

EXAMPLES Specific examples of the present invention will be described below.

Example 1 In this example, the present invention is applied to the processing of contact holes, and CSF ₂ (thiocarbonyl fluoride) is used to form SiO 2.
_{2 This} is an example of etching the interlayer insulating film. This process will be described with reference to FIG. As shown in FIG. 1A, the wafer used as a sample in this example has a SiO ₂ interlayer insulating film 3 formed on a single crystal silicon substrate 1 on which an impurity diffusion region 2 has been formed in advance. As a mask for etching the SiO ₂ interlayer insulating film 3, a resist pattern 4 having a thickness of about 1 μm is formed. The resist pattern 4 is made of a novolac-based positive photoresist material (manufactured by Tokyo Ohka Kogyo Co., Ltd .; trade name TSMR-V3), and an opening 4a having a diameter of about 0.5 μm is formed by photolithography using a g-line stepper and development processing. It is provided.

The above-mentioned wafer was set on the wafer mounting electrode of the RF bias application type magnetic field microwave plasma etching apparatus. Here, the wafer mounting electrode has a built-in cooling pipe, and a cooling device such as a chiller connected to the outside of the apparatus supplies a coolant to the cooling pipe to circulate the cooling pipe, thereby keeping the wafer temperature during etching to a predetermined value. It is possible to control the temperature. As an example, the SiO ₂ interlayer insulating film 3 was etched under the following conditions.

CSF ₂ flow rate 50 SCCM Gas pressure 0.5 Pa Microwave power 1200 W (2.45 GH)
z) RF bias power 250W (800kHz) Magnetic field strength 1.50 × 10 ^-2 T (= 150G) Wafer temperature 20 ° C (using ethanol-based refrigerant)

In this etching process, the CSF is formed on the surface of the SiO ₂ interlayer insulating film 3 exposed in the opening 4a.
Etching progressed by a mechanism in which a radical reaction by F ^* generated by dissociation from ₂ was assisted by the incident energy of ions such as CF _x ⁺ , CS ⁺ , SF _x ⁺ generated from CSF ₂ . At this time, carbon-based polymer and S are also produced from CSF ₂ at the same time, and in principle, these depositable substances are deposited on the pattern side wall portion where vertical incidence of ions does not occur, and exert a side wall protection effect. Proceeded anisotropically.

Further, when the underlying single crystal silicon substrate 1 (more precisely, the impurity diffusion region 2) is exposed, the carbon-based polymer and S are deposited on the exposed surface, and the etching rate is significantly lowered, and the selectivity ratio to Si is increased. A high value of about 12 was achieved. Further, since the above etching reaction system does not contain hydrogen, no substrate damage due to H ⁺ is observed even when the cross section of the wafer after etching is observed with a TEM (transmission electron microscope). It was

By this etching, as shown in FIG. 1B, the contact hole 5 having an anisotropic shape is formed.
Could be formed.

After the etching was completed, when the wafer was heated to about 100 ° C., S deposited on the side wall of the pattern and the exposed surface of the impurity diffusion region 2 was easily removed by sublimation.
Furthermore, when the resist pattern 4 is removed by O ₂ plasma ashing, the carbon-based polymer that has contributed to sidewall protection and the residual S are completely burned and removed, and no particle contamination occurs on the wafer. There was no.

Embodiment 2 In this embodiment, similarly, in the contact hole processing, the etching of the SiO ₂ interlayer insulating film using CSF ₂ is divided into two stages, a just etching process and an overetching process, and the latter process is carried out at the wafer temperature. Is an example in which the selectivity is further improved by relatively lowering. This process will be described with reference to FIG. 2 and FIG. 1 above.

In this embodiment, a magnetron RIE (reactive ion etching) apparatus of a multi-chamber type in which two etching chambers each having a different wafer temperature setting are connected under a high vacuum via a wafer handling unit. Was used. First, in one etching chamber, as an example, the interlayer insulating film 3 was etched by just 0.9 μm (just etching) under the following conditions.

CSF ₂ flow rate 50 SCCM gas pressure 3 Pa RF power density 7.9 W / cm
² (13.56MHz) Magnetic field strength 1.50 × 10 ^-2 T (= 150
G) Self-bias potential (V _dc ) -200 V Wafer temperature 20 ° C. (using ethanol-based coolant) In this just etching step, anisotropic etching proceeds by the mechanism described in Example 1, and as shown in FIG. , The contact hole 5 was formed halfway.
The remaining portion 3a of the interlayer insulating film 3 was left on the bottom of the contact hole 5 by about 0.1 μm.

Next, the wafer was transferred to another etching chamber, and the remaining portion 3a was etched (over-etched) under the following conditions as an example. CSF ₂ flow rate 50 SCCM gas pressure 3 Pa RF power density 3.9 W / cm
² (13.56MHz) Magnetic flux density 1.50 × 10 ^-2 T (= 150
G) Self-bias potential (V _dc ) -80V Wafer temperature -60 ° C (using ethanol-based coolant) In this over-etching process, the wafer temperature was lowered more than in the just-etching process, so that the deposition of carbon-based polymer and S Was promoted and the reactivity of F ^* was lowered. Therefore, if normal
A high selection ratio of 50 or more has been achieved with respect to the underlying single crystal silicon substrate 1 which is etched at high speed depending on the mode. Moreover, since the RF power density and the self-bias potential are reduced, incident ion energy is reduced, and irradiation damage due to ions can be avoided. H
Of course, the damage caused by ⁺ did not occur.

The present invention has been described above based on the two embodiments, but the present invention is not limited to these embodiments. For example, in the above examples, CSF ₂ was used as the thiocarbonyl compound. This compound structurally has two fluorine atoms bonded to the carbon atom of the thiocarbonyl group. As the thiocarbonyl compound used in the present invention, a compound in which one of the fluorine atoms is replaced with another halogen atom such as Cl, Br and I can also be used. However, considering that the magnitude relationship of the interatomic bond energy is Si-F>Si-O> Si-Cl (Br) >> Si-Si, fluorine is effective as an etching species for the SiO ₂ -based material layer. .. Further, Cl, Br, etc. are usually used as etching species for the silicon-based material layer, and a compound containing a large number of these halogen atoms in one molecule is likely to lower the underlayer selectivity. Therefore, the thiocarbonyl compound used in the present invention is preferably a compound which does not contain a hydrogen atom and mainly contains fluorine as a halogen atom.

The silicon oxide material layer to be etched according to the present invention is not limited to the above-mentioned SiO ₂ , but PSG, BSG, BPSG, AsSG, AsP.
It may be SG, AsBSG or the like. Needless to say, the configuration of the wafer, the etching apparatus used, the etching conditions, etc. can be changed as appropriate.

[0033]

As is apparent from the above description, in the present invention, the etching gas is mainly composed of a thiocarbonyl compound having a fluorine atom as a constituent element and not having a hydrogen atom, so that the underlying silicon H ^{+ in the} system material layer
It is possible to perform highly selective etching of the silicon oxide based material layer without damaging the silicon oxide based material. Moreover, in addition to the conventional carbon-based polymer as a depositable substance, S
Therefore, the amount of carbon-based polymer that contributes to sidewall protection and achievement of underlayer selectivity can be relatively reduced, and particle contamination can be significantly reduced.

The present invention is extremely suitable for manufacturing a semiconductor device which is designed based on a fine design rule and which requires high integration, high performance and high reliability.

[Brief description of drawings]

FIG. 1 is a schematic cross-sectional view showing an example of a process in which the present invention is applied to processing a contact hole in the order of steps, (a) showing a state where a resist pattern is formed on a SiO ₂ interlayer insulating film, (b) ) Indicates that the contact holes are opened.

FIG. 2 is a schematic cross-sectional view showing a state where a contact hole is formed halfway in another process example in which the present invention is applied to a contact hole.

[Explanation of symbols]

1 ... monocrystalline silicon substrate 2 ... impurity diffusion regions 3 ... SiO ₂ interlayer insulating film 3a ... (the SiO ₂ interlayer insulating film) remainder 4 ... resist pattern 4a ... opening Part 5: Contact hole

Claims (2)

[Claims] 1. A dry etching method characterized by etching a silicon oxide material layer using an etching gas containing a thiocarbonyl compound having at least a thiocarbonyl group and a fluorine atom in the molecule. 2. Just etching for etching a silicon oxide material layer to a depth substantially not exceeding the layer thickness thereof by using an etching gas containing a thiocarbonyl compound having at least a thiocarbonyl group and a fluorine atom in the molecule. Dry etching characterized by including a step and an over-etching step of etching the remaining portion of the silicon oxide based material layer by using the etching gas under the condition that the wafer temperature is lower than that in the just etching step. Method.