JPH06326058A - Treatment method of semiconductor substrate - Google Patents

Abstract

PURPOSE:To reduce the degree of a damaged layer formed on the surface of an Si substrate by a method wherein, as a condition under which a silicon oxide film on the Si substrate is etched by an RIE method, the power density of a high-frequency power supply just before at least the Si substrate is exposed is set at less than a specific value. CONSTITUTION:In a wafer 7 in which a silicon oxide film has been formed on the surface of a single-crystal Si substrate, only the silicon oxide film is etched and removed by using an RIE apparatus 1. As an etching condition at this time, the power density of a high-frequency power supply 4 just before at least the silicon substrate is exposed is set at less than about 1.0W/cm<2>. Thereby, the degree of a damaged layer formed on the surface of the Si substrate can be reduced.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a technique for etching SiO ₂ or Si ₃ N ₄ formed on a Si substrate by the RIE method.

[0002]

2. Description of the Related Art Since RIE (Reactive Ion Etching) is a well known technique, only the basic structure will be described with reference to FIG. FIG. 2 is a diagram conceptually showing the RIE device 1. When the inside of the etching chamber 2 is evacuated, a reaction gas (for example, CF ₄ ) 3 is put therein, and high-frequency power is applied from the high-frequency power source 4, electric discharge is generated to generate plasma 5. In this plasma 5, gas is dissociated by collision with electrons accelerated by an electric field, and ions and chemically active atoms and molecules are generated.

The latter atoms and molecules are called radicals (fluorine F in CF ₄ ) and can be used for isotropic plasma etching. The RIE method uses the former ions (CF ₄ is CF ₃ ⁺ ,
CF ₂ ⁺ and other positive ions are used, and the cathode 6 and the anode (not shown) have a parallel plate structure. When the wafer 7 is placed on the cathode 6, the positive ions are accelerated by the electric field and the surface of the wafer 7 is accelerated. Impact, degenerate and etch. Since the ion bombardment occurs only in the depth direction, the etching proceeds in the vertical direction, resulting in anisotropic etching.

In the RIE method, in order to anisotropically etch a Si oxide film or a Si nitride film formed on a Si substrate, a CF _x or CH _x F _y type gas is used as a reaction gas. For example, in the proceedings 28a-NC-6 of the 1992 Joint Lecture on Applied Physics, CF ₄ / H ₂ mixed gas is used as the reaction gas, and the power density of the high frequency power source is 2.7 W / cm. It is described that it is set to ² .

[0005]

In the RIE method, S
When the Si oxide film or Si nitride film formed on the i substrate is anisotropically etched, a damaged layer is formed on the surface of the silicon substrate. This damage is damage due to etching gas containing carbon (C) (etching damage)
And the damage caused by ion implantation.

Etching Damage Due to Etching Gas Containing Carbon In dry etching of a silicon oxide film (SiO ₂ ) and a silicon nitride film (Si ₃ N ₄ ), etching gas containing carbon (CHF ₃ , C
_{F 4, CH 2 F 2,} C 3 F 8, C 2 F 6, CCl 4 , etc.) is widely used. In this case, carbon atoms generated during etching cause the surface of the silicon substrate to change to silicon carbide (S
The SiC damage to be converted to iC) occurs, and the SiC layer is formed. In addition, regarding the conversion of the silicon surface to SiC, Su
rface & Interface Anal., 9,275 (1986).

Further, under the SiC layer formed on the surface of the silicon substrate, amorphization damage that disturbs the crystal structure of the silicon substrate occurs, and an amorphous layer (amorphous layer) is formed. . In this amorphous layer, carbon atoms generated during etching are struck on the silicon substrate,
It is considered to be formed by carelessly driving the substrate.

Further, when a fluorocarbon gas (CHF ₃ , CF ₄ , CH ₂ F ₂ , C ₃ F _8, etc.) is used as an etching gas, CF is formed on the SiC layer on the surface of the silicon substrate.
_{An X-} based polymer is formed. Such a damaged layer causes various adverse effects in the process of manufacturing a semiconductor device. For example, LDD (Lightly Doped Dr
When manufacturing a MOS transistor with an ein) structure,
After the Si oxide film on the source or drain is removed by etching by the RIE method, high-concentration ions are implanted into the source or drain, or the Si oxide film on the source or drain is removed by etching, and the portion is removed again. Although thermal oxidation is performed and high-concentration ions are implanted into the source and drain from the top of this oxide film, if a damaged layer is formed on the Si substrate, ion implantation on the Si substrate surface will be performed smoothly. If not, it may become an obstacle when forming an oxide film again on the surface of the Si substrate.

Also, when connecting the bit line and the source of the MOS transistor in the process of manufacturing the DRAM, the oxide film on the MOS transistor is etched by the RIE method to form a contact hole, and the bit line is formed on the source. Polysilicon is deposited, but if a damaged layer is formed on the Si substrate, the Si substrate (source)
The contact resistance between the bit line and the bit line increases.

Generally, the C--F _X polymer layer can be easily removed because it can be dissolved by heating a mixed solution of sulfuric acid and hydrogen peroxide at 140 ° C. Further, C-F _X-based polymer layer can also be removed by heat treatment above 400 ° C.. Also, the amorphous layer can be normally crystallized again by a heat treatment at about 900 ° C.

Although the SiC layer can be removed by dry etching, it is expected that such etching treatment will be extremely difficult in consideration of further miniaturization of the device in the future. For example, in a 1-G DRAM class (design rule 0.15 μm) ULSI, it is expected that the diffusion layers such as the source and drain will be as shallow as about 60 nm. In order to accurately control such etching on the order of several nm, There is a risk that problems may occur in terms of reproducibility.

Further, in the above conventional example, 2.7 W /
In order to apply high frequency voltage with high density of cm ² ,
As the kinetic energy and plasma density of carbon increase, S
Immediately after the i oxide film or the Si nitride film is etched, charged particles such as ions collide with the surface of the Si substrate violently due to a strong electric field, and there is a problem that damage mainly to the SiC layer is likely to increase.

In view of the above problems, the present invention provides a method for treating a semiconductor substrate that reduces the degree of a damage layer formed on the surface of a Si substrate. A second object of the present invention is to provide a method for processing a semiconductor substrate that can remove the SiC damage layer with high accuracy.

[0014]

A first method for processing a semiconductor substrate according to the present invention is a method for reacting a silicon oxide film (SiO ₂ ) or a silicon nitride film (Si ₃ N ₄ ) formed on a silicon substrate with reactivity. A method of etching by an ion etching (RIE) method, wherein as a condition of the RIE, at least a power density of a high frequency power source immediately before the silicon substrate is exposed (hereinafter referred to as RF power density) is about 1.0 W.
/ Cm ² is set.

The reaction gas is a fluorocarbon gas such as CF _x or CH _x F _y itself, a mixed gas thereof, or O ₂ , N ₂ , H ₂ or an inert gas (Ar, He, etc.) in these gases. CF _x or CH _x F _y type gas such as added mixed gas is used. The second semiconductor substrate processing method of the present invention is directed to a silicon oxide film (SiO ₂ ) or a silicon nitride film (Si) formed on a silicon substrate.
₃ N ₄ ) etc. are dry-etched and then subjected to O ₂ RIE treatment.

A third semiconductor substrate processing method according to the present invention is a silicon oxide film (S) formed on a silicon substrate.
iO ₂ ) or silicon nitride film (Si ₃ N ₄ ) or the like to form a contact hole by dry etching, and then,
At least the bottom surface of the contact hole is subjected to O ₂ RIE treatment.

[0017]

That is, if the RF power density is about 1.0 W / cm ² and lower than that, the degree of damage on the surface of the Si substrate is reduced, and at least immediately before the exposure of the Si substrate. By setting the RF power density to less than about 1.0 W / cm ² , the Si substrate surface is less likely to be damaged.

Further, the silicon SiC layer which is the plasma damage is removed by the reaction of SiC + 2O ₂ → SiO ₂ + CO ₂ ↑ by being accompanied by oxidation by O ₂ RIE, and SiO ₂ is formed. If this SiO ₂ is removed by wet cleaning or the like, a silicon substrate surface without damage can be obtained.

[0019]

EXAMPLE A first example of the present invention will be described below. S
When a damage layer mainly composed of a SiC layer is formed on the surface of the i substrate, the damage layer becomes an obstacle, and, for example,
When the Si substrate is thermally oxidized, the surface oxidation is suppressed.

The applicant has proved such fact by the following experiment. First, a wafer having a silicon oxide film formed on the surface of a single crystal Si substrate is removed by etching using a normal RIE apparatus. The etching conditions at this time are as follows. Gas used: CHF ₃ + Ar (same conditions as sample wafers A to F) Gas pressure: 0.2 Torr (same conditions as sample wafers A to F) Sample wafer A ... RF power density: 0.4 W / cm ² sample wafer B ... RF power density: 0.6 W / cm ² sample wafer C ... RF power density: 0.8 W / cm ² sample wafer D ... RF power density: 1.0 W / cm ² sample wafer E ... RF power density: 1 .2 W / cm ² sample wafer F ··· RF power density: 1.4 W / cm ² Each sample wafer A to F was placed in an oxidation furnace and placed in an oxygen atmosphere.
Thermal oxidation is performed at 900 ° C. for 65 minutes. The conditions of this thermal oxidation were set so that an oxide film having a film thickness of 200 Å was formed when a single crystal Si substrate with no damage (the above work was not performed) was used.

FIG. 1 shows the results of measuring the film thickness of the silicon oxide film formed again on the surfaces of the samples A to F by ellipsometry (optical film thickness measuring device). It can be seen from FIG. 1 that when the RF power density is less than about 1.0 W / cm ² , the Si oxide film can be formed again in the subsequent thermal oxidation process.
In other words, when the RF power density is increased, the surface of the Si substrate is severely damaged immediately after the Si oxide film is etched, and the damaged layer thereby prevents the subsequent growth of the Si oxide film.

Therefore, for example, when the Si oxide film on the Si substrate is etched by the RIE apparatus, the RF power density is set to 0.6 W / cm ² . This allows Si
The degree of damage on the surface of the substrate is reduced, and when an oxide film is formed, ions are implanted, and wiring is connected thereafter, an element having excellent characteristics can be obtained. Also, the RF power density is set to 0.
When it is set to 6 W / cm ² , the etching rate is slower as compared with the one having a high RF power density, and thus there is a fear that the throughput is lowered.
Have configured the power density of 2.0 W / cm ^2, the RF power density just before the Si substrate is exposed may be reduced to 0.6 W / cm ^2. In short, the RF power density just before the Si substrate is exposed may be such that the damaged layer on the surface of the Si substrate is reduced.

Next, a second embodiment of the present invention will be described below. 3 and 4 show a process of forming a contact hole in an insulating film on a silicon substrate. First, in FIG. 3A, a field oxide film 9, a gate electrode 10 and impurity diffusion regions 11 and 12 as sources and drains are formed on a single crystal silicon substrate 8, and a silicon oxide film 13 is formed thereon by, for example, a CVD method. After being deposited, a resist pattern 14 for forming a contact hole is formed on the silicon oxide film 13.

Next, referring to FIG. 3B, the resist 14 is used.
By using RIE (etching condition RF power density: 2 W / cm ² , gas pressure: 0.2 Torr, working gas: CHF ₃ + Ar) as a mask.
3, the contact hole 1 reaching the silicon substrate 8
5 and 16 are formed. At this time, the contact hole 1
S is formed on the bottom surface of the silicon substrate 8, that is, on the bottom surface of the silicon substrate 8.
The iC conversion damage layer 17 is formed.

Then, in FIG. 3C, the resist 1 is formed.
4 is subjected to O ₂ plasma ashing and immersed in a mixed solution of sulfuric acid and hydrogen peroxide solution to be removed. Now, when a damage layer mainly made of a SiC layer is formed on the surface of the Si substrate,
When the damaged layer becomes an obstacle and the Si substrate is thermally oxidized, for example, the oxidation of the surface is suppressed, and therefore it is necessary to remove it.

The Applicant first prepared 4 samples of the state shown in FIG. 3C.
Sheets (Sample G to Sample J) were prepared and subjected to the following treatments, respectively, followed by thermal oxidation. Sample wafer G..O ₂ RIE processing (O ₂ is used as a processing gas in an ordinary RIE device) Sample wafer H..O ₃ processing (substrate temperature 300 ° C., O ₃ + O)
₂ (concentration 5% + N ₂ atmosphere) Sample wafer I · · O ₂ Plasma downflow (irradiates only radicals of microwave discharge plasma) Sample wafer J · · Untreated * Sample wafer K · · Simple silicon wafer (ie, Si
FIG. 5 shows the results of measuring the oxide film thickness on the bottom surfaces of the contact holes 15 and 16 after thermal oxidation. Si on the silicon surface
As described above, if the carbonization damage remains, the growth of the oxide film thereafter is hindered. From this figure, O ₂
The sample subjected to the RIE process shows almost the same value as the sample wafer K.

From this fact, it is possible to obtain Si by O ₂ RIE treatment.
It can be seen that the C damage can be completely removed. Samples GI automatically improve the damage of the polymer layer described above, but some amorphous layers remain. Therefore, in FIG. 4D, an O ₂ RIE is performed on the substrate by using an ordinary RIE apparatus.
Process (etching condition RF power density: 0.2
~ 0.5 W / cm ² , gas pressure: 0.001-0.3T
orr, gas used: O ₂ ). As a result, as shown in FIG. 4E, the SiC damage portion is modified, and the silicon oxide film (SiO ₂ ) 18 is formed in that portion.

FIG. 6 shows the film thickness of the silicon oxide film 18 formed when the O ₂ RIE process is performed for 20 seconds and the RF at that time.
The relationship with the power density is shown. As is clear from this figure, the silicon oxide film 1 is changed according to the change in RF power.
It can be seen that the film thickness of No. 8 changes on the order of several nm. This silicon oxide film is to be removed by wet cleaning as described later, but not limited to this, it is not limited to normal R
When the SiC damage layer is formed on the silicon surface by IE, the damage layer can be completely removed by performing the O ₂ RIE treatment. For example, as described in the section “Problems to be solved by the invention”. As described above, when an oxide film is formed again after RIE as in the case of forming a transistor having an LDD structure, the film thickness can be controlled on the order of several nm.

The silicon oxide film is removed because it is formed on the bottom surface of the contact hole. However, if the silicon oxide film can be used as it is, it is not necessary to remove it. do it. Moreover, since the processing temperature of O ₂ RIE is near room temperature, re-diffusion of impurities is suppressed, and it is possible to sufficiently cope with shallow junctions.

Now, referring to FIG. 4E, the silicon oxide film 18 is wet-cleaned (for example, H ₂ O: HF = 20: 1).
The surface of the silicon substrate which is not damaged is exposed. After that, an aluminum alloy or a refractory metal is formed in the contact holes 15 and 16 by a sputtering method or the like and processed as wirings 19 and 20.

As described above, since the SiC damage layer is removed by O ₂ RIE, the metal-Si is also experimentally tested.
The contact resistance between the substrates was measured to be low. FIG. 7 shows the contact resistance when the wiring is processed after the processing of the sample G and the sample H (two each) (contact hole size: 0.25 μm ² , wiring material: polysilicon). ).

As is apparent by comparing the two, the contact resistance can be reduced only by removing the SiC damage layer (Sample G). Further, variations in resistance are small and reliability is improved.

[0033]

According to the first semiconductor substrate processing method of the present invention, the Si oxide or Si nitride film on the Si substrate is subjected to RI.
It is possible to reduce the degree of the damage layer formed on the surface of the Si substrate when the etching is performed by the E method. In addition, in the second and third semiconductor substrate manufacturing methods,
The damaged layer after RIE can be removed.

Therefore, when an oxide film is formed, ions are implanted, wiring is connected, etc., an element having good characteristics can be obtained.

[Brief description of drawings]

FIG. 1 is an R in the RIE method according to the first embodiment of the present invention.
It is a graph which shows the relationship between F power density and the thermally-oxidized film thickness formed after that.

FIG. 2 is a conceptual diagram of a normal RIE device.

FIG. 3 is a cross-sectional view showing the manufacturing process of the semiconductor device according to the second embodiment of the present invention.

FIG. 4 is a cross-sectional view showing the manufacturing process of the semiconductor device according to the second embodiment of the invention.

FIG. 5 is a graph showing the thermal oxide film thickness after various damage layer removal test treatments in the second embodiment of the present invention.

FIG. 6 shows R in the RIE method in the second embodiment of the present invention.
6 is a graph showing a relationship between F power density and an oxide film thickness formed during O ₂ RIE processing.

FIG. 7 is a diagram showing contact resistances with and without a SiC damage layer in the second embodiment of the present invention.

[Explanation of symbols]

 1 RIE device 8 Silicon substrate 13 Silicon oxide film 15, 16 Contact hole

Claims (3)

[Claims] 1. A method of etching a silicon oxide film (SiO ₂ ) or a silicon nitride film (Si ₃ N ₄ ) formed on a silicon substrate by a reactive ion etching (RIE) method, which comprises: As a condition, at least the power density of the high-frequency power source immediately before the silicon substrate is exposed is set to less than about 1.0 W / cm ² , and the semiconductor substrate processing method. 2. A semiconductor substrate comprising a silicon oxide film (SiO ₂ ) or a silicon nitride film (Si ₃ N ₄ ) formed on a silicon substrate, which is dry-etched and then processed by O ₂ RIE. Processing method. 3. A contact hole is formed in a silicon oxide film (SiO ₂ ) or a silicon nitride film (Si ₃ N ₄ ) formed on a silicon substrate by dry etching,
Then, at least the bottom surface of the contact hole is O ₂
A method for processing a semiconductor substrate, which comprises processing by RIE.