JP3384622B2 - Substrate processing method - Google Patents

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 a silicon oxide film (SiO ₂ ) or a silicon nitride film (Si ₃ N ₄ ) formed on a substrate such as silicon by RIE.

[0002]

2. Description of the Related Art Since the RIE method (Reactive Ion Etching) is a well known technology, only the basic structure will be described with reference to FIG. FIG. 8 is a diagram conceptually showing the RIE apparatus 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 and plasma 5 is generated. 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 layer is formed of a damage layer associated with an etching gas containing carbon (C) and a damage layer associated with an etching gas containing hydrogen (H) (GS Orhrlein, et al., J. Vac. Sci.Technol., A4 (3) (1
986) 750).

Regarding the damage caused by the etching gas containing carbon, silicon oxide film (SiO ₂ ) and silicon nitride film (Si ₃
In dry etching with N ₄ ) or the like, an etching gas containing carbon (CHF ₃ , CH ₂ F ₂ , etc.) is widely used. In this case, carbon atoms generated during etching cause the surface of the silicon substrate to change to silicon carbide (Si
The SiC damage to be converted into C) occurs, and a SiC damage layer is formed.

Regarding Damage Due to Etching Gas Containing Hydrogen When hydrogen is contained in the etching gas, hydrogen ions penetrate below the SiC layer, and the hydrogen ions inactivate the donors and acceptors in the silicon substrate. Damage (referred to as a hydrogen-penetration damage layer) such that the silicon is crystallized or the crystallinity of silicon is disturbed occurs.

Such a damaged layer causes various harmful effects in the process of manufacturing a semiconductor device. For example, in the case of manufacturing a MOS transistor having an LDD (Lightly Doped Drain) structure, the Si oxide film on the source and drain is removed by etching by the RIE method, and then high concentration ions are implanted into the source and drain, or After the Si oxide film on the source and drain is removed by etching, the part is thermally oxidized again and a high concentration of ions is injected into the source and drain from above this oxide film, but the Si substrate is damaged. When the layer is formed, the ion implantation to the surface of the Si substrate may not be performed smoothly, or may become an obstacle when the oxide film is formed 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)
And the contact resistance between the bit line and the bit line increases.

The SiC damage layer can be removed by isotropic dry etching, but it is expected that such etching treatment will be extremely difficult in consideration of further miniaturization of the device in the future. For example, 1
U of GDRAM class (design rule 0.15 μm)
In an LSI, the diffusion layers such as the source and drain are expected to be shallow to about 60 nm, and in order to accurately control such etching on the order of several nm, there is a risk of problems in terms of reproducibility and the like. .

In view of the above problems, the present invention provides a method for treating a substrate in which the degree of damage of a damage layer formed on the surface of a Si substrate is reduced.

[0012]

A method of processing a substrate according to claim 1,
The method consists of a silicon oxide film or a film formed on a silicon substrate.
After dry etching the insulating film such as the recon nitride film,
Ions are implanted into the surface of the recon substrate and then the RTA method is used.
Rapid heat treatment by means of the RTA treatment
The point is to carry out O ₂ RIE processing before processing.
It

A method of treating a substrate according to claim 2 is a silicon-based material.
Such as silicon oxide film and silicon nitride film formed on the plate
Surface of silicon substrate after dry etching of insulating film
Ions are implanted into the substrate, and then the RTA method is used for rapid heating.
Before applying the RTA process, the slide
The main point is to perform the etching process.

A method of treating a substrate according to a third aspect is the method according to the second aspect.
In the described invention, the slight etching treatment is
A gas containing at least fluorine (F) or chlorine (Cl)
The main point is what is used.

[0015]

[0016]

[0017]

Function: That is, a silicon oxide film (SiO ₂ ) or a silicon nitride film (Si) formed on a substrate such as silicon.
_When an insulating film such as ₃ N ₄ ) is dry-etched by the RIE method or the like, a SiC damage layer and a hydrogen penetration damage layer are formed on the surface of the substrate, and the characteristics (contact resistance, etc.) of this portion are deteriorated. By the heat treatment, hydrogen in the portion of the hydrogen-penetration damaged layer is diffused outward and disorder of the crystallinity of this portion is improved, and at least the degree of damage of the hydrogen-penetration damaged layer is recovered.

Further, performing this RIE method using a gas containing carbon (C), the etching reaction of SiO _{2 is, SiO 2 + CF 4 → SiF} 4 ↑ + CO 2 ↑ next, Si in F is, C This is because it is considered that O is etched in each case. Further, this RIE method is performed using a gas containing hydrogen (H), because F generated by the dissociation reaction of CF ₄ → CF ₃ + F etches Si by the reaction of Si + F ₂ → SiF ₂ ↑. However, in order to avoid degrading the SiO ₂ / Si etching selectivity, F + H
→ It is because it tries to remove by the reaction of HF.

Further, by implanting ions into the surface exposed by etching, the crystal in this portion once becomes amorphous. Therefore, when the disorder of the crystallinity is improved by the subsequent heat treatment, the improvement effect is obtained. growing. Further, as the heat treatment, by performing rapid heating by RTA method, hardly affect the quality of the oxide film or the like other than the etching.

Further, by performing O ₂ RIE treatment or slight etching treatment before the heat treatment, it is possible to recover not only the hydrogen intrusion damage layer but also the SiC damage layer. Further, this slight etching treatment is performed using a gas containing at least fluorine (F) or chlorine (Cl) because F, Cl, etc. have a strong reactivity with Si and reaction products (SiF ₄ , SiCl ₄ Etc.) is likely to evaporate.

[0021]

An embodiment embodying the present invention will be described below. As described above, when the SiC layer damage layer and the hydrogen penetration damage layer are formed on the surface of the Si substrate, various harmful effects are brought about. First, the present inventor conducted the following experiment based on this fact.

Five n-type (100) single crystal Si substrates were prepared and subjected to the following treatments, and samples A to E were prepared.
And Irradiating fluorocarbon gas plasma is
This is to make the state the same as when RIE is performed, whereby a SiC damage layer and hydrogen penetration damage are formed on the surface of the substrate. Sample A: Untreated sample B: Plasma irradiation only Sample C: Plasma irradiation + O ₂ RIE Sample D: Plasma irradiation + RTA Sample E: Plasma irradiation + O ₂ RIE + RTA (Plasma processing conditions) Gas pressure: 200 mTorr, RF Power: 700 W, gas flow rate: CHF ₃ = 30 sccm, CF ₄ = 5 sccm, Ar = 50
sccm (condition of O ₂ RIE) Gas pressure: 100 mTorr, RF power: 300 W, gas flow rate: O ₂ = 20 sccm (condition of RTA) Temperature: 400 ° C., pressure: 0.1 Torr, time: 30 seconds The above for each sample The process is summarized in the table below.

[0023]

[Table 1]

FIG. 1 shows the measured sheet resistance and contact resistance of Samples A to E in this state. The sheet resistance was measured by the four-probe method, and the contact resistance was measured by the four-probe Kelvin method. Since no damage was given (from the result of Sample A), both the sheet resistance and the contact resistance show low values. (From the result of the sample B) Plasma irradiation causes a damaged layer to be formed on the surface of the substrate, which shows high sheet resistance and high contact resistance. (From the result of Sample C) The O ₂ RIE treatment repaired the SiC damage layer and the contact resistance also showed a low value, but the hydrogen penetration damage layer thereunder could not be repaired, so that damage still existed, and the sheet The resistance also shows a high value. (From the result of the sample D) The hydrogen penetration damage layer is repaired by the RTA treatment, and the sheet resistance is reduced to almost the same value as the sample A. Along with this, the contact resistance also shows a low value. (From the result of the sample E) The damage layer made of SiC is repaired by O ₂ RIE treatment, the hydrogen penetration damage layer is repaired by RTA treatment, and both the sheet resistance and the contact resistance are
It decreases to almost the same value as the sample A.

Considering from the above results, a sheet having a damaged layer on the surface of the substrate, that is, a layer in which the lower hydrogen-penetrating damaged layer is not repaired has a high sheet resistance. Therefore, the degree of damage to this portion can be evaluated by measuring the exposed sheet surface resistance of the substrate after RIE.

FIG. 2 is a block diagram showing the arrangement of an etching damage evaluation apparatus according to this embodiment. The computer 8 stores in advance the sheet resistance of the substrate surface which is not damaged at all. The measurement result from the sheet resistance measuring device 9 is input to the computer 8 and compared with a reference value stored in advance to determine the degree of damage.

The computer 8 displays information such as the measurement result of the sheet resistance measuring device 9 and the degree of damage on the substrate surface on the printer 10 or the CRT 11 as a display device, and according to an operator's instruction or automatically. Commands various devices to execute the damage repair measures described below. Of course, the operator himself may operate the various devices based on the information from the computer 8.

For example, the computer 8 displays the sheet resistance of the substrate which is evaluated for damage in several ranks with the sheet resistance of the substrate which is not damaged as a reference. Furthermore, if it is a predetermined rank, it is instructed to perform the repair work. Here, the repair effect of the hydrogen penetration damage layer by the RTA method will be described based on experimental values.

First, an n-type silicon substrate (sample 1) and a p-type silicon substrate (sample 2) are prepared. Step: a p ⁺ diffusion layer is formed on the article 1, to form an n ⁺ diffusion layer in the sample 2. Step: A silicon oxide film is formed on the surface of each substrate, and the oxide film is partially etched by the RIE method to form a contact hole communicating with each diffusion layer.

Process: Each sample is subjected to RTA at a temperature of 400 ° C. for 30 seconds. FIG. 3 is a graph obtained by measuring the sheet resistance of the substrate surface in each process for each sample. In Sample 1, the sheet resistance was 140Ω / □ in the step before etching, but 540Ω in the step after etching.
It is increasing to / □. However, by performing RTA in the process, the sheet resistance was reduced to 240Ω / □. The material 2 also shows the same tendency as the sample 1, although the sheet resistance value is different.

The sheet resistance increased in the process because hydrogen ions were implanted into the substrate surface during etching, the donors and acceptors were inactivated, the crystallinity of the substrate was disturbed, and the diffusion layer was diffused. Indicates that the surface of the substrate has been damaged due to the fact that the thickness of the substrate has decreased. After that, RTA is performed in the process, whereby hydrogen in the hydrogen intrusion damage layer portion is diffused outward and disorder of crystallinity is improved, and as a result, the degree of damage in this portion is recovered and the sheet resistance is also reduced.

The RTA temperature at this time is 200 ° C.
〜1200 ℃ is effective, 400 ℃ ～ 8
00 ° C. is suitable, and the range of 400 ° C. to 600 ° C. is most effective. FIG. 4 shows profiles of the hydrogen concentration in the depth direction in the steps 1 to 3. After the etching, the high-concentration hydrogen is present deep in the substrate by the process, but the process causes the hydrogen to be scattered near the surface of the substrate. It can be seen that the concentration is also low.

As described above, it was proved that the hydrogen intrusion damage layer can be repaired by performing the RTA. Then O
₂ The repair effect of the SiC damage layer by the RIE method will be described based on experimental values. First, a silicon oxide film is formed on the surface of the substrate, and the oxide film is partially etched by the RIE method to form a contact hole communicating with each diffusion layer. Four samples (Sample F to Sample I) were prepared and subjected to the following treatments, respectively, followed by thermal oxidation.

Sample F ·· O ₂ RIE processing (O ₂ is used as a processing gas in a normal RIE apparatus) Sample G ·· O ₃ processing (substrate temperature 300 ° C., O ₃ + O ₂ (concentration 5%) + N ₂ atmosphere) ) Sample H · · O ₂ plasma downflow (irradiating only radicals of microwave discharge plasma) Sample I · · Untreated * Sample J · · Simple silicon wafer (without SiC damage at all) Figure 5 shows after thermal oxidation 3 is a result of measuring the oxide film thickness on the bottom surface of the contact hole. As described above, if the siliconization damage remains on the silicon surface, the subsequent growth of the oxide film is hindered. From this figure, the sample subjected to the O ₂ RIE treatment shows almost the same value as the sample wafer J.

From this fact, Si is treated by O ₂ RIE treatment.
It can be seen that C damage can be completely removed. From the above results, the process of forming a contact hole in the insulating film on the silicon substrate will be described below with reference to FIG.
First, in FIG. 6A, an n-type diffusion layer 13 is formed on the surface of a p-type single crystal silicon substrate 12, and, for example, CV is formed thereon.
A silicon oxide film 14 is deposited by the D method, and a resist pattern (not shown) for forming a contact hole is further formed on the silicon oxide film 14.

Using this resist as a mask, RIE (etching condition RF power: 700 to 1000 W, gas pressure: 0.05 to 0.5 Torr, working gas: CHF ₃ + CF _4).
+ Ar), a contact hole 15 reaching the silicon substrate 12 is formed in the silicon oxide film 14. At this time, the SiC damage layer 16 is formed on the bottom surface of the contact hole 15, that is, the surface of the silicon substrate 12, and the hydrogen intrusion damage layer 17 is further formed under the SiC damage layer 16.
Is formed.

Next, referring to FIG. 6B, the resist is replaced with O.
₂ Plasma ashing and dipping in a mixed solution of sulfuric acid and hydrogen peroxide to remove it. Now, when a damage layer mainly made of SiC is formed on the surface of the Si substrate, this damage layer becomes an obstacle and, for example, when the Si substrate is thermally oxidized, the oxidation of the surface is suppressed. It is necessary to remove this.

Therefore, the substrate is subjected to O ₂ RIE processing using a normal RIE apparatus (etching condition RF power: 200 to 1000 W, gas pressure: 0.001 to 1.0).
Torr, gas used: O ₂ ). As a result, the SiC damaged portion is modified, and a silicon oxide film (SiO 2
₂ ) 18 is formed. Next, in FIG. 6C, the silicon oxide film 18 is subjected to wet cleaning (for example, H ₂ O: HF).
= 20: 1 soaking for 30 seconds) and the like to expose the hydrogen intrusion damage layer 17.

Therefore, in order to repair the damaged layer, heat treatment is performed at a temperature of 400 ° C. for 30 seconds by using the RTA method. As a result, hydrogen in the damaged layer diffuses outward, and the damage is repaired. Finally, in FIG. 6D, a normal Al alloy wiring 19 is vapor-deposited by a sputtering method or the like.
At this time, various damaged layers at the bottom of the contact hole 15 are improved and the contact resistance on the surface of the diffusion layer 13 is lowered, so that the Al wiring 19 and the diffusion layer 13 can be connected in a good state.

FIG. 7 shows the results of measuring the contact resistance between the SiC-damaged layer and the hydrogen-penetration damaged layer repaired according to the present invention and those not repaired conventionally as in the above method. . In the case where the damage is repaired as in the present invention, the contact resistance is as small as 30Ω and the variation is small, but in the case where the damage is not repaired, the resistance value is up to about 100Ω and the variation after the measurement is large. It turns out that there is a problem with reproducibility.

In addition to the above embodiments, the following modifications are possible. 1) In order to remove the SiC damage layer, the above O ₂ R
Instead of the IE treatment, as in the case of the sample H, the damaged layer may be removed by performing a slight etching using a plasma downflow type etching apparatus. At the time of this slight etching, a gas containing fluorine such as CF ₄ , NF ₃ and SF ₆ , a gas containing chlorine such as Cl ₂ , BCl ₃ and SiCl ₄ , or these gases and O ₂ , N ₂ , Ar and H.
A mixed gas with e or the like is used. 2) In the embodiment, the hydrogenated damage layer 17 is repaired after removing the SiC damage layer 16, but this work may be performed in reverse. 3) In the embodiment, the damage when the contact hole is formed by RIE is improved. However, the damage is not limited to the contact hole and may be used for improving the damage on the silicon substrate surface exposed by RIE. 4) The film etched by RIE may be a silicon nitride film or a polysilicon film other than the silicon oxide film, and may be conductive or non-conductive. 5) When repairing the hydrogen intrusion damage layer 17, ions such as Si and Ar, or ions of the same conduction type (for example, p ⁺ if B ⁺ , BF ₂ ⁺ , Al ⁺ , n ⁺ if damage layer 17 is repaired. For example, ions such as P ⁺ , As ⁺ , Sb ⁺ ) are implanted to make this portion amorphous, and then heat treatment is performed. 6) Instead of the RTA method, an electric furnace is used and heating is performed at a temperature of 1200 ° C. or lower for a long time (about 20 to 1000 minutes).

The heating temperature in the electric furnace at this time is 5
The range of 00 ° C to 1200 ° C is effective, of which 500 is
C. to 900.degree. C. is suitable, and the range of 550.degree. C. to 700.degree. C. is most effective.

[0043]

According to the method for treating a membrane of the present invention,
After being dry-etched by the RIE method or the like,
In addition to recovery to the hydrogen penetration damage layer formed on the surface of the plate
The SiC damage layer can be recovered,
The characteristics of the conductor substrate are improved, and the device formed on the substrate
The reliability of the chair can be improved. Moreover, Io
The surface of the silicon substrate is once amorphized by
Since the RTA treatment after that improves the crystal disorder,
The effect of improving the
You can get sex.

[0044]

[0045]

[Brief description of drawings]

FIG. 1 is a graph showing sheet resistance and contact resistance of each sample after various damage layer removal test treatments in one example of the present invention.

FIG. 2 is a block configuration diagram of an apparatus for evaluating the degree of damage from sheet resistance.

FIG. 3 is a graph showing the sheet resistance of the substrate before and after the repair treatment of the hydrogen penetration damage layer.

FIG. 4 is a graph showing the profile of hydrogen existing in the substrate before and after the hydrogen intrusion damage layer repair processing.

FIG. 5 is a graph showing the thermal oxide film thickness after the SiC damage layer removal test treatment.

FIG. 6 is a cross-sectional view of a substrate sequentially showing a damage improving process according to an embodiment of the present invention.

FIG. 7 is a graph comparing the contact resistance after the image improvement treatment in one example of the present invention with the conventional one.

FIG. 8 is a diagram illustrating the principle of a normal RIE device.

[Explanation of symbols] 1 RIE device 12 Silicon substrate 14 Silicon oxide film 15 contact holes

─────────────────────────────────────────────────── --- Continuation of the front page (56) Reference JP-A-5-102183 (JP, A) JP-A-6-151840 (JP, A) JP-A-56-51580 (JP, A) JP-A-64- 81229 (JP, A) (58) Fields surveyed (Int.Cl. ⁷ , DB name) H01L 21/3065 H01L 21/324 H01L 21/265

Claims (3)

(57) [Claims] 1. A silicon acid formed on a silicon substrate.
Dry etching of insulating film such as oxide film and silicon nitride film
After exposing the silicon substrate by
Ions are implanted into the surface and then RTA (Rapid Thermal A
nnealing) rapid heat treatment,
A special feature is that O ₂ RIE processing is performed before the RTA processing.
The method of treating the substrate. 2. A silicon acid formed on a silicon substrate.
Dry etching of insulating film such as oxide film and silicon nitride film
After exposing the silicon substrate by
Ions are implanted into the surface and then RTA (Rapid Thermal A
nnealing) rapid heat treatment,
Before the RTA process, a slight etching process is performed.
A method for treating a substrate, which is characterized by the above. 3. The method for treating a substrate according to claim 2 , wherein the slight etching treatment is performed using a gas containing at least fluorine (F) or chlorine (Cl).