DE10053780A1 - Process for structuring a silicon oxide layer - Google Patents

Abstract

The invention relates to a method for structuring a silicon oxide layer. According to said method, a substrate comprising a silicon oxide layer with a mask is provided in a plasma reactor. The silicon oxide layer is exposed to a plasma which is produced from an etching gas containing at least one fluorocarbon compound that is selected from the group consisting of compounds of the empirical formula CxHyFz, wherein x = 1 to 5, y = 0 to 4 and z = 2 to 10. The process is optimised by direct switching between the etching and deposition modes, which is achieved by varying the potential difference between the substrate and the plasma.

Description

The invention relates to a method for structuring a silicon oxide layer.

Integrated in the structuring process to build Circuits play processes for etching silicon oxide Layers play a significant role. In the integrated Semiconductor circuits are used under silicon oxide layers other than insulating, passivating layers or yourself as hard masks. Silicon oxide layers find z. B. Application in trench isolation technology, where they are used for isolation neighboring transistors can be used. Furthermore they serve as insulation layers in the Multi-layer wiring or building z. B. MOS Transistors. Building integrated Semiconductor circuits therefore require provision suitable etching process by means of which one time deposited or generated by thermal oxidation Silicon oxide layer can be structured. As Etching processes are used here, in particular, plasma etching processes Commitment.

Due to the ever increasing integration density of the circuits have to get smaller and smaller with the etching process critical dimensions and ever increasing ones Aspect ratios can be realized. To structures such. B. Contact holes, vias or hard masks with bigger and bigger ones To be able to etch aspect ratios, the one run as anisotropically as possible. In addition, should the etching has the highest possible selectivity to that of the  Etching used as a mask materials such. B. silicon or polymeric lacquer masks. Assigns the etching only low selectivity, so the mask with the Etching process in particular to one extent on their profile flanks attacked, causing an undesirable expansion of the the mask has given structure. This will both the aspect ratio to be achieved as well as the critical dimension reached adversely affected. In addition, the selectivity of the Etching process reduces the etching depth to be achieved, since the Mask itself is removed very quickly. The improvement the selectivity of etching processes for silicon oxide layers is therefore the subject of constant research in the Semiconductor technology.

Processes which use fluorocarbons or fluorocarbons in the etching gases have become established as the plasma etching process for silicon oxide layers. A condition arises in the plasma gas in which, in addition to the etching, polymeric materials are deposited at the same time. The deposition and the etching rates are in an interplay and are different from different materials. Through a suitable choice of the process parameters, they can be set so that an effective etching can be achieved selectively for one material, whereas at the same time the deposition predominates on another material. So it is z. B. when using CF ₄ in the etching gas possible to set the etching parameters so that a fluorine-containing polymer is deposited on silicon and silicon nitride, whereas silicon oxide is etched by the plasma. The etching parameters can therefore be set in such a way that the material of the layer to be structured is etched and at the same time a polymer is deposited on the material of the mask.

The previous attempts at the selectivity of Essentially, to increase etching processes focused, increasing the selectivity through the Use of new etching gases, the variation of the system parameters in etching mode or to achieve the change in chamber design. In doing so, those used in these procedures Etching parameters always compromise between protecting the Mask through the polymer deposition on one side and the etching of the silicon oxide layer in the exposed Areas on the other side. Conditional on this In these processes, compromise is neither the optimum Etching rate for the material to be structured, nor the optimal deposition rate of the polymer on the mask reached.

An etching process is disclosed in US Pat. No. 6,074,959 described in which an early termination of the Etching due to excessive polymer deposition in structures with a high aspect ratio is avoided by the fact that the Etching process is carried out in a two-step process. In a first step, an etching recipe is selected with which the oxide layer is quickly but unselectively etched. In a second step is by changing the etching chemistry, d. H. the fluorine-containing compounds, as well as in the Plasmar reactor coupled services more selective Etching conditions created.

In addition to the general disadvantages described above Another disadvantage of this process is that the increase a change in the selectivity of the etching process  Etching chemicals conditional. The plasma is between the Change in etching chemistry not maintained. This change thus entails waiting times in which to reappear must set steady state in the plasma.

The present invention is therefore based on the object based on a method for structuring a Provide silicon oxide layer, which the above described disadvantages reduced or avoided entirely. In particular, it is the object of the present invention to provide a method by which structures with high Aspect ratio with a high selectivity compared to the used mask are etched in a silicon oxide layer can.

This task is performed by the structuring process solved a silicon oxide layer according to claim 1. Further advantageous embodiments, configurations and Aspects of the present invention result from the dependent claims, the description and the Characters.

According to the invention, a method for structuring a silicon oxide layer is provided, which comprises the following steps: A substrate, which comprises a silicon oxide layer and a mask partially covering the silicon oxide layer, is provided in a plasma reactor. A plasma is generated from an etching gas which contains at least one fluorocarbon or fluorocarbon compound selected from the group consisting of compounds of the empirical formula C _x H _y F _z , where x = 1 to 5, y = 0 to 4 and z = 2 to 10 is included. For at least a first period of time, a first potential difference is set between the substrate and the plasma generated from the above-mentioned etching gas, which is selected such that at least the silicon oxide layer undergoes an etching removal (method step c). For at least a second period of time, a second, different from the first potential difference between the substrate and the plasma generated from the above-mentioned etching gas is set, which is chosen such that a layer of a fluorine-containing polymeric material is deposited on the mask, the layer thickness of which during the second period grows. (Process step d).

As plasma reactors all come for the common ones chemical-physical dry etching process applicable Plasma reactors in question. Such dry etching processes can z. B. reactive ion etching, anodically coupled plasma etching Reactive assisted in parallel plate reactor, magnetic field Ion etching, triodes reactive ion etching, inductive coupled plasma etching or etching with inductively coupled Be a plasma source. As masks are within the scope of the present Invention to understand layers of materials that are suitable, a silicon oxide layer before etching removal protect with a plasma etch. Fall in particular including materials such as As silicon, silicon nitride or polymeric materials used as photolithography masks or Paint masks can be used. It is expressly excluded here only silicon oxide itself.

In the context of the present invention, the term “fluorocarbon compound” is understood to mean both compounds which are composed only of fluorine and carbon or compounds which also contain hydrogen in addition to fluorine and carbon. Such connections can e.g. B. be. CF ₄ , CH ₃ F, C ₂ F ₄ , C ₂ F ₆ , CaF ₆ , CaF ₈ , C ₄ F ₆ , C ₄ F ₈ , C ₄ F ₁₀ , CH ₂ F ₂ , C ₂ HF ₃ , C ₂ HF ₅ , C ₃ HF ₅ , C ₃ H ₂ F ₆ , C ₄ F ₈ or C ₅ F ₈ . In a preferred embodiment of the present invention, C ₄ F _{8 is} used as the fluorocarbon compound, the constitutional isomer of this compound not being important.

In an advantageous variant of the method according to the invention, the gas flow rate of the C ₄ F _{8 is} between 10 and 50 sccm, in particular between 20 and 50 sccm. The higher gas flow rates are preferred since higher etching or deposition rates can be achieved when they are used.

Under the potential difference between the plasma and the In the context of the present invention, the substrate Understood the difference in potential between the Forms plasma shell and the adjacent substrate. By this potential difference determines the energy with which the ions from the plasma accelerated to the substrate become. This potential difference can be determined by different am Plasma reactor influences adjustable process parameters become. As a rule, the potential difference is due to Change in the coupled in the plasma reactor Radio frequency power varies. This performance is also called called "bias power". The coupling can depend on Plasma reactor type inductive and / or capacitive. In a preferred embodiment of the invention The process becomes the first (in process step c) and the second potential difference (in process step d) between the substrate and the generated from the etching gas used Plasma by coupling a power into the plasma reactor set. The variant at is particularly preferred which capacitively couples this power into the reactor becomes. This can e.g. B. done in addition to the plasma an inductively coupled power additional power  thereby being coupled in by the substrate or the Capacitive electrode on which the substrate is attached a high frequency source is connected.

The sequence of process steps c) and d) is not specified in the process according to the invention. The method can be designed in such a way that the SiO ₂ layer is etched in a first etching step and the polymer is deposited on the mask in a subsequent deposition step. Conversely, the polymer can first be deposited on the mask and then the silicon oxide layer can be etched. In the first case, the mask is reinforced by the deposition after the etching, in the second case the mask is reinforced before the etching.

For the first period in the invention The first potential difference is chosen so that the Silicon oxide layer experiences an etching removal. Only can the silicon layer alone or the protective layer Mask are etched. If both the silicon oxide layer and the mask must also be etched, so the first period be sized so that the mask is not complete in any area is removed.

In a preferred embodiment of the inventive method is the performance in the Plasma reactor is coupled and with which the first Potential difference set during the first period is at least 400 W, preferably at least 600 W and particularly preferably at least 800 W.

It is particularly advantageous if the parameters that can be set on the plasma generator are set such that the etching of the SiO ₂ layer already has a high selectivity with respect to the mask during the first period.

In a preferred variant of the invention The first potential difference is set in such a way that during the first period there is a Layer of fluorine-containing polymer forms, the layer thickness remains essentially constant during the first period. I.e. the potential difference is chosen here so that during the first period a balance between the Etching of the mask and the deposition of the polymeric material on the mask. The depositing layer is in usually only a few nm thick.

For the second period in the invention Process the second potential difference between the substrate and the plasma generated from the etching gas are chosen such that a layer of a fluorine-containing polymer on the mask Deposits material whose layer thickness during the second Period grows.

The preferred performance for hiring the second Potential difference during the second period is less than 400 W, preferably at most 200 W.

In a particularly advantageous variant of the method according to the invention, the deposition rate of the fluorine-containing, polymeric material on the mask is at least 50 nmmin ^-1 , preferably at least 240 nmmin ^-1 , in particular at least 350 nmmin ^-1 .

By separating out over the second period The polymer layer becomes the mask against further etching  protected. This protective effect ensures that Selectivity of the etching process between silicon oxide and the Mask material significantly during the second period improved. In addition, the mask is made by the Polymer deposition renewed so that it follows one can withstand renewed etching longer. This will make the achievable etching depth increased.

The change in the first potential difference to the second potential difference can e.g. B. by simple Change in the power coupled into the plasma reactor respectively. Switching the coupled power, and thus the changeover from etching mode to deposition mode takes place thereby instantaneous, d. H. without a delay of the Process.

The method according to the invention thus offers the advantage that rapid, selective etching of the silicon oxide layer can be achieved without making time-consuming changes to have to make on the plasma.

The etching chemistry of the process according to the invention generated plasma is crucially based on the use a fluorocarbon compound which is suitable from the Plasma is a fluorine-containing, polymeric material on the mask deposit. This component is all over Maintain the duration of the process in the etching gas. In this The term "the etching gas mentioned in b) also makes sense generated plasma "in the context of the present invention understand. The other etching gas components can during the entire process can be varied. To increase the Selectivity of the process can include additional gas components either during the entire duration of the procedure or also  only be mixed in during individual steps.

In particular, the etching gas during process step c) additional components which increase the etching rate are admixed become. The use of molecular oxygen as an additional component in the etching gas prefers.

During the second period, the Polymer separation in addition to increasing the selectivity of the Etching removal another advantage. In addition, the mask by selectively taking place on the mask material Deposition intensified so that the mask then reappears a relatively unselective one over a longer period of time Etching step can be exposed. This will be in one particularly preferred variant of the invention Process used in that process steps c) and d) can be repeated several times.

With these repetitions, the respective duration of the first and second periods from that of the first and previous cycle. Furthermore, the respective first and second potential differences in the Repetition steps can be changed. This also applies all other selectable process parameters, insofar as their Changes possible without lengthy delays By changing the process parameters in the Repeat steps can be the etching and Separation conditions optimal in every step Aspect ratios of the structure to be etched during the be adapted to the respective cycle. This will make a higher one Selectivity and better profile control when etching achieved, with time consuming changes to the Process conditions can be dispensed with.  

In a further preferred variant of the inventive method additionally contains the etching gas an inert gas, preferably argon. This is preferably Gas flow rate between 100 and 1000 sccm, particularly preferred between 200 and 700 sccm, in particular between 200 and 500 sccm.

It is further preferred that the etching gas additionally contains molecular oxygen O ₂ . It is particularly preferred here that the gas flow rate of the molecular oxygen is between 5 and 25 sccm, in particular 10 sccm. By adding molecular oxygen, the potential difference or the power coupled into the plasma generator, at which the deposition of the fluorine-containing polymeric material converts into an etching of the polymeric fluorine-containing material, can be shifted to lower potential differences or coupled-in powers.

In addition, the etching can be removed in process step c) further when using molecular oxygen in the etching gas increase. In another particularly advantageous Variant of the method according to the invention contains the etching gas only in process step c) additional molecular Oxygen.

The method according to the invention is described below of the embodiments and in connection with the Drawings are explained in more detail. It shows

Fig. 1: A graph showing the dependence of the deposition rate of the fluorine-containing, polymeric material on silicon on the capacitively coupled power (bias power) for different etching gases.

Embodiment 1

In this example, the polymer deposition from the Plasma on a silicon mask depending on the capacitive coupled power determined.

For this purpose, silicon wafers were placed in one Plasma generator of the type IPS Dielectric Etcher from the company Applied materials introduced and exposed to a plasma. For various capacitively coupled services then the polymer deposition on the silicon wafers Scanning electron microscopy determined.

The following basic recipe was used in this series of experiments:
Argon gas flow rate: 200 sccm
Gas flow rate C ₄ F ₈ : 20 sccm
Power (inner source): 600 W.
Power (outer source): 200 W.
Chamber pressure: 13 m Torr
He pressure: 5 torr
Chiller (heat exchanger): 20 ° C
Roof: 200 ° C
Ring: 375 ° C
Bias power: 0-400 W.

Two series of measurements were carried out. The basic recipe was used in the first series of measurements; in the second series of measurements, additional molecular oxygen was added to the basic recipe with a gas flow rate of 10 sccm. The measured values of the first series of measurements are represented in the graph shown in FIG. 1 by the full symbols. The full circles correspond to the measured values at the edge of the silicon wafers, the full squares represent the measured values in the center of the silicon wafers.

The measured values of the second series of measurements are given by the represented half-open symbols, again the circles the measured values on the edge and the squares the measured values in Play the center of the silicon wafers.

It can be seen from the measurement data that the Deposition rate with increasing, capacitively coupled Performance decreases and turns in from a certain performance converts an etching rate.

The addition rate of molecular oxygen reduces the deposition rate. In addition, the deposition rate shows only slight local deviations. For the first series of measurements (basic recipe), the deposition rate for an arbitrarily selected power results according to the formula: r _D = 417.3 nm / min - 1.06714 nm / min WP _B (r _D = deposition rate; P _B = capacitively coupled power ). For the second series of measurements (oxygen-containing recipe), the respective deposition rate can be calculated using the formula r _D = 389.3 nm / min - 1.583 nm / min WP _B (r _D = deposition rate; P _B = capacitively coupled power).

An optimized time can be obtained from these deposition rates can be determined to separate a defined Layer thickness is required.  

Embodiment 2

In this example, an SiO ₂ layer was structured with a silicon mask. The SiO ₂ layer already had contact holes with an approximate depth of 500 nm and an aspect ratio of about 5.

The following two-step process was used: In a first step (D1), the etching conditions were chosen such that a deposition took place on the silicon mask. In a subsequent etching step (E1), the etching conditions were chosen so that the SiO ₂ layer was etched.

The process parameters for both steps are in the table 1 listed.

Table 1

Process parameters for D1 and E1

Under these conditions, deposition step D1 about 80 nm thick within 12 seconds Polymer layer deposited on the mask. On the Profile edges found only one negligible Deposition instead. A separation within the Contact hole was not observed.

In the subsequent etching step E1, approximately 150 nm of SiO _{2 were} etched within the contact hole within 20 seconds. The polymer layer on the mask had almost completely disappeared after the etching step E1. 150 nm of SiO ₂ silicon oxide could thus be etched without loss of mask material.

Embodiment 3

In this embodiment, the analog Embodiment 2 proceed, except that Process conditions for the deposition step (D2) changed were. The process parameters are given in Table 2.  

Table 2

Process parameters for D2 and E2

This process control shows results similar to those in embodiment 2. However, with these process parameters, a slight edge coverage of the mask can be determined. In addition, the SiO ₂ layer in the contact holes is already etched in the deposition step D2 in this process.

Claims (17)

1. A method for structuring a silicon oxide layer, comprising the steps:

• a) a substrate comprising a silicon oxide layer and a mask partially covering the silicon oxide layer is provided in a plasma reactor,
• b) a plasma is generated from an etching gas which contains at least one fluorocarbon or fluorocarbon compound compound selected from the group consisting of compounds of the empirical formula C _x H _y F _z , where x = 1 to 5, y = 0 to 4 and z = 2 to 10 is comprised
• c) for at least a first period of time, a first potential difference is set between the substrate and the plasma generated from the etching gas mentioned in b), which is selected such that the silicon oxide layer experiences an etching removal, and
• d) for at least a second period of time, a second potential difference, different from the first, between the substrate and the plasma generated from the etching gas mentioned in b) is set, which is selected such that a layer of a fluorine-containing polymeric material is deposited on the mask whose layer thickness increases during the second period.

2. The method according to claim 1, characterized in that the steps c) and d) are repeated several times. 3. The method according to claim 1 or 2, characterized in that the first and second potential difference between the Substrate and the generated from the etching gas mentioned in b) Plasma by coupling a power into the Plasma reactor takes place. 4. The method according to claim 3, characterized in that the Power is capacitively coupled into the plasma reactor. 5. The method according to any one of the preceding claims, characterized in that the etching gas as a fluorocarbon or fluorocarbon compound, a compound selected from the group consisting of CF ₄ , CH ₃ F, CH ₂ F ₂ , C ₂ F ₄ , C ₂ F ₆ , C ₂ HF ₃ , C ₂ HF ₅ , C ₃ F ₆ , C ₃ HF ₅ , C ₃ F ₈ , C ₃ H ₂ F ₆ , C ₄ F ₆ , C ₄ F ₈ , C ₄ F ₁₀ , or C ₅ F ₈ contains. 6. The method according to any one of the preceding claims, characterized in that the etching gas contains C ₄ F ₈ as the fluorocarbon compound. 7. The method according to claim 6, characterized in that the gas flow rate of C ₄ F _{8 is} between 10 and 50 sccm, preferably 20 sccm. 8. The method according to any one of the preceding claims, characterized in that the  Etching gas contains an inert gas, preferably argon. 9. The method according to claim 8, characterized in that the Argon gas flow rate between 100 and 1000 sccm, preferably between 200 and 700 sscm, in particular is between 200 and 500 sccm. 10. The method according to any one of the preceding claims, characterized in that the etching gas additionally contains molecular oxygen O ₂ . 11. The method according to claim 10, characterized in that the Molecular oxygen gas flow rate between 5 and 25 sccm, preferably 10 sccm. 12. The method according to any one of claims 10 or 11 characterized in that the Etching gas only in step c) additional molecular oxygen contains. 13. The method according to any one of the preceding claims, characterized in that the Power for setting the potential difference between the plasma and the substrate in step c) at least 400 W, preferably at least 600 W, in particular at least Is 800 W and less than 400 W in step d), is preferably at most 200 W. 14. The method according to any one of the preceding claims, characterized in that the first potential difference between the substrate and the  the etching gas generated in b) set so will that on the mask during the first period forms a layer of fluorine-containing polymeric material, whose layer thickness during the first period in remains essentially constant. 15. The method according to any one of the preceding claims, characterized in that the deposition rate of the fluorine-containing polymeric material on the mask during the second period is at least 50 nmmin ^-1, preferably at least 240 nmmin ^-1 , in particular at least 350 nmmin ^-1 . 16. The method according to any one of the preceding claims, characterized in that the Mask is a silicon mask. 17. The method according to any one of the preceding claims, characterized in that the Mask is a paint mask.